FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/dmu_objset.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) 2012, 2020 by Delphix. All rights reserved.
     * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
     * Copyright (c) 2013, Joyent, Inc. All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     * Copyright (c) 2015, STRATO AG, Inc. All rights reserved.
     * Copyright (c) 2016 Actifio, Inc. All rights reserved.
     * Copyright 2017 Nexenta Systems, Inc.
     * Copyright (c) 2017 Open-E, Inc. All Rights Reserved.
     * Copyright (c) 2018, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
     * Copyright (c) 2019, Klara Inc.
     * Copyright (c) 2019, Allan Jude
     * Copyright (c) 2022 Hewlett Packard Enterprise Development LP.
     */
    
    /* Portions Copyright 2010 Robert Milkowski */
    
    #include <sys/cred.h>
    #include <sys/zfs_context.h>
    #include <sys/dmu_objset.h>
    #include <sys/dsl_dir.h>
    #include <sys/dsl_dataset.h>
    #include <sys/dsl_prop.h>
    #include <sys/dsl_pool.h>
    #include <sys/dsl_synctask.h>
    #include <sys/dsl_deleg.h>
    #include <sys/dnode.h>
    #include <sys/dbuf.h>
    #include <sys/zvol.h>
    #include <sys/dmu_tx.h>
    #include <sys/zap.h>
    #include <sys/zil.h>
    #include <sys/dmu_impl.h>
    #include <sys/zfs_ioctl.h>
    #include <sys/sa.h>
    #include <sys/zfs_onexit.h>
    #include <sys/dsl_destroy.h>
    #include <sys/vdev.h>
    #include <sys/zfeature.h>
    #include <sys/policy.h>
    #include <sys/spa_impl.h>
    #include <sys/dmu_recv.h>
    #include <sys/zfs_project.h>
    #include "zfs_namecheck.h"
    #include <sys/vdev_impl.h>
    #include <sys/arc.h>
    
    /*
     * Needed to close a window in dnode_move() that allows the objset to be freed
     * before it can be safely accessed.
     */
    krwlock_t os_lock;
    
    /*
     * Tunable to overwrite the maximum number of threads for the parallelization
     * of dmu_objset_find_dp, needed to speed up the import of pools with many
     * datasets.
     * Default is 4 times the number of leaf vdevs.
     */
    static const int dmu_find_threads = 0;
    
    /*
     * Backfill lower metadnode objects after this many have been freed.
     * Backfilling negatively impacts object creation rates, so only do it
     * if there are enough holes to fill.
     */
    static const int dmu_rescan_dnode_threshold = 1 << DN_MAX_INDBLKSHIFT;
    
    static const char *upgrade_tag = "upgrade_tag";
    
    static void dmu_objset_find_dp_cb(void *arg);
    
    static void dmu_objset_upgrade(objset_t *os, dmu_objset_upgrade_cb_t cb);
    static void dmu_objset_upgrade_stop(objset_t *os);
    
    void
    dmu_objset_init(void)
   {
           rw_init(&os_lock, NULL, RW_DEFAULT, NULL);
   }
   
   void
   dmu_objset_fini(void)
   {
           rw_destroy(&os_lock);
   }
   
   spa_t *
   dmu_objset_spa(objset_t *os)
   {
           return (os->os_spa);
   }
   
   zilog_t *
   dmu_objset_zil(objset_t *os)
   {
           return (os->os_zil);
   }
   
   dsl_pool_t *
   dmu_objset_pool(objset_t *os)
   {
           dsl_dataset_t *ds;
   
           if ((ds = os->os_dsl_dataset) != NULL && ds->ds_dir)
                   return (ds->ds_dir->dd_pool);
           else
                   return (spa_get_dsl(os->os_spa));
   }
   
   dsl_dataset_t *
   dmu_objset_ds(objset_t *os)
   {
           return (os->os_dsl_dataset);
   }
   
   dmu_objset_type_t
   dmu_objset_type(objset_t *os)
   {
           return (os->os_phys->os_type);
   }
   
   void
   dmu_objset_name(objset_t *os, char *buf)
   {
           dsl_dataset_name(os->os_dsl_dataset, buf);
   }
   
   uint64_t
   dmu_objset_id(objset_t *os)
   {
           dsl_dataset_t *ds = os->os_dsl_dataset;
   
           return (ds ? ds->ds_object : 0);
   }
   
   uint64_t
   dmu_objset_dnodesize(objset_t *os)
   {
           return (os->os_dnodesize);
   }
   
   zfs_sync_type_t
   dmu_objset_syncprop(objset_t *os)
   {
           return (os->os_sync);
   }
   
   zfs_logbias_op_t
   dmu_objset_logbias(objset_t *os)
   {
           return (os->os_logbias);
   }
   
   static void
   checksum_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance should have been done by now.
            */
           ASSERT(newval != ZIO_CHECKSUM_INHERIT);
   
           os->os_checksum = zio_checksum_select(newval, ZIO_CHECKSUM_ON_VALUE);
   }
   
   static void
   compression_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval != ZIO_COMPRESS_INHERIT);
   
           os->os_compress = zio_compress_select(os->os_spa,
               ZIO_COMPRESS_ALGO(newval), ZIO_COMPRESS_ON);
           os->os_complevel = zio_complevel_select(os->os_spa, os->os_compress,
               ZIO_COMPRESS_LEVEL(newval), ZIO_COMPLEVEL_DEFAULT);
   }
   
   static void
   copies_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval > 0);
           ASSERT(newval <= spa_max_replication(os->os_spa));
   
           os->os_copies = newval;
   }
   
   static void
   dedup_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
           spa_t *spa = os->os_spa;
           enum zio_checksum checksum;
   
           /*
            * Inheritance should have been done by now.
            */
           ASSERT(newval != ZIO_CHECKSUM_INHERIT);
   
           checksum = zio_checksum_dedup_select(spa, newval, ZIO_CHECKSUM_OFF);
   
           os->os_dedup_checksum = checksum & ZIO_CHECKSUM_MASK;
           os->os_dedup_verify = !!(checksum & ZIO_CHECKSUM_VERIFY);
   }
   
   static void
   primary_cache_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval == ZFS_CACHE_ALL || newval == ZFS_CACHE_NONE ||
               newval == ZFS_CACHE_METADATA);
   
           os->os_primary_cache = newval;
   }
   
   static void
   secondary_cache_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval == ZFS_CACHE_ALL || newval == ZFS_CACHE_NONE ||
               newval == ZFS_CACHE_METADATA);
   
           os->os_secondary_cache = newval;
   }
   
   static void
   sync_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval == ZFS_SYNC_STANDARD || newval == ZFS_SYNC_ALWAYS ||
               newval == ZFS_SYNC_DISABLED);
   
           os->os_sync = newval;
           if (os->os_zil)
                   zil_set_sync(os->os_zil, newval);
   }
   
   static void
   redundant_metadata_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval == ZFS_REDUNDANT_METADATA_ALL ||
               newval == ZFS_REDUNDANT_METADATA_MOST ||
               newval == ZFS_REDUNDANT_METADATA_SOME ||
               newval == ZFS_REDUNDANT_METADATA_NONE);
   
           os->os_redundant_metadata = newval;
   }
   
   static void
   dnodesize_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           switch (newval) {
           case ZFS_DNSIZE_LEGACY:
                   os->os_dnodesize = DNODE_MIN_SIZE;
                   break;
           case ZFS_DNSIZE_AUTO:
                   /*
                    * Choose a dnode size that will work well for most
                    * workloads if the user specified "auto". Future code
                    * improvements could dynamically select a dnode size
                    * based on observed workload patterns.
                    */
                   os->os_dnodesize = DNODE_MIN_SIZE * 2;
                   break;
           case ZFS_DNSIZE_1K:
           case ZFS_DNSIZE_2K:
           case ZFS_DNSIZE_4K:
           case ZFS_DNSIZE_8K:
           case ZFS_DNSIZE_16K:
                   os->os_dnodesize = newval;
                   break;
           }
   }
   
   static void
   smallblk_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           /*
            * Inheritance and range checking should have been done by now.
            */
           ASSERT(newval <= SPA_MAXBLOCKSIZE);
           ASSERT(ISP2(newval));
   
           os->os_zpl_special_smallblock = newval;
   }
   
   static void
   logbias_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           ASSERT(newval == ZFS_LOGBIAS_LATENCY ||
               newval == ZFS_LOGBIAS_THROUGHPUT);
           os->os_logbias = newval;
           if (os->os_zil)
                   zil_set_logbias(os->os_zil, newval);
   }
   
   static void
   recordsize_changed_cb(void *arg, uint64_t newval)
   {
           objset_t *os = arg;
   
           os->os_recordsize = newval;
   }
   
   void
   dmu_objset_byteswap(void *buf, size_t size)
   {
           objset_phys_t *osp = buf;
   
           ASSERT(size == OBJSET_PHYS_SIZE_V1 || size == OBJSET_PHYS_SIZE_V2 ||
               size == sizeof (objset_phys_t));
           dnode_byteswap(&osp->os_meta_dnode);
           byteswap_uint64_array(&osp->os_zil_header, sizeof (zil_header_t));
           osp->os_type = BSWAP_64(osp->os_type);
           osp->os_flags = BSWAP_64(osp->os_flags);
           if (size >= OBJSET_PHYS_SIZE_V2) {
                   dnode_byteswap(&osp->os_userused_dnode);
                   dnode_byteswap(&osp->os_groupused_dnode);
                   if (size >= sizeof (objset_phys_t))
                           dnode_byteswap(&osp->os_projectused_dnode);
           }
   }
   
   /*
    * The hash is a CRC-based hash of the objset_t pointer and the object number.
    */
   static uint64_t
   dnode_hash(const objset_t *os, uint64_t obj)
   {
           uintptr_t osv = (uintptr_t)os;
           uint64_t crc = -1ULL;
   
           ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
           /*
            * The low 6 bits of the pointer don't have much entropy, because
            * the objset_t is larger than 2^6 bytes long.
            */
           crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 6)) & 0xFF];
           crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF];
           crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF];
           crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 16)) & 0xFF];
   
           crc ^= (osv>>14) ^ (obj>>24);
   
           return (crc);
   }
   
   static unsigned int
   dnode_multilist_index_func(multilist_t *ml, void *obj)
   {
           dnode_t *dn = obj;
   
           /*
            * The low order bits of the hash value are thought to be
            * distributed evenly. Otherwise, in the case that the multilist
            * has a power of two number of sublists, each sublists' usage
            * would not be evenly distributed. In this context full 64bit
            * division would be a waste of time, so limit it to 32 bits.
            */
           return ((unsigned int)dnode_hash(dn->dn_objset, dn->dn_object) %
               multilist_get_num_sublists(ml));
   }
   
   static inline boolean_t
   dmu_os_is_l2cacheable(objset_t *os)
   {
           vdev_t *vd = NULL;
           zfs_cache_type_t cache = os->os_secondary_cache;
           blkptr_t *bp = os->os_rootbp;
   
           if (bp != NULL && !BP_IS_HOLE(bp)) {
                   uint64_t vdev = DVA_GET_VDEV(bp->blk_dva);
                   vdev_t *rvd = os->os_spa->spa_root_vdev;
   
                   if (vdev < rvd->vdev_children)
                           vd = rvd->vdev_child[vdev];
   
                   if (cache == ZFS_CACHE_ALL || cache == ZFS_CACHE_METADATA) {
                           if (vd == NULL)
                                   return (B_TRUE);
   
                           if ((vd->vdev_alloc_bias != VDEV_BIAS_SPECIAL &&
                               vd->vdev_alloc_bias != VDEV_BIAS_DEDUP) ||
                               l2arc_exclude_special == 0)
                                   return (B_TRUE);
                   }
           }
   
           return (B_FALSE);
   }
   
   /*
    * Instantiates the objset_t in-memory structure corresponding to the
    * objset_phys_t that's pointed to by the specified blkptr_t.
    */
   int
   dmu_objset_open_impl(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
       objset_t **osp)
   {
           objset_t *os;
           int i, err;
   
           ASSERT(ds == NULL || MUTEX_HELD(&ds->ds_opening_lock));
           ASSERT(!BP_IS_REDACTED(bp));
   
           /*
            * We need the pool config lock to get properties.
            */
           ASSERT(ds == NULL || dsl_pool_config_held(ds->ds_dir->dd_pool));
   
           /*
            * The $ORIGIN dataset (if it exists) doesn't have an associated
            * objset, so there's no reason to open it. The $ORIGIN dataset
            * will not exist on pools older than SPA_VERSION_ORIGIN.
            */
           if (ds != NULL && spa_get_dsl(spa) != NULL &&
               spa_get_dsl(spa)->dp_origin_snap != NULL) {
                   ASSERT3P(ds->ds_dir, !=,
                       spa_get_dsl(spa)->dp_origin_snap->ds_dir);
           }
   
           os = kmem_zalloc(sizeof (objset_t), KM_SLEEP);
           os->os_dsl_dataset = ds;
           os->os_spa = spa;
           os->os_rootbp = bp;
           if (!BP_IS_HOLE(os->os_rootbp)) {
                   arc_flags_t aflags = ARC_FLAG_WAIT;
                   zbookmark_phys_t zb;
                   int size;
                   zio_flag_t zio_flags = ZIO_FLAG_CANFAIL;
                   SET_BOOKMARK(&zb, ds ? ds->ds_object : DMU_META_OBJSET,
                       ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
   
                   if (dmu_os_is_l2cacheable(os))
                           aflags |= ARC_FLAG_L2CACHE;
   
                   if (ds != NULL && ds->ds_dir->dd_crypto_obj != 0) {
                           ASSERT3U(BP_GET_COMPRESS(bp), ==, ZIO_COMPRESS_OFF);
                           ASSERT(BP_IS_AUTHENTICATED(bp));
                           zio_flags |= ZIO_FLAG_RAW;
                   }
   
                   dprintf_bp(os->os_rootbp, "reading %s", "");
                   err = arc_read(NULL, spa, os->os_rootbp,
                       arc_getbuf_func, &os->os_phys_buf,
                       ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
                   if (err != 0) {
                           kmem_free(os, sizeof (objset_t));
                           /* convert checksum errors into IO errors */
                           if (err == ECKSUM)
                                   err = SET_ERROR(EIO);
                           return (err);
                   }
   
                   if (spa_version(spa) < SPA_VERSION_USERSPACE)
                           size = OBJSET_PHYS_SIZE_V1;
                   else if (!spa_feature_is_enabled(spa,
                       SPA_FEATURE_PROJECT_QUOTA))
                           size = OBJSET_PHYS_SIZE_V2;
                   else
                           size = sizeof (objset_phys_t);
   
