FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/spa_misc.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, 2019 by Delphix. All rights reserved.
     * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     * Copyright 2013 Saso Kiselkov. All rights reserved.
     * Copyright (c) 2017 Datto Inc.
     * Copyright (c) 2017, Intel Corporation.
     * Copyright (c) 2019, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/zfs_chksum.h>
    #include <sys/spa_impl.h>
    #include <sys/zio.h>
    #include <sys/zio_checksum.h>
    #include <sys/zio_compress.h>
    #include <sys/dmu.h>
    #include <sys/dmu_tx.h>
    #include <sys/zap.h>
    #include <sys/zil.h>
    #include <sys/vdev_impl.h>
    #include <sys/vdev_initialize.h>
    #include <sys/vdev_trim.h>
    #include <sys/vdev_file.h>
    #include <sys/vdev_raidz.h>
    #include <sys/metaslab.h>
    #include <sys/uberblock_impl.h>
    #include <sys/txg.h>
    #include <sys/avl.h>
    #include <sys/unique.h>
    #include <sys/dsl_pool.h>
    #include <sys/dsl_dir.h>
    #include <sys/dsl_prop.h>
    #include <sys/fm/util.h>
    #include <sys/dsl_scan.h>
    #include <sys/fs/zfs.h>
    #include <sys/metaslab_impl.h>
    #include <sys/arc.h>
    #include <sys/ddt.h>
    #include <sys/kstat.h>
    #include "zfs_prop.h"
    #include <sys/btree.h>
    #include <sys/zfeature.h>
    #include <sys/qat.h>
    #include <sys/zstd/zstd.h>
    
    /*
     * SPA locking
     *
     * There are three basic locks for managing spa_t structures:
     *
     * spa_namespace_lock (global mutex)
     *
     *      This lock must be acquired to do any of the following:
     *
     *              - Lookup a spa_t by name
     *              - Add or remove a spa_t from the namespace
     *              - Increase spa_refcount from non-zero
     *              - Check if spa_refcount is zero
     *              - Rename a spa_t
     *              - add/remove/attach/detach devices
     *              - Held for the duration of create/destroy/import/export
     *
     *      It does not need to handle recursion.  A create or destroy may
     *      reference objects (files or zvols) in other pools, but by
     *      definition they must have an existing reference, and will never need
     *      to lookup a spa_t by name.
     *
     * spa_refcount (per-spa zfs_refcount_t protected by mutex)
     *
     *      This reference count keep track of any active users of the spa_t.  The
     *      spa_t cannot be destroyed or freed while this is non-zero.  Internally,
     *      the refcount is never really 'zero' - opening a pool implicitly keeps
     *      some references in the DMU.  Internally we check against spa_minref, but
     *      present the image of a zero/non-zero value to consumers.
     *
     * spa_config_lock[] (per-spa array of rwlocks)
     *
    *      This protects the spa_t from config changes, and must be held in
    *      the following circumstances:
    *
    *              - RW_READER to perform I/O to the spa
    *              - RW_WRITER to change the vdev config
    *
    * The locking order is fairly straightforward:
    *
    *              spa_namespace_lock      ->      spa_refcount
    *
    *      The namespace lock must be acquired to increase the refcount from 0
    *      or to check if it is zero.
    *
    *              spa_refcount            ->      spa_config_lock[]
    *
    *      There must be at least one valid reference on the spa_t to acquire
    *      the config lock.
    *
    *              spa_namespace_lock      ->      spa_config_lock[]
    *
    *      The namespace lock must always be taken before the config lock.
    *
    *
    * The spa_namespace_lock can be acquired directly and is globally visible.
    *
    * The namespace is manipulated using the following functions, all of which
    * require the spa_namespace_lock to be held.
    *
    *      spa_lookup()            Lookup a spa_t by name.
    *
    *      spa_add()               Create a new spa_t in the namespace.
    *
    *      spa_remove()            Remove a spa_t from the namespace.  This also
    *                              frees up any memory associated with the spa_t.
    *
    *      spa_next()              Returns the next spa_t in the system, or the
    *                              first if NULL is passed.
    *
    *      spa_evict_all()         Shutdown and remove all spa_t structures in
    *                              the system.
    *
    *      spa_guid_exists()       Determine whether a pool/device guid exists.
    *
    * The spa_refcount is manipulated using the following functions:
    *
    *      spa_open_ref()          Adds a reference to the given spa_t.  Must be
    *                              called with spa_namespace_lock held if the
    *                              refcount is currently zero.
    *
    *      spa_close()             Remove a reference from the spa_t.  This will
    *                              not free the spa_t or remove it from the
    *                              namespace.  No locking is required.
    *
    *      spa_refcount_zero()     Returns true if the refcount is currently
    *                              zero.  Must be called with spa_namespace_lock
    *                              held.
    *
    * The spa_config_lock[] is an array of rwlocks, ordered as follows:
    * SCL_CONFIG > SCL_STATE > SCL_ALLOC > SCL_ZIO > SCL_FREE > SCL_VDEV.
    * spa_config_lock[] is manipulated with spa_config_{enter,exit,held}().
    *
    * To read the configuration, it suffices to hold one of these locks as reader.
    * To modify the configuration, you must hold all locks as writer.  To modify
    * vdev state without altering the vdev tree's topology (e.g. online/offline),
    * you must hold SCL_STATE and SCL_ZIO as writer.
    *
    * We use these distinct config locks to avoid recursive lock entry.
    * For example, spa_sync() (which holds SCL_CONFIG as reader) induces
    * block allocations (SCL_ALLOC), which may require reading space maps
    * from disk (dmu_read() -> zio_read() -> SCL_ZIO).
    *
    * The spa config locks cannot be normal rwlocks because we need the
    * ability to hand off ownership.  For example, SCL_ZIO is acquired
    * by the issuing thread and later released by an interrupt thread.
    * They do, however, obey the usual write-wanted semantics to prevent
    * writer (i.e. system administrator) starvation.
    *
    * The lock acquisition rules are as follows:
    *
    * SCL_CONFIG
    *      Protects changes to the vdev tree topology, such as vdev
    *      add/remove/attach/detach.  Protects the dirty config list
    *      (spa_config_dirty_list) and the set of spares and l2arc devices.
    *
    * SCL_STATE
    *      Protects changes to pool state and vdev state, such as vdev
    *      online/offline/fault/degrade/clear.  Protects the dirty state list
    *      (spa_state_dirty_list) and global pool state (spa_state).
    *
    * SCL_ALLOC
    *      Protects changes to metaslab groups and classes.
    *      Held as reader by metaslab_alloc() and metaslab_claim().
    *
    * SCL_ZIO
    *      Held by bp-level zios (those which have no io_vd upon entry)
    *      to prevent changes to the vdev tree.  The bp-level zio implicitly
    *      protects all of its vdev child zios, which do not hold SCL_ZIO.
    *
    * SCL_FREE
    *      Protects changes to metaslab groups and classes.
    *      Held as reader by metaslab_free().  SCL_FREE is distinct from
    *      SCL_ALLOC, and lower than SCL_ZIO, so that we can safely free
    *      blocks in zio_done() while another i/o that holds either
    *      SCL_ALLOC or SCL_ZIO is waiting for this i/o to complete.
    *
    * SCL_VDEV
    *      Held as reader to prevent changes to the vdev tree during trivial
    *      inquiries such as bp_get_dsize().  SCL_VDEV is distinct from the
    *      other locks, and lower than all of them, to ensure that it's safe
    *      to acquire regardless of caller context.
    *
    * In addition, the following rules apply:
    *
    * (a)  spa_props_lock protects pool properties, spa_config and spa_config_list.
    *      The lock ordering is SCL_CONFIG > spa_props_lock.
    *
    * (b)  I/O operations on leaf vdevs.  For any zio operation that takes
    *      an explicit vdev_t argument -- such as zio_ioctl(), zio_read_phys(),
    *      or zio_write_phys() -- the caller must ensure that the config cannot
    *      cannot change in the interim, and that the vdev cannot be reopened.
    *      SCL_STATE as reader suffices for both.
    *
    * The vdev configuration is protected by spa_vdev_enter() / spa_vdev_exit().
    *
    *      spa_vdev_enter()        Acquire the namespace lock and the config lock
    *                              for writing.
    *
    *      spa_vdev_exit()         Release the config lock, wait for all I/O
    *                              to complete, sync the updated configs to the
    *                              cache, and release the namespace lock.
    *
    * vdev state is protected by spa_vdev_state_enter() / spa_vdev_state_exit().
    * Like spa_vdev_enter/exit, these are convenience wrappers -- the actual
    * locking is, always, based on spa_namespace_lock and spa_config_lock[].
    */
   
   static avl_tree_t spa_namespace_avl;
   kmutex_t spa_namespace_lock;
   static kcondvar_t spa_namespace_cv;
   static const int spa_max_replication_override = SPA_DVAS_PER_BP;
   
   static kmutex_t spa_spare_lock;
   static avl_tree_t spa_spare_avl;
   static kmutex_t spa_l2cache_lock;
   static avl_tree_t spa_l2cache_avl;
   
   spa_mode_t spa_mode_global = SPA_MODE_UNINIT;
   
   #ifdef ZFS_DEBUG
   /*
    * Everything except dprintf, set_error, spa, and indirect_remap is on
    * by default in debug builds.
    */
   int zfs_flags = ~(ZFS_DEBUG_DPRINTF | ZFS_DEBUG_SET_ERROR |
       ZFS_DEBUG_INDIRECT_REMAP);
   #else
   int zfs_flags = 0;
   #endif
   
   /*
    * zfs_recover can be set to nonzero to attempt to recover from
    * otherwise-fatal errors, typically caused by on-disk corruption.  When
    * set, calls to zfs_panic_recover() will turn into warning messages.
    * This should only be used as a last resort, as it typically results
    * in leaked space, or worse.
    */
   int zfs_recover = B_FALSE;
   
   /*
    * If destroy encounters an EIO while reading metadata (e.g. indirect
    * blocks), space referenced by the missing metadata can not be freed.
    * Normally this causes the background destroy to become "stalled", as
    * it is unable to make forward progress.  While in this stalled state,
    * all remaining space to free from the error-encountering filesystem is
    * "temporarily leaked".  Set this flag to cause it to ignore the EIO,
    * permanently leak the space from indirect blocks that can not be read,
    * and continue to free everything else that it can.
    *
    * The default, "stalling" behavior is useful if the storage partially
    * fails (i.e. some but not all i/os fail), and then later recovers.  In
    * this case, we will be able to continue pool operations while it is
    * partially failed, and when it recovers, we can continue to free the
    * space, with no leaks.  However, note that this case is actually
    * fairly rare.
    *
    * Typically pools either (a) fail completely (but perhaps temporarily,
    * e.g. a top-level vdev going offline), or (b) have localized,
    * permanent errors (e.g. disk returns the wrong data due to bit flip or
    * firmware bug).  In case (a), this setting does not matter because the
    * pool will be suspended and the sync thread will not be able to make
    * forward progress regardless.  In case (b), because the error is
    * permanent, the best we can do is leak the minimum amount of space,
    * which is what setting this flag will do.  Therefore, it is reasonable
    * for this flag to normally be set, but we chose the more conservative
    * approach of not setting it, so that there is no possibility of
    * leaking space in the "partial temporary" failure case.
    */
   int zfs_free_leak_on_eio = B_FALSE;
   
   /*
    * Expiration time in milliseconds. This value has two meanings. First it is
    * used to determine when the spa_deadman() logic should fire. By default the
    * spa_deadman() will fire if spa_sync() has not completed in 600 seconds.
    * Secondly, the value determines if an I/O is considered "hung". Any I/O that
    * has not completed in zfs_deadman_synctime_ms is considered "hung" resulting
    * in one of three behaviors controlled by zfs_deadman_failmode.
    */
   uint64_t zfs_deadman_synctime_ms = 600000UL;  /* 10 min. */
   
   /*
    * This value controls the maximum amount of time zio_wait() will block for an
    * outstanding IO.  By default this is 300 seconds at which point the "hung"
    * behavior will be applied as described for zfs_deadman_synctime_ms.
    */
   uint64_t zfs_deadman_ziotime_ms = 300000UL;  /* 5 min. */
   
   /*
    * Check time in milliseconds. This defines the frequency at which we check
    * for hung I/O.
    */
   uint64_t zfs_deadman_checktime_ms = 60000UL;  /* 1 min. */
   
   /*
    * By default the deadman is enabled.
    */
   int zfs_deadman_enabled = B_TRUE;
   
