FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/spa.c

     /*
      * CDDL HEADER START
      *
      * The contents of this file are subject to the terms of the
      * Common Development and Distribution License (the "License").
      * You may not use this file except in compliance with the License.
      *
      * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      * or https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    
    /*
     * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
     * Copyright (c) 2011, 2020 by Delphix. All rights reserved.
     * Copyright (c) 2018, Nexenta Systems, Inc.  All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     * Copyright 2013 Saso Kiselkov. All rights reserved.
     * Copyright (c) 2014 Integros [integros.com]
     * Copyright 2016 Toomas Soome <tsoome@me.com>
     * Copyright (c) 2016 Actifio, Inc. All rights reserved.
     * Copyright 2018 Joyent, Inc.
     * Copyright (c) 2017, 2019, Datto Inc. All rights reserved.
     * Copyright 2017 Joyent, Inc.
     * Copyright (c) 2017, Intel Corporation.
     * Copyright (c) 2021, Colm Buckley <colm@tuatha.org>
     */
    
    /*
     * SPA: Storage Pool Allocator
     *
     * This file contains all the routines used when modifying on-disk SPA state.
     * This includes opening, importing, destroying, exporting a pool, and syncing a
     * pool.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/fm/fs/zfs.h>
    #include <sys/spa_impl.h>
    #include <sys/zio.h>
    #include <sys/zio_checksum.h>
    #include <sys/dmu.h>
    #include <sys/dmu_tx.h>
    #include <sys/zap.h>
    #include <sys/zil.h>
    #include <sys/ddt.h>
    #include <sys/vdev_impl.h>
    #include <sys/vdev_removal.h>
    #include <sys/vdev_indirect_mapping.h>
    #include <sys/vdev_indirect_births.h>
    #include <sys/vdev_initialize.h>
    #include <sys/vdev_rebuild.h>
    #include <sys/vdev_trim.h>
    #include <sys/vdev_disk.h>
    #include <sys/vdev_draid.h>
    #include <sys/metaslab.h>
    #include <sys/metaslab_impl.h>
    #include <sys/mmp.h>
    #include <sys/uberblock_impl.h>
    #include <sys/txg.h>
    #include <sys/avl.h>
    #include <sys/bpobj.h>
    #include <sys/dmu_traverse.h>
    #include <sys/dmu_objset.h>
    #include <sys/unique.h>
    #include <sys/dsl_pool.h>
    #include <sys/dsl_dataset.h>
    #include <sys/dsl_dir.h>
    #include <sys/dsl_prop.h>
    #include <sys/dsl_synctask.h>
    #include <sys/fs/zfs.h>
    #include <sys/arc.h>
    #include <sys/callb.h>
    #include <sys/systeminfo.h>
    #include <sys/zfs_ioctl.h>
    #include <sys/dsl_scan.h>
    #include <sys/zfeature.h>
    #include <sys/dsl_destroy.h>
    #include <sys/zvol.h>
    
    #ifdef  _KERNEL
    #include <sys/fm/protocol.h>
    #include <sys/fm/util.h>
    #include <sys/callb.h>
    #include <sys/zone.h>
    #include <sys/vmsystm.h>
    #endif  /* _KERNEL */
    
    #include "zfs_prop.h"
    #include "zfs_comutil.h"
   
   /*
    * The interval, in seconds, at which failed configuration cache file writes
    * should be retried.
    */
   int zfs_ccw_retry_interval = 300;
   
   typedef enum zti_modes {
           ZTI_MODE_FIXED,                 /* value is # of threads (min 1) */
           ZTI_MODE_BATCH,                 /* cpu-intensive; value is ignored */
           ZTI_MODE_SCALE,                 /* Taskqs scale with CPUs. */
           ZTI_MODE_NULL,                  /* don't create a taskq */
           ZTI_NMODES
   } zti_modes_t;
   
   #define ZTI_P(n, q)     { ZTI_MODE_FIXED, (n), (q) }
   #define ZTI_PCT(n)      { ZTI_MODE_ONLINE_PERCENT, (n), 1 }
   #define ZTI_BATCH       { ZTI_MODE_BATCH, 0, 1 }
   #define ZTI_SCALE       { ZTI_MODE_SCALE, 0, 1 }
   #define ZTI_NULL        { ZTI_MODE_NULL, 0, 0 }
   
   #define ZTI_N(n)        ZTI_P(n, 1)
   #define ZTI_ONE         ZTI_N(1)
   
   typedef struct zio_taskq_info {
           zti_modes_t zti_mode;
           uint_t zti_value;
           uint_t zti_count;
   } zio_taskq_info_t;
   
   static const char *const zio_taskq_types[ZIO_TASKQ_TYPES] = {
           "iss", "iss_h", "int", "int_h"
   };
   
   /*
    * This table defines the taskq settings for each ZFS I/O type. When
    * initializing a pool, we use this table to create an appropriately sized
    * taskq. Some operations are low volume and therefore have a small, static
    * number of threads assigned to their taskqs using the ZTI_N(#) or ZTI_ONE
    * macros. Other operations process a large amount of data; the ZTI_BATCH
    * macro causes us to create a taskq oriented for throughput. Some operations
    * are so high frequency and short-lived that the taskq itself can become a
    * point of lock contention. The ZTI_P(#, #) macro indicates that we need an
    * additional degree of parallelism specified by the number of threads per-
    * taskq and the number of taskqs; when dispatching an event in this case, the
    * particular taskq is chosen at random. ZTI_SCALE is similar to ZTI_BATCH,
    * but with number of taskqs also scaling with number of CPUs.
    *
    * The different taskq priorities are to handle the different contexts (issue
    * and interrupt) and then to reserve threads for ZIO_PRIORITY_NOW I/Os that
    * need to be handled with minimum delay.
    */
   static const zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
           /* ISSUE        ISSUE_HIGH      INTR            INTR_HIGH */
           { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* NULL */
           { ZTI_N(8),     ZTI_NULL,       ZTI_SCALE,      ZTI_NULL }, /* READ */
           { ZTI_BATCH,    ZTI_N(5),       ZTI_SCALE,      ZTI_N(5) }, /* WRITE */
           { ZTI_SCALE,    ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* FREE */
           { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* CLAIM */
           { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* IOCTL */
           { ZTI_N(4),     ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* TRIM */
   };
   
   static void spa_sync_version(void *arg, dmu_tx_t *tx);
   static void spa_sync_props(void *arg, dmu_tx_t *tx);
   static boolean_t spa_has_active_shared_spare(spa_t *spa);
   static int spa_load_impl(spa_t *spa, spa_import_type_t type,
       const char **ereport);
   static void spa_vdev_resilver_done(spa_t *spa);
   
   static uint_t   zio_taskq_batch_pct = 80;         /* 1 thread per cpu in pset */
   static uint_t   zio_taskq_batch_tpq;              /* threads per taskq */
   static const boolean_t  zio_taskq_sysdc = B_TRUE; /* use SDC scheduling class */
   static const uint_t     zio_taskq_basedc = 80;    /* base duty cycle */
   
   static const boolean_t spa_create_process = B_TRUE; /* no process => no sysdc */
   
   /*
    * Report any spa_load_verify errors found, but do not fail spa_load.
    * This is used by zdb to analyze non-idle pools.
    */
   boolean_t       spa_load_verify_dryrun = B_FALSE;
   
   /*
    * Allow read spacemaps in case of readonly import (spa_mode == SPA_MODE_READ).
    * This is used by zdb for spacemaps verification.
    */
   boolean_t       spa_mode_readable_spacemaps = B_FALSE;
   
   /*
    * This (illegal) pool name is used when temporarily importing a spa_t in order
    * to get the vdev stats associated with the imported devices.
    */
   #define TRYIMPORT_NAME  "$import"
   
   /*
    * For debugging purposes: print out vdev tree during pool import.
    */
   static int              spa_load_print_vdev_tree = B_FALSE;
   
   /*
    * A non-zero value for zfs_max_missing_tvds means that we allow importing
    * pools with missing top-level vdevs. This is strictly intended for advanced
    * pool recovery cases since missing data is almost inevitable. Pools with
    * missing devices can only be imported read-only for safety reasons, and their
    * fail-mode will be automatically set to "continue".
    *
    * With 1 missing vdev we should be able to import the pool and mount all
    * datasets. User data that was not modified after the missing device has been
    * added should be recoverable. This means that snapshots created prior to the
    * addition of that device should be completely intact.
    *
    * With 2 missing vdevs, some datasets may fail to mount since there are
    * dataset statistics that are stored as regular metadata. Some data might be
    * recoverable if those vdevs were added recently.
    *
    * With 3 or more missing vdevs, the pool is severely damaged and MOS entries
    * may be missing entirely. Chances of data recovery are very low. Note that
    * there are also risks of performing an inadvertent rewind as we might be
    * missing all the vdevs with the latest uberblocks.
    */
   uint64_t        zfs_max_missing_tvds = 0;
   
   /*
    * The parameters below are similar to zfs_max_missing_tvds but are only
    * intended for a preliminary open of the pool with an untrusted config which
    * might be incomplete or out-dated.
    *
    * We are more tolerant for pools opened from a cachefile since we could have
    * an out-dated cachefile where a device removal was not registered.
    * We could have set the limit arbitrarily high but in the case where devices
    * are really missing we would want to return the proper error codes; we chose
    * SPA_DVAS_PER_BP - 1 so that some copies of the MOS would still be available
    * and we get a chance to retrieve the trusted config.
    */
   uint64_t        zfs_max_missing_tvds_cachefile = SPA_DVAS_PER_BP - 1;
   
   /*
    * In the case where config was assembled by scanning device paths (/dev/dsks
    * by default) we are less tolerant since all the existing devices should have
    * been detected and we want spa_load to return the right error codes.
    */
   uint64_t        zfs_max_missing_tvds_scan = 0;
   
   /*
    * Debugging aid that pauses spa_sync() towards the end.
    */
   static const boolean_t  zfs_pause_spa_sync = B_FALSE;
   
   /*
    * Variables to indicate the livelist condense zthr func should wait at certain
    * points for the livelist to be removed - used to test condense/destroy races
    */
   static int zfs_livelist_condense_zthr_pause = 0;
   static int zfs_livelist_condense_sync_pause = 0;
   
   /*
    * Variables to track whether or not condense cancellation has been
    * triggered in testing.
    */
   static int zfs_livelist_condense_sync_cancel = 0;
   static int zfs_livelist_condense_zthr_cancel = 0;
   
   /*
    * Variable to track whether or not extra ALLOC blkptrs were added to a
    * livelist entry while it was being condensed (caused by the way we track
    * remapped blkptrs in dbuf_remap_impl)
    */
   static int zfs_livelist_condense_new_alloc = 0;
   
   /*
    * ==========================================================================
    * SPA properties routines
    * ==========================================================================
    */
   
   /*
    * Add a (source=src, propname=propval) list to an nvlist.
    */
   static void
   spa_prop_add_list(nvlist_t *nvl, zpool_prop_t prop, const char *strval,
       uint64_t intval, zprop_source_t src)
   {
           const char *propname = zpool_prop_to_name(prop);
           nvlist_t *propval;
   
           propval = fnvlist_alloc();
           fnvlist_add_uint64(propval, ZPROP_SOURCE, src);
   
           if (strval != NULL)
                   fnvlist_add_string(propval, ZPROP_VALUE, strval);
           else
                   fnvlist_add_uint64(propval, ZPROP_VALUE, intval);
   
           fnvlist_add_nvlist(nvl, propname, propval);
           nvlist_free(propval);
   }
   
   /*
    * Get property values from the spa configuration.
    */
   static void
   spa_prop_get_config(spa_t *spa, nvlist_t **nvp)
   {
           vdev_t *rvd = spa->spa_root_vdev;
           dsl_pool_t *pool = spa->spa_dsl_pool;
           uint64_t size, alloc, cap, version;
           const zprop_source_t src = ZPROP_SRC_NONE;
           spa_config_dirent_t *dp;
           metaslab_class_t *mc = spa_normal_class(spa);
   
           ASSERT(MUTEX_HELD(&spa->spa_props_lock));
   
           if (rvd != NULL) {
                   alloc = metaslab_class_get_alloc(mc);
                   alloc += metaslab_class_get_alloc(spa_special_class(spa));
                   alloc += metaslab_class_get_alloc(spa_dedup_class(spa));
                   alloc += metaslab_class_get_alloc(spa_embedded_log_class(spa));
   
                   size = metaslab_class_get_space(mc);
                   size += metaslab_class_get_space(spa_special_class(spa));
                   size += metaslab_class_get_space(spa_dedup_class(spa));
                   size += metaslab_class_get_space(spa_embedded_log_class(spa));
   
                   spa_prop_add_list(*nvp, ZPOOL_PROP_NAME, spa_name(spa), 0, src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_SIZE, NULL, size, src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_ALLOCATED, NULL, alloc, src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_FREE, NULL,
                       size - alloc, src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_CHECKPOINT, NULL,
                       spa->spa_checkpoint_info.sci_dspace, src);
   
                   spa_prop_add_list(*nvp, ZPOOL_PROP_FRAGMENTATION, NULL,
                       metaslab_class_fragmentation(mc), src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_EXPANDSZ, NULL,
                       metaslab_class_expandable_space(mc), src);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_READONLY, NULL,
                       (spa_mode(spa) == SPA_MODE_READ), src);
   
                   cap = (size == 0) ? 0 : (alloc * 100 / size);
                   spa_prop_add_list(*nvp, ZPOOL_PROP_CAPACITY, NULL, cap, src);
   
                   spa_prop_add_list(*nvp, ZPOOL_PROP_DEDUPRATIO, NULL,
                       ddt_get_pool_dedup_ratio(spa), src);
   
                   spa_prop_add_list(*nvp, ZPOOL_PROP_HEALTH, NULL,
                       rvd->vdev_state, src);
   
                   version = spa_version(spa);
                   if (version == zpool_prop_default_numeric(ZPOOL_PROP_VERSION)) {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_VERSION, NULL,
                               version, ZPROP_SRC_DEFAULT);
                   } else {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_VERSION, NULL,
                               version, ZPROP_SRC_LOCAL);
                   }
                   spa_prop_add_list(*nvp, ZPOOL_PROP_LOAD_GUID,
                       NULL, spa_load_guid(spa), src);
           }
   
           if (pool != NULL) {
                   /*
                    * The $FREE directory was introduced in SPA_VERSION_DEADLISTS,
                    * when opening pools before this version freedir will be NULL.
                    */
                   if (pool->dp_free_dir != NULL) {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_FREEING, NULL,
                               dsl_dir_phys(pool->dp_free_dir)->dd_used_bytes,
                               src);
                   } else {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_FREEING,
                               NULL, 0, src);
                   }
   
                   if (pool->dp_leak_dir != NULL) {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_LEAKED, NULL,
                               dsl_dir_phys(pool->dp_leak_dir)->dd_used_bytes,
                               src);
                   } else {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_LEAKED,
                               NULL, 0, src);
                   }
           }
   
           spa_prop_add_list(*nvp, ZPOOL_PROP_GUID, NULL, spa_guid(spa), src);
   
           if (spa->spa_comment != NULL) {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_COMMENT, spa->spa_comment,
                       0, ZPROP_SRC_LOCAL);
           }
   
           if (spa->spa_compatibility != NULL) {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_COMPATIBILITY,
                       spa->spa_compatibility, 0, ZPROP_SRC_LOCAL);
           }
   
           if (spa->spa_root != NULL)
                   spa_prop_add_list(*nvp, ZPOOL_PROP_ALTROOT, spa->spa_root,
                       0, ZPROP_SRC_LOCAL);
   
           if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_BLOCKS)) {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_MAXBLOCKSIZE, NULL,
                       MIN(zfs_max_recordsize, SPA_MAXBLOCKSIZE), ZPROP_SRC_NONE);
           } else {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_MAXBLOCKSIZE, NULL,
                       SPA_OLD_MAXBLOCKSIZE, ZPROP_SRC_NONE);
           }
   
           if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_DNODE)) {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_MAXDNODESIZE, NULL,
                       DNODE_MAX_SIZE, ZPROP_SRC_NONE);
           } else {
                   spa_prop_add_list(*nvp, ZPOOL_PROP_MAXDNODESIZE, NULL,
                       DNODE_MIN_SIZE, ZPROP_SRC_NONE);
           }
   
           if ((dp = list_head(&spa->spa_config_list)) != NULL) {
                   if (dp->scd_path == NULL) {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_CACHEFILE,
                               "none", 0, ZPROP_SRC_LOCAL);
                   } else if (strcmp(dp->scd_path, spa_config_path) != 0) {
                           spa_prop_add_list(*nvp, ZPOOL_PROP_CACHEFILE,
                               dp->scd_path, 0, ZPROP_SRC_LOCAL);
                   }
           }
   }
   
   /*
    * Get zpool property values.
    */
   int
   spa_prop_get(spa_t *spa, nvlist_t **nvp)
   {
           objset_t *mos = spa->spa_meta_objset;
           zap_cursor_t zc;
           zap_attribute_t za;
           dsl_pool_t *dp;
           int err;
   
           err = nvlist_alloc(nvp, NV_UNIQUE_NAME, KM_SLEEP);
           if (err)
                   return (err);
   
           dp = spa_get_dsl(spa);
           dsl_pool_config_enter(dp, FTAG);
           mutex_enter(&spa->spa_props_lock);
   
           /*
            * Get properties from the spa config.
            */
           spa_prop_get_config(spa, nvp);
   
           /* If no pool property object, no more prop to get. */
           if (mos == NULL || spa->spa_pool_props_object == 0)
                   goto out;
   
           /*
            * Get properties from the MOS pool property object.
            */
           for (zap_cursor_init(&zc, mos, spa->spa_pool_props_object);
               (err = zap_cursor_retrieve(&zc, &za)) == 0;
               zap_cursor_advance(&zc)) {
                   uint64_t intval = 0;
                   char *strval = NULL;
                   zprop_source_t src = ZPROP_SRC_DEFAULT;
                   zpool_prop_t prop;
   
                   if ((prop = zpool_name_to_prop(za.za_name)) == ZPOOL_PROP_INVAL)
                           continue;
   
                   switch (za.za_integer_length) {
                   case 8:
                           /* integer property */
                           if (za.za_first_integer !=
                               zpool_prop_default_numeric(prop))
                                   src = ZPROP_SRC_LOCAL;
   
                           if (prop == ZPOOL_PROP_BOOTFS) {
                                   dsl_dataset_t *ds = NULL;
   
                                   err = dsl_dataset_hold_obj(dp,
                                       za.za_first_integer, FTAG, &ds);
                                   if (err != 0)
                                           break;
   
                                   strval = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN,
                                       KM_SLEEP);
                                   dsl_dataset_name(ds, strval);
                                   dsl_dataset_rele(ds, FTAG);
                           } else {
                                   strval = NULL;
                                   intval = za.za_first_integer;
                           }
   
                           spa_prop_add_list(*nvp, prop, strval, intval, src);
   
                           if (strval != NULL)
                                   kmem_free(strval, ZFS_MAX_DATASET_NAME_LEN);
   
                           break;
   
                   case 1:
                           /* string property */
                           strval = kmem_alloc(za.za_num_integers, KM_SLEEP);
                           err = zap_lookup(mos, spa->spa_pool_props_object,
                               za.za_name, 1, za.za_num_integers, strval);
                           if (err) {
                                   kmem_free(strval, za.za_num_integers);
                                   break;
                           }
                           spa_prop_add_list(*nvp, prop, strval, 0, src);
                           kmem_free(strval, za.za_num_integers);
                           break;
   
                   default:
                           break;
                   }
           }
           zap_cursor_fini(&zc);
   out:
           mutex_exit(&spa->spa_props_lock);
           dsl_pool_config_exit(dp, FTAG);
           if (err && err != ENOENT) {
                   nvlist_free(*nvp);
                   *nvp = NULL;
                   return (err);
           }
   
           return (0);
   }
   
   /*
    * Validate the given pool properties nvlist and modify the list
    * for the property values to be set.
    */
   static int
   spa_prop_validate(spa_t *spa, nvlist_t *props)
   {
           nvpair_t *elem;
           int error = 0, reset_bootfs = 0;
           uint64_t objnum = 0;
           boolean_t has_feature = B_FALSE;
   
           elem = NULL;
           while ((elem = nvlist_next_nvpair(props, elem)) != NULL) {
                   uint64_t intval;
                   char *strval, *slash, *check, *fname;
                   const char *propname = nvpair_name(elem);
                   zpool_prop_t prop = zpool_name_to_prop(propname);
   
                   switch (prop) {
                   case ZPOOL_PROP_INVAL:
                           if (!zpool_prop_feature(propname)) {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           /*
                            * Sanitize the input.
                            */
                           if (nvpair_type(elem) != DATA_TYPE_UINT64) {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           if (nvpair_value_uint64(elem, &intval) != 0) {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           if (intval != 0) {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           fname = strchr(propname, '@') + 1;
                           if (zfeature_lookup_name(fname, NULL) != 0) {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           has_feature = B_TRUE;
                           break;
   
                   case ZPOOL_PROP_VERSION:
                           error = nvpair_value_uint64(elem, &intval);
                           if (!error &&
                               (intval < spa_version(spa) ||
                               intval > SPA_VERSION_BEFORE_FEATURES ||
                               has_feature))
                                   error = SET_ERROR(EINVAL);
                           break;
   
                   case ZPOOL_PROP_DELEGATION:
                   case ZPOOL_PROP_AUTOREPLACE:
                   case ZPOOL_PROP_LISTSNAPS:
                   case ZPOOL_PROP_AUTOEXPAND:
                   case ZPOOL_PROP_AUTOTRIM:
                           error = nvpair_value_uint64(elem, &intval);
                           if (!error && intval > 1)
                                   error = SET_ERROR(EINVAL);
                           break;
   
                   case ZPOOL_PROP_MULTIHOST:
                           error = nvpair_value_uint64(elem, &intval);
                           if (!error && intval > 1)
                                   error = SET_ERROR(EINVAL);
   
                           if (!error) {
                                   uint32_t hostid = zone_get_hostid(NULL);
                                   if (hostid)
                                           spa->spa_hostid = hostid;
                                   else
                                           error = SET_ERROR(ENOTSUP);
                           }
   
                           break;
   
                   case ZPOOL_PROP_BOOTFS:
                           /*
                            * If the pool version is less than SPA_VERSION_BOOTFS,
                            * or the pool is still being created (version == 0),
                            * the bootfs property cannot be set.
                            */
                           if (spa_version(spa) < SPA_VERSION_BOOTFS) {
                                   error = SET_ERROR(ENOTSUP);
                                   break;
                           }
   
                           /*
                            * Make sure the vdev config is bootable
                            */
                           if (!vdev_is_bootable(spa->spa_root_vdev)) {
                                   error = SET_ERROR(ENOTSUP);
                                   break;
                           }
   
                           reset_bootfs = 1;
   
                           error = nvpair_value_string(elem, &strval);
   
                           if (!error) {
                                   objset_t *os;
   
                                   if (strval == NULL || strval[0] == '\0') {
                                           objnum = zpool_prop_default_numeric(
                                               ZPOOL_PROP_BOOTFS);
                                           break;
                                   }
   
                                   error = dmu_objset_hold(strval, FTAG, &os);
                                   if (error != 0)
                                           break;
   
                                   /* Must be ZPL. */
                                   if (dmu_objset_type(os) != DMU_OST_ZFS) {
                                           error = SET_ERROR(ENOTSUP);
                                   } else {
                                           objnum = dmu_objset_id(os);
                                   }
                                   dmu_objset_rele(os, FTAG);
                           }
                           break;
   
                   case ZPOOL_PROP_FAILUREMODE:
                           error = nvpair_value_uint64(elem, &intval);
                           if (!error && intval > ZIO_FAILURE_MODE_PANIC)
                                   error = SET_ERROR(EINVAL);
   
                           /*
                            * This is a special case which only occurs when
                            * the pool has completely failed. This allows
                            * the user to change the in-core failmode property
                            * without syncing it out to disk (I/Os might
                            * currently be blocked). We do this by returning
                            * EIO to the caller (spa_prop_set) to trick it
                            * into thinking we encountered a property validation
                            * error.
                            */
                           if (!error && spa_suspended(spa)) {
                                   spa->spa_failmode = intval;
                                   error = SET_ERROR(EIO);
                           }
                           break;
   
                   case ZPOOL_PROP_CACHEFILE:
                           if ((error = nvpair_value_string(elem, &strval)) != 0)
                                   break;
   
                           if (strval[0] == '\0')
                                   break;
   
                           if (strcmp(strval, "none") == 0)
                                   break;
   
                           if (strval[0] != '/') {
                                   error = SET_ERROR(EINVAL);
                                   break;
                           }
   
                           slash = strrchr(strval, '/');
                           ASSERT(slash != NULL);
   
                           if (slash[1] == '\0' || strcmp(slash, "/.") == 0 ||
                               strcmp(slash, "/..") == 0)
                                   error = SET_ERROR(EINVAL);
                           break;
   
                   case ZPOOL_PROP_COMMENT:
                           if ((error = nvpair_value_string(elem, &strval)) != 0)
                                   break;
                           for (check = strval; *check != '\0'; check++) {
                                   if (!isprint(*check)) {
                                           error = SET_ERROR(EINVAL);
                                           break;
                                   }
                           }
                           if (strlen(strval) > ZPROP_MAX_COMMENT)
                                   error = SET_ERROR(E2BIG);
                           break;
   
                   default:
                           break;
                   }
   
                   if (error)
                           break;
           }
   
           (void) nvlist_remove_all(props,
               zpool_prop_to_name(ZPOOL_PROP_DEDUPDITTO));
   
           if (!error && reset_bootfs) {
                   error = nvlist_remove(props,
                       zpool_prop_to_name(ZPOOL_PROP_BOOTFS), DATA_TYPE_STRING);
   
                   if (!error) {
                           error = nvlist_add_uint64(props,
                               zpool_prop_to_name(ZPOOL_PROP_BOOTFS), objnum);
                   }
           }
   
           return (error);
   }
   
   void
   spa_configfile_set(spa_t *spa, nvlist_t *nvp, boolean_t need_sync)
   {
           char *cachefile;
           spa_config_dirent_t *dp;
   
           if (nvlist_lookup_string(nvp, zpool_prop_to_name(ZPOOL_PROP_CACHEFILE),
               &cachefile) != 0)
                   return;
   
           dp = kmem_alloc(sizeof (spa_config_dirent_t),
               KM_SLEEP);
   
           if (cachefile[0] == '\0')
                   dp->scd_path = spa_strdup(spa_config_path);
           else if (strcmp(cachefile, "none") == 0)
                   dp->scd_path = NULL;
           else
                   dp->scd_path = spa_strdup(cachefile);
   
           list_insert_head(&spa->spa_config_list, dp);
           if (need_sync)
                   spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
   }
   
   int
   spa_prop_set(spa_t *spa, nvlist_t *nvp)
   {
           int error;
           nvpair_t *elem = NULL;
           boolean_t need_sync = B_FALSE;
   
           if ((error = spa_prop_validate(spa, nvp)) != 0)
                   return (error);
   
           while ((elem = nvlist_next_nvpair(nvp, elem)) != NULL) {
                   zpool_prop_t prop = zpool_name_to_prop(nvpair_name(elem));
   
                   if (prop == ZPOOL_PROP_CACHEFILE ||
                       prop == ZPOOL_PROP_ALTROOT ||
                       prop == ZPOOL_PROP_READONLY)
                           continue;
   
                   if (prop == ZPOOL_PROP_VERSION || prop == ZPOOL_PROP_INVAL) {
                           uint64_t ver = 0;
   
                           if (prop == ZPOOL_PROP_VERSION) {
                                   VERIFY(nvpair_value_uint64(elem, &ver) == 0);
                           } else {
                                   ASSERT(zpool_prop_feature(nvpair_name(elem)));
                                   ver = SPA_VERSION_FEATURES;
                                   need_sync = B_TRUE;
                           }
   
                           /* Save time if the version is already set. */
                           if (ver == spa_version(spa))
                                   continue;
   
                           /*
                            * In addition to the pool directory object, we might
                            * create the pool properties object, the features for
                            * read object, the features for write object, or the
                            * feature descriptions object.
                            */
                           error = dsl_sync_task(spa->spa_name, NULL,
                               spa_sync_version, &ver,
                               6, ZFS_SPACE_CHECK_RESERVED);
                           if (error)
                                   return (error);
                           continue;
                   }
   
                   need_sync = B_TRUE;
                   break;
           }
   
           if (need_sync) {
                   return (dsl_sync_task(spa->spa_name, NULL, spa_sync_props,
                       nvp, 6, ZFS_SPACE_CHECK_RESERVED));
           }
   
           return (0);
   }
   
   /*
    * If the bootfs property value is dsobj, clear it.
    */
   void
   spa_prop_clear_bootfs(spa_t *spa, uint64_t dsobj, dmu_tx_t *tx)
   {
           if (spa->spa_bootfs == dsobj && spa->spa_pool_props_object != 0) {
                   VERIFY(zap_remove(spa->spa_meta_objset,
                       spa->spa_pool_props_object,
                       zpool_prop_to_name(ZPOOL_PROP_BOOTFS), tx) == 0);
                   spa->spa_bootfs = 0;
           }
   }
   
   static int
   spa_change_guid_check(void *arg, dmu_tx_t *tx)
   {
           uint64_t *newguid __maybe_unused = arg;
           spa_t *spa = dmu_tx_pool(tx)->dp_spa;
           vdev_t *rvd = spa->spa_root_vdev;
           uint64_t vdev_state;
   
           if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
                   int error = (spa_has_checkpoint(spa)) ?
                       ZFS_ERR_CHECKPOINT_EXISTS : ZFS_ERR_DISCARDING_CHECKPOINT;
                   return (SET_ERROR(error));
           }
   
           spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
           vdev_state = rvd->vdev_state;
           spa_config_exit(spa, SCL_STATE, FTAG);
   
           if (vdev_state != VDEV_STATE_HEALTHY)
                   return (SET_ERROR(ENXIO));
   
           ASSERT3U(spa_guid(spa), !=, *newguid);
   
           return (0);
   }
   
   static void
   spa_change_guid_sync(void *arg, dmu_tx_t *tx)
   {
           uint64_t *newguid = arg;
           spa_t *spa = dmu_tx_pool(tx)->dp_spa;
           uint64_t oldguid;
           vdev_t *rvd = spa->spa_root_vdev;
   
           oldguid = spa_guid(spa);
   
           spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
           rvd->vdev_guid = *newguid;
           rvd->vdev_guid_sum += (*newguid - oldguid);
           vdev_config_dirty(rvd);
           spa_config_exit(spa, SCL_STATE, FTAG);
   
           spa_history_log_internal(spa, "guid change", tx, "old=%llu new=%llu",
               (u_longlong_t)oldguid, (u_longlong_t)*newguid);
   }
   
   /*
    * Change the GUID for the pool.  This is done so that we can later
    * re-import a pool built from a clone of our own vdevs.  We will modify
    * the root vdev's guid, our own pool guid, and then mark all of our
    * vdevs dirty.  Note that we must make sure that all our vdevs are
    * online when we do this, or else any vdevs that weren't present
    * would be orphaned from our pool.  We are also going to issue a
    * sysevent to update any watchers.
    */
   int
   spa_change_guid(spa_t *spa)
   {
           int error;
           uint64_t guid;
   
           mutex_enter(&spa->spa_vdev_top_lock);
           mutex_enter(&spa_namespace_lock);
           guid = spa_generate_guid(NULL);
   
           error = dsl_sync_task(spa->spa_name, spa_change_guid_check,
               spa_change_guid_sync, &guid, 5, ZFS_SPACE_CHECK_RESERVED);
   
           if (error == 0) {
                   /*
                    * Clear the kobj flag from all the vdevs to allow
                    * vdev_cache_process_kobj_evt() to post events to all the
                    * vdevs since GUID is updated.
                    */
                   vdev_clear_kobj_evt(spa->spa_root_vdev);
                   for (int i = 0; i < spa->spa_l2cache.sav_count; i++)
                           vdev_clear_kobj_evt(spa->spa_l2cache.sav_vdevs[i]);
   
                   spa_write_cachefile(spa, B_FALSE, B_TRUE, B_TRUE);
                   spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_REGUID);
           }
   
           mutex_exit(&spa_namespace_lock);
           mutex_exit(&spa->spa_vdev_top_lock);
   
           return (error);
   }
   
   /*
    * ==========================================================================
    * SPA state manipulation (open/create/destroy/import/export)
    * ==========================================================================
    */
   
   static int
   spa_error_entry_compare(const void *a, const void *b)
   {
           const spa_error_entry_t *sa = (const spa_error_entry_t *)a;
           const spa_error_entry_t *sb = (const spa_error_entry_t *)b;
           int ret;
   
           ret = memcmp(&sa->se_bookmark, &sb->se_bookmark,
               sizeof (zbookmark_phys_t));
   
           return (TREE_ISIGN(ret));
   }
   
   /*
    * Utility function which retrieves copies of the current logs and
    * re-initializes them in the process.
    */
   void
   spa_get_errlists(spa_t *spa, avl_tree_t *last, avl_tree_t *scrub)
   {
           ASSERT(MUTEX_HELD(&spa->spa_errlist_lock));
   
           memcpy(last, &spa->spa_errlist_last, sizeof (avl_tree_t));
           memcpy(scrub, &spa->spa_errlist_scrub, sizeof (avl_tree_t));
   
           avl_create(&spa->spa_errlist_scrub,
               spa_error_entry_compare, sizeof (spa_error_entry_t),
               offsetof(spa_error_entry_t, se_avl));
           avl_create(&spa->spa_errlist_last,
               spa_error_entry_compare, sizeof (spa_error_entry_t),
               offsetof(spa_error_entry_t, se_avl));
   }
   
   static void
   spa_taskqs_init(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
   {
           const zio_taskq_info_t *ztip = &zio_taskqs[t][q];
           enum zti_modes mode = ztip->zti_mode;
           uint_t value = ztip->zti_value;
           uint_t count = ztip->zti_count;
           spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
           uint_t cpus, flags = TASKQ_DYNAMIC;
           boolean_t batch = B_FALSE;
   
           switch (mode) {
           case ZTI_MODE_FIXED:
                   ASSERT3U(value, >, 0);
                   break;
   
           case ZTI_MODE_BATCH:
                   batch = B_TRUE;
                   flags |= TASKQ_THREADS_CPU_PCT;
                   value = MIN(zio_taskq_batch_pct, 100);
                   break;
   
           case ZTI_MODE_SCALE:
                   flags |= TASKQ_THREADS_CPU_PCT;
                   /*
                    * We want more taskqs to reduce lock contention, but we want
                    * less for better request ordering and CPU utilization.
                    */
                   cpus = MAX(1, boot_ncpus * zio_taskq_batch_pct / 100);
                   if (zio_taskq_batch_tpq > 0) {
                          count = MAX(1, (cpus + zio_taskq_batch_tpq / 2) /
                              zio_taskq_batch_tpq);
                  } else {
                          /*
                           * Prefer 6 threads per taskq, but no more taskqs
                           * than threads in them on large systems. For 80%:
                           *
                           *                 taskq   taskq   total
                           * cpus    taskqs  percent threads threads
                           * ------- ------- ------- ------- -------
                           * 1       1       80%     1       1
                           * 2       1       80%     1       1
                           * 4       1       80%     3       3
                           * 8       2       40%     3       6
                           * 16      3       27%     4       12
                           * 32      5       16%     5       25
                           * 64      7       11%     7       49
                           * 128     10      8%      10      100
                           * 256     14      6%      15      210
                           */
                          count = 1 + cpus / 6;
                          while (count * count > cpus)
                                  count--;
                  }
                  /* Limit each taskq within 100% to not trigger assertion. */
                  count = MAX(count, (zio_taskq_batch_pct + 99) / 100);
                  value = (zio_taskq_batch_pct + count / 2) / count;
                  break;
  
          case ZTI_MODE_NULL:
                  tqs->stqs_count = 0;
                  tqs->stqs_taskq = NULL;
                  return;
  
          default:
                  panic("unrecognized mode for %s_%s taskq (%u:%u) in "
                      "spa_activate()",
                      zio_type_name[t], zio_taskq_types[q], mode, value);
                  break;
          }
  
          ASSERT3U(count, >, 0);
          tqs->stqs_count = count;
          tqs->stqs_taskq = kmem_alloc(count * sizeof (taskq_t *), KM_SLEEP);
  
          for (uint_t i = 0; i < count; i++) {
                  taskq_t *tq;
                  char name[32];
  
                  if (count > 1)
                          (void) snprintf(name, sizeof (name), "%s_%s_%u",
                              zio_type_name[t], zio_taskq_types[q], i);
                  else
                          (void) snprintf(name, sizeof (name), "%s_%s",
                              zio_type_name[t], zio_taskq_types[q]);
  
                  if (zio_taskq_sysdc && spa->spa_proc != &p0) {
                          if (batch)
                                  flags |= TASKQ_DC_BATCH;
  
                          (void) zio_taskq_basedc;
                          tq = taskq_create_sysdc(name, value, 50, INT_MAX,
                              spa->spa_proc, zio_taskq_basedc, flags);
                  } else {
                          pri_t pri = maxclsyspri;
                          /*
                           * The write issue taskq can be extremely CPU
                           * intensive.  Run it at slightly less important
                           * priority than the other taskqs.
                           *
                           * Under Linux and FreeBSD this means incrementing
                           * the priority value as opposed to platforms like
                           * illumos where it should be decremented.
                           *
                           * On FreeBSD, if priorities divided by four (RQ_PPQ)
                           * are equal then a difference between them is
                           * insignificant.
                           */
                          if (t == ZIO_TYPE_WRITE && q == ZIO_TASKQ_ISSUE) {
  #if defined(__linux__)
                                  pri++;
  #elif defined(__FreeBSD__)
                                  pri += 4;
  #else
  #error "unknown OS"
  #endif
                          }
                          tq = taskq_create_proc(name, value, pri, 50,
                              INT_MAX, spa->spa_proc, flags);
                  }
  
                  tqs->stqs_taskq[i] = tq;
          }
  }
  
  static void
  spa_taskqs_fini(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
  {
          spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
  
          if (tqs->stqs_taskq == NULL) {
                  ASSERT3U(tqs->stqs_count, ==, 0);
                  return;
          }
  
          for (uint_t i = 0; i < tqs->stqs_count; i++) {
                  ASSERT3P(tqs->stqs_taskq[i], !=, NULL);
                  taskq_destroy(tqs->stqs_taskq[i]);
          }
  
          kmem_free(tqs->stqs_taskq, tqs->stqs_count * sizeof (taskq_t *));
          tqs->stqs_taskq = NULL;
  }
  
  /*
   * Dispatch a task to the appropriate taskq for the ZFS I/O type and priority.
   * Note that a type may have multiple discrete taskqs to avoid lock contention
   * on the taskq itself. In that case we choose which taskq at random by using
   * the low bits of gethrtime().
   */
  void
  spa_taskq_dispatch_ent(spa_t *spa, zio_type_t t, zio_taskq_type_t q,
      task_func_t *func, void *arg, uint_t flags, taskq_ent_t *ent)
  {
          spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
          taskq_t *tq;
  
          ASSERT3P(tqs->stqs_taskq, !=, NULL);
          ASSERT3U(tqs->stqs_count, !=, 0);
  
          if (tqs->stqs_count == 1) {
                  tq = tqs->stqs_taskq[0];
          } else {
                  tq = tqs->stqs_taskq[((uint64_t)gethrtime()) % tqs->stqs_count];
          }
  
          taskq_dispatch_ent(tq, func, arg, flags, ent);
  }
  
  /*
   * Same as spa_taskq_dispatch_ent() but block on the task until completion.
   */
  void
  spa_taskq_dispatch_sync(spa_t *spa, zio_type_t t, zio_taskq_type_t q,
      task_func_t *func, void *arg, uint_t flags)
  {
          spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
          taskq_t *tq;
          taskqid_t id;
  
          ASSERT3P(tqs->stqs_taskq, !=, NULL);
          ASSERT3U(tqs->stqs_count, !=, 0);
  
          if (tqs->stqs_count == 1) {
                  tq = tqs->stqs_taskq[0];
          } else {
                  tq = tqs->stqs_taskq[((uint64_t)gethrtime()) % tqs->stqs_count];
          }
  
          id = taskq_dispatch(tq, func, arg, flags);
          if (id)
                  taskq_wait_id(tq, id);
  }
  
  static void
  spa_create_zio_taskqs(spa_t *spa)
  {
          for (int t = 0; t < ZIO_TYPES; t++) {
                  for (int q = 0; q < ZIO_TASKQ_TYPES; q++) {
                          spa_taskqs_init(spa, t, q);
                  }
          }
  }
  
  /*
   * Disabled until spa_thread() can be adapted for Linux.
   */
  #undef HAVE_SPA_THREAD
  
  #if defined(_KERNEL) && defined(HAVE_SPA_THREAD)
  static void
  spa_thread(void *arg)
  {
          psetid_t zio_taskq_psrset_bind = PS_NONE;
          callb_cpr_t cprinfo;
  
          spa_t *spa = arg;
          user_t *pu = PTOU(curproc);
  
          CALLB_CPR_INIT(&cprinfo, &spa->spa_proc_lock, callb_generic_cpr,
              spa->spa_name);
  
          ASSERT(curproc != &p0);
          (void) snprintf(pu->u_psargs, sizeof (pu->u_psargs),
              "zpool-%s", spa->spa_name);
          (void) strlcpy(pu->u_comm, pu->u_psargs, sizeof (pu->u_comm));
  
          /* bind this thread to the requested psrset */
          if (zio_taskq_psrset_bind != PS_NONE) {
                  pool_lock();
                  mutex_enter(&cpu_lock);
                  mutex_enter(&pidlock);
                  mutex_enter(&curproc->p_lock);
  
                  if (cpupart_bind_thread(curthread, zio_taskq_psrset_bind,
                      0, NULL, NULL) == 0)  {
                          curthread->t_bind_pset = zio_taskq_psrset_bind;
                  } else {
                          cmn_err(CE_WARN,
                              "Couldn't bind process for zfs pool \"%s\" to "
                              "pset %d\n", spa->spa_name, zio_taskq_psrset_bind);
                  }
  
                  mutex_exit(&curproc->p_lock);
                  mutex_exit(&pidlock);
                  mutex_exit(&cpu_lock);
                  pool_unlock();
          }
  
          if (zio_taskq_sysdc) {
                  sysdc_thread_enter(curthread, 100, 0);
          }
  
          spa->spa_proc = curproc;
          spa->spa_did = curthread->t_did;
  
          spa_create_zio_taskqs(spa);
  
          mutex_enter(&spa->spa_proc_lock);
          ASSERT(spa->spa_proc_state == SPA_PROC_CREATED);
  
          spa->spa_proc_state = SPA_PROC_ACTIVE;
          cv_broadcast(&spa->spa_proc_cv);
  
          CALLB_CPR_SAFE_BEGIN(&cprinfo);
          while (spa->spa_proc_state == SPA_PROC_ACTIVE)
                  cv_wait(&spa->spa_proc_cv, &spa->spa_proc_lock);
          CALLB_CPR_SAFE_END(&cprinfo, &spa->spa_proc_lock);
  
          ASSERT(spa->spa_proc_state == SPA_PROC_DEACTIVATE);
          spa->spa_proc_state = SPA_PROC_GONE;
          spa->spa_proc = &p0;
          cv_broadcast(&spa->spa_proc_cv);
          CALLB_CPR_EXIT(&cprinfo);       /* drops spa_proc_lock */
  
          mutex_enter(&curproc->p_lock);
          lwp_exit();
  }
  #endif
  
  /*
   * Activate an uninitialized pool.
   */
  static void
  spa_activate(spa_t *spa, spa_mode_t mode)
  {
          ASSERT(spa->spa_state == POOL_STATE_UNINITIALIZED);
  
          spa->spa_state = POOL_STATE_ACTIVE;
          spa->spa_mode = mode;
          spa->spa_read_spacemaps = spa_mode_readable_spacemaps;
  
          spa->spa_normal_class = metaslab_class_create(spa, &zfs_metaslab_ops);
          spa->spa_log_class = metaslab_class_create(spa, &zfs_metaslab_ops);
          spa->spa_embedded_log_class =
              metaslab_class_create(spa, &zfs_metaslab_ops);
          spa->spa_special_class = metaslab_class_create(spa, &zfs_metaslab_ops);
          spa->spa_dedup_class = metaslab_class_create(spa, &zfs_metaslab_ops);
  