                   /* Increase the blocksize if we are permitted. */
                   if (arc_buf_size(os->os_phys_buf) < size) {
                           arc_buf_t *buf = arc_alloc_buf(spa, &os->os_phys_buf,
                               ARC_BUFC_METADATA, size);
                           memset(buf->b_data, 0, size);
                           memcpy(buf->b_data, os->os_phys_buf->b_data,
                               arc_buf_size(os->os_phys_buf));
                           arc_buf_destroy(os->os_phys_buf, &os->os_phys_buf);
                           os->os_phys_buf = buf;
                   }
   
                   os->os_phys = os->os_phys_buf->b_data;
                   os->os_flags = os->os_phys->os_flags;
           } else {
                   int size = spa_version(spa) >= SPA_VERSION_USERSPACE ?
                       sizeof (objset_phys_t) : OBJSET_PHYS_SIZE_V1;
                   os->os_phys_buf = arc_alloc_buf(spa, &os->os_phys_buf,
                       ARC_BUFC_METADATA, size);
                   os->os_phys = os->os_phys_buf->b_data;
                   memset(os->os_phys, 0, size);
           }
           /*
            * These properties will be filled in by the logic in zfs_get_zplprop()
            * when they are queried for the first time.
            */
           os->os_version = OBJSET_PROP_UNINITIALIZED;
           os->os_normalization = OBJSET_PROP_UNINITIALIZED;
           os->os_utf8only = OBJSET_PROP_UNINITIALIZED;
           os->os_casesensitivity = OBJSET_PROP_UNINITIALIZED;
   
           /*
            * Note: the changed_cb will be called once before the register
            * func returns, thus changing the checksum/compression from the
            * default (fletcher2/off).  Snapshots don't need to know about
            * checksum/compression/copies.
            */
           if (ds != NULL) {
                   os->os_encrypted = (ds->ds_dir->dd_crypto_obj != 0);
   
                   err = dsl_prop_register(ds,
                       zfs_prop_to_name(ZFS_PROP_PRIMARYCACHE),
                       primary_cache_changed_cb, os);
                   if (err == 0) {
                           err = dsl_prop_register(ds,
                               zfs_prop_to_name(ZFS_PROP_SECONDARYCACHE),
                               secondary_cache_changed_cb, os);
                   }
                   if (!ds->ds_is_snapshot) {
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_CHECKSUM),
                                       checksum_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_COMPRESSION),
                                       compression_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_COPIES),
                                       copies_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_DEDUP),
                                       dedup_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_LOGBIAS),
                                       logbias_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_SYNC),
                                       sync_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(
                                       ZFS_PROP_REDUNDANT_METADATA),
                                       redundant_metadata_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_RECORDSIZE),
                                       recordsize_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(ZFS_PROP_DNODESIZE),
                                       dnodesize_changed_cb, os);
                           }
                           if (err == 0) {
                                   err = dsl_prop_register(ds,
                                       zfs_prop_to_name(
                                       ZFS_PROP_SPECIAL_SMALL_BLOCKS),
                                       smallblk_changed_cb, os);
                           }
                   }
                   if (err != 0) {
                           arc_buf_destroy(os->os_phys_buf, &os->os_phys_buf);
                           kmem_free(os, sizeof (objset_t));
                           return (err);
                   }
           } else {
                   /* It's the meta-objset. */
                   os->os_checksum = ZIO_CHECKSUM_FLETCHER_4;
                   os->os_compress = ZIO_COMPRESS_ON;
                   os->os_complevel = ZIO_COMPLEVEL_DEFAULT;
                   os->os_encrypted = B_FALSE;
                   os->os_copies = spa_max_replication(spa);
                   os->os_dedup_checksum = ZIO_CHECKSUM_OFF;
                   os->os_dedup_verify = B_FALSE;
                   os->os_logbias = ZFS_LOGBIAS_LATENCY;
                   os->os_sync = ZFS_SYNC_STANDARD;
                   os->os_primary_cache = ZFS_CACHE_ALL;
                   os->os_secondary_cache = ZFS_CACHE_ALL;
                   os->os_dnodesize = DNODE_MIN_SIZE;
           }
   
           if (ds == NULL || !ds->ds_is_snapshot)
                   os->os_zil_header = os->os_phys->os_zil_header;
           os->os_zil = zil_alloc(os, &os->os_zil_header);
   
           for (i = 0; i < TXG_SIZE; i++) {
                   multilist_create(&os->os_dirty_dnodes[i], sizeof (dnode_t),
                       offsetof(dnode_t, dn_dirty_link[i]),
                       dnode_multilist_index_func);
           }
           list_create(&os->os_dnodes, sizeof (dnode_t),
               offsetof(dnode_t, dn_link));
           list_create(&os->os_downgraded_dbufs, sizeof (dmu_buf_impl_t),
               offsetof(dmu_buf_impl_t, db_link));
   
           list_link_init(&os->os_evicting_node);
   
           mutex_init(&os->os_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&os->os_userused_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&os->os_obj_lock, NULL, MUTEX_DEFAULT, NULL);
           mutex_init(&os->os_user_ptr_lock, NULL, MUTEX_DEFAULT, NULL);
           os->os_obj_next_percpu_len = boot_ncpus;
           os->os_obj_next_percpu = kmem_zalloc(os->os_obj_next_percpu_len *
               sizeof (os->os_obj_next_percpu[0]), KM_SLEEP);
   
           dnode_special_open(os, &os->os_phys->os_meta_dnode,
               DMU_META_DNODE_OBJECT, &os->os_meta_dnode);
           if (OBJSET_BUF_HAS_USERUSED(os->os_phys_buf)) {
                   dnode_special_open(os, &os->os_phys->os_userused_dnode,
                       DMU_USERUSED_OBJECT, &os->os_userused_dnode);
                   dnode_special_open(os, &os->os_phys->os_groupused_dnode,
                       DMU_GROUPUSED_OBJECT, &os->os_groupused_dnode);
                   if (OBJSET_BUF_HAS_PROJECTUSED(os->os_phys_buf))
                           dnode_special_open(os,
                               &os->os_phys->os_projectused_dnode,
                               DMU_PROJECTUSED_OBJECT, &os->os_projectused_dnode);
           }
   
           mutex_init(&os->os_upgrade_lock, NULL, MUTEX_DEFAULT, NULL);
   
           *osp = os;
           return (0);
   }
   
   int
   dmu_objset_from_ds(dsl_dataset_t *ds, objset_t **osp)
   {
           int err = 0;
   
           /*
            * We need the pool_config lock to manipulate the dsl_dataset_t.
            * Even if the dataset is long-held, we need the pool_config lock
            * to open the objset, as it needs to get properties.
            */
           ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool));
   
           mutex_enter(&ds->ds_opening_lock);
           if (ds->ds_objset == NULL) {
                   objset_t *os;
                   rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
                   err = dmu_objset_open_impl(dsl_dataset_get_spa(ds),
                       ds, dsl_dataset_get_blkptr(ds), &os);
                   rrw_exit(&ds->ds_bp_rwlock, FTAG);
   
                   if (err == 0) {
                           mutex_enter(&ds->ds_lock);
                           ASSERT(ds->ds_objset == NULL);
                           ds->ds_objset = os;
                           mutex_exit(&ds->ds_lock);
                   }
           }
           *osp = ds->ds_objset;
           mutex_exit(&ds->ds_opening_lock);
           return (err);
   }
   
   /*
    * Holds the pool while the objset is held.  Therefore only one objset
    * can be held at a time.
    */
   int
   dmu_objset_hold_flags(const char *name, boolean_t decrypt, const void *tag,
       objset_t **osp)
   {
           dsl_pool_t *dp;
           dsl_dataset_t *ds;
           int err;
           ds_hold_flags_t flags;
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           err = dsl_pool_hold(name, tag, &dp);
           if (err != 0)
                   return (err);
           err = dsl_dataset_hold_flags(dp, name, flags, tag, &ds);
           if (err != 0) {
                   dsl_pool_rele(dp, tag);
                   return (err);
           }
   
           err = dmu_objset_from_ds(ds, osp);
           if (err != 0) {
                   dsl_dataset_rele(ds, tag);
                   dsl_pool_rele(dp, tag);
           }
   
           return (err);
   }
   
   int
   dmu_objset_hold(const char *name, const void *tag, objset_t **osp)
   {
           return (dmu_objset_hold_flags(name, B_FALSE, tag, osp));
   }
   
   static int
   dmu_objset_own_impl(dsl_dataset_t *ds, dmu_objset_type_t type,
       boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
   {
           (void) tag;
   
           int err = dmu_objset_from_ds(ds, osp);
           if (err != 0) {
                   return (err);
           } else if (type != DMU_OST_ANY && type != (*osp)->os_phys->os_type) {
                   return (SET_ERROR(EINVAL));
           } else if (!readonly && dsl_dataset_is_snapshot(ds)) {
                   return (SET_ERROR(EROFS));
           } else if (!readonly && decrypt &&
               dsl_dir_incompatible_encryption_version(ds->ds_dir)) {
                   return (SET_ERROR(EROFS));
           }
   
           /* if we are decrypting, we can now check MACs in os->os_phys_buf */
           if (decrypt && arc_is_unauthenticated((*osp)->os_phys_buf)) {
                   zbookmark_phys_t zb;
   
                   SET_BOOKMARK(&zb, ds->ds_object, ZB_ROOT_OBJECT,
                       ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
                   err = arc_untransform((*osp)->os_phys_buf, (*osp)->os_spa,
                       &zb, B_FALSE);
                   if (err != 0)
                           return (err);
   
                   ASSERT0(arc_is_unauthenticated((*osp)->os_phys_buf));
           }
   
           return (0);
   }
   
   /*
    * dsl_pool must not be held when this is called.
    * Upon successful return, there will be a longhold on the dataset,
    * and the dsl_pool will not be held.
    */
   int
   dmu_objset_own(const char *name, dmu_objset_type_t type,
       boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
   {
           dsl_pool_t *dp;
           dsl_dataset_t *ds;
           int err;
           ds_hold_flags_t flags;
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           err = dsl_pool_hold(name, FTAG, &dp);
           if (err != 0)
                   return (err);
           err = dsl_dataset_own(dp, name, flags, tag, &ds);
           if (err != 0) {
                   dsl_pool_rele(dp, FTAG);
                   return (err);
           }
           err = dmu_objset_own_impl(ds, type, readonly, decrypt, tag, osp);
           if (err != 0) {
                   dsl_dataset_disown(ds, flags, tag);
                   dsl_pool_rele(dp, FTAG);
                   return (err);
           }
   
           /*
            * User accounting requires the dataset to be decrypted and rw.
            * We also don't begin user accounting during claiming to help
            * speed up pool import times and to keep this txg reserved
            * completely for recovery work.
            */
           if (!readonly && !dp->dp_spa->spa_claiming &&
               (ds->ds_dir->dd_crypto_obj == 0 || decrypt)) {
                   if (dmu_objset_userobjspace_upgradable(*osp) ||
                       dmu_objset_projectquota_upgradable(*osp)) {
                           dmu_objset_id_quota_upgrade(*osp);
                   } else if (dmu_objset_userused_enabled(*osp)) {
                           dmu_objset_userspace_upgrade(*osp);
                   }
           }
   
           dsl_pool_rele(dp, FTAG);
           return (0);
   }
   
   int
   dmu_objset_own_obj(dsl_pool_t *dp, uint64_t obj, dmu_objset_type_t type,
       boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
   {
           dsl_dataset_t *ds;
           int err;
           ds_hold_flags_t flags;
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           err = dsl_dataset_own_obj(dp, obj, flags, tag, &ds);
           if (err != 0)
                   return (err);
   
           err = dmu_objset_own_impl(ds, type, readonly, decrypt, tag, osp);
           if (err != 0) {
                   dsl_dataset_disown(ds, flags, tag);
                   return (err);
           }
   
           return (0);
   }
   
   void
   dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, const void *tag)
   {
           ds_hold_flags_t flags;
           dsl_pool_t *dp = dmu_objset_pool(os);
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           dsl_dataset_rele_flags(os->os_dsl_dataset, flags, tag);
           dsl_pool_rele(dp, tag);
   }
   
   void
   dmu_objset_rele(objset_t *os, const void *tag)
   {
           dmu_objset_rele_flags(os, B_FALSE, tag);
   }
   