   /*
    * Controls the behavior of the deadman when it detects a "hung" I/O.
    * Valid values are zfs_deadman_failmode=<wait|continue|panic>.
    *
    * wait     - Wait for the "hung" I/O (default)
    * continue - Attempt to recover from a "hung" I/O
    * panic    - Panic the system
    */
   const char *zfs_deadman_failmode = "wait";
   
   /*
    * The worst case is single-sector max-parity RAID-Z blocks, in which
    * case the space requirement is exactly (VDEV_RAIDZ_MAXPARITY + 1)
    * times the size; so just assume that.  Add to this the fact that
    * we can have up to 3 DVAs per bp, and one more factor of 2 because
    * the block may be dittoed with up to 3 DVAs by ddt_sync().  All together,
    * the worst case is:
    *     (VDEV_RAIDZ_MAXPARITY + 1) * SPA_DVAS_PER_BP * 2 == 24
    */
   uint_t spa_asize_inflation = 24;
   
   /*
    * Normally, we don't allow the last 3.2% (1/(2^spa_slop_shift)) of space in
    * the pool to be consumed (bounded by spa_max_slop).  This ensures that we
    * don't run the pool completely out of space, due to unaccounted changes (e.g.
    * to the MOS).  It also limits the worst-case time to allocate space.  If we
    * have less than this amount of free space, most ZPL operations (e.g.  write,
    * create) will return ENOSPC.  The ZIL metaslabs (spa_embedded_log_class) are
    * also part of this 3.2% of space which can't be consumed by normal writes;
    * the slop space "proper" (spa_get_slop_space()) is decreased by the embedded
    * log space.
    *
    * Certain operations (e.g. file removal, most administrative actions) can
    * use half the slop space.  They will only return ENOSPC if less than half
    * the slop space is free.  Typically, once the pool has less than the slop
    * space free, the user will use these operations to free up space in the pool.
    * These are the operations that call dsl_pool_adjustedsize() with the netfree
    * argument set to TRUE.
    *
    * Operations that are almost guaranteed to free up space in the absence of
    * a pool checkpoint can use up to three quarters of the slop space
    * (e.g zfs destroy).
    *
    * A very restricted set of operations are always permitted, regardless of
    * the amount of free space.  These are the operations that call
    * dsl_sync_task(ZFS_SPACE_CHECK_NONE). If these operations result in a net
    * increase in the amount of space used, it is possible to run the pool
    * completely out of space, causing it to be permanently read-only.
    *
    * Note that on very small pools, the slop space will be larger than
    * 3.2%, in an effort to have it be at least spa_min_slop (128MB),
    * but we never allow it to be more than half the pool size.
    *
    * Further, on very large pools, the slop space will be smaller than
    * 3.2%, to avoid reserving much more space than we actually need; bounded
    * by spa_max_slop (128GB).
    *
    * See also the comments in zfs_space_check_t.
    */
   uint_t spa_slop_shift = 5;
   static const uint64_t spa_min_slop = 128ULL * 1024 * 1024;
   static const uint64_t spa_max_slop = 128ULL * 1024 * 1024 * 1024;
   static const int spa_allocators = 4;
   
   
   void
   spa_load_failed(spa_t *spa, const char *fmt, ...)
   {
           va_list adx;
           char buf[256];
   
           va_start(adx, fmt);
           (void) vsnprintf(buf, sizeof (buf), fmt, adx);
           va_end(adx);
   
           zfs_dbgmsg("spa_load(%s, config %s): FAILED: %s", spa->spa_name,
               spa->spa_trust_config ? "trusted" : "untrusted", buf);
   }
   
   void
   spa_load_note(spa_t *spa, const char *fmt, ...)
   {
           va_list adx;
           char buf[256];
   
           va_start(adx, fmt);
           (void) vsnprintf(buf, sizeof (buf), fmt, adx);
           va_end(adx);
   
           zfs_dbgmsg("spa_load(%s, config %s): %s", spa->spa_name,
               spa->spa_trust_config ? "trusted" : "untrusted", buf);
   }
   
   /*
    * By default dedup and user data indirects land in the special class
    */
   static int zfs_ddt_data_is_special = B_TRUE;
   static int zfs_user_indirect_is_special = B_TRUE;
   
   /*
    * The percentage of special class final space reserved for metadata only.
    * Once we allocate 100 - zfs_special_class_metadata_reserve_pct we only
    * let metadata into the class.
    */
   static uint_t zfs_special_class_metadata_reserve_pct = 25;
   
   /*
    * ==========================================================================
    * SPA config locking
    * ==========================================================================
    */
   static void
   spa_config_lock_init(spa_t *spa)
   {
           for (int i = 0; i < SCL_LOCKS; i++) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   mutex_init(&scl->scl_lock, NULL, MUTEX_DEFAULT, NULL);
                   cv_init(&scl->scl_cv, NULL, CV_DEFAULT, NULL);
                   scl->scl_writer = NULL;
                   scl->scl_write_wanted = 0;
                   scl->scl_count = 0;
           }
   }
   
   static void
   spa_config_lock_destroy(spa_t *spa)
   {
           for (int i = 0; i < SCL_LOCKS; i++) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   mutex_destroy(&scl->scl_lock);
                   cv_destroy(&scl->scl_cv);
                   ASSERT(scl->scl_writer == NULL);
                   ASSERT(scl->scl_write_wanted == 0);
                   ASSERT(scl->scl_count == 0);
           }
   }
   
   int
   spa_config_tryenter(spa_t *spa, int locks, const void *tag, krw_t rw)
   {
           for (int i = 0; i < SCL_LOCKS; i++) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   if (!(locks & (1 << i)))
                           continue;
                   mutex_enter(&scl->scl_lock);
                   if (rw == RW_READER) {
                           if (scl->scl_writer || scl->scl_write_wanted) {
                                   mutex_exit(&scl->scl_lock);
                                   spa_config_exit(spa, locks & ((1 << i) - 1),
                                       tag);
                                   return (0);
                           }
                   } else {
                           ASSERT(scl->scl_writer != curthread);
                           if (scl->scl_count != 0) {
                                   mutex_exit(&scl->scl_lock);
                                   spa_config_exit(spa, locks & ((1 << i) - 1),
                                       tag);
                                   return (0);
                           }
                           scl->scl_writer = curthread;
                   }
                   scl->scl_count++;
                   mutex_exit(&scl->scl_lock);
           }
           return (1);
   }
   
   void
   spa_config_enter(spa_t *spa, int locks, const void *tag, krw_t rw)
   {
           (void) tag;
           int wlocks_held = 0;
   
           ASSERT3U(SCL_LOCKS, <, sizeof (wlocks_held) * NBBY);
   
           for (int i = 0; i < SCL_LOCKS; i++) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   if (scl->scl_writer == curthread)
                           wlocks_held |= (1 << i);
                   if (!(locks & (1 << i)))
                           continue;
                   mutex_enter(&scl->scl_lock);
                   if (rw == RW_READER) {
                           while (scl->scl_writer || scl->scl_write_wanted) {
                                   cv_wait(&scl->scl_cv, &scl->scl_lock);
                           }
                   } else {
                           ASSERT(scl->scl_writer != curthread);
                           while (scl->scl_count != 0) {
                                   scl->scl_write_wanted++;
                                   cv_wait(&scl->scl_cv, &scl->scl_lock);
                                   scl->scl_write_wanted--;
                           }
                           scl->scl_writer = curthread;
                   }
                   scl->scl_count++;
                   mutex_exit(&scl->scl_lock);
           }
           ASSERT3U(wlocks_held, <=, locks);
   }
   
   void
   spa_config_exit(spa_t *spa, int locks, const void *tag)
   {
           (void) tag;
           for (int i = SCL_LOCKS - 1; i >= 0; i--) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   if (!(locks & (1 << i)))
                           continue;
                   mutex_enter(&scl->scl_lock);
                   ASSERT(scl->scl_count > 0);
                   if (--scl->scl_count == 0) {
                           ASSERT(scl->scl_writer == NULL ||
                               scl->scl_writer == curthread);
                           scl->scl_writer = NULL; /* OK in either case */
                           cv_broadcast(&scl->scl_cv);
                   }
                   mutex_exit(&scl->scl_lock);
           }
   }
   
   int
   spa_config_held(spa_t *spa, int locks, krw_t rw)
   {
           int locks_held = 0;
   
           for (int i = 0; i < SCL_LOCKS; i++) {
                   spa_config_lock_t *scl = &spa->spa_config_lock[i];
                   if (!(locks & (1 << i)))
                           continue;
                   if ((rw == RW_READER && scl->scl_count != 0) ||
                       (rw == RW_WRITER && scl->scl_writer == curthread))
                           locks_held |= 1 << i;
           }
   
           return (locks_held);
   }
   
   /*
    * ==========================================================================
    * SPA namespace functions
    * ==========================================================================
    */
   
   /*
    * Lookup the named spa_t in the AVL tree.  The spa_namespace_lock must be held.
    * Returns NULL if no matching spa_t is found.
    */
   spa_t *
   spa_lookup(const char *name)
   {
           static spa_t search;    /* spa_t is large; don't allocate on stack */
           spa_t *spa;
           avl_index_t where;
           char *cp;
   
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           (void) strlcpy(search.spa_name, name, sizeof (search.spa_name));
   
           /*
            * If it's a full dataset name, figure out the pool name and
            * just use that.
            */
           cp = strpbrk(search.spa_name, "/@#");
           if (cp != NULL)
                   *cp = '\0';
   
           spa = avl_find(&spa_namespace_avl, &search, &where);
   
           return (spa);
   }
   
   /*
    * Fires when spa_sync has not completed within zfs_deadman_synctime_ms.
    * If the zfs_deadman_enabled flag is set then it inspects all vdev queues
    * looking for potentially hung I/Os.
    */
   void
   spa_deadman(void *arg)
   {
           spa_t *spa = arg;
   
           /* Disable the deadman if the pool is suspended. */
           if (spa_suspended(spa))
                   return;
   
           zfs_dbgmsg("slow spa_sync: started %llu seconds ago, calls %llu",
               (gethrtime() - spa->spa_sync_starttime) / NANOSEC,
               (u_longlong_t)++spa->spa_deadman_calls);
           if (zfs_deadman_enabled)
                   vdev_deadman(spa->spa_root_vdev, FTAG);
   
           spa->spa_deadman_tqid = taskq_dispatch_delay(system_delay_taskq,
               spa_deadman, spa, TQ_SLEEP, ddi_get_lbolt() +
               MSEC_TO_TICK(zfs_deadman_checktime_ms));
   }
   
   static int
   spa_log_sm_sort_by_txg(const void *va, const void *vb)
   {
           const spa_log_sm_t *a = va;
           const spa_log_sm_t *b = vb;
   
           return (TREE_CMP(a->sls_txg, b->sls_txg));
   }
   
   /*
    * Create an uninitialized spa_t with the given name.  Requires
    * spa_namespace_lock.  The caller must ensure that the spa_t doesn't already
    * exist by calling spa_lookup() first.
    */
   spa_t *
   spa_add(const char *name, nvlist_t *config, const char *altroot)
   {
           spa_t *spa;
           spa_config_dirent_t *dp;
   
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           spa = kmem_zalloc(sizeof (spa_t), KM_SLEEP);
   
           mutex_init(&spa->spa_async_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_errlist_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_errlog_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_evicting_os_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_history_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_proc_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_props_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_cksum_tmpls_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_scrub_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_suspend_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_vdev_top_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_feat_stats_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_flushed_ms_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&spa->spa_activities_lock, NULL, MUTEX_DEFAULT, NULL);
   
           cv_init(&spa->spa_async_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_evicting_os_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_proc_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_scrub_io_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_suspend_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_activities_cv, NULL, CV_DEFAULT, NULL);
           cv_init(&spa->spa_waiters_cv, NULL, CV_DEFAULT, NULL);
   
           for (int t = 0; t < TXG_SIZE; t++)
                   bplist_create(&spa->spa_free_bplist[t]);
   
           (void) strlcpy(spa->spa_name, name, sizeof (spa->spa_name));
           spa->spa_state = POOL_STATE_UNINITIALIZED;
           spa->spa_freeze_txg = UINT64_MAX;
           spa->spa_final_txg = UINT64_MAX;
           spa->spa_load_max_txg = UINT64_MAX;
           spa->spa_proc = &p0;
           spa->spa_proc_state = SPA_PROC_NONE;
           spa->spa_trust_config = B_TRUE;
           spa->spa_hostid = zone_get_hostid(NULL);
   
           spa->spa_deadman_synctime = MSEC2NSEC(zfs_deadman_synctime_ms);
           spa->spa_deadman_ziotime = MSEC2NSEC(zfs_deadman_ziotime_ms);
           spa_set_deadman_failmode(spa, zfs_deadman_failmode);
   
           zfs_refcount_create(&spa->spa_refcount);
           spa_config_lock_init(spa);
           spa_stats_init(spa);
   
           avl_add(&spa_namespace_avl, spa);
   