          /* Try to create a covering process */
          mutex_enter(&spa->spa_proc_lock);
          ASSERT(spa->spa_proc_state == SPA_PROC_NONE);
          ASSERT(spa->spa_proc == &p0);
          spa->spa_did = 0;
  
          (void) spa_create_process;
  #ifdef HAVE_SPA_THREAD
          /* Only create a process if we're going to be around a while. */
          if (spa_create_process && strcmp(spa->spa_name, TRYIMPORT_NAME) != 0) {
                  if (newproc(spa_thread, (caddr_t)spa, syscid, maxclsyspri,
                      NULL, 0) == 0) {
                          spa->spa_proc_state = SPA_PROC_CREATED;
                          while (spa->spa_proc_state == SPA_PROC_CREATED) {
                                  cv_wait(&spa->spa_proc_cv,
                                      &spa->spa_proc_lock);
                          }
                          ASSERT(spa->spa_proc_state == SPA_PROC_ACTIVE);
                          ASSERT(spa->spa_proc != &p0);
                          ASSERT(spa->spa_did != 0);
                  } else {
  #ifdef _KERNEL
                          cmn_err(CE_WARN,
                              "Couldn't create process for zfs pool \"%s\"\n",
                              spa->spa_name);
  #endif
                  }
          }
  #endif /* HAVE_SPA_THREAD */
          mutex_exit(&spa->spa_proc_lock);
  
          /* If we didn't create a process, we need to create our taskqs. */
          if (spa->spa_proc == &p0) {
                  spa_create_zio_taskqs(spa);
          }
  
          for (size_t i = 0; i < TXG_SIZE; i++) {
                  spa->spa_txg_zio[i] = zio_root(spa, NULL, NULL,
                      ZIO_FLAG_CANFAIL);
          }
  
          list_create(&spa->spa_config_dirty_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_config_dirty_node));
          list_create(&spa->spa_evicting_os_list, sizeof (objset_t),
              offsetof(objset_t, os_evicting_node));
          list_create(&spa->spa_state_dirty_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_state_dirty_node));
  
          txg_list_create(&spa->spa_vdev_txg_list, spa,
              offsetof(struct vdev, vdev_txg_node));
  
          avl_create(&spa->spa_errlist_scrub,
              spa_error_entry_compare, sizeof (spa_error_entry_t),
              offsetof(spa_error_entry_t, se_avl));
          avl_create(&spa->spa_errlist_last,
              spa_error_entry_compare, sizeof (spa_error_entry_t),
              offsetof(spa_error_entry_t, se_avl));
          avl_create(&spa->spa_errlist_healed,
              spa_error_entry_compare, sizeof (spa_error_entry_t),
              offsetof(spa_error_entry_t, se_avl));
  
          spa_activate_os(spa);
  
          spa_keystore_init(&spa->spa_keystore);
  
          /*
           * This taskq is used to perform zvol-minor-related tasks
           * asynchronously. This has several advantages, including easy
           * resolution of various deadlocks.
           *
           * The taskq must be single threaded to ensure tasks are always
           * processed in the order in which they were dispatched.
           *
           * A taskq per pool allows one to keep the pools independent.
           * This way if one pool is suspended, it will not impact another.
           *
           * The preferred location to dispatch a zvol minor task is a sync
           * task. In this context, there is easy access to the spa_t and minimal
           * error handling is required because the sync task must succeed.
           */
          spa->spa_zvol_taskq = taskq_create("z_zvol", 1, defclsyspri,
              1, INT_MAX, 0);
  
          /*
           * Taskq dedicated to prefetcher threads: this is used to prevent the
           * pool traverse code from monopolizing the global (and limited)
           * system_taskq by inappropriately scheduling long running tasks on it.
           */
          spa->spa_prefetch_taskq = taskq_create("z_prefetch", 100,
              defclsyspri, 1, INT_MAX, TASKQ_DYNAMIC | TASKQ_THREADS_CPU_PCT);
  
          /*
           * The taskq to upgrade datasets in this pool. Currently used by
           * feature SPA_FEATURE_USEROBJ_ACCOUNTING/SPA_FEATURE_PROJECT_QUOTA.
           */
          spa->spa_upgrade_taskq = taskq_create("z_upgrade", 100,
              defclsyspri, 1, INT_MAX, TASKQ_DYNAMIC | TASKQ_THREADS_CPU_PCT);
  }
  
  /*
   * Opposite of spa_activate().
   */
  static void
  spa_deactivate(spa_t *spa)
  {
          ASSERT(spa->spa_sync_on == B_FALSE);
          ASSERT(spa->spa_dsl_pool == NULL);
          ASSERT(spa->spa_root_vdev == NULL);
          ASSERT(spa->spa_async_zio_root == NULL);
          ASSERT(spa->spa_state != POOL_STATE_UNINITIALIZED);
  
          spa_evicting_os_wait(spa);
  
          if (spa->spa_zvol_taskq) {
                  taskq_destroy(spa->spa_zvol_taskq);
                  spa->spa_zvol_taskq = NULL;
          }
  
          if (spa->spa_prefetch_taskq) {
                  taskq_destroy(spa->spa_prefetch_taskq);
                  spa->spa_prefetch_taskq = NULL;
          }
  
          if (spa->spa_upgrade_taskq) {
                  taskq_destroy(spa->spa_upgrade_taskq);
                  spa->spa_upgrade_taskq = NULL;
          }
  
          txg_list_destroy(&spa->spa_vdev_txg_list);
  
          list_destroy(&spa->spa_config_dirty_list);
          list_destroy(&spa->spa_evicting_os_list);
          list_destroy(&spa->spa_state_dirty_list);
  
          taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);
  
          for (int t = 0; t < ZIO_TYPES; t++) {
                  for (int q = 0; q < ZIO_TASKQ_TYPES; q++) {
                          spa_taskqs_fini(spa, t, q);
                  }
          }
  
          for (size_t i = 0; i < TXG_SIZE; i++) {
                  ASSERT3P(spa->spa_txg_zio[i], !=, NULL);
                  VERIFY0(zio_wait(spa->spa_txg_zio[i]));
                  spa->spa_txg_zio[i] = NULL;
          }
  
          metaslab_class_destroy(spa->spa_normal_class);
          spa->spa_normal_class = NULL;
  
          metaslab_class_destroy(spa->spa_log_class);
          spa->spa_log_class = NULL;
  
          metaslab_class_destroy(spa->spa_embedded_log_class);
          spa->spa_embedded_log_class = NULL;
  
          metaslab_class_destroy(spa->spa_special_class);
          spa->spa_special_class = NULL;
  
          metaslab_class_destroy(spa->spa_dedup_class);
          spa->spa_dedup_class = NULL;
  
          /*
           * If this was part of an import or the open otherwise failed, we may
           * still have errors left in the queues.  Empty them just in case.
           */
          spa_errlog_drain(spa);
          avl_destroy(&spa->spa_errlist_scrub);
          avl_destroy(&spa->spa_errlist_last);
          avl_destroy(&spa->spa_errlist_healed);
  
          spa_keystore_fini(&spa->spa_keystore);
  
          spa->spa_state = POOL_STATE_UNINITIALIZED;
  
          mutex_enter(&spa->spa_proc_lock);
          if (spa->spa_proc_state != SPA_PROC_NONE) {
                  ASSERT(spa->spa_proc_state == SPA_PROC_ACTIVE);
                  spa->spa_proc_state = SPA_PROC_DEACTIVATE;
                  cv_broadcast(&spa->spa_proc_cv);
                  while (spa->spa_proc_state == SPA_PROC_DEACTIVATE) {
                          ASSERT(spa->spa_proc != &p0);
                          cv_wait(&spa->spa_proc_cv, &spa->spa_proc_lock);
                  }
                  ASSERT(spa->spa_proc_state == SPA_PROC_GONE);
                  spa->spa_proc_state = SPA_PROC_NONE;
          }
          ASSERT(spa->spa_proc == &p0);
          mutex_exit(&spa->spa_proc_lock);
  
          /*
           * We want to make sure spa_thread() has actually exited the ZFS
           * module, so that the module can't be unloaded out from underneath
           * it.
           */
          if (spa->spa_did != 0) {
                  thread_join(spa->spa_did);
                  spa->spa_did = 0;
          }
  
          spa_deactivate_os(spa);
  
  }
  
  /*
   * Verify a pool configuration, and construct the vdev tree appropriately.  This
   * will create all the necessary vdevs in the appropriate layout, with each vdev
   * in the CLOSED state.  This will prep the pool before open/creation/import.
   * All vdev validation is done by the vdev_alloc() routine.
   */
  int
  spa_config_parse(spa_t *spa, vdev_t **vdp, nvlist_t *nv, vdev_t *parent,
      uint_t id, int atype)
  {
          nvlist_t **child;
          uint_t children;
          int error;
  
          if ((error = vdev_alloc(spa, vdp, nv, parent, id, atype)) != 0)
                  return (error);
  
          if ((*vdp)->vdev_ops->vdev_op_leaf)
                  return (0);
  
          error = nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
              &child, &children);
  
          if (error == ENOENT)
                  return (0);
  
          if (error) {
                  vdev_free(*vdp);
                  *vdp = NULL;
                  return (SET_ERROR(EINVAL));
          }
  
          for (int c = 0; c < children; c++) {
                  vdev_t *vd;
                  if ((error = spa_config_parse(spa, &vd, child[c], *vdp, c,
                      atype)) != 0) {
                          vdev_free(*vdp);
                          *vdp = NULL;
                          return (error);
                  }
          }
  
          ASSERT(*vdp != NULL);
  
          return (0);
  }
  
  static boolean_t
  spa_should_flush_logs_on_unload(spa_t *spa)
  {
          if (!spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP))
                  return (B_FALSE);
  
          if (!spa_writeable(spa))
                  return (B_FALSE);
  
          if (!spa->spa_sync_on)
                  return (B_FALSE);
  
          if (spa_state(spa) != POOL_STATE_EXPORTED)
                  return (B_FALSE);
  
          if (zfs_keep_log_spacemaps_at_export)
                  return (B_FALSE);
  
          return (B_TRUE);
  }
  
  /*
   * Opens a transaction that will set the flag that will instruct
   * spa_sync to attempt to flush all the metaslabs for that txg.
   */
  static void
  spa_unload_log_sm_flush_all(spa_t *spa)
  {
          dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
          VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
  
          ASSERT3U(spa->spa_log_flushall_txg, ==, 0);
          spa->spa_log_flushall_txg = dmu_tx_get_txg(tx);
  
          dmu_tx_commit(tx);
          txg_wait_synced(spa_get_dsl(spa), spa->spa_log_flushall_txg);
  }
  
  static void
  spa_unload_log_sm_metadata(spa_t *spa)
  {
          void *cookie = NULL;
          spa_log_sm_t *sls;
          while ((sls = avl_destroy_nodes(&spa->spa_sm_logs_by_txg,
              &cookie)) != NULL) {
                  VERIFY0(sls->sls_mscount);
                  kmem_free(sls, sizeof (spa_log_sm_t));
          }
  
          for (log_summary_entry_t *e = list_head(&spa->spa_log_summary);
              e != NULL; e = list_head(&spa->spa_log_summary)) {
                  VERIFY0(e->lse_mscount);
                  list_remove(&spa->spa_log_summary, e);
                  kmem_free(e, sizeof (log_summary_entry_t));
          }
  
          spa->spa_unflushed_stats.sus_nblocks = 0;
          spa->spa_unflushed_stats.sus_memused = 0;
          spa->spa_unflushed_stats.sus_blocklimit = 0;
  }
  
  static void
  spa_destroy_aux_threads(spa_t *spa)
  {
          if (spa->spa_condense_zthr != NULL) {
                  zthr_destroy(spa->spa_condense_zthr);
                  spa->spa_condense_zthr = NULL;
          }
          if (spa->spa_checkpoint_discard_zthr != NULL) {
                  zthr_destroy(spa->spa_checkpoint_discard_zthr);
                  spa->spa_checkpoint_discard_zthr = NULL;
          }
          if (spa->spa_livelist_delete_zthr != NULL) {
                  zthr_destroy(spa->spa_livelist_delete_zthr);
                  spa->spa_livelist_delete_zthr = NULL;
          }
          if (spa->spa_livelist_condense_zthr != NULL) {
                  zthr_destroy(spa->spa_livelist_condense_zthr);
                  spa->spa_livelist_condense_zthr = NULL;
          }
  }
  
  /*
   * Opposite of spa_load().
   */
  static void
  spa_unload(spa_t *spa)
  {
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa_state(spa) != POOL_STATE_UNINITIALIZED);
  
          spa_import_progress_remove(spa_guid(spa));
          spa_load_note(spa, "UNLOADING");
  
          spa_wake_waiters(spa);
  
          /*
           * If we have set the spa_final_txg, we have already performed the
           * tasks below in spa_export_common(). We should not redo it here since
           * we delay the final TXGs beyond what spa_final_txg is set at.
           */
          if (spa->spa_final_txg == UINT64_MAX) {
                  /*
                   * If the log space map feature is enabled and the pool is
                   * getting exported (but not destroyed), we want to spend some
                   * time flushing as many metaslabs as we can in an attempt to
                   * destroy log space maps and save import time.
                   */
                  if (spa_should_flush_logs_on_unload(spa))
                          spa_unload_log_sm_flush_all(spa);
  
                  /*
                   * Stop async tasks.
                   */
                  spa_async_suspend(spa);
  
                  if (spa->spa_root_vdev) {
                          vdev_t *root_vdev = spa->spa_root_vdev;
                          vdev_initialize_stop_all(root_vdev,
                              VDEV_INITIALIZE_ACTIVE);
                          vdev_trim_stop_all(root_vdev, VDEV_TRIM_ACTIVE);
                          vdev_autotrim_stop_all(spa);
                          vdev_rebuild_stop_all(spa);
                  }
          }
  
          /*
           * Stop syncing.
           */
          if (spa->spa_sync_on) {
                  txg_sync_stop(spa->spa_dsl_pool);
                  spa->spa_sync_on = B_FALSE;
          }
  
          /*
           * This ensures that there is no async metaslab prefetching
           * while we attempt to unload the spa.
           */
          if (spa->spa_root_vdev != NULL) {
                  for (int c = 0; c < spa->spa_root_vdev->vdev_children; c++) {
                          vdev_t *vc = spa->spa_root_vdev->vdev_child[c];
                          if (vc->vdev_mg != NULL)
                                  taskq_wait(vc->vdev_mg->mg_taskq);
                  }
          }
  
          if (spa->spa_mmp.mmp_thread)
                  mmp_thread_stop(spa);
  
          /*
           * Wait for any outstanding async I/O to complete.
           */
          if (spa->spa_async_zio_root != NULL) {
                  for (int i = 0; i < max_ncpus; i++)
                          (void) zio_wait(spa->spa_async_zio_root[i]);
                  kmem_free(spa->spa_async_zio_root, max_ncpus * sizeof (void *));
                  spa->spa_async_zio_root = NULL;
          }
  
          if (spa->spa_vdev_removal != NULL) {
                  spa_vdev_removal_destroy(spa->spa_vdev_removal);
                  spa->spa_vdev_removal = NULL;
          }
  
          spa_destroy_aux_threads(spa);
  
          spa_condense_fini(spa);
  
          bpobj_close(&spa->spa_deferred_bpobj);
  
          spa_config_enter(spa, SCL_ALL, spa, RW_WRITER);
  
          /*
           * Close all vdevs.
           */
          if (spa->spa_root_vdev)
                  vdev_free(spa->spa_root_vdev);
          ASSERT(spa->spa_root_vdev == NULL);
  
          /*
           * Close the dsl pool.
           */
          if (spa->spa_dsl_pool) {
                  dsl_pool_close(spa->spa_dsl_pool);
                  spa->spa_dsl_pool = NULL;
                  spa->spa_meta_objset = NULL;
          }
  
          ddt_unload(spa);
          spa_unload_log_sm_metadata(spa);
  
          /*
           * Drop and purge level 2 cache
           */
          spa_l2cache_drop(spa);
  
          for (int i = 0; i < spa->spa_spares.sav_count; i++)
                  vdev_free(spa->spa_spares.sav_vdevs[i]);
          if (spa->spa_spares.sav_vdevs) {
                  kmem_free(spa->spa_spares.sav_vdevs,
                      spa->spa_spares.sav_count * sizeof (void *));
                  spa->spa_spares.sav_vdevs = NULL;
          }
          if (spa->spa_spares.sav_config) {
                  nvlist_free(spa->spa_spares.sav_config);
                  spa->spa_spares.sav_config = NULL;
          }
          spa->spa_spares.sav_count = 0;
  
          for (int i = 0; i < spa->spa_l2cache.sav_count; i++) {
                  vdev_clear_stats(spa->spa_l2cache.sav_vdevs[i]);
                  vdev_free(spa->spa_l2cache.sav_vdevs[i]);
          }
          if (spa->spa_l2cache.sav_vdevs) {
                  kmem_free(spa->spa_l2cache.sav_vdevs,
                      spa->spa_l2cache.sav_count * sizeof (void *));
                  spa->spa_l2cache.sav_vdevs = NULL;
          }
          if (spa->spa_l2cache.sav_config) {
                  nvlist_free(spa->spa_l2cache.sav_config);
                  spa->spa_l2cache.sav_config = NULL;
          }
          spa->spa_l2cache.sav_count = 0;
  
          spa->spa_async_suspended = 0;
  
          spa->spa_indirect_vdevs_loaded = B_FALSE;
  
          if (spa->spa_comment != NULL) {
                  spa_strfree(spa->spa_comment);
                  spa->spa_comment = NULL;
          }
          if (spa->spa_compatibility != NULL) {
                  spa_strfree(spa->spa_compatibility);
                  spa->spa_compatibility = NULL;
          }
  
          spa_config_exit(spa, SCL_ALL, spa);
  }
  
  /*
   * Load (or re-load) the current list of vdevs describing the active spares for
   * this pool.  When this is called, we have some form of basic information in
   * 'spa_spares.sav_config'.  We parse this into vdevs, try to open them, and
   * then re-generate a more complete list including status information.
   */
  void
  spa_load_spares(spa_t *spa)
  {
          nvlist_t **spares;
          uint_t nspares;
          int i;
          vdev_t *vd, *tvd;
  
  #ifndef _KERNEL
          /*
           * zdb opens both the current state of the pool and the
           * checkpointed state (if present), with a different spa_t.
           *
           * As spare vdevs are shared among open pools, we skip loading
           * them when we load the checkpointed state of the pool.
           */
          if (!spa_writeable(spa))
                  return;
  #endif
  
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          /*
           * First, close and free any existing spare vdevs.
           */
          for (i = 0; i < spa->spa_spares.sav_count; i++) {
                  vd = spa->spa_spares.sav_vdevs[i];
  
                  /* Undo the call to spa_activate() below */
                  if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
                      B_FALSE)) != NULL && tvd->vdev_isspare)
                          spa_spare_remove(tvd);
                  vdev_close(vd);
                  vdev_free(vd);
          }
  
          if (spa->spa_spares.sav_vdevs)
                  kmem_free(spa->spa_spares.sav_vdevs,
                      spa->spa_spares.sav_count * sizeof (void *));
  
          if (spa->spa_spares.sav_config == NULL)
                  nspares = 0;
          else
                  VERIFY0(nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
                      ZPOOL_CONFIG_SPARES, &spares, &nspares));
  
          spa->spa_spares.sav_count = (int)nspares;
          spa->spa_spares.sav_vdevs = NULL;
  
          if (nspares == 0)
                  return;
  
          /*
           * Construct the array of vdevs, opening them to get status in the
           * process.   For each spare, there is potentially two different vdev_t
           * structures associated with it: one in the list of spares (used only
           * for basic validation purposes) and one in the active vdev
           * configuration (if it's spared in).  During this phase we open and
           * validate each vdev on the spare list.  If the vdev also exists in the
           * active configuration, then we also mark this vdev as an active spare.
           */
          spa->spa_spares.sav_vdevs = kmem_zalloc(nspares * sizeof (void *),
              KM_SLEEP);
          for (i = 0; i < spa->spa_spares.sav_count; i++) {
                  VERIFY(spa_config_parse(spa, &vd, spares[i], NULL, 0,
                      VDEV_ALLOC_SPARE) == 0);
                  ASSERT(vd != NULL);
  
                  spa->spa_spares.sav_vdevs[i] = vd;
  
                  if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
                      B_FALSE)) != NULL) {
                          if (!tvd->vdev_isspare)
                                  spa_spare_add(tvd);
  
                          /*
                           * We only mark the spare active if we were successfully
                           * able to load the vdev.  Otherwise, importing a pool
                           * with a bad active spare would result in strange
                           * behavior, because multiple pool would think the spare
                           * is actively in use.
                           *
                           * There is a vulnerability here to an equally bizarre
                           * circumstance, where a dead active spare is later
                           * brought back to life (onlined or otherwise).  Given
                           * the rarity of this scenario, and the extra complexity
                           * it adds, we ignore the possibility.
                           */
                          if (!vdev_is_dead(tvd))
                                  spa_spare_activate(tvd);
                  }
  
                  vd->vdev_top = vd;
                  vd->vdev_aux = &spa->spa_spares;
  
                  if (vdev_open(vd) != 0)
                          continue;
  
                  if (vdev_validate_aux(vd) == 0)
                          spa_spare_add(vd);
          }
  
          /*
           * Recompute the stashed list of spares, with status information
           * this time.
           */
          fnvlist_remove(spa->spa_spares.sav_config, ZPOOL_CONFIG_SPARES);
  
          spares = kmem_alloc(spa->spa_spares.sav_count * sizeof (void *),
              KM_SLEEP);
          for (i = 0; i < spa->spa_spares.sav_count; i++)
                  spares[i] = vdev_config_generate(spa,
                      spa->spa_spares.sav_vdevs[i], B_TRUE, VDEV_CONFIG_SPARE);
          fnvlist_add_nvlist_array(spa->spa_spares.sav_config,
              ZPOOL_CONFIG_SPARES, (const nvlist_t * const *)spares,
              spa->spa_spares.sav_count);
          for (i = 0; i < spa->spa_spares.sav_count; i++)
                  nvlist_free(spares[i]);
          kmem_free(spares, spa->spa_spares.sav_count * sizeof (void *));
  }
  
  /*
   * Load (or re-load) the current list of vdevs describing the active l2cache for
   * this pool.  When this is called, we have some form of basic information in
   * 'spa_l2cache.sav_config'.  We parse this into vdevs, try to open them, and
   * then re-generate a more complete list including status information.
   * Devices which are already active have their details maintained, and are
   * not re-opened.
   */
  void
  spa_load_l2cache(spa_t *spa)
  {
          nvlist_t **l2cache = NULL;
          uint_t nl2cache;
          int i, j, oldnvdevs;
          uint64_t guid;
          vdev_t *vd, **oldvdevs, **newvdevs;
          spa_aux_vdev_t *sav = &spa->spa_l2cache;
  
  #ifndef _KERNEL
          /*
           * zdb opens both the current state of the pool and the
           * checkpointed state (if present), with a different spa_t.
           *
           * As L2 caches are part of the ARC which is shared among open
           * pools, we skip loading them when we load the checkpointed
           * state of the pool.
           */
          if (!spa_writeable(spa))
                  return;
  #endif
  
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          oldvdevs = sav->sav_vdevs;
          oldnvdevs = sav->sav_count;
          sav->sav_vdevs = NULL;
          sav->sav_count = 0;
  
          if (sav->sav_config == NULL) {
                  nl2cache = 0;
                  newvdevs = NULL;
                  goto out;
          }
  
          VERIFY0(nvlist_lookup_nvlist_array(sav->sav_config,
              ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache));
          newvdevs = kmem_alloc(nl2cache * sizeof (void *), KM_SLEEP);
  
          /*
           * Process new nvlist of vdevs.
           */
          for (i = 0; i < nl2cache; i++) {
                  guid = fnvlist_lookup_uint64(l2cache[i], ZPOOL_CONFIG_GUID);
  
                  newvdevs[i] = NULL;
                  for (j = 0; j < oldnvdevs; j++) {
                          vd = oldvdevs[j];
                          if (vd != NULL && guid == vd->vdev_guid) {
                                  /*
                                   * Retain previous vdev for add/remove ops.
                                   */
                                  newvdevs[i] = vd;
                                  oldvdevs[j] = NULL;
                                  break;
                          }
                  }
  
                  if (newvdevs[i] == NULL) {
                          /*
                           * Create new vdev
                           */
                          VERIFY(spa_config_parse(spa, &vd, l2cache[i], NULL, 0,
                              VDEV_ALLOC_L2CACHE) == 0);
                          ASSERT(vd != NULL);
                          newvdevs[i] = vd;
  
                          /*
                           * Commit this vdev as an l2cache device,
                           * even if it fails to open.
                           */
                          spa_l2cache_add(vd);
  
                          vd->vdev_top = vd;
                          vd->vdev_aux = sav;
  
                          spa_l2cache_activate(vd);
  
                          if (vdev_open(vd) != 0)
                                  continue;
  
                          (void) vdev_validate_aux(vd);
  
                          if (!vdev_is_dead(vd))
                                  l2arc_add_vdev(spa, vd);
  
                          /*
                           * Upon cache device addition to a pool or pool
                           * creation with a cache device or if the header
                           * of the device is invalid we issue an async
                           * TRIM command for the whole device which will
                           * execute if l2arc_trim_ahead > 0.
                           */
                          spa_async_request(spa, SPA_ASYNC_L2CACHE_TRIM);
                  }
          }
  
          sav->sav_vdevs = newvdevs;
          sav->sav_count = (int)nl2cache;
  
          /*
           * Recompute the stashed list of l2cache devices, with status
           * information this time.
           */
          fnvlist_remove(sav->sav_config, ZPOOL_CONFIG_L2CACHE);
  
          if (sav->sav_count > 0)
                  l2cache = kmem_alloc(sav->sav_count * sizeof (void *),
                      KM_SLEEP);
          for (i = 0; i < sav->sav_count; i++)
                  l2cache[i] = vdev_config_generate(spa,
                      sav->sav_vdevs[i], B_TRUE, VDEV_CONFIG_L2CACHE);
          fnvlist_add_nvlist_array(sav->sav_config, ZPOOL_CONFIG_L2CACHE,
              (const nvlist_t * const *)l2cache, sav->sav_count);
  
  out:
          /*
           * Purge vdevs that were dropped
           */
          for (i = 0; i < oldnvdevs; i++) {
                  uint64_t pool;
  
                  vd = oldvdevs[i];
                  if (vd != NULL) {
                          ASSERT(vd->vdev_isl2cache);
  
                          if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
                              pool != 0ULL && l2arc_vdev_present(vd))
                                  l2arc_remove_vdev(vd);
                          vdev_clear_stats(vd);
                          vdev_free(vd);
                  }
          }
  
          if (oldvdevs)
                  kmem_free(oldvdevs, oldnvdevs * sizeof (void *));
  
          for (i = 0; i < sav->sav_count; i++)
                  nvlist_free(l2cache[i]);
          if (sav->sav_count)
                  kmem_free(l2cache, sav->sav_count * sizeof (void *));
  }
  
  static int
  load_nvlist(spa_t *spa, uint64_t obj, nvlist_t **value)
  {
          dmu_buf_t *db;
          char *packed = NULL;
          size_t nvsize = 0;
          int error;
          *value = NULL;
  
          error = dmu_bonus_hold(spa->spa_meta_objset, obj, FTAG, &db);
          if (error)
                  return (error);
  
          nvsize = *(uint64_t *)db->db_data;
          dmu_buf_rele(db, FTAG);
  
          packed = vmem_alloc(nvsize, KM_SLEEP);
          error = dmu_read(spa->spa_meta_objset, obj, 0, nvsize, packed,
              DMU_READ_PREFETCH);
          if (error == 0)
                  error = nvlist_unpack(packed, nvsize, value, 0);
          vmem_free(packed, nvsize);
  
          return (error);
  }
  
  /*
   * Concrete top-level vdevs that are not missing and are not logs. At every
   * spa_sync we write new uberblocks to at least SPA_SYNC_MIN_VDEVS core tvds.
   */
  static uint64_t
  spa_healthy_core_tvds(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          uint64_t tvds = 0;
  
          for (uint64_t i = 0; i < rvd->vdev_children; i++) {
                  vdev_t *vd = rvd->vdev_child[i];
                  if (vd->vdev_islog)
                          continue;
                  if (vdev_is_concrete(vd) && !vdev_is_dead(vd))
                          tvds++;
          }
  
          return (tvds);
  }
  
  /*
   * Checks to see if the given vdev could not be opened, in which case we post a
   * sysevent to notify the autoreplace code that the device has been removed.
   */
  static void
  spa_check_removed(vdev_t *vd)
  {
          for (uint64_t c = 0; c < vd->vdev_children; c++)
                  spa_check_removed(vd->vdev_child[c]);
  
          if (vd->vdev_ops->vdev_op_leaf && vdev_is_dead(vd) &&
              vdev_is_concrete(vd)) {
                  zfs_post_autoreplace(vd->vdev_spa, vd);
                  spa_event_notify(vd->vdev_spa, vd, NULL, ESC_ZFS_VDEV_CHECK);
          }
  }
  
  static int
  spa_check_for_missing_logs(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
  
          /*
           * If we're doing a normal import, then build up any additional
           * diagnostic information about missing log devices.
           * We'll pass this up to the user for further processing.
           */
          if (!(spa->spa_import_flags & ZFS_IMPORT_MISSING_LOG)) {
                  nvlist_t **child, *nv;
                  uint64_t idx = 0;
  
                  child = kmem_alloc(rvd->vdev_children * sizeof (nvlist_t *),
                      KM_SLEEP);
                  nv = fnvlist_alloc();
  
                  for (uint64_t c = 0; c < rvd->vdev_children; c++) {
                          vdev_t *tvd = rvd->vdev_child[c];
  
                          /*
                           * We consider a device as missing only if it failed
                           * to open (i.e. offline or faulted is not considered
                           * as missing).
                           */
                          if (tvd->vdev_islog &&
                              tvd->vdev_state == VDEV_STATE_CANT_OPEN) {
                                  child[idx++] = vdev_config_generate(spa, tvd,
                                      B_FALSE, VDEV_CONFIG_MISSING);
                          }
                  }
  
                  if (idx > 0) {
                          fnvlist_add_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
                              (const nvlist_t * const *)child, idx);
                          fnvlist_add_nvlist(spa->spa_load_info,
                              ZPOOL_CONFIG_MISSING_DEVICES, nv);
  
                          for (uint64_t i = 0; i < idx; i++)
                                  nvlist_free(child[i]);
                  }
                  nvlist_free(nv);
                  kmem_free(child, rvd->vdev_children * sizeof (char **));
  
                  if (idx > 0) {
                          spa_load_failed(spa, "some log devices are missing");
                          vdev_dbgmsg_print_tree(rvd, 2);
                          return (SET_ERROR(ENXIO));
                  }
          } else {
                  for (uint64_t c = 0; c < rvd->vdev_children; c++) {
                          vdev_t *tvd = rvd->vdev_child[c];
  
                          if (tvd->vdev_islog &&
                              tvd->vdev_state == VDEV_STATE_CANT_OPEN) {
                                  spa_set_log_state(spa, SPA_LOG_CLEAR);
                                  spa_load_note(spa, "some log devices are "
                                      "missing, ZIL is dropped.");
                                  vdev_dbgmsg_print_tree(rvd, 2);
                                  break;
                          }
                  }
          }
  
          return (0);
  }
  
  /*
   * Check for missing log devices
   */
  static boolean_t
  spa_check_logs(spa_t *spa)
  {
          boolean_t rv = B_FALSE;
          dsl_pool_t *dp = spa_get_dsl(spa);
  
          switch (spa->spa_log_state) {
          default:
                  break;
          case SPA_LOG_MISSING:
                  /* need to recheck in case slog has been restored */
          case SPA_LOG_UNKNOWN:
                  rv = (dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
                      zil_check_log_chain, NULL, DS_FIND_CHILDREN) != 0);
                  if (rv)
                          spa_set_log_state(spa, SPA_LOG_MISSING);
                  break;
          }
          return (rv);
  }
  
  /*
   * Passivate any log vdevs (note, does not apply to embedded log metaslabs).
   */
  static boolean_t
  spa_passivate_log(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          boolean_t slog_found = B_FALSE;
  
          ASSERT(spa_config_held(spa, SCL_ALLOC, RW_WRITER));
  
          for (int c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *tvd = rvd->vdev_child[c];
  
                  if (tvd->vdev_islog) {
                          ASSERT3P(tvd->vdev_log_mg, ==, NULL);
                          metaslab_group_passivate(tvd->vdev_mg);
                          slog_found = B_TRUE;
                  }
          }
  
          return (slog_found);
  }
  
  /*
   * Activate any log vdevs (note, does not apply to embedded log metaslabs).
   */
  static void
  spa_activate_log(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
  
          ASSERT(spa_config_held(spa, SCL_ALLOC, RW_WRITER));
  
          for (int c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *tvd = rvd->vdev_child[c];
  
                  if (tvd->vdev_islog) {
                          ASSERT3P(tvd->vdev_log_mg, ==, NULL);
                          metaslab_group_activate(tvd->vdev_mg);
                  }
          }
  }
  
  int
  spa_reset_logs(spa_t *spa)
  {
          int error;
  
          error = dmu_objset_find(spa_name(spa), zil_reset,
              NULL, DS_FIND_CHILDREN);
          if (error == 0) {
                  /*
                   * We successfully offlined the log device, sync out the
                   * current txg so that the "stubby" block can be removed
                   * by zil_sync().
                   */
                  txg_wait_synced(spa->spa_dsl_pool, 0);
          }
          return (error);
  }
  
  static void
  spa_aux_check_removed(spa_aux_vdev_t *sav)
  {
          for (int i = 0; i < sav->sav_count; i++)
                  spa_check_removed(sav->sav_vdevs[i]);
  }
  
  void
  spa_claim_notify(zio_t *zio)
  {
          spa_t *spa = zio->io_spa;
  
          if (zio->io_error)
                  return;
  
          mutex_enter(&spa->spa_props_lock);      /* any mutex will do */
          if (spa->spa_claim_max_txg < zio->io_bp->blk_birth)
                  spa->spa_claim_max_txg = zio->io_bp->blk_birth;
          mutex_exit(&spa->spa_props_lock);
  }
  
  typedef struct spa_load_error {
          boolean_t       sle_verify_data;
          uint64_t        sle_meta_count;
          uint64_t        sle_data_count;
  } spa_load_error_t;
  
  static void
  spa_load_verify_done(zio_t *zio)
  {
          blkptr_t *bp = zio->io_bp;
          spa_load_error_t *sle = zio->io_private;
          dmu_object_type_t type = BP_GET_TYPE(bp);
          int error = zio->io_error;
          spa_t *spa = zio->io_spa;
  
          abd_free(zio->io_abd);
          if (error) {
                  if ((BP_GET_LEVEL(bp) != 0 || DMU_OT_IS_METADATA(type)) &&
                      type != DMU_OT_INTENT_LOG)
                          atomic_inc_64(&sle->sle_meta_count);
                  else
                          atomic_inc_64(&sle->sle_data_count);
          }
  
          mutex_enter(&spa->spa_scrub_lock);
          spa->spa_load_verify_bytes -= BP_GET_PSIZE(bp);
          cv_broadcast(&spa->spa_scrub_io_cv);
          mutex_exit(&spa->spa_scrub_lock);
  }
  
  /*
   * Maximum number of inflight bytes is the log2 fraction of the arc size.
   * By default, we set it to 1/16th of the arc.
   */
  static uint_t spa_load_verify_shift = 4;
  static int spa_load_verify_metadata = B_TRUE;
  static int spa_load_verify_data = B_TRUE;
  
  static int
  spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
      const zbookmark_phys_t *zb, const dnode_phys_t *dnp, void *arg)
  {
          zio_t *rio = arg;
          spa_load_error_t *sle = rio->io_private;
  
          (void) zilog, (void) dnp;
  
          /*
           * Note: normally this routine will not be called if
           * spa_load_verify_metadata is not set.  However, it may be useful
           * to manually set the flag after the traversal has begun.
           */
          if (!spa_load_verify_metadata)
                  return (0);
  
          /*
           * Sanity check the block pointer in order to detect obvious damage
           * before using the contents in subsequent checks or in zio_read().
           * When damaged consider it to be a metadata error since we cannot
           * trust the BP_GET_TYPE and BP_GET_LEVEL values.
           */
          if (!zfs_blkptr_verify(spa, bp, B_FALSE, BLK_VERIFY_LOG)) {
                  atomic_inc_64(&sle->sle_meta_count);
                  return (0);
          }
  
          if (zb->zb_level == ZB_DNODE_LEVEL || BP_IS_HOLE(bp) ||
              BP_IS_EMBEDDED(bp) || BP_IS_REDACTED(bp))
                  return (0);
  
          if (!BP_IS_METADATA(bp) &&
              (!spa_load_verify_data || !sle->sle_verify_data))
                  return (0);
  
          uint64_t maxinflight_bytes =
              arc_target_bytes() >> spa_load_verify_shift;
          size_t size = BP_GET_PSIZE(bp);
  
          mutex_enter(&spa->spa_scrub_lock);
          while (spa->spa_load_verify_bytes >= maxinflight_bytes)
                  cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
          spa->spa_load_verify_bytes += size;
          mutex_exit(&spa->spa_scrub_lock);
  
          zio_nowait(zio_read(rio, spa, bp, abd_alloc_for_io(size, B_FALSE), size,
              spa_load_verify_done, rio->io_private, ZIO_PRIORITY_SCRUB,
              ZIO_FLAG_SPECULATIVE | ZIO_FLAG_CANFAIL |
              ZIO_FLAG_SCRUB | ZIO_FLAG_RAW, zb));
          return (0);
  }
  
  static int
  verify_dataset_name_len(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
  {
          (void) dp, (void) arg;
  
          if (dsl_dataset_namelen(ds) >= ZFS_MAX_DATASET_NAME_LEN)
                  return (SET_ERROR(ENAMETOOLONG));
  
          return (0);
  }
  
  static int
  spa_load_verify(spa_t *spa)
  {
          zio_t *rio;
          spa_load_error_t sle = { 0 };
          zpool_load_policy_t policy;
          boolean_t verify_ok = B_FALSE;
          int error = 0;
  
          zpool_get_load_policy(spa->spa_config, &policy);
  
          if (policy.zlp_rewind & ZPOOL_NEVER_REWIND ||
              policy.zlp_maxmeta == UINT64_MAX)
                  return (0);
  
          dsl_pool_config_enter(spa->spa_dsl_pool, FTAG);
          error = dmu_objset_find_dp(spa->spa_dsl_pool,
              spa->spa_dsl_pool->dp_root_dir_obj, verify_dataset_name_len, NULL,
              DS_FIND_CHILDREN);
          dsl_pool_config_exit(spa->spa_dsl_pool, FTAG);
          if (error != 0)
                  return (error);
  
          /*
           * Verify data only if we are rewinding or error limit was set.
           * Otherwise nothing except dbgmsg care about it to waste time.
           */
          sle.sle_verify_data = (policy.zlp_rewind & ZPOOL_REWIND_MASK) ||
              (policy.zlp_maxdata < UINT64_MAX);
  
          rio = zio_root(spa, NULL, &sle,
              ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE);
  
          if (spa_load_verify_metadata) {
                  if (spa->spa_extreme_rewind) {
                          spa_load_note(spa, "performing a complete scan of the "
                              "pool since extreme rewind is on. This may take "
                              "a very long time.\n  (spa_load_verify_data=%u, "
                              "spa_load_verify_metadata=%u)",
                              spa_load_verify_data, spa_load_verify_metadata);
                  }
  
                  error = traverse_pool(spa, spa->spa_verify_min_txg,
                      TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA |
                      TRAVERSE_NO_DECRYPT, spa_load_verify_cb, rio);
          }
  
          (void) zio_wait(rio);
          ASSERT0(spa->spa_load_verify_bytes);
  
          spa->spa_load_meta_errors = sle.sle_meta_count;
          spa->spa_load_data_errors = sle.sle_data_count;
  
          if (sle.sle_meta_count != 0 || sle.sle_data_count != 0) {
                  spa_load_note(spa, "spa_load_verify found %llu metadata errors "
                      "and %llu data errors", (u_longlong_t)sle.sle_meta_count,
                      (u_longlong_t)sle.sle_data_count);
          }
  
          if (spa_load_verify_dryrun ||
              (!error && sle.sle_meta_count <= policy.zlp_maxmeta &&
              sle.sle_data_count <= policy.zlp_maxdata)) {
                  int64_t loss = 0;
  
                  verify_ok = B_TRUE;
                  spa->spa_load_txg = spa->spa_uberblock.ub_txg;
                  spa->spa_load_txg_ts = spa->spa_uberblock.ub_timestamp;
  
                  loss = spa->spa_last_ubsync_txg_ts - spa->spa_load_txg_ts;
                  fnvlist_add_uint64(spa->spa_load_info, ZPOOL_CONFIG_LOAD_TIME,
                      spa->spa_load_txg_ts);
                  fnvlist_add_int64(spa->spa_load_info, ZPOOL_CONFIG_REWIND_TIME,
                      loss);
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_LOAD_META_ERRORS, sle.sle_meta_count);
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_LOAD_DATA_ERRORS, sle.sle_data_count);
          } else {
                  spa->spa_load_max_txg = spa->spa_uberblock.ub_txg;
          }
  
          if (spa_load_verify_dryrun)
                  return (0);
  
          if (error) {
                  if (error != ENXIO && error != EIO)
                          error = SET_ERROR(EIO);
                  return (error);
          }
  
          return (verify_ok ? 0 : EIO);
  }
  
  /*
   * Find a value in the pool props object.
   */
  static void
  spa_prop_find(spa_t *spa, zpool_prop_t prop, uint64_t *val)
  {
          (void) zap_lookup(spa->spa_meta_objset, spa->spa_pool_props_object,
              zpool_prop_to_name(prop), sizeof (uint64_t), 1, val);
  }
  
  /*
   * Find a value in the pool directory object.
   */
  static int
  spa_dir_prop(spa_t *spa, const char *name, uint64_t *val, boolean_t log_enoent)
  {
          int error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              name, sizeof (uint64_t), 1, val);
  
          if (error != 0 && (error != ENOENT || log_enoent)) {
                  spa_load_failed(spa, "couldn't get '%s' value in MOS directory "
                      "[error=%d]", name, error);
          }
  
          return (error);
  }
  
  static int
  spa_vdev_err(vdev_t *vdev, vdev_aux_t aux, int err)
  {
          vdev_set_state(vdev, B_TRUE, VDEV_STATE_CANT_OPEN, aux);
          return (SET_ERROR(err));
  }
  
  boolean_t
  spa_livelist_delete_check(spa_t *spa)
  {
          return (spa->spa_livelists_to_delete != 0);
  }
  
  static boolean_t
  spa_livelist_delete_cb_check(void *arg, zthr_t *z)
  {
          (void) z;
          spa_t *spa = arg;
          return (spa_livelist_delete_check(spa));
  }
  
  static int
  delete_blkptr_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
  {
          spa_t *spa = arg;
          zio_free(spa, tx->tx_txg, bp);
          dsl_dir_diduse_space(tx->tx_pool->dp_free_dir, DD_USED_HEAD,
              -bp_get_dsize_sync(spa, bp),
              -BP_GET_PSIZE(bp), -BP_GET_UCSIZE(bp), tx);
          return (0);
  }
  
  static int
  dsl_get_next_livelist_obj(objset_t *os, uint64_t zap_obj, uint64_t *llp)
  {
          int err;
          zap_cursor_t zc;
          zap_attribute_t za;
          zap_cursor_init(&zc, os, zap_obj);
          err = zap_cursor_retrieve(&zc, &za);
          zap_cursor_fini(&zc);
          if (err == 0)
                  *llp = za.za_first_integer;
          return (err);
  }
  