   /*
    * When we are called, os MUST refer to an objset associated with a dataset
    * that is owned by 'tag'; that is, is held and long held by 'tag' and ds_owner
    * == tag.  We will then release and reacquire ownership of the dataset while
    * holding the pool config_rwlock to avoid intervening namespace or ownership
    * changes may occur.
    *
    * This exists solely to accommodate zfs_ioc_userspace_upgrade()'s desire to
    * release the hold on its dataset and acquire a new one on the dataset of the
    * same name so that it can be partially torn down and reconstructed.
    */
   void
   dmu_objset_refresh_ownership(dsl_dataset_t *ds, dsl_dataset_t **newds,
       boolean_t decrypt, const void *tag)
   {
           dsl_pool_t *dp;
           char name[ZFS_MAX_DATASET_NAME_LEN];
           ds_hold_flags_t flags;
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           VERIFY3P(ds, !=, NULL);
           VERIFY3P(ds->ds_owner, ==, tag);
           VERIFY(dsl_dataset_long_held(ds));
   
           dsl_dataset_name(ds, name);
           dp = ds->ds_dir->dd_pool;
           dsl_pool_config_enter(dp, FTAG);
           dsl_dataset_disown(ds, flags, tag);
           VERIFY0(dsl_dataset_own(dp, name, flags, tag, newds));
           dsl_pool_config_exit(dp, FTAG);
   }
   
   void
   dmu_objset_disown(objset_t *os, boolean_t decrypt, const void *tag)
   {
           ds_hold_flags_t flags;
   
           flags = (decrypt) ? DS_HOLD_FLAG_DECRYPT : DS_HOLD_FLAG_NONE;
           /*
            * Stop upgrading thread
            */
           dmu_objset_upgrade_stop(os);
           dsl_dataset_disown(os->os_dsl_dataset, flags, tag);
   }
   
   void
   dmu_objset_evict_dbufs(objset_t *os)
   {
           dnode_t *dn_marker;
           dnode_t *dn;
   
           dn_marker = kmem_alloc(sizeof (dnode_t), KM_SLEEP);
   
           mutex_enter(&os->os_lock);
           dn = list_head(&os->os_dnodes);
           while (dn != NULL) {
                   /*
                    * Skip dnodes without holds.  We have to do this dance
                    * because dnode_add_ref() only works if there is already a
                    * hold.  If the dnode has no holds, then it has no dbufs.
                    */
                   if (dnode_add_ref(dn, FTAG)) {
                           list_insert_after(&os->os_dnodes, dn, dn_marker);
                           mutex_exit(&os->os_lock);
   
                           dnode_evict_dbufs(dn);
                           dnode_rele(dn, FTAG);
   
                           mutex_enter(&os->os_lock);
                           dn = list_next(&os->os_dnodes, dn_marker);
                           list_remove(&os->os_dnodes, dn_marker);
                   } else {
                           dn = list_next(&os->os_dnodes, dn);
                   }
           }
           mutex_exit(&os->os_lock);
   
           kmem_free(dn_marker, sizeof (dnode_t));
   
           if (DMU_USERUSED_DNODE(os) != NULL) {
                   if (DMU_PROJECTUSED_DNODE(os) != NULL)
                           dnode_evict_dbufs(DMU_PROJECTUSED_DNODE(os));
                   dnode_evict_dbufs(DMU_GROUPUSED_DNODE(os));
                   dnode_evict_dbufs(DMU_USERUSED_DNODE(os));
           }
           dnode_evict_dbufs(DMU_META_DNODE(os));
   }
   
   /*
    * Objset eviction processing is split into into two pieces.
    * The first marks the objset as evicting, evicts any dbufs that
    * have a refcount of zero, and then queues up the objset for the
    * second phase of eviction.  Once os->os_dnodes has been cleared by
    * dnode_buf_pageout()->dnode_destroy(), the second phase is executed.
    * The second phase closes the special dnodes, dequeues the objset from
    * the list of those undergoing eviction, and finally frees the objset.
    *
    * NOTE: Due to asynchronous eviction processing (invocation of
    *       dnode_buf_pageout()), it is possible for the meta dnode for the
    *       objset to have no holds even though os->os_dnodes is not empty.
    */
   void
   dmu_objset_evict(objset_t *os)
   {
           dsl_dataset_t *ds = os->os_dsl_dataset;
   
           for (int t = 0; t < TXG_SIZE; t++)
                   ASSERT(!dmu_objset_is_dirty(os, t));
   
           if (ds)
                   dsl_prop_unregister_all(ds, os);
   
           if (os->os_sa)
                   sa_tear_down(os);
   
           dmu_objset_evict_dbufs(os);
   
           mutex_enter(&os->os_lock);
           spa_evicting_os_register(os->os_spa, os);
           if (list_is_empty(&os->os_dnodes)) {
                   mutex_exit(&os->os_lock);
                   dmu_objset_evict_done(os);
           } else {
                  mutex_exit(&os->os_lock);
          }
  
  
  }
  
  void
  dmu_objset_evict_done(objset_t *os)
  {
          ASSERT3P(list_head(&os->os_dnodes), ==, NULL);
  
          dnode_special_close(&os->os_meta_dnode);
          if (DMU_USERUSED_DNODE(os)) {
                  if (DMU_PROJECTUSED_DNODE(os))
                          dnode_special_close(&os->os_projectused_dnode);
                  dnode_special_close(&os->os_userused_dnode);
                  dnode_special_close(&os->os_groupused_dnode);
          }
          zil_free(os->os_zil);
  
          arc_buf_destroy(os->os_phys_buf, &os->os_phys_buf);
  
          /*
           * This is a barrier to prevent the objset from going away in
           * dnode_move() until we can safely ensure that the objset is still in
           * use. We consider the objset valid before the barrier and invalid
           * after the barrier.
           */
          rw_enter(&os_lock, RW_READER);
          rw_exit(&os_lock);
  
          kmem_free(os->os_obj_next_percpu,
              os->os_obj_next_percpu_len * sizeof (os->os_obj_next_percpu[0]));
  
          mutex_destroy(&os->os_lock);
          mutex_destroy(&os->os_userused_lock);
          mutex_destroy(&os->os_obj_lock);
          mutex_destroy(&os->os_user_ptr_lock);
          mutex_destroy(&os->os_upgrade_lock);
          for (int i = 0; i < TXG_SIZE; i++)
                  multilist_destroy(&os->os_dirty_dnodes[i]);
          spa_evicting_os_deregister(os->os_spa, os);
          kmem_free(os, sizeof (objset_t));
  }
  
  inode_timespec_t
  dmu_objset_snap_cmtime(objset_t *os)
  {
          return (dsl_dir_snap_cmtime(os->os_dsl_dataset->ds_dir));
  }
  
  objset_t *
  dmu_objset_create_impl_dnstats(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
      dmu_objset_type_t type, int levels, int blksz, int ibs, dmu_tx_t *tx)
  {
          objset_t *os;
          dnode_t *mdn;
  
          ASSERT(dmu_tx_is_syncing(tx));
  
          if (blksz == 0)
                  blksz = DNODE_BLOCK_SIZE;
          if (ibs == 0)
                  ibs = DN_MAX_INDBLKSHIFT;
  
          if (ds != NULL)
                  VERIFY0(dmu_objset_from_ds(ds, &os));
          else
                  VERIFY0(dmu_objset_open_impl(spa, NULL, bp, &os));
  
          mdn = DMU_META_DNODE(os);
  
          dnode_allocate(mdn, DMU_OT_DNODE, blksz, ibs, DMU_OT_NONE, 0,
              DNODE_MIN_SLOTS, tx);
  
          /*
           * We don't want to have to increase the meta-dnode's nlevels
           * later, because then we could do it in quiescing context while
           * we are also accessing it in open context.
           *
           * This precaution is not necessary for the MOS (ds == NULL),
           * because the MOS is only updated in syncing context.
           * This is most fortunate: the MOS is the only objset that
           * needs to be synced multiple times as spa_sync() iterates
           * to convergence, so minimizing its dn_nlevels matters.
           */
          if (ds != NULL) {
                  if (levels == 0) {
                          levels = 1;
  
                          /*
                           * Determine the number of levels necessary for the
                           * meta-dnode to contain DN_MAX_OBJECT dnodes.  Note
                           * that in order to ensure that we do not overflow
                           * 64 bits, there has to be a nlevels that gives us a
                           * number of blocks > DN_MAX_OBJECT but < 2^64.
                           * Therefore, (mdn->dn_indblkshift - SPA_BLKPTRSHIFT)
                           * (10) must be less than (64 - log2(DN_MAX_OBJECT))
                           * (16).
                           */
                          while ((uint64_t)mdn->dn_nblkptr <<
                              (mdn->dn_datablkshift - DNODE_SHIFT + (levels - 1) *
                              (mdn->dn_indblkshift - SPA_BLKPTRSHIFT)) <
                              DN_MAX_OBJECT)
                                  levels++;
                  }
  
                  mdn->dn_next_nlevels[tx->tx_txg & TXG_MASK] =
                      mdn->dn_nlevels = levels;
          }
  
          ASSERT(type != DMU_OST_NONE);
          ASSERT(type != DMU_OST_ANY);
          ASSERT(type < DMU_OST_NUMTYPES);
          os->os_phys->os_type = type;
  
          /*
           * Enable user accounting if it is enabled and this is not an
           * encrypted receive.
           */
          if (dmu_objset_userused_enabled(os) &&
              (!os->os_encrypted || !dmu_objset_is_receiving(os))) {
                  os->os_phys->os_flags |= OBJSET_FLAG_USERACCOUNTING_COMPLETE;
                  if (dmu_objset_userobjused_enabled(os)) {
                          ds->ds_feature_activation[
                              SPA_FEATURE_USEROBJ_ACCOUNTING] = (void *)B_TRUE;
                          os->os_phys->os_flags |=
                              OBJSET_FLAG_USEROBJACCOUNTING_COMPLETE;
                  }
                  if (dmu_objset_projectquota_enabled(os)) {
                          ds->ds_feature_activation[
                              SPA_FEATURE_PROJECT_QUOTA] = (void *)B_TRUE;
                          os->os_phys->os_flags |=
                              OBJSET_FLAG_PROJECTQUOTA_COMPLETE;
                  }
                  os->os_flags = os->os_phys->os_flags;
          }
  
          dsl_dataset_dirty(ds, tx);
  
          return (os);
  }
  
  /* called from dsl for meta-objset */
  objset_t *
  dmu_objset_create_impl(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
      dmu_objset_type_t type, dmu_tx_t *tx)
  {
          return (dmu_objset_create_impl_dnstats(spa, ds, bp, type, 0, 0, 0, tx));
  }
  
  typedef struct dmu_objset_create_arg {
          const char *doca_name;
          cred_t *doca_cred;
          proc_t *doca_proc;
          void (*doca_userfunc)(objset_t *os, void *arg,
              cred_t *cr, dmu_tx_t *tx);
          void *doca_userarg;
          dmu_objset_type_t doca_type;
          uint64_t doca_flags;
          dsl_crypto_params_t *doca_dcp;
  } dmu_objset_create_arg_t;
  
  static int
  dmu_objset_create_check(void *arg, dmu_tx_t *tx)
  {
          dmu_objset_create_arg_t *doca = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *pdd;
          dsl_dataset_t *parentds;
          objset_t *parentos;
          const char *tail;
          int error;
  
          if (strchr(doca->doca_name, '@') != NULL)
                  return (SET_ERROR(EINVAL));
  
          if (strlen(doca->doca_name) >= ZFS_MAX_DATASET_NAME_LEN)
                  return (SET_ERROR(ENAMETOOLONG));
  
          if (dataset_nestcheck(doca->doca_name) != 0)
                  return (SET_ERROR(ENAMETOOLONG));
  
          error = dsl_dir_hold(dp, doca->doca_name, FTAG, &pdd, &tail);
          if (error != 0)
                  return (error);
          if (tail == NULL) {
                  dsl_dir_rele(pdd, FTAG);
                  return (SET_ERROR(EEXIST));
          }
  
          error = dmu_objset_create_crypt_check(pdd, doca->doca_dcp, NULL);
          if (error != 0) {
                  dsl_dir_rele(pdd, FTAG);
                  return (error);
          }
  
          error = dsl_fs_ss_limit_check(pdd, 1, ZFS_PROP_FILESYSTEM_LIMIT, NULL,
              doca->doca_cred, doca->doca_proc);
          if (error != 0) {
                  dsl_dir_rele(pdd, FTAG);
                  return (error);
          }
  
          /* can't create below anything but filesystems (eg. no ZVOLs) */
          error = dsl_dataset_hold_obj(pdd->dd_pool,
              dsl_dir_phys(pdd)->dd_head_dataset_obj, FTAG, &parentds);
          if (error != 0) {
                  dsl_dir_rele(pdd, FTAG);
                  return (error);
          }
          error = dmu_objset_from_ds(parentds, &parentos);
          if (error != 0) {
                  dsl_dataset_rele(parentds, FTAG);
                  dsl_dir_rele(pdd, FTAG);
                  return (error);
          }
          if (dmu_objset_type(parentos) != DMU_OST_ZFS) {
                  dsl_dataset_rele(parentds, FTAG);
                  dsl_dir_rele(pdd, FTAG);
                  return (SET_ERROR(ZFS_ERR_WRONG_PARENT));
          }
          dsl_dataset_rele(parentds, FTAG);
          dsl_dir_rele(pdd, FTAG);
  
          return (error);
  }
  
  static void
  dmu_objset_create_sync(void *arg, dmu_tx_t *tx)
  {
          dmu_objset_create_arg_t *doca = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          spa_t *spa = dp->dp_spa;
          dsl_dir_t *pdd;
          const char *tail;
          dsl_dataset_t *ds;
          uint64_t obj;
          blkptr_t *bp;
          objset_t *os;
          zio_t *rzio;
  
          VERIFY0(dsl_dir_hold(dp, doca->doca_name, FTAG, &pdd, &tail));
  
          obj = dsl_dataset_create_sync(pdd, tail, NULL, doca->doca_flags,
              doca->doca_cred, doca->doca_dcp, tx);
  
          VERIFY0(dsl_dataset_hold_obj_flags(pdd->dd_pool, obj,
              DS_HOLD_FLAG_DECRYPT, FTAG, &ds));
          rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
          bp = dsl_dataset_get_blkptr(ds);
          os = dmu_objset_create_impl(spa, ds, bp, doca->doca_type, tx);
          rrw_exit(&ds->ds_bp_rwlock, FTAG);
  
          if (doca->doca_userfunc != NULL) {
                  doca->doca_userfunc(os, doca->doca_userarg,
                      doca->doca_cred, tx);
          }
  