           /*
            * Set the alternate root, if there is one.
            */
           if (altroot)
                   spa->spa_root = spa_strdup(altroot);
   
           spa->spa_alloc_count = spa_allocators;
           spa->spa_allocs = kmem_zalloc(spa->spa_alloc_count *
               sizeof (spa_alloc_t), KM_SLEEP);
           for (int i = 0; i < spa->spa_alloc_count; i++) {
                   mutex_init(&spa->spa_allocs[i].spaa_lock, NULL, MUTEX_DEFAULT,
                       NULL);
                   avl_create(&spa->spa_allocs[i].spaa_tree, zio_bookmark_compare,
                       sizeof (zio_t), offsetof(zio_t, io_alloc_node));
           }
           avl_create(&spa->spa_metaslabs_by_flushed, metaslab_sort_by_flushed,
               sizeof (metaslab_t), offsetof(metaslab_t, ms_spa_txg_node));
           avl_create(&spa->spa_sm_logs_by_txg, spa_log_sm_sort_by_txg,
               sizeof (spa_log_sm_t), offsetof(spa_log_sm_t, sls_node));
           list_create(&spa->spa_log_summary, sizeof (log_summary_entry_t),
               offsetof(log_summary_entry_t, lse_node));
   
           /*
            * Every pool starts with the default cachefile
            */
           list_create(&spa->spa_config_list, sizeof (spa_config_dirent_t),
               offsetof(spa_config_dirent_t, scd_link));
   
           dp = kmem_zalloc(sizeof (spa_config_dirent_t), KM_SLEEP);
           dp->scd_path = altroot ? NULL : spa_strdup(spa_config_path);
           list_insert_head(&spa->spa_config_list, dp);
   
           VERIFY(nvlist_alloc(&spa->spa_load_info, NV_UNIQUE_NAME,
               KM_SLEEP) == 0);
   
           if (config != NULL) {
                   nvlist_t *features;
   
                   if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_FEATURES_FOR_READ,
                       &features) == 0) {
                           VERIFY(nvlist_dup(features, &spa->spa_label_features,
                               0) == 0);
                   }
   
                   VERIFY(nvlist_dup(config, &spa->spa_config, 0) == 0);
           }
   
           if (spa->spa_label_features == NULL) {
                   VERIFY(nvlist_alloc(&spa->spa_label_features, NV_UNIQUE_NAME,
                       KM_SLEEP) == 0);
           }
   
           spa->spa_min_ashift = INT_MAX;
           spa->spa_max_ashift = 0;
           spa->spa_min_alloc = INT_MAX;
   
           /* Reset cached value */
           spa->spa_dedup_dspace = ~0ULL;
   
           /*
            * As a pool is being created, treat all features as disabled by
            * setting SPA_FEATURE_DISABLED for all entries in the feature
            * refcount cache.
            */
           for (int i = 0; i < SPA_FEATURES; i++) {
                   spa->spa_feat_refcount_cache[i] = SPA_FEATURE_DISABLED;
           }
   
           list_create(&spa->spa_leaf_list, sizeof (vdev_t),
               offsetof(vdev_t, vdev_leaf_node));
   
           return (spa);
   }
   
   /*
    * Removes a spa_t from the namespace, freeing up any memory used.  Requires
    * spa_namespace_lock.  This is called only after the spa_t has been closed and
    * deactivated.
    */
   void
   spa_remove(spa_t *spa)
   {
           spa_config_dirent_t *dp;
   
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
           ASSERT(spa_state(spa) == POOL_STATE_UNINITIALIZED);
           ASSERT3U(zfs_refcount_count(&spa->spa_refcount), ==, 0);
           ASSERT0(spa->spa_waiters);
   
           nvlist_free(spa->spa_config_splitting);
   
           avl_remove(&spa_namespace_avl, spa);
           cv_broadcast(&spa_namespace_cv);
   
           if (spa->spa_root)
                   spa_strfree(spa->spa_root);
   
           while ((dp = list_head(&spa->spa_config_list)) != NULL) {
                   list_remove(&spa->spa_config_list, dp);
                   if (dp->scd_path != NULL)
                           spa_strfree(dp->scd_path);
                   kmem_free(dp, sizeof (spa_config_dirent_t));
           }
   
           for (int i = 0; i < spa->spa_alloc_count; i++) {
                   avl_destroy(&spa->spa_allocs[i].spaa_tree);
                   mutex_destroy(&spa->spa_allocs[i].spaa_lock);
           }
           kmem_free(spa->spa_allocs, spa->spa_alloc_count *
               sizeof (spa_alloc_t));
   
           avl_destroy(&spa->spa_metaslabs_by_flushed);
           avl_destroy(&spa->spa_sm_logs_by_txg);
           list_destroy(&spa->spa_log_summary);
           list_destroy(&spa->spa_config_list);
           list_destroy(&spa->spa_leaf_list);
   
           nvlist_free(spa->spa_label_features);
           nvlist_free(spa->spa_load_info);
           nvlist_free(spa->spa_feat_stats);
           spa_config_set(spa, NULL);
   
           zfs_refcount_destroy(&spa->spa_refcount);
   
           spa_stats_destroy(spa);
           spa_config_lock_destroy(spa);
   
           for (int t = 0; t < TXG_SIZE; t++)
                   bplist_destroy(&spa->spa_free_bplist[t]);
   
           zio_checksum_templates_free(spa);
   
           cv_destroy(&spa->spa_async_cv);
           cv_destroy(&spa->spa_evicting_os_cv);
           cv_destroy(&spa->spa_proc_cv);
           cv_destroy(&spa->spa_scrub_io_cv);
           cv_destroy(&spa->spa_suspend_cv);
           cv_destroy(&spa->spa_activities_cv);
           cv_destroy(&spa->spa_waiters_cv);
   
           mutex_destroy(&spa->spa_flushed_ms_lock);
           mutex_destroy(&spa->spa_async_lock);
           mutex_destroy(&spa->spa_errlist_lock);
           mutex_destroy(&spa->spa_errlog_lock);
           mutex_destroy(&spa->spa_evicting_os_lock);
           mutex_destroy(&spa->spa_history_lock);
           mutex_destroy(&spa->spa_proc_lock);
           mutex_destroy(&spa->spa_props_lock);
           mutex_destroy(&spa->spa_cksum_tmpls_lock);
           mutex_destroy(&spa->spa_scrub_lock);
           mutex_destroy(&spa->spa_suspend_lock);
           mutex_destroy(&spa->spa_vdev_top_lock);
           mutex_destroy(&spa->spa_feat_stats_lock);
           mutex_destroy(&spa->spa_activities_lock);
   
           kmem_free(spa, sizeof (spa_t));
   }
   
   /*
    * Given a pool, return the next pool in the namespace, or NULL if there is
    * none.  If 'prev' is NULL, return the first pool.
    */
   spa_t *
   spa_next(spa_t *prev)
   {
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           if (prev)
                   return (AVL_NEXT(&spa_namespace_avl, prev));
           else
                   return (avl_first(&spa_namespace_avl));
   }
   
   /*
    * ==========================================================================
    * SPA refcount functions
    * ==========================================================================
    */
   
   /*
    * Add a reference to the given spa_t.  Must have at least one reference, or
    * have the namespace lock held.
    */
   void
   spa_open_ref(spa_t *spa, const void *tag)
   {
           ASSERT(zfs_refcount_count(&spa->spa_refcount) >= spa->spa_minref ||
               MUTEX_HELD(&spa_namespace_lock));
           (void) zfs_refcount_add(&spa->spa_refcount, tag);
   }
   
   /*
    * Remove a reference to the given spa_t.  Must have at least one reference, or
    * have the namespace lock held.
    */
   void
   spa_close(spa_t *spa, const void *tag)
   {
           ASSERT(zfs_refcount_count(&spa->spa_refcount) > spa->spa_minref ||
               MUTEX_HELD(&spa_namespace_lock));
           (void) zfs_refcount_remove(&spa->spa_refcount, tag);
   }
   
   /*
    * Remove a reference to the given spa_t held by a dsl dir that is
    * being asynchronously released.  Async releases occur from a taskq
    * performing eviction of dsl datasets and dirs.  The namespace lock
    * isn't held and the hold by the object being evicted may contribute to
    * spa_minref (e.g. dataset or directory released during pool export),
    * so the asserts in spa_close() do not apply.
    */
   void
   spa_async_close(spa_t *spa, const void *tag)
   {
           (void) zfs_refcount_remove(&spa->spa_refcount, tag);
   }
   
   /*
    * Check to see if the spa refcount is zero.  Must be called with
    * spa_namespace_lock held.  We really compare against spa_minref, which is the
    * number of references acquired when opening a pool
    */
   boolean_t
   spa_refcount_zero(spa_t *spa)
   {
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           return (zfs_refcount_count(&spa->spa_refcount) == spa->spa_minref);
   }
   
   /*
    * ==========================================================================
    * SPA spare and l2cache tracking
    * ==========================================================================
    */
   
   /*
    * Hot spares and cache devices are tracked using the same code below,
    * for 'auxiliary' devices.
    */
   
   typedef struct spa_aux {
           uint64_t        aux_guid;
           uint64_t        aux_pool;
           avl_node_t      aux_avl;
           int             aux_count;
   } spa_aux_t;
   
   static inline int
   spa_aux_compare(const void *a, const void *b)
   {
           const spa_aux_t *sa = (const spa_aux_t *)a;
           const spa_aux_t *sb = (const spa_aux_t *)b;
   
           return (TREE_CMP(sa->aux_guid, sb->aux_guid));
   }
   
   static void
   spa_aux_add(vdev_t *vd, avl_tree_t *avl)
   {
           avl_index_t where;
           spa_aux_t search;
           spa_aux_t *aux;
   
           search.aux_guid = vd->vdev_guid;
           if ((aux = avl_find(avl, &search, &where)) != NULL) {
                   aux->aux_count++;
           } else {
                   aux = kmem_zalloc(sizeof (spa_aux_t), KM_SLEEP);
                   aux->aux_guid = vd->vdev_guid;
                   aux->aux_count = 1;
                   avl_insert(avl, aux, where);
           }
   }
   
   static void
   spa_aux_remove(vdev_t *vd, avl_tree_t *avl)
   {
           spa_aux_t search;
           spa_aux_t *aux;
           avl_index_t where;
   
           search.aux_guid = vd->vdev_guid;
           aux = avl_find(avl, &search, &where);
   