  /*
   * Components of livelist deletion that must be performed in syncing
   * context: freeing block pointers and updating the pool-wide data
   * structures to indicate how much work is left to do
   */
  typedef struct sublist_delete_arg {
          spa_t *spa;
          dsl_deadlist_t *ll;
          uint64_t key;
          bplist_t *to_free;
  } sublist_delete_arg_t;
  
  static void
  sublist_delete_sync(void *arg, dmu_tx_t *tx)
  {
          sublist_delete_arg_t *sda = arg;
          spa_t *spa = sda->spa;
          dsl_deadlist_t *ll = sda->ll;
          uint64_t key = sda->key;
          bplist_t *to_free = sda->to_free;
  
          bplist_iterate(to_free, delete_blkptr_cb, spa, tx);
          dsl_deadlist_remove_entry(ll, key, tx);
  }
  
  typedef struct livelist_delete_arg {
          spa_t *spa;
          uint64_t ll_obj;
          uint64_t zap_obj;
  } livelist_delete_arg_t;
  
  static void
  livelist_delete_sync(void *arg, dmu_tx_t *tx)
  {
          livelist_delete_arg_t *lda = arg;
          spa_t *spa = lda->spa;
          uint64_t ll_obj = lda->ll_obj;
          uint64_t zap_obj = lda->zap_obj;
          objset_t *mos = spa->spa_meta_objset;
          uint64_t count;
  
          /* free the livelist and decrement the feature count */
          VERIFY0(zap_remove_int(mos, zap_obj, ll_obj, tx));
          dsl_deadlist_free(mos, ll_obj, tx);
          spa_feature_decr(spa, SPA_FEATURE_LIVELIST, tx);
          VERIFY0(zap_count(mos, zap_obj, &count));
          if (count == 0) {
                  /* no more livelists to delete */
                  VERIFY0(zap_remove(mos, DMU_POOL_DIRECTORY_OBJECT,
                      DMU_POOL_DELETED_CLONES, tx));
                  VERIFY0(zap_destroy(mos, zap_obj, tx));
                  spa->spa_livelists_to_delete = 0;
                  spa_notify_waiters(spa);
          }
  }
  
  /*
   * Load in the value for the livelist to be removed and open it. Then,
   * load its first sublist and determine which block pointers should actually
   * be freed. Then, call a synctask which performs the actual frees and updates
   * the pool-wide livelist data.
   */
  static void
  spa_livelist_delete_cb(void *arg, zthr_t *z)
  {
          spa_t *spa = arg;
          uint64_t ll_obj = 0, count;
          objset_t *mos = spa->spa_meta_objset;
          uint64_t zap_obj = spa->spa_livelists_to_delete;
          /*
           * Determine the next livelist to delete. This function should only
           * be called if there is at least one deleted clone.
           */
          VERIFY0(dsl_get_next_livelist_obj(mos, zap_obj, &ll_obj));
          VERIFY0(zap_count(mos, ll_obj, &count));
          if (count > 0) {
                  dsl_deadlist_t *ll;
                  dsl_deadlist_entry_t *dle;
                  bplist_t to_free;
                  ll = kmem_zalloc(sizeof (dsl_deadlist_t), KM_SLEEP);
                  dsl_deadlist_open(ll, mos, ll_obj);
                  dle = dsl_deadlist_first(ll);
                  ASSERT3P(dle, !=, NULL);
                  bplist_create(&to_free);
                  int err = dsl_process_sub_livelist(&dle->dle_bpobj, &to_free,
                      z, NULL);
                  if (err == 0) {
                          sublist_delete_arg_t sync_arg = {
                              .spa = spa,
                              .ll = ll,
                              .key = dle->dle_mintxg,
                              .to_free = &to_free
                          };
                          zfs_dbgmsg("deleting sublist (id %llu) from"
                              " livelist %llu, %lld remaining",
                              (u_longlong_t)dle->dle_bpobj.bpo_object,
                              (u_longlong_t)ll_obj, (longlong_t)count - 1);
                          VERIFY0(dsl_sync_task(spa_name(spa), NULL,
                              sublist_delete_sync, &sync_arg, 0,
                              ZFS_SPACE_CHECK_DESTROY));
                  } else {
                          VERIFY3U(err, ==, EINTR);
                  }
                  bplist_clear(&to_free);
                  bplist_destroy(&to_free);
                  dsl_deadlist_close(ll);
                  kmem_free(ll, sizeof (dsl_deadlist_t));
          } else {
                  livelist_delete_arg_t sync_arg = {
                      .spa = spa,
                      .ll_obj = ll_obj,
                      .zap_obj = zap_obj
                  };
                  zfs_dbgmsg("deletion of livelist %llu completed",
                      (u_longlong_t)ll_obj);
                  VERIFY0(dsl_sync_task(spa_name(spa), NULL, livelist_delete_sync,
                      &sync_arg, 0, ZFS_SPACE_CHECK_DESTROY));
          }
  }
  
  static void
  spa_start_livelist_destroy_thread(spa_t *spa)
  {
          ASSERT3P(spa->spa_livelist_delete_zthr, ==, NULL);
          spa->spa_livelist_delete_zthr =
              zthr_create("z_livelist_destroy",
              spa_livelist_delete_cb_check, spa_livelist_delete_cb, spa,
              minclsyspri);
  }
  
  typedef struct livelist_new_arg {
          bplist_t *allocs;
          bplist_t *frees;
  } livelist_new_arg_t;
  
  static int
  livelist_track_new_cb(void *arg, const blkptr_t *bp, boolean_t bp_freed,
      dmu_tx_t *tx)
  {
          ASSERT(tx == NULL);
          livelist_new_arg_t *lna = arg;
          if (bp_freed) {
                  bplist_append(lna->frees, bp);
          } else {
                  bplist_append(lna->allocs, bp);
                  zfs_livelist_condense_new_alloc++;
          }
          return (0);
  }
  
  typedef struct livelist_condense_arg {
          spa_t *spa;
          bplist_t to_keep;
          uint64_t first_size;
          uint64_t next_size;
  } livelist_condense_arg_t;
  
  static void
  spa_livelist_condense_sync(void *arg, dmu_tx_t *tx)
  {
          livelist_condense_arg_t *lca = arg;
          spa_t *spa = lca->spa;
          bplist_t new_frees;
          dsl_dataset_t *ds = spa->spa_to_condense.ds;
  
          /* Have we been cancelled? */
          if (spa->spa_to_condense.cancelled) {
                  zfs_livelist_condense_sync_cancel++;
                  goto out;
          }
  
          dsl_deadlist_entry_t *first = spa->spa_to_condense.first;
          dsl_deadlist_entry_t *next = spa->spa_to_condense.next;
          dsl_deadlist_t *ll = &ds->ds_dir->dd_livelist;
  
          /*
           * It's possible that the livelist was changed while the zthr was
           * running. Therefore, we need to check for new blkptrs in the two
           * entries being condensed and continue to track them in the livelist.
           * Because of the way we handle remapped blkptrs (see dbuf_remap_impl),
           * it's possible that the newly added blkptrs are FREEs or ALLOCs so
           * we need to sort them into two different bplists.
           */
          uint64_t first_obj = first->dle_bpobj.bpo_object;
          uint64_t next_obj = next->dle_bpobj.bpo_object;
          uint64_t cur_first_size = first->dle_bpobj.bpo_phys->bpo_num_blkptrs;
          uint64_t cur_next_size = next->dle_bpobj.bpo_phys->bpo_num_blkptrs;
  
          bplist_create(&new_frees);
          livelist_new_arg_t new_bps = {
              .allocs = &lca->to_keep,
              .frees = &new_frees,
          };
  
          if (cur_first_size > lca->first_size) {
                  VERIFY0(livelist_bpobj_iterate_from_nofree(&first->dle_bpobj,
                      livelist_track_new_cb, &new_bps, lca->first_size));
          }
          if (cur_next_size > lca->next_size) {
                  VERIFY0(livelist_bpobj_iterate_from_nofree(&next->dle_bpobj,
                      livelist_track_new_cb, &new_bps, lca->next_size));
          }
  
          dsl_deadlist_clear_entry(first, ll, tx);
          ASSERT(bpobj_is_empty(&first->dle_bpobj));
          dsl_deadlist_remove_entry(ll, next->dle_mintxg, tx);
  
          bplist_iterate(&lca->to_keep, dsl_deadlist_insert_alloc_cb, ll, tx);
          bplist_iterate(&new_frees, dsl_deadlist_insert_free_cb, ll, tx);
          bplist_destroy(&new_frees);
  
          char dsname[ZFS_MAX_DATASET_NAME_LEN];
          dsl_dataset_name(ds, dsname);
          zfs_dbgmsg("txg %llu condensing livelist of %s (id %llu), bpobj %llu "
              "(%llu blkptrs) and bpobj %llu (%llu blkptrs) -> bpobj %llu "
              "(%llu blkptrs)", (u_longlong_t)tx->tx_txg, dsname,
              (u_longlong_t)ds->ds_object, (u_longlong_t)first_obj,
              (u_longlong_t)cur_first_size, (u_longlong_t)next_obj,
              (u_longlong_t)cur_next_size,
              (u_longlong_t)first->dle_bpobj.bpo_object,
              (u_longlong_t)first->dle_bpobj.bpo_phys->bpo_num_blkptrs);
  out:
          dmu_buf_rele(ds->ds_dbuf, spa);
          spa->spa_to_condense.ds = NULL;
          bplist_clear(&lca->to_keep);
          bplist_destroy(&lca->to_keep);
          kmem_free(lca, sizeof (livelist_condense_arg_t));
          spa->spa_to_condense.syncing = B_FALSE;
  }
  
  static void
  spa_livelist_condense_cb(void *arg, zthr_t *t)
  {
          while (zfs_livelist_condense_zthr_pause &&
              !(zthr_has_waiters(t) || zthr_iscancelled(t)))
                  delay(1);
  
          spa_t *spa = arg;
          dsl_deadlist_entry_t *first = spa->spa_to_condense.first;
          dsl_deadlist_entry_t *next = spa->spa_to_condense.next;
          uint64_t first_size, next_size;
  
          livelist_condense_arg_t *lca =
              kmem_alloc(sizeof (livelist_condense_arg_t), KM_SLEEP);
          bplist_create(&lca->to_keep);
  
          /*
           * Process the livelists (matching FREEs and ALLOCs) in open context
           * so we have minimal work in syncing context to condense.
           *
           * We save bpobj sizes (first_size and next_size) to use later in
           * syncing context to determine if entries were added to these sublists
           * while in open context. This is possible because the clone is still
           * active and open for normal writes and we want to make sure the new,
           * unprocessed blockpointers are inserted into the livelist normally.
           *
           * Note that dsl_process_sub_livelist() both stores the size number of
           * blockpointers and iterates over them while the bpobj's lock held, so
           * the sizes returned to us are consistent which what was actually
           * processed.
           */
          int err = dsl_process_sub_livelist(&first->dle_bpobj, &lca->to_keep, t,
              &first_size);
          if (err == 0)
                  err = dsl_process_sub_livelist(&next->dle_bpobj, &lca->to_keep,
                      t, &next_size);
  
          if (err == 0) {
                  while (zfs_livelist_condense_sync_pause &&
                      !(zthr_has_waiters(t) || zthr_iscancelled(t)))
                          delay(1);
  
                  dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
                  dmu_tx_mark_netfree(tx);
                  dmu_tx_hold_space(tx, 1);
                  err = dmu_tx_assign(tx, TXG_NOWAIT | TXG_NOTHROTTLE);
                  if (err == 0) {
                          /*
                           * Prevent the condense zthr restarting before
                           * the synctask completes.
                           */
                          spa->spa_to_condense.syncing = B_TRUE;
                          lca->spa = spa;
                          lca->first_size = first_size;
                          lca->next_size = next_size;
                          dsl_sync_task_nowait(spa_get_dsl(spa),
                              spa_livelist_condense_sync, lca, tx);
                          dmu_tx_commit(tx);
                          return;
                  }
          }
          /*
           * Condensing can not continue: either it was externally stopped or
           * we were unable to assign to a tx because the pool has run out of
           * space. In the second case, we'll just end up trying to condense
           * again in a later txg.
           */
          ASSERT(err != 0);
          bplist_clear(&lca->to_keep);
          bplist_destroy(&lca->to_keep);
          kmem_free(lca, sizeof (livelist_condense_arg_t));
          dmu_buf_rele(spa->spa_to_condense.ds->ds_dbuf, spa);
          spa->spa_to_condense.ds = NULL;
          if (err == EINTR)
                  zfs_livelist_condense_zthr_cancel++;
  }
  
  /*
   * Check that there is something to condense but that a condense is not
   * already in progress and that condensing has not been cancelled.
   */
  static boolean_t
  spa_livelist_condense_cb_check(void *arg, zthr_t *z)
  {
          (void) z;
          spa_t *spa = arg;
          if ((spa->spa_to_condense.ds != NULL) &&
              (spa->spa_to_condense.syncing == B_FALSE) &&
              (spa->spa_to_condense.cancelled == B_FALSE)) {
                  return (B_TRUE);
          }
          return (B_FALSE);
  }
  
  static void
  spa_start_livelist_condensing_thread(spa_t *spa)
  {
          spa->spa_to_condense.ds = NULL;
          spa->spa_to_condense.first = NULL;
          spa->spa_to_condense.next = NULL;
          spa->spa_to_condense.syncing = B_FALSE;
          spa->spa_to_condense.cancelled = B_FALSE;
  
          ASSERT3P(spa->spa_livelist_condense_zthr, ==, NULL);
          spa->spa_livelist_condense_zthr =
              zthr_create("z_livelist_condense",
              spa_livelist_condense_cb_check,
              spa_livelist_condense_cb, spa, minclsyspri);
  }
  
  static void
  spa_spawn_aux_threads(spa_t *spa)
  {
          ASSERT(spa_writeable(spa));
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          spa_start_indirect_condensing_thread(spa);
          spa_start_livelist_destroy_thread(spa);
          spa_start_livelist_condensing_thread(spa);
  
          ASSERT3P(spa->spa_checkpoint_discard_zthr, ==, NULL);
          spa->spa_checkpoint_discard_zthr =
              zthr_create("z_checkpoint_discard",
              spa_checkpoint_discard_thread_check,
              spa_checkpoint_discard_thread, spa, minclsyspri);
  }
  
  /*
   * Fix up config after a partly-completed split.  This is done with the
   * ZPOOL_CONFIG_SPLIT nvlist.  Both the splitting pool and the split-off
   * pool have that entry in their config, but only the splitting one contains
   * a list of all the guids of the vdevs that are being split off.
   *
   * This function determines what to do with that list: either rejoin
   * all the disks to the pool, or complete the splitting process.  To attempt
   * the rejoin, each disk that is offlined is marked online again, and
   * we do a reopen() call.  If the vdev label for every disk that was
   * marked online indicates it was successfully split off (VDEV_AUX_SPLIT_POOL)
   * then we call vdev_split() on each disk, and complete the split.
   *
   * Otherwise we leave the config alone, with all the vdevs in place in
   * the original pool.
   */
  static void
  spa_try_repair(spa_t *spa, nvlist_t *config)
  {
          uint_t extracted;
          uint64_t *glist;
          uint_t i, gcount;
          nvlist_t *nvl;
          vdev_t **vd;
          boolean_t attempt_reopen;
  
          if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_SPLIT, &nvl) != 0)
                  return;
  
          /* check that the config is complete */
          if (nvlist_lookup_uint64_array(nvl, ZPOOL_CONFIG_SPLIT_LIST,
              &glist, &gcount) != 0)
                  return;
  
          vd = kmem_zalloc(gcount * sizeof (vdev_t *), KM_SLEEP);
  
          /* attempt to online all the vdevs & validate */
          attempt_reopen = B_TRUE;
          for (i = 0; i < gcount; i++) {
                  if (glist[i] == 0)      /* vdev is hole */
                          continue;
  
                  vd[i] = spa_lookup_by_guid(spa, glist[i], B_FALSE);
                  if (vd[i] == NULL) {
                          /*
                           * Don't bother attempting to reopen the disks;
                           * just do the split.
                           */
                          attempt_reopen = B_FALSE;
                  } else {
                          /* attempt to re-online it */
                          vd[i]->vdev_offline = B_FALSE;
                  }
          }
  
          if (attempt_reopen) {
                  vdev_reopen(spa->spa_root_vdev);
  
                  /* check each device to see what state it's in */
                  for (extracted = 0, i = 0; i < gcount; i++) {
                          if (vd[i] != NULL &&
                              vd[i]->vdev_stat.vs_aux != VDEV_AUX_SPLIT_POOL)
                                  break;
                          ++extracted;
                  }
          }
  
          /*
           * If every disk has been moved to the new pool, or if we never
           * even attempted to look at them, then we split them off for
           * good.
           */
          if (!attempt_reopen || gcount == extracted) {
                  for (i = 0; i < gcount; i++)
                          if (vd[i] != NULL)
                                  vdev_split(vd[i]);
                  vdev_reopen(spa->spa_root_vdev);
          }
  
          kmem_free(vd, gcount * sizeof (vdev_t *));
  }
  
  static int
  spa_load(spa_t *spa, spa_load_state_t state, spa_import_type_t type)
  {
          const char *ereport = FM_EREPORT_ZFS_POOL;
          int error;
  
          spa->spa_load_state = state;
          (void) spa_import_progress_set_state(spa_guid(spa),
              spa_load_state(spa));
  
          gethrestime(&spa->spa_loaded_ts);
          error = spa_load_impl(spa, type, &ereport);
  
          /*
           * Don't count references from objsets that are already closed
           * and are making their way through the eviction process.
           */
          spa_evicting_os_wait(spa);
          spa->spa_minref = zfs_refcount_count(&spa->spa_refcount);
          if (error) {
                  if (error != EEXIST) {
                          spa->spa_loaded_ts.tv_sec = 0;
                          spa->spa_loaded_ts.tv_nsec = 0;
                  }
                  if (error != EBADF) {
                          (void) zfs_ereport_post(ereport, spa,
                              NULL, NULL, NULL, 0);
                  }
          }
          spa->spa_load_state = error ? SPA_LOAD_ERROR : SPA_LOAD_NONE;
          spa->spa_ena = 0;
  
          (void) spa_import_progress_set_state(spa_guid(spa),
              spa_load_state(spa));
  
          return (error);
  }
  
  #ifdef ZFS_DEBUG
  /*
   * Count the number of per-vdev ZAPs associated with all of the vdevs in the
   * vdev tree rooted in the given vd, and ensure that each ZAP is present in the
   * spa's per-vdev ZAP list.
   */
  static uint64_t
  vdev_count_verify_zaps(vdev_t *vd)
  {
          spa_t *spa = vd->vdev_spa;
          uint64_t total = 0;
  
          if (vd->vdev_top_zap != 0) {
                  total++;
                  ASSERT0(zap_lookup_int(spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps, vd->vdev_top_zap));
          }
          if (vd->vdev_leaf_zap != 0) {
                  total++;
                  ASSERT0(zap_lookup_int(spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps, vd->vdev_leaf_zap));
          }
  
          for (uint64_t i = 0; i < vd->vdev_children; i++) {
                  total += vdev_count_verify_zaps(vd->vdev_child[i]);
          }
  
          return (total);
  }
  #else
  #define vdev_count_verify_zaps(vd) ((void) sizeof (vd), 0)
  #endif
  
  /*
   * Determine whether the activity check is required.
   */
  static boolean_t
  spa_activity_check_required(spa_t *spa, uberblock_t *ub, nvlist_t *label,
      nvlist_t *config)
  {
          uint64_t state = 0;
          uint64_t hostid = 0;
          uint64_t tryconfig_txg = 0;
          uint64_t tryconfig_timestamp = 0;
          uint16_t tryconfig_mmp_seq = 0;
          nvlist_t *nvinfo;
  
          if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
                  nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
                  (void) nvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG,
                      &tryconfig_txg);
                  (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
                      &tryconfig_timestamp);
                  (void) nvlist_lookup_uint16(nvinfo, ZPOOL_CONFIG_MMP_SEQ,
                      &tryconfig_mmp_seq);
          }
  
          (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE, &state);
  
          /*
           * Disable the MMP activity check - This is used by zdb which
           * is intended to be used on potentially active pools.
           */
          if (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP)
                  return (B_FALSE);
  
          /*
           * Skip the activity check when the MMP feature is disabled.
           */
          if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay == 0)
                  return (B_FALSE);
  
          /*
           * If the tryconfig_ values are nonzero, they are the results of an
           * earlier tryimport.  If they all match the uberblock we just found,
           * then the pool has not changed and we return false so we do not test
           * a second time.
           */
          if (tryconfig_txg && tryconfig_txg == ub->ub_txg &&
              tryconfig_timestamp && tryconfig_timestamp == ub->ub_timestamp &&
              tryconfig_mmp_seq && tryconfig_mmp_seq ==
              (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0))
                  return (B_FALSE);
  
          /*
           * Allow the activity check to be skipped when importing the pool
           * on the same host which last imported it.  Since the hostid from
           * configuration may be stale use the one read from the label.
           */
          if (nvlist_exists(label, ZPOOL_CONFIG_HOSTID))
                  hostid = fnvlist_lookup_uint64(label, ZPOOL_CONFIG_HOSTID);
  
          if (hostid == spa_get_hostid(spa))
                  return (B_FALSE);
  
          /*
           * Skip the activity test when the pool was cleanly exported.
           */
          if (state != POOL_STATE_ACTIVE)
                  return (B_FALSE);
  
          return (B_TRUE);
  }
  
  /*
   * Nanoseconds the activity check must watch for changes on-disk.
   */
  static uint64_t
  spa_activity_check_duration(spa_t *spa, uberblock_t *ub)
  {
          uint64_t import_intervals = MAX(zfs_multihost_import_intervals, 1);
          uint64_t multihost_interval = MSEC2NSEC(
              MMP_INTERVAL_OK(zfs_multihost_interval));
          uint64_t import_delay = MAX(NANOSEC, import_intervals *
              multihost_interval);
  
          /*
           * Local tunables determine a minimum duration except for the case
           * where we know when the remote host will suspend the pool if MMP
           * writes do not land.
           *
           * See Big Theory comment at the top of mmp.c for the reasoning behind
           * these cases and times.
           */
  
          ASSERT(MMP_IMPORT_SAFETY_FACTOR >= 100);
  
          if (MMP_INTERVAL_VALID(ub) && MMP_FAIL_INT_VALID(ub) &&
              MMP_FAIL_INT(ub) > 0) {
  
                  /* MMP on remote host will suspend pool after failed writes */
                  import_delay = MMP_FAIL_INT(ub) * MSEC2NSEC(MMP_INTERVAL(ub)) *
                      MMP_IMPORT_SAFETY_FACTOR / 100;
  
                  zfs_dbgmsg("fail_intvals>0 import_delay=%llu ub_mmp "
                      "mmp_fails=%llu ub_mmp mmp_interval=%llu "
                      "import_intervals=%llu", (u_longlong_t)import_delay,
                      (u_longlong_t)MMP_FAIL_INT(ub),
                      (u_longlong_t)MMP_INTERVAL(ub),
                      (u_longlong_t)import_intervals);
  
          } else if (MMP_INTERVAL_VALID(ub) && MMP_FAIL_INT_VALID(ub) &&
              MMP_FAIL_INT(ub) == 0) {
  
                  /* MMP on remote host will never suspend pool */
                  import_delay = MAX(import_delay, (MSEC2NSEC(MMP_INTERVAL(ub)) +
                      ub->ub_mmp_delay) * import_intervals);
  
                  zfs_dbgmsg("fail_intvals=0 import_delay=%llu ub_mmp "
                      "mmp_interval=%llu ub_mmp_delay=%llu "
                      "import_intervals=%llu", (u_longlong_t)import_delay,
                      (u_longlong_t)MMP_INTERVAL(ub),
                      (u_longlong_t)ub->ub_mmp_delay,
                      (u_longlong_t)import_intervals);
  
          } else if (MMP_VALID(ub)) {
                  /*
                   * zfs-0.7 compatibility case
                   */
  
                  import_delay = MAX(import_delay, (multihost_interval +
                      ub->ub_mmp_delay) * import_intervals);
  
                  zfs_dbgmsg("import_delay=%llu ub_mmp_delay=%llu "
                      "import_intervals=%llu leaves=%u",
                      (u_longlong_t)import_delay,
                      (u_longlong_t)ub->ub_mmp_delay,
                      (u_longlong_t)import_intervals,
                      vdev_count_leaves(spa));
          } else {
                  /* Using local tunings is the only reasonable option */
                  zfs_dbgmsg("pool last imported on non-MMP aware "
                      "host using import_delay=%llu multihost_interval=%llu "
                      "import_intervals=%llu", (u_longlong_t)import_delay,
                      (u_longlong_t)multihost_interval,
                      (u_longlong_t)import_intervals);
          }
  
          return (import_delay);
  }
  
  /*
   * Perform the import activity check.  If the user canceled the import or
   * we detected activity then fail.
   */
  static int
  spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist_t *config)
  {
          uint64_t txg = ub->ub_txg;
          uint64_t timestamp = ub->ub_timestamp;
          uint64_t mmp_config = ub->ub_mmp_config;
          uint16_t mmp_seq = MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0;
          uint64_t import_delay;
          hrtime_t import_expire;
          nvlist_t *mmp_label = NULL;
          vdev_t *rvd = spa->spa_root_vdev;
          kcondvar_t cv;
          kmutex_t mtx;
          int error = 0;
  
          cv_init(&cv, NULL, CV_DEFAULT, NULL);
          mutex_init(&mtx, NULL, MUTEX_DEFAULT, NULL);
          mutex_enter(&mtx);
  
          /*
           * If ZPOOL_CONFIG_MMP_TXG is present an activity check was performed
           * during the earlier tryimport.  If the txg recorded there is 0 then
           * the pool is known to be active on another host.
           *
           * Otherwise, the pool might be in use on another host.  Check for
           * changes in the uberblocks on disk if necessary.
           */
          if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
                  nvlist_t *nvinfo = fnvlist_lookup_nvlist(config,
                      ZPOOL_CONFIG_LOAD_INFO);
  
                  if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_TXG) &&
                      fnvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG) == 0) {
                          vdev_uberblock_load(rvd, ub, &mmp_label);
                          error = SET_ERROR(EREMOTEIO);
                          goto out;
                  }
          }
  
          import_delay = spa_activity_check_duration(spa, ub);
  
          /* Add a small random factor in case of simultaneous imports (0-25%) */
          import_delay += import_delay * random_in_range(250) / 1000;
  
          import_expire = gethrtime() + import_delay;
  
          while (gethrtime() < import_expire) {
                  (void) spa_import_progress_set_mmp_check(spa_guid(spa),
                      NSEC2SEC(import_expire - gethrtime()));
  
                  vdev_uberblock_load(rvd, ub, &mmp_label);
  
                  if (txg != ub->ub_txg || timestamp != ub->ub_timestamp ||
                      mmp_seq != (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0)) {
                          zfs_dbgmsg("multihost activity detected "
                              "txg %llu ub_txg  %llu "
                              "timestamp %llu ub_timestamp  %llu "
                              "mmp_config %#llx ub_mmp_config %#llx",
                              (u_longlong_t)txg, (u_longlong_t)ub->ub_txg,
                              (u_longlong_t)timestamp,
                              (u_longlong_t)ub->ub_timestamp,
                              (u_longlong_t)mmp_config,
                              (u_longlong_t)ub->ub_mmp_config);
  
                          error = SET_ERROR(EREMOTEIO);
                          break;
                  }
  
                  if (mmp_label) {
                          nvlist_free(mmp_label);
                          mmp_label = NULL;
                  }
  
                  error = cv_timedwait_sig(&cv, &mtx, ddi_get_lbolt() + hz);
                  if (error != -1) {
                          error = SET_ERROR(EINTR);
                          break;
                  }
                  error = 0;
          }
  
  out:
          mutex_exit(&mtx);
          mutex_destroy(&mtx);
          cv_destroy(&cv);
  
          /*
           * If the pool is determined to be active store the status in the
           * spa->spa_load_info nvlist.  If the remote hostname or hostid are
           * available from configuration read from disk store them as well.
           * This allows 'zpool import' to generate a more useful message.
           *
           * ZPOOL_CONFIG_MMP_STATE    - observed pool status (mandatory)
           * ZPOOL_CONFIG_MMP_HOSTNAME - hostname from the active pool
           * ZPOOL_CONFIG_MMP_HOSTID   - hostid from the active pool
           */
          if (error == EREMOTEIO) {
                  const char *hostname = "<unknown>";
                  uint64_t hostid = 0;
  
                  if (mmp_label) {
                          if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTNAME)) {
                                  hostname = fnvlist_lookup_string(mmp_label,
                                      ZPOOL_CONFIG_HOSTNAME);
                                  fnvlist_add_string(spa->spa_load_info,
                                      ZPOOL_CONFIG_MMP_HOSTNAME, hostname);
                          }
  
                          if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTID)) {
                                  hostid = fnvlist_lookup_uint64(mmp_label,
                                      ZPOOL_CONFIG_HOSTID);
                                  fnvlist_add_uint64(spa->spa_load_info,
                                      ZPOOL_CONFIG_MMP_HOSTID, hostid);
                          }
                  }
  
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_STATE, MMP_STATE_ACTIVE);
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_TXG, 0);
  
                  error = spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO);
          }
  
          if (mmp_label)
                  nvlist_free(mmp_label);
  
          return (error);
  }
  
  static int
  spa_verify_host(spa_t *spa, nvlist_t *mos_config)
  {
          uint64_t hostid;
          char *hostname;
          uint64_t myhostid = 0;
  
          if (!spa_is_root(spa) && nvlist_lookup_uint64(mos_config,
              ZPOOL_CONFIG_HOSTID, &hostid) == 0) {
                  hostname = fnvlist_lookup_string(mos_config,
                      ZPOOL_CONFIG_HOSTNAME);
  
                  myhostid = zone_get_hostid(NULL);
  
                  if (hostid != 0 && myhostid != 0 && hostid != myhostid) {
                          cmn_err(CE_WARN, "pool '%s' could not be "
                              "loaded as it was last accessed by "
                              "another system (host: %s hostid: 0x%llx). "
                              "See: https://openzfs.github.io/openzfs-docs/msg/"
                              "ZFS-8000-EY",
                              spa_name(spa), hostname, (u_longlong_t)hostid);
                          spa_load_failed(spa, "hostid verification failed: pool "
                              "last accessed by host: %s (hostid: 0x%llx)",
                              hostname, (u_longlong_t)hostid);
                          return (SET_ERROR(EBADF));
                  }
          }
  
          return (0);
  }
  
  static int
  spa_ld_parse_config(spa_t *spa, spa_import_type_t type)
  {
          int error = 0;
          nvlist_t *nvtree, *nvl, *config = spa->spa_config;
          int parse;
          vdev_t *rvd;
          uint64_t pool_guid;
          char *comment;
          char *compatibility;
  
          /*
           * Versioning wasn't explicitly added to the label until later, so if
           * it's not present treat it as the initial version.
           */
          if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_VERSION,
              &spa->spa_ubsync.ub_version) != 0)
                  spa->spa_ubsync.ub_version = SPA_VERSION_INITIAL;
  
          if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_GUID, &pool_guid)) {
                  spa_load_failed(spa, "invalid config provided: '%s' missing",
                      ZPOOL_CONFIG_POOL_GUID);
                  return (SET_ERROR(EINVAL));
          }
  
          /*
           * If we are doing an import, ensure that the pool is not already
           * imported by checking if its pool guid already exists in the
           * spa namespace.
           *
           * The only case that we allow an already imported pool to be
           * imported again, is when the pool is checkpointed and we want to
           * look at its checkpointed state from userland tools like zdb.
           */
  #ifdef _KERNEL
          if ((spa->spa_load_state == SPA_LOAD_IMPORT ||
              spa->spa_load_state == SPA_LOAD_TRYIMPORT) &&
              spa_guid_exists(pool_guid, 0)) {
  #else
          if ((spa->spa_load_state == SPA_LOAD_IMPORT ||
              spa->spa_load_state == SPA_LOAD_TRYIMPORT) &&
              spa_guid_exists(pool_guid, 0) &&
              !spa_importing_readonly_checkpoint(spa)) {
  #endif
                  spa_load_failed(spa, "a pool with guid %llu is already open",
                      (u_longlong_t)pool_guid);
                  return (SET_ERROR(EEXIST));
          }
  
          spa->spa_config_guid = pool_guid;
  
          nvlist_free(spa->spa_load_info);
          spa->spa_load_info = fnvlist_alloc();
  
          ASSERT(spa->spa_comment == NULL);
          if (nvlist_lookup_string(config, ZPOOL_CONFIG_COMMENT, &comment) == 0)
                  spa->spa_comment = spa_strdup(comment);
  
          ASSERT(spa->spa_compatibility == NULL);
          if (nvlist_lookup_string(config, ZPOOL_CONFIG_COMPATIBILITY,
              &compatibility) == 0)
                  spa->spa_compatibility = spa_strdup(compatibility);
  
          (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_TXG,
              &spa->spa_config_txg);
  
          if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_SPLIT, &nvl) == 0)
                  spa->spa_config_splitting = fnvlist_dup(nvl);
  
          if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &nvtree)) {
                  spa_load_failed(spa, "invalid config provided: '%s' missing",
                      ZPOOL_CONFIG_VDEV_TREE);
                  return (SET_ERROR(EINVAL));
          }
  
          /*
           * Create "The Godfather" zio to hold all async IOs
           */
          spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
              KM_SLEEP);
          for (int i = 0; i < max_ncpus; i++) {
                  spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
                      ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
                      ZIO_FLAG_GODFATHER);
          }
  
          /*
           * Parse the configuration into a vdev tree.  We explicitly set the
           * value that will be returned by spa_version() since parsing the
           * configuration requires knowing the version number.
           */
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          parse = (type == SPA_IMPORT_EXISTING ?
              VDEV_ALLOC_LOAD : VDEV_ALLOC_SPLIT);
          error = spa_config_parse(spa, &rvd, nvtree, NULL, 0, parse);
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          if (error != 0) {
                  spa_load_failed(spa, "unable to parse config [error=%d]",
                      error);
                  return (error);
          }
  
          ASSERT(spa->spa_root_vdev == rvd);
          ASSERT3U(spa->spa_min_ashift, >=, SPA_MINBLOCKSHIFT);
          ASSERT3U(spa->spa_max_ashift, <=, SPA_MAXBLOCKSHIFT);
  
          if (type != SPA_IMPORT_ASSEMBLE) {
                  ASSERT(spa_guid(spa) == pool_guid);
          }
  
          return (0);
  }
  
  /*
   * Recursively open all vdevs in the vdev tree. This function is called twice:
   * first with the untrusted config, then with the trusted config.
   */
  static int
  spa_ld_open_vdevs(spa_t *spa)
  {
          int error = 0;
  
          /*
           * spa_missing_tvds_allowed defines how many top-level vdevs can be
           * missing/unopenable for the root vdev to be still considered openable.
           */
          if (spa->spa_trust_config) {
                  spa->spa_missing_tvds_allowed = zfs_max_missing_tvds;
          } else if (spa->spa_config_source == SPA_CONFIG_SRC_CACHEFILE) {
                  spa->spa_missing_tvds_allowed = zfs_max_missing_tvds_cachefile;
          } else if (spa->spa_config_source == SPA_CONFIG_SRC_SCAN) {
                  spa->spa_missing_tvds_allowed = zfs_max_missing_tvds_scan;
          } else {
                  spa->spa_missing_tvds_allowed = 0;
          }
  
          spa->spa_missing_tvds_allowed =
              MAX(zfs_max_missing_tvds, spa->spa_missing_tvds_allowed);
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          error = vdev_open(spa->spa_root_vdev);
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          if (spa->spa_missing_tvds != 0) {
                  spa_load_note(spa, "vdev tree has %lld missing top-level "
                      "vdevs.", (u_longlong_t)spa->spa_missing_tvds);
                  if (spa->spa_trust_config && (spa->spa_mode & SPA_MODE_WRITE)) {
                          /*
                           * Although theoretically we could allow users to open
                           * incomplete pools in RW mode, we'd need to add a lot
                           * of extra logic (e.g. adjust pool space to account
                           * for missing vdevs).
                           * This limitation also prevents users from accidentally
                           * opening the pool in RW mode during data recovery and
                           * damaging it further.
                           */
                          spa_load_note(spa, "pools with missing top-level "
                              "vdevs can only be opened in read-only mode.");
                          error = SET_ERROR(ENXIO);
                  } else {
                          spa_load_note(spa, "current settings allow for maximum "
                              "%lld missing top-level vdevs at this stage.",
                              (u_longlong_t)spa->spa_missing_tvds_allowed);
                  }
          }
          if (error != 0) {
                  spa_load_failed(spa, "unable to open vdev tree [error=%d]",
                      error);
          }
          if (spa->spa_missing_tvds != 0 || error != 0)
                  vdev_dbgmsg_print_tree(spa->spa_root_vdev, 2);
  
          return (error);
  }
  
  /*
   * We need to validate the vdev labels against the configuration that
   * we have in hand. This function is called twice: first with an untrusted
   * config, then with a trusted config. The validation is more strict when the
   * config is trusted.
   */
  static int
  spa_ld_validate_vdevs(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          error = vdev_validate(rvd);
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          if (error != 0) {
                  spa_load_failed(spa, "vdev_validate failed [error=%d]", error);
                  return (error);
          }
  
          if (rvd->vdev_state <= VDEV_STATE_CANT_OPEN) {
                  spa_load_failed(spa, "cannot open vdev tree after invalidating "
                      "some vdevs");
                  vdev_dbgmsg_print_tree(rvd, 2);
                  return (SET_ERROR(ENXIO));
          }
  
          return (0);
  }
  
  static void
  spa_ld_select_uberblock_done(spa_t *spa, uberblock_t *ub)
  {
          spa->spa_state = POOL_STATE_ACTIVE;
          spa->spa_ubsync = spa->spa_uberblock;
          spa->spa_verify_min_txg = spa->spa_extreme_rewind ?
              TXG_INITIAL - 1 : spa_last_synced_txg(spa) - TXG_DEFER_SIZE - 1;
          spa->spa_first_txg = spa->spa_last_ubsync_txg ?
              spa->spa_last_ubsync_txg : spa_last_synced_txg(spa) + 1;
          spa->spa_claim_max_txg = spa->spa_first_txg;
          spa->spa_prev_software_version = ub->ub_software_version;
  }
  
  static int
  spa_ld_select_uberblock(spa_t *spa, spa_import_type_t type)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          nvlist_t *label;
          uberblock_t *ub = &spa->spa_uberblock;
          boolean_t activity_check = B_FALSE;
  
          /*
           * If we are opening the checkpointed state of the pool by
           * rewinding to it, at this point we will have written the
           * checkpointed uberblock to the vdev labels, so searching
           * the labels will find the right uberblock.  However, if
           * we are opening the checkpointed state read-only, we have
           * not modified the labels. Therefore, we must ignore the
           * labels and continue using the spa_uberblock that was set
           * by spa_ld_checkpoint_rewind.
           *
           * Note that it would be fine to ignore the labels when
           * rewinding (opening writeable) as well. However, if we
           * crash just after writing the labels, we will end up
           * searching the labels. Doing so in the common case means
           * that this code path gets exercised normally, rather than
           * just in the edge case.
           */
          if (ub->ub_checkpoint_txg != 0 &&
              spa_importing_readonly_checkpoint(spa)) {
                  spa_ld_select_uberblock_done(spa, ub);
                  return (0);
          }
  
          /*
           * Find the best uberblock.
           */
          vdev_uberblock_load(rvd, ub, &label);
  
          /*
           * If we weren't able to find a single valid uberblock, return failure.
           */
          if (ub->ub_txg == 0) {
                  nvlist_free(label);
                  spa_load_failed(spa, "no valid uberblock found");
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, ENXIO));
          }
  
          if (spa->spa_load_max_txg != UINT64_MAX) {
                  (void) spa_import_progress_set_max_txg(spa_guid(spa),
                      (u_longlong_t)spa->spa_load_max_txg);
          }
          spa_load_note(spa, "using uberblock with txg=%llu",
              (u_longlong_t)ub->ub_txg);
  
  
          /*
           * For pools which have the multihost property on determine if the
           * pool is truly inactive and can be safely imported.  Prevent
           * hosts which don't have a hostid set from importing the pool.
           */
          activity_check = spa_activity_check_required(spa, ub, label,
              spa->spa_config);
          if (activity_check) {
                  if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay &&
                      spa_get_hostid(spa) == 0) {
                          nvlist_free(label);
                          fnvlist_add_uint64(spa->spa_load_info,
                              ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
                          return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
                  }
  
                  int error = spa_activity_check(spa, ub, spa->spa_config);
                  if (error) {
                          nvlist_free(label);
                          return (error);
                  }
  
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_STATE, MMP_STATE_INACTIVE);
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_TXG, ub->ub_txg);
                  fnvlist_add_uint16(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_SEQ,
                      (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0));
          }
  
          /*
           * If the pool has an unsupported version we can't open it.
           */
          if (!SPA_VERSION_IS_SUPPORTED(ub->ub_version)) {
                  nvlist_free(label);
                  spa_load_failed(spa, "version %llu is not supported",
                      (u_longlong_t)ub->ub_version);
                  return (spa_vdev_err(rvd, VDEV_AUX_VERSION_NEWER, ENOTSUP));
          }
  
          if (ub->ub_version >= SPA_VERSION_FEATURES) {
                  nvlist_t *features;
  
                  /*
                   * If we weren't able to find what's necessary for reading the
                   * MOS in the label, return failure.
                   */
                  if (label == NULL) {
                          spa_load_failed(spa, "label config unavailable");
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA,
                              ENXIO));
                  }
  
                  if (nvlist_lookup_nvlist(label, ZPOOL_CONFIG_FEATURES_FOR_READ,
                      &features) != 0) {
                          nvlist_free(label);
                          spa_load_failed(spa, "invalid label: '%s' missing",
                              ZPOOL_CONFIG_FEATURES_FOR_READ);
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA,
                              ENXIO));
                  }
  
                  /*
                   * Update our in-core representation with the definitive values
                   * from the label.
                   */
                  nvlist_free(spa->spa_label_features);
                  spa->spa_label_features = fnvlist_dup(features);
          }
  
          nvlist_free(label);
  
          /*
           * Look through entries in the label nvlist's features_for_read. If
           * there is a feature listed there which we don't understand then we
           * cannot open a pool.
           */
          if (ub->ub_version >= SPA_VERSION_FEATURES) {
                  nvlist_t *unsup_feat;
  
                  unsup_feat = fnvlist_alloc();
  
                  for (nvpair_t *nvp = nvlist_next_nvpair(spa->spa_label_features,
                      NULL); nvp != NULL;
                      nvp = nvlist_next_nvpair(spa->spa_label_features, nvp)) {
                          if (!zfeature_is_supported(nvpair_name(nvp))) {
                                  fnvlist_add_string(unsup_feat,
                                      nvpair_name(nvp), "");
                          }
                  }
  
                  if (!nvlist_empty(unsup_feat)) {
                          fnvlist_add_nvlist(spa->spa_load_info,
                              ZPOOL_CONFIG_UNSUP_FEAT, unsup_feat);
                          nvlist_free(unsup_feat);
                          spa_load_failed(spa, "some features are unsupported");
                          return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT,
                              ENOTSUP));
                  }
  
                  nvlist_free(unsup_feat);
          }
  
          if (type != SPA_IMPORT_ASSEMBLE && spa->spa_config_splitting) {
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_try_repair(spa, spa->spa_config);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  nvlist_free(spa->spa_config_splitting);
                  spa->spa_config_splitting = NULL;
          }
  
