OpenZFS 8199 - multi-threaded dmu_object_alloc()

[mirror_zfs.git] / 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 http://www.opensolaris.org/os/licensing.
 * 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, 2017 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.
 */

/* Portions Copyright 2010 Robert Milkowski */

#include <sys/zfeature.h>
#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/policy.h>
#include <sys/spa_impl.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.
 */
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.
 */
int dmu_rescan_dnode_threshold = 1 << DN_MAX_INDBLKSHIFT;

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, newval,
            ZIO_COMPRESS_ON);
}

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);

        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
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_OLD_PHYS_SIZE || 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 == sizeof (objset_phys_t)) {
                dnode_byteswap(&osp->os_userused_dnode);
                dnode_byteswap(&osp->os_groupused_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);
}

unsigned int
dnode_multilist_index_func(multilist_t *ml, void *obj)
{
        dnode_t *dn = obj;
        return (dnode_hash(dn->dn_objset, dn->dn_object) %
            multilist_get_num_sublists(ml));
}

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));

        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;
                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;

                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_FLAG_CANFAIL, &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);
                }

                /* Increase the blocksize if we are permitted. */
                if (spa_version(spa) >= SPA_VERSION_USERSPACE &&
                    arc_buf_size(os->os_phys_buf) < sizeof (objset_phys_t)) {
                        arc_buf_t *buf = arc_alloc_buf(spa, &os->os_phys_buf,
                            ARC_BUFC_METADATA, sizeof (objset_phys_t));
                        bzero(buf->b_data, sizeof (objset_phys_t));
                        bcopy(os->os_phys_buf->b_data, 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_OLD_PHYS_SIZE;
                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;
                bzero(os->os_phys, size);
        }

        /*
         * 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) {
                boolean_t needlock = B_FALSE;

                /*
                 * Note: it's valid to open the objset if the dataset is
                 * long-held, in which case the pool_config lock will not
                 * be held.
                 */
                if (!dsl_pool_config_held(dmu_objset_pool(os))) {
                        needlock = B_TRUE;
                        dsl_pool_config_enter(dmu_objset_pool(os), FTAG);
                }
                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 (needlock)
                        dsl_pool_config_exit(dmu_objset_pool(os), FTAG);
                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_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++) {
                os->os_dirty_dnodes[i] = multilist_create(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 (arc_buf_size(os->os_phys_buf) >= sizeof (objset_phys_t)) {
                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);
        }

        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 shouldn't be doing anything with dsl_dataset_t's unless the
         * pool_config lock is held, or the dataset is long-held.
         */
        ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool) ||
            dsl_dataset_long_held(ds));

        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(const char *name, void *tag, objset_t **osp)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        int err;

        err = dsl_pool_hold(name, tag, &dp);
        if (err != 0)
                return (err);
        err = dsl_dataset_hold(dp, name, 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);
}

static int
dmu_objset_own_impl(dsl_dataset_t *ds, dmu_objset_type_t type,
    boolean_t readonly, void *tag, objset_t **osp)
{
        int err;

        err = dmu_objset_from_ds(ds, osp);
        if (err != 0) {
                dsl_dataset_disown(ds, tag);
        } else if (type != DMU_OST_ANY && type != (*osp)->os_phys->os_type) {
                dsl_dataset_disown(ds, tag);
                return (SET_ERROR(EINVAL));
        } else if (!readonly && dsl_dataset_is_snapshot(ds)) {
                dsl_dataset_disown(ds, tag);
                return (SET_ERROR(EROFS));
        }
        return (err);
}

/*
 * 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, void *tag, objset_t **osp)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        int err;

        err = dsl_pool_hold(name, FTAG, &dp);
        if (err != 0)
                return (err);
        err = dsl_dataset_own(dp, name, tag, &ds);
        if (err != 0) {
                dsl_pool_rele(dp, FTAG);
                return (err);
        }
        err = dmu_objset_own_impl(ds, type, readonly, tag, osp);
        dsl_pool_rele(dp, FTAG);

        if (err == 0 && dmu_objset_userobjspace_upgradable(*osp))
                dmu_objset_userobjspace_upgrade(*osp);

        return (err);
}

int
dmu_objset_own_obj(dsl_pool_t *dp, uint64_t obj, dmu_objset_type_t type,
    boolean_t readonly, void *tag, objset_t **osp)
{
        dsl_dataset_t *ds;
        int err;

        err = dsl_dataset_own_obj(dp, obj, tag, &ds);
        if (err != 0)
                return (err);

        return (dmu_objset_own_impl(ds, type, readonly, tag, osp));
}

void
dmu_objset_rele(objset_t *os, void *tag)
{
        dsl_pool_t *dp = dmu_objset_pool(os);
        dsl_dataset_rele(os->os_dsl_dataset, tag);
        dsl_pool_rele(dp, 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(objset_t *os, void *tag)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds, *newds;
        char name[ZFS_MAX_DATASET_NAME_LEN];

        ds = os->os_dsl_dataset;
        VERIFY3P(ds, !=, NULL);
        VERIFY3P(ds->ds_owner, ==, tag);
        VERIFY(dsl_dataset_long_held(ds));