           ASSERT(aux != NULL);
   
           if (--aux->aux_count == 0) {
                   avl_remove(avl, aux);
                   kmem_free(aux, sizeof (spa_aux_t));
           } else if (aux->aux_pool == spa_guid(vd->vdev_spa)) {
                   aux->aux_pool = 0ULL;
           }
   }
   
   static boolean_t
   spa_aux_exists(uint64_t guid, uint64_t *pool, int *refcnt, avl_tree_t *avl)
   {
           spa_aux_t search, *found;
   
           search.aux_guid = guid;
           found = avl_find(avl, &search, NULL);
   
           if (pool) {
                  if (found)
                          *pool = found->aux_pool;
                  else
                          *pool = 0ULL;
          }
  
          if (refcnt) {
                  if (found)
                          *refcnt = found->aux_count;
                  else
                          *refcnt = 0;
          }
  
          return (found != NULL);
  }
  
  static void
  spa_aux_activate(vdev_t *vd, avl_tree_t *avl)
  {
          spa_aux_t search, *found;
          avl_index_t where;
  
          search.aux_guid = vd->vdev_guid;
          found = avl_find(avl, &search, &where);
          ASSERT(found != NULL);
          ASSERT(found->aux_pool == 0ULL);
  
          found->aux_pool = spa_guid(vd->vdev_spa);
  }
  
  /*
   * Spares are tracked globally due to the following constraints:
   *
   *      - A spare may be part of multiple pools.
   *      - A spare may be added to a pool even if it's actively in use within
   *        another pool.
   *      - A spare in use in any pool can only be the source of a replacement if
   *        the target is a spare in the same pool.
   *
   * We keep track of all spares on the system through the use of a reference
   * counted AVL tree.  When a vdev is added as a spare, or used as a replacement
   * spare, then we bump the reference count in the AVL tree.  In addition, we set
   * the 'vdev_isspare' member to indicate that the device is a spare (active or
   * inactive).  When a spare is made active (used to replace a device in the
   * pool), we also keep track of which pool its been made a part of.
   *
   * The 'spa_spare_lock' protects the AVL tree.  These functions are normally
   * called under the spa_namespace lock as part of vdev reconfiguration.  The
   * separate spare lock exists for the status query path, which does not need to
   * be completely consistent with respect to other vdev configuration changes.
   */
  
  static int
  spa_spare_compare(const void *a, const void *b)
  {
          return (spa_aux_compare(a, b));
  }
  
  void
  spa_spare_add(vdev_t *vd)
  {
          mutex_enter(&spa_spare_lock);
          ASSERT(!vd->vdev_isspare);
          spa_aux_add(vd, &spa_spare_avl);
          vd->vdev_isspare = B_TRUE;
          mutex_exit(&spa_spare_lock);
  }
  
  void
  spa_spare_remove(vdev_t *vd)
  {
          mutex_enter(&spa_spare_lock);
          ASSERT(vd->vdev_isspare);
          spa_aux_remove(vd, &spa_spare_avl);
          vd->vdev_isspare = B_FALSE;
          mutex_exit(&spa_spare_lock);
  }
  
  boolean_t
  spa_spare_exists(uint64_t guid, uint64_t *pool, int *refcnt)
  {
          boolean_t found;
  
          mutex_enter(&spa_spare_lock);
          found = spa_aux_exists(guid, pool, refcnt, &spa_spare_avl);
          mutex_exit(&spa_spare_lock);
  
          return (found);
  }
  
  void
  spa_spare_activate(vdev_t *vd)
  {
          mutex_enter(&spa_spare_lock);
          ASSERT(vd->vdev_isspare);
          spa_aux_activate(vd, &spa_spare_avl);
          mutex_exit(&spa_spare_lock);
  }
  
  /*
   * Level 2 ARC devices are tracked globally for the same reasons as spares.
   * Cache devices currently only support one pool per cache device, and so
   * for these devices the aux reference count is currently unused beyond 1.
   */
  
  static int
  spa_l2cache_compare(const void *a, const void *b)
  {
          return (spa_aux_compare(a, b));
  }
  
  void
  spa_l2cache_add(vdev_t *vd)
  {
          mutex_enter(&spa_l2cache_lock);
          ASSERT(!vd->vdev_isl2cache);
          spa_aux_add(vd, &spa_l2cache_avl);
          vd->vdev_isl2cache = B_TRUE;
          mutex_exit(&spa_l2cache_lock);
  }
  
  void
  spa_l2cache_remove(vdev_t *vd)
  {
          mutex_enter(&spa_l2cache_lock);
          ASSERT(vd->vdev_isl2cache);
          spa_aux_remove(vd, &spa_l2cache_avl);
          vd->vdev_isl2cache = B_FALSE;
          mutex_exit(&spa_l2cache_lock);
  }
  
  boolean_t
  spa_l2cache_exists(uint64_t guid, uint64_t *pool)
  {
          boolean_t found;
  
          mutex_enter(&spa_l2cache_lock);
          found = spa_aux_exists(guid, pool, NULL, &spa_l2cache_avl);
          mutex_exit(&spa_l2cache_lock);
  
          return (found);
  }
  
  void
  spa_l2cache_activate(vdev_t *vd)
  {
          mutex_enter(&spa_l2cache_lock);
          ASSERT(vd->vdev_isl2cache);
          spa_aux_activate(vd, &spa_l2cache_avl);
          mutex_exit(&spa_l2cache_lock);
  }
  
  /*
   * ==========================================================================
   * SPA vdev locking
   * ==========================================================================
   */
  
  /*
   * Lock the given spa_t for the purpose of adding or removing a vdev.
   * Grabs the global spa_namespace_lock plus the spa config lock for writing.
   * It returns the next transaction group for the spa_t.
   */
  uint64_t
  spa_vdev_enter(spa_t *spa)
  {
          mutex_enter(&spa->spa_vdev_top_lock);
          mutex_enter(&spa_namespace_lock);
  
          vdev_autotrim_stop_all(spa);
  
          return (spa_vdev_config_enter(spa));
  }
  
  /*
   * The same as spa_vdev_enter() above but additionally takes the guid of
   * the vdev being detached.  When there is a rebuild in process it will be
   * suspended while the vdev tree is modified then resumed by spa_vdev_exit().
   * The rebuild is canceled if only a single child remains after the detach.
   */
  uint64_t
  spa_vdev_detach_enter(spa_t *spa, uint64_t guid)
  {
          mutex_enter(&spa->spa_vdev_top_lock);
          mutex_enter(&spa_namespace_lock);
  
          vdev_autotrim_stop_all(spa);
  
          if (guid != 0) {
                  vdev_t *vd = spa_lookup_by_guid(spa, guid, B_FALSE);
                  if (vd) {
                          vdev_rebuild_stop_wait(vd->vdev_top);
                  }
          }
  
          return (spa_vdev_config_enter(spa));
  }
  
  /*
   * Internal implementation for spa_vdev_enter().  Used when a vdev
   * operation requires multiple syncs (i.e. removing a device) while
   * keeping the spa_namespace_lock held.
   */
  uint64_t
  spa_vdev_config_enter(spa_t *spa)
  {
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          spa_config_enter(spa, SCL_ALL, spa, RW_WRITER);
  
          return (spa_last_synced_txg(spa) + 1);
  }
  
  /*
   * Used in combination with spa_vdev_config_enter() to allow the syncing
   * of multiple transactions without releasing the spa_namespace_lock.
   */
  void
  spa_vdev_config_exit(spa_t *spa, vdev_t *vd, uint64_t txg, int error,
      const char *tag)
  {
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          int config_changed = B_FALSE;
  
          ASSERT(txg > spa_last_synced_txg(spa));
  
          spa->spa_pending_vdev = NULL;
  
          /*
           * Reassess the DTLs.
           */
          vdev_dtl_reassess(spa->spa_root_vdev, 0, 0, B_FALSE, B_FALSE);
  
          if (error == 0 && !list_is_empty(&spa->spa_config_dirty_list)) {
                  config_changed = B_TRUE;
                  spa->spa_config_generation++;
          }
  
          /*
           * Verify the metaslab classes.
           */
          ASSERT(metaslab_class_validate(spa_normal_class(spa)) == 0);
          ASSERT(metaslab_class_validate(spa_log_class(spa)) == 0);
          ASSERT(metaslab_class_validate(spa_embedded_log_class(spa)) == 0);
          ASSERT(metaslab_class_validate(spa_special_class(spa)) == 0);
          ASSERT(metaslab_class_validate(spa_dedup_class(spa)) == 0);
  
          spa_config_exit(spa, SCL_ALL, spa);
  
          /*
           * Panic the system if the specified tag requires it.  This
           * is useful for ensuring that configurations are updated
           * transactionally.
           */
          if (zio_injection_enabled)
                  zio_handle_panic_injection(spa, tag, 0);
  
          /*
           * Note: this txg_wait_synced() is important because it ensures
           * that there won't be more than one config change per txg.
           * This allows us to use the txg as the generation number.
           */
          if (error == 0)
                  txg_wait_synced(spa->spa_dsl_pool, txg);
  
          if (vd != NULL) {
                  ASSERT(!vd->vdev_detached || vd->vdev_dtl_sm == NULL);
                  if (vd->vdev_ops->vdev_op_leaf) {
                          mutex_enter(&vd->vdev_initialize_lock);
                          vdev_initialize_stop(vd, VDEV_INITIALIZE_CANCELED,
                              NULL);
                          mutex_exit(&vd->vdev_initialize_lock);
  
                          mutex_enter(&vd->vdev_trim_lock);
                          vdev_trim_stop(vd, VDEV_TRIM_CANCELED, NULL);
                          mutex_exit(&vd->vdev_trim_lock);
                  }
  
                  /*
                   * The vdev may be both a leaf and top-level device.
                   */
                  vdev_autotrim_stop_wait(vd);
  
                  spa_config_enter(spa, SCL_STATE_ALL, spa, RW_WRITER);
                  vdev_free(vd);
                  spa_config_exit(spa, SCL_STATE_ALL, spa);
          }
  
          /*
           * If the config changed, update the config cache.
           */
          if (config_changed)
                  spa_write_cachefile(spa, B_FALSE, B_TRUE, B_TRUE);
  }
  
  /*
   * Unlock the spa_t after adding or removing a vdev.  Besides undoing the
   * locking of spa_vdev_enter(), we also want make sure the transactions have
   * synced to disk, and then update the global configuration cache with the new
   * information.
   */
  int
  spa_vdev_exit(spa_t *spa, vdev_t *vd, uint64_t txg, int error)
  {
          vdev_autotrim_restart(spa);
          vdev_rebuild_restart(spa);
  
          spa_vdev_config_exit(spa, vd, txg, error, FTAG);
          mutex_exit(&spa_namespace_lock);
          mutex_exit(&spa->spa_vdev_top_lock);
  
          return (error);
  }
  
  /*
   * Lock the given spa_t for the purpose of changing vdev state.
   */
  void
  spa_vdev_state_enter(spa_t *spa, int oplocks)
  {
          int locks = SCL_STATE_ALL | oplocks;
  
          /*
           * Root pools may need to read of the underlying devfs filesystem
           * when opening up a vdev.  Unfortunately if we're holding the
           * SCL_ZIO lock it will result in a deadlock when we try to issue
           * the read from the root filesystem.  Instead we "prefetch"
           * the associated vnodes that we need prior to opening the
           * underlying devices and cache them so that we can prevent
           * any I/O when we are doing the actual open.
           */
          if (spa_is_root(spa)) {
                  int low = locks & ~(SCL_ZIO - 1);
                  int high = locks & ~low;
  
                  spa_config_enter(spa, high, spa, RW_WRITER);
                  vdev_hold(spa->spa_root_vdev);
                  spa_config_enter(spa, low, spa, RW_WRITER);
          } else {
                  spa_config_enter(spa, locks, spa, RW_WRITER);
          }
          spa->spa_vdev_locks = locks;
  }
  
  int
  spa_vdev_state_exit(spa_t *spa, vdev_t *vd, int error)
  {
          boolean_t config_changed = B_FALSE;
          vdev_t *vdev_top;
  
          if (vd == NULL || vd == spa->spa_root_vdev) {
                  vdev_top = spa->spa_root_vdev;
          } else {
                  vdev_top = vd->vdev_top;
          }
  
          if (vd != NULL || error == 0)
                  vdev_dtl_reassess(vdev_top, 0, 0, B_FALSE, B_FALSE);
  
          if (vd != NULL) {
                  if (vd != spa->spa_root_vdev)
                          vdev_state_dirty(vdev_top);
  
                  config_changed = B_TRUE;
                  spa->spa_config_generation++;
          }
  
          if (spa_is_root(spa))
                  vdev_rele(spa->spa_root_vdev);
  
          ASSERT3U(spa->spa_vdev_locks, >=, SCL_STATE_ALL);
          spa_config_exit(spa, spa->spa_vdev_locks, spa);
  
          /*
           * If anything changed, wait for it to sync.  This ensures that,
           * from the system administrator's perspective, zpool(8) commands
           * are synchronous.  This is important for things like zpool offline:
           * when the command completes, you expect no further I/O from ZFS.
           */
          if (vd != NULL)
                  txg_wait_synced(spa->spa_dsl_pool, 0);
  
          /*
           * If the config changed, update the config cache.
           */
          if (config_changed) {
                  mutex_enter(&spa_namespace_lock);
                  spa_write_cachefile(spa, B_FALSE, B_TRUE, B_FALSE);
                  mutex_exit(&spa_namespace_lock);
          }
  
          return (error);
  }
  
  /*
   * ==========================================================================
   * Miscellaneous functions
   * ==========================================================================
   */
  
  void
  spa_activate_mos_feature(spa_t *spa, const char *feature, dmu_tx_t *tx)
  {
          if (!nvlist_exists(spa->spa_label_features, feature)) {
                  fnvlist_add_boolean(spa->spa_label_features, feature);
                  /*
                   * When we are creating the pool (tx_txg==TXG_INITIAL), we can't
                   * dirty the vdev config because lock SCL_CONFIG is not held.
                   * Thankfully, in this case we don't need to dirty the config
                   * because it will be written out anyway when we finish
                   * creating the pool.
                   */
                  if (tx->tx_txg != TXG_INITIAL)
                          vdev_config_dirty(spa->spa_root_vdev);
          }
  }
  
  void
  spa_deactivate_mos_feature(spa_t *spa, const char *feature)
  {
          if (nvlist_remove_all(spa->spa_label_features, feature) == 0)
                  vdev_config_dirty(spa->spa_root_vdev);
  }
  