          /*
           * The doca_userfunc() may write out some data that needs to be
           * encrypted if the dataset is encrypted (specifically the root
           * directory).  This data must be written out before the encryption
           * key mapping is removed by dsl_dataset_rele_flags().  Force the
           * I/O to occur immediately by invoking the relevant sections of
           * dsl_pool_sync().
           */
          if (os->os_encrypted) {
                  dsl_dataset_t *tmpds = NULL;
                  boolean_t need_sync_done = B_FALSE;
  
                  mutex_enter(&ds->ds_lock);
                  ds->ds_owner = FTAG;
                  mutex_exit(&ds->ds_lock);
  
                  rzio = zio_root(spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
                  tmpds = txg_list_remove_this(&dp->dp_dirty_datasets, ds,
                      tx->tx_txg);
                  if (tmpds != NULL) {
                          dsl_dataset_sync(ds, rzio, tx);
                          need_sync_done = B_TRUE;
                  }
                  VERIFY0(zio_wait(rzio));
  
                  dmu_objset_sync_done(os, tx);
                  taskq_wait(dp->dp_sync_taskq);
                  if (txg_list_member(&dp->dp_dirty_datasets, ds, tx->tx_txg)) {
                          ASSERT3P(ds->ds_key_mapping, !=, NULL);
                          key_mapping_rele(spa, ds->ds_key_mapping, ds);
                  }
  
                  rzio = zio_root(spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
                  tmpds = txg_list_remove_this(&dp->dp_dirty_datasets, ds,
                      tx->tx_txg);
                  if (tmpds != NULL) {
                          dmu_buf_rele(ds->ds_dbuf, ds);
                          dsl_dataset_sync(ds, rzio, tx);
                  }
                  VERIFY0(zio_wait(rzio));
  
                  if (need_sync_done) {
                          ASSERT3P(ds->ds_key_mapping, !=, NULL);
                          key_mapping_rele(spa, ds->ds_key_mapping, ds);
                          dsl_dataset_sync_done(ds, tx);
                  }
  
                  mutex_enter(&ds->ds_lock);
                  ds->ds_owner = NULL;
                  mutex_exit(&ds->ds_lock);
          }
  
          spa_history_log_internal_ds(ds, "create", tx, " ");
  
          dsl_dataset_rele_flags(ds, DS_HOLD_FLAG_DECRYPT, FTAG);
          dsl_dir_rele(pdd, FTAG);
  }
  
  int
  dmu_objset_create(const char *name, dmu_objset_type_t type, uint64_t flags,
      dsl_crypto_params_t *dcp, dmu_objset_create_sync_func_t func, void *arg)
  {
          dmu_objset_create_arg_t doca;
          dsl_crypto_params_t tmp_dcp = { 0 };
  
          doca.doca_name = name;
          doca.doca_cred = CRED();
          doca.doca_proc = curproc;
          doca.doca_flags = flags;
          doca.doca_userfunc = func;
          doca.doca_userarg = arg;
          doca.doca_type = type;
  
          /*
           * Some callers (mostly for testing) do not provide a dcp on their
           * own but various code inside the sync task will require it to be
           * allocated. Rather than adding NULL checks throughout this code
           * or adding dummy dcp's to all of the callers we simply create a
           * dummy one here and use that. This zero dcp will have the same
           * effect as asking for inheritance of all encryption params.
           */
          doca.doca_dcp = (dcp != NULL) ? dcp : &tmp_dcp;
  
          int rv = dsl_sync_task(name,
              dmu_objset_create_check, dmu_objset_create_sync, &doca,
              6, ZFS_SPACE_CHECK_NORMAL);
  
          if (rv == 0)
                  zvol_create_minor(name);
          return (rv);
  }
  
  typedef struct dmu_objset_clone_arg {
          const char *doca_clone;
          const char *doca_origin;
          cred_t *doca_cred;
          proc_t *doca_proc;
  } dmu_objset_clone_arg_t;
  
  static int
  dmu_objset_clone_check(void *arg, dmu_tx_t *tx)
  {
          dmu_objset_clone_arg_t *doca = arg;
          dsl_dir_t *pdd;
          const char *tail;
          int error;
          dsl_dataset_t *origin;
          dsl_pool_t *dp = dmu_tx_pool(tx);
  
          if (strchr(doca->doca_clone, '@') != NULL)
                  return (SET_ERROR(EINVAL));
  
          if (strlen(doca->doca_clone) >= ZFS_MAX_DATASET_NAME_LEN)
                  return (SET_ERROR(ENAMETOOLONG));
  
          error = dsl_dir_hold(dp, doca->doca_clone, FTAG, &pdd, &tail);
          if (error != 0)
                  return (error);
          if (tail == NULL) {
                  dsl_dir_rele(pdd, FTAG);
                  return (SET_ERROR(EEXIST));
          }
  
          error = dsl_fs_ss_limit_check(pdd, 1, ZFS_PROP_FILESYSTEM_LIMIT, NULL,
              doca->doca_cred, doca->doca_proc);
          if (error != 0) {
                  dsl_dir_rele(pdd, FTAG);
                  return (SET_ERROR(EDQUOT));
          }
  
          error = dsl_dataset_hold(dp, doca->doca_origin, FTAG, &origin);
          if (error != 0) {
                  dsl_dir_rele(pdd, FTAG);
                  return (error);
          }
  
          /* You can only clone snapshots, not the head datasets. */
          if (!origin->ds_is_snapshot) {
                  dsl_dataset_rele(origin, FTAG);
                  dsl_dir_rele(pdd, FTAG);
                  return (SET_ERROR(EINVAL));
          }
  
          dsl_dataset_rele(origin, FTAG);
          dsl_dir_rele(pdd, FTAG);
  
          return (0);
  }
  
  static void
  dmu_objset_clone_sync(void *arg, dmu_tx_t *tx)
  {
          dmu_objset_clone_arg_t *doca = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *pdd;
          const char *tail;
          dsl_dataset_t *origin, *ds;
          uint64_t obj;
          char namebuf[ZFS_MAX_DATASET_NAME_LEN];
  
          VERIFY0(dsl_dir_hold(dp, doca->doca_clone, FTAG, &pdd, &tail));
          VERIFY0(dsl_dataset_hold(dp, doca->doca_origin, FTAG, &origin));
  
          obj = dsl_dataset_create_sync(pdd, tail, origin, 0,
              doca->doca_cred, NULL, tx);
  
          VERIFY0(dsl_dataset_hold_obj(pdd->dd_pool, obj, FTAG, &ds));
          dsl_dataset_name(origin, namebuf);
          spa_history_log_internal_ds(ds, "clone", tx,
              "origin=%s (%llu)", namebuf, (u_longlong_t)origin->ds_object);
          dsl_dataset_rele(ds, FTAG);
          dsl_dataset_rele(origin, FTAG);
          dsl_dir_rele(pdd, FTAG);
  }
  
  int
  dmu_objset_clone(const char *clone, const char *origin)
  {
          dmu_objset_clone_arg_t doca;
  
          doca.doca_clone = clone;
          doca.doca_origin = origin;
          doca.doca_cred = CRED();
          doca.doca_proc = curproc;
  
          int rv = dsl_sync_task(clone,
              dmu_objset_clone_check, dmu_objset_clone_sync, &doca,
              6, ZFS_SPACE_CHECK_NORMAL);
  
          if (rv == 0)
                  zvol_create_minor(clone);
  
          return (rv);
  }
  
  int
  dmu_objset_snapshot_one(const char *fsname, const char *snapname)
  {
          int err;
          char *longsnap = kmem_asprintf("%s@%s", fsname, snapname);
          nvlist_t *snaps = fnvlist_alloc();
  
          fnvlist_add_boolean(snaps, longsnap);
          kmem_strfree(longsnap);
          err = dsl_dataset_snapshot(snaps, NULL, NULL);
          fnvlist_free(snaps);
          return (err);
  }
  
  static void
  dmu_objset_upgrade_task_cb(void *data)
  {
          objset_t *os = data;
  
          mutex_enter(&os->os_upgrade_lock);
          os->os_upgrade_status = EINTR;
          if (!os->os_upgrade_exit) {
                  int status;
  
                  mutex_exit(&os->os_upgrade_lock);
  
                  status = os->os_upgrade_cb(os);
  
                  mutex_enter(&os->os_upgrade_lock);
  
                  os->os_upgrade_status = status;
          }
          os->os_upgrade_exit = B_TRUE;
          os->os_upgrade_id = 0;
          mutex_exit(&os->os_upgrade_lock);
          dsl_dataset_long_rele(dmu_objset_ds(os), upgrade_tag);
  }
  
  static void
  dmu_objset_upgrade(objset_t *os, dmu_objset_upgrade_cb_t cb)
  {
          if (os->os_upgrade_id != 0)
                  return;
  
          ASSERT(dsl_pool_config_held(dmu_objset_pool(os)));
          dsl_dataset_long_hold(dmu_objset_ds(os), upgrade_tag);
  
          mutex_enter(&os->os_upgrade_lock);
          if (os->os_upgrade_id == 0 && os->os_upgrade_status == 0) {
                  os->os_upgrade_exit = B_FALSE;
                  os->os_upgrade_cb = cb;
                  os->os_upgrade_id = taskq_dispatch(
                      os->os_spa->spa_upgrade_taskq,
                      dmu_objset_upgrade_task_cb, os, TQ_SLEEP);
                  if (os->os_upgrade_id == TASKQID_INVALID) {
                          dsl_dataset_long_rele(dmu_objset_ds(os), upgrade_tag);
                          os->os_upgrade_status = ENOMEM;
                  }
          } else {
                  dsl_dataset_long_rele(dmu_objset_ds(os), upgrade_tag);
          }
          mutex_exit(&os->os_upgrade_lock);
  }
  
  static void
  dmu_objset_upgrade_stop(objset_t *os)
  {
          mutex_enter(&os->os_upgrade_lock);
          os->os_upgrade_exit = B_TRUE;
          if (os->os_upgrade_id != 0) {
                  taskqid_t id = os->os_upgrade_id;
  
                  os->os_upgrade_id = 0;
                  mutex_exit(&os->os_upgrade_lock);
  
                  if ((taskq_cancel_id(os->os_spa->spa_upgrade_taskq, id)) == 0) {
                          dsl_dataset_long_rele(dmu_objset_ds(os), upgrade_tag);
                  }
                  txg_wait_synced(os->os_spa->spa_dsl_pool, 0);
          } else {
                  mutex_exit(&os->os_upgrade_lock);
          }
  }
  
  static void
  dmu_objset_sync_dnodes(multilist_sublist_t *list, dmu_tx_t *tx)
  {
          dnode_t *dn;
  
          while ((dn = multilist_sublist_head(list)) != NULL) {
                  ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT);
                  ASSERT(dn->dn_dbuf->db_data_pending);
                  /*
                   * Initialize dn_zio outside dnode_sync() because the
                   * meta-dnode needs to set it outside dnode_sync().
                   */
                  dn->dn_zio = dn->dn_dbuf->db_data_pending->dr_zio;
                  ASSERT(dn->dn_zio);
  
                  ASSERT3U(dn->dn_nlevels, <=, DN_MAX_LEVELS);
                  multilist_sublist_remove(list, dn);
  
                  /*
                   * See the comment above dnode_rele_task() for an explanation
                   * of why this dnode hold is always needed (even when not
                   * doing user accounting).
                   */
                  multilist_t *newlist = &dn->dn_objset->os_synced_dnodes;
                  (void) dnode_add_ref(dn, newlist);
                  multilist_insert(newlist, dn);
  
                  dnode_sync(dn, tx);
          }
  }
  
  static void
  dmu_objset_write_ready(zio_t *zio, arc_buf_t *abuf, void *arg)
  {
          (void) abuf;
          blkptr_t *bp = zio->io_bp;
          objset_t *os = arg;
          dnode_phys_t *dnp = &os->os_phys->os_meta_dnode;
          uint64_t fill = 0;
  
          ASSERT(!BP_IS_EMBEDDED(bp));
          ASSERT3U(BP_GET_TYPE(bp), ==, DMU_OT_OBJSET);
          ASSERT0(BP_GET_LEVEL(bp));
  
          /*
           * Update rootbp fill count: it should be the number of objects
           * allocated in the object set (not counting the "special"
           * objects that are stored in the objset_phys_t -- the meta
           * dnode and user/group/project accounting objects).
           */
          for (int i = 0; i < dnp->dn_nblkptr; i++)
                  fill += BP_GET_FILL(&dnp->dn_blkptr[i]);
  
          BP_SET_FILL(bp, fill);
  
          if (os->os_dsl_dataset != NULL)
                  rrw_enter(&os->os_dsl_dataset->ds_bp_rwlock, RW_WRITER, FTAG);
          *os->os_rootbp = *bp;
          if (os->os_dsl_dataset != NULL)
                  rrw_exit(&os->os_dsl_dataset->ds_bp_rwlock, FTAG);
  }
  
  static void
  dmu_objset_write_done(zio_t *zio, arc_buf_t *abuf, void *arg)
  {
          (void) abuf;
          blkptr_t *bp = zio->io_bp;
          blkptr_t *bp_orig = &zio->io_bp_orig;
          objset_t *os = arg;
  
          if (zio->io_flags & ZIO_FLAG_IO_REWRITE) {
                  ASSERT(BP_EQUAL(bp, bp_orig));
          } else {
                  dsl_dataset_t *ds = os->os_dsl_dataset;
                  dmu_tx_t *tx = os->os_synctx;
  