          /*
           * Initialize internal SPA structures.
           */
          spa_ld_select_uberblock_done(spa, ub);
  
          return (0);
  }
  
  static int
  spa_ld_open_rootbp(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          error = dsl_pool_init(spa, spa->spa_first_txg, &spa->spa_dsl_pool);
          if (error != 0) {
                  spa_load_failed(spa, "unable to open rootbp in dsl_pool_init "
                      "[error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
          spa->spa_meta_objset = spa->spa_dsl_pool->dp_meta_objset;
  
          return (0);
  }
  
  static int
  spa_ld_trusted_config(spa_t *spa, spa_import_type_t type,
      boolean_t reloading)
  {
          vdev_t *mrvd, *rvd = spa->spa_root_vdev;
          nvlist_t *nv, *mos_config, *policy;
          int error = 0, copy_error;
          uint64_t healthy_tvds, healthy_tvds_mos;
          uint64_t mos_config_txg;
  
          if (spa_dir_prop(spa, DMU_POOL_CONFIG, &spa->spa_config_object, B_TRUE)
              != 0)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          /*
           * If we're assembling a pool from a split, the config provided is
           * already trusted so there is nothing to do.
           */
          if (type == SPA_IMPORT_ASSEMBLE)
                  return (0);
  
          healthy_tvds = spa_healthy_core_tvds(spa);
  
          if (load_nvlist(spa, spa->spa_config_object, &mos_config)
              != 0) {
                  spa_load_failed(spa, "unable to retrieve MOS config");
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          /*
           * If we are doing an open, pool owner wasn't verified yet, thus do
           * the verification here.
           */
          if (spa->spa_load_state == SPA_LOAD_OPEN) {
                  error = spa_verify_host(spa, mos_config);
                  if (error != 0) {
                          nvlist_free(mos_config);
                          return (error);
                  }
          }
  
          nv = fnvlist_lookup_nvlist(mos_config, ZPOOL_CONFIG_VDEV_TREE);
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
  
          /*
           * Build a new vdev tree from the trusted config
           */
          error = spa_config_parse(spa, &mrvd, nv, NULL, 0, VDEV_ALLOC_LOAD);
          if (error != 0) {
                  nvlist_free(mos_config);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  spa_load_failed(spa, "spa_config_parse failed [error=%d]",
                      error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, error));
          }
  
          /*
           * Vdev paths in the MOS may be obsolete. If the untrusted config was
           * obtained by scanning /dev/dsk, then it will have the right vdev
           * paths. We update the trusted MOS config with this information.
           * We first try to copy the paths with vdev_copy_path_strict, which
           * succeeds only when both configs have exactly the same vdev tree.
           * If that fails, we fall back to a more flexible method that has a
           * best effort policy.
           */
          copy_error = vdev_copy_path_strict(rvd, mrvd);
          if (copy_error != 0 || spa_load_print_vdev_tree) {
                  spa_load_note(spa, "provided vdev tree:");
                  vdev_dbgmsg_print_tree(rvd, 2);
                  spa_load_note(spa, "MOS vdev tree:");
                  vdev_dbgmsg_print_tree(mrvd, 2);
          }
          if (copy_error != 0) {
                  spa_load_note(spa, "vdev_copy_path_strict failed, falling "
                      "back to vdev_copy_path_relaxed");
                  vdev_copy_path_relaxed(rvd, mrvd);
          }
  
          vdev_close(rvd);
          vdev_free(rvd);
          spa->spa_root_vdev = mrvd;
          rvd = mrvd;
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          /*
           * We will use spa_config if we decide to reload the spa or if spa_load
           * fails and we rewind. We must thus regenerate the config using the
           * MOS information with the updated paths. ZPOOL_LOAD_POLICY is used to
           * pass settings on how to load the pool and is not stored in the MOS.
           * We copy it over to our new, trusted config.
           */
          mos_config_txg = fnvlist_lookup_uint64(mos_config,
              ZPOOL_CONFIG_POOL_TXG);
          nvlist_free(mos_config);
          mos_config = spa_config_generate(spa, NULL, mos_config_txg, B_FALSE);
          if (nvlist_lookup_nvlist(spa->spa_config, ZPOOL_LOAD_POLICY,
              &policy) == 0)
                  fnvlist_add_nvlist(mos_config, ZPOOL_LOAD_POLICY, policy);
          spa_config_set(spa, mos_config);
          spa->spa_config_source = SPA_CONFIG_SRC_MOS;
  
          /*
           * Now that we got the config from the MOS, we should be more strict
           * in checking blkptrs and can make assumptions about the consistency
           * of the vdev tree. spa_trust_config must be set to true before opening
           * vdevs in order for them to be writeable.
           */
          spa->spa_trust_config = B_TRUE;
  
          /*
           * Open and validate the new vdev tree
           */
          error = spa_ld_open_vdevs(spa);
          if (error != 0)
                  return (error);
  
          error = spa_ld_validate_vdevs(spa);
          if (error != 0)
                  return (error);
  
          if (copy_error != 0 || spa_load_print_vdev_tree) {
                  spa_load_note(spa, "final vdev tree:");
                  vdev_dbgmsg_print_tree(rvd, 2);
          }
  
          if (spa->spa_load_state != SPA_LOAD_TRYIMPORT &&
              !spa->spa_extreme_rewind && zfs_max_missing_tvds == 0) {
                  /*
                   * Sanity check to make sure that we are indeed loading the
                   * latest uberblock. If we missed SPA_SYNC_MIN_VDEVS tvds
                   * in the config provided and they happened to be the only ones
                   * to have the latest uberblock, we could involuntarily perform
                   * an extreme rewind.
                   */
                  healthy_tvds_mos = spa_healthy_core_tvds(spa);
                  if (healthy_tvds_mos - healthy_tvds >=
                      SPA_SYNC_MIN_VDEVS) {
                          spa_load_note(spa, "config provided misses too many "
                              "top-level vdevs compared to MOS (%lld vs %lld). ",
                              (u_longlong_t)healthy_tvds,
                              (u_longlong_t)healthy_tvds_mos);
                          spa_load_note(spa, "vdev tree:");
                          vdev_dbgmsg_print_tree(rvd, 2);
                          if (reloading) {
                                  spa_load_failed(spa, "config was already "
                                      "provided from MOS. Aborting.");
                                  return (spa_vdev_err(rvd,
                                      VDEV_AUX_CORRUPT_DATA, EIO));
                          }
                          spa_load_note(spa, "spa must be reloaded using MOS "
                              "config");
                          return (SET_ERROR(EAGAIN));
                  }
          }
  
          error = spa_check_for_missing_logs(spa);
          if (error != 0)
                  return (spa_vdev_err(rvd, VDEV_AUX_BAD_GUID_SUM, ENXIO));
  
          if (rvd->vdev_guid_sum != spa->spa_uberblock.ub_guid_sum) {
                  spa_load_failed(spa, "uberblock guid sum doesn't match MOS "
                      "guid sum (%llu != %llu)",
                      (u_longlong_t)spa->spa_uberblock.ub_guid_sum,
                      (u_longlong_t)rvd->vdev_guid_sum);
                  return (spa_vdev_err(rvd, VDEV_AUX_BAD_GUID_SUM,
                      ENXIO));
          }
  
          return (0);
  }
  
  static int
  spa_ld_open_indirect_vdev_metadata(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          /*
           * Everything that we read before spa_remove_init() must be stored
           * on concreted vdevs.  Therefore we do this as early as possible.
           */
          error = spa_remove_init(spa);
          if (error != 0) {
                  spa_load_failed(spa, "spa_remove_init failed [error=%d]",
                      error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          /*
           * Retrieve information needed to condense indirect vdev mappings.
           */
          error = spa_condense_init(spa);
          if (error != 0) {
                  spa_load_failed(spa, "spa_condense_init failed [error=%d]",
                      error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, error));
          }
  
          return (0);
  }
  
  static int
  spa_ld_check_features(spa_t *spa, boolean_t *missing_feat_writep)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          if (spa_version(spa) >= SPA_VERSION_FEATURES) {
                  boolean_t missing_feat_read = B_FALSE;
                  nvlist_t *unsup_feat, *enabled_feat;
  
                  if (spa_dir_prop(spa, DMU_POOL_FEATURES_FOR_READ,
                      &spa->spa_feat_for_read_obj, B_TRUE) != 0) {
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                  }
  
                  if (spa_dir_prop(spa, DMU_POOL_FEATURES_FOR_WRITE,
                      &spa->spa_feat_for_write_obj, B_TRUE) != 0) {
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                  }
  
                  if (spa_dir_prop(spa, DMU_POOL_FEATURE_DESCRIPTIONS,
                      &spa->spa_feat_desc_obj, B_TRUE) != 0) {
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                  }
  
                  enabled_feat = fnvlist_alloc();
                  unsup_feat = fnvlist_alloc();
  
                  if (!spa_features_check(spa, B_FALSE,
                      unsup_feat, enabled_feat))
                          missing_feat_read = B_TRUE;
  
                  if (spa_writeable(spa) ||
                      spa->spa_load_state == SPA_LOAD_TRYIMPORT) {
                          if (!spa_features_check(spa, B_TRUE,
                              unsup_feat, enabled_feat)) {
                                  *missing_feat_writep = B_TRUE;
                          }
                  }
  
                  fnvlist_add_nvlist(spa->spa_load_info,
                      ZPOOL_CONFIG_ENABLED_FEAT, enabled_feat);
  
                  if (!nvlist_empty(unsup_feat)) {
                          fnvlist_add_nvlist(spa->spa_load_info,
                              ZPOOL_CONFIG_UNSUP_FEAT, unsup_feat);
                  }
  
                  fnvlist_free(enabled_feat);
                  fnvlist_free(unsup_feat);
  
                  if (!missing_feat_read) {
                          fnvlist_add_boolean(spa->spa_load_info,
                              ZPOOL_CONFIG_CAN_RDONLY);
                  }
  
                  /*
                   * If the state is SPA_LOAD_TRYIMPORT, our objective is
                   * twofold: to determine whether the pool is available for
                   * import in read-write mode and (if it is not) whether the
                   * pool is available for import in read-only mode. If the pool
                   * is available for import in read-write mode, it is displayed
                   * as available in userland; if it is not available for import
                   * in read-only mode, it is displayed as unavailable in
                   * userland. If the pool is available for import in read-only
                   * mode but not read-write mode, it is displayed as unavailable
                   * in userland with a special note that the pool is actually
                   * available for open in read-only mode.
                   *
                   * As a result, if the state is SPA_LOAD_TRYIMPORT and we are
                   * missing a feature for write, we must first determine whether
                   * the pool can be opened read-only before returning to
                   * userland in order to know whether to display the
                   * abovementioned note.
                   */
                  if (missing_feat_read || (*missing_feat_writep &&
                      spa_writeable(spa))) {
                          spa_load_failed(spa, "pool uses unsupported features");
                          return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT,
                              ENOTSUP));
                  }
  
                  /*
                   * Load refcounts for ZFS features from disk into an in-memory
                   * cache during SPA initialization.
                   */
                  for (spa_feature_t i = 0; i < SPA_FEATURES; i++) {
                          uint64_t refcount;
  
                          error = feature_get_refcount_from_disk(spa,
                              &spa_feature_table[i], &refcount);
                          if (error == 0) {
                                  spa->spa_feat_refcount_cache[i] = refcount;
                          } else if (error == ENOTSUP) {
                                  spa->spa_feat_refcount_cache[i] =
                                      SPA_FEATURE_DISABLED;
                          } else {
                                  spa_load_failed(spa, "error getting refcount "
                                      "for feature %s [error=%d]",
                                      spa_feature_table[i].fi_guid, error);
                                  return (spa_vdev_err(rvd,
                                      VDEV_AUX_CORRUPT_DATA, EIO));
                          }
                  }
          }
  
          if (spa_feature_is_active(spa, SPA_FEATURE_ENABLED_TXG)) {
                  if (spa_dir_prop(spa, DMU_POOL_FEATURE_ENABLED_TXG,
                      &spa->spa_feat_enabled_txg_obj, B_TRUE) != 0)
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          /*
           * Encryption was added before bookmark_v2, even though bookmark_v2
           * is now a dependency. If this pool has encryption enabled without
           * bookmark_v2, trigger an errata message.
           */
          if (spa_feature_is_enabled(spa, SPA_FEATURE_ENCRYPTION) &&
              !spa_feature_is_enabled(spa, SPA_FEATURE_BOOKMARK_V2)) {
                  spa->spa_errata = ZPOOL_ERRATA_ZOL_8308_ENCRYPTION;
          }
  
          return (0);
  }
  
  static int
  spa_ld_load_special_directories(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          spa->spa_is_initializing = B_TRUE;
          error = dsl_pool_open(spa->spa_dsl_pool);
          spa->spa_is_initializing = B_FALSE;
          if (error != 0) {
                  spa_load_failed(spa, "dsl_pool_open failed [error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          return (0);
  }
  
  static int
  spa_ld_get_props(spa_t *spa)
  {
          int error = 0;
          uint64_t obj;
          vdev_t *rvd = spa->spa_root_vdev;
  
          /* Grab the checksum salt from the MOS. */
          error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_CHECKSUM_SALT, 1,
              sizeof (spa->spa_cksum_salt.zcs_bytes),
              spa->spa_cksum_salt.zcs_bytes);
          if (error == ENOENT) {
                  /* Generate a new salt for subsequent use */
                  (void) random_get_pseudo_bytes(spa->spa_cksum_salt.zcs_bytes,
                      sizeof (spa->spa_cksum_salt.zcs_bytes));
          } else if (error != 0) {
                  spa_load_failed(spa, "unable to retrieve checksum salt from "
                      "MOS [error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          if (spa_dir_prop(spa, DMU_POOL_SYNC_BPOBJ, &obj, B_TRUE) != 0)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          error = bpobj_open(&spa->spa_deferred_bpobj, spa->spa_meta_objset, obj);
          if (error != 0) {
                  spa_load_failed(spa, "error opening deferred-frees bpobj "
                      "[error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          /*
           * Load the bit that tells us to use the new accounting function
           * (raid-z deflation).  If we have an older pool, this will not
           * be present.
           */
          error = spa_dir_prop(spa, DMU_POOL_DEFLATE, &spa->spa_deflate, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          error = spa_dir_prop(spa, DMU_POOL_CREATION_VERSION,
              &spa->spa_creation_version, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          /*
           * Load the persistent error log.  If we have an older pool, this will
           * not be present.
           */
          error = spa_dir_prop(spa, DMU_POOL_ERRLOG_LAST, &spa->spa_errlog_last,
              B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          error = spa_dir_prop(spa, DMU_POOL_ERRLOG_SCRUB,
              &spa->spa_errlog_scrub, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          /*
           * Load the livelist deletion field. If a livelist is queued for
           * deletion, indicate that in the spa
           */
          error = spa_dir_prop(spa, DMU_POOL_DELETED_CLONES,
              &spa->spa_livelists_to_delete, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          /*
           * Load the history object.  If we have an older pool, this
           * will not be present.
           */
          error = spa_dir_prop(spa, DMU_POOL_HISTORY, &spa->spa_history, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          /*
           * Load the per-vdev ZAP map. If we have an older pool, this will not
           * be present; in this case, defer its creation to a later time to
           * avoid dirtying the MOS this early / out of sync context. See
           * spa_sync_config_object.
           */
  
          /* The sentinel is only available in the MOS config. */
          nvlist_t *mos_config;
          if (load_nvlist(spa, spa->spa_config_object, &mos_config) != 0) {
                  spa_load_failed(spa, "unable to retrieve MOS config");
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          error = spa_dir_prop(spa, DMU_POOL_VDEV_ZAP_MAP,
              &spa->spa_all_vdev_zaps, B_FALSE);
  
          if (error == ENOENT) {
                  VERIFY(!nvlist_exists(mos_config,
                      ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS));
                  spa->spa_avz_action = AVZ_ACTION_INITIALIZE;
                  ASSERT0(vdev_count_verify_zaps(spa->spa_root_vdev));
          } else if (error != 0) {
                  nvlist_free(mos_config);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          } else if (!nvlist_exists(mos_config, ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS)) {
                  /*
                   * An older version of ZFS overwrote the sentinel value, so
                   * we have orphaned per-vdev ZAPs in the MOS. Defer their
                   * destruction to later; see spa_sync_config_object.
                   */
                  spa->spa_avz_action = AVZ_ACTION_DESTROY;
                  /*
                   * We're assuming that no vdevs have had their ZAPs created
                   * before this. Better be sure of it.
                   */
                  ASSERT0(vdev_count_verify_zaps(spa->spa_root_vdev));
          }
          nvlist_free(mos_config);
  
          spa->spa_delegation = zpool_prop_default_numeric(ZPOOL_PROP_DELEGATION);
  
          error = spa_dir_prop(spa, DMU_POOL_PROPS, &spa->spa_pool_props_object,
              B_FALSE);
          if (error && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
  
          if (error == 0) {
                  uint64_t autoreplace = 0;
  
                  spa_prop_find(spa, ZPOOL_PROP_BOOTFS, &spa->spa_bootfs);
                  spa_prop_find(spa, ZPOOL_PROP_AUTOREPLACE, &autoreplace);
                  spa_prop_find(spa, ZPOOL_PROP_DELEGATION, &spa->spa_delegation);
                  spa_prop_find(spa, ZPOOL_PROP_FAILUREMODE, &spa->spa_failmode);
                  spa_prop_find(spa, ZPOOL_PROP_AUTOEXPAND, &spa->spa_autoexpand);
                  spa_prop_find(spa, ZPOOL_PROP_MULTIHOST, &spa->spa_multihost);
                  spa_prop_find(spa, ZPOOL_PROP_AUTOTRIM, &spa->spa_autotrim);
                  spa->spa_autoreplace = (autoreplace != 0);
          }
  
          /*
           * If we are importing a pool with missing top-level vdevs,
           * we enforce that the pool doesn't panic or get suspended on
           * error since the likelihood of missing data is extremely high.
           */
          if (spa->spa_missing_tvds > 0 &&
              spa->spa_failmode != ZIO_FAILURE_MODE_CONTINUE &&
              spa->spa_load_state != SPA_LOAD_TRYIMPORT) {
                  spa_load_note(spa, "forcing failmode to 'continue' "
                      "as some top level vdevs are missing");
                  spa->spa_failmode = ZIO_FAILURE_MODE_CONTINUE;
          }
  
          return (0);
  }
  
  static int
  spa_ld_open_aux_vdevs(spa_t *spa, spa_import_type_t type)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          /*
           * If we're assembling the pool from the split-off vdevs of
           * an existing pool, we don't want to attach the spares & cache
           * devices.
           */
  
          /*
           * Load any hot spares for this pool.
           */
          error = spa_dir_prop(spa, DMU_POOL_SPARES, &spa->spa_spares.sav_object,
              B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          if (error == 0 && type != SPA_IMPORT_ASSEMBLE) {
                  ASSERT(spa_version(spa) >= SPA_VERSION_SPARES);
                  if (load_nvlist(spa, spa->spa_spares.sav_object,
                      &spa->spa_spares.sav_config) != 0) {
                          spa_load_failed(spa, "error loading spares nvlist");
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                  }
  
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_spares(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
          } else if (error == 0) {
                  spa->spa_spares.sav_sync = B_TRUE;
          }
  
          /*
           * Load any level 2 ARC devices for this pool.
           */
          error = spa_dir_prop(spa, DMU_POOL_L2CACHE,
              &spa->spa_l2cache.sav_object, B_FALSE);
          if (error != 0 && error != ENOENT)
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          if (error == 0 && type != SPA_IMPORT_ASSEMBLE) {
                  ASSERT(spa_version(spa) >= SPA_VERSION_L2CACHE);
                  if (load_nvlist(spa, spa->spa_l2cache.sav_object,
                      &spa->spa_l2cache.sav_config) != 0) {
                          spa_load_failed(spa, "error loading l2cache nvlist");
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                  }
  
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_l2cache(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
          } else if (error == 0) {
                  spa->spa_l2cache.sav_sync = B_TRUE;
          }
  
          return (0);
  }
  
  static int
  spa_ld_load_vdev_metadata(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          /*
           * If the 'multihost' property is set, then never allow a pool to
           * be imported when the system hostid is zero.  The exception to
           * this rule is zdb which is always allowed to access pools.
           */
          if (spa_multihost(spa) && spa_get_hostid(spa) == 0 &&
              (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP) == 0) {
                  fnvlist_add_uint64(spa->spa_load_info,
                      ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
                  return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
          }
  
          /*
           * If the 'autoreplace' property is set, then post a resource notifying
           * the ZFS DE that it should not issue any faults for unopenable
           * devices.  We also iterate over the vdevs, and post a sysevent for any
           * unopenable vdevs so that the normal autoreplace handler can take
           * over.
           */
          if (spa->spa_autoreplace && spa->spa_load_state != SPA_LOAD_TRYIMPORT) {
                  spa_check_removed(spa->spa_root_vdev);
                  /*
                   * For the import case, this is done in spa_import(), because
                   * at this point we're using the spare definitions from
                   * the MOS config, not necessarily from the userland config.
                   */
                  if (spa->spa_load_state != SPA_LOAD_IMPORT) {
                          spa_aux_check_removed(&spa->spa_spares);
                          spa_aux_check_removed(&spa->spa_l2cache);
                  }
          }
  
          /*
           * Load the vdev metadata such as metaslabs, DTLs, spacemap object, etc.
           */
          error = vdev_load(rvd);
          if (error != 0) {
                  spa_load_failed(spa, "vdev_load failed [error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, error));
          }
  
          error = spa_ld_log_spacemaps(spa);
          if (error != 0) {
                  spa_load_failed(spa, "spa_ld_log_spacemaps failed [error=%d]",
                      error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, error));
          }
  
          /*
           * Propagate the leaf DTLs we just loaded all the way up the vdev tree.
           */
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          vdev_dtl_reassess(rvd, 0, 0, B_FALSE, B_FALSE);
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          return (0);
  }
  
  static int
  spa_ld_load_dedup_tables(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          error = ddt_load(spa);
          if (error != 0) {
                  spa_load_failed(spa, "ddt_load failed [error=%d]", error);
                  return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
          }
  
          return (0);
  }
  
  static int
  spa_ld_verify_logs(spa_t *spa, spa_import_type_t type, const char **ereport)
  {
          vdev_t *rvd = spa->spa_root_vdev;
  
          if (type != SPA_IMPORT_ASSEMBLE && spa_writeable(spa)) {
                  boolean_t missing = spa_check_logs(spa);
                  if (missing) {
                          if (spa->spa_missing_tvds != 0) {
                                  spa_load_note(spa, "spa_check_logs failed "
                                      "so dropping the logs");
                          } else {
                                  *ereport = FM_EREPORT_ZFS_LOG_REPLAY;
                                  spa_load_failed(spa, "spa_check_logs failed");
                                  return (spa_vdev_err(rvd, VDEV_AUX_BAD_LOG,
                                      ENXIO));
                          }
                  }
          }
  
          return (0);
  }
  
  static int
  spa_ld_verify_pool_data(spa_t *spa)
  {
          int error = 0;
          vdev_t *rvd = spa->spa_root_vdev;
  
          /*
           * We've successfully opened the pool, verify that we're ready
           * to start pushing transactions.
           */
          if (spa->spa_load_state != SPA_LOAD_TRYIMPORT) {
                  error = spa_load_verify(spa);
                  if (error != 0) {
                          spa_load_failed(spa, "spa_load_verify failed "
                              "[error=%d]", error);
                          return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA,
                              error));
                  }
          }
  
          return (0);
  }
  
  static void
  spa_ld_claim_log_blocks(spa_t *spa)
  {
          dmu_tx_t *tx;
          dsl_pool_t *dp = spa_get_dsl(spa);
  
          /*
           * Claim log blocks that haven't been committed yet.
           * This must all happen in a single txg.
           * Note: spa_claim_max_txg is updated by spa_claim_notify(),
           * invoked from zil_claim_log_block()'s i/o done callback.
           * Price of rollback is that we abandon the log.
           */
          spa->spa_claiming = B_TRUE;
  
          tx = dmu_tx_create_assigned(dp, spa_first_txg(spa));
          (void) dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
              zil_claim, tx, DS_FIND_CHILDREN);
          dmu_tx_commit(tx);
  
          spa->spa_claiming = B_FALSE;
  
          spa_set_log_state(spa, SPA_LOG_GOOD);
  }
  
  static void
  spa_ld_check_for_config_update(spa_t *spa, uint64_t config_cache_txg,
      boolean_t update_config_cache)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          int need_update = B_FALSE;
  
          /*
           * If the config cache is stale, or we have uninitialized
           * metaslabs (see spa_vdev_add()), then update the config.
           *
           * If this is a verbatim import, trust the current
           * in-core spa_config and update the disk labels.
           */
          if (update_config_cache || config_cache_txg != spa->spa_config_txg ||
              spa->spa_load_state == SPA_LOAD_IMPORT ||
              spa->spa_load_state == SPA_LOAD_RECOVER ||
              (spa->spa_import_flags & ZFS_IMPORT_VERBATIM))
                  need_update = B_TRUE;
  
          for (int c = 0; c < rvd->vdev_children; c++)
                  if (rvd->vdev_child[c]->vdev_ms_array == 0)
                          need_update = B_TRUE;
  
          /*
           * Update the config cache asynchronously in case we're the
           * root pool, in which case the config cache isn't writable yet.
           */
          if (need_update)
                  spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
  }
  
  static void
  spa_ld_prepare_for_reload(spa_t *spa)
  {
          spa_mode_t mode = spa->spa_mode;
          int async_suspended = spa->spa_async_suspended;
  
          spa_unload(spa);
          spa_deactivate(spa);
          spa_activate(spa, mode);
  
          /*
           * We save the value of spa_async_suspended as it gets reset to 0 by
           * spa_unload(). We want to restore it back to the original value before
           * returning as we might be calling spa_async_resume() later.
           */
          spa->spa_async_suspended = async_suspended;
  }
  
  static int
  spa_ld_read_checkpoint_txg(spa_t *spa)
  {
          uberblock_t checkpoint;
          int error = 0;
  
          ASSERT0(spa->spa_checkpoint_txg);
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_ZPOOL_CHECKPOINT, sizeof (uint64_t),
              sizeof (uberblock_t) / sizeof (uint64_t), &checkpoint);
  
          if (error == ENOENT)
                  return (0);
  
          if (error != 0)
                  return (error);
  
          ASSERT3U(checkpoint.ub_txg, !=, 0);
          ASSERT3U(checkpoint.ub_checkpoint_txg, !=, 0);
          ASSERT3U(checkpoint.ub_timestamp, !=, 0);
          spa->spa_checkpoint_txg = checkpoint.ub_txg;
          spa->spa_checkpoint_info.sci_timestamp = checkpoint.ub_timestamp;
  
          return (0);
  }
  
  static int
  spa_ld_mos_init(spa_t *spa, spa_import_type_t type)
  {
          int error = 0;
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa->spa_config_source != SPA_CONFIG_SRC_NONE);
  
          /*
           * Never trust the config that is provided unless we are assembling
           * a pool following a split.
           * This means don't trust blkptrs and the vdev tree in general. This
           * also effectively puts the spa in read-only mode since
           * spa_writeable() checks for spa_trust_config to be true.
           * We will later load a trusted config from the MOS.
           */
          if (type != SPA_IMPORT_ASSEMBLE)
                  spa->spa_trust_config = B_FALSE;
  
          /*
           * Parse the config provided to create a vdev tree.
           */
          error = spa_ld_parse_config(spa, type);
          if (error != 0)
                  return (error);
  
          spa_import_progress_add(spa);
  
          /*
           * Now that we have the vdev tree, try to open each vdev. This involves
           * opening the underlying physical device, retrieving its geometry and
           * probing the vdev with a dummy I/O. The state of each vdev will be set
           * based on the success of those operations. After this we'll be ready
           * to read from the vdevs.
           */
          error = spa_ld_open_vdevs(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Read the label of each vdev and make sure that the GUIDs stored
           * there match the GUIDs in the config provided.
           * If we're assembling a new pool that's been split off from an
           * existing pool, the labels haven't yet been updated so we skip
           * validation for now.
           */
          if (type != SPA_IMPORT_ASSEMBLE) {
                  error = spa_ld_validate_vdevs(spa);
                  if (error != 0)
                          return (error);
          }
  
          /*
           * Read all vdev labels to find the best uberblock (i.e. latest,
           * unless spa_load_max_txg is set) and store it in spa_uberblock. We
           * get the list of features required to read blkptrs in the MOS from
           * the vdev label with the best uberblock and verify that our version
           * of zfs supports them all.
           */
          error = spa_ld_select_uberblock(spa, type);
          if (error != 0)
                  return (error);
  
          /*
           * Pass that uberblock to the dsl_pool layer which will open the root
           * blkptr. This blkptr points to the latest version of the MOS and will
           * allow us to read its contents.
           */
          error = spa_ld_open_rootbp(spa);
          if (error != 0)
                  return (error);
  
          return (0);
  }
  
  static int
  spa_ld_checkpoint_rewind(spa_t *spa)
  {
          uberblock_t checkpoint;
          int error = 0;
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa->spa_import_flags & ZFS_IMPORT_CHECKPOINT);
  
          error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_ZPOOL_CHECKPOINT, sizeof (uint64_t),
              sizeof (uberblock_t) / sizeof (uint64_t), &checkpoint);
  
          if (error != 0) {
                  spa_load_failed(spa, "unable to retrieve checkpointed "
                      "uberblock from the MOS config [error=%d]", error);
  
                  if (error == ENOENT)
                          error = ZFS_ERR_NO_CHECKPOINT;
  
                  return (error);
          }
  
          ASSERT3U(checkpoint.ub_txg, <, spa->spa_uberblock.ub_txg);
          ASSERT3U(checkpoint.ub_txg, ==, checkpoint.ub_checkpoint_txg);
  
          /*
           * We need to update the txg and timestamp of the checkpointed
           * uberblock to be higher than the latest one. This ensures that
           * the checkpointed uberblock is selected if we were to close and
           * reopen the pool right after we've written it in the vdev labels.
           * (also see block comment in vdev_uberblock_compare)
           */
          checkpoint.ub_txg = spa->spa_uberblock.ub_txg + 1;
          checkpoint.ub_timestamp = gethrestime_sec();
  
          /*
           * Set current uberblock to be the checkpointed uberblock.
           */
          spa->spa_uberblock = checkpoint;
  
          /*
           * If we are doing a normal rewind, then the pool is open for
           * writing and we sync the "updated" checkpointed uberblock to
           * disk. Once this is done, we've basically rewound the whole
           * pool and there is no way back.
           *
           * There are cases when we don't want to attempt and sync the
           * checkpointed uberblock to disk because we are opening a
           * pool as read-only. Specifically, verifying the checkpointed
           * state with zdb, and importing the checkpointed state to get
           * a "preview" of its content.
           */
          if (spa_writeable(spa)) {
                  vdev_t *rvd = spa->spa_root_vdev;
  
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  vdev_t *svd[SPA_SYNC_MIN_VDEVS] = { NULL };
                  int svdcount = 0;
                  int children = rvd->vdev_children;
                  int c0 = random_in_range(children);
  
                  for (int c = 0; c < children; c++) {
                          vdev_t *vd = rvd->vdev_child[(c0 + c) % children];
  
                          /* Stop when revisiting the first vdev */
                          if (c > 0 && svd[0] == vd)
                                  break;
  
                          if (vd->vdev_ms_array == 0 || vd->vdev_islog ||
                              !vdev_is_concrete(vd))
                                  continue;
  
                          svd[svdcount++] = vd;
                          if (svdcount == SPA_SYNC_MIN_VDEVS)
                                  break;
                  }
                  error = vdev_config_sync(svd, svdcount, spa->spa_first_txg);
                  if (error == 0)
                          spa->spa_last_synced_guid = rvd->vdev_guid;
                  spa_config_exit(spa, SCL_ALL, FTAG);
  
                  if (error != 0) {
                          spa_load_failed(spa, "failed to write checkpointed "
                              "uberblock to the vdev labels [error=%d]", error);
                          return (error);
                  }
          }
  
          return (0);
  }
  
  static int
  spa_ld_mos_with_trusted_config(spa_t *spa, spa_import_type_t type,
      boolean_t *update_config_cache)
  {
          int error;
  
          /*
           * Parse the config for pool, open and validate vdevs,
           * select an uberblock, and use that uberblock to open
           * the MOS.
           */
          error = spa_ld_mos_init(spa, type);
          if (error != 0)
                  return (error);
  
          /*
           * Retrieve the trusted config stored in the MOS and use it to create
           * a new, exact version of the vdev tree, then reopen all vdevs.
           */
          error = spa_ld_trusted_config(spa, type, B_FALSE);
          if (error == EAGAIN) {
                  if (update_config_cache != NULL)
                          *update_config_cache = B_TRUE;
  
                  /*
                   * Redo the loading process with the trusted config if it is
                   * too different from the untrusted config.
                   */
                  spa_ld_prepare_for_reload(spa);
                  spa_load_note(spa, "RELOADING");
                  error = spa_ld_mos_init(spa, type);
                  if (error != 0)
                          return (error);
  
                  error = spa_ld_trusted_config(spa, type, B_TRUE);
                  if (error != 0)
                          return (error);
  
          } else if (error != 0) {
                  return (error);
          }
  
          return (0);
  }
  
  /*
   * Load an existing storage pool, using the config provided. This config
   * describes which vdevs are part of the pool and is later validated against
   * partial configs present in each vdev's label and an entire copy of the
   * config stored in the MOS.
   */
  static int
  spa_load_impl(spa_t *spa, spa_import_type_t type, const char **ereport)
  {
          int error = 0;
          boolean_t missing_feat_write = B_FALSE;
          boolean_t checkpoint_rewind =
              (spa->spa_import_flags & ZFS_IMPORT_CHECKPOINT);
          boolean_t update_config_cache = B_FALSE;
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa->spa_config_source != SPA_CONFIG_SRC_NONE);
  
          spa_load_note(spa, "LOADING");
  
          error = spa_ld_mos_with_trusted_config(spa, type, &update_config_cache);
          if (error != 0)
                  return (error);
  
          /*
           * If we are rewinding to the checkpoint then we need to repeat
           * everything we've done so far in this function but this time
           * selecting the checkpointed uberblock and using that to open
           * the MOS.
           */
          if (checkpoint_rewind) {
                  /*
                   * If we are rewinding to the checkpoint update config cache
                   * anyway.
                   */
                  update_config_cache = B_TRUE;
  
                  /*
                   * Extract the checkpointed uberblock from the current MOS
                   * and use this as the pool's uberblock from now on. If the
                   * pool is imported as writeable we also write the checkpoint
                   * uberblock to the labels, making the rewind permanent.
                   */
                  error = spa_ld_checkpoint_rewind(spa);
                  if (error != 0)
                          return (error);
  
                  /*
                   * Redo the loading process again with the
                   * checkpointed uberblock.
                   */
                  spa_ld_prepare_for_reload(spa);
                  spa_load_note(spa, "LOADING checkpointed uberblock");
                  error = spa_ld_mos_with_trusted_config(spa, type, NULL);
                  if (error != 0)
                          return (error);
          }
  
          /*
           * Retrieve the checkpoint txg if the pool has a checkpoint.
           */
          error = spa_ld_read_checkpoint_txg(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Retrieve the mapping of indirect vdevs. Those vdevs were removed
           * from the pool and their contents were re-mapped to other vdevs. Note
           * that everything that we read before this step must have been
           * rewritten on concrete vdevs after the last device removal was
           * initiated. Otherwise we could be reading from indirect vdevs before
           * we have loaded their mappings.
           */
          error = spa_ld_open_indirect_vdev_metadata(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Retrieve the full list of active features from the MOS and check if
           * they are all supported.
           */
          error = spa_ld_check_features(spa, &missing_feat_write);
          if (error != 0)
                  return (error);
  
          /*
           * Load several special directories from the MOS needed by the dsl_pool
           * layer.
           */
          error = spa_ld_load_special_directories(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Retrieve pool properties from the MOS.
           */
          error = spa_ld_get_props(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Retrieve the list of auxiliary devices - cache devices and spares -
           * and open them.
           */
          error = spa_ld_open_aux_vdevs(spa, type);
          if (error != 0)
                  return (error);
  
          /*
           * Load the metadata for all vdevs. Also check if unopenable devices
           * should be autoreplaced.
           */
          error = spa_ld_load_vdev_metadata(spa);
          if (error != 0)
                  return (error);
  
          error = spa_ld_load_dedup_tables(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Verify the logs now to make sure we don't have any unexpected errors
           * when we claim log blocks later.
           */
          error = spa_ld_verify_logs(spa, type, ereport);
          if (error != 0)
                  return (error);
  
          if (missing_feat_write) {
                  ASSERT(spa->spa_load_state == SPA_LOAD_TRYIMPORT);
  
                  /*
                   * At this point, we know that we can open the pool in
                   * read-only mode but not read-write mode. We now have enough
                   * information and can return to userland.
                   */
                  return (spa_vdev_err(spa->spa_root_vdev, VDEV_AUX_UNSUP_FEAT,
                      ENOTSUP));
          }
  
          /*
           * Traverse the last txgs to make sure the pool was left off in a safe
           * state. When performing an extreme rewind, we verify the whole pool,
           * which can take a very long time.
           */
          error = spa_ld_verify_pool_data(spa);
          if (error != 0)
                  return (error);
  
          /*
           * Calculate the deflated space for the pool. This must be done before
           * we write anything to the pool because we'd need to update the space
           * accounting using the deflated sizes.
           */
          spa_update_dspace(spa);
  
          /*
           * We have now retrieved all the information we needed to open the
           * pool. If we are importing the pool in read-write mode, a few
           * additional steps must be performed to finish the import.
           */
          if (spa_writeable(spa) && (spa->spa_load_state == SPA_LOAD_RECOVER ||
              spa->spa_load_max_txg == UINT64_MAX)) {
                  uint64_t config_cache_txg = spa->spa_config_txg;
  
                  ASSERT(spa->spa_load_state != SPA_LOAD_TRYIMPORT);
  
                  /*
                   * In case of a checkpoint rewind, log the original txg
                   * of the checkpointed uberblock.
                   */
                  if (checkpoint_rewind) {
                          spa_history_log_internal(spa, "checkpoint rewind",
                              NULL, "rewound state to txg=%llu",
                              (u_longlong_t)spa->spa_uberblock.ub_checkpoint_txg);
                  }
  
                  /*
                   * Traverse the ZIL and claim all blocks.
                   */
                  spa_ld_claim_log_blocks(spa);
  
                  /*
                   * Kick-off the syncing thread.
                   */
                  spa->spa_sync_on = B_TRUE;
                  txg_sync_start(spa->spa_dsl_pool);
                  mmp_thread_start(spa);
  
                  /*
                   * Wait for all claims to sync.  We sync up to the highest
                   * claimed log block birth time so that claimed log blocks
                   * don't appear to be from the future.  spa_claim_max_txg
                   * will have been set for us by ZIL traversal operations
                   * performed above.
                   */
                  txg_wait_synced(spa->spa_dsl_pool, spa->spa_claim_max_txg);
  
                  /*
                   * Check if we need to request an update of the config. On the
                   * next sync, we would update the config stored in vdev labels
                   * and the cachefile (by default /etc/zfs/zpool.cache).
                   */
                  spa_ld_check_for_config_update(spa, config_cache_txg,
                      update_config_cache);
  
                  /*
                   * Check if a rebuild was in progress and if so resume it.
                   * Then check all DTLs to see if anything needs resilvering.
                   * The resilver will be deferred if a rebuild was started.
                   */
                  if (vdev_rebuild_active(spa->spa_root_vdev)) {
                          vdev_rebuild_restart(spa);
                  } else if (!dsl_scan_resilvering(spa->spa_dsl_pool) &&
                      vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL)) {
                          spa_async_request(spa, SPA_ASYNC_RESILVER);
                  }
  
                  /*
                   * Log the fact that we booted up (so that we can detect if
                   * we rebooted in the middle of an operation).
                   */
                  spa_history_log_version(spa, "open", NULL);
  
                  spa_restart_removal(spa);
                  spa_spawn_aux_threads(spa);
  
                  /*
                   * Delete any inconsistent datasets.
                   *
                   * Note:
                   * Since we may be issuing deletes for clones here,
                   * we make sure to do so after we've spawned all the
                   * auxiliary threads above (from which the livelist
                   * deletion zthr is part of).
                   */
                  (void) dmu_objset_find(spa_name(spa),
                      dsl_destroy_inconsistent, NULL, DS_FIND_CHILDREN);
  
                  /*
                   * Clean up any stale temporary dataset userrefs.
                   */
                  dsl_pool_clean_tmp_userrefs(spa->spa_dsl_pool);
  
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  vdev_initialize_restart(spa->spa_root_vdev);
                  vdev_trim_restart(spa->spa_root_vdev);
                  vdev_autotrim_restart(spa);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
          }
  
          spa_import_progress_remove(spa_guid(spa));
          spa_async_request(spa, SPA_ASYNC_L2CACHE_REBUILD);
  
          spa_load_note(spa, "LOADED");
  
          return (0);
  }
  
  static int
  spa_load_retry(spa_t *spa, spa_load_state_t state)
  {
          spa_mode_t mode = spa->spa_mode;
  
          spa_unload(spa);
          spa_deactivate(spa);
  
          spa->spa_load_max_txg = spa->spa_uberblock.ub_txg - 1;
  
          spa_activate(spa, mode);
          spa_async_suspend(spa);
  
          spa_load_note(spa, "spa_load_retry: rewind, max txg: %llu",
              (u_longlong_t)spa->spa_load_max_txg);
  
          return (spa_load(spa, state, SPA_IMPORT_EXISTING));
  }
  
  /*
   * If spa_load() fails this function will try loading prior txg's. If
   * 'state' is SPA_LOAD_RECOVER and one of these loads succeeds the pool
   * will be rewound to that txg. If 'state' is not SPA_LOAD_RECOVER this
   * function will not rewind the pool and will return the same error as
   * spa_load().
   */
  static int
  spa_load_best(spa_t *spa, spa_load_state_t state, uint64_t max_request,
      int rewind_flags)
  {
          nvlist_t *loadinfo = NULL;
          nvlist_t *config = NULL;
          int load_error, rewind_error;
          uint64_t safe_rewind_txg;
          uint64_t min_txg;
  
          if (spa->spa_load_txg && state == SPA_LOAD_RECOVER) {
                  spa->spa_load_max_txg = spa->spa_load_txg;
                  spa_set_log_state(spa, SPA_LOG_CLEAR);
          } else {
                  spa->spa_load_max_txg = max_request;
                  if (max_request != UINT64_MAX)
                          spa->spa_extreme_rewind = B_TRUE;
          }
  
          load_error = rewind_error = spa_load(spa, state, SPA_IMPORT_EXISTING);
          if (load_error == 0)
                  return (0);
          if (load_error == ZFS_ERR_NO_CHECKPOINT) {
                  /*
                   * When attempting checkpoint-rewind on a pool with no
                   * checkpoint, we should not attempt to load uberblocks
                   * from previous txgs when spa_load fails.
                   */
                  ASSERT(spa->spa_import_flags & ZFS_IMPORT_CHECKPOINT);
                  spa_import_progress_remove(spa_guid(spa));
                  return (load_error);
          }
  
          if (spa->spa_root_vdev != NULL)
                  config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);
  
          spa->spa_last_ubsync_txg = spa->spa_uberblock.ub_txg;
          spa->spa_last_ubsync_txg_ts = spa->spa_uberblock.ub_timestamp;
  
          if (rewind_flags & ZPOOL_NEVER_REWIND) {
                  nvlist_free(config);
                  spa_import_progress_remove(spa_guid(spa));
                  return (load_error);
          }
  
          if (state == SPA_LOAD_RECOVER) {
                  /* Price of rolling back is discarding txgs, including log */
                  spa_set_log_state(spa, SPA_LOG_CLEAR);
          } else {
                  /*
                   * If we aren't rolling back save the load info from our first
                   * import attempt so that we can restore it after attempting
                   * to rewind.
                   */
                  loadinfo = spa->spa_load_info;
                  spa->spa_load_info = fnvlist_alloc();
          }
  
          spa->spa_load_max_txg = spa->spa_last_ubsync_txg;
          safe_rewind_txg = spa->spa_last_ubsync_txg - TXG_DEFER_SIZE;
          min_txg = (rewind_flags & ZPOOL_EXTREME_REWIND) ?
              TXG_INITIAL : safe_rewind_txg;
  