  /*
   * Return the spa_t associated with given pool_guid, if it exists.  If
   * device_guid is non-zero, determine whether the pool exists *and* contains
   * a device with the specified device_guid.
   */
  spa_t *
  spa_by_guid(uint64_t pool_guid, uint64_t device_guid)
  {
          spa_t *spa;
          avl_tree_t *t = &spa_namespace_avl;
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          for (spa = avl_first(t); spa != NULL; spa = AVL_NEXT(t, spa)) {
                  if (spa->spa_state == POOL_STATE_UNINITIALIZED)
                          continue;
                  if (spa->spa_root_vdev == NULL)
                          continue;
                  if (spa_guid(spa) == pool_guid) {
                          if (device_guid == 0)
                                  break;
  
                          if (vdev_lookup_by_guid(spa->spa_root_vdev,
                              device_guid) != NULL)
                                  break;
  
                          /*
                           * Check any devices we may be in the process of adding.
                           */
                          if (spa->spa_pending_vdev) {
                                  if (vdev_lookup_by_guid(spa->spa_pending_vdev,
                                      device_guid) != NULL)
                                          break;
                          }
                  }
          }
  
          return (spa);
  }
  
  /*
   * Determine whether a pool with the given pool_guid exists.
   */
  boolean_t
  spa_guid_exists(uint64_t pool_guid, uint64_t device_guid)
  {
          return (spa_by_guid(pool_guid, device_guid) != NULL);
  }
  
  char *
  spa_strdup(const char *s)
  {
          size_t len;
          char *new;
  
          len = strlen(s);
          new = kmem_alloc(len + 1, KM_SLEEP);
          memcpy(new, s, len + 1);
  
          return (new);
  }
  
  void
  spa_strfree(char *s)
  {
          kmem_free(s, strlen(s) + 1);
  }
  
  uint64_t
  spa_generate_guid(spa_t *spa)
  {
          uint64_t guid;
  
          if (spa != NULL) {
                  do {
                          (void) random_get_pseudo_bytes((void *)&guid,
                              sizeof (guid));
                  } while (guid == 0 || spa_guid_exists(spa_guid(spa), guid));
          } else {
                  do {
                          (void) random_get_pseudo_bytes((void *)&guid,
                              sizeof (guid));
                  } while (guid == 0 || spa_guid_exists(guid, 0));
          }
  
          return (guid);
  }
  
  void
  snprintf_blkptr(char *buf, size_t buflen, const blkptr_t *bp)
  {
          char type[256];
          const char *checksum = NULL;
          const char *compress = NULL;
  
          if (bp != NULL) {
                  if (BP_GET_TYPE(bp) & DMU_OT_NEWTYPE) {
                          dmu_object_byteswap_t bswap =
                              DMU_OT_BYTESWAP(BP_GET_TYPE(bp));
                          (void) snprintf(type, sizeof (type), "bswap %s %s",
                              DMU_OT_IS_METADATA(BP_GET_TYPE(bp)) ?
                              "metadata" : "data",
                              dmu_ot_byteswap[bswap].ob_name);
                  } else {
                          (void) strlcpy(type, dmu_ot[BP_GET_TYPE(bp)].ot_name,
                              sizeof (type));
                  }
                  if (!BP_IS_EMBEDDED(bp)) {
                          checksum =
                              zio_checksum_table[BP_GET_CHECKSUM(bp)].ci_name;
                  }
                  compress = zio_compress_table[BP_GET_COMPRESS(bp)].ci_name;
          }
  
          SNPRINTF_BLKPTR(kmem_scnprintf, ' ', buf, buflen, bp, type, checksum,
              compress);
  }
  
  void
  spa_freeze(spa_t *spa)
  {
          uint64_t freeze_txg = 0;
  
          spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
          if (spa->spa_freeze_txg == UINT64_MAX) {
                  freeze_txg = spa_last_synced_txg(spa) + TXG_SIZE;
                  spa->spa_freeze_txg = freeze_txg;
          }
          spa_config_exit(spa, SCL_ALL, FTAG);
          if (freeze_txg != 0)
                  txg_wait_synced(spa_get_dsl(spa), freeze_txg);
  }
  
  void
  zfs_panic_recover(const char *fmt, ...)
  {
          va_list adx;
  
          va_start(adx, fmt);
          vcmn_err(zfs_recover ? CE_WARN : CE_PANIC, fmt, adx);
          va_end(adx);
  }
  
  /*
   * This is a stripped-down version of strtoull, suitable only for converting
   * lowercase hexadecimal numbers that don't overflow.
   */
  uint64_t
  zfs_strtonum(const char *str, char **nptr)
  {
          uint64_t val = 0;
          char c;
          int digit;
  
          while ((c = *str) != '\0') {
                  if (c >= '' && c <= '9')
                          digit = c - '';
                  else if (c >= 'a' && c <= 'f')
                          digit = 10 + c - 'a';
                  else
                          break;
  
                  val *= 16;
                  val += digit;
  
                  str++;
          }
  
          if (nptr)
                  *nptr = (char *)str;
  
          return (val);
  }
  
  void
  spa_activate_allocation_classes(spa_t *spa, dmu_tx_t *tx)
  {
          /*
           * We bump the feature refcount for each special vdev added to the pool
           */
          ASSERT(spa_feature_is_enabled(spa, SPA_FEATURE_ALLOCATION_CLASSES));
          spa_feature_incr(spa, SPA_FEATURE_ALLOCATION_CLASSES, tx);
  }
  
  /*
   * ==========================================================================
   * Accessor functions
   * ==========================================================================
   */
  
  boolean_t
  spa_shutting_down(spa_t *spa)
  {
          return (spa->spa_async_suspended);
  }
  
  dsl_pool_t *
  spa_get_dsl(spa_t *spa)
  {
          return (spa->spa_dsl_pool);
  }
  
  boolean_t
  spa_is_initializing(spa_t *spa)
  {
          return (spa->spa_is_initializing);
  }
  
  boolean_t
  spa_indirect_vdevs_loaded(spa_t *spa)
  {
          return (spa->spa_indirect_vdevs_loaded);
  }
  
  blkptr_t *
  spa_get_rootblkptr(spa_t *spa)
  {
          return (&spa->spa_ubsync.ub_rootbp);
  }
  
  void
  spa_set_rootblkptr(spa_t *spa, const blkptr_t *bp)
  {
          spa->spa_uberblock.ub_rootbp = *bp;
  }
  
  void
  spa_altroot(spa_t *spa, char *buf, size_t buflen)
  {
          if (spa->spa_root == NULL)
                  buf[0] = '\0';
          else
                  (void) strlcpy(buf, spa->spa_root, buflen);
  }
  
  uint32_t
  spa_sync_pass(spa_t *spa)
  {
          return (spa->spa_sync_pass);
  }
  
  char *
  spa_name(spa_t *spa)
  {
          return (spa->spa_name);
  }
  
  uint64_t
  spa_guid(spa_t *spa)
  {
          dsl_pool_t *dp = spa_get_dsl(spa);
          uint64_t guid;
  
          /*
           * If we fail to parse the config during spa_load(), we can go through
           * the error path (which posts an ereport) and end up here with no root
           * vdev.  We stash the original pool guid in 'spa_config_guid' to handle
           * this case.
           */
          if (spa->spa_root_vdev == NULL)
                  return (spa->spa_config_guid);
  
          guid = spa->spa_last_synced_guid != 0 ?
              spa->spa_last_synced_guid : spa->spa_root_vdev->vdev_guid;
  
          /*
           * Return the most recently synced out guid unless we're
           * in syncing context.
           */
          if (dp && dsl_pool_sync_context(dp))
                  return (spa->spa_root_vdev->vdev_guid);
          else
                  return (guid);
  }
  
  uint64_t
  spa_load_guid(spa_t *spa)
  {
          /*
           * This is a GUID that exists solely as a reference for the
           * purposes of the arc.  It is generated at load time, and
           * is never written to persistent storage.
           */
          return (spa->spa_load_guid);
  }
  
  uint64_t
  spa_last_synced_txg(spa_t *spa)
  {
          return (spa->spa_ubsync.ub_txg);
  }
  
  uint64_t
  spa_first_txg(spa_t *spa)
  {
          return (spa->spa_first_txg);
  }
  
  uint64_t
  spa_syncing_txg(spa_t *spa)
  {
          return (spa->spa_syncing_txg);
  }
  
  /*
   * Return the last txg where data can be dirtied. The final txgs
   * will be used to just clear out any deferred frees that remain.
   */
  uint64_t
  spa_final_dirty_txg(spa_t *spa)
  {
          return (spa->spa_final_txg - TXG_DEFER_SIZE);
  }
  
  pool_state_t
  spa_state(spa_t *spa)
  {
          return (spa->spa_state);
  }
  
  spa_load_state_t
  spa_load_state(spa_t *spa)
  {
          return (spa->spa_load_state);
  }
  
  uint64_t
  spa_freeze_txg(spa_t *spa)
  {
          return (spa->spa_freeze_txg);
  }
  
  /*
   * Return the inflated asize for a logical write in bytes. This is used by the
   * DMU to calculate the space a logical write will require on disk.
   * If lsize is smaller than the largest physical block size allocatable on this
   * pool we use its value instead, since the write will end up using the whole
   * block anyway.
   */
  uint64_t
  spa_get_worst_case_asize(spa_t *spa, uint64_t lsize)
  {
          if (lsize == 0)
                  return (0);     /* No inflation needed */
          return (MAX(lsize, 1 << spa->spa_max_ashift) * spa_asize_inflation);
  }
  
  /*
   * Return the amount of slop space in bytes.  It is typically 1/32 of the pool
   * (3.2%), minus the embedded log space.  On very small pools, it may be
   * slightly larger than this.  On very large pools, it will be capped to
   * the value of spa_max_slop.  The embedded log space is not included in
   * spa_dspace.  By subtracting it, the usable space (per "zfs list") is a
   * constant 97% of the total space, regardless of metaslab size (assuming the
   * default spa_slop_shift=5 and a non-tiny pool).
   *
   * See the comment above spa_slop_shift for more details.
   */
  uint64_t
  spa_get_slop_space(spa_t *spa)
  {
          uint64_t space = 0;
          uint64_t slop = 0;
  
          /*
           * Make sure spa_dedup_dspace has been set.
           */
          if (spa->spa_dedup_dspace == ~0ULL)
                  spa_update_dspace(spa);
  
          /*
           * spa_get_dspace() includes the space only logically "used" by
           * deduplicated data, so since it's not useful to reserve more
           * space with more deduplicated data, we subtract that out here.
           */
          space = spa_get_dspace(spa) - spa->spa_dedup_dspace;
          slop = MIN(space >> spa_slop_shift, spa_max_slop);
  
          /*
           * Subtract the embedded log space, but no more than half the (3.2%)
           * unusable space.  Note, the "no more than half" is only relevant if
           * zfs_embedded_slog_min_ms >> spa_slop_shift < 2, which is not true by
           * default.
           */
          uint64_t embedded_log =
              metaslab_class_get_dspace(spa_embedded_log_class(spa));
          slop -= MIN(embedded_log, slop >> 1);
  
          /*
           * Slop space should be at least spa_min_slop, but no more than half
           * the entire pool.
           */
          slop = MAX(slop, MIN(space >> 1, spa_min_slop));
          return (slop);
  }
  
  uint64_t
  spa_get_dspace(spa_t *spa)
  {
          return (spa->spa_dspace);
  }
  
  uint64_t
  spa_get_checkpoint_space(spa_t *spa)
  {
          return (spa->spa_checkpoint_info.sci_dspace);
  }
  
  void
  spa_update_dspace(spa_t *spa)
  {
          spa->spa_dspace = metaslab_class_get_dspace(spa_normal_class(spa)) +
              ddt_get_dedup_dspace(spa);
          if (spa->spa_nonallocating_dspace > 0) {
                  /*
                   * Subtract the space provided by all non-allocating vdevs that
                   * contribute to dspace.  If a file is overwritten, its old
                   * blocks are freed and new blocks are allocated.  If there are
                   * no snapshots of the file, the available space should remain
                   * the same.  The old blocks could be freed from the
                   * non-allocating vdev, but the new blocks must be allocated on
                   * other (allocating) vdevs.  By reserving the entire size of
                   * the non-allocating vdevs (including allocated space), we
                   * ensure that there will be enough space on the allocating
                   * vdevs for this file overwrite to succeed.
                   *
                   * Note that the DMU/DSL doesn't actually know or care
                   * how much space is allocated (it does its own tracking
                   * of how much space has been logically used).  So it
                   * doesn't matter that the data we are moving may be
                   * allocated twice (on the old device and the new device).
                   */
                  ASSERT3U(spa->spa_dspace, >=, spa->spa_nonallocating_dspace);
                  spa->spa_dspace -= spa->spa_nonallocating_dspace;
          }
  }
  