                  (void) dsl_dataset_block_kill(ds, bp_orig, tx, B_TRUE);
                  dsl_dataset_block_born(ds, bp, tx);
          }
          kmem_free(bp, sizeof (*bp));
  }
  
  typedef struct sync_dnodes_arg {
          multilist_t *sda_list;
          int sda_sublist_idx;
          multilist_t *sda_newlist;
          dmu_tx_t *sda_tx;
  } sync_dnodes_arg_t;
  
  static void
  sync_dnodes_task(void *arg)
  {
          sync_dnodes_arg_t *sda = arg;
  
          multilist_sublist_t *ms =
              multilist_sublist_lock(sda->sda_list, sda->sda_sublist_idx);
  
          dmu_objset_sync_dnodes(ms, sda->sda_tx);
  
          multilist_sublist_unlock(ms);
  
          kmem_free(sda, sizeof (*sda));
  }
  
  
  /* called from dsl */
  void
  dmu_objset_sync(objset_t *os, zio_t *pio, dmu_tx_t *tx)
  {
          int txgoff;
          zbookmark_phys_t zb;
          zio_prop_t zp;
          zio_t *zio;
          list_t *list;
          dbuf_dirty_record_t *dr;
          int num_sublists;
          multilist_t *ml;
          blkptr_t *blkptr_copy = kmem_alloc(sizeof (*os->os_rootbp), KM_SLEEP);
          *blkptr_copy = *os->os_rootbp;
  
          dprintf_ds(os->os_dsl_dataset, "txg=%llu\n", (u_longlong_t)tx->tx_txg);
  
          ASSERT(dmu_tx_is_syncing(tx));
          /* XXX the write_done callback should really give us the tx... */
          os->os_synctx = tx;
  
          if (os->os_dsl_dataset == NULL) {
                  /*
                   * This is the MOS.  If we have upgraded,
                   * spa_max_replication() could change, so reset
                   * os_copies here.
                   */
                  os->os_copies = spa_max_replication(os->os_spa);
          }
  
          /*
           * Create the root block IO
           */
          SET_BOOKMARK(&zb, os->os_dsl_dataset ?
              os->os_dsl_dataset->ds_object : DMU_META_OBJSET,
              ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
          arc_release(os->os_phys_buf, &os->os_phys_buf);
  
          dmu_write_policy(os, NULL, 0, 0, &zp);
  
          /*
           * If we are either claiming the ZIL or doing a raw receive, write
           * out the os_phys_buf raw. Neither of these actions will effect the
           * MAC at this point.
           */
          if (os->os_raw_receive ||
              os->os_next_write_raw[tx->tx_txg & TXG_MASK]) {
                  ASSERT(os->os_encrypted);
                  arc_convert_to_raw(os->os_phys_buf,
                      os->os_dsl_dataset->ds_object, ZFS_HOST_BYTEORDER,
                      DMU_OT_OBJSET, NULL, NULL, NULL);
          }
  
          zio = arc_write(pio, os->os_spa, tx->tx_txg,
              blkptr_copy, os->os_phys_buf, B_FALSE, dmu_os_is_l2cacheable(os),
              &zp, dmu_objset_write_ready, NULL, NULL, dmu_objset_write_done,
              os, ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
  
          /*
           * Sync special dnodes - the parent IO for the sync is the root block
           */
          DMU_META_DNODE(os)->dn_zio = zio;
          dnode_sync(DMU_META_DNODE(os), tx);
  
          os->os_phys->os_flags = os->os_flags;
  
          if (DMU_USERUSED_DNODE(os) &&
              DMU_USERUSED_DNODE(os)->dn_type != DMU_OT_NONE) {
                  DMU_USERUSED_DNODE(os)->dn_zio = zio;
                  dnode_sync(DMU_USERUSED_DNODE(os), tx);
                  DMU_GROUPUSED_DNODE(os)->dn_zio = zio;
                  dnode_sync(DMU_GROUPUSED_DNODE(os), tx);
          }
  
          if (DMU_PROJECTUSED_DNODE(os) &&
              DMU_PROJECTUSED_DNODE(os)->dn_type != DMU_OT_NONE) {
                  DMU_PROJECTUSED_DNODE(os)->dn_zio = zio;
                  dnode_sync(DMU_PROJECTUSED_DNODE(os), tx);
          }
  
          txgoff = tx->tx_txg & TXG_MASK;
  
          /*
           * We must create the list here because it uses the
           * dn_dirty_link[] of this txg.  But it may already
           * exist because we call dsl_dataset_sync() twice per txg.
           */
          if (os->os_synced_dnodes.ml_sublists == NULL) {
                  multilist_create(&os->os_synced_dnodes, sizeof (dnode_t),
                      offsetof(dnode_t, dn_dirty_link[txgoff]),
                      dnode_multilist_index_func);
          } else {
                  ASSERT3U(os->os_synced_dnodes.ml_offset, ==,
                      offsetof(dnode_t, dn_dirty_link[txgoff]));
          }
  
          ml = &os->os_dirty_dnodes[txgoff];
          num_sublists = multilist_get_num_sublists(ml);
          for (int i = 0; i < num_sublists; i++) {
                  if (multilist_sublist_is_empty_idx(ml, i))
                          continue;
                  sync_dnodes_arg_t *sda = kmem_alloc(sizeof (*sda), KM_SLEEP);
                  sda->sda_list = ml;
                  sda->sda_sublist_idx = i;
                  sda->sda_tx = tx;
                  (void) taskq_dispatch(dmu_objset_pool(os)->dp_sync_taskq,
                      sync_dnodes_task, sda, 0);
                  /* callback frees sda */
          }
          taskq_wait(dmu_objset_pool(os)->dp_sync_taskq);
  
          list = &DMU_META_DNODE(os)->dn_dirty_records[txgoff];
          while ((dr = list_head(list)) != NULL) {
                  ASSERT0(dr->dr_dbuf->db_level);
                  list_remove(list, dr);
                  zio_nowait(dr->dr_zio);
          }
  
          /* Enable dnode backfill if enough objects have been freed. */
          if (os->os_freed_dnodes >= dmu_rescan_dnode_threshold) {
                  os->os_rescan_dnodes = B_TRUE;
                  os->os_freed_dnodes = 0;
          }
  
          /*
           * Free intent log blocks up to this tx.
           */
          zil_sync(os->os_zil, tx);
          os->os_phys->os_zil_header = os->os_zil_header;
          zio_nowait(zio);
  }
  
  boolean_t
  dmu_objset_is_dirty(objset_t *os, uint64_t txg)
  {
          return (!multilist_is_empty(&os->os_dirty_dnodes[txg & TXG_MASK]));
  }
  
  static file_info_cb_t *file_cbs[DMU_OST_NUMTYPES];
  
  void
  dmu_objset_register_type(dmu_objset_type_t ost, file_info_cb_t *cb)
  {
          file_cbs[ost] = cb;
  }
  
  int
  dmu_get_file_info(objset_t *os, dmu_object_type_t bonustype, const void *data,
      zfs_file_info_t *zfi)
  {
          file_info_cb_t *cb = file_cbs[os->os_phys->os_type];
          if (cb == NULL)
                  return (EINVAL);
          return (cb(bonustype, data, zfi));
  }
  
  boolean_t
  dmu_objset_userused_enabled(objset_t *os)
  {
          return (spa_version(os->os_spa) >= SPA_VERSION_USERSPACE &&
              file_cbs[os->os_phys->os_type] != NULL &&
              DMU_USERUSED_DNODE(os) != NULL);
  }
  
  boolean_t
  dmu_objset_userobjused_enabled(objset_t *os)
  {
          return (dmu_objset_userused_enabled(os) &&
              spa_feature_is_enabled(os->os_spa, SPA_FEATURE_USEROBJ_ACCOUNTING));
  }
  
  boolean_t
  dmu_objset_projectquota_enabled(objset_t *os)
  {
          return (file_cbs[os->os_phys->os_type] != NULL &&
              DMU_PROJECTUSED_DNODE(os) != NULL &&
              spa_feature_is_enabled(os->os_spa, SPA_FEATURE_PROJECT_QUOTA));
  }
  
  typedef struct userquota_node {
          /* must be in the first filed, see userquota_update_cache() */
          char            uqn_id[20 + DMU_OBJACCT_PREFIX_LEN];
          int64_t         uqn_delta;
          avl_node_t      uqn_node;
  } userquota_node_t;
  
  typedef struct userquota_cache {
          avl_tree_t uqc_user_deltas;
          avl_tree_t uqc_group_deltas;
          avl_tree_t uqc_project_deltas;
  } userquota_cache_t;
  
  static int
  userquota_compare(const void *l, const void *r)
  {
          const userquota_node_t *luqn = l;
          const userquota_node_t *ruqn = r;
          int rv;
  
          /*
           * NB: can only access uqn_id because userquota_update_cache() doesn't
           * pass in an entire userquota_node_t.
           */
          rv = strcmp(luqn->uqn_id, ruqn->uqn_id);
  
          return (TREE_ISIGN(rv));
  }
  
  static void
  do_userquota_cacheflush(objset_t *os, userquota_cache_t *cache, dmu_tx_t *tx)
  {
          void *cookie;
          userquota_node_t *uqn;
  
          ASSERT(dmu_tx_is_syncing(tx));
  
          cookie = NULL;
          while ((uqn = avl_destroy_nodes(&cache->uqc_user_deltas,
              &cookie)) != NULL) {
                  /*
                   * os_userused_lock protects against concurrent calls to
                   * zap_increment_int().  It's needed because zap_increment_int()
                   * is not thread-safe (i.e. not atomic).
                   */
                  mutex_enter(&os->os_userused_lock);
                  VERIFY0(zap_increment(os, DMU_USERUSED_OBJECT,
                      uqn->uqn_id, uqn->uqn_delta, tx));
                  mutex_exit(&os->os_userused_lock);
                  kmem_free(uqn, sizeof (*uqn));
          }
          avl_destroy(&cache->uqc_user_deltas);
  
          cookie = NULL;
          while ((uqn = avl_destroy_nodes(&cache->uqc_group_deltas,
              &cookie)) != NULL) {
                  mutex_enter(&os->os_userused_lock);
                  VERIFY0(zap_increment(os, DMU_GROUPUSED_OBJECT,
                      uqn->uqn_id, uqn->uqn_delta, tx));
                  mutex_exit(&os->os_userused_lock);
                  kmem_free(uqn, sizeof (*uqn));
          }
          avl_destroy(&cache->uqc_group_deltas);
  
          if (dmu_objset_projectquota_enabled(os)) {
                  cookie = NULL;
                  while ((uqn = avl_destroy_nodes(&cache->uqc_project_deltas,
                      &cookie)) != NULL) {
                          mutex_enter(&os->os_userused_lock);
                          VERIFY0(zap_increment(os, DMU_PROJECTUSED_OBJECT,
                              uqn->uqn_id, uqn->uqn_delta, tx));
                          mutex_exit(&os->os_userused_lock);
                          kmem_free(uqn, sizeof (*uqn));
                  }
                  avl_destroy(&cache->uqc_project_deltas);
          }
  }
  
  static void
  userquota_update_cache(avl_tree_t *avl, const char *id, int64_t delta)
  {
          userquota_node_t *uqn;
          avl_index_t idx;
  
          ASSERT(strlen(id) < sizeof (uqn->uqn_id));
          /*
           * Use id directly for searching because uqn_id is the first field of
           * userquota_node_t and fields after uqn_id won't be accessed in
           * avl_find().
           */
          uqn = avl_find(avl, (const void *)id, &idx);
          if (uqn == NULL) {
                  uqn = kmem_zalloc(sizeof (*uqn), KM_SLEEP);
                  strlcpy(uqn->uqn_id, id, sizeof (uqn->uqn_id));
                  avl_insert(avl, uqn, idx);
          }
          uqn->uqn_delta += delta;
  }
  
  static void
  do_userquota_update(objset_t *os, userquota_cache_t *cache, uint64_t used,
      uint64_t flags, uint64_t user, uint64_t group, uint64_t project,
      boolean_t subtract)
  {
          if (flags & DNODE_FLAG_USERUSED_ACCOUNTED) {
                  int64_t delta = DNODE_MIN_SIZE + used;
                  char name[20];
  
                  if (subtract)
                          delta = -delta;
  
                  (void) snprintf(name, sizeof (name), "%llx", (longlong_t)user);
                  userquota_update_cache(&cache->uqc_user_deltas, name, delta);
  
                  (void) snprintf(name, sizeof (name), "%llx", (longlong_t)group);
                  userquota_update_cache(&cache->uqc_group_deltas, name, delta);
  
                  if (dmu_objset_projectquota_enabled(os)) {
                          (void) snprintf(name, sizeof (name), "%llx",
                              (longlong_t)project);
                          userquota_update_cache(&cache->uqc_project_deltas,
                              name, delta);
                  }
          }
  }
  
  static void
  do_userobjquota_update(objset_t *os, userquota_cache_t *cache, uint64_t flags,
      uint64_t user, uint64_t group, uint64_t project, boolean_t subtract)
  {
          if (flags & DNODE_FLAG_USEROBJUSED_ACCOUNTED) {
                  char name[20 + DMU_OBJACCT_PREFIX_LEN];
                  int delta = subtract ? -1 : 1;
  
                  (void) snprintf(name, sizeof (name), DMU_OBJACCT_PREFIX "%llx",
                      (longlong_t)user);
                  userquota_update_cache(&cache->uqc_user_deltas, name, delta);
  
                  (void) snprintf(name, sizeof (name), DMU_OBJACCT_PREFIX "%llx",
                      (longlong_t)group);
                  userquota_update_cache(&cache->uqc_group_deltas, name, delta);
  
                  if (dmu_objset_projectquota_enabled(os)) {
                          (void) snprintf(name, sizeof (name),
                              DMU_OBJACCT_PREFIX "%llx", (longlong_t)project);
                          userquota_update_cache(&cache->uqc_project_deltas,
                              name, delta);
                  }
          }
  }
  
  typedef struct userquota_updates_arg {
          objset_t *uua_os;
          int uua_sublist_idx;
          dmu_tx_t *uua_tx;
  } userquota_updates_arg_t;
  
  static void
  userquota_updates_task(void *arg)
  {
          userquota_updates_arg_t *uua = arg;
          objset_t *os = uua->uua_os;
          dmu_tx_t *tx = uua->uua_tx;
          dnode_t *dn;
          userquota_cache_t cache = { { 0 } };
  
          multilist_sublist_t *list =
              multilist_sublist_lock(&os->os_synced_dnodes, uua->uua_sublist_idx);
  