          /*
           * Continue as long as we're finding errors, we're still within
           * the acceptable rewind range, and we're still finding uberblocks
           */
          while (rewind_error && spa->spa_uberblock.ub_txg >= min_txg &&
              spa->spa_uberblock.ub_txg <= spa->spa_load_max_txg) {
                  if (spa->spa_load_max_txg < safe_rewind_txg)
                          spa->spa_extreme_rewind = B_TRUE;
                  rewind_error = spa_load_retry(spa, state);
          }
  
          spa->spa_extreme_rewind = B_FALSE;
          spa->spa_load_max_txg = UINT64_MAX;
  
          if (config && (rewind_error || state != SPA_LOAD_RECOVER))
                  spa_config_set(spa, config);
          else
                  nvlist_free(config);
  
          if (state == SPA_LOAD_RECOVER) {
                  ASSERT3P(loadinfo, ==, NULL);
                  spa_import_progress_remove(spa_guid(spa));
                  return (rewind_error);
          } else {
                  /* Store the rewind info as part of the initial load info */
                  fnvlist_add_nvlist(loadinfo, ZPOOL_CONFIG_REWIND_INFO,
                      spa->spa_load_info);
  
                  /* Restore the initial load info */
                  fnvlist_free(spa->spa_load_info);
                  spa->spa_load_info = loadinfo;
  
                  spa_import_progress_remove(spa_guid(spa));
                  return (load_error);
          }
  }
  
  /*
   * Pool Open/Import
   *
   * The import case is identical to an open except that the configuration is sent
   * down from userland, instead of grabbed from the configuration cache.  For the
   * case of an open, the pool configuration will exist in the
   * POOL_STATE_UNINITIALIZED state.
   *
   * The stats information (gen/count/ustats) is used to gather vdev statistics at
   * the same time open the pool, without having to keep around the spa_t in some
   * ambiguous state.
   */
  static int
  spa_open_common(const char *pool, spa_t **spapp, const void *tag,
      nvlist_t *nvpolicy, nvlist_t **config)
  {
          spa_t *spa;
          spa_load_state_t state = SPA_LOAD_OPEN;
          int error;
          int locked = B_FALSE;
          int firstopen = B_FALSE;
  
          *spapp = NULL;
  
          /*
           * As disgusting as this is, we need to support recursive calls to this
           * function because dsl_dir_open() is called during spa_load(), and ends
           * up calling spa_open() again.  The real fix is to figure out how to
           * avoid dsl_dir_open() calling this in the first place.
           */
          if (MUTEX_NOT_HELD(&spa_namespace_lock)) {
                  mutex_enter(&spa_namespace_lock);
                  locked = B_TRUE;
          }
  
          if ((spa = spa_lookup(pool)) == NULL) {
                  if (locked)
                          mutex_exit(&spa_namespace_lock);
                  return (SET_ERROR(ENOENT));
          }
  
          if (spa->spa_state == POOL_STATE_UNINITIALIZED) {
                  zpool_load_policy_t policy;
  
                  firstopen = B_TRUE;
  
                  zpool_get_load_policy(nvpolicy ? nvpolicy : spa->spa_config,
                      &policy);
                  if (policy.zlp_rewind & ZPOOL_DO_REWIND)
                          state = SPA_LOAD_RECOVER;
  
                  spa_activate(spa, spa_mode_global);
  
                  if (state != SPA_LOAD_RECOVER)
                          spa->spa_last_ubsync_txg = spa->spa_load_txg = 0;
                  spa->spa_config_source = SPA_CONFIG_SRC_CACHEFILE;
  
                  zfs_dbgmsg("spa_open_common: opening %s", pool);
                  error = spa_load_best(spa, state, policy.zlp_txg,
                      policy.zlp_rewind);
  
                  if (error == EBADF) {
                          /*
                           * If vdev_validate() returns failure (indicated by
                           * EBADF), it indicates that one of the vdevs indicates
                           * that the pool has been exported or destroyed.  If
                           * this is the case, the config cache is out of sync and
                           * we should remove the pool from the namespace.
                           */
                          spa_unload(spa);
                          spa_deactivate(spa);
                          spa_write_cachefile(spa, B_TRUE, B_TRUE, B_FALSE);
                          spa_remove(spa);
                          if (locked)
                                  mutex_exit(&spa_namespace_lock);
                          return (SET_ERROR(ENOENT));
                  }
  
                  if (error) {
                          /*
                           * We can't open the pool, but we still have useful
                           * information: the state of each vdev after the
                           * attempted vdev_open().  Return this to the user.
                           */
                          if (config != NULL && spa->spa_config) {
                                  *config = fnvlist_dup(spa->spa_config);
                                  fnvlist_add_nvlist(*config,
                                      ZPOOL_CONFIG_LOAD_INFO,
                                      spa->spa_load_info);
                          }
                          spa_unload(spa);
                          spa_deactivate(spa);
                          spa->spa_last_open_failed = error;
                          if (locked)
                                  mutex_exit(&spa_namespace_lock);
                          *spapp = NULL;
                          return (error);
                  }
          }
  
          spa_open_ref(spa, tag);
  
          if (config != NULL)
                  *config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);
  
          /*
           * If we've recovered the pool, pass back any information we
           * gathered while doing the load.
           */
          if (state == SPA_LOAD_RECOVER && config != NULL) {
                  fnvlist_add_nvlist(*config, ZPOOL_CONFIG_LOAD_INFO,
                      spa->spa_load_info);
          }
  
          if (locked) {
                  spa->spa_last_open_failed = 0;
                  spa->spa_last_ubsync_txg = 0;
                  spa->spa_load_txg = 0;
                  mutex_exit(&spa_namespace_lock);
          }
  
          if (firstopen)
                  zvol_create_minors_recursive(spa_name(spa));
  
          *spapp = spa;
  
          return (0);
  }
  
  int
  spa_open_rewind(const char *name, spa_t **spapp, const void *tag,
      nvlist_t *policy, nvlist_t **config)
  {
          return (spa_open_common(name, spapp, tag, policy, config));
  }
  
  int
  spa_open(const char *name, spa_t **spapp, const void *tag)
  {
          return (spa_open_common(name, spapp, tag, NULL, NULL));
  }
  
  /*
   * Lookup the given spa_t, incrementing the inject count in the process,
   * preventing it from being exported or destroyed.
   */
  spa_t *
  spa_inject_addref(char *name)
  {
          spa_t *spa;
  
          mutex_enter(&spa_namespace_lock);
          if ((spa = spa_lookup(name)) == NULL) {
                  mutex_exit(&spa_namespace_lock);
                  return (NULL);
          }
          spa->spa_inject_ref++;
          mutex_exit(&spa_namespace_lock);
  
          return (spa);
  }
  
  void
  spa_inject_delref(spa_t *spa)
  {
          mutex_enter(&spa_namespace_lock);
          spa->spa_inject_ref--;
          mutex_exit(&spa_namespace_lock);
  }
  
  /*
   * Add spares device information to the nvlist.
   */
  static void
  spa_add_spares(spa_t *spa, nvlist_t *config)
  {
          nvlist_t **spares;
          uint_t i, nspares;
          nvlist_t *nvroot;
          uint64_t guid;
          vdev_stat_t *vs;
          uint_t vsc;
          uint64_t pool;
  
          ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
  
          if (spa->spa_spares.sav_count == 0)
                  return;
  
          nvroot = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE);
          VERIFY0(nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
              ZPOOL_CONFIG_SPARES, &spares, &nspares));
          if (nspares != 0) {
                  fnvlist_add_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
                      (const nvlist_t * const *)spares, nspares);
                  VERIFY0(nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
                      &spares, &nspares));
  
                  /*
                   * Go through and find any spares which have since been
                   * repurposed as an active spare.  If this is the case, update
                   * their status appropriately.
                   */
                  for (i = 0; i < nspares; i++) {
                          guid = fnvlist_lookup_uint64(spares[i],
                              ZPOOL_CONFIG_GUID);
                          if (spa_spare_exists(guid, &pool, NULL) &&
                              pool != 0ULL) {
                                  VERIFY0(nvlist_lookup_uint64_array(spares[i],
                                      ZPOOL_CONFIG_VDEV_STATS, (uint64_t **)&vs,
                                      &vsc));
                                  vs->vs_state = VDEV_STATE_CANT_OPEN;
                                  vs->vs_aux = VDEV_AUX_SPARED;
                          }
                  }
          }
  }
  
  /*
   * Add l2cache device information to the nvlist, including vdev stats.
   */
  static void
  spa_add_l2cache(spa_t *spa, nvlist_t *config)
  {
          nvlist_t **l2cache;
          uint_t i, j, nl2cache;
          nvlist_t *nvroot;
          uint64_t guid;
          vdev_t *vd;
          vdev_stat_t *vs;
          uint_t vsc;
  
          ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
  
          if (spa->spa_l2cache.sav_count == 0)
                  return;
  
          nvroot = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE);
          VERIFY0(nvlist_lookup_nvlist_array(spa->spa_l2cache.sav_config,
              ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache));
          if (nl2cache != 0) {
                  fnvlist_add_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
                      (const nvlist_t * const *)l2cache, nl2cache);
                  VERIFY0(nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
                      &l2cache, &nl2cache));
  
                  /*
                   * Update level 2 cache device stats.
                   */
  
                  for (i = 0; i < nl2cache; i++) {
                          guid = fnvlist_lookup_uint64(l2cache[i],
                              ZPOOL_CONFIG_GUID);
  
                          vd = NULL;
                          for (j = 0; j < spa->spa_l2cache.sav_count; j++) {
                                  if (guid ==
                                      spa->spa_l2cache.sav_vdevs[j]->vdev_guid) {
                                          vd = spa->spa_l2cache.sav_vdevs[j];
                                          break;
                                  }
                          }
                          ASSERT(vd != NULL);
  
                          VERIFY0(nvlist_lookup_uint64_array(l2cache[i],
                              ZPOOL_CONFIG_VDEV_STATS, (uint64_t **)&vs, &vsc));
                          vdev_get_stats(vd, vs);
                          vdev_config_generate_stats(vd, l2cache[i]);
  
                  }
          }
  }
  
  static void
  spa_feature_stats_from_disk(spa_t *spa, nvlist_t *features)
  {
          zap_cursor_t zc;
          zap_attribute_t za;
  
          if (spa->spa_feat_for_read_obj != 0) {
                  for (zap_cursor_init(&zc, spa->spa_meta_objset,
                      spa->spa_feat_for_read_obj);
                      zap_cursor_retrieve(&zc, &za) == 0;
                      zap_cursor_advance(&zc)) {
                          ASSERT(za.za_integer_length == sizeof (uint64_t) &&
                              za.za_num_integers == 1);
                          VERIFY0(nvlist_add_uint64(features, za.za_name,
                              za.za_first_integer));
                  }
                  zap_cursor_fini(&zc);
          }
  
          if (spa->spa_feat_for_write_obj != 0) {
                  for (zap_cursor_init(&zc, spa->spa_meta_objset,
                      spa->spa_feat_for_write_obj);
                      zap_cursor_retrieve(&zc, &za) == 0;
                      zap_cursor_advance(&zc)) {
                          ASSERT(za.za_integer_length == sizeof (uint64_t) &&
                              za.za_num_integers == 1);
                          VERIFY0(nvlist_add_uint64(features, za.za_name,
                              za.za_first_integer));
                  }
                  zap_cursor_fini(&zc);
          }
  }
  
  static void
  spa_feature_stats_from_cache(spa_t *spa, nvlist_t *features)
  {
          int i;
  
          for (i = 0; i < SPA_FEATURES; i++) {
                  zfeature_info_t feature = spa_feature_table[i];
                  uint64_t refcount;
  
                  if (feature_get_refcount(spa, &feature, &refcount) != 0)
                          continue;
  
                  VERIFY0(nvlist_add_uint64(features, feature.fi_guid, refcount));
          }
  }
  
  /*
   * Store a list of pool features and their reference counts in the
   * config.
   *
   * The first time this is called on a spa, allocate a new nvlist, fetch
   * the pool features and reference counts from disk, then save the list
   * in the spa. In subsequent calls on the same spa use the saved nvlist
   * and refresh its values from the cached reference counts.  This
   * ensures we don't block here on I/O on a suspended pool so 'zpool
   * clear' can resume the pool.
   */
  static void
  spa_add_feature_stats(spa_t *spa, nvlist_t *config)
  {
          nvlist_t *features;
  
          ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
  
          mutex_enter(&spa->spa_feat_stats_lock);
          features = spa->spa_feat_stats;
  
          if (features != NULL) {
                  spa_feature_stats_from_cache(spa, features);
          } else {
                  VERIFY0(nvlist_alloc(&features, NV_UNIQUE_NAME, KM_SLEEP));
                  spa->spa_feat_stats = features;
                  spa_feature_stats_from_disk(spa, features);
          }
  
          VERIFY0(nvlist_add_nvlist(config, ZPOOL_CONFIG_FEATURE_STATS,
              features));
  
          mutex_exit(&spa->spa_feat_stats_lock);
  }
  
  int
  spa_get_stats(const char *name, nvlist_t **config,
      char *altroot, size_t buflen)
  {
          int error;
          spa_t *spa;
  
          *config = NULL;
          error = spa_open_common(name, &spa, FTAG, NULL, config);
  
          if (spa != NULL) {
                  /*
                   * This still leaves a window of inconsistency where the spares
                   * or l2cache devices could change and the config would be
                   * self-inconsistent.
                   */
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
  
                  if (*config != NULL) {
                          uint64_t loadtimes[2];
  
                          loadtimes[0] = spa->spa_loaded_ts.tv_sec;
                          loadtimes[1] = spa->spa_loaded_ts.tv_nsec;
                          fnvlist_add_uint64_array(*config,
                              ZPOOL_CONFIG_LOADED_TIME, loadtimes, 2);
  
                          fnvlist_add_uint64(*config,
                              ZPOOL_CONFIG_ERRCOUNT,
                              spa_approx_errlog_size(spa));
  
                          if (spa_suspended(spa)) {
                                  fnvlist_add_uint64(*config,
                                      ZPOOL_CONFIG_SUSPENDED,
                                      spa->spa_failmode);
                                  fnvlist_add_uint64(*config,
                                      ZPOOL_CONFIG_SUSPENDED_REASON,
                                      spa->spa_suspended);
                          }
  
                          spa_add_spares(spa, *config);
                          spa_add_l2cache(spa, *config);
                          spa_add_feature_stats(spa, *config);
                  }
          }
  
          /*
           * We want to get the alternate root even for faulted pools, so we cheat
           * and call spa_lookup() directly.
           */
          if (altroot) {
                  if (spa == NULL) {
                          mutex_enter(&spa_namespace_lock);
                          spa = spa_lookup(name);
                          if (spa)
                                  spa_altroot(spa, altroot, buflen);
                          else
                                  altroot[0] = '\0';
                          spa = NULL;
                          mutex_exit(&spa_namespace_lock);
                  } else {
                          spa_altroot(spa, altroot, buflen);
                  }
          }
  
          if (spa != NULL) {
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
                  spa_close(spa, FTAG);
          }
  
          return (error);
  }
  
  /*
   * Validate that the auxiliary device array is well formed.  We must have an
   * array of nvlists, each which describes a valid leaf vdev.  If this is an
   * import (mode is VDEV_ALLOC_SPARE), then we allow corrupted spares to be
   * specified, as long as they are well-formed.
   */
  static int
  spa_validate_aux_devs(spa_t *spa, nvlist_t *nvroot, uint64_t crtxg, int mode,
      spa_aux_vdev_t *sav, const char *config, uint64_t version,
      vdev_labeltype_t label)
  {
          nvlist_t **dev;
          uint_t i, ndev;
          vdev_t *vd;
          int error;
  
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          /*
           * It's acceptable to have no devs specified.
           */
          if (nvlist_lookup_nvlist_array(nvroot, config, &dev, &ndev) != 0)
                  return (0);
  
          if (ndev == 0)
                  return (SET_ERROR(EINVAL));
  
          /*
           * Make sure the pool is formatted with a version that supports this
           * device type.
           */
          if (spa_version(spa) < version)
                  return (SET_ERROR(ENOTSUP));
  
          /*
           * Set the pending device list so we correctly handle device in-use
           * checking.
           */
          sav->sav_pending = dev;
          sav->sav_npending = ndev;
  
          for (i = 0; i < ndev; i++) {
                  if ((error = spa_config_parse(spa, &vd, dev[i], NULL, 0,
                      mode)) != 0)
                          goto out;
  
                  if (!vd->vdev_ops->vdev_op_leaf) {
                          vdev_free(vd);
                          error = SET_ERROR(EINVAL);
                          goto out;
                  }
  
                  vd->vdev_top = vd;
  
                  if ((error = vdev_open(vd)) == 0 &&
                      (error = vdev_label_init(vd, crtxg, label)) == 0) {
                          fnvlist_add_uint64(dev[i], ZPOOL_CONFIG_GUID,
                              vd->vdev_guid);
                  }
  
                  vdev_free(vd);
  
                  if (error &&
                      (mode != VDEV_ALLOC_SPARE && mode != VDEV_ALLOC_L2CACHE))
                          goto out;
                  else
                          error = 0;
          }
  
  out:
          sav->sav_pending = NULL;
          sav->sav_npending = 0;
          return (error);
  }
  
  static int
  spa_validate_aux(spa_t *spa, nvlist_t *nvroot, uint64_t crtxg, int mode)
  {
          int error;
  
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          if ((error = spa_validate_aux_devs(spa, nvroot, crtxg, mode,
              &spa->spa_spares, ZPOOL_CONFIG_SPARES, SPA_VERSION_SPARES,
              VDEV_LABEL_SPARE)) != 0) {
                  return (error);
          }
  
          return (spa_validate_aux_devs(spa, nvroot, crtxg, mode,
              &spa->spa_l2cache, ZPOOL_CONFIG_L2CACHE, SPA_VERSION_L2CACHE,
              VDEV_LABEL_L2CACHE));
  }
  
  static void
  spa_set_aux_vdevs(spa_aux_vdev_t *sav, nvlist_t **devs, int ndevs,
      const char *config)
  {
          int i;
  
          if (sav->sav_config != NULL) {
                  nvlist_t **olddevs;
                  uint_t oldndevs;
                  nvlist_t **newdevs;
  
                  /*
                   * Generate new dev list by concatenating with the
                   * current dev list.
                   */
                  VERIFY0(nvlist_lookup_nvlist_array(sav->sav_config, config,
                      &olddevs, &oldndevs));
  
                  newdevs = kmem_alloc(sizeof (void *) *
                      (ndevs + oldndevs), KM_SLEEP);
                  for (i = 0; i < oldndevs; i++)
                          newdevs[i] = fnvlist_dup(olddevs[i]);
                  for (i = 0; i < ndevs; i++)
                          newdevs[i + oldndevs] = fnvlist_dup(devs[i]);
  
                  fnvlist_remove(sav->sav_config, config);
  
                  fnvlist_add_nvlist_array(sav->sav_config, config,
                      (const nvlist_t * const *)newdevs, ndevs + oldndevs);
                  for (i = 0; i < oldndevs + ndevs; i++)
                          nvlist_free(newdevs[i]);
                  kmem_free(newdevs, (oldndevs + ndevs) * sizeof (void *));
          } else {
                  /*
                   * Generate a new dev list.
                   */
                  sav->sav_config = fnvlist_alloc();
                  fnvlist_add_nvlist_array(sav->sav_config, config,
                      (const nvlist_t * const *)devs, ndevs);
          }
  }
  
  /*
   * Stop and drop level 2 ARC devices
   */
  void
  spa_l2cache_drop(spa_t *spa)
  {
          vdev_t *vd;
          int i;
          spa_aux_vdev_t *sav = &spa->spa_l2cache;
  
          for (i = 0; i < sav->sav_count; i++) {
                  uint64_t pool;
  
                  vd = sav->sav_vdevs[i];
                  ASSERT(vd != NULL);
  
                  if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
                      pool != 0ULL && l2arc_vdev_present(vd))
                          l2arc_remove_vdev(vd);
          }
  }
  
  /*
   * Verify encryption parameters for spa creation. If we are encrypting, we must
   * have the encryption feature flag enabled.
   */
  static int
  spa_create_check_encryption_params(dsl_crypto_params_t *dcp,
      boolean_t has_encryption)
  {
          if (dcp->cp_crypt != ZIO_CRYPT_OFF &&
              dcp->cp_crypt != ZIO_CRYPT_INHERIT &&
              !has_encryption)
                  return (SET_ERROR(ENOTSUP));
  
          return (dmu_objset_create_crypt_check(NULL, dcp, NULL));
  }
  
  /*
   * Pool Creation
   */
  int
  spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
      nvlist_t *zplprops, dsl_crypto_params_t *dcp)
  {
          spa_t *spa;
          char *altroot = NULL;
          vdev_t *rvd;
          dsl_pool_t *dp;
          dmu_tx_t *tx;
          int error = 0;
          uint64_t txg = TXG_INITIAL;
          nvlist_t **spares, **l2cache;
          uint_t nspares, nl2cache;
          uint64_t version, obj, ndraid = 0;
          boolean_t has_features;
          boolean_t has_encryption;
          boolean_t has_allocclass;
          spa_feature_t feat;
          char *feat_name;
          char *poolname;
          nvlist_t *nvl;
  
          if (props == NULL ||
              nvlist_lookup_string(props, "tname", &poolname) != 0)
                  poolname = (char *)pool;
  
          /*
           * If this pool already exists, return failure.
           */
          mutex_enter(&spa_namespace_lock);
          if (spa_lookup(poolname) != NULL) {
                  mutex_exit(&spa_namespace_lock);
                  return (SET_ERROR(EEXIST));
          }
  
          /*
           * Allocate a new spa_t structure.
           */
          nvl = fnvlist_alloc();
          fnvlist_add_string(nvl, ZPOOL_CONFIG_POOL_NAME, pool);
          (void) nvlist_lookup_string(props,
              zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
          spa = spa_add(poolname, nvl, altroot);
          fnvlist_free(nvl);
          spa_activate(spa, spa_mode_global);
  
          if (props && (error = spa_prop_validate(spa, props))) {
                  spa_deactivate(spa);
                  spa_remove(spa);
                  mutex_exit(&spa_namespace_lock);
                  return (error);
          }
  
          /*
           * Temporary pool names should never be written to disk.
           */
          if (poolname != pool)
                  spa->spa_import_flags |= ZFS_IMPORT_TEMP_NAME;
  
          has_features = B_FALSE;
          has_encryption = B_FALSE;
          has_allocclass = B_FALSE;
          for (nvpair_t *elem = nvlist_next_nvpair(props, NULL);
              elem != NULL; elem = nvlist_next_nvpair(props, elem)) {
                  if (zpool_prop_feature(nvpair_name(elem))) {
                          has_features = B_TRUE;
  
                          feat_name = strchr(nvpair_name(elem), '@') + 1;
                          VERIFY0(zfeature_lookup_name(feat_name, &feat));
                          if (feat == SPA_FEATURE_ENCRYPTION)
                                  has_encryption = B_TRUE;
                          if (feat == SPA_FEATURE_ALLOCATION_CLASSES)
                                  has_allocclass = B_TRUE;
                  }
          }
  
          /* verify encryption params, if they were provided */
          if (dcp != NULL) {
                  error = spa_create_check_encryption_params(dcp, has_encryption);
                  if (error != 0) {
                          spa_deactivate(spa);
                          spa_remove(spa);
                          mutex_exit(&spa_namespace_lock);
                          return (error);
                  }
          }
          if (!has_allocclass && zfs_special_devs(nvroot, NULL)) {
                  spa_deactivate(spa);
                  spa_remove(spa);
                  mutex_exit(&spa_namespace_lock);
                  return (ENOTSUP);
          }
  
          if (has_features || nvlist_lookup_uint64(props,
              zpool_prop_to_name(ZPOOL_PROP_VERSION), &version) != 0) {
                  version = SPA_VERSION;
          }
          ASSERT(SPA_VERSION_IS_SUPPORTED(version));
  
          spa->spa_first_txg = txg;
          spa->spa_uberblock.ub_txg = txg - 1;
          spa->spa_uberblock.ub_version = version;
          spa->spa_ubsync = spa->spa_uberblock;
          spa->spa_load_state = SPA_LOAD_CREATE;
          spa->spa_removing_phys.sr_state = DSS_NONE;
          spa->spa_removing_phys.sr_removing_vdev = -1;
          spa->spa_removing_phys.sr_prev_indirect_vdev = -1;
          spa->spa_indirect_vdevs_loaded = B_TRUE;
  
          /*
           * Create "The Godfather" zio to hold all async IOs
           */
          spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
              KM_SLEEP);
          for (int i = 0; i < max_ncpus; i++) {
                  spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
                      ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
                      ZIO_FLAG_GODFATHER);
          }
  
          /*
           * Create the root vdev.
           */
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
  
          error = spa_config_parse(spa, &rvd, nvroot, NULL, 0, VDEV_ALLOC_ADD);
  
          ASSERT(error != 0 || rvd != NULL);
          ASSERT(error != 0 || spa->spa_root_vdev == rvd);
  
          if (error == 0 && !zfs_allocatable_devs(nvroot))
                  error = SET_ERROR(EINVAL);
  
          if (error == 0 &&
              (error = vdev_create(rvd, txg, B_FALSE)) == 0 &&
              (error = vdev_draid_spare_create(nvroot, rvd, &ndraid, 0)) == 0 &&
              (error = spa_validate_aux(spa, nvroot, txg, VDEV_ALLOC_ADD)) == 0) {
                  /*
                   * instantiate the metaslab groups (this will dirty the vdevs)
                   * we can no longer error exit past this point
                   */
                  for (int c = 0; error == 0 && c < rvd->vdev_children; c++) {
                          vdev_t *vd = rvd->vdev_child[c];
  
                          vdev_metaslab_set_size(vd);
                          vdev_expand(vd, txg);
                  }
          }
  
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          if (error != 0) {
                  spa_unload(spa);
                  spa_deactivate(spa);
                  spa_remove(spa);
                  mutex_exit(&spa_namespace_lock);
                  return (error);
          }
  
          /*
           * Get the list of spares, if specified.
           */
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
              &spares, &nspares) == 0) {
                  spa->spa_spares.sav_config = fnvlist_alloc();
                  fnvlist_add_nvlist_array(spa->spa_spares.sav_config,
                      ZPOOL_CONFIG_SPARES, (const nvlist_t * const *)spares,
                      nspares);
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_spares(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  spa->spa_spares.sav_sync = B_TRUE;
          }
  
          /*
           * Get the list of level 2 cache devices, if specified.
           */
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
              &l2cache, &nl2cache) == 0) {
                  VERIFY0(nvlist_alloc(&spa->spa_l2cache.sav_config,
                      NV_UNIQUE_NAME, KM_SLEEP));
                  fnvlist_add_nvlist_array(spa->spa_l2cache.sav_config,
                      ZPOOL_CONFIG_L2CACHE, (const nvlist_t * const *)l2cache,
                      nl2cache);
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_l2cache(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  spa->spa_l2cache.sav_sync = B_TRUE;
          }
  
          spa->spa_is_initializing = B_TRUE;
          spa->spa_dsl_pool = dp = dsl_pool_create(spa, zplprops, dcp, txg);
          spa->spa_is_initializing = B_FALSE;
  
          /*
           * Create DDTs (dedup tables).
           */
          ddt_create(spa);
  
          spa_update_dspace(spa);
  
          tx = dmu_tx_create_assigned(dp, txg);
  
          /*
           * Create the pool's history object.
           */
          if (version >= SPA_VERSION_ZPOOL_HISTORY && !spa->spa_history)
                  spa_history_create_obj(spa, tx);
  
          spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_CREATE);
          spa_history_log_version(spa, "create", tx);
  
          /*
           * Create the pool config object.
           */
          spa->spa_config_object = dmu_object_alloc(spa->spa_meta_objset,
              DMU_OT_PACKED_NVLIST, SPA_CONFIG_BLOCKSIZE,
              DMU_OT_PACKED_NVLIST_SIZE, sizeof (uint64_t), tx);
  
          if (zap_add(spa->spa_meta_objset,
              DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CONFIG,
              sizeof (uint64_t), 1, &spa->spa_config_object, tx) != 0) {
                  cmn_err(CE_PANIC, "failed to add pool config");
          }
  
          if (zap_add(spa->spa_meta_objset,
              DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CREATION_VERSION,
              sizeof (uint64_t), 1, &version, tx) != 0) {
                  cmn_err(CE_PANIC, "failed to add pool version");
          }
  
          /* Newly created pools with the right version are always deflated. */
          if (version >= SPA_VERSION_RAIDZ_DEFLATE) {
                  spa->spa_deflate = TRUE;
                  if (zap_add(spa->spa_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_DEFLATE,
                      sizeof (uint64_t), 1, &spa->spa_deflate, tx) != 0) {
                          cmn_err(CE_PANIC, "failed to add deflate");
                  }
          }
  
          /*
           * Create the deferred-free bpobj.  Turn off compression
           * because sync-to-convergence takes longer if the blocksize
           * keeps changing.
           */
          obj = bpobj_alloc(spa->spa_meta_objset, 1 << 14, tx);
          dmu_object_set_compress(spa->spa_meta_objset, obj,
              ZIO_COMPRESS_OFF, tx);
          if (zap_add(spa->spa_meta_objset,
              DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_SYNC_BPOBJ,
              sizeof (uint64_t), 1, &obj, tx) != 0) {
                  cmn_err(CE_PANIC, "failed to add bpobj");
          }
          VERIFY3U(0, ==, bpobj_open(&spa->spa_deferred_bpobj,
              spa->spa_meta_objset, obj));
  
          /*
           * Generate some random noise for salted checksums to operate on.
           */
          (void) random_get_pseudo_bytes(spa->spa_cksum_salt.zcs_bytes,
              sizeof (spa->spa_cksum_salt.zcs_bytes));
  
          /*
           * Set pool properties.
           */
          spa->spa_bootfs = zpool_prop_default_numeric(ZPOOL_PROP_BOOTFS);
          spa->spa_delegation = zpool_prop_default_numeric(ZPOOL_PROP_DELEGATION);
          spa->spa_failmode = zpool_prop_default_numeric(ZPOOL_PROP_FAILUREMODE);
          spa->spa_autoexpand = zpool_prop_default_numeric(ZPOOL_PROP_AUTOEXPAND);
          spa->spa_multihost = zpool_prop_default_numeric(ZPOOL_PROP_MULTIHOST);
          spa->spa_autotrim = zpool_prop_default_numeric(ZPOOL_PROP_AUTOTRIM);
  
          if (props != NULL) {
                  spa_configfile_set(spa, props, B_FALSE);
                  spa_sync_props(props, tx);
          }
  
          for (int i = 0; i < ndraid; i++)
                  spa_feature_incr(spa, SPA_FEATURE_DRAID, tx);
  
          dmu_tx_commit(tx);
  
          spa->spa_sync_on = B_TRUE;
          txg_sync_start(dp);
          mmp_thread_start(spa);
          txg_wait_synced(dp, txg);
  
          spa_spawn_aux_threads(spa);
  
          spa_write_cachefile(spa, B_FALSE, B_TRUE, B_TRUE);
  
          /*
           * Don't count references from objsets that are already closed
           * and are making their way through the eviction process.
           */
          spa_evicting_os_wait(spa);
          spa->spa_minref = zfs_refcount_count(&spa->spa_refcount);
          spa->spa_load_state = SPA_LOAD_NONE;
  
          spa_import_os(spa);
  
          mutex_exit(&spa_namespace_lock);
  
          return (0);
  }
  
  /*
   * Import a non-root pool into the system.
   */
  int
  spa_import(char *pool, nvlist_t *config, nvlist_t *props, uint64_t flags)
  {
          spa_t *spa;
          char *altroot = NULL;
          spa_load_state_t state = SPA_LOAD_IMPORT;
          zpool_load_policy_t policy;
          spa_mode_t mode = spa_mode_global;
          uint64_t readonly = B_FALSE;
          int error;
          nvlist_t *nvroot;
          nvlist_t **spares, **l2cache;
          uint_t nspares, nl2cache;
  
          /*
           * If a pool with this name exists, return failure.
           */
          mutex_enter(&spa_namespace_lock);
          if (spa_lookup(pool) != NULL) {
                  mutex_exit(&spa_namespace_lock);
                  return (SET_ERROR(EEXIST));
          }
  
          /*
           * Create and initialize the spa structure.
           */
          (void) nvlist_lookup_string(props,
              zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
          (void) nvlist_lookup_uint64(props,
              zpool_prop_to_name(ZPOOL_PROP_READONLY), &readonly);
          if (readonly)
                  mode = SPA_MODE_READ;
          spa = spa_add(pool, config, altroot);
          spa->spa_import_flags = flags;
  
          /*
           * Verbatim import - Take a pool and insert it into the namespace
           * as if it had been loaded at boot.
           */
          if (spa->spa_import_flags & ZFS_IMPORT_VERBATIM) {
                  if (props != NULL)
                          spa_configfile_set(spa, props, B_FALSE);
  
                  spa_write_cachefile(spa, B_FALSE, B_TRUE, B_FALSE);
                  spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_IMPORT);
                  zfs_dbgmsg("spa_import: verbatim import of %s", pool);
                  mutex_exit(&spa_namespace_lock);
                  return (0);
          }
  
          spa_activate(spa, mode);
  
          /*
           * Don't start async tasks until we know everything is healthy.
           */
          spa_async_suspend(spa);
  
          zpool_get_load_policy(config, &policy);
          if (policy.zlp_rewind & ZPOOL_DO_REWIND)
                  state = SPA_LOAD_RECOVER;
  
          spa->spa_config_source = SPA_CONFIG_SRC_TRYIMPORT;
  
          if (state != SPA_LOAD_RECOVER) {
                  spa->spa_last_ubsync_txg = spa->spa_load_txg = 0;
                  zfs_dbgmsg("spa_import: importing %s", pool);
          } else {
                  zfs_dbgmsg("spa_import: importing %s, max_txg=%lld "
                      "(RECOVERY MODE)", pool, (longlong_t)policy.zlp_txg);
          }
          error = spa_load_best(spa, state, policy.zlp_txg, policy.zlp_rewind);
  
          /*
           * Propagate anything learned while loading the pool and pass it
           * back to caller (i.e. rewind info, missing devices, etc).
           */
          fnvlist_add_nvlist(config, ZPOOL_CONFIG_LOAD_INFO, spa->spa_load_info);
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          /*
           * Toss any existing sparelist, as it doesn't have any validity
           * anymore, and conflicts with spa_has_spare().
           */
          if (spa->spa_spares.sav_config) {
                  nvlist_free(spa->spa_spares.sav_config);
                  spa->spa_spares.sav_config = NULL;
                  spa_load_spares(spa);
          }
          if (spa->spa_l2cache.sav_config) {
                  nvlist_free(spa->spa_l2cache.sav_config);
                  spa->spa_l2cache.sav_config = NULL;
                  spa_load_l2cache(spa);
          }
  
          nvroot = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE);
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          if (props != NULL)
                  spa_configfile_set(spa, props, B_FALSE);
  
          if (error != 0 || (props && spa_writeable(spa) &&
              (error = spa_prop_set(spa, props)))) {
                  spa_unload(spa);
                  spa_deactivate(spa);
                  spa_remove(spa);
                  mutex_exit(&spa_namespace_lock);
                  return (error);
          }
  
          spa_async_resume(spa);
  
          /*
           * Override any spares and level 2 cache devices as specified by
           * the user, as these may have correct device names/devids, etc.
           */
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
              &spares, &nspares) == 0) {
                  if (spa->spa_spares.sav_config)
                          fnvlist_remove(spa->spa_spares.sav_config,
                              ZPOOL_CONFIG_SPARES);
                  else
                          spa->spa_spares.sav_config = fnvlist_alloc();
                  fnvlist_add_nvlist_array(spa->spa_spares.sav_config,
                      ZPOOL_CONFIG_SPARES, (const nvlist_t * const *)spares,
                      nspares);
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_spares(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  spa->spa_spares.sav_sync = B_TRUE;
          }
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
              &l2cache, &nl2cache) == 0) {
                  if (spa->spa_l2cache.sav_config)
                          fnvlist_remove(spa->spa_l2cache.sav_config,
                              ZPOOL_CONFIG_L2CACHE);
                  else
                          spa->spa_l2cache.sav_config = fnvlist_alloc();
                  fnvlist_add_nvlist_array(spa->spa_l2cache.sav_config,
                      ZPOOL_CONFIG_L2CACHE, (const nvlist_t * const *)l2cache,
                      nl2cache);
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                  spa_load_l2cache(spa);
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  spa->spa_l2cache.sav_sync = B_TRUE;
          }
  
          /*
           * Check for any removed devices.
           */
          if (spa->spa_autoreplace) {
                  spa_aux_check_removed(&spa->spa_spares);
                  spa_aux_check_removed(&spa->spa_l2cache);
          }
  
          if (spa_writeable(spa)) {
                  /*
                   * Update the config cache to include the newly-imported pool.
                   */
                  spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
          }
  
          /*
           * It's possible that the pool was expanded while it was exported.
           * We kick off an async task to handle this for us.
           */
          spa_async_request(spa, SPA_ASYNC_AUTOEXPAND);
  
          spa_history_log_version(spa, "import", NULL);
  
          spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_IMPORT);
  
          mutex_exit(&spa_namespace_lock);
  
          zvol_create_minors_recursive(pool);
  
          spa_import_os(spa);
  
          return (0);
  }
  
  nvlist_t *
  spa_tryimport(nvlist_t *tryconfig)
  {
          nvlist_t *config = NULL;
          char *poolname, *cachefile;
          spa_t *spa;
          uint64_t state;
          int error;
          zpool_load_policy_t policy;
  
          if (nvlist_lookup_string(tryconfig, ZPOOL_CONFIG_POOL_NAME, &poolname))
                  return (NULL);
  
          if (nvlist_lookup_uint64(tryconfig, ZPOOL_CONFIG_POOL_STATE, &state))
                  return (NULL);
  
          /*
           * Create and initialize the spa structure.
           */
          mutex_enter(&spa_namespace_lock);
          spa = spa_add(TRYIMPORT_NAME, tryconfig, NULL);
          spa_activate(spa, SPA_MODE_READ);
  
          /*
           * Rewind pool if a max txg was provided.
           */
          zpool_get_load_policy(spa->spa_config, &policy);
          if (policy.zlp_txg != UINT64_MAX) {
                  spa->spa_load_max_txg = policy.zlp_txg;
                  spa->spa_extreme_rewind = B_TRUE;
                  zfs_dbgmsg("spa_tryimport: importing %s, max_txg=%lld",
                      poolname, (longlong_t)policy.zlp_txg);
          } else {
                  zfs_dbgmsg("spa_tryimport: importing %s", poolname);
          }
  
          if (nvlist_lookup_string(tryconfig, ZPOOL_CONFIG_CACHEFILE, &cachefile)
              == 0) {
                  zfs_dbgmsg("spa_tryimport: using cachefile '%s'", cachefile);
                  spa->spa_config_source = SPA_CONFIG_SRC_CACHEFILE;
          } else {
                  spa->spa_config_source = SPA_CONFIG_SRC_SCAN;
          }
  
          error = spa_load(spa, SPA_LOAD_TRYIMPORT, SPA_IMPORT_EXISTING);
  
          /*
           * If 'tryconfig' was at least parsable, return the current config.
           */
          if (spa->spa_root_vdev != NULL) {
                  config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);
                  fnvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME, poolname);
                  fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE, state);
                  fnvlist_add_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
                      spa->spa_uberblock.ub_timestamp);
                  fnvlist_add_nvlist(config, ZPOOL_CONFIG_LOAD_INFO,
                      spa->spa_load_info);
                  fnvlist_add_uint64(config, ZPOOL_CONFIG_ERRATA,
                      spa->spa_errata);
  
                  /*
                   * If the bootfs property exists on this pool then we
                   * copy it out so that external consumers can tell which
                   * pools are bootable.
                   */
                  if ((!error || error == EEXIST) && spa->spa_bootfs) {
                          char *tmpname = kmem_alloc(MAXPATHLEN, KM_SLEEP);
  
                          /*
                           * We have to play games with the name since the
                           * pool was opened as TRYIMPORT_NAME.
                           */
                          if (dsl_dsobj_to_dsname(spa_name(spa),
                              spa->spa_bootfs, tmpname) == 0) {
                                  char *cp;
                                  char *dsname;
  
                                  dsname = kmem_alloc(MAXPATHLEN, KM_SLEEP);
  
                                  cp = strchr(tmpname, '/');
                                  if (cp == NULL) {
                                          (void) strlcpy(dsname, tmpname,
                                              MAXPATHLEN);
                                  } else {
                                          (void) snprintf(dsname, MAXPATHLEN,
                                              "%s/%s", poolname, ++cp);
                                  }
                                  fnvlist_add_string(config, ZPOOL_CONFIG_BOOTFS,
                                      dsname);
                                  kmem_free(dsname, MAXPATHLEN);
                          }
                          kmem_free(tmpname, MAXPATHLEN);
                  }
  
                  /*
                   * Add the list of hot spares and level 2 cache devices.
                   */
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  spa_add_spares(spa, config);
                  spa_add_l2cache(spa, config);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
          }
  
          spa_unload(spa);
          spa_deactivate(spa);
          spa_remove(spa);
          mutex_exit(&spa_namespace_lock);
  
          return (config);
  }
  
  /*
   * Pool export/destroy
   *
   * The act of destroying or exporting a pool is very simple.  We make sure there
   * is no more pending I/O and any references to the pool are gone.  Then, we
   * update the pool state and sync all the labels to disk, removing the
   * configuration from the cache afterwards. If the 'hardforce' flag is set, then
   * we don't sync the labels or remove the configuration cache.
   */
  static int
  spa_export_common(const char *pool, int new_state, nvlist_t **oldconfig,
      boolean_t force, boolean_t hardforce)
  {
          int error;
          spa_t *spa;
  
          if (oldconfig)
                  *oldconfig = NULL;
  
          if (!(spa_mode_global & SPA_MODE_WRITE))
                  return (SET_ERROR(EROFS));
  
          mutex_enter(&spa_namespace_lock);
          if ((spa = spa_lookup(pool)) == NULL) {
                  mutex_exit(&spa_namespace_lock);
                  return (SET_ERROR(ENOENT));
          }
  
          if (spa->spa_is_exporting) {
                  /* the pool is being exported by another thread */
                  mutex_exit(&spa_namespace_lock);
                  return (SET_ERROR(ZFS_ERR_EXPORT_IN_PROGRESS));
          }
          spa->spa_is_exporting = B_TRUE;
  
          /*
           * Put a hold on the pool, drop the namespace lock, stop async tasks,
           * reacquire the namespace lock, and see if we can export.
           */
          spa_open_ref(spa, FTAG);
          mutex_exit(&spa_namespace_lock);
          spa_async_suspend(spa);
          if (spa->spa_zvol_taskq) {
                  zvol_remove_minors(spa, spa_name(spa), B_TRUE);
                  taskq_wait(spa->spa_zvol_taskq);
          }
          mutex_enter(&spa_namespace_lock);
          spa_close(spa, FTAG);
  
          if (spa->spa_state == POOL_STATE_UNINITIALIZED)
                  goto export_spa;
          /*
           * The pool will be in core if it's openable, in which case we can
           * modify its state.  Objsets may be open only because they're dirty,
           * so we have to force it to sync before checking spa_refcnt.
           */
          if (spa->spa_sync_on) {
                  txg_wait_synced(spa->spa_dsl_pool, 0);
                  spa_evicting_os_wait(spa);
          }
  