  /*
   * Return the failure mode that has been set to this pool. The default
   * behavior will be to block all I/Os when a complete failure occurs.
   */
  uint64_t
  spa_get_failmode(spa_t *spa)
  {
          return (spa->spa_failmode);
  }
  
  boolean_t
  spa_suspended(spa_t *spa)
  {
          return (spa->spa_suspended != ZIO_SUSPEND_NONE);
  }
  
  uint64_t
  spa_version(spa_t *spa)
  {
          return (spa->spa_ubsync.ub_version);
  }
  
  boolean_t
  spa_deflate(spa_t *spa)
  {
          return (spa->spa_deflate);
  }
  
  metaslab_class_t *
  spa_normal_class(spa_t *spa)
  {
          return (spa->spa_normal_class);
  }
  
  metaslab_class_t *
  spa_log_class(spa_t *spa)
  {
          return (spa->spa_log_class);
  }
  
  metaslab_class_t *
  spa_embedded_log_class(spa_t *spa)
  {
          return (spa->spa_embedded_log_class);
  }
  
  metaslab_class_t *
  spa_special_class(spa_t *spa)
  {
          return (spa->spa_special_class);
  }
  
  metaslab_class_t *
  spa_dedup_class(spa_t *spa)
  {
          return (spa->spa_dedup_class);
  }
  
  /*
   * Locate an appropriate allocation class
   */
  metaslab_class_t *
  spa_preferred_class(spa_t *spa, uint64_t size, dmu_object_type_t objtype,
      uint_t level, uint_t special_smallblk)
  {
          /*
           * ZIL allocations determine their class in zio_alloc_zil().
           */
          ASSERT(objtype != DMU_OT_INTENT_LOG);
  
          boolean_t has_special_class = spa->spa_special_class->mc_groups != 0;
  
          if (DMU_OT_IS_DDT(objtype)) {
                  if (spa->spa_dedup_class->mc_groups != 0)
                          return (spa_dedup_class(spa));
                  else if (has_special_class && zfs_ddt_data_is_special)
                          return (spa_special_class(spa));
                  else
                          return (spa_normal_class(spa));
          }
  
          /* Indirect blocks for user data can land in special if allowed */
          if (level > 0 && (DMU_OT_IS_FILE(objtype) || objtype == DMU_OT_ZVOL)) {
                  if (has_special_class && zfs_user_indirect_is_special)
                          return (spa_special_class(spa));
                  else
                          return (spa_normal_class(spa));
          }
  
          if (DMU_OT_IS_METADATA(objtype) || level > 0) {
                  if (has_special_class)
                          return (spa_special_class(spa));
                  else
                          return (spa_normal_class(spa));
          }
  
          /*
           * Allow small file blocks in special class in some cases (like
           * for the dRAID vdev feature). But always leave a reserve of
           * zfs_special_class_metadata_reserve_pct exclusively for metadata.
           */
          if (DMU_OT_IS_FILE(objtype) &&
              has_special_class && size <= special_smallblk) {
                  metaslab_class_t *special = spa_special_class(spa);
                  uint64_t alloc = metaslab_class_get_alloc(special);
                  uint64_t space = metaslab_class_get_space(special);
                  uint64_t limit =
                      (space * (100 - zfs_special_class_metadata_reserve_pct))
                      / 100;
  
                  if (alloc < limit)
                          return (special);
          }
  
          return (spa_normal_class(spa));
  }
  
  void
  spa_evicting_os_register(spa_t *spa, objset_t *os)
  {
          mutex_enter(&spa->spa_evicting_os_lock);
          list_insert_head(&spa->spa_evicting_os_list, os);
          mutex_exit(&spa->spa_evicting_os_lock);
  }
  
  void
  spa_evicting_os_deregister(spa_t *spa, objset_t *os)
  {
          mutex_enter(&spa->spa_evicting_os_lock);
          list_remove(&spa->spa_evicting_os_list, os);
          cv_broadcast(&spa->spa_evicting_os_cv);
          mutex_exit(&spa->spa_evicting_os_lock);
  }
  
  void
  spa_evicting_os_wait(spa_t *spa)
  {
          mutex_enter(&spa->spa_evicting_os_lock);
          while (!list_is_empty(&spa->spa_evicting_os_list))
                  cv_wait(&spa->spa_evicting_os_cv, &spa->spa_evicting_os_lock);
          mutex_exit(&spa->spa_evicting_os_lock);
  
          dmu_buf_user_evict_wait();
  }
  
  int
  spa_max_replication(spa_t *spa)
  {
          /*
           * As of SPA_VERSION == SPA_VERSION_DITTO_BLOCKS, we are able to
           * handle BPs with more than one DVA allocated.  Set our max
           * replication level accordingly.
           */
          if (spa_version(spa) < SPA_VERSION_DITTO_BLOCKS)
                  return (1);
          return (MIN(SPA_DVAS_PER_BP, spa_max_replication_override));
  }
  
  int
  spa_prev_software_version(spa_t *spa)
  {
          return (spa->spa_prev_software_version);
  }
  
  uint64_t
  spa_deadman_synctime(spa_t *spa)
  {
          return (spa->spa_deadman_synctime);
  }
  
  spa_autotrim_t
  spa_get_autotrim(spa_t *spa)
  {
          return (spa->spa_autotrim);
  }
  
  uint64_t
  spa_deadman_ziotime(spa_t *spa)
  {
          return (spa->spa_deadman_ziotime);
  }
  
  uint64_t
  spa_get_deadman_failmode(spa_t *spa)
  {
          return (spa->spa_deadman_failmode);
  }
  
  void
  spa_set_deadman_failmode(spa_t *spa, const char *failmode)
  {
          if (strcmp(failmode, "wait") == 0)
                  spa->spa_deadman_failmode = ZIO_FAILURE_MODE_WAIT;
          else if (strcmp(failmode, "continue") == 0)
                  spa->spa_deadman_failmode = ZIO_FAILURE_MODE_CONTINUE;
          else if (strcmp(failmode, "panic") == 0)
                  spa->spa_deadman_failmode = ZIO_FAILURE_MODE_PANIC;
          else
                  spa->spa_deadman_failmode = ZIO_FAILURE_MODE_WAIT;
  }
  
  void
  spa_set_deadman_ziotime(hrtime_t ns)
  {
          spa_t *spa = NULL;
  
          if (spa_mode_global != SPA_MODE_UNINIT) {
                  mutex_enter(&spa_namespace_lock);
                  while ((spa = spa_next(spa)) != NULL)
                          spa->spa_deadman_ziotime = ns;
                  mutex_exit(&spa_namespace_lock);
          }
  }
  
  void
  spa_set_deadman_synctime(hrtime_t ns)
  {
          spa_t *spa = NULL;
  
          if (spa_mode_global != SPA_MODE_UNINIT) {
                  mutex_enter(&spa_namespace_lock);
                  while ((spa = spa_next(spa)) != NULL)
                          spa->spa_deadman_synctime = ns;
                  mutex_exit(&spa_namespace_lock);
          }
  }
  
  uint64_t
  dva_get_dsize_sync(spa_t *spa, const dva_t *dva)
  {
          uint64_t asize = DVA_GET_ASIZE(dva);
          uint64_t dsize = asize;
  
          ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);
  
          if (asize != 0 && spa->spa_deflate) {
                  vdev_t *vd = vdev_lookup_top(spa, DVA_GET_VDEV(dva));
                  if (vd != NULL)
                          dsize = (asize >> SPA_MINBLOCKSHIFT) *
                              vd->vdev_deflate_ratio;
          }
  
          return (dsize);
  }
  
  uint64_t
  bp_get_dsize_sync(spa_t *spa, const blkptr_t *bp)
  {
          uint64_t dsize = 0;
  
          for (int d = 0; d < BP_GET_NDVAS(bp); d++)
                  dsize += dva_get_dsize_sync(spa, &bp->blk_dva[d]);
  
          return (dsize);
  }
  
  uint64_t
  bp_get_dsize(spa_t *spa, const blkptr_t *bp)
  {
          uint64_t dsize = 0;
  
          spa_config_enter(spa, SCL_VDEV, FTAG, RW_READER);
  
          for (int d = 0; d < BP_GET_NDVAS(bp); d++)
                  dsize += dva_get_dsize_sync(spa, &bp->blk_dva[d]);
  
          spa_config_exit(spa, SCL_VDEV, FTAG);
  
          return (dsize);
  }
  
  uint64_t
  spa_dirty_data(spa_t *spa)
  {
          return (spa->spa_dsl_pool->dp_dirty_total);
  }
  
  /*
   * ==========================================================================
   * SPA Import Progress Routines
   * ==========================================================================
   */
  
  typedef struct spa_import_progress {
          uint64_t                pool_guid;      /* unique id for updates */
          char                    *pool_name;
          spa_load_state_t        spa_load_state;
          uint64_t                mmp_sec_remaining;      /* MMP activity check */
          uint64_t                spa_load_max_txg;       /* rewind txg */
          procfs_list_node_t      smh_node;
  } spa_import_progress_t;
  
  spa_history_list_t *spa_import_progress_list = NULL;
  
  static int
  spa_import_progress_show_header(struct seq_file *f)
  {
          seq_printf(f, "%-20s %-14s %-14s %-12s %s\n", "pool_guid",
              "load_state", "multihost_secs", "max_txg",
              "pool_name");
          return (0);
  }
  
  static int
  spa_import_progress_show(struct seq_file *f, void *data)
  {
          spa_import_progress_t *sip = (spa_import_progress_t *)data;
  
          seq_printf(f, "%-20llu %-14llu %-14llu %-12llu %s\n",
              (u_longlong_t)sip->pool_guid, (u_longlong_t)sip->spa_load_state,
              (u_longlong_t)sip->mmp_sec_remaining,
              (u_longlong_t)sip->spa_load_max_txg,
              (sip->pool_name ? sip->pool_name : "-"));
  
          return (0);
  }
  
  /* Remove oldest elements from list until there are no more than 'size' left */
  static void
  spa_import_progress_truncate(spa_history_list_t *shl, unsigned int size)
  {
          spa_import_progress_t *sip;
          while (shl->size > size) {
                  sip = list_remove_head(&shl->procfs_list.pl_list);
                  if (sip->pool_name)
                          spa_strfree(sip->pool_name);
                  kmem_free(sip, sizeof (spa_import_progress_t));
                  shl->size--;
          }
  