          ASSERT(multilist_sublist_head(list) == NULL ||
              dmu_objset_userused_enabled(os));
          avl_create(&cache.uqc_user_deltas, userquota_compare,
              sizeof (userquota_node_t), offsetof(userquota_node_t, uqn_node));
          avl_create(&cache.uqc_group_deltas, userquota_compare,
              sizeof (userquota_node_t), offsetof(userquota_node_t, uqn_node));
          if (dmu_objset_projectquota_enabled(os))
                  avl_create(&cache.uqc_project_deltas, userquota_compare,
                      sizeof (userquota_node_t), offsetof(userquota_node_t,
                      uqn_node));
  
          while ((dn = multilist_sublist_head(list)) != NULL) {
                  int flags;
                  ASSERT(!DMU_OBJECT_IS_SPECIAL(dn->dn_object));
                  ASSERT(dn->dn_phys->dn_type == DMU_OT_NONE ||
                      dn->dn_phys->dn_flags &
                      DNODE_FLAG_USERUSED_ACCOUNTED);
  
                  flags = dn->dn_id_flags;
                  ASSERT(flags);
                  if (flags & DN_ID_OLD_EXIST)  {
                          do_userquota_update(os, &cache, dn->dn_oldused,
                              dn->dn_oldflags, dn->dn_olduid, dn->dn_oldgid,
                              dn->dn_oldprojid, B_TRUE);
                          do_userobjquota_update(os, &cache, dn->dn_oldflags,
                              dn->dn_olduid, dn->dn_oldgid,
                              dn->dn_oldprojid, B_TRUE);
                  }
                  if (flags & DN_ID_NEW_EXIST) {
                          do_userquota_update(os, &cache,
                              DN_USED_BYTES(dn->dn_phys), dn->dn_phys->dn_flags,
                              dn->dn_newuid, dn->dn_newgid,
                              dn->dn_newprojid, B_FALSE);
                          do_userobjquota_update(os, &cache,
                              dn->dn_phys->dn_flags, dn->dn_newuid, dn->dn_newgid,
                              dn->dn_newprojid, B_FALSE);
                  }
  
                  mutex_enter(&dn->dn_mtx);
                  dn->dn_oldused = 0;
                  dn->dn_oldflags = 0;
                  if (dn->dn_id_flags & DN_ID_NEW_EXIST) {
                          dn->dn_olduid = dn->dn_newuid;
                          dn->dn_oldgid = dn->dn_newgid;
                          dn->dn_oldprojid = dn->dn_newprojid;
                          dn->dn_id_flags |= DN_ID_OLD_EXIST;
                          if (dn->dn_bonuslen == 0)
                                  dn->dn_id_flags |= DN_ID_CHKED_SPILL;
                          else
                                  dn->dn_id_flags |= DN_ID_CHKED_BONUS;
                  }
                  dn->dn_id_flags &= ~(DN_ID_NEW_EXIST);
                  mutex_exit(&dn->dn_mtx);
  
                  multilist_sublist_remove(list, dn);
                  dnode_rele(dn, &os->os_synced_dnodes);
          }
          do_userquota_cacheflush(os, &cache, tx);
          multilist_sublist_unlock(list);
          kmem_free(uua, sizeof (*uua));
  }
  
  /*
   * Release dnode holds from dmu_objset_sync_dnodes().  When the dnode is being
   * synced (i.e. we have issued the zio's for blocks in the dnode), it can't be
   * evicted because the block containing the dnode can't be evicted until it is
   * written out.  However, this hold is necessary to prevent the dnode_t from
   * being moved (via dnode_move()) while it's still referenced by
   * dbuf_dirty_record_t:dr_dnode.  And dr_dnode is needed for
   * dirty_lightweight_leaf-type dirty records.
   *
   * If we are doing user-object accounting, the dnode_rele() happens from
   * userquota_updates_task() instead.
   */
  static void
  dnode_rele_task(void *arg)
  {
          userquota_updates_arg_t *uua = arg;
          objset_t *os = uua->uua_os;
  
          multilist_sublist_t *list =
              multilist_sublist_lock(&os->os_synced_dnodes, uua->uua_sublist_idx);
  
          dnode_t *dn;
          while ((dn = multilist_sublist_head(list)) != NULL) {
                  multilist_sublist_remove(list, dn);
                  dnode_rele(dn, &os->os_synced_dnodes);
          }
          multilist_sublist_unlock(list);
          kmem_free(uua, sizeof (*uua));
  }
  
  /*
   * Return TRUE if userquota updates are needed.
   */
  static boolean_t
  dmu_objset_do_userquota_updates_prep(objset_t *os, dmu_tx_t *tx)
  {
          if (!dmu_objset_userused_enabled(os))
                  return (B_FALSE);
  
          /*
           * If this is a raw receive just return and handle accounting
           * later when we have the keys loaded. We also don't do user
           * accounting during claiming since the datasets are not owned
           * for the duration of claiming and this txg should only be
           * used for recovery.
           */
          if (os->os_encrypted && dmu_objset_is_receiving(os))
                  return (B_FALSE);
  
          if (tx->tx_txg <= os->os_spa->spa_claim_max_txg)
                  return (B_FALSE);
  
          /* Allocate the user/group/project used objects if necessary. */
          if (DMU_USERUSED_DNODE(os)->dn_type == DMU_OT_NONE) {
                  VERIFY0(zap_create_claim(os,
                      DMU_USERUSED_OBJECT,
                      DMU_OT_USERGROUP_USED, DMU_OT_NONE, 0, tx));
                  VERIFY0(zap_create_claim(os,
                      DMU_GROUPUSED_OBJECT,
                      DMU_OT_USERGROUP_USED, DMU_OT_NONE, 0, tx));
          }
  
          if (dmu_objset_projectquota_enabled(os) &&
              DMU_PROJECTUSED_DNODE(os)->dn_type == DMU_OT_NONE) {
                  VERIFY0(zap_create_claim(os, DMU_PROJECTUSED_OBJECT,
                      DMU_OT_USERGROUP_USED, DMU_OT_NONE, 0, tx));
          }
          return (B_TRUE);
  }
  
  /*
   * Dispatch taskq tasks to dp_sync_taskq to update the user accounting, and
   * also release the holds on the dnodes from dmu_objset_sync_dnodes().
   * The caller must taskq_wait(dp_sync_taskq).
   */
  void
  dmu_objset_sync_done(objset_t *os, dmu_tx_t *tx)
  {
          boolean_t need_userquota = dmu_objset_do_userquota_updates_prep(os, tx);
  
          int num_sublists = multilist_get_num_sublists(&os->os_synced_dnodes);
          for (int i = 0; i < num_sublists; i++) {
                  userquota_updates_arg_t *uua =
                      kmem_alloc(sizeof (*uua), KM_SLEEP);
                  uua->uua_os = os;
                  uua->uua_sublist_idx = i;
                  uua->uua_tx = tx;
  
                  /*
                   * If we don't need to update userquotas, use
                   * dnode_rele_task() to call dnode_rele()
                   */
                  (void) taskq_dispatch(dmu_objset_pool(os)->dp_sync_taskq,
                      need_userquota ? userquota_updates_task : dnode_rele_task,
                      uua, 0);
                  /* callback frees uua */
          }
  }
  
  
  /*
   * Returns a pointer to data to find uid/gid from
   *
   * If a dirty record for transaction group that is syncing can't
   * be found then NULL is returned.  In the NULL case it is assumed
   * the uid/gid aren't changing.
   */
  static void *
  dmu_objset_userquota_find_data(dmu_buf_impl_t *db, dmu_tx_t *tx)
  {
          dbuf_dirty_record_t *dr;
          void *data;
  
          if (db->db_dirtycnt == 0)
                  return (db->db.db_data);  /* Nothing is changing */
  
          dr = dbuf_find_dirty_eq(db, tx->tx_txg);
  
          if (dr == NULL) {
                  data = NULL;
          } else {
                  if (dr->dr_dnode->dn_bonuslen == 0 &&
                      dr->dr_dbuf->db_blkid == DMU_SPILL_BLKID)
                          data = dr->dt.dl.dr_data->b_data;
                  else
                          data = dr->dt.dl.dr_data;
          }
  
          return (data);
  }
  
  void
  dmu_objset_userquota_get_ids(dnode_t *dn, boolean_t before, dmu_tx_t *tx)
  {
          objset_t *os = dn->dn_objset;
          void *data = NULL;
          dmu_buf_impl_t *db = NULL;
          int flags = dn->dn_id_flags;
          int error;
          boolean_t have_spill = B_FALSE;
  
          if (!dmu_objset_userused_enabled(dn->dn_objset))
                  return;
  
          /*
           * Raw receives introduce a problem with user accounting. Raw
           * receives cannot update the user accounting info because the
           * user ids and the sizes are encrypted. To guarantee that we
           * never end up with bad user accounting, we simply disable it
           * during raw receives. We also disable this for normal receives
           * so that an incremental raw receive may be done on top of an
           * existing non-raw receive.
           */
          if (os->os_encrypted && dmu_objset_is_receiving(os))
                  return;
  
          if (before && (flags & (DN_ID_CHKED_BONUS|DN_ID_OLD_EXIST|
              DN_ID_CHKED_SPILL)))
                  return;
  
          if (before && dn->dn_bonuslen != 0)
                  data = DN_BONUS(dn->dn_phys);
          else if (!before && dn->dn_bonuslen != 0) {
                  if (dn->dn_bonus) {
                          db = dn->dn_bonus;
                          mutex_enter(&db->db_mtx);
                          data = dmu_objset_userquota_find_data(db, tx);
                  } else {
                          data = DN_BONUS(dn->dn_phys);
                  }
          } else if (dn->dn_bonuslen == 0 && dn->dn_bonustype == DMU_OT_SA) {
                          int rf = 0;
  
                          if (RW_WRITE_HELD(&dn->dn_struct_rwlock))
                                  rf |= DB_RF_HAVESTRUCT;
                          error = dmu_spill_hold_by_dnode(dn,
                              rf | DB_RF_MUST_SUCCEED,
                              FTAG, (dmu_buf_t **)&db);
                          ASSERT(error == 0);
                          mutex_enter(&db->db_mtx);
                          data = (before) ? db->db.db_data :
                              dmu_objset_userquota_find_data(db, tx);
                          have_spill = B_TRUE;
          } else {
                  mutex_enter(&dn->dn_mtx);
                  dn->dn_id_flags |= DN_ID_CHKED_BONUS;
                  mutex_exit(&dn->dn_mtx);
                  return;
          }
  
          /*
           * Must always call the callback in case the object
           * type has changed and that type isn't an object type to track
           */
          zfs_file_info_t zfi;
          error = file_cbs[os->os_phys->os_type](dn->dn_bonustype, data, &zfi);
  
          if (before) {
                  ASSERT(data);
                  dn->dn_olduid = zfi.zfi_user;
                  dn->dn_oldgid = zfi.zfi_group;
                  dn->dn_oldprojid = zfi.zfi_project;
          } else if (data) {
                  dn->dn_newuid = zfi.zfi_user;
                  dn->dn_newgid = zfi.zfi_group;
                  dn->dn_newprojid = zfi.zfi_project;
          }
  
          /*
           * Preserve existing uid/gid when the callback can't determine
           * what the new uid/gid are and the callback returned EEXIST.
           * The EEXIST error tells us to just use the existing uid/gid.
           * If we don't know what the old values are then just assign
           * them to 0, since that is a new file  being created.
           */
          if (!before && data == NULL && error == EEXIST) {
                  if (flags & DN_ID_OLD_EXIST) {
                          dn->dn_newuid = dn->dn_olduid;
                          dn->dn_newgid = dn->dn_oldgid;
                          dn->dn_newprojid = dn->dn_oldprojid;
                  } else {
                          dn->dn_newuid = 0;
                          dn->dn_newgid = 0;
                          dn->dn_newprojid = ZFS_DEFAULT_PROJID;
                  }
                  error = 0;
          }
  
          if (db)
                  mutex_exit(&db->db_mtx);
  
          mutex_enter(&dn->dn_mtx);
          if (error == 0 && before)
                  dn->dn_id_flags |= DN_ID_OLD_EXIST;
          if (error == 0 && !before)
                  dn->dn_id_flags |= DN_ID_NEW_EXIST;
  
          if (have_spill) {
                  dn->dn_id_flags |= DN_ID_CHKED_SPILL;
          } else {
                  dn->dn_id_flags |= DN_ID_CHKED_BONUS;
          }
          mutex_exit(&dn->dn_mtx);
          if (have_spill)
                  dmu_buf_rele((dmu_buf_t *)db, FTAG);
  }
  
  boolean_t
  dmu_objset_userspace_present(objset_t *os)
  {
          return (os->os_phys->os_flags &
              OBJSET_FLAG_USERACCOUNTING_COMPLETE);
  }
  
  boolean_t
  dmu_objset_userobjspace_present(objset_t *os)
  {
          return (os->os_phys->os_flags &
              OBJSET_FLAG_USEROBJACCOUNTING_COMPLETE);
  }
  
  boolean_t
  dmu_objset_projectquota_present(objset_t *os)
  {
          return (os->os_phys->os_flags &
              OBJSET_FLAG_PROJECTQUOTA_COMPLETE);
  }
  
  static int
  dmu_objset_space_upgrade(objset_t *os)
  {
          uint64_t obj;
          int err = 0;
  