          /*
           * A pool cannot be exported or destroyed if there are active
           * references.  If we are resetting a pool, allow references by
           * fault injection handlers.
           */
          if (!spa_refcount_zero(spa) || (spa->spa_inject_ref != 0)) {
                  error = SET_ERROR(EBUSY);
                  goto fail;
          }
  
          if (spa->spa_sync_on) {
                  vdev_t *rvd = spa->spa_root_vdev;
                  /*
                   * A pool cannot be exported if it has an active shared spare.
                   * This is to prevent other pools stealing the active spare
                   * from an exported pool. At user's own will, such pool can
                   * be forcedly exported.
                   */
                  if (!force && new_state == POOL_STATE_EXPORTED &&
                      spa_has_active_shared_spare(spa)) {
                          error = SET_ERROR(EXDEV);
                          goto fail;
                  }
  
                  /*
                   * We're about to export or destroy this pool. Make sure
                   * we stop all initialization and trim activity here before
                   * we set the spa_final_txg. This will ensure that all
                   * dirty data resulting from the initialization is
                   * committed to disk before we unload the pool.
                   */
                  vdev_initialize_stop_all(rvd, VDEV_INITIALIZE_ACTIVE);
                  vdev_trim_stop_all(rvd, VDEV_TRIM_ACTIVE);
                  vdev_autotrim_stop_all(spa);
                  vdev_rebuild_stop_all(spa);
  
                  /*
                   * We want this to be reflected on every label,
                   * so mark them all dirty.  spa_unload() will do the
                   * final sync that pushes these changes out.
                   */
                  if (new_state != POOL_STATE_UNINITIALIZED && !hardforce) {
                          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                          spa->spa_state = new_state;
                          vdev_config_dirty(rvd);
                          spa_config_exit(spa, SCL_ALL, FTAG);
                  }
  
                  /*
                   * If the log space map feature is enabled and the pool is
                   * getting exported (but not destroyed), we want to spend some
                   * time flushing as many metaslabs as we can in an attempt to
                   * destroy log space maps and save import time. This has to be
                   * done before we set the spa_final_txg, otherwise
                   * spa_sync() -> spa_flush_metaslabs() may dirty the final TXGs.
                   * spa_should_flush_logs_on_unload() should be called after
                   * spa_state has been set to the new_state.
                   */
                  if (spa_should_flush_logs_on_unload(spa))
                          spa_unload_log_sm_flush_all(spa);
  
                  if (new_state != POOL_STATE_UNINITIALIZED && !hardforce) {
                          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                          spa->spa_final_txg = spa_last_synced_txg(spa) +
                              TXG_DEFER_SIZE + 1;
                          spa_config_exit(spa, SCL_ALL, FTAG);
                  }
          }
  
  export_spa:
          spa_export_os(spa);
  
          if (new_state == POOL_STATE_DESTROYED)
                  spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_DESTROY);
          else if (new_state == POOL_STATE_EXPORTED)
                  spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_EXPORT);
  
          if (spa->spa_state != POOL_STATE_UNINITIALIZED) {
                  spa_unload(spa);
                  spa_deactivate(spa);
          }
  
          if (oldconfig && spa->spa_config)
                  *oldconfig = fnvlist_dup(spa->spa_config);
  
          if (new_state != POOL_STATE_UNINITIALIZED) {
                  if (!hardforce)
                          spa_write_cachefile(spa, B_TRUE, B_TRUE, B_FALSE);
                  spa_remove(spa);
          } else {
                  /*
                   * If spa_remove() is not called for this spa_t and
                   * there is any possibility that it can be reused,
                   * we make sure to reset the exporting flag.
                   */
                  spa->spa_is_exporting = B_FALSE;
          }
  
          mutex_exit(&spa_namespace_lock);
          return (0);
  
  fail:
          spa->spa_is_exporting = B_FALSE;
          spa_async_resume(spa);
          mutex_exit(&spa_namespace_lock);
          return (error);
  }
  
  /*
   * Destroy a storage pool.
   */
  int
  spa_destroy(const char *pool)
  {
          return (spa_export_common(pool, POOL_STATE_DESTROYED, NULL,
              B_FALSE, B_FALSE));
  }
  
  /*
   * Export a storage pool.
   */
  int
  spa_export(const char *pool, nvlist_t **oldconfig, boolean_t force,
      boolean_t hardforce)
  {
          return (spa_export_common(pool, POOL_STATE_EXPORTED, oldconfig,
              force, hardforce));
  }
  
  /*
   * Similar to spa_export(), this unloads the spa_t without actually removing it
   * from the namespace in any way.
   */
  int
  spa_reset(const char *pool)
  {
          return (spa_export_common(pool, POOL_STATE_UNINITIALIZED, NULL,
              B_FALSE, B_FALSE));
  }
  
  /*
   * ==========================================================================
   * Device manipulation
   * ==========================================================================
   */
  
  /*
   * This is called as a synctask to increment the draid feature flag
   */
  static void
  spa_draid_feature_incr(void *arg, dmu_tx_t *tx)
  {
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
          int draid = (int)(uintptr_t)arg;
  
          for (int c = 0; c < draid; c++)
                  spa_feature_incr(spa, SPA_FEATURE_DRAID, tx);
  }
  
  /*
   * Add a device to a storage pool.
   */
  int
  spa_vdev_add(spa_t *spa, nvlist_t *nvroot)
  {
          uint64_t txg, ndraid = 0;
          int error;
          vdev_t *rvd = spa->spa_root_vdev;
          vdev_t *vd, *tvd;
          nvlist_t **spares, **l2cache;
          uint_t nspares, nl2cache;
  
          ASSERT(spa_writeable(spa));
  
          txg = spa_vdev_enter(spa);
  
          if ((error = spa_config_parse(spa, &vd, nvroot, NULL, 0,
              VDEV_ALLOC_ADD)) != 0)
                  return (spa_vdev_exit(spa, NULL, txg, error));
  
          spa->spa_pending_vdev = vd;     /* spa_vdev_exit() will clear this */
  
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES, &spares,
              &nspares) != 0)
                  nspares = 0;
  
          if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE, &l2cache,
              &nl2cache) != 0)
                  nl2cache = 0;
  
          if (vd->vdev_children == 0 && nspares == 0 && nl2cache == 0)
                  return (spa_vdev_exit(spa, vd, txg, EINVAL));
  
          if (vd->vdev_children != 0 &&
              (error = vdev_create(vd, txg, B_FALSE)) != 0) {
                  return (spa_vdev_exit(spa, vd, txg, error));
          }
  
          /*
           * The virtual dRAID spares must be added after vdev tree is created
           * and the vdev guids are generated.  The guid of their associated
           * dRAID is stored in the config and used when opening the spare.
           */
          if ((error = vdev_draid_spare_create(nvroot, vd, &ndraid,
              rvd->vdev_children)) == 0) {
                  if (ndraid > 0 && nvlist_lookup_nvlist_array(nvroot,
                      ZPOOL_CONFIG_SPARES, &spares, &nspares) != 0)
                          nspares = 0;
          } else {
                  return (spa_vdev_exit(spa, vd, txg, error));
          }
  
          /*
           * We must validate the spares and l2cache devices after checking the
           * children.  Otherwise, vdev_inuse() will blindly overwrite the spare.
           */
          if ((error = spa_validate_aux(spa, nvroot, txg, VDEV_ALLOC_ADD)) != 0)
                  return (spa_vdev_exit(spa, vd, txg, error));
  
          /*
           * If we are in the middle of a device removal, we can only add
           * devices which match the existing devices in the pool.
           * If we are in the middle of a removal, or have some indirect
           * vdevs, we can not add raidz or dRAID top levels.
           */
          if (spa->spa_vdev_removal != NULL ||
              spa->spa_removing_phys.sr_prev_indirect_vdev != -1) {
                  for (int c = 0; c < vd->vdev_children; c++) {
                          tvd = vd->vdev_child[c];
                          if (spa->spa_vdev_removal != NULL &&
                              tvd->vdev_ashift != spa->spa_max_ashift) {
                                  return (spa_vdev_exit(spa, vd, txg, EINVAL));
                          }
                          /* Fail if top level vdev is raidz or a dRAID */
                          if (vdev_get_nparity(tvd) != 0)
                                  return (spa_vdev_exit(spa, vd, txg, EINVAL));
  
                          /*
                           * Need the top level mirror to be
                           * a mirror of leaf vdevs only
                           */
                          if (tvd->vdev_ops == &vdev_mirror_ops) {
                                  for (uint64_t cid = 0;
                                      cid < tvd->vdev_children; cid++) {
                                          vdev_t *cvd = tvd->vdev_child[cid];
                                          if (!cvd->vdev_ops->vdev_op_leaf) {
                                                  return (spa_vdev_exit(spa, vd,
                                                      txg, EINVAL));
                                          }
                                  }
                          }
                  }
          }
  
          for (int c = 0; c < vd->vdev_children; c++) {
                  tvd = vd->vdev_child[c];
                  vdev_remove_child(vd, tvd);
                  tvd->vdev_id = rvd->vdev_children;
                  vdev_add_child(rvd, tvd);
                  vdev_config_dirty(tvd);
          }
  
          if (nspares != 0) {
                  spa_set_aux_vdevs(&spa->spa_spares, spares, nspares,
                      ZPOOL_CONFIG_SPARES);
                  spa_load_spares(spa);
                  spa->spa_spares.sav_sync = B_TRUE;
          }
  
          if (nl2cache != 0) {
                  spa_set_aux_vdevs(&spa->spa_l2cache, l2cache, nl2cache,
                      ZPOOL_CONFIG_L2CACHE);
                  spa_load_l2cache(spa);
                  spa->spa_l2cache.sav_sync = B_TRUE;
          }
  
          /*
           * We can't increment a feature while holding spa_vdev so we
           * have to do it in a synctask.
           */
          if (ndraid != 0) {
                  dmu_tx_t *tx;
  
                  tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);
                  dsl_sync_task_nowait(spa->spa_dsl_pool, spa_draid_feature_incr,
                      (void *)(uintptr_t)ndraid, tx);
                  dmu_tx_commit(tx);
          }
  
          /*
           * We have to be careful when adding new vdevs to an existing pool.
           * If other threads start allocating from these vdevs before we
           * sync the config cache, and we lose power, then upon reboot we may
           * fail to open the pool because there are DVAs that the config cache
           * can't translate.  Therefore, we first add the vdevs without
           * initializing metaslabs; sync the config cache (via spa_vdev_exit());
           * and then let spa_config_update() initialize the new metaslabs.
           *
           * spa_load() checks for added-but-not-initialized vdevs, so that
           * if we lose power at any point in this sequence, the remaining
           * steps will be completed the next time we load the pool.
           */
          (void) spa_vdev_exit(spa, vd, txg, 0);
  
          mutex_enter(&spa_namespace_lock);
          spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
          spa_event_notify(spa, NULL, NULL, ESC_ZFS_VDEV_ADD);
          mutex_exit(&spa_namespace_lock);
  
          return (0);
  }
  
  /*
   * Attach a device to a mirror.  The arguments are the path to any device
   * in the mirror, and the nvroot for the new device.  If the path specifies
   * a device that is not mirrored, we automatically insert the mirror vdev.
   *
   * If 'replacing' is specified, the new device is intended to replace the
   * existing device; in this case the two devices are made into their own
   * mirror using the 'replacing' vdev, which is functionally identical to
   * the mirror vdev (it actually reuses all the same ops) but has a few
   * extra rules: you can't attach to it after it's been created, and upon
   * completion of resilvering, the first disk (the one being replaced)
   * is automatically detached.
   *
   * If 'rebuild' is specified, then sequential reconstruction (a.ka. rebuild)
   * should be performed instead of traditional healing reconstruction.  From
   * an administrators perspective these are both resilver operations.
   */
  int
  spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing,
      int rebuild)
  {
          uint64_t txg, dtl_max_txg;
          vdev_t *rvd = spa->spa_root_vdev;
          vdev_t *oldvd, *newvd, *newrootvd, *pvd, *tvd;
          vdev_ops_t *pvops;
          char *oldvdpath, *newvdpath;
          int newvd_isspare;
          int error;
  
          ASSERT(spa_writeable(spa));
  
          txg = spa_vdev_enter(spa);
  
          oldvd = spa_lookup_by_guid(spa, guid, B_FALSE);
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
                  error = (spa_has_checkpoint(spa)) ?
                      ZFS_ERR_CHECKPOINT_EXISTS : ZFS_ERR_DISCARDING_CHECKPOINT;
                  return (spa_vdev_exit(spa, NULL, txg, error));
          }
  
          if (rebuild) {
                  if (!spa_feature_is_enabled(spa, SPA_FEATURE_DEVICE_REBUILD))
                          return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));
  
                  if (dsl_scan_resilvering(spa_get_dsl(spa)))
                          return (spa_vdev_exit(spa, NULL, txg,
                              ZFS_ERR_RESILVER_IN_PROGRESS));
          } else {
                  if (vdev_rebuild_active(rvd))
                          return (spa_vdev_exit(spa, NULL, txg,
                              ZFS_ERR_REBUILD_IN_PROGRESS));
          }
  
          if (spa->spa_vdev_removal != NULL)
                  return (spa_vdev_exit(spa, NULL, txg, EBUSY));
  
          if (oldvd == NULL)
                  return (spa_vdev_exit(spa, NULL, txg, ENODEV));
  
          if (!oldvd->vdev_ops->vdev_op_leaf)
                  return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));
  
          pvd = oldvd->vdev_parent;
  
          if (spa_config_parse(spa, &newrootvd, nvroot, NULL, 0,
              VDEV_ALLOC_ATTACH) != 0)
                  return (spa_vdev_exit(spa, NULL, txg, EINVAL));
  
          if (newrootvd->vdev_children != 1)
                  return (spa_vdev_exit(spa, newrootvd, txg, EINVAL));
  
          newvd = newrootvd->vdev_child[0];
  
          if (!newvd->vdev_ops->vdev_op_leaf)
                  return (spa_vdev_exit(spa, newrootvd, txg, EINVAL));
  
          if ((error = vdev_create(newrootvd, txg, replacing)) != 0)
                  return (spa_vdev_exit(spa, newrootvd, txg, error));
  
          /*
           * log, dedup and special vdevs should not be replaced by spares.
           */
          if ((oldvd->vdev_top->vdev_alloc_bias != VDEV_BIAS_NONE ||
              oldvd->vdev_top->vdev_islog) && newvd->vdev_isspare) {
                  return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
          }
  
          /*
           * A dRAID spare can only replace a child of its parent dRAID vdev.
           */
          if (newvd->vdev_ops == &vdev_draid_spare_ops &&
              oldvd->vdev_top != vdev_draid_spare_get_parent(newvd)) {
                  return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
          }
  
          if (rebuild) {
                  /*
                   * For rebuilds, the top vdev must support reconstruction
                   * using only space maps.  This means the only allowable
                   * vdevs types are the root vdev, a mirror, or dRAID.
                   */
                  tvd = pvd;
                  if (pvd->vdev_top != NULL)
                          tvd = pvd->vdev_top;
  
                  if (tvd->vdev_ops != &vdev_mirror_ops &&
                      tvd->vdev_ops != &vdev_root_ops &&
                      tvd->vdev_ops != &vdev_draid_ops) {
                          return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
                  }
          }
  
          if (!replacing) {
                  /*
                   * For attach, the only allowable parent is a mirror or the root
                   * vdev.
                   */
                  if (pvd->vdev_ops != &vdev_mirror_ops &&
                      pvd->vdev_ops != &vdev_root_ops)
                          return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
  
                  pvops = &vdev_mirror_ops;
          } else {
                  /*
                   * Active hot spares can only be replaced by inactive hot
                   * spares.
                   */
                  if (pvd->vdev_ops == &vdev_spare_ops &&
                      oldvd->vdev_isspare &&
                      !spa_has_spare(spa, newvd->vdev_guid))
                          return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
  
                  /*
                   * If the source is a hot spare, and the parent isn't already a
                   * spare, then we want to create a new hot spare.  Otherwise, we
                   * want to create a replacing vdev.  The user is not allowed to
                   * attach to a spared vdev child unless the 'isspare' state is
                   * the same (spare replaces spare, non-spare replaces
                   * non-spare).
                   */
                  if (pvd->vdev_ops == &vdev_replacing_ops &&
                      spa_version(spa) < SPA_VERSION_MULTI_REPLACE) {
                          return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
                  } else if (pvd->vdev_ops == &vdev_spare_ops &&
                      newvd->vdev_isspare != oldvd->vdev_isspare) {
                          return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
                  }
  
                  if (newvd->vdev_isspare)
                          pvops = &vdev_spare_ops;
                  else
                          pvops = &vdev_replacing_ops;
          }
  
          /*
           * Make sure the new device is big enough.
           */
          if (newvd->vdev_asize < vdev_get_min_asize(oldvd))
                  return (spa_vdev_exit(spa, newrootvd, txg, EOVERFLOW));
  
          /*
           * The new device cannot have a higher alignment requirement
           * than the top-level vdev.
           */
          if (newvd->vdev_ashift > oldvd->vdev_top->vdev_ashift)
                  return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
  
          /*
           * If this is an in-place replacement, update oldvd's path and devid
           * to make it distinguishable from newvd, and unopenable from now on.
           */
          if (strcmp(oldvd->vdev_path, newvd->vdev_path) == 0) {
                  spa_strfree(oldvd->vdev_path);
                  oldvd->vdev_path = kmem_alloc(strlen(newvd->vdev_path) + 5,
                      KM_SLEEP);
                  (void) snprintf(oldvd->vdev_path, strlen(newvd->vdev_path) + 5,
                      "%s/%s", newvd->vdev_path, "old");
                  if (oldvd->vdev_devid != NULL) {
                          spa_strfree(oldvd->vdev_devid);
                          oldvd->vdev_devid = NULL;
                  }
          }
  
          /*
           * If the parent is not a mirror, or if we're replacing, insert the new
           * mirror/replacing/spare vdev above oldvd.
           */
          if (pvd->vdev_ops != pvops)
                  pvd = vdev_add_parent(oldvd, pvops);
  
          ASSERT(pvd->vdev_top->vdev_parent == rvd);
          ASSERT(pvd->vdev_ops == pvops);
          ASSERT(oldvd->vdev_parent == pvd);
  
          /*
           * Extract the new device from its root and add it to pvd.
           */
          vdev_remove_child(newrootvd, newvd);
          newvd->vdev_id = pvd->vdev_children;
          newvd->vdev_crtxg = oldvd->vdev_crtxg;
          vdev_add_child(pvd, newvd);
  
          /*
           * Reevaluate the parent vdev state.
           */
          vdev_propagate_state(pvd);
  
          tvd = newvd->vdev_top;
          ASSERT(pvd->vdev_top == tvd);
          ASSERT(tvd->vdev_parent == rvd);
  
          vdev_config_dirty(tvd);
  
          /*
           * Set newvd's DTL to [TXG_INITIAL, dtl_max_txg) so that we account
           * for any dmu_sync-ed blocks.  It will propagate upward when
           * spa_vdev_exit() calls vdev_dtl_reassess().
           */
          dtl_max_txg = txg + TXG_CONCURRENT_STATES;
  
          vdev_dtl_dirty(newvd, DTL_MISSING,
              TXG_INITIAL, dtl_max_txg - TXG_INITIAL);
  
          if (newvd->vdev_isspare) {
                  spa_spare_activate(newvd);
                  spa_event_notify(spa, newvd, NULL, ESC_ZFS_VDEV_SPARE);
          }
  
          oldvdpath = spa_strdup(oldvd->vdev_path);
          newvdpath = spa_strdup(newvd->vdev_path);
          newvd_isspare = newvd->vdev_isspare;
  
          /*
           * Mark newvd's DTL dirty in this txg.
           */
          vdev_dirty(tvd, VDD_DTL, newvd, txg);
  
          /*
           * Schedule the resilver or rebuild to restart in the future. We do
           * this to ensure that dmu_sync-ed blocks have been stitched into the
           * respective datasets.
           */
          if (rebuild) {
                  newvd->vdev_rebuild_txg = txg;
  
                  vdev_rebuild(tvd);
          } else {
                  newvd->vdev_resilver_txg = txg;
  
                  if (dsl_scan_resilvering(spa_get_dsl(spa)) &&
                      spa_feature_is_enabled(spa, SPA_FEATURE_RESILVER_DEFER)) {
                          vdev_defer_resilver(newvd);
                  } else {
                          dsl_scan_restart_resilver(spa->spa_dsl_pool,
                              dtl_max_txg);
                  }
          }
  
          if (spa->spa_bootfs)
                  spa_event_notify(spa, newvd, NULL, ESC_ZFS_BOOTFS_VDEV_ATTACH);
  
          spa_event_notify(spa, newvd, NULL, ESC_ZFS_VDEV_ATTACH);
  
          /*
           * Commit the config
           */
          (void) spa_vdev_exit(spa, newrootvd, dtl_max_txg, 0);
  
          spa_history_log_internal(spa, "vdev attach", NULL,
              "%s vdev=%s %s vdev=%s",
              replacing && newvd_isspare ? "spare in" :
              replacing ? "replace" : "attach", newvdpath,
              replacing ? "for" : "to", oldvdpath);
  
          spa_strfree(oldvdpath);
          spa_strfree(newvdpath);
  
          return (0);
  }
  
  /*
   * Detach a device from a mirror or replacing vdev.
   *
   * If 'replace_done' is specified, only detach if the parent
   * is a replacing vdev.
   */
  int
  spa_vdev_detach(spa_t *spa, uint64_t guid, uint64_t pguid, int replace_done)
  {
          uint64_t txg;
          int error;
          vdev_t *rvd __maybe_unused = spa->spa_root_vdev;
          vdev_t *vd, *pvd, *cvd, *tvd;
          boolean_t unspare = B_FALSE;
          uint64_t unspare_guid = 0;
          char *vdpath;
  
          ASSERT(spa_writeable(spa));
  
          txg = spa_vdev_detach_enter(spa, guid);
  
          vd = spa_lookup_by_guid(spa, guid, B_FALSE);
  
          /*
           * Besides being called directly from the userland through the
           * ioctl interface, spa_vdev_detach() can be potentially called
           * at the end of spa_vdev_resilver_done().
           *
           * In the regular case, when we have a checkpoint this shouldn't
           * happen as we never empty the DTLs of a vdev during the scrub
           * [see comment in dsl_scan_done()]. Thus spa_vdev_resilvering_done()
           * should never get here when we have a checkpoint.
           *
           * That said, even in a case when we checkpoint the pool exactly
           * as spa_vdev_resilver_done() calls this function everything
           * should be fine as the resilver will return right away.
           */
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
                  error = (spa_has_checkpoint(spa)) ?
                      ZFS_ERR_CHECKPOINT_EXISTS : ZFS_ERR_DISCARDING_CHECKPOINT;
                  return (spa_vdev_exit(spa, NULL, txg, error));
          }
  
          if (vd == NULL)
                  return (spa_vdev_exit(spa, NULL, txg, ENODEV));
  
          if (!vd->vdev_ops->vdev_op_leaf)
                  return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));
  
          pvd = vd->vdev_parent;
  
          /*
           * If the parent/child relationship is not as expected, don't do it.
           * Consider M(A,R(B,C)) -- that is, a mirror of A with a replacing
           * vdev that's replacing B with C.  The user's intent in replacing
           * is to go from M(A,B) to M(A,C).  If the user decides to cancel
           * the replace by detaching C, the expected behavior is to end up
           * M(A,B).  But suppose that right after deciding to detach C,
           * the replacement of B completes.  We would have M(A,C), and then
           * ask to detach C, which would leave us with just A -- not what
           * the user wanted.  To prevent this, we make sure that the
           * parent/child relationship hasn't changed -- in this example,
           * that C's parent is still the replacing vdev R.
           */
          if (pvd->vdev_guid != pguid && pguid != 0)
                  return (spa_vdev_exit(spa, NULL, txg, EBUSY));
  
          /*
           * Only 'replacing' or 'spare' vdevs can be replaced.
           */
          if (replace_done && pvd->vdev_ops != &vdev_replacing_ops &&
              pvd->vdev_ops != &vdev_spare_ops)
                  return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));
  
          ASSERT(pvd->vdev_ops != &vdev_spare_ops ||
              spa_version(spa) >= SPA_VERSION_SPARES);
  
          /*
           * Only mirror, replacing, and spare vdevs support detach.
           */
          if (pvd->vdev_ops != &vdev_replacing_ops &&
              pvd->vdev_ops != &vdev_mirror_ops &&
              pvd->vdev_ops != &vdev_spare_ops)
                  return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));
  
          /*
           * If this device has the only valid copy of some data,
           * we cannot safely detach it.
           */
          if (vdev_dtl_required(vd))
                  return (spa_vdev_exit(spa, NULL, txg, EBUSY));
  
          ASSERT(pvd->vdev_children >= 2);
  
          /*
           * If we are detaching the second disk from a replacing vdev, then
           * check to see if we changed the original vdev's path to have "/old"
           * at the end in spa_vdev_attach().  If so, undo that change now.
           */
          if (pvd->vdev_ops == &vdev_replacing_ops && vd->vdev_id > 0 &&
              vd->vdev_path != NULL) {
                  size_t len = strlen(vd->vdev_path);
  
                  for (int c = 0; c < pvd->vdev_children; c++) {
                          cvd = pvd->vdev_child[c];
  
                          if (cvd == vd || cvd->vdev_path == NULL)
                                  continue;
  
                          if (strncmp(cvd->vdev_path, vd->vdev_path, len) == 0 &&
                              strcmp(cvd->vdev_path + len, "/old") == 0) {
                                  spa_strfree(cvd->vdev_path);
                                  cvd->vdev_path = spa_strdup(vd->vdev_path);
                                  break;
                          }
                  }
          }
  
          /*
           * If we are detaching the original disk from a normal spare, then it
           * implies that the spare should become a real disk, and be removed
           * from the active spare list for the pool.  dRAID spares on the
           * other hand are coupled to the pool and thus should never be removed
           * from the spares list.
           */
          if (pvd->vdev_ops == &vdev_spare_ops && vd->vdev_id == 0) {
                  vdev_t *last_cvd = pvd->vdev_child[pvd->vdev_children - 1];
  
                  if (last_cvd->vdev_isspare &&
                      last_cvd->vdev_ops != &vdev_draid_spare_ops) {
                          unspare = B_TRUE;
                  }
          }
  
          /*
           * Erase the disk labels so the disk can be used for other things.
           * This must be done after all other error cases are handled,
           * but before we disembowel vd (so we can still do I/O to it).
           * But if we can't do it, don't treat the error as fatal --
           * it may be that the unwritability of the disk is the reason
           * it's being detached!
           */
          (void) vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);
  
          /*
           * Remove vd from its parent and compact the parent's children.
           */
          vdev_remove_child(pvd, vd);
          vdev_compact_children(pvd);
  
          /*
           * Remember one of the remaining children so we can get tvd below.
           */
          cvd = pvd->vdev_child[pvd->vdev_children - 1];
  
          /*
           * If we need to remove the remaining child from the list of hot spares,
           * do it now, marking the vdev as no longer a spare in the process.
           * We must do this before vdev_remove_parent(), because that can
           * change the GUID if it creates a new toplevel GUID.  For a similar
           * reason, we must remove the spare now, in the same txg as the detach;
           * otherwise someone could attach a new sibling, change the GUID, and
           * the subsequent attempt to spa_vdev_remove(unspare_guid) would fail.
           */
          if (unspare) {
                  ASSERT(cvd->vdev_isspare);
                  spa_spare_remove(cvd);
                  unspare_guid = cvd->vdev_guid;
                  (void) spa_vdev_remove(spa, unspare_guid, B_TRUE);
                  cvd->vdev_unspare = B_TRUE;
          }
  
          /*
           * If the parent mirror/replacing vdev only has one child,
           * the parent is no longer needed.  Remove it from the tree.
           */
          if (pvd->vdev_children == 1) {
                  if (pvd->vdev_ops == &vdev_spare_ops)
                          cvd->vdev_unspare = B_FALSE;
                  vdev_remove_parent(cvd);
          }
  
          /*
           * We don't set tvd until now because the parent we just removed
           * may have been the previous top-level vdev.
           */
          tvd = cvd->vdev_top;
          ASSERT(tvd->vdev_parent == rvd);
  
          /*
           * Reevaluate the parent vdev state.
           */
          vdev_propagate_state(cvd);
  
          /*
           * If the 'autoexpand' property is set on the pool then automatically
           * try to expand the size of the pool. For example if the device we
           * just detached was smaller than the others, it may be possible to
           * add metaslabs (i.e. grow the pool). We need to reopen the vdev
           * first so that we can obtain the updated sizes of the leaf vdevs.
           */
          if (spa->spa_autoexpand) {
                  vdev_reopen(tvd);
                  vdev_expand(tvd, txg);
          }
  
          vdev_config_dirty(tvd);
  
          /*
           * Mark vd's DTL as dirty in this txg.  vdev_dtl_sync() will see that
           * vd->vdev_detached is set and free vd's DTL object in syncing context.
           * But first make sure we're not on any *other* txg's DTL list, to
           * prevent vd from being accessed after it's freed.
           */
          vdpath = spa_strdup(vd->vdev_path ? vd->vdev_path : "none");
          for (int t = 0; t < TXG_SIZE; t++)
                  (void) txg_list_remove_this(&tvd->vdev_dtl_list, vd, t);
          vd->vdev_detached = B_TRUE;
          vdev_dirty(tvd, VDD_DTL, vd, txg);
  
          spa_event_notify(spa, vd, NULL, ESC_ZFS_VDEV_REMOVE);
          spa_notify_waiters(spa);
  
          /* hang on to the spa before we release the lock */
          spa_open_ref(spa, FTAG);
  
          error = spa_vdev_exit(spa, vd, txg, 0);
  
          spa_history_log_internal(spa, "detach", NULL,
              "vdev=%s", vdpath);
          spa_strfree(vdpath);
  
          /*
           * If this was the removal of the original device in a hot spare vdev,
           * then we want to go through and remove the device from the hot spare
           * list of every other pool.
           */
          if (unspare) {
                  spa_t *altspa = NULL;
  
                  mutex_enter(&spa_namespace_lock);
                  while ((altspa = spa_next(altspa)) != NULL) {
                          if (altspa->spa_state != POOL_STATE_ACTIVE ||
                              altspa == spa)
                                  continue;
  
                          spa_open_ref(altspa, FTAG);
                          mutex_exit(&spa_namespace_lock);
                          (void) spa_vdev_remove(altspa, unspare_guid, B_TRUE);
                          mutex_enter(&spa_namespace_lock);
                          spa_close(altspa, FTAG);
                  }
                  mutex_exit(&spa_namespace_lock);
  
                  /* search the rest of the vdevs for spares to remove */
                  spa_vdev_resilver_done(spa);
          }
  
          /* all done with the spa; OK to release */
          mutex_enter(&spa_namespace_lock);
          spa_close(spa, FTAG);
          mutex_exit(&spa_namespace_lock);
  
          return (error);
  }
  
  static int
  spa_vdev_initialize_impl(spa_t *spa, uint64_t guid, uint64_t cmd_type,
      list_t *vd_list)
  {
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
  
          /* Look up vdev and ensure it's a leaf. */
          vdev_t *vd = spa_lookup_by_guid(spa, guid, B_FALSE);
          if (vd == NULL || vd->vdev_detached) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(ENODEV));
          } else if (!vd->vdev_ops->vdev_op_leaf || !vdev_is_concrete(vd)) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EINVAL));
          } else if (!vdev_writeable(vd)) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EROFS));
          }
          mutex_enter(&vd->vdev_initialize_lock);
          spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
  
          /*
           * When we activate an initialize action we check to see
           * if the vdev_initialize_thread is NULL. We do this instead
           * of using the vdev_initialize_state since there might be
           * a previous initialization process which has completed but
           * the thread is not exited.
           */
          if (cmd_type == POOL_INITIALIZE_START &&
              (vd->vdev_initialize_thread != NULL ||
              vd->vdev_top->vdev_removing)) {
                  mutex_exit(&vd->vdev_initialize_lock);
                  return (SET_ERROR(EBUSY));
          } else if (cmd_type == POOL_INITIALIZE_CANCEL &&
              (vd->vdev_initialize_state != VDEV_INITIALIZE_ACTIVE &&
              vd->vdev_initialize_state != VDEV_INITIALIZE_SUSPENDED)) {
                  mutex_exit(&vd->vdev_initialize_lock);
                  return (SET_ERROR(ESRCH));
          } else if (cmd_type == POOL_INITIALIZE_SUSPEND &&
              vd->vdev_initialize_state != VDEV_INITIALIZE_ACTIVE) {
                  mutex_exit(&vd->vdev_initialize_lock);
                  return (SET_ERROR(ESRCH));
          }
  
          switch (cmd_type) {
          case POOL_INITIALIZE_START:
                  vdev_initialize(vd);
                  break;
          case POOL_INITIALIZE_CANCEL:
                  vdev_initialize_stop(vd, VDEV_INITIALIZE_CANCELED, vd_list);
                  break;
          case POOL_INITIALIZE_SUSPEND:
                  vdev_initialize_stop(vd, VDEV_INITIALIZE_SUSPENDED, vd_list);
                  break;
          default:
                  panic("invalid cmd_type %llu", (unsigned long long)cmd_type);
          }
          mutex_exit(&vd->vdev_initialize_lock);
  
          return (0);
  }
  
  int
  spa_vdev_initialize(spa_t *spa, nvlist_t *nv, uint64_t cmd_type,
      nvlist_t *vdev_errlist)
  {
          int total_errors = 0;
          list_t vd_list;
  
          list_create(&vd_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_initialize_node));
  
          /*
           * We hold the namespace lock through the whole function
           * to prevent any changes to the pool while we're starting or
           * stopping initialization. The config and state locks are held so that
           * we can properly assess the vdev state before we commit to
           * the initializing operation.
           */
          mutex_enter(&spa_namespace_lock);
  
          for (nvpair_t *pair = nvlist_next_nvpair(nv, NULL);
              pair != NULL; pair = nvlist_next_nvpair(nv, pair)) {
                  uint64_t vdev_guid = fnvpair_value_uint64(pair);
  
                  int error = spa_vdev_initialize_impl(spa, vdev_guid, cmd_type,
                      &vd_list);
                  if (error != 0) {
                          char guid_as_str[MAXNAMELEN];
  
                          (void) snprintf(guid_as_str, sizeof (guid_as_str),
                              "%llu", (unsigned long long)vdev_guid);
                          fnvlist_add_int64(vdev_errlist, guid_as_str, error);
                          total_errors++;
                  }
          }
  
          /* Wait for all initialize threads to stop. */
          vdev_initialize_stop_wait(spa, &vd_list);
  
          /* Sync out the initializing state */
          txg_wait_synced(spa->spa_dsl_pool, 0);
          mutex_exit(&spa_namespace_lock);
  
          list_destroy(&vd_list);
  
          return (total_errors);
  }
  
  static int
  spa_vdev_trim_impl(spa_t *spa, uint64_t guid, uint64_t cmd_type,
      uint64_t rate, boolean_t partial, boolean_t secure, list_t *vd_list)
  {
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
  
          /* Look up vdev and ensure it's a leaf. */
          vdev_t *vd = spa_lookup_by_guid(spa, guid, B_FALSE);
          if (vd == NULL || vd->vdev_detached) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(ENODEV));
          } else if (!vd->vdev_ops->vdev_op_leaf || !vdev_is_concrete(vd)) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EINVAL));
          } else if (!vdev_writeable(vd)) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EROFS));
          } else if (!vd->vdev_has_trim) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EOPNOTSUPP));
          } else if (secure && !vd->vdev_has_securetrim) {
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  return (SET_ERROR(EOPNOTSUPP));
          }
          mutex_enter(&vd->vdev_trim_lock);
          spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
  
          /*
           * When we activate a TRIM action we check to see if the
           * vdev_trim_thread is NULL. We do this instead of using the
           * vdev_trim_state since there might be a previous TRIM process
           * which has completed but the thread is not exited.
           */
          if (cmd_type == POOL_TRIM_START &&
              (vd->vdev_trim_thread != NULL || vd->vdev_top->vdev_removing)) {
                  mutex_exit(&vd->vdev_trim_lock);
                  return (SET_ERROR(EBUSY));
          } else if (cmd_type == POOL_TRIM_CANCEL &&
              (vd->vdev_trim_state != VDEV_TRIM_ACTIVE &&
              vd->vdev_trim_state != VDEV_TRIM_SUSPENDED)) {
                  mutex_exit(&vd->vdev_trim_lock);
                  return (SET_ERROR(ESRCH));
          } else if (cmd_type == POOL_TRIM_SUSPEND &&
              vd->vdev_trim_state != VDEV_TRIM_ACTIVE) {
                  mutex_exit(&vd->vdev_trim_lock);
                  return (SET_ERROR(ESRCH));
          }
  
          switch (cmd_type) {
          case POOL_TRIM_START:
                  vdev_trim(vd, rate, partial, secure);
                  break;
          case POOL_TRIM_CANCEL:
                  vdev_trim_stop(vd, VDEV_TRIM_CANCELED, vd_list);
                  break;
          case POOL_TRIM_SUSPEND:
                  vdev_trim_stop(vd, VDEV_TRIM_SUSPENDED, vd_list);
                  break;
          default:
                  panic("invalid cmd_type %llu", (unsigned long long)cmd_type);
          }
          mutex_exit(&vd->vdev_trim_lock);
  
          return (0);
  }
  
  /*
   * Initiates a manual TRIM for the requested vdevs. This kicks off individual
   * TRIM threads for each child vdev.  These threads pass over all of the free
   * space in the vdev's metaslabs and issues TRIM commands for that space.
   */
  int
  spa_vdev_trim(spa_t *spa, nvlist_t *nv, uint64_t cmd_type, uint64_t rate,
      boolean_t partial, boolean_t secure, nvlist_t *vdev_errlist)
  {
          int total_errors = 0;
          list_t vd_list;
  
          list_create(&vd_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_trim_node));
  
          /*
           * We hold the namespace lock through the whole function
           * to prevent any changes to the pool while we're starting or
           * stopping TRIM. The config and state locks are held so that
           * we can properly assess the vdev state before we commit to
           * the TRIM operation.
           */
          mutex_enter(&spa_namespace_lock);
  
          for (nvpair_t *pair = nvlist_next_nvpair(nv, NULL);
              pair != NULL; pair = nvlist_next_nvpair(nv, pair)) {
                  uint64_t vdev_guid = fnvpair_value_uint64(pair);
  
                  int error = spa_vdev_trim_impl(spa, vdev_guid, cmd_type,
                      rate, partial, secure, &vd_list);
                  if (error != 0) {
                          char guid_as_str[MAXNAMELEN];
  
                          (void) snprintf(guid_as_str, sizeof (guid_as_str),
                              "%llu", (unsigned long long)vdev_guid);
                          fnvlist_add_int64(vdev_errlist, guid_as_str, error);
                          total_errors++;
                  }
          }
  
          /* Wait for all TRIM threads to stop. */
          vdev_trim_stop_wait(spa, &vd_list);
  
          /* Sync out the TRIM state */
          txg_wait_synced(spa->spa_dsl_pool, 0);
          mutex_exit(&spa_namespace_lock);
  
          list_destroy(&vd_list);
  
          return (total_errors);
  }
  
  /*
   * Split a set of devices from their mirrors, and create a new pool from them.
   */
  int
  spa_vdev_split_mirror(spa_t *spa, const char *newname, nvlist_t *config,
      nvlist_t *props, boolean_t exp)
  {
          int error = 0;
          uint64_t txg, *glist;
          spa_t *newspa;
          uint_t c, children, lastlog;
          nvlist_t **child, *nvl, *tmp;
          dmu_tx_t *tx;
          char *altroot = NULL;
          vdev_t *rvd, **vml = NULL;                      /* vdev modify list */
          boolean_t activate_slog;
  
          ASSERT(spa_writeable(spa));
  
          txg = spa_vdev_enter(spa);
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
                  error = (spa_has_checkpoint(spa)) ?
                      ZFS_ERR_CHECKPOINT_EXISTS : ZFS_ERR_DISCARDING_CHECKPOINT;
                  return (spa_vdev_exit(spa, NULL, txg, error));
          }
  
          /* clear the log and flush everything up to now */
          activate_slog = spa_passivate_log(spa);
          (void) spa_vdev_config_exit(spa, NULL, txg, 0, FTAG);
          error = spa_reset_logs(spa);
          txg = spa_vdev_config_enter(spa);
  
          if (activate_slog)
                  spa_activate_log(spa);
  
          if (error != 0)
                  return (spa_vdev_exit(spa, NULL, txg, error));
  
          /* check new spa name before going any further */
          if (spa_lookup(newname) != NULL)
                  return (spa_vdev_exit(spa, NULL, txg, EEXIST));
  
          /*
           * scan through all the children to ensure they're all mirrors
           */
          if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &nvl) != 0 ||
              nvlist_lookup_nvlist_array(nvl, ZPOOL_CONFIG_CHILDREN, &child,
              &children) != 0)
                  return (spa_vdev_exit(spa, NULL, txg, EINVAL));
  
          /* first, check to ensure we've got the right child count */
          rvd = spa->spa_root_vdev;
          lastlog = 0;
          for (c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *vd = rvd->vdev_child[c];
  
                  /* don't count the holes & logs as children */
                  if (vd->vdev_islog || (vd->vdev_ops != &vdev_indirect_ops &&
                      !vdev_is_concrete(vd))) {
                          if (lastlog == 0)
                                  lastlog = c;
                          continue;
                  }
  
                  lastlog = 0;
          }
          if (children != (lastlog != 0 ? lastlog : rvd->vdev_children))
                  return (spa_vdev_exit(spa, NULL, txg, EINVAL));
  
          /* next, ensure no spare or cache devices are part of the split */
          if (nvlist_lookup_nvlist(nvl, ZPOOL_CONFIG_SPARES, &tmp) == 0 ||
              nvlist_lookup_nvlist(nvl, ZPOOL_CONFIG_L2CACHE, &tmp) == 0)
                  return (spa_vdev_exit(spa, NULL, txg, EINVAL));
  
          vml = kmem_zalloc(children * sizeof (vdev_t *), KM_SLEEP);
          glist = kmem_zalloc(children * sizeof (uint64_t), KM_SLEEP);
  
          /* then, loop over each vdev and validate it */
          for (c = 0; c < children; c++) {
                  uint64_t is_hole = 0;
  
                  (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_HOLE,
                      &is_hole);
  
                  if (is_hole != 0) {
                          if (spa->spa_root_vdev->vdev_child[c]->vdev_ishole ||
                              spa->spa_root_vdev->vdev_child[c]->vdev_islog) {
                                  continue;
                          } else {
                                  error = SET_ERROR(EINVAL);
                                  break;
                          }
                  }
  
                  /* deal with indirect vdevs */
                  if (spa->spa_root_vdev->vdev_child[c]->vdev_ops ==
                      &vdev_indirect_ops)
                          continue;
  
                  /* which disk is going to be split? */
                  if (nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_GUID,
                      &glist[c]) != 0) {
                          error = SET_ERROR(EINVAL);
                          break;
                  }
  
                  /* look it up in the spa */
                  vml[c] = spa_lookup_by_guid(spa, glist[c], B_FALSE);
                  if (vml[c] == NULL) {
                          error = SET_ERROR(ENODEV);
                          break;
                  }
  