          IMPLY(size == 0, list_is_empty(&shl->procfs_list.pl_list));
  }
  
  static void
  spa_import_progress_init(void)
  {
          spa_import_progress_list = kmem_zalloc(sizeof (spa_history_list_t),
              KM_SLEEP);
  
          spa_import_progress_list->size = 0;
  
          spa_import_progress_list->procfs_list.pl_private =
              spa_import_progress_list;
  
          procfs_list_install("zfs",
              NULL,
              "import_progress",
              0644,
              &spa_import_progress_list->procfs_list,
              spa_import_progress_show,
              spa_import_progress_show_header,
              NULL,
              offsetof(spa_import_progress_t, smh_node));
  }
  
  static void
  spa_import_progress_destroy(void)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          procfs_list_uninstall(&shl->procfs_list);
          spa_import_progress_truncate(shl, 0);
          procfs_list_destroy(&shl->procfs_list);
          kmem_free(shl, sizeof (spa_history_list_t));
  }
  
  int
  spa_import_progress_set_state(uint64_t pool_guid,
      spa_load_state_t load_state)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          spa_import_progress_t *sip;
          int error = ENOENT;
  
          if (shl->size == 0)
                  return (0);
  
          mutex_enter(&shl->procfs_list.pl_lock);
          for (sip = list_tail(&shl->procfs_list.pl_list); sip != NULL;
              sip = list_prev(&shl->procfs_list.pl_list, sip)) {
                  if (sip->pool_guid == pool_guid) {
                          sip->spa_load_state = load_state;
                          error = 0;
                          break;
                  }
          }
          mutex_exit(&shl->procfs_list.pl_lock);
  
          return (error);
  }
  
  int
  spa_import_progress_set_max_txg(uint64_t pool_guid, uint64_t load_max_txg)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          spa_import_progress_t *sip;
          int error = ENOENT;
  
          if (shl->size == 0)
                  return (0);
  
          mutex_enter(&shl->procfs_list.pl_lock);
          for (sip = list_tail(&shl->procfs_list.pl_list); sip != NULL;
              sip = list_prev(&shl->procfs_list.pl_list, sip)) {
                  if (sip->pool_guid == pool_guid) {
                          sip->spa_load_max_txg = load_max_txg;
                          error = 0;
                          break;
                  }
          }
          mutex_exit(&shl->procfs_list.pl_lock);
  
          return (error);
  }
  
  int
  spa_import_progress_set_mmp_check(uint64_t pool_guid,
      uint64_t mmp_sec_remaining)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          spa_import_progress_t *sip;
          int error = ENOENT;
  
          if (shl->size == 0)
                  return (0);
  
          mutex_enter(&shl->procfs_list.pl_lock);
          for (sip = list_tail(&shl->procfs_list.pl_list); sip != NULL;
              sip = list_prev(&shl->procfs_list.pl_list, sip)) {
                  if (sip->pool_guid == pool_guid) {
                          sip->mmp_sec_remaining = mmp_sec_remaining;
                          error = 0;
                          break;
                  }
          }
          mutex_exit(&shl->procfs_list.pl_lock);
  
          return (error);
  }
  
  /*
   * A new import is in progress, add an entry.
   */
  void
  spa_import_progress_add(spa_t *spa)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          spa_import_progress_t *sip;
          char *poolname = NULL;
  
          sip = kmem_zalloc(sizeof (spa_import_progress_t), KM_SLEEP);
          sip->pool_guid = spa_guid(spa);
  
          (void) nvlist_lookup_string(spa->spa_config, ZPOOL_CONFIG_POOL_NAME,
              &poolname);
          if (poolname == NULL)
                  poolname = spa_name(spa);
          sip->pool_name = spa_strdup(poolname);
          sip->spa_load_state = spa_load_state(spa);
  
          mutex_enter(&shl->procfs_list.pl_lock);
          procfs_list_add(&shl->procfs_list, sip);
          shl->size++;
          mutex_exit(&shl->procfs_list.pl_lock);
  }
  
  void
  spa_import_progress_remove(uint64_t pool_guid)
  {
          spa_history_list_t *shl = spa_import_progress_list;
          spa_import_progress_t *sip;
  
          mutex_enter(&shl->procfs_list.pl_lock);
          for (sip = list_tail(&shl->procfs_list.pl_list); sip != NULL;
              sip = list_prev(&shl->procfs_list.pl_list, sip)) {
                  if (sip->pool_guid == pool_guid) {
                          if (sip->pool_name)
                                  spa_strfree(sip->pool_name);
                          list_remove(&shl->procfs_list.pl_list, sip);
                          shl->size--;
                          kmem_free(sip, sizeof (spa_import_progress_t));
                          break;
                  }
          }
          mutex_exit(&shl->procfs_list.pl_lock);
  }
  
  /*
   * ==========================================================================
   * Initialization and Termination
   * ==========================================================================
   */
  
  static int
  spa_name_compare(const void *a1, const void *a2)
  {
          const spa_t *s1 = a1;
          const spa_t *s2 = a2;
          int s;
  
          s = strcmp(s1->spa_name, s2->spa_name);
  
          return (TREE_ISIGN(s));
  }
  
  void
  spa_boot_init(void)
  {
          spa_config_load();
  }
  
  void
  spa_init(spa_mode_t mode)
  {
          mutex_init(&spa_namespace_lock, NULL, MUTEX_DEFAULT, NULL);
          mutex_init(&spa_spare_lock, NULL, MUTEX_DEFAULT, NULL);
          mutex_init(&spa_l2cache_lock, NULL, MUTEX_DEFAULT, NULL);
          cv_init(&spa_namespace_cv, NULL, CV_DEFAULT, NULL);
  
          avl_create(&spa_namespace_avl, spa_name_compare, sizeof (spa_t),
              offsetof(spa_t, spa_avl));
  
          avl_create(&spa_spare_avl, spa_spare_compare, sizeof (spa_aux_t),
              offsetof(spa_aux_t, aux_avl));
  
          avl_create(&spa_l2cache_avl, spa_l2cache_compare, sizeof (spa_aux_t),
              offsetof(spa_aux_t, aux_avl));
  
          spa_mode_global = mode;
  
  #ifndef _KERNEL
          if (spa_mode_global != SPA_MODE_READ && dprintf_find_string("watch")) {
                  struct sigaction sa;
  
                  sa.sa_flags = SA_SIGINFO;
                  sigemptyset(&sa.sa_mask);
                  sa.sa_sigaction = arc_buf_sigsegv;
  
                  if (sigaction(SIGSEGV, &sa, NULL) == -1) {
                          perror("could not enable watchpoints: "
                              "sigaction(SIGSEGV, ...) = ");
                  } else {
                          arc_watch = B_TRUE;
                  }
          }
  #endif
  
          fm_init();
          zfs_refcount_init();
          unique_init();
          zfs_btree_init();
          metaslab_stat_init();
          ddt_init();
          zio_init();
          dmu_init();
          zil_init();
          vdev_cache_stat_init();
          vdev_mirror_stat_init();
          vdev_raidz_math_init();
          vdev_file_init();
          zfs_prop_init();
          chksum_init();
          zpool_prop_init();
          zpool_feature_init();
          spa_config_load();
          vdev_prop_init();
          l2arc_start();
          scan_init();
          qat_init();
          spa_import_progress_init();
  }
  
  void
  spa_fini(void)
  {
          l2arc_stop();
  
          spa_evict_all();
  
          vdev_file_fini();
          vdev_cache_stat_fini();
          vdev_mirror_stat_fini();
          vdev_raidz_math_fini();
          chksum_fini();
          zil_fini();
          dmu_fini();
          zio_fini();
          ddt_fini();
          metaslab_stat_fini();
          zfs_btree_fini();
          unique_fini();
          zfs_refcount_fini();
          fm_fini();
          scan_fini();
          qat_fini();
          spa_import_progress_destroy();
  
          avl_destroy(&spa_namespace_avl);
          avl_destroy(&spa_spare_avl);
          avl_destroy(&spa_l2cache_avl);
  
          cv_destroy(&spa_namespace_cv);
          mutex_destroy(&spa_namespace_lock);
          mutex_destroy(&spa_spare_lock);
          mutex_destroy(&spa_l2cache_lock);
  }
  
  /*
   * Return whether this pool has a dedicated slog device. No locking needed.
   * It's not a problem if the wrong answer is returned as it's only for
   * performance and not correctness.
   */
  boolean_t
  spa_has_slogs(spa_t *spa)
  {
          return (spa->spa_log_class->mc_groups != 0);
  }
  
  spa_log_state_t
  spa_get_log_state(spa_t *spa)
  {
          return (spa->spa_log_state);
  }
  
  void
  spa_set_log_state(spa_t *spa, spa_log_state_t state)
  {
          spa->spa_log_state = state;
  }
  
  boolean_t
  spa_is_root(spa_t *spa)
  {
          return (spa->spa_is_root);
  }
  
  boolean_t
  spa_writeable(spa_t *spa)
  {
          return (!!(spa->spa_mode & SPA_MODE_WRITE) && spa->spa_trust_config);
  }
  
  /*
   * Returns true if there is a pending sync task in any of the current
   * syncing txg, the current quiescing txg, or the current open txg.
   */
  boolean_t
  spa_has_pending_synctask(spa_t *spa)
  {
          return (!txg_all_lists_empty(&spa->spa_dsl_pool->dp_sync_tasks) ||
              !txg_all_lists_empty(&spa->spa_dsl_pool->dp_early_sync_tasks));
  }
  
  spa_mode_t
  spa_mode(spa_t *spa)
  {
          return (spa->spa_mode);
  }
  
  uint64_t
  spa_bootfs(spa_t *spa)
  {
          return (spa->spa_bootfs);
  }
  
  uint64_t
  spa_delegation(spa_t *spa)
  {
          return (spa->spa_delegation);
  }
  
  objset_t *
  spa_meta_objset(spa_t *spa)
  {
          return (spa->spa_meta_objset);
  }
  
  enum zio_checksum
  spa_dedup_checksum(spa_t *spa)
  {
          return (spa->spa_dedup_checksum);
  }
  
  /*
   * Reset pool scan stat per scan pass (or reboot).
   */
  void
  spa_scan_stat_init(spa_t *spa)
  {
          /* data not stored on disk */
          spa->spa_scan_pass_start = gethrestime_sec();
          if (dsl_scan_is_paused_scrub(spa->spa_dsl_pool->dp_scan))
                  spa->spa_scan_pass_scrub_pause = spa->spa_scan_pass_start;
          else
                  spa->spa_scan_pass_scrub_pause = 0;
          spa->spa_scan_pass_scrub_spent_paused = 0;
          spa->spa_scan_pass_exam = 0;
          spa->spa_scan_pass_issued = 0;
          vdev_scan_stat_init(spa->spa_root_vdev);
  }
  
  /*
   * Get scan stats for zpool status reports
   */
  int
  spa_scan_get_stats(spa_t *spa, pool_scan_stat_t *ps)
  {
          dsl_scan_t *scn = spa->spa_dsl_pool ? spa->spa_dsl_pool->dp_scan : NULL;
  
          if (scn == NULL || scn->scn_phys.scn_func == POOL_SCAN_NONE)
                  return (SET_ERROR(ENOENT));
          memset(ps, 0, sizeof (pool_scan_stat_t));
  
          /* data stored on disk */
          ps->pss_func = scn->scn_phys.scn_func;
          ps->pss_state = scn->scn_phys.scn_state;
          ps->pss_start_time = scn->scn_phys.scn_start_time;
          ps->pss_end_time = scn->scn_phys.scn_end_time;
          ps->pss_to_examine = scn->scn_phys.scn_to_examine;
          ps->pss_examined = scn->scn_phys.scn_examined;
          ps->pss_to_process = scn->scn_phys.scn_to_process;
          ps->pss_processed = scn->scn_phys.scn_processed;
          ps->pss_errors = scn->scn_phys.scn_errors;
  
          /* data not stored on disk */
          ps->pss_pass_exam = spa->spa_scan_pass_exam;
          ps->pss_pass_start = spa->spa_scan_pass_start;
          ps->pss_pass_scrub_pause = spa->spa_scan_pass_scrub_pause;
          ps->pss_pass_scrub_spent_paused = spa->spa_scan_pass_scrub_spent_paused;
          ps->pss_pass_issued = spa->spa_scan_pass_issued;
          ps->pss_issued =
              scn->scn_issued_before_pass + spa->spa_scan_pass_issued;
  
          return (0);
  }
  
  int
  spa_maxblocksize(spa_t *spa)
  {
          if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_BLOCKS))
                  return (SPA_MAXBLOCKSIZE);
          else
                  return (SPA_OLD_MAXBLOCKSIZE);
  }
  
  
  /*
   * Returns the txg that the last device removal completed. No indirect mappings
   * have been added since this txg.
   */
  uint64_t
  spa_get_last_removal_txg(spa_t *spa)
  {
          uint64_t vdevid;
          uint64_t ret = -1ULL;
  
          spa_config_enter(spa, SCL_VDEV, FTAG, RW_READER);
          /*
           * sr_prev_indirect_vdev is only modified while holding all the
           * config locks, so it is sufficient to hold SCL_VDEV as reader when
           * examining it.
           */
          vdevid = spa->spa_removing_phys.sr_prev_indirect_vdev;
  
          while (vdevid != -1ULL) {
                  vdev_t *vd = vdev_lookup_top(spa, vdevid);
                  vdev_indirect_births_t *vib = vd->vdev_indirect_births;
  
                  ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
  
                  /*
                   * If the removal did not remap any data, we don't care.
                   */
                  if (vdev_indirect_births_count(vib) != 0) {
                          ret = vdev_indirect_births_last_entry_txg(vib);
                          break;
                  }
  
                  vdevid = vd->vdev_indirect_config.vic_prev_indirect_vdev;
          }
          spa_config_exit(spa, SCL_VDEV, FTAG);
  