          /*
           * We simply need to mark every object dirty, so that it will be
           * synced out and now accounted.  If this is called
           * concurrently, or if we already did some work before crashing,
           * that's fine, since we track each object's accounted state
           * independently.
           */
  
          for (obj = 0; err == 0; err = dmu_object_next(os, &obj, FALSE, 0)) {
                  dmu_tx_t *tx;
                  dmu_buf_t *db;
                  int objerr;
  
                  mutex_enter(&os->os_upgrade_lock);
                  if (os->os_upgrade_exit)
                          err = SET_ERROR(EINTR);
                  mutex_exit(&os->os_upgrade_lock);
                  if (err != 0)
                          return (err);
  
                  if (issig(JUSTLOOKING) && issig(FORREAL))
                          return (SET_ERROR(EINTR));
  
                  objerr = dmu_bonus_hold(os, obj, FTAG, &db);
                  if (objerr != 0)
                          continue;
                  tx = dmu_tx_create(os);
                  dmu_tx_hold_bonus(tx, obj);
                  objerr = dmu_tx_assign(tx, TXG_WAIT);
                  if (objerr != 0) {
                          dmu_buf_rele(db, FTAG);
                          dmu_tx_abort(tx);
                          continue;
                  }
                  dmu_buf_will_dirty(db, tx);
                  dmu_buf_rele(db, FTAG);
                  dmu_tx_commit(tx);
          }
          return (0);
  }
  
  static int
  dmu_objset_userspace_upgrade_cb(objset_t *os)
  {
          int err = 0;
  
          if (dmu_objset_userspace_present(os))
                  return (0);
          if (dmu_objset_is_snapshot(os))
                  return (SET_ERROR(EINVAL));
          if (!dmu_objset_userused_enabled(os))
                  return (SET_ERROR(ENOTSUP));
  
          err = dmu_objset_space_upgrade(os);
          if (err)
                  return (err);
  
          os->os_flags |= OBJSET_FLAG_USERACCOUNTING_COMPLETE;
          txg_wait_synced(dmu_objset_pool(os), 0);
          return (0);
  }
  
  void
  dmu_objset_userspace_upgrade(objset_t *os)
  {
          dmu_objset_upgrade(os, dmu_objset_userspace_upgrade_cb);
  }
  
  static int
  dmu_objset_id_quota_upgrade_cb(objset_t *os)
  {
          int err = 0;
  
          if (dmu_objset_userobjspace_present(os) &&
              dmu_objset_projectquota_present(os))
                  return (0);
          if (dmu_objset_is_snapshot(os))
                  return (SET_ERROR(EINVAL));
          if (!dmu_objset_userused_enabled(os))
                  return (SET_ERROR(ENOTSUP));
          if (!dmu_objset_projectquota_enabled(os) &&
              dmu_objset_userobjspace_present(os))
                  return (SET_ERROR(ENOTSUP));
  
          err = dmu_objset_space_upgrade(os);
          if (err)
                  return (err);
  
          os->os_flags |= OBJSET_FLAG_USERACCOUNTING_COMPLETE;
          if (dmu_objset_userobjused_enabled(os))
                  os->os_flags |= OBJSET_FLAG_USEROBJACCOUNTING_COMPLETE;
          if (dmu_objset_projectquota_enabled(os))
                  os->os_flags |= OBJSET_FLAG_PROJECTQUOTA_COMPLETE;
  
          txg_wait_synced(dmu_objset_pool(os), 0);
          return (0);
  }
  
  void
  dmu_objset_id_quota_upgrade(objset_t *os)
  {
          dmu_objset_upgrade(os, dmu_objset_id_quota_upgrade_cb);
  }
  
  boolean_t
  dmu_objset_userobjspace_upgradable(objset_t *os)
  {
          return (dmu_objset_type(os) == DMU_OST_ZFS &&
              !dmu_objset_is_snapshot(os) &&
              dmu_objset_userobjused_enabled(os) &&
              !dmu_objset_userobjspace_present(os) &&
              spa_writeable(dmu_objset_spa(os)));
  }
  
  boolean_t
  dmu_objset_projectquota_upgradable(objset_t *os)
  {
          return (dmu_objset_type(os) == DMU_OST_ZFS &&
              !dmu_objset_is_snapshot(os) &&
              dmu_objset_projectquota_enabled(os) &&
              !dmu_objset_projectquota_present(os) &&
              spa_writeable(dmu_objset_spa(os)));
  }
  
  void
  dmu_objset_space(objset_t *os, uint64_t *refdbytesp, uint64_t *availbytesp,
      uint64_t *usedobjsp, uint64_t *availobjsp)
  {
          dsl_dataset_space(os->os_dsl_dataset, refdbytesp, availbytesp,
              usedobjsp, availobjsp);
  }
  
  uint64_t
  dmu_objset_fsid_guid(objset_t *os)
  {
          return (dsl_dataset_fsid_guid(os->os_dsl_dataset));
  }
  
  void
  dmu_objset_fast_stat(objset_t *os, dmu_objset_stats_t *stat)
  {
          stat->dds_type = os->os_phys->os_type;
          if (os->os_dsl_dataset)
                  dsl_dataset_fast_stat(os->os_dsl_dataset, stat);
  }
  
  void
  dmu_objset_stats(objset_t *os, nvlist_t *nv)
  {
          ASSERT(os->os_dsl_dataset ||
              os->os_phys->os_type == DMU_OST_META);
  
          if (os->os_dsl_dataset != NULL)
                  dsl_dataset_stats(os->os_dsl_dataset, nv);
  
          dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_TYPE,
              os->os_phys->os_type);
          dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_USERACCOUNTING,
              dmu_objset_userspace_present(os));
  }
  
  int
  dmu_objset_is_snapshot(objset_t *os)
  {
          if (os->os_dsl_dataset != NULL)
                  return (os->os_dsl_dataset->ds_is_snapshot);
          else
                  return (B_FALSE);
  }
  
  int
  dmu_snapshot_realname(objset_t *os, const char *name, char *real, int maxlen,
      boolean_t *conflict)
  {
          dsl_dataset_t *ds = os->os_dsl_dataset;
          uint64_t ignored;
  
          if (dsl_dataset_phys(ds)->ds_snapnames_zapobj == 0)
                  return (SET_ERROR(ENOENT));
  
          return (zap_lookup_norm(ds->ds_dir->dd_pool->dp_meta_objset,
              dsl_dataset_phys(ds)->ds_snapnames_zapobj, name, 8, 1, &ignored,
              MT_NORMALIZE, real, maxlen, conflict));
  }
  
  int
  dmu_snapshot_list_next(objset_t *os, int namelen, char *name,
      uint64_t *idp, uint64_t *offp, boolean_t *case_conflict)
  {
          dsl_dataset_t *ds = os->os_dsl_dataset;
          zap_cursor_t cursor;
          zap_attribute_t attr;
  
          ASSERT(dsl_pool_config_held(dmu_objset_pool(os)));
  
          if (dsl_dataset_phys(ds)->ds_snapnames_zapobj == 0)
                  return (SET_ERROR(ENOENT));
  
          zap_cursor_init_serialized(&cursor,
              ds->ds_dir->dd_pool->dp_meta_objset,
              dsl_dataset_phys(ds)->ds_snapnames_zapobj, *offp);
  
          if (zap_cursor_retrieve(&cursor, &attr) != 0) {
                  zap_cursor_fini(&cursor);
                  return (SET_ERROR(ENOENT));
          }
  
          if (strlen(attr.za_name) + 1 > namelen) {
                  zap_cursor_fini(&cursor);
                  return (SET_ERROR(ENAMETOOLONG));
          }
  
          (void) strlcpy(name, attr.za_name, namelen);
          if (idp)
                  *idp = attr.za_first_integer;
          if (case_conflict)
                  *case_conflict = attr.za_normalization_conflict;
          zap_cursor_advance(&cursor);
          *offp = zap_cursor_serialize(&cursor);
          zap_cursor_fini(&cursor);
  
          return (0);
  }
  
  int
  dmu_snapshot_lookup(objset_t *os, const char *name, uint64_t *value)
  {
          return (dsl_dataset_snap_lookup(os->os_dsl_dataset, name, value));
  }
  
  int
  dmu_dir_list_next(objset_t *os, int namelen, char *name,
      uint64_t *idp, uint64_t *offp)
  {
          dsl_dir_t *dd = os->os_dsl_dataset->ds_dir;
          zap_cursor_t cursor;
          zap_attribute_t attr;
  
          /* there is no next dir on a snapshot! */
          if (os->os_dsl_dataset->ds_object !=
              dsl_dir_phys(dd)->dd_head_dataset_obj)
                  return (SET_ERROR(ENOENT));
  
          zap_cursor_init_serialized(&cursor,
              dd->dd_pool->dp_meta_objset,
              dsl_dir_phys(dd)->dd_child_dir_zapobj, *offp);
  
          if (zap_cursor_retrieve(&cursor, &attr) != 0) {
                  zap_cursor_fini(&cursor);
                  return (SET_ERROR(ENOENT));
          }
  
          if (strlen(attr.za_name) + 1 > namelen) {
                  zap_cursor_fini(&cursor);
                  return (SET_ERROR(ENAMETOOLONG));
          }
  
          (void) strlcpy(name, attr.za_name, namelen);
          if (idp)
                  *idp = attr.za_first_integer;
          zap_cursor_advance(&cursor);
          *offp = zap_cursor_serialize(&cursor);
          zap_cursor_fini(&cursor);
  
          return (0);
  }
  
  typedef struct dmu_objset_find_ctx {
          taskq_t         *dc_tq;
          dsl_pool_t      *dc_dp;
          uint64_t        dc_ddobj;
          char            *dc_ddname; /* last component of ddobj's name */
          int             (*dc_func)(dsl_pool_t *, dsl_dataset_t *, void *);
          void            *dc_arg;
          int             dc_flags;
          kmutex_t        *dc_error_lock;
          int             *dc_error;
  } dmu_objset_find_ctx_t;
  
  static void
  dmu_objset_find_dp_impl(dmu_objset_find_ctx_t *dcp)
  {
          dsl_pool_t *dp = dcp->dc_dp;
          dsl_dir_t *dd;
          dsl_dataset_t *ds;
          zap_cursor_t zc;
          zap_attribute_t *attr;
          uint64_t thisobj;
          int err = 0;
  
          /* don't process if there already was an error */
          if (*dcp->dc_error != 0)
                  goto out;
  
          /*
           * Note: passing the name (dc_ddname) here is optional, but it
           * improves performance because we don't need to call
           * zap_value_search() to determine the name.
           */
          err = dsl_dir_hold_obj(dp, dcp->dc_ddobj, dcp->dc_ddname, FTAG, &dd);
          if (err != 0)
                  goto out;
  
          /* Don't visit hidden ($MOS & $ORIGIN) objsets. */
          if (dd->dd_myname[0] == '$') {
                  dsl_dir_rele(dd, FTAG);
                  goto out;
          }
  
          thisobj = dsl_dir_phys(dd)->dd_head_dataset_obj;
          attr = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
  
          /*
           * Iterate over all children.
           */
          if (dcp->dc_flags & DS_FIND_CHILDREN) {
                  for (zap_cursor_init(&zc, dp->dp_meta_objset,
                      dsl_dir_phys(dd)->dd_child_dir_zapobj);
                      zap_cursor_retrieve(&zc, attr) == 0;
                      (void) zap_cursor_advance(&zc)) {
                          ASSERT3U(attr->za_integer_length, ==,
                              sizeof (uint64_t));
                          ASSERT3U(attr->za_num_integers, ==, 1);
  
                          dmu_objset_find_ctx_t *child_dcp =
                              kmem_alloc(sizeof (*child_dcp), KM_SLEEP);
                          *child_dcp = *dcp;
                          child_dcp->dc_ddobj = attr->za_first_integer;
                          child_dcp->dc_ddname = spa_strdup(attr->za_name);
                          if (dcp->dc_tq != NULL)
                                  (void) taskq_dispatch(dcp->dc_tq,
                                      dmu_objset_find_dp_cb, child_dcp, TQ_SLEEP);
                          else
                                  dmu_objset_find_dp_impl(child_dcp);
                  }
                  zap_cursor_fini(&zc);
          }
  
          /*
           * Iterate over all snapshots.
           */
          if (dcp->dc_flags & DS_FIND_SNAPSHOTS) {
                  dsl_dataset_t *ds;
                  err = dsl_dataset_hold_obj(dp, thisobj, FTAG, &ds);
  
                  if (err == 0) {
                          uint64_t snapobj;
  
                          snapobj = dsl_dataset_phys(ds)->ds_snapnames_zapobj;
                          dsl_dataset_rele(ds, FTAG);
  
                          for (zap_cursor_init(&zc, dp->dp_meta_objset, snapobj);
                              zap_cursor_retrieve(&zc, attr) == 0;
                              (void) zap_cursor_advance(&zc)) {
                                  ASSERT3U(attr->za_integer_length, ==,
                                      sizeof (uint64_t));
                                  ASSERT3U(attr->za_num_integers, ==, 1);
  
                                  err = dsl_dataset_hold_obj(dp,
                                      attr->za_first_integer, FTAG, &ds);
                                  if (err != 0)
                                          break;
                                  err = dcp->dc_func(dp, ds, dcp->dc_arg);
                                  dsl_dataset_rele(ds, FTAG);
                                  if (err != 0)
                                          break;
                          }
                          zap_cursor_fini(&zc);
                  }
          }
  
          kmem_free(attr, sizeof (zap_attribute_t));
  
          if (err != 0) {
                  dsl_dir_rele(dd, FTAG);
                  goto out;
          }
  
          /*
           * Apply to self.
           */
          err = dsl_dataset_hold_obj(dp, thisobj, FTAG, &ds);
  