                  /* make sure there's nothing stopping the split */
                  if (vml[c]->vdev_parent->vdev_ops != &vdev_mirror_ops ||
                      vml[c]->vdev_islog ||
                      !vdev_is_concrete(vml[c]) ||
                      vml[c]->vdev_isspare ||
                      vml[c]->vdev_isl2cache ||
                      !vdev_writeable(vml[c]) ||
                      vml[c]->vdev_children != 0 ||
                      vml[c]->vdev_state != VDEV_STATE_HEALTHY ||
                      c != spa->spa_root_vdev->vdev_child[c]->vdev_id) {
                          error = SET_ERROR(EINVAL);
                          break;
                  }
  
                  if (vdev_dtl_required(vml[c]) ||
                      vdev_resilver_needed(vml[c], NULL, NULL)) {
                          error = SET_ERROR(EBUSY);
                          break;
                  }
  
                  /* we need certain info from the top level */
                  fnvlist_add_uint64(child[c], ZPOOL_CONFIG_METASLAB_ARRAY,
                      vml[c]->vdev_top->vdev_ms_array);
                  fnvlist_add_uint64(child[c], ZPOOL_CONFIG_METASLAB_SHIFT,
                      vml[c]->vdev_top->vdev_ms_shift);
                  fnvlist_add_uint64(child[c], ZPOOL_CONFIG_ASIZE,
                      vml[c]->vdev_top->vdev_asize);
                  fnvlist_add_uint64(child[c], ZPOOL_CONFIG_ASHIFT,
                      vml[c]->vdev_top->vdev_ashift);
  
                  /* transfer per-vdev ZAPs */
                  ASSERT3U(vml[c]->vdev_leaf_zap, !=, 0);
                  VERIFY0(nvlist_add_uint64(child[c],
                      ZPOOL_CONFIG_VDEV_LEAF_ZAP, vml[c]->vdev_leaf_zap));
  
                  ASSERT3U(vml[c]->vdev_top->vdev_top_zap, !=, 0);
                  VERIFY0(nvlist_add_uint64(child[c],
                      ZPOOL_CONFIG_VDEV_TOP_ZAP,
                      vml[c]->vdev_parent->vdev_top_zap));
          }
  
          if (error != 0) {
                  kmem_free(vml, children * sizeof (vdev_t *));
                  kmem_free(glist, children * sizeof (uint64_t));
                  return (spa_vdev_exit(spa, NULL, txg, error));
          }
  
          /* stop writers from using the disks */
          for (c = 0; c < children; c++) {
                  if (vml[c] != NULL)
                          vml[c]->vdev_offline = B_TRUE;
          }
          vdev_reopen(spa->spa_root_vdev);
  
          /*
           * Temporarily record the splitting vdevs in the spa config.  This
           * will disappear once the config is regenerated.
           */
          nvl = fnvlist_alloc();
          fnvlist_add_uint64_array(nvl, ZPOOL_CONFIG_SPLIT_LIST, glist, children);
          kmem_free(glist, children * sizeof (uint64_t));
  
          mutex_enter(&spa->spa_props_lock);
          fnvlist_add_nvlist(spa->spa_config, ZPOOL_CONFIG_SPLIT, nvl);
          mutex_exit(&spa->spa_props_lock);
          spa->spa_config_splitting = nvl;
          vdev_config_dirty(spa->spa_root_vdev);
  
          /* configure and create the new pool */
          fnvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME, newname);
          fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE,
              exp ? POOL_STATE_EXPORTED : POOL_STATE_ACTIVE);
          fnvlist_add_uint64(config, ZPOOL_CONFIG_VERSION, spa_version(spa));
          fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_TXG, spa->spa_config_txg);
          fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_GUID,
              spa_generate_guid(NULL));
          VERIFY0(nvlist_add_boolean(config, ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS));
          (void) nvlist_lookup_string(props,
              zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
  
          /* add the new pool to the namespace */
          newspa = spa_add(newname, config, altroot);
          newspa->spa_avz_action = AVZ_ACTION_REBUILD;
          newspa->spa_config_txg = spa->spa_config_txg;
          spa_set_log_state(newspa, SPA_LOG_CLEAR);
  
          /* release the spa config lock, retaining the namespace lock */
          spa_vdev_config_exit(spa, NULL, txg, 0, FTAG);
  
          if (zio_injection_enabled)
                  zio_handle_panic_injection(spa, FTAG, 1);
  
          spa_activate(newspa, spa_mode_global);
          spa_async_suspend(newspa);
  
          /*
           * Temporarily stop the initializing and TRIM activity.  We set the
           * state to ACTIVE so that we know to resume initializing or TRIM
           * once the split has completed.
           */
          list_t vd_initialize_list;
          list_create(&vd_initialize_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_initialize_node));
  
          list_t vd_trim_list;
          list_create(&vd_trim_list, sizeof (vdev_t),
              offsetof(vdev_t, vdev_trim_node));
  
          for (c = 0; c < children; c++) {
                  if (vml[c] != NULL && vml[c]->vdev_ops != &vdev_indirect_ops) {
                          mutex_enter(&vml[c]->vdev_initialize_lock);
                          vdev_initialize_stop(vml[c],
                              VDEV_INITIALIZE_ACTIVE, &vd_initialize_list);
                          mutex_exit(&vml[c]->vdev_initialize_lock);
  
                          mutex_enter(&vml[c]->vdev_trim_lock);
                          vdev_trim_stop(vml[c], VDEV_TRIM_ACTIVE, &vd_trim_list);
                          mutex_exit(&vml[c]->vdev_trim_lock);
                  }
          }
  
          vdev_initialize_stop_wait(spa, &vd_initialize_list);
          vdev_trim_stop_wait(spa, &vd_trim_list);
  
          list_destroy(&vd_initialize_list);
          list_destroy(&vd_trim_list);
  
          newspa->spa_config_source = SPA_CONFIG_SRC_SPLIT;
          newspa->spa_is_splitting = B_TRUE;
  
          /* create the new pool from the disks of the original pool */
          error = spa_load(newspa, SPA_LOAD_IMPORT, SPA_IMPORT_ASSEMBLE);
          if (error)
                  goto out;
  
          /* if that worked, generate a real config for the new pool */
          if (newspa->spa_root_vdev != NULL) {
                  newspa->spa_config_splitting = fnvlist_alloc();
                  fnvlist_add_uint64(newspa->spa_config_splitting,
                      ZPOOL_CONFIG_SPLIT_GUID, spa_guid(spa));
                  spa_config_set(newspa, spa_config_generate(newspa, NULL, -1ULL,
                      B_TRUE));
          }
  
          /* set the props */
          if (props != NULL) {
                  spa_configfile_set(newspa, props, B_FALSE);
                  error = spa_prop_set(newspa, props);
                  if (error)
                          goto out;
          }
  
          /* flush everything */
          txg = spa_vdev_config_enter(newspa);
          vdev_config_dirty(newspa->spa_root_vdev);
          (void) spa_vdev_config_exit(newspa, NULL, txg, 0, FTAG);
  
          if (zio_injection_enabled)
                  zio_handle_panic_injection(spa, FTAG, 2);
  
          spa_async_resume(newspa);
  
          /* finally, update the original pool's config */
          txg = spa_vdev_config_enter(spa);
          tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
          error = dmu_tx_assign(tx, TXG_WAIT);
          if (error != 0)
                  dmu_tx_abort(tx);
          for (c = 0; c < children; c++) {
                  if (vml[c] != NULL && vml[c]->vdev_ops != &vdev_indirect_ops) {
                          vdev_t *tvd = vml[c]->vdev_top;
  
                          /*
                           * Need to be sure the detachable VDEV is not
                           * on any *other* txg's DTL list to prevent it
                           * from being accessed after it's freed.
                           */
                          for (int t = 0; t < TXG_SIZE; t++) {
                                  (void) txg_list_remove_this(
                                      &tvd->vdev_dtl_list, vml[c], t);
                          }
  
                          vdev_split(vml[c]);
                          if (error == 0)
                                  spa_history_log_internal(spa, "detach", tx,
                                      "vdev=%s", vml[c]->vdev_path);
  
                          vdev_free(vml[c]);
                  }
          }
          spa->spa_avz_action = AVZ_ACTION_REBUILD;
          vdev_config_dirty(spa->spa_root_vdev);
          spa->spa_config_splitting = NULL;
          nvlist_free(nvl);
          if (error == 0)
                  dmu_tx_commit(tx);
          (void) spa_vdev_exit(spa, NULL, txg, 0);
  
          if (zio_injection_enabled)
                  zio_handle_panic_injection(spa, FTAG, 3);
  
          /* split is complete; log a history record */
          spa_history_log_internal(newspa, "split", NULL,
              "from pool %s", spa_name(spa));
  
          newspa->spa_is_splitting = B_FALSE;
          kmem_free(vml, children * sizeof (vdev_t *));
  
          /* if we're not going to mount the filesystems in userland, export */
          if (exp)
                  error = spa_export_common(newname, POOL_STATE_EXPORTED, NULL,
                      B_FALSE, B_FALSE);
  
          return (error);
  
  out:
          spa_unload(newspa);
          spa_deactivate(newspa);
          spa_remove(newspa);
  
          txg = spa_vdev_config_enter(spa);
  
          /* re-online all offlined disks */
          for (c = 0; c < children; c++) {
                  if (vml[c] != NULL)
                          vml[c]->vdev_offline = B_FALSE;
          }
  
          /* restart initializing or trimming disks as necessary */
          spa_async_request(spa, SPA_ASYNC_INITIALIZE_RESTART);
          spa_async_request(spa, SPA_ASYNC_TRIM_RESTART);
          spa_async_request(spa, SPA_ASYNC_AUTOTRIM_RESTART);
  
          vdev_reopen(spa->spa_root_vdev);
  
          nvlist_free(spa->spa_config_splitting);
          spa->spa_config_splitting = NULL;
          (void) spa_vdev_exit(spa, NULL, txg, error);
  
          kmem_free(vml, children * sizeof (vdev_t *));
          return (error);
  }
  
  /*
   * Find any device that's done replacing, or a vdev marked 'unspare' that's
   * currently spared, so we can detach it.
   */
  static vdev_t *
  spa_vdev_resilver_done_hunt(vdev_t *vd)
  {
          vdev_t *newvd, *oldvd;
  
          for (int c = 0; c < vd->vdev_children; c++) {
                  oldvd = spa_vdev_resilver_done_hunt(vd->vdev_child[c]);
                  if (oldvd != NULL)
                          return (oldvd);
          }
  
          /*
           * Check for a completed replacement.  We always consider the first
           * vdev in the list to be the oldest vdev, and the last one to be
           * the newest (see spa_vdev_attach() for how that works).  In
           * the case where the newest vdev is faulted, we will not automatically
           * remove it after a resilver completes.  This is OK as it will require
           * user intervention to determine which disk the admin wishes to keep.
           */
          if (vd->vdev_ops == &vdev_replacing_ops) {
                  ASSERT(vd->vdev_children > 1);
  
                  newvd = vd->vdev_child[vd->vdev_children - 1];
                  oldvd = vd->vdev_child[0];
  
                  if (vdev_dtl_empty(newvd, DTL_MISSING) &&
                      vdev_dtl_empty(newvd, DTL_OUTAGE) &&
                      !vdev_dtl_required(oldvd))
                          return (oldvd);
          }
  
          /*
           * Check for a completed resilver with the 'unspare' flag set.
           * Also potentially update faulted state.
           */
          if (vd->vdev_ops == &vdev_spare_ops) {
                  vdev_t *first = vd->vdev_child[0];
                  vdev_t *last = vd->vdev_child[vd->vdev_children - 1];
  
                  if (last->vdev_unspare) {
                          oldvd = first;
                          newvd = last;
                  } else if (first->vdev_unspare) {
                          oldvd = last;
                          newvd = first;
                  } else {
                          oldvd = NULL;
                  }
  
                  if (oldvd != NULL &&
                      vdev_dtl_empty(newvd, DTL_MISSING) &&
                      vdev_dtl_empty(newvd, DTL_OUTAGE) &&
                      !vdev_dtl_required(oldvd))
                          return (oldvd);
  
                  vdev_propagate_state(vd);
  
                  /*
                   * If there are more than two spares attached to a disk,
                   * and those spares are not required, then we want to
                   * attempt to free them up now so that they can be used
                   * by other pools.  Once we're back down to a single
                   * disk+spare, we stop removing them.
                   */
                  if (vd->vdev_children > 2) {
                          newvd = vd->vdev_child[1];
  
                          if (newvd->vdev_isspare && last->vdev_isspare &&
                              vdev_dtl_empty(last, DTL_MISSING) &&
                              vdev_dtl_empty(last, DTL_OUTAGE) &&
                              !vdev_dtl_required(newvd))
                                  return (newvd);
                  }
          }
  
          return (NULL);
  }
  
  static void
  spa_vdev_resilver_done(spa_t *spa)
  {
          vdev_t *vd, *pvd, *ppvd;
          uint64_t guid, sguid, pguid, ppguid;
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
  
          while ((vd = spa_vdev_resilver_done_hunt(spa->spa_root_vdev)) != NULL) {
                  pvd = vd->vdev_parent;
                  ppvd = pvd->vdev_parent;
                  guid = vd->vdev_guid;
                  pguid = pvd->vdev_guid;
                  ppguid = ppvd->vdev_guid;
                  sguid = 0;
                  /*
                   * If we have just finished replacing a hot spared device, then
                   * we need to detach the parent's first child (the original hot
                   * spare) as well.
                   */
                  if (ppvd->vdev_ops == &vdev_spare_ops && pvd->vdev_id == 0 &&
                      ppvd->vdev_children == 2) {
                          ASSERT(pvd->vdev_ops == &vdev_replacing_ops);
                          sguid = ppvd->vdev_child[1]->vdev_guid;
                  }
                  ASSERT(vd->vdev_resilver_txg == 0 || !vdev_dtl_required(vd));
  
                  spa_config_exit(spa, SCL_ALL, FTAG);
                  if (spa_vdev_detach(spa, guid, pguid, B_TRUE) != 0)
                          return;
                  if (sguid && spa_vdev_detach(spa, sguid, ppguid, B_TRUE) != 0)
                          return;
                  spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          }
  
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          /*
           * If a detach was not performed above replace waiters will not have
           * been notified.  In which case we must do so now.
           */
          spa_notify_waiters(spa);
  }
  
  /*
   * Update the stored path or FRU for this vdev.
   */
  static int
  spa_vdev_set_common(spa_t *spa, uint64_t guid, const char *value,
      boolean_t ispath)
  {
          vdev_t *vd;
          boolean_t sync = B_FALSE;
  
          ASSERT(spa_writeable(spa));
  
          spa_vdev_state_enter(spa, SCL_ALL);
  
          if ((vd = spa_lookup_by_guid(spa, guid, B_TRUE)) == NULL)
                  return (spa_vdev_state_exit(spa, NULL, ENOENT));
  
          if (!vd->vdev_ops->vdev_op_leaf)
                  return (spa_vdev_state_exit(spa, NULL, ENOTSUP));
  
          if (ispath) {
                  if (strcmp(value, vd->vdev_path) != 0) {
                          spa_strfree(vd->vdev_path);
                          vd->vdev_path = spa_strdup(value);
                          sync = B_TRUE;
                  }
          } else {
                  if (vd->vdev_fru == NULL) {
                          vd->vdev_fru = spa_strdup(value);
                          sync = B_TRUE;
                  } else if (strcmp(value, vd->vdev_fru) != 0) {
                          spa_strfree(vd->vdev_fru);
                          vd->vdev_fru = spa_strdup(value);
                          sync = B_TRUE;
                  }
          }
  
          return (spa_vdev_state_exit(spa, sync ? vd : NULL, 0));
  }
  
  int
  spa_vdev_setpath(spa_t *spa, uint64_t guid, const char *newpath)
  {
          return (spa_vdev_set_common(spa, guid, newpath, B_TRUE));
  }
  
  int
  spa_vdev_setfru(spa_t *spa, uint64_t guid, const char *newfru)
  {
          return (spa_vdev_set_common(spa, guid, newfru, B_FALSE));
  }
  
  /*
   * ==========================================================================
   * SPA Scanning
   * ==========================================================================
   */
  int
  spa_scrub_pause_resume(spa_t *spa, pool_scrub_cmd_t cmd)
  {
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);
  
          if (dsl_scan_resilvering(spa->spa_dsl_pool))
                  return (SET_ERROR(EBUSY));
  
          return (dsl_scrub_set_pause_resume(spa->spa_dsl_pool, cmd));
  }
  
  int
  spa_scan_stop(spa_t *spa)
  {
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);
          if (dsl_scan_resilvering(spa->spa_dsl_pool))
                  return (SET_ERROR(EBUSY));
          return (dsl_scan_cancel(spa->spa_dsl_pool));
  }
  
  int
  spa_scan(spa_t *spa, pool_scan_func_t func)
  {
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);
  
          if (func >= POOL_SCAN_FUNCS || func == POOL_SCAN_NONE)
                  return (SET_ERROR(ENOTSUP));
  
          if (func == POOL_SCAN_RESILVER &&
              !spa_feature_is_enabled(spa, SPA_FEATURE_RESILVER_DEFER))
                  return (SET_ERROR(ENOTSUP));
  
          /*
           * If a resilver was requested, but there is no DTL on a
           * writeable leaf device, we have nothing to do.
           */
          if (func == POOL_SCAN_RESILVER &&
              !vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL)) {
                  spa_async_request(spa, SPA_ASYNC_RESILVER_DONE);
                  return (0);
          }
  
          return (dsl_scan(spa->spa_dsl_pool, func));
  }
  
  /*
   * ==========================================================================
   * SPA async task processing
   * ==========================================================================
   */
  
  static void
  spa_async_remove(spa_t *spa, vdev_t *vd)
  {
          if (vd->vdev_remove_wanted) {
                  vd->vdev_remove_wanted = B_FALSE;
                  vd->vdev_delayed_close = B_FALSE;
                  vdev_set_state(vd, B_FALSE, VDEV_STATE_REMOVED, VDEV_AUX_NONE);
  
                  /*
                   * We want to clear the stats, but we don't want to do a full
                   * vdev_clear() as that will cause us to throw away
                   * degraded/faulted state as well as attempt to reopen the
                   * device, all of which is a waste.
                   */
                  vd->vdev_stat.vs_read_errors = 0;
                  vd->vdev_stat.vs_write_errors = 0;
                  vd->vdev_stat.vs_checksum_errors = 0;
  
                  vdev_state_dirty(vd->vdev_top);
  
                  /* Tell userspace that the vdev is gone. */
                  zfs_post_remove(spa, vd);
          }
  
          for (int c = 0; c < vd->vdev_children; c++)
                  spa_async_remove(spa, vd->vdev_child[c]);
  }
  
  static void
  spa_async_probe(spa_t *spa, vdev_t *vd)
  {
          if (vd->vdev_probe_wanted) {
                  vd->vdev_probe_wanted = B_FALSE;
                  vdev_reopen(vd);        /* vdev_open() does the actual probe */
          }
  
          for (int c = 0; c < vd->vdev_children; c++)
                  spa_async_probe(spa, vd->vdev_child[c]);
  }
  
  static void
  spa_async_autoexpand(spa_t *spa, vdev_t *vd)
  {
          if (!spa->spa_autoexpand)
                  return;
  
          for (int c = 0; c < vd->vdev_children; c++) {
                  vdev_t *cvd = vd->vdev_child[c];
                  spa_async_autoexpand(spa, cvd);
          }
  
          if (!vd->vdev_ops->vdev_op_leaf || vd->vdev_physpath == NULL)
                  return;
  
          spa_event_notify(vd->vdev_spa, vd, NULL, ESC_ZFS_VDEV_AUTOEXPAND);
  }
  
  static __attribute__((noreturn)) void
  spa_async_thread(void *arg)
  {
          spa_t *spa = (spa_t *)arg;
          dsl_pool_t *dp = spa->spa_dsl_pool;
          int tasks;
  
          ASSERT(spa->spa_sync_on);
  
          mutex_enter(&spa->spa_async_lock);
          tasks = spa->spa_async_tasks;
          spa->spa_async_tasks = 0;
          mutex_exit(&spa->spa_async_lock);
  
          /*
           * See if the config needs to be updated.
           */
          if (tasks & SPA_ASYNC_CONFIG_UPDATE) {
                  uint64_t old_space, new_space;
  
                  mutex_enter(&spa_namespace_lock);
                  old_space = metaslab_class_get_space(spa_normal_class(spa));
                  old_space += metaslab_class_get_space(spa_special_class(spa));
                  old_space += metaslab_class_get_space(spa_dedup_class(spa));
                  old_space += metaslab_class_get_space(
                      spa_embedded_log_class(spa));
  
                  spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
  
                  new_space = metaslab_class_get_space(spa_normal_class(spa));
                  new_space += metaslab_class_get_space(spa_special_class(spa));
                  new_space += metaslab_class_get_space(spa_dedup_class(spa));
                  new_space += metaslab_class_get_space(
                      spa_embedded_log_class(spa));
                  mutex_exit(&spa_namespace_lock);
  
                  /*
                   * If the pool grew as a result of the config update,
                   * then log an internal history event.
                   */
                  if (new_space != old_space) {
                          spa_history_log_internal(spa, "vdev online", NULL,
                              "pool '%s' size: %llu(+%llu)",
                              spa_name(spa), (u_longlong_t)new_space,
                              (u_longlong_t)(new_space - old_space));
                  }
          }
  
          /*
           * See if any devices need to be marked REMOVED.
           */
          if (tasks & SPA_ASYNC_REMOVE) {
                  spa_vdev_state_enter(spa, SCL_NONE);
                  spa_async_remove(spa, spa->spa_root_vdev);
                  for (int i = 0; i < spa->spa_l2cache.sav_count; i++)
                          spa_async_remove(spa, spa->spa_l2cache.sav_vdevs[i]);
                  for (int i = 0; i < spa->spa_spares.sav_count; i++)
                          spa_async_remove(spa, spa->spa_spares.sav_vdevs[i]);
                  (void) spa_vdev_state_exit(spa, NULL, 0);
          }
  
          if ((tasks & SPA_ASYNC_AUTOEXPAND) && !spa_suspended(spa)) {
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  spa_async_autoexpand(spa, spa->spa_root_vdev);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
          }
  
          /*
           * See if any devices need to be probed.
           */
          if (tasks & SPA_ASYNC_PROBE) {
                  spa_vdev_state_enter(spa, SCL_NONE);
                  spa_async_probe(spa, spa->spa_root_vdev);
                  (void) spa_vdev_state_exit(spa, NULL, 0);
          }
  
          /*
           * If any devices are done replacing, detach them.
           */
          if (tasks & SPA_ASYNC_RESILVER_DONE ||
              tasks & SPA_ASYNC_REBUILD_DONE) {
                  spa_vdev_resilver_done(spa);
          }
  
          /*
           * Kick off a resilver.
           */
          if (tasks & SPA_ASYNC_RESILVER &&
              !vdev_rebuild_active(spa->spa_root_vdev) &&
              (!dsl_scan_resilvering(dp) ||
              !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_RESILVER_DEFER)))
                  dsl_scan_restart_resilver(dp, 0);
  
          if (tasks & SPA_ASYNC_INITIALIZE_RESTART) {
                  mutex_enter(&spa_namespace_lock);
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  vdev_initialize_restart(spa->spa_root_vdev);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
                  mutex_exit(&spa_namespace_lock);
          }
  
          if (tasks & SPA_ASYNC_TRIM_RESTART) {
                  mutex_enter(&spa_namespace_lock);
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  vdev_trim_restart(spa->spa_root_vdev);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
                  mutex_exit(&spa_namespace_lock);
          }
  
          if (tasks & SPA_ASYNC_AUTOTRIM_RESTART) {
                  mutex_enter(&spa_namespace_lock);
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  vdev_autotrim_restart(spa);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
                  mutex_exit(&spa_namespace_lock);
          }
  
          /*
           * Kick off L2 cache whole device TRIM.
           */
          if (tasks & SPA_ASYNC_L2CACHE_TRIM) {
                  mutex_enter(&spa_namespace_lock);
                  spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                  vdev_trim_l2arc(spa);
                  spa_config_exit(spa, SCL_CONFIG, FTAG);
                  mutex_exit(&spa_namespace_lock);
          }
  
          /*
           * Kick off L2 cache rebuilding.
           */
          if (tasks & SPA_ASYNC_L2CACHE_REBUILD) {
                  mutex_enter(&spa_namespace_lock);
                  spa_config_enter(spa, SCL_L2ARC, FTAG, RW_READER);
                  l2arc_spa_rebuild_start(spa);
                  spa_config_exit(spa, SCL_L2ARC, FTAG);
                  mutex_exit(&spa_namespace_lock);
          }
  
          /*
           * Let the world know that we're done.
           */
          mutex_enter(&spa->spa_async_lock);
          spa->spa_async_thread = NULL;
          cv_broadcast(&spa->spa_async_cv);
          mutex_exit(&spa->spa_async_lock);
          thread_exit();
  }
  
  void
  spa_async_suspend(spa_t *spa)
  {
          mutex_enter(&spa->spa_async_lock);
          spa->spa_async_suspended++;
          while (spa->spa_async_thread != NULL)
                  cv_wait(&spa->spa_async_cv, &spa->spa_async_lock);
          mutex_exit(&spa->spa_async_lock);
  
          spa_vdev_remove_suspend(spa);
  
          zthr_t *condense_thread = spa->spa_condense_zthr;
          if (condense_thread != NULL)
                  zthr_cancel(condense_thread);
  
          zthr_t *discard_thread = spa->spa_checkpoint_discard_zthr;
          if (discard_thread != NULL)
                  zthr_cancel(discard_thread);
  
          zthr_t *ll_delete_thread = spa->spa_livelist_delete_zthr;
          if (ll_delete_thread != NULL)
                  zthr_cancel(ll_delete_thread);
  
          zthr_t *ll_condense_thread = spa->spa_livelist_condense_zthr;
          if (ll_condense_thread != NULL)
                  zthr_cancel(ll_condense_thread);
  }
  
  void
  spa_async_resume(spa_t *spa)
  {
          mutex_enter(&spa->spa_async_lock);
          ASSERT(spa->spa_async_suspended != 0);
          spa->spa_async_suspended--;
          mutex_exit(&spa->spa_async_lock);
          spa_restart_removal(spa);
  
          zthr_t *condense_thread = spa->spa_condense_zthr;
          if (condense_thread != NULL)
                  zthr_resume(condense_thread);
  
          zthr_t *discard_thread = spa->spa_checkpoint_discard_zthr;
          if (discard_thread != NULL)
                  zthr_resume(discard_thread);
  
          zthr_t *ll_delete_thread = spa->spa_livelist_delete_zthr;
          if (ll_delete_thread != NULL)
                  zthr_resume(ll_delete_thread);
  
          zthr_t *ll_condense_thread = spa->spa_livelist_condense_zthr;
          if (ll_condense_thread != NULL)
                  zthr_resume(ll_condense_thread);
  }
  
  static boolean_t
  spa_async_tasks_pending(spa_t *spa)
  {
          uint_t non_config_tasks;
          uint_t config_task;
          boolean_t config_task_suspended;
  
          non_config_tasks = spa->spa_async_tasks & ~SPA_ASYNC_CONFIG_UPDATE;
          config_task = spa->spa_async_tasks & SPA_ASYNC_CONFIG_UPDATE;
          if (spa->spa_ccw_fail_time == 0) {
                  config_task_suspended = B_FALSE;
          } else {
                  config_task_suspended =
                      (gethrtime() - spa->spa_ccw_fail_time) <
                      ((hrtime_t)zfs_ccw_retry_interval * NANOSEC);
          }
  
          return (non_config_tasks || (config_task && !config_task_suspended));
  }
  
  static void
  spa_async_dispatch(spa_t *spa)
  {
          mutex_enter(&spa->spa_async_lock);
          if (spa_async_tasks_pending(spa) &&
              !spa->spa_async_suspended &&
              spa->spa_async_thread == NULL)
                  spa->spa_async_thread = thread_create(NULL, 0,
                      spa_async_thread, spa, 0, &p0, TS_RUN, maxclsyspri);
          mutex_exit(&spa->spa_async_lock);
  }
  
  void
  spa_async_request(spa_t *spa, int task)
  {
          zfs_dbgmsg("spa=%s async request task=%u", spa->spa_name, task);
          mutex_enter(&spa->spa_async_lock);
          spa->spa_async_tasks |= task;
          mutex_exit(&spa->spa_async_lock);
  }
  
  int
  spa_async_tasks(spa_t *spa)
  {
          return (spa->spa_async_tasks);
  }
  
  /*
   * ==========================================================================
   * SPA syncing routines
   * ==========================================================================
   */
  
  
  static int
  bpobj_enqueue_cb(void *arg, const blkptr_t *bp, boolean_t bp_freed,
      dmu_tx_t *tx)
  {
          bpobj_t *bpo = arg;
          bpobj_enqueue(bpo, bp, bp_freed, tx);
          return (0);
  }
  
  int
  bpobj_enqueue_alloc_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
  {
          return (bpobj_enqueue_cb(arg, bp, B_FALSE, tx));
  }
  
  int
  bpobj_enqueue_free_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
  {
          return (bpobj_enqueue_cb(arg, bp, B_TRUE, tx));
  }
  
  static int
  spa_free_sync_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
  {
          zio_t *pio = arg;
  
          zio_nowait(zio_free_sync(pio, pio->io_spa, dmu_tx_get_txg(tx), bp,
              pio->io_flags));
          return (0);
  }
  
  static int
  bpobj_spa_free_sync_cb(void *arg, const blkptr_t *bp, boolean_t bp_freed,
      dmu_tx_t *tx)
  {
          ASSERT(!bp_freed);
          return (spa_free_sync_cb(arg, bp, tx));
  }
  
  /*
   * Note: this simple function is not inlined to make it easier to dtrace the
   * amount of time spent syncing frees.
   */
  static void
  spa_sync_frees(spa_t *spa, bplist_t *bpl, dmu_tx_t *tx)
  {
          zio_t *zio = zio_root(spa, NULL, NULL, 0);
          bplist_iterate(bpl, spa_free_sync_cb, zio, tx);
          VERIFY(zio_wait(zio) == 0);
  }
  
  /*
   * Note: this simple function is not inlined to make it easier to dtrace the
   * amount of time spent syncing deferred frees.
   */
  static void
  spa_sync_deferred_frees(spa_t *spa, dmu_tx_t *tx)
  {
          if (spa_sync_pass(spa) != 1)
                  return;
  
          /*
           * Note:
           * If the log space map feature is active, we stop deferring
           * frees to the next TXG and therefore running this function
           * would be considered a no-op as spa_deferred_bpobj should
           * not have any entries.
           *
           * That said we run this function anyway (instead of returning
           * immediately) for the edge-case scenario where we just
           * activated the log space map feature in this TXG but we have
           * deferred frees from the previous TXG.
           */
          zio_t *zio = zio_root(spa, NULL, NULL, 0);
          VERIFY3U(bpobj_iterate(&spa->spa_deferred_bpobj,
              bpobj_spa_free_sync_cb, zio, tx), ==, 0);
          VERIFY0(zio_wait(zio));
  }
  
  static void
  spa_sync_nvlist(spa_t *spa, uint64_t obj, nvlist_t *nv, dmu_tx_t *tx)
  {
          char *packed = NULL;
          size_t bufsize;
          size_t nvsize = 0;
          dmu_buf_t *db;
  
          VERIFY(nvlist_size(nv, &nvsize, NV_ENCODE_XDR) == 0);
  
          /*
           * Write full (SPA_CONFIG_BLOCKSIZE) blocks of configuration
           * information.  This avoids the dmu_buf_will_dirty() path and
           * saves us a pre-read to get data we don't actually care about.
           */
          bufsize = P2ROUNDUP((uint64_t)nvsize, SPA_CONFIG_BLOCKSIZE);
          packed = vmem_alloc(bufsize, KM_SLEEP);
  
          VERIFY(nvlist_pack(nv, &packed, &nvsize, NV_ENCODE_XDR,
              KM_SLEEP) == 0);
          memset(packed + nvsize, 0, bufsize - nvsize);
  
          dmu_write(spa->spa_meta_objset, obj, 0, bufsize, packed, tx);
  
          vmem_free(packed, bufsize);
  
          VERIFY(0 == dmu_bonus_hold(spa->spa_meta_objset, obj, FTAG, &db));
          dmu_buf_will_dirty(db, tx);
          *(uint64_t *)db->db_data = nvsize;
          dmu_buf_rele(db, FTAG);
  }
  
  static void
  spa_sync_aux_dev(spa_t *spa, spa_aux_vdev_t *sav, dmu_tx_t *tx,
      const char *config, const char *entry)
  {
          nvlist_t *nvroot;
          nvlist_t **list;
          int i;
  
          if (!sav->sav_sync)
                  return;
  
          /*
           * Update the MOS nvlist describing the list of available devices.
           * spa_validate_aux() will have already made sure this nvlist is
           * valid and the vdevs are labeled appropriately.
           */
          if (sav->sav_object == 0) {
                  sav->sav_object = dmu_object_alloc(spa->spa_meta_objset,
                      DMU_OT_PACKED_NVLIST, 1 << 14, DMU_OT_PACKED_NVLIST_SIZE,
                      sizeof (uint64_t), tx);
                  VERIFY(zap_update(spa->spa_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT, entry, sizeof (uint64_t), 1,
                      &sav->sav_object, tx) == 0);
          }
  
          nvroot = fnvlist_alloc();
          if (sav->sav_count == 0) {
                  fnvlist_add_nvlist_array(nvroot, config,
                      (const nvlist_t * const *)NULL, 0);
          } else {
                  list = kmem_alloc(sav->sav_count*sizeof (void *), KM_SLEEP);
                  for (i = 0; i < sav->sav_count; i++)
                          list[i] = vdev_config_generate(spa, sav->sav_vdevs[i],
                              B_FALSE, VDEV_CONFIG_L2CACHE);
                  fnvlist_add_nvlist_array(nvroot, config,
                      (const nvlist_t * const *)list, sav->sav_count);
                  for (i = 0; i < sav->sav_count; i++)
                          nvlist_free(list[i]);
                  kmem_free(list, sav->sav_count * sizeof (void *));
          }
  
          spa_sync_nvlist(spa, sav->sav_object, nvroot, tx);
          nvlist_free(nvroot);
  
          sav->sav_sync = B_FALSE;
  }
  
  /*
   * Rebuild spa's all-vdev ZAP from the vdev ZAPs indicated in each vdev_t.
   * The all-vdev ZAP must be empty.
   */
  static void
  spa_avz_build(vdev_t *vd, uint64_t avz, dmu_tx_t *tx)
  {
          spa_t *spa = vd->vdev_spa;
  
          if (vd->vdev_top_zap != 0) {
                  VERIFY0(zap_add_int(spa->spa_meta_objset, avz,
                      vd->vdev_top_zap, tx));
          }
          if (vd->vdev_leaf_zap != 0) {
                  VERIFY0(zap_add_int(spa->spa_meta_objset, avz,
                      vd->vdev_leaf_zap, tx));
          }
          for (uint64_t i = 0; i < vd->vdev_children; i++) {
                  spa_avz_build(vd->vdev_child[i], avz, tx);
          }
  }
  
  static void
  spa_sync_config_object(spa_t *spa, dmu_tx_t *tx)
  {
          nvlist_t *config;
  
          /*
           * If the pool is being imported from a pre-per-vdev-ZAP version of ZFS,
           * its config may not be dirty but we still need to build per-vdev ZAPs.
           * Similarly, if the pool is being assembled (e.g. after a split), we
           * need to rebuild the AVZ although the config may not be dirty.
           */
          if (list_is_empty(&spa->spa_config_dirty_list) &&
              spa->spa_avz_action == AVZ_ACTION_NONE)
                  return;
  
          spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
  
          ASSERT(spa->spa_avz_action == AVZ_ACTION_NONE ||
              spa->spa_avz_action == AVZ_ACTION_INITIALIZE ||
              spa->spa_all_vdev_zaps != 0);
  
          if (spa->spa_avz_action == AVZ_ACTION_REBUILD) {
                  /* Make and build the new AVZ */
                  uint64_t new_avz = zap_create(spa->spa_meta_objset,
                      DMU_OTN_ZAP_METADATA, DMU_OT_NONE, 0, tx);
                  spa_avz_build(spa->spa_root_vdev, new_avz, tx);
  
                  /* Diff old AVZ with new one */
                  zap_cursor_t zc;
                  zap_attribute_t za;
  
                  for (zap_cursor_init(&zc, spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps);
                      zap_cursor_retrieve(&zc, &za) == 0;
                      zap_cursor_advance(&zc)) {
                          uint64_t vdzap = za.za_first_integer;
                          if (zap_lookup_int(spa->spa_meta_objset, new_avz,
                              vdzap) == ENOENT) {
                                  /*
                                   * ZAP is listed in old AVZ but not in new one;
                                   * destroy it
                                   */
                                  VERIFY0(zap_destroy(spa->spa_meta_objset, vdzap,
                                      tx));
                          }
                  }
  
                  zap_cursor_fini(&zc);
  
                  /* Destroy the old AVZ */
                  VERIFY0(zap_destroy(spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps, tx));
  
                  /* Replace the old AVZ in the dir obj with the new one */
                  VERIFY0(zap_update(spa->spa_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_VDEV_ZAP_MAP,
                      sizeof (new_avz), 1, &new_avz, tx));
  
                  spa->spa_all_vdev_zaps = new_avz;
          } else if (spa->spa_avz_action == AVZ_ACTION_DESTROY) {
                  zap_cursor_t zc;
                  zap_attribute_t za;
  
                  /* Walk through the AVZ and destroy all listed ZAPs */
                  for (zap_cursor_init(&zc, spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps);
                      zap_cursor_retrieve(&zc, &za) == 0;
                      zap_cursor_advance(&zc)) {
                          uint64_t zap = za.za_first_integer;
                          VERIFY0(zap_destroy(spa->spa_meta_objset, zap, tx));
                  }
  
                  zap_cursor_fini(&zc);
  
                  /* Destroy and unlink the AVZ itself */
                  VERIFY0(zap_destroy(spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps, tx));
                  VERIFY0(zap_remove(spa->spa_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_VDEV_ZAP_MAP, tx));
                  spa->spa_all_vdev_zaps = 0;
          }
  
          if (spa->spa_all_vdev_zaps == 0) {
                  spa->spa_all_vdev_zaps = zap_create_link(spa->spa_meta_objset,
                      DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
                      DMU_POOL_VDEV_ZAP_MAP, tx);
          }
          spa->spa_avz_action = AVZ_ACTION_NONE;
  
          /* Create ZAPs for vdevs that don't have them. */
          vdev_construct_zaps(spa->spa_root_vdev, tx);
  
          config = spa_config_generate(spa, spa->spa_root_vdev,
              dmu_tx_get_txg(tx), B_FALSE);
  
          /*
           * If we're upgrading the spa version then make sure that
           * the config object gets updated with the correct version.
           */
          if (spa->spa_ubsync.ub_version < spa->spa_uberblock.ub_version)
                  fnvlist_add_uint64(config, ZPOOL_CONFIG_VERSION,
                      spa->spa_uberblock.ub_version);
  
          spa_config_exit(spa, SCL_STATE, FTAG);
  
          nvlist_free(spa->spa_config_syncing);
          spa->spa_config_syncing = config;
  
          spa_sync_nvlist(spa, spa->spa_config_object, config, tx);
  }
  
  static void
  spa_sync_version(void *arg, dmu_tx_t *tx)
  {
          uint64_t *versionp = arg;
          uint64_t version = *versionp;
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
          /*
           * Setting the version is special cased when first creating the pool.
           */
          ASSERT(tx->tx_txg != TXG_INITIAL);
  
          ASSERT(SPA_VERSION_IS_SUPPORTED(version));
          ASSERT(version >= spa_version(spa));
  
          spa->spa_uberblock.ub_version = version;
          vdev_config_dirty(spa->spa_root_vdev);
          spa_history_log_internal(spa, "set", tx, "version=%lld",
              (longlong_t)version);
  }
  
  /*
   * Set zpool properties.
   */
  static void
  spa_sync_props(void *arg, dmu_tx_t *tx)
  {
          nvlist_t *nvp = arg;
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
          objset_t *mos = spa->spa_meta_objset;
          nvpair_t *elem = NULL;
  
          mutex_enter(&spa->spa_props_lock);
  
          while ((elem = nvlist_next_nvpair(nvp, elem))) {
                  uint64_t intval;
                  char *strval, *fname;
                  zpool_prop_t prop;
                  const char *propname;
                  zprop_type_t proptype;
                  spa_feature_t fid;
  
                  switch (prop = zpool_name_to_prop(nvpair_name(elem))) {
                  case ZPOOL_PROP_INVAL:
                          /*
                           * We checked this earlier in spa_prop_validate().
                           */
                          ASSERT(zpool_prop_feature(nvpair_name(elem)));
  
                          fname = strchr(nvpair_name(elem), '@') + 1;
                          VERIFY0(zfeature_lookup_name(fname, &fid));
  
                          spa_feature_enable(spa, fid, tx);
                          spa_history_log_internal(spa, "set", tx,
                              "%s=enabled", nvpair_name(elem));
                          break;
  
                  case ZPOOL_PROP_VERSION:
                          intval = fnvpair_value_uint64(elem);
                          /*
                           * The version is synced separately before other
                           * properties and should be correct by now.
                           */
                          ASSERT3U(spa_version(spa), >=, intval);
                          break;
  
                  case ZPOOL_PROP_ALTROOT:
                          /*
                           * 'altroot' is a non-persistent property. It should
                           * have been set temporarily at creation or import time.
                           */
                          ASSERT(spa->spa_root != NULL);
                          break;
  
                  case ZPOOL_PROP_READONLY:
                  case ZPOOL_PROP_CACHEFILE:
                          /*
                           * 'readonly' and 'cachefile' are also non-persistent
                           * properties.
                           */
                          break;
                  case ZPOOL_PROP_COMMENT:
                          strval = fnvpair_value_string(elem);
                          if (spa->spa_comment != NULL)
                                  spa_strfree(spa->spa_comment);
                          spa->spa_comment = spa_strdup(strval);
                          /*
                           * We need to dirty the configuration on all the vdevs
                           * so that their labels get updated.  We also need to
                           * update the cache file to keep it in sync with the
                           * MOS version. It's unnecessary to do this for pool
                           * creation since the vdev's configuration has already
                           * been dirtied.
                           */
                          if (tx->tx_txg != TXG_INITIAL) {
                                  vdev_config_dirty(spa->spa_root_vdev);
                                  spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
                          }
                          spa_history_log_internal(spa, "set", tx,
                              "%s=%s", nvpair_name(elem), strval);
                          break;
                  case ZPOOL_PROP_COMPATIBILITY:
                          strval = fnvpair_value_string(elem);
                          if (spa->spa_compatibility != NULL)
                                  spa_strfree(spa->spa_compatibility);
                          spa->spa_compatibility = spa_strdup(strval);
                          /*
                           * Dirty the configuration on vdevs as above.
                           */
                          if (tx->tx_txg != TXG_INITIAL) {
                                  vdev_config_dirty(spa->spa_root_vdev);
                                  spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
                          }
  
                          spa_history_log_internal(spa, "set", tx,
                              "%s=%s", nvpair_name(elem), strval);
                          break;
  
                  default:
                          /*
                           * Set pool property values in the poolprops mos object.
                           */
                          if (spa->spa_pool_props_object == 0) {
                                  spa->spa_pool_props_object =
                                      zap_create_link(mos, DMU_OT_POOL_PROPS,
                                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_PROPS,
                                      tx);
                          }
  
                          /* normalize the property name */
                          propname = zpool_prop_to_name(prop);
                          proptype = zpool_prop_get_type(prop);
  
                          if (nvpair_type(elem) == DATA_TYPE_STRING) {
                                  ASSERT(proptype == PROP_TYPE_STRING);
                                  strval = fnvpair_value_string(elem);
                                  VERIFY0(zap_update(mos,
                                      spa->spa_pool_props_object, propname,
                                      1, strlen(strval) + 1, strval, tx));
                                  spa_history_log_internal(spa, "set", tx,
                                      "%s=%s", nvpair_name(elem), strval);
                          } else if (nvpair_type(elem) == DATA_TYPE_UINT64) {
                                  intval = fnvpair_value_uint64(elem);
  