          IMPLY(ret != -1ULL,
              spa_feature_is_active(spa, SPA_FEATURE_DEVICE_REMOVAL));
  
          return (ret);
  }
  
  int
  spa_maxdnodesize(spa_t *spa)
  {
          if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_DNODE))
                  return (DNODE_MAX_SIZE);
          else
                  return (DNODE_MIN_SIZE);
  }
  
  boolean_t
  spa_multihost(spa_t *spa)
  {
          return (spa->spa_multihost ? B_TRUE : B_FALSE);
  }
  
  uint32_t
  spa_get_hostid(spa_t *spa)
  {
          return (spa->spa_hostid);
  }
  
  boolean_t
  spa_trust_config(spa_t *spa)
  {
          return (spa->spa_trust_config);
  }
  
  uint64_t
  spa_missing_tvds_allowed(spa_t *spa)
  {
          return (spa->spa_missing_tvds_allowed);
  }
  
  space_map_t *
  spa_syncing_log_sm(spa_t *spa)
  {
          return (spa->spa_syncing_log_sm);
  }
  
  void
  spa_set_missing_tvds(spa_t *spa, uint64_t missing)
  {
          spa->spa_missing_tvds = missing;
  }
  
  /*
   * Return the pool state string ("ONLINE", "DEGRADED", "SUSPENDED", etc).
   */
  const char *
  spa_state_to_name(spa_t *spa)
  {
          ASSERT3P(spa, !=, NULL);
  
          /*
           * it is possible for the spa to exist, without root vdev
           * as the spa transitions during import/export
           */
          vdev_t *rvd = spa->spa_root_vdev;
          if (rvd == NULL) {
                  return ("TRANSITIONING");
          }
          vdev_state_t state = rvd->vdev_state;
          vdev_aux_t aux = rvd->vdev_stat.vs_aux;
  
          if (spa_suspended(spa) &&
              (spa_get_failmode(spa) != ZIO_FAILURE_MODE_CONTINUE))
                  return ("SUSPENDED");
  
          switch (state) {
          case VDEV_STATE_CLOSED:
          case VDEV_STATE_OFFLINE:
                  return ("OFFLINE");
          case VDEV_STATE_REMOVED:
                  return ("REMOVED");
          case VDEV_STATE_CANT_OPEN:
                  if (aux == VDEV_AUX_CORRUPT_DATA || aux == VDEV_AUX_BAD_LOG)
                          return ("FAULTED");
                  else if (aux == VDEV_AUX_SPLIT_POOL)
                          return ("SPLIT");
                  else
                          return ("UNAVAIL");
          case VDEV_STATE_FAULTED:
                  return ("FAULTED");
          case VDEV_STATE_DEGRADED:
                  return ("DEGRADED");
          case VDEV_STATE_HEALTHY:
                  return ("ONLINE");
          default:
                  break;
          }
  
          return ("UNKNOWN");
  }
  
  boolean_t
  spa_top_vdevs_spacemap_addressable(spa_t *spa)
  {
          vdev_t *rvd = spa->spa_root_vdev;
          for (uint64_t c = 0; c < rvd->vdev_children; c++) {
                  if (!vdev_is_spacemap_addressable(rvd->vdev_child[c]))
                          return (B_FALSE);
          }
          return (B_TRUE);
  }
  
  boolean_t
  spa_has_checkpoint(spa_t *spa)
  {
          return (spa->spa_checkpoint_txg != 0);
  }
  
  boolean_t
  spa_importing_readonly_checkpoint(spa_t *spa)
  {
          return ((spa->spa_import_flags & ZFS_IMPORT_CHECKPOINT) &&
              spa->spa_mode == SPA_MODE_READ);
  }
  
  uint64_t
  spa_min_claim_txg(spa_t *spa)
  {
          uint64_t checkpoint_txg = spa->spa_uberblock.ub_checkpoint_txg;
  
          if (checkpoint_txg != 0)
                  return (checkpoint_txg + 1);
  
          return (spa->spa_first_txg);
  }
  
  /*
   * If there is a checkpoint, async destroys may consume more space from
   * the pool instead of freeing it. In an attempt to save the pool from
   * getting suspended when it is about to run out of space, we stop
   * processing async destroys.
   */
  boolean_t
  spa_suspend_async_destroy(spa_t *spa)
  {
          dsl_pool_t *dp = spa_get_dsl(spa);
  
          uint64_t unreserved = dsl_pool_unreserved_space(dp,
              ZFS_SPACE_CHECK_EXTRA_RESERVED);
          uint64_t used = dsl_dir_phys(dp->dp_root_dir)->dd_used_bytes;
          uint64_t avail = (unreserved > used) ? (unreserved - used) : 0;
  
          if (spa_has_checkpoint(spa) && avail == 0)
                  return (B_TRUE);
  
          return (B_FALSE);
  }
  
  #if defined(_KERNEL)
  
  int
  param_set_deadman_failmode_common(const char *val)
  {
          spa_t *spa = NULL;
          char *p;
  
          if (val == NULL)
                  return (SET_ERROR(EINVAL));
  
          if ((p = strchr(val, '\n')) != NULL)
                  *p = '\0';
  
          if (strcmp(val, "wait") != 0 && strcmp(val, "continue") != 0 &&
              strcmp(val, "panic"))
                  return (SET_ERROR(EINVAL));
  
          if (spa_mode_global != SPA_MODE_UNINIT) {
                  mutex_enter(&spa_namespace_lock);
                  while ((spa = spa_next(spa)) != NULL)
                          spa_set_deadman_failmode(spa, val);
                  mutex_exit(&spa_namespace_lock);
          }
  
          return (0);
  }
  #endif
  
  /* Namespace manipulation */
  EXPORT_SYMBOL(spa_lookup);
  EXPORT_SYMBOL(spa_add);
  EXPORT_SYMBOL(spa_remove);
  EXPORT_SYMBOL(spa_next);
  
  /* Refcount functions */
  EXPORT_SYMBOL(spa_open_ref);
  EXPORT_SYMBOL(spa_close);
  EXPORT_SYMBOL(spa_refcount_zero);
  
  /* Pool configuration lock */
  EXPORT_SYMBOL(spa_config_tryenter);
  EXPORT_SYMBOL(spa_config_enter);
  EXPORT_SYMBOL(spa_config_exit);
  EXPORT_SYMBOL(spa_config_held);
  
  /* Pool vdev add/remove lock */
  EXPORT_SYMBOL(spa_vdev_enter);
  EXPORT_SYMBOL(spa_vdev_exit);
  
  /* Pool vdev state change lock */
  EXPORT_SYMBOL(spa_vdev_state_enter);
  EXPORT_SYMBOL(spa_vdev_state_exit);
  
  /* Accessor functions */
  EXPORT_SYMBOL(spa_shutting_down);
  EXPORT_SYMBOL(spa_get_dsl);
  EXPORT_SYMBOL(spa_get_rootblkptr);
  EXPORT_SYMBOL(spa_set_rootblkptr);
  EXPORT_SYMBOL(spa_altroot);
  EXPORT_SYMBOL(spa_sync_pass);
  EXPORT_SYMBOL(spa_name);
  EXPORT_SYMBOL(spa_guid);
  EXPORT_SYMBOL(spa_last_synced_txg);
  EXPORT_SYMBOL(spa_first_txg);
  EXPORT_SYMBOL(spa_syncing_txg);
  EXPORT_SYMBOL(spa_version);
  EXPORT_SYMBOL(spa_state);
  EXPORT_SYMBOL(spa_load_state);
  EXPORT_SYMBOL(spa_freeze_txg);
  EXPORT_SYMBOL(spa_get_dspace);
  EXPORT_SYMBOL(spa_update_dspace);
  EXPORT_SYMBOL(spa_deflate);
  EXPORT_SYMBOL(spa_normal_class);
  EXPORT_SYMBOL(spa_log_class);
  EXPORT_SYMBOL(spa_special_class);
  EXPORT_SYMBOL(spa_preferred_class);
  EXPORT_SYMBOL(spa_max_replication);
  EXPORT_SYMBOL(spa_prev_software_version);
  EXPORT_SYMBOL(spa_get_failmode);
  EXPORT_SYMBOL(spa_suspended);
  EXPORT_SYMBOL(spa_bootfs);
  EXPORT_SYMBOL(spa_delegation);
  EXPORT_SYMBOL(spa_meta_objset);
  EXPORT_SYMBOL(spa_maxblocksize);
  EXPORT_SYMBOL(spa_maxdnodesize);
  
  /* Miscellaneous support routines */
  EXPORT_SYMBOL(spa_guid_exists);
  EXPORT_SYMBOL(spa_strdup);
  EXPORT_SYMBOL(spa_strfree);
  EXPORT_SYMBOL(spa_generate_guid);
  EXPORT_SYMBOL(snprintf_blkptr);
  EXPORT_SYMBOL(spa_freeze);
  EXPORT_SYMBOL(spa_upgrade);
  EXPORT_SYMBOL(spa_evict_all);
  EXPORT_SYMBOL(spa_lookup_by_guid);
  EXPORT_SYMBOL(spa_has_spare);
  EXPORT_SYMBOL(dva_get_dsize_sync);
  EXPORT_SYMBOL(bp_get_dsize_sync);
  EXPORT_SYMBOL(bp_get_dsize);
  EXPORT_SYMBOL(spa_has_slogs);
  EXPORT_SYMBOL(spa_is_root);
  EXPORT_SYMBOL(spa_writeable);
  EXPORT_SYMBOL(spa_mode);
  EXPORT_SYMBOL(spa_namespace_lock);
  EXPORT_SYMBOL(spa_trust_config);
  EXPORT_SYMBOL(spa_missing_tvds_allowed);
  EXPORT_SYMBOL(spa_set_missing_tvds);
  EXPORT_SYMBOL(spa_state_to_name);
  EXPORT_SYMBOL(spa_importing_readonly_checkpoint);
  EXPORT_SYMBOL(spa_min_claim_txg);
  EXPORT_SYMBOL(spa_suspend_async_destroy);
  EXPORT_SYMBOL(spa_has_checkpoint);
  EXPORT_SYMBOL(spa_top_vdevs_spacemap_addressable);
  
  ZFS_MODULE_PARAM(zfs, zfs_, flags, UINT, ZMOD_RW,
          "Set additional debugging flags");
  
  ZFS_MODULE_PARAM(zfs, zfs_, recover, INT, ZMOD_RW,
          "Set to attempt to recover from fatal errors");
  
  ZFS_MODULE_PARAM(zfs, zfs_, free_leak_on_eio, INT, ZMOD_RW,
          "Set to ignore IO errors during free and permanently leak the space");
  
  ZFS_MODULE_PARAM(zfs_deadman, zfs_deadman_, checktime_ms, U64, ZMOD_RW,
          "Dead I/O check interval in milliseconds");
  
  ZFS_MODULE_PARAM(zfs_deadman, zfs_deadman_, enabled, INT, ZMOD_RW,
          "Enable deadman timer");
  
  ZFS_MODULE_PARAM(zfs_spa, spa_, asize_inflation, UINT, ZMOD_RW,
          "SPA size estimate multiplication factor");
  
  ZFS_MODULE_PARAM(zfs, zfs_, ddt_data_is_special, INT, ZMOD_RW,
          "Place DDT data into the special class");
  
  ZFS_MODULE_PARAM(zfs, zfs_, user_indirect_is_special, INT, ZMOD_RW,
          "Place user data indirect blocks into the special class");
  
  /* BEGIN CSTYLED */
  ZFS_MODULE_PARAM_CALL(zfs_deadman, zfs_deadman_, failmode,
          param_set_deadman_failmode, param_get_charp, ZMOD_RW,
          "Failmode for deadman timer");
  
  ZFS_MODULE_PARAM_CALL(zfs_deadman, zfs_deadman_, synctime_ms,
          param_set_deadman_synctime, spl_param_get_u64, ZMOD_RW,
          "Pool sync expiration time in milliseconds");
  
  ZFS_MODULE_PARAM_CALL(zfs_deadman, zfs_deadman_, ziotime_ms,
          param_set_deadman_ziotime, spl_param_get_u64, ZMOD_RW,
          "IO expiration time in milliseconds");
  
  ZFS_MODULE_PARAM(zfs, zfs_, special_class_metadata_reserve_pct, UINT, ZMOD_RW,
          "Small file blocks in special vdevs depends on this much "
          "free space available");
  /* END CSTYLED */
  
  ZFS_MODULE_PARAM_CALL(zfs_spa, spa_, slop_shift, param_set_slop_shift,
          param_get_uint, ZMOD_RW, "Reserved free space in pool");

Cache object: 01635faf788891d9d2789ff73ea788f2