          /*
           * Note: we hold the dir while calling dsl_dataset_hold_obj() so
           * that the dir will remain cached, and we won't have to re-instantiate
           * it (which could be expensive due to finding its name via
           * zap_value_search()).
           */
          dsl_dir_rele(dd, FTAG);
          if (err != 0)
                  goto out;
          err = dcp->dc_func(dp, ds, dcp->dc_arg);
          dsl_dataset_rele(ds, FTAG);
  
  out:
          if (err != 0) {
                  mutex_enter(dcp->dc_error_lock);
                  /* only keep first error */
                  if (*dcp->dc_error == 0)
                          *dcp->dc_error = err;
                  mutex_exit(dcp->dc_error_lock);
          }
  
          if (dcp->dc_ddname != NULL)
                  spa_strfree(dcp->dc_ddname);
          kmem_free(dcp, sizeof (*dcp));
  }
  
  static void
  dmu_objset_find_dp_cb(void *arg)
  {
          dmu_objset_find_ctx_t *dcp = arg;
          dsl_pool_t *dp = dcp->dc_dp;
  
          /*
           * We need to get a pool_config_lock here, as there are several
           * assert(pool_config_held) down the stack. Getting a lock via
           * dsl_pool_config_enter is risky, as it might be stalled by a
           * pending writer. This would deadlock, as the write lock can
           * only be granted when our parent thread gives up the lock.
           * The _prio interface gives us priority over a pending writer.
           */
          dsl_pool_config_enter_prio(dp, FTAG);
  
          dmu_objset_find_dp_impl(dcp);
  
          dsl_pool_config_exit(dp, FTAG);
  }
  
  /*
   * Find objsets under and including ddobj, call func(ds) on each.
   * The order for the enumeration is completely undefined.
   * func is called with dsl_pool_config held.
   */
  int
  dmu_objset_find_dp(dsl_pool_t *dp, uint64_t ddobj,
      int func(dsl_pool_t *, dsl_dataset_t *, void *), void *arg, int flags)
  {
          int error = 0;
          taskq_t *tq = NULL;
          int ntasks;
          dmu_objset_find_ctx_t *dcp;
          kmutex_t err_lock;
  
          mutex_init(&err_lock, NULL, MUTEX_DEFAULT, NULL);
          dcp = kmem_alloc(sizeof (*dcp), KM_SLEEP);
          dcp->dc_tq = NULL;
          dcp->dc_dp = dp;
          dcp->dc_ddobj = ddobj;
          dcp->dc_ddname = NULL;
          dcp->dc_func = func;
          dcp->dc_arg = arg;
          dcp->dc_flags = flags;
          dcp->dc_error_lock = &err_lock;
          dcp->dc_error = &error;
  
          if ((flags & DS_FIND_SERIALIZE) || dsl_pool_config_held_writer(dp)) {
                  /*
                   * In case a write lock is held we can't make use of
                   * parallelism, as down the stack of the worker threads
                   * the lock is asserted via dsl_pool_config_held.
                   * In case of a read lock this is solved by getting a read
                   * lock in each worker thread, which isn't possible in case
                   * of a writer lock. So we fall back to the synchronous path
                   * here.
                   * In the future it might be possible to get some magic into
                   * dsl_pool_config_held in a way that it returns true for
                   * the worker threads so that a single lock held from this
                   * thread suffices. For now, stay single threaded.
                   */
                  dmu_objset_find_dp_impl(dcp);
                  mutex_destroy(&err_lock);
  
                  return (error);
          }
  
          ntasks = dmu_find_threads;
          if (ntasks == 0)
                  ntasks = vdev_count_leaves(dp->dp_spa) * 4;
          tq = taskq_create("dmu_objset_find", ntasks, maxclsyspri, ntasks,
              INT_MAX, 0);
          if (tq == NULL) {
                  kmem_free(dcp, sizeof (*dcp));
                  mutex_destroy(&err_lock);
  
                  return (SET_ERROR(ENOMEM));
          }
          dcp->dc_tq = tq;
  
          /* dcp will be freed by task */
          (void) taskq_dispatch(tq, dmu_objset_find_dp_cb, dcp, TQ_SLEEP);
  
          /*
           * PORTING: this code relies on the property of taskq_wait to wait
           * until no more tasks are queued and no more tasks are active. As
           * we always queue new tasks from within other tasks, task_wait
           * reliably waits for the full recursion to finish, even though we
           * enqueue new tasks after taskq_wait has been called.
           * On platforms other than illumos, taskq_wait may not have this
           * property.
           */
          taskq_wait(tq);
          taskq_destroy(tq);
          mutex_destroy(&err_lock);
  
          return (error);
  }
  
  /*
   * Find all objsets under name, and for each, call 'func(child_name, arg)'.
   * The dp_config_rwlock must not be held when this is called, and it
   * will not be held when the callback is called.
   * Therefore this function should only be used when the pool is not changing
   * (e.g. in syncing context), or the callback can deal with the possible races.
   */
  static int
  dmu_objset_find_impl(spa_t *spa, const char *name,
      int func(const char *, void *), void *arg, int flags)
  {
          dsl_dir_t *dd;
          dsl_pool_t *dp = spa_get_dsl(spa);
          dsl_dataset_t *ds;
          zap_cursor_t zc;
          zap_attribute_t *attr;
          char *child;
          uint64_t thisobj;
          int err;
  
          dsl_pool_config_enter(dp, FTAG);
  
          err = dsl_dir_hold(dp, name, FTAG, &dd, NULL);
          if (err != 0) {
                  dsl_pool_config_exit(dp, FTAG);
                  return (err);
          }
  
          /* Don't visit hidden ($MOS & $ORIGIN) objsets. */
          if (dd->dd_myname[0] == '$') {
                  dsl_dir_rele(dd, FTAG);
                  dsl_pool_config_exit(dp, FTAG);
                  return (0);
          }
  
          thisobj = dsl_dir_phys(dd)->dd_head_dataset_obj;
          attr = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
  
          /*
           * Iterate over all children.
           */
          if (flags & DS_FIND_CHILDREN) {
                  for (zap_cursor_init(&zc, dp->dp_meta_objset,
                      dsl_dir_phys(dd)->dd_child_dir_zapobj);
                      zap_cursor_retrieve(&zc, attr) == 0;
                      (void) zap_cursor_advance(&zc)) {
                          ASSERT3U(attr->za_integer_length, ==,
                              sizeof (uint64_t));
                          ASSERT3U(attr->za_num_integers, ==, 1);
  
                          child = kmem_asprintf("%s/%s", name, attr->za_name);
                          dsl_pool_config_exit(dp, FTAG);
                          err = dmu_objset_find_impl(spa, child,
                              func, arg, flags);
                          dsl_pool_config_enter(dp, FTAG);
                          kmem_strfree(child);
                          if (err != 0)
                                  break;
                  }
                  zap_cursor_fini(&zc);
  
                  if (err != 0) {
                          dsl_dir_rele(dd, FTAG);
                          dsl_pool_config_exit(dp, FTAG);
                          kmem_free(attr, sizeof (zap_attribute_t));
                          return (err);
                  }
          }
  
          /*
           * Iterate over all snapshots.
           */
          if (flags & DS_FIND_SNAPSHOTS) {
                  err = dsl_dataset_hold_obj(dp, thisobj, FTAG, &ds);
  
                  if (err == 0) {
                          uint64_t snapobj;
  
                          snapobj = dsl_dataset_phys(ds)->ds_snapnames_zapobj;
                          dsl_dataset_rele(ds, FTAG);
  
                          for (zap_cursor_init(&zc, dp->dp_meta_objset, snapobj);
                              zap_cursor_retrieve(&zc, attr) == 0;
                              (void) zap_cursor_advance(&zc)) {
                                  ASSERT3U(attr->za_integer_length, ==,
                                      sizeof (uint64_t));
                                  ASSERT3U(attr->za_num_integers, ==, 1);
  
                                  child = kmem_asprintf("%s@%s",
                                      name, attr->za_name);
                                  dsl_pool_config_exit(dp, FTAG);
                                  err = func(child, arg);
                                  dsl_pool_config_enter(dp, FTAG);
                                  kmem_strfree(child);
                                  if (err != 0)
                                          break;
                          }
                          zap_cursor_fini(&zc);
                  }
          }
  
          dsl_dir_rele(dd, FTAG);
          kmem_free(attr, sizeof (zap_attribute_t));
          dsl_pool_config_exit(dp, FTAG);
  
          if (err != 0)
                  return (err);
  
          /* Apply to self. */
          return (func(name, arg));
  }
  
  /*
   * See comment above dmu_objset_find_impl().
   */
  int
  dmu_objset_find(const char *name, int func(const char *, void *), void *arg,
      int flags)
  {
          spa_t *spa;
          int error;
  
          error = spa_open(name, &spa, FTAG);
          if (error != 0)
                  return (error);
          error = dmu_objset_find_impl(spa, name, func, arg, flags);
          spa_close(spa, FTAG);
          return (error);
  }
  
  boolean_t
  dmu_objset_incompatible_encryption_version(objset_t *os)
  {
          return (dsl_dir_incompatible_encryption_version(
              os->os_dsl_dataset->ds_dir));
  }
  
  void
  dmu_objset_set_user(objset_t *os, void *user_ptr)
  {
          ASSERT(MUTEX_HELD(&os->os_user_ptr_lock));
          os->os_user_ptr = user_ptr;
  }
  
  void *
  dmu_objset_get_user(objset_t *os)
  {
          ASSERT(MUTEX_HELD(&os->os_user_ptr_lock));
          return (os->os_user_ptr);
  }
  
  /*
   * Determine name of filesystem, given name of snapshot.
   * buf must be at least ZFS_MAX_DATASET_NAME_LEN bytes
   */
  int
  dmu_fsname(const char *snapname, char *buf)
  {
          char *atp = strchr(snapname, '@');
          if (atp == NULL)
                  return (SET_ERROR(EINVAL));
          if (atp - snapname >= ZFS_MAX_DATASET_NAME_LEN)
                  return (SET_ERROR(ENAMETOOLONG));
          (void) strlcpy(buf, snapname, atp - snapname + 1);
          return (0);
  }
  
  /*
   * Call when we think we're going to write/free space in open context
   * to track the amount of dirty data in the open txg, which is also the
   * amount of memory that can not be evicted until this txg syncs.
   *
   * Note that there are two conditions where this can be called from
   * syncing context:
   *
   * [1] When we just created the dataset, in which case we go on with
   *     updating any accounting of dirty data as usual.
   * [2] When we are dirtying MOS data, in which case we only update the
   *     pool's accounting of dirty data.
   */
  void
  dmu_objset_willuse_space(objset_t *os, int64_t space, dmu_tx_t *tx)
  {
          dsl_dataset_t *ds = os->os_dsl_dataset;
          int64_t aspace = spa_get_worst_case_asize(os->os_spa, space);
  
          if (ds != NULL) {
                  dsl_dir_willuse_space(ds->ds_dir, aspace, tx);
          }
  
          dsl_pool_dirty_space(dmu_tx_pool(tx), space, tx);
  }
  
  #if defined(_KERNEL)
  EXPORT_SYMBOL(dmu_objset_zil);
  EXPORT_SYMBOL(dmu_objset_pool);
  EXPORT_SYMBOL(dmu_objset_ds);
  EXPORT_SYMBOL(dmu_objset_type);
  EXPORT_SYMBOL(dmu_objset_name);
  EXPORT_SYMBOL(dmu_objset_hold);
  EXPORT_SYMBOL(dmu_objset_hold_flags);
  EXPORT_SYMBOL(dmu_objset_own);
  EXPORT_SYMBOL(dmu_objset_rele);
  EXPORT_SYMBOL(dmu_objset_rele_flags);
  EXPORT_SYMBOL(dmu_objset_disown);
  EXPORT_SYMBOL(dmu_objset_from_ds);
  EXPORT_SYMBOL(dmu_objset_create);
  EXPORT_SYMBOL(dmu_objset_clone);
  EXPORT_SYMBOL(dmu_objset_stats);
  EXPORT_SYMBOL(dmu_objset_fast_stat);
  EXPORT_SYMBOL(dmu_objset_spa);
  EXPORT_SYMBOL(dmu_objset_space);
  EXPORT_SYMBOL(dmu_objset_fsid_guid);
  EXPORT_SYMBOL(dmu_objset_find);
  EXPORT_SYMBOL(dmu_objset_byteswap);
  EXPORT_SYMBOL(dmu_objset_evict_dbufs);
  EXPORT_SYMBOL(dmu_objset_snap_cmtime);
  EXPORT_SYMBOL(dmu_objset_dnodesize);
  
  EXPORT_SYMBOL(dmu_objset_sync);
  EXPORT_SYMBOL(dmu_objset_is_dirty);
  EXPORT_SYMBOL(dmu_objset_create_impl_dnstats);
  EXPORT_SYMBOL(dmu_objset_create_impl);
  EXPORT_SYMBOL(dmu_objset_open_impl);
  EXPORT_SYMBOL(dmu_objset_evict);
  EXPORT_SYMBOL(dmu_objset_register_type);
  EXPORT_SYMBOL(dmu_objset_sync_done);
  EXPORT_SYMBOL(dmu_objset_userquota_get_ids);
  EXPORT_SYMBOL(dmu_objset_userused_enabled);
  EXPORT_SYMBOL(dmu_objset_userspace_upgrade);
  EXPORT_SYMBOL(dmu_objset_userspace_present);
  EXPORT_SYMBOL(dmu_objset_userobjused_enabled);
  EXPORT_SYMBOL(dmu_objset_userobjspace_upgradable);
  EXPORT_SYMBOL(dmu_objset_userobjspace_present);
  EXPORT_SYMBOL(dmu_objset_projectquota_enabled);
  EXPORT_SYMBOL(dmu_objset_projectquota_present);
  EXPORT_SYMBOL(dmu_objset_projectquota_upgradable);
  EXPORT_SYMBOL(dmu_objset_id_quota_upgrade);
  #endif

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