                                  if (proptype == PROP_TYPE_INDEX) {
                                          const char *unused;
                                          VERIFY0(zpool_prop_index_to_string(
                                              prop, intval, &unused));
                                  }
                                  VERIFY0(zap_update(mos,
                                      spa->spa_pool_props_object, propname,
                                      8, 1, &intval, tx));
                                  spa_history_log_internal(spa, "set", tx,
                                      "%s=%lld", nvpair_name(elem),
                                      (longlong_t)intval);
  
                                  switch (prop) {
                                  case ZPOOL_PROP_DELEGATION:
                                          spa->spa_delegation = intval;
                                          break;
                                  case ZPOOL_PROP_BOOTFS:
                                          spa->spa_bootfs = intval;
                                          break;
                                  case ZPOOL_PROP_FAILUREMODE:
                                          spa->spa_failmode = intval;
                                          break;
                                  case ZPOOL_PROP_AUTOTRIM:
                                          spa->spa_autotrim = intval;
                                          spa_async_request(spa,
                                              SPA_ASYNC_AUTOTRIM_RESTART);
                                          break;
                                  case ZPOOL_PROP_AUTOEXPAND:
                                          spa->spa_autoexpand = intval;
                                          if (tx->tx_txg != TXG_INITIAL)
                                                  spa_async_request(spa,
                                                      SPA_ASYNC_AUTOEXPAND);
                                          break;
                                  case ZPOOL_PROP_MULTIHOST:
                                          spa->spa_multihost = intval;
                                          break;
                                  default:
                                          break;
                                  }
                          } else {
                                  ASSERT(0); /* not allowed */
                          }
                  }
  
          }
  
          mutex_exit(&spa->spa_props_lock);
  }
  
  /*
   * Perform one-time upgrade on-disk changes.  spa_version() does not
   * reflect the new version this txg, so there must be no changes this
   * txg to anything that the upgrade code depends on after it executes.
   * Therefore this must be called after dsl_pool_sync() does the sync
   * tasks.
   */
  static void
  spa_sync_upgrades(spa_t *spa, dmu_tx_t *tx)
  {
          if (spa_sync_pass(spa) != 1)
                  return;
  
          dsl_pool_t *dp = spa->spa_dsl_pool;
          rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
  
          if (spa->spa_ubsync.ub_version < SPA_VERSION_ORIGIN &&
              spa->spa_uberblock.ub_version >= SPA_VERSION_ORIGIN) {
                  dsl_pool_create_origin(dp, tx);
  
                  /* Keeping the origin open increases spa_minref */
                  spa->spa_minref += 3;
          }
  
          if (spa->spa_ubsync.ub_version < SPA_VERSION_NEXT_CLONES &&
              spa->spa_uberblock.ub_version >= SPA_VERSION_NEXT_CLONES) {
                  dsl_pool_upgrade_clones(dp, tx);
          }
  
          if (spa->spa_ubsync.ub_version < SPA_VERSION_DIR_CLONES &&
              spa->spa_uberblock.ub_version >= SPA_VERSION_DIR_CLONES) {
                  dsl_pool_upgrade_dir_clones(dp, tx);
  
                  /* Keeping the freedir open increases spa_minref */
                  spa->spa_minref += 3;
          }
  
          if (spa->spa_ubsync.ub_version < SPA_VERSION_FEATURES &&
              spa->spa_uberblock.ub_version >= SPA_VERSION_FEATURES) {
                  spa_feature_create_zap_objects(spa, tx);
          }
  
          /*
           * LZ4_COMPRESS feature's behaviour was changed to activate_on_enable
           * when possibility to use lz4 compression for metadata was added
           * Old pools that have this feature enabled must be upgraded to have
           * this feature active
           */
          if (spa->spa_uberblock.ub_version >= SPA_VERSION_FEATURES) {
                  boolean_t lz4_en = spa_feature_is_enabled(spa,
                      SPA_FEATURE_LZ4_COMPRESS);
                  boolean_t lz4_ac = spa_feature_is_active(spa,
                      SPA_FEATURE_LZ4_COMPRESS);
  
                  if (lz4_en && !lz4_ac)
                          spa_feature_incr(spa, SPA_FEATURE_LZ4_COMPRESS, tx);
          }
  
          /*
           * If we haven't written the salt, do so now.  Note that the
           * feature may not be activated yet, but that's fine since
           * the presence of this ZAP entry is backwards compatible.
           */
          if (zap_contains(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_CHECKSUM_SALT) == ENOENT) {
                  VERIFY0(zap_add(spa->spa_meta_objset,
                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CHECKSUM_SALT, 1,
                      sizeof (spa->spa_cksum_salt.zcs_bytes),
                      spa->spa_cksum_salt.zcs_bytes, tx));
          }
  
          rrw_exit(&dp->dp_config_rwlock, FTAG);
  }
  
  static void
  vdev_indirect_state_sync_verify(vdev_t *vd)
  {
          vdev_indirect_mapping_t *vim __maybe_unused = vd->vdev_indirect_mapping;
          vdev_indirect_births_t *vib __maybe_unused = vd->vdev_indirect_births;
  
          if (vd->vdev_ops == &vdev_indirect_ops) {
                  ASSERT(vim != NULL);
                  ASSERT(vib != NULL);
          }
  
          uint64_t obsolete_sm_object = 0;
          ASSERT0(vdev_obsolete_sm_object(vd, &obsolete_sm_object));
          if (obsolete_sm_object != 0) {
                  ASSERT(vd->vdev_obsolete_sm != NULL);
                  ASSERT(vd->vdev_removing ||
                      vd->vdev_ops == &vdev_indirect_ops);
                  ASSERT(vdev_indirect_mapping_num_entries(vim) > 0);
                  ASSERT(vdev_indirect_mapping_bytes_mapped(vim) > 0);
                  ASSERT3U(obsolete_sm_object, ==,
                      space_map_object(vd->vdev_obsolete_sm));
                  ASSERT3U(vdev_indirect_mapping_bytes_mapped(vim), >=,
                      space_map_allocated(vd->vdev_obsolete_sm));
          }
          ASSERT(vd->vdev_obsolete_segments != NULL);
  
          /*
           * Since frees / remaps to an indirect vdev can only
           * happen in syncing context, the obsolete segments
           * tree must be empty when we start syncing.
           */
          ASSERT0(range_tree_space(vd->vdev_obsolete_segments));
  }
  
  /*
   * Set the top-level vdev's max queue depth. Evaluate each top-level's
   * async write queue depth in case it changed. The max queue depth will
   * not change in the middle of syncing out this txg.
   */
  static void
  spa_sync_adjust_vdev_max_queue_depth(spa_t *spa)
  {
          ASSERT(spa_writeable(spa));
  
          vdev_t *rvd = spa->spa_root_vdev;
          uint32_t max_queue_depth = zfs_vdev_async_write_max_active *
              zfs_vdev_queue_depth_pct / 100;
          metaslab_class_t *normal = spa_normal_class(spa);
          metaslab_class_t *special = spa_special_class(spa);
          metaslab_class_t *dedup = spa_dedup_class(spa);
  
          uint64_t slots_per_allocator = 0;
          for (int c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *tvd = rvd->vdev_child[c];
  
                  metaslab_group_t *mg = tvd->vdev_mg;
                  if (mg == NULL || !metaslab_group_initialized(mg))
                          continue;
  
                  metaslab_class_t *mc = mg->mg_class;
                  if (mc != normal && mc != special && mc != dedup)
                          continue;
  
                  /*
                   * It is safe to do a lock-free check here because only async
                   * allocations look at mg_max_alloc_queue_depth, and async
                   * allocations all happen from spa_sync().
                   */
                  for (int i = 0; i < mg->mg_allocators; i++) {
                          ASSERT0(zfs_refcount_count(
                              &(mg->mg_allocator[i].mga_alloc_queue_depth)));
                  }
                  mg->mg_max_alloc_queue_depth = max_queue_depth;
  
                  for (int i = 0; i < mg->mg_allocators; i++) {
                          mg->mg_allocator[i].mga_cur_max_alloc_queue_depth =
                              zfs_vdev_def_queue_depth;
                  }
                  slots_per_allocator += zfs_vdev_def_queue_depth;
          }
  
          for (int i = 0; i < spa->spa_alloc_count; i++) {
                  ASSERT0(zfs_refcount_count(&normal->mc_allocator[i].
                      mca_alloc_slots));
                  ASSERT0(zfs_refcount_count(&special->mc_allocator[i].
                      mca_alloc_slots));
                  ASSERT0(zfs_refcount_count(&dedup->mc_allocator[i].
                      mca_alloc_slots));
                  normal->mc_allocator[i].mca_alloc_max_slots =
                      slots_per_allocator;
                  special->mc_allocator[i].mca_alloc_max_slots =
                      slots_per_allocator;
                  dedup->mc_allocator[i].mca_alloc_max_slots =
                      slots_per_allocator;
          }
          normal->mc_alloc_throttle_enabled = zio_dva_throttle_enabled;
          special->mc_alloc_throttle_enabled = zio_dva_throttle_enabled;
          dedup->mc_alloc_throttle_enabled = zio_dva_throttle_enabled;
  }
  
  static void
  spa_sync_condense_indirect(spa_t *spa, dmu_tx_t *tx)
  {
          ASSERT(spa_writeable(spa));
  
          vdev_t *rvd = spa->spa_root_vdev;
          for (int c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *vd = rvd->vdev_child[c];
                  vdev_indirect_state_sync_verify(vd);
  
                  if (vdev_indirect_should_condense(vd)) {
                          spa_condense_indirect_start_sync(vd, tx);
                          break;
                  }
          }
  }
  
  static void
  spa_sync_iterate_to_convergence(spa_t *spa, dmu_tx_t *tx)
  {
          objset_t *mos = spa->spa_meta_objset;
          dsl_pool_t *dp = spa->spa_dsl_pool;
          uint64_t txg = tx->tx_txg;
          bplist_t *free_bpl = &spa->spa_free_bplist[txg & TXG_MASK];
  
          do {
                  int pass = ++spa->spa_sync_pass;
  
                  spa_sync_config_object(spa, tx);
                  spa_sync_aux_dev(spa, &spa->spa_spares, tx,
                      ZPOOL_CONFIG_SPARES, DMU_POOL_SPARES);
                  spa_sync_aux_dev(spa, &spa->spa_l2cache, tx,
                      ZPOOL_CONFIG_L2CACHE, DMU_POOL_L2CACHE);
                  spa_errlog_sync(spa, txg);
                  dsl_pool_sync(dp, txg);
  
                  if (pass < zfs_sync_pass_deferred_free ||
                      spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)) {
                          /*
                           * If the log space map feature is active we don't
                           * care about deferred frees and the deferred bpobj
                           * as the log space map should effectively have the
                           * same results (i.e. appending only to one object).
                           */
                          spa_sync_frees(spa, free_bpl, tx);
                  } else {
                          /*
                           * We can not defer frees in pass 1, because
                           * we sync the deferred frees later in pass 1.
                           */
                          ASSERT3U(pass, >, 1);
                          bplist_iterate(free_bpl, bpobj_enqueue_alloc_cb,
                              &spa->spa_deferred_bpobj, tx);
                  }
  
                  ddt_sync(spa, txg);
                  dsl_scan_sync(dp, tx);
                  svr_sync(spa, tx);
                  spa_sync_upgrades(spa, tx);
  
                  spa_flush_metaslabs(spa, tx);
  
                  vdev_t *vd = NULL;
                  while ((vd = txg_list_remove(&spa->spa_vdev_txg_list, txg))
                      != NULL)
                          vdev_sync(vd, txg);
  
                  /*
                   * Note: We need to check if the MOS is dirty because we could
                   * have marked the MOS dirty without updating the uberblock
                   * (e.g. if we have sync tasks but no dirty user data). We need
                   * to check the uberblock's rootbp because it is updated if we
                   * have synced out dirty data (though in this case the MOS will
                   * most likely also be dirty due to second order effects, we
                   * don't want to rely on that here).
                   */
                  if (pass == 1 &&
                      spa->spa_uberblock.ub_rootbp.blk_birth < txg &&
                      !dmu_objset_is_dirty(mos, txg)) {
                          /*
                           * Nothing changed on the first pass, therefore this
                           * TXG is a no-op. Avoid syncing deferred frees, so
                           * that we can keep this TXG as a no-op.
                           */
                          ASSERT(txg_list_empty(&dp->dp_dirty_datasets, txg));
                          ASSERT(txg_list_empty(&dp->dp_dirty_dirs, txg));
                          ASSERT(txg_list_empty(&dp->dp_sync_tasks, txg));
                          ASSERT(txg_list_empty(&dp->dp_early_sync_tasks, txg));
                          break;
                  }
  
                  spa_sync_deferred_frees(spa, tx);
          } while (dmu_objset_is_dirty(mos, txg));
  }
  
  /*
   * Rewrite the vdev configuration (which includes the uberblock) to
   * commit the transaction group.
   *
   * If there are no dirty vdevs, we sync the uberblock to a few random
   * top-level vdevs that are known to be visible in the config cache
   * (see spa_vdev_add() for a complete description). If there *are* dirty
   * vdevs, sync the uberblock to all vdevs.
   */
  static void
  spa_sync_rewrite_vdev_config(spa_t *spa, dmu_tx_t *tx)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          uint64_t txg = tx->tx_txg;
  
          for (;;) {
                  int error = 0;
  
                  /*
                   * We hold SCL_STATE to prevent vdev open/close/etc.
                   * while we're attempting to write the vdev labels.
                   */
                  spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
  
                  if (list_is_empty(&spa->spa_config_dirty_list)) {
                          vdev_t *svd[SPA_SYNC_MIN_VDEVS] = { NULL };
                          int svdcount = 0;
                          int children = rvd->vdev_children;
                          int c0 = random_in_range(children);
  
                          for (int c = 0; c < children; c++) {
                                  vdev_t *vd =
                                      rvd->vdev_child[(c0 + c) % children];
  
                                  /* Stop when revisiting the first vdev */
                                  if (c > 0 && svd[0] == vd)
                                          break;
  
                                  if (vd->vdev_ms_array == 0 ||
                                      vd->vdev_islog ||
                                      !vdev_is_concrete(vd))
                                          continue;
  
                                  svd[svdcount++] = vd;
                                  if (svdcount == SPA_SYNC_MIN_VDEVS)
                                          break;
                          }
                          error = vdev_config_sync(svd, svdcount, txg);
                  } else {
                          error = vdev_config_sync(rvd->vdev_child,
                              rvd->vdev_children, txg);
                  }
  
                  if (error == 0)
                          spa->spa_last_synced_guid = rvd->vdev_guid;
  
                  spa_config_exit(spa, SCL_STATE, FTAG);
  
                  if (error == 0)
                          break;
                  zio_suspend(spa, NULL, ZIO_SUSPEND_IOERR);
                  zio_resume_wait(spa);
          }
  }
  
  /*
   * Sync the specified transaction group.  New blocks may be dirtied as
   * part of the process, so we iterate until it converges.
   */
  void
  spa_sync(spa_t *spa, uint64_t txg)
  {
          vdev_t *vd = NULL;
  
          VERIFY(spa_writeable(spa));
  
          /*
           * Wait for i/os issued in open context that need to complete
           * before this txg syncs.
           */
          (void) zio_wait(spa->spa_txg_zio[txg & TXG_MASK]);
          spa->spa_txg_zio[txg & TXG_MASK] = zio_root(spa, NULL, NULL,
              ZIO_FLAG_CANFAIL);
  
          /*
           * Lock out configuration changes.
           */
          spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
  
          spa->spa_syncing_txg = txg;
          spa->spa_sync_pass = 0;
  
          for (int i = 0; i < spa->spa_alloc_count; i++) {
                  mutex_enter(&spa->spa_allocs[i].spaa_lock);
                  VERIFY0(avl_numnodes(&spa->spa_allocs[i].spaa_tree));
                  mutex_exit(&spa->spa_allocs[i].spaa_lock);
          }
  
          /*
           * If there are any pending vdev state changes, convert them
           * into config changes that go out with this transaction group.
           */
          spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
          while (list_head(&spa->spa_state_dirty_list) != NULL) {
                  /*
                   * We need the write lock here because, for aux vdevs,
                   * calling vdev_config_dirty() modifies sav_config.
                   * This is ugly and will become unnecessary when we
                   * eliminate the aux vdev wart by integrating all vdevs
                   * into the root vdev tree.
                   */
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_WRITER);
                  while ((vd = list_head(&spa->spa_state_dirty_list)) != NULL) {
                          vdev_state_clean(vd);
                          vdev_config_dirty(vd);
                  }
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
          }
          spa_config_exit(spa, SCL_STATE, FTAG);
  
          dsl_pool_t *dp = spa->spa_dsl_pool;
          dmu_tx_t *tx = dmu_tx_create_assigned(dp, txg);
  
          spa->spa_sync_starttime = gethrtime();
          taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);
          spa->spa_deadman_tqid = taskq_dispatch_delay(system_delay_taskq,
              spa_deadman, spa, TQ_SLEEP, ddi_get_lbolt() +
              NSEC_TO_TICK(spa->spa_deadman_synctime));
  
          /*
           * If we are upgrading to SPA_VERSION_RAIDZ_DEFLATE this txg,
           * set spa_deflate if we have no raid-z vdevs.
           */
          if (spa->spa_ubsync.ub_version < SPA_VERSION_RAIDZ_DEFLATE &&
              spa->spa_uberblock.ub_version >= SPA_VERSION_RAIDZ_DEFLATE) {
                  vdev_t *rvd = spa->spa_root_vdev;
  
                  int i;
                  for (i = 0; i < rvd->vdev_children; i++) {
                          vd = rvd->vdev_child[i];
                          if (vd->vdev_deflate_ratio != SPA_MINBLOCKSIZE)
                                  break;
                  }
                  if (i == rvd->vdev_children) {
                          spa->spa_deflate = TRUE;
                          VERIFY0(zap_add(spa->spa_meta_objset,
                              DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_DEFLATE,
                              sizeof (uint64_t), 1, &spa->spa_deflate, tx));
                  }
          }
  
          spa_sync_adjust_vdev_max_queue_depth(spa);
  
          spa_sync_condense_indirect(spa, tx);
  
          spa_sync_iterate_to_convergence(spa, tx);
  
  #ifdef ZFS_DEBUG
          if (!list_is_empty(&spa->spa_config_dirty_list)) {
          /*
           * Make sure that the number of ZAPs for all the vdevs matches
           * the number of ZAPs in the per-vdev ZAP list. This only gets
           * called if the config is dirty; otherwise there may be
           * outstanding AVZ operations that weren't completed in
           * spa_sync_config_object.
           */
                  uint64_t all_vdev_zap_entry_count;
                  ASSERT0(zap_count(spa->spa_meta_objset,
                      spa->spa_all_vdev_zaps, &all_vdev_zap_entry_count));
                  ASSERT3U(vdev_count_verify_zaps(spa->spa_root_vdev), ==,
                      all_vdev_zap_entry_count);
          }
  #endif
  
          if (spa->spa_vdev_removal != NULL) {
                  ASSERT0(spa->spa_vdev_removal->svr_bytes_done[txg & TXG_MASK]);
          }
  
          spa_sync_rewrite_vdev_config(spa, tx);
          dmu_tx_commit(tx);
  
          taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);
          spa->spa_deadman_tqid = 0;
  
          /*
           * Clear the dirty config list.
           */
          while ((vd = list_head(&spa->spa_config_dirty_list)) != NULL)
                  vdev_config_clean(vd);
  
          /*
           * Now that the new config has synced transactionally,
           * let it become visible to the config cache.
           */
          if (spa->spa_config_syncing != NULL) {
                  spa_config_set(spa, spa->spa_config_syncing);
                  spa->spa_config_txg = txg;
                  spa->spa_config_syncing = NULL;
          }
  
          dsl_pool_sync_done(dp, txg);
  
          for (int i = 0; i < spa->spa_alloc_count; i++) {
                  mutex_enter(&spa->spa_allocs[i].spaa_lock);
                  VERIFY0(avl_numnodes(&spa->spa_allocs[i].spaa_tree));
                  mutex_exit(&spa->spa_allocs[i].spaa_lock);
          }
  
          /*
           * Update usable space statistics.
           */
          while ((vd = txg_list_remove(&spa->spa_vdev_txg_list, TXG_CLEAN(txg)))
              != NULL)
                  vdev_sync_done(vd, txg);
  
          metaslab_class_evict_old(spa->spa_normal_class, txg);
          metaslab_class_evict_old(spa->spa_log_class, txg);
  
          spa_sync_close_syncing_log_sm(spa);
  
          spa_update_dspace(spa);
  
          /*
           * It had better be the case that we didn't dirty anything
           * since vdev_config_sync().
           */
          ASSERT(txg_list_empty(&dp->dp_dirty_datasets, txg));
          ASSERT(txg_list_empty(&dp->dp_dirty_dirs, txg));
          ASSERT(txg_list_empty(&spa->spa_vdev_txg_list, txg));
  
          while (zfs_pause_spa_sync)
                  delay(1);
  
          spa->spa_sync_pass = 0;
  
          /*
           * Update the last synced uberblock here. We want to do this at
           * the end of spa_sync() so that consumers of spa_last_synced_txg()
           * will be guaranteed that all the processing associated with
           * that txg has been completed.
           */
          spa->spa_ubsync = spa->spa_uberblock;
          spa_config_exit(spa, SCL_CONFIG, FTAG);
  
          spa_handle_ignored_writes(spa);
  
          /*
           * If any async tasks have been requested, kick them off.
           */
          spa_async_dispatch(spa);
  }
  
  /*
   * Sync all pools.  We don't want to hold the namespace lock across these
   * operations, so we take a reference on the spa_t and drop the lock during the
   * sync.
   */
  void
  spa_sync_allpools(void)
  {
          spa_t *spa = NULL;
          mutex_enter(&spa_namespace_lock);
          while ((spa = spa_next(spa)) != NULL) {
                  if (spa_state(spa) != POOL_STATE_ACTIVE ||
                      !spa_writeable(spa) || spa_suspended(spa))
                          continue;
                  spa_open_ref(spa, FTAG);
                  mutex_exit(&spa_namespace_lock);
                  txg_wait_synced(spa_get_dsl(spa), 0);
                  mutex_enter(&spa_namespace_lock);
                  spa_close(spa, FTAG);
          }
          mutex_exit(&spa_namespace_lock);
  }
  
  /*
   * ==========================================================================
   * Miscellaneous routines
   * ==========================================================================
   */
  
  /*
   * Remove all pools in the system.
   */
  void
  spa_evict_all(void)
  {
          spa_t *spa;
  
          /*
           * Remove all cached state.  All pools should be closed now,
           * so every spa in the AVL tree should be unreferenced.
           */
          mutex_enter(&spa_namespace_lock);
          while ((spa = spa_next(NULL)) != NULL) {
                  /*
                   * Stop async tasks.  The async thread may need to detach
                   * a device that's been replaced, which requires grabbing
                   * spa_namespace_lock, so we must drop it here.
                   */
                  spa_open_ref(spa, FTAG);
                  mutex_exit(&spa_namespace_lock);
                  spa_async_suspend(spa);
                  mutex_enter(&spa_namespace_lock);
                  spa_close(spa, FTAG);
  
                  if (spa->spa_state != POOL_STATE_UNINITIALIZED) {
                          spa_unload(spa);
                          spa_deactivate(spa);
                  }
                  spa_remove(spa);
          }
          mutex_exit(&spa_namespace_lock);
  }
  
  vdev_t *
  spa_lookup_by_guid(spa_t *spa, uint64_t guid, boolean_t aux)
  {
          vdev_t *vd;
          int i;
  
          if ((vd = vdev_lookup_by_guid(spa->spa_root_vdev, guid)) != NULL)
                  return (vd);
  
          if (aux) {
                  for (i = 0; i < spa->spa_l2cache.sav_count; i++) {
                          vd = spa->spa_l2cache.sav_vdevs[i];
                          if (vd->vdev_guid == guid)
                                  return (vd);
                  }
  
                  for (i = 0; i < spa->spa_spares.sav_count; i++) {
                          vd = spa->spa_spares.sav_vdevs[i];
                          if (vd->vdev_guid == guid)
                                  return (vd);
                  }
          }
  
          return (NULL);
  }
  
  void
  spa_upgrade(spa_t *spa, uint64_t version)
  {
          ASSERT(spa_writeable(spa));
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
  
          /*
           * This should only be called for a non-faulted pool, and since a
           * future version would result in an unopenable pool, this shouldn't be
           * possible.
           */
          ASSERT(SPA_VERSION_IS_SUPPORTED(spa->spa_uberblock.ub_version));
          ASSERT3U(version, >=, spa->spa_uberblock.ub_version);
  
          spa->spa_uberblock.ub_version = version;
          vdev_config_dirty(spa->spa_root_vdev);
  
          spa_config_exit(spa, SCL_ALL, FTAG);
  
          txg_wait_synced(spa_get_dsl(spa), 0);
  }
  
  static boolean_t
  spa_has_aux_vdev(spa_t *spa, uint64_t guid, spa_aux_vdev_t *sav)
  {
          (void) spa;
          int i;
          uint64_t vdev_guid;
  
          for (i = 0; i < sav->sav_count; i++)
                  if (sav->sav_vdevs[i]->vdev_guid == guid)
                          return (B_TRUE);
  
          for (i = 0; i < sav->sav_npending; i++) {
                  if (nvlist_lookup_uint64(sav->sav_pending[i], ZPOOL_CONFIG_GUID,
                      &vdev_guid) == 0 && vdev_guid == guid)
                          return (B_TRUE);
          }
  
          return (B_FALSE);
  }
  
  boolean_t
  spa_has_l2cache(spa_t *spa, uint64_t guid)
  {
          return (spa_has_aux_vdev(spa, guid, &spa->spa_l2cache));
  }
  
  boolean_t
  spa_has_spare(spa_t *spa, uint64_t guid)
  {
          return (spa_has_aux_vdev(spa, guid, &spa->spa_spares));
  }
  
  /*
   * Check if a pool has an active shared spare device.
   * Note: reference count of an active spare is 2, as a spare and as a replace
   */
  static boolean_t
  spa_has_active_shared_spare(spa_t *spa)
  {
          int i, refcnt;
          uint64_t pool;
          spa_aux_vdev_t *sav = &spa->spa_spares;
  
          for (i = 0; i < sav->sav_count; i++) {
                  if (spa_spare_exists(sav->sav_vdevs[i]->vdev_guid, &pool,
                      &refcnt) && pool != 0ULL && pool == spa_guid(spa) &&
                      refcnt > 2)
                          return (B_TRUE);
          }
  
          return (B_FALSE);
  }
  
  uint64_t
  spa_total_metaslabs(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
  
          uint64_t m = 0;
          for (uint64_t c = 0; c < rvd->vdev_children; c++) {
                  vdev_t *vd = rvd->vdev_child[c];
                  if (!vdev_is_concrete(vd))
                          continue;
                  m += vd->vdev_ms_count;
          }
          return (m);
  }
  
  /*
   * Notify any waiting threads that some activity has switched from being in-
   * progress to not-in-progress so that the thread can wake up and determine
   * whether it is finished waiting.
   */
  void
  spa_notify_waiters(spa_t *spa)
  {
          /*
           * Acquiring spa_activities_lock here prevents the cv_broadcast from
           * happening between the waiting thread's check and cv_wait.
           */
          mutex_enter(&spa->spa_activities_lock);
          cv_broadcast(&spa->spa_activities_cv);
          mutex_exit(&spa->spa_activities_lock);
  }
  
  /*
   * Notify any waiting threads that the pool is exporting, and then block until
   * they are finished using the spa_t.
   */
  void
  spa_wake_waiters(spa_t *spa)
  {
          mutex_enter(&spa->spa_activities_lock);
          spa->spa_waiters_cancel = B_TRUE;
          cv_broadcast(&spa->spa_activities_cv);
          while (spa->spa_waiters != 0)
                  cv_wait(&spa->spa_waiters_cv, &spa->spa_activities_lock);
          spa->spa_waiters_cancel = B_FALSE;
          mutex_exit(&spa->spa_activities_lock);
  }
  
  /* Whether the vdev or any of its descendants are being initialized/trimmed. */
  static boolean_t
  spa_vdev_activity_in_progress_impl(vdev_t *vd, zpool_wait_activity_t activity)
  {
          spa_t *spa = vd->vdev_spa;
  
          ASSERT(spa_config_held(spa, SCL_CONFIG | SCL_STATE, RW_READER));
          ASSERT(MUTEX_HELD(&spa->spa_activities_lock));
          ASSERT(activity == ZPOOL_WAIT_INITIALIZE ||
              activity == ZPOOL_WAIT_TRIM);
  
          kmutex_t *lock = activity == ZPOOL_WAIT_INITIALIZE ?
              &vd->vdev_initialize_lock : &vd->vdev_trim_lock;
  
          mutex_exit(&spa->spa_activities_lock);
          mutex_enter(lock);
          mutex_enter(&spa->spa_activities_lock);
  
          boolean_t in_progress = (activity == ZPOOL_WAIT_INITIALIZE) ?
              (vd->vdev_initialize_state == VDEV_INITIALIZE_ACTIVE) :
              (vd->vdev_trim_state == VDEV_TRIM_ACTIVE);
          mutex_exit(lock);
  
          if (in_progress)
                  return (B_TRUE);
  
          for (int i = 0; i < vd->vdev_children; i++) {
                  if (spa_vdev_activity_in_progress_impl(vd->vdev_child[i],
                      activity))
                          return (B_TRUE);
          }
  
          return (B_FALSE);
  }
  
  /*
   * If use_guid is true, this checks whether the vdev specified by guid is
   * being initialized/trimmed. Otherwise, it checks whether any vdev in the pool
   * is being initialized/trimmed. The caller must hold the config lock and
   * spa_activities_lock.
   */
  static int
  spa_vdev_activity_in_progress(spa_t *spa, boolean_t use_guid, uint64_t guid,
      zpool_wait_activity_t activity, boolean_t *in_progress)
  {
          mutex_exit(&spa->spa_activities_lock);
          spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
          mutex_enter(&spa->spa_activities_lock);
  
          vdev_t *vd;
          if (use_guid) {
                  vd = spa_lookup_by_guid(spa, guid, B_FALSE);
                  if (vd == NULL || !vd->vdev_ops->vdev_op_leaf) {
                          spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                          return (EINVAL);
                  }
          } else {
                  vd = spa->spa_root_vdev;
          }
  
          *in_progress = spa_vdev_activity_in_progress_impl(vd, activity);
  
          spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
          return (0);
  }
  
  /*
   * Locking for waiting threads
   * ---------------------------
   *
   * Waiting threads need a way to check whether a given activity is in progress,
   * and then, if it is, wait for it to complete. Each activity will have some
   * in-memory representation of the relevant on-disk state which can be used to
   * determine whether or not the activity is in progress. The in-memory state and
   * the locking used to protect it will be different for each activity, and may
   * not be suitable for use with a cvar (e.g., some state is protected by the
   * config lock). To allow waiting threads to wait without any races, another
   * lock, spa_activities_lock, is used.
   *
   * When the state is checked, both the activity-specific lock (if there is one)
   * and spa_activities_lock are held. In some cases, the activity-specific lock
   * is acquired explicitly (e.g. the config lock). In others, the locking is
   * internal to some check (e.g. bpobj_is_empty). After checking, the waiting
   * thread releases the activity-specific lock and, if the activity is in
   * progress, then cv_waits using spa_activities_lock.
   *
   * The waiting thread is woken when another thread, one completing some
   * activity, updates the state of the activity and then calls
   * spa_notify_waiters, which will cv_broadcast. This 'completing' thread only
   * needs to hold its activity-specific lock when updating the state, and this
   * lock can (but doesn't have to) be dropped before calling spa_notify_waiters.
   *
   * Because spa_notify_waiters acquires spa_activities_lock before broadcasting,
   * and because it is held when the waiting thread checks the state of the
   * activity, it can never be the case that the completing thread both updates
   * the activity state and cv_broadcasts in between the waiting thread's check
   * and cv_wait. Thus, a waiting thread can never miss a wakeup.
   *
   * In order to prevent deadlock, when the waiting thread does its check, in some
   * cases it will temporarily drop spa_activities_lock in order to acquire the
   * activity-specific lock. The order in which spa_activities_lock and the
   * activity specific lock are acquired in the waiting thread is determined by
   * the order in which they are acquired in the completing thread; if the
   * completing thread calls spa_notify_waiters with the activity-specific lock
   * held, then the waiting thread must also acquire the activity-specific lock
   * first.
   */
  
  static int
  spa_activity_in_progress(spa_t *spa, zpool_wait_activity_t activity,
      boolean_t use_tag, uint64_t tag, boolean_t *in_progress)
  {
          int error = 0;
  
          ASSERT(MUTEX_HELD(&spa->spa_activities_lock));
  
          switch (activity) {
          case ZPOOL_WAIT_CKPT_DISCARD:
                  *in_progress =
                      (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT) &&
                      zap_contains(spa_meta_objset(spa),
                      DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT) ==
                      ENOENT);
                  break;
          case ZPOOL_WAIT_FREE:
                  *in_progress = ((spa_version(spa) >= SPA_VERSION_DEADLISTS &&
                      !bpobj_is_empty(&spa->spa_dsl_pool->dp_free_bpobj)) ||
                      spa_feature_is_active(spa, SPA_FEATURE_ASYNC_DESTROY) ||
                      spa_livelist_delete_check(spa));
                  break;
          case ZPOOL_WAIT_INITIALIZE:
          case ZPOOL_WAIT_TRIM:
                  error = spa_vdev_activity_in_progress(spa, use_tag, tag,
                      activity, in_progress);
                  break;
          case ZPOOL_WAIT_REPLACE:
                  mutex_exit(&spa->spa_activities_lock);
                  spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
                  mutex_enter(&spa->spa_activities_lock);
  
                  *in_progress = vdev_replace_in_progress(spa->spa_root_vdev);
                  spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                  break;
          case ZPOOL_WAIT_REMOVE:
                  *in_progress = (spa->spa_removing_phys.sr_state ==
                      DSS_SCANNING);
                  break;
          case ZPOOL_WAIT_RESILVER:
                  if ((*in_progress = vdev_rebuild_active(spa->spa_root_vdev)))
                          break;
                  zfs_fallthrough;
          case ZPOOL_WAIT_SCRUB:
          {
                  boolean_t scanning, paused, is_scrub;
                  dsl_scan_t *scn =  spa->spa_dsl_pool->dp_scan;
  
                  is_scrub = (scn->scn_phys.scn_func == POOL_SCAN_SCRUB);
                  scanning = (scn->scn_phys.scn_state == DSS_SCANNING);
                  paused = dsl_scan_is_paused_scrub(scn);
                  *in_progress = (scanning && !paused &&
                      is_scrub == (activity == ZPOOL_WAIT_SCRUB));
                  break;
          }
          default:
                  panic("unrecognized value for activity %d", activity);
          }
  
          return (error);
  }
  
  static int
  spa_wait_common(const char *pool, zpool_wait_activity_t activity,
      boolean_t use_tag, uint64_t tag, boolean_t *waited)
  {
          /*
           * The tag is used to distinguish between instances of an activity.
           * 'initialize' and 'trim' are the only activities that we use this for.
           * The other activities can only have a single instance in progress in a
           * pool at one time, making the tag unnecessary.
           *
           * There can be multiple devices being replaced at once, but since they
           * all finish once resilvering finishes, we don't bother keeping track
           * of them individually, we just wait for them all to finish.
           */
          if (use_tag && activity != ZPOOL_WAIT_INITIALIZE &&
              activity != ZPOOL_WAIT_TRIM)
                  return (EINVAL);
  
          if (activity < 0 || activity >= ZPOOL_WAIT_NUM_ACTIVITIES)
                  return (EINVAL);
  
          spa_t *spa;
          int error = spa_open(pool, &spa, FTAG);
          if (error != 0)
                  return (error);
  
          /*
           * Increment the spa's waiter count so that we can call spa_close and
           * still ensure that the spa_t doesn't get freed before this thread is
           * finished with it when the pool is exported. We want to call spa_close
           * before we start waiting because otherwise the additional ref would
           * prevent the pool from being exported or destroyed throughout the
           * potentially long wait.
           */
          mutex_enter(&spa->spa_activities_lock);
          spa->spa_waiters++;
          spa_close(spa, FTAG);
  
          *waited = B_FALSE;
          for (;;) {
                  boolean_t in_progress;
                  error = spa_activity_in_progress(spa, activity, use_tag, tag,
                      &in_progress);
  
                  if (error || !in_progress || spa->spa_waiters_cancel)
                          break;
  
                  *waited = B_TRUE;
  
                  if (cv_wait_sig(&spa->spa_activities_cv,
                      &spa->spa_activities_lock) == 0) {
                          error = EINTR;
                          break;
                  }
          }
  
          spa->spa_waiters--;
          cv_signal(&spa->spa_waiters_cv);
          mutex_exit(&spa->spa_activities_lock);
  
          return (error);
  }
  
  /*
   * Wait for a particular instance of the specified activity to complete, where
   * the instance is identified by 'tag'
   */
  int
  spa_wait_tag(const char *pool, zpool_wait_activity_t activity, uint64_t tag,
      boolean_t *waited)
  {
          return (spa_wait_common(pool, activity, B_TRUE, tag, waited));
  }
  
  /*
   * Wait for all instances of the specified activity complete
   */
  int
  spa_wait(const char *pool, zpool_wait_activity_t activity, boolean_t *waited)
  {
  
          return (spa_wait_common(pool, activity, B_FALSE, 0, waited));
  }
  
  sysevent_t *
  spa_event_create(spa_t *spa, vdev_t *vd, nvlist_t *hist_nvl, const char *name)
  {
          sysevent_t *ev = NULL;
  #ifdef _KERNEL
          nvlist_t *resource;
  
          resource = zfs_event_create(spa, vd, FM_SYSEVENT_CLASS, name, hist_nvl);
          if (resource) {
                  ev = kmem_alloc(sizeof (sysevent_t), KM_SLEEP);
                  ev->resource = resource;
          }
  #else
          (void) spa, (void) vd, (void) hist_nvl, (void) name;
  #endif
          return (ev);
  }
  
  void
  spa_event_post(sysevent_t *ev)
  {
  #ifdef _KERNEL
          if (ev) {
                  zfs_zevent_post(ev->resource, NULL, zfs_zevent_post_cb);
                  kmem_free(ev, sizeof (*ev));
          }
  #else
          (void) ev;
  #endif
  }
  
  /*
   * Post a zevent corresponding to the given sysevent.   The 'name' must be one
   * of the event definitions in sys/sysevent/eventdefs.h.  The payload will be
   * filled in from the spa and (optionally) the vdev.  This doesn't do anything
   * in the userland libzpool, as we don't want consumers to misinterpret ztest
   * or zdb as real changes.
   */
  void
  spa_event_notify(spa_t *spa, vdev_t *vd, nvlist_t *hist_nvl, const char *name)
  {
          spa_event_post(spa_event_create(spa, vd, hist_nvl, name));
  }
  
  /* state manipulation functions */
  EXPORT_SYMBOL(spa_open);
  EXPORT_SYMBOL(spa_open_rewind);
  EXPORT_SYMBOL(spa_get_stats);
  EXPORT_SYMBOL(spa_create);
  EXPORT_SYMBOL(spa_import);
  EXPORT_SYMBOL(spa_tryimport);
  EXPORT_SYMBOL(spa_destroy);
  EXPORT_SYMBOL(spa_export);
  EXPORT_SYMBOL(spa_reset);
  EXPORT_SYMBOL(spa_async_request);
  EXPORT_SYMBOL(spa_async_suspend);
  EXPORT_SYMBOL(spa_async_resume);
  EXPORT_SYMBOL(spa_inject_addref);
  EXPORT_SYMBOL(spa_inject_delref);
  EXPORT_SYMBOL(spa_scan_stat_init);
  EXPORT_SYMBOL(spa_scan_get_stats);
  
  /* device manipulation */
  EXPORT_SYMBOL(spa_vdev_add);
  EXPORT_SYMBOL(spa_vdev_attach);
  EXPORT_SYMBOL(spa_vdev_detach);
  EXPORT_SYMBOL(spa_vdev_setpath);
  EXPORT_SYMBOL(spa_vdev_setfru);
  EXPORT_SYMBOL(spa_vdev_split_mirror);
  
  /* spare statech is global across all pools) */
  EXPORT_SYMBOL(spa_spare_add);
  EXPORT_SYMBOL(spa_spare_remove);
  EXPORT_SYMBOL(spa_spare_exists);
  EXPORT_SYMBOL(spa_spare_activate);
  
  /* L2ARC statech is global across all pools) */
  EXPORT_SYMBOL(spa_l2cache_add);
  EXPORT_SYMBOL(spa_l2cache_remove);
  EXPORT_SYMBOL(spa_l2cache_exists);
  EXPORT_SYMBOL(spa_l2cache_activate);
  EXPORT_SYMBOL(spa_l2cache_drop);
  
  /* scanning */
  EXPORT_SYMBOL(spa_scan);
  EXPORT_SYMBOL(spa_scan_stop);
  
  /* spa syncing */
  EXPORT_SYMBOL(spa_sync); /* only for DMU use */
  EXPORT_SYMBOL(spa_sync_allpools);
  
  /* properties */
  EXPORT_SYMBOL(spa_prop_set);
  EXPORT_SYMBOL(spa_prop_get);
  EXPORT_SYMBOL(spa_prop_clear_bootfs);
  
  /* asynchronous event notification */
  EXPORT_SYMBOL(spa_event_notify);
  
  /* BEGIN CSTYLED */
 ZFS_MODULE_PARAM(zfs_spa, spa_, load_verify_shift, UINT, ZMOD_RW,
         "log2 fraction of arc that can be used by inflight I/Os when "
         "verifying pool during import");
 /* END CSTYLED */
 
 ZFS_MODULE_PARAM(zfs_spa, spa_, load_verify_metadata, INT, ZMOD_RW,
         "Set to traverse metadata on pool import");
 
 ZFS_MODULE_PARAM(zfs_spa, spa_, load_verify_data, INT, ZMOD_RW,
         "Set to traverse data on pool import");
 
 ZFS_MODULE_PARAM(zfs_spa, spa_, load_print_vdev_tree, INT, ZMOD_RW,
         "Print vdev tree to zfs_dbgmsg during pool import");
 
 ZFS_MODULE_PARAM(zfs_zio, zio_, taskq_batch_pct, UINT, ZMOD_RD,
         "Percentage of CPUs to run an IO worker thread");
 
 ZFS_MODULE_PARAM(zfs_zio, zio_, taskq_batch_tpq, UINT, ZMOD_RD,
         "Number of threads per IO worker taskqueue");
 
 /* BEGIN CSTYLED */
 ZFS_MODULE_PARAM(zfs, zfs_, max_missing_tvds, U64, ZMOD_RW,
         "Allow importing pool with up to this number of missing top-level "
         "vdevs (in read-only mode)");
 /* END CSTYLED */
 
 ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, zthr_pause, INT,
         ZMOD_RW, "Set the livelist condense zthr to pause");
 
 ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, sync_pause, INT,
         ZMOD_RW, "Set the livelist condense synctask to pause");
 
 /* BEGIN CSTYLED */
 ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, sync_cancel,
         INT, ZMOD_RW,
         "Whether livelist condensing was canceled in the synctask");
 
 ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, zthr_cancel,
         INT, ZMOD_RW,
         "Whether livelist condensing was canceled in the zthr function");
 
 ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, new_alloc, INT,
         ZMOD_RW,
         "Whether extra ALLOC blkptrs were added to a livelist entry while it "
         "was being condensed");
 /* END CSTYLED */