        dsl_dataset_name(ds, name);
        dp = dmu_objset_pool(os);
        dsl_pool_config_enter(dp, FTAG);
        dmu_objset_disown(os, tag);
        VERIFY0(dsl_dataset_own(dp, name, tag, &newds));
        VERIFY3P(newds, ==, os->os_dsl_dataset);
        dsl_pool_config_exit(dp, FTAG);
}

void
dmu_objset_disown(objset_t *os, void *tag)
{
        /*
         * Stop upgrading thread
         */
        dmu_objset_upgrade_stop(os);
        dsl_dataset_disown(os->os_dsl_dataset, 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) {
                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)
{
        int t;

        dsl_dataset_t *ds = os->os_dsl_dataset;

        for (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)) {
                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));
}

timestruc_t
dmu_objset_snap_cmtime(objset_t *os)
{
        return (dsl_dir_snap_cmtime(os->os_dsl_dataset->ds_dir));
}

/* 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)
{
        objset_t *os;
        dnode_t *mdn;

        ASSERT(dmu_tx_is_syncing(tx));

        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, DNODE_BLOCK_SIZE, DN_MAX_INDBLKSHIFT,
            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 quescing 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) {
                int 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;
        if (dmu_objset_userused_enabled(os)) {
                os->os_phys->os_flags |= OBJSET_FLAG_USERACCOUNTING_COMPLETE;
                if (dmu_objset_userobjused_enabled(os)) {
                        ds->ds_feature_activation_needed[
                            SPA_FEATURE_USEROBJ_ACCOUNTING] = B_TRUE;
                        os->os_phys->os_flags |=
                            OBJSET_FLAG_USEROBJACCOUNTING_COMPLETE;
                }
                os->os_flags = os->os_phys->os_flags;
        }

        dsl_dataset_dirty(ds, tx);

        return (os);
}

typedef struct dmu_objset_create_arg {
        const char *doca_name;
        cred_t *doca_cred;
        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;
} dmu_objset_create_arg_t;

/*ARGSUSED*/
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;
        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));

        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 = dsl_fs_ss_limit_check(pdd, 1, ZFS_PROP_FILESYSTEM_LIMIT, NULL,
            doca->doca_cred);
        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);
        dsl_dir_t *pdd;
        const char *tail;
        dsl_dataset_t *ds;
        uint64_t obj;
        blkptr_t *bp;
        objset_t *os;

        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, tx);

        VERIFY0(dsl_dataset_hold_obj(pdd->dd_pool, obj, FTAG, &ds));
        rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
        bp = dsl_dataset_get_blkptr(ds);
        os = dmu_objset_create_impl(pdd->dd_pool->dp_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);
        }

        spa_history_log_internal_ds(ds, "create", tx, "");
        zvol_create_minors(dp->dp_spa, doca->doca_name, B_TRUE);

        dsl_dataset_rele(ds, FTAG);
        dsl_dir_rele(pdd, FTAG);
}

int
dmu_objset_create(const char *name, dmu_objset_type_t type, uint64_t flags,
    void (*func)(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx), void *arg)
{
        dmu_objset_create_arg_t doca;

        doca.doca_name = name;
        doca.doca_cred = CRED();
        doca.doca_flags = flags;
        doca.doca_userfunc = func;
        doca.doca_userarg = arg;
        doca.doca_type = type;

        return (dsl_sync_task(name,
            dmu_objset_create_check, dmu_objset_create_sync, &doca,
            5, ZFS_SPACE_CHECK_NORMAL));
}

typedef struct dmu_objset_clone_arg {
        const char *doca_clone;
        const char *doca_origin;
        cred_t *doca_cred;
} dmu_objset_clone_arg_t;

/*ARGSUSED*/
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);
        if (error != 0) {
                dsl_dir_rele(pdd, FTAG);
                return (SET_ERROR(EDQUOT));
        }
        dsl_dir_rele(pdd, FTAG);

        error = dsl_dataset_hold(dp, doca->doca_origin, FTAG, &origin);
        if (error != 0)
                return (error);

        /* You can only clone snapshots, not the head datasets. */
        if (!origin->ds_is_snapshot) {
                dsl_dataset_rele(origin, FTAG);
                return (SET_ERROR(EINVAL));
        }
        dsl_dataset_rele(origin, 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, 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, origin->ds_object);
        zvol_create_minors(dp->dp_spa, doca->doca_clone, B_TRUE);
        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();

        return (dsl_sync_task(clone,
            dmu_objset_clone_check, dmu_objset_clone_sync, &doca,
            5, ZFS_SPACE_CHECK_NORMAL));
}

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);
        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) {
                mutex_exit(&os->os_upgrade_lock);

                os->os_upgrade_status = os->os_upgrade_cb(os);
                mutex_enter(&os->os_upgrade_lock);
        }
        os->os_upgrade_exit = B_TRUE;
        os->os_upgrade_id = 0;
        mutex_exit(&os->os_upgrade_lock);
}

static void
dmu_objset_upgrade(objset_t *os, dmu_objset_upgrade_cb_t cb)
{
        if (os->os_upgrade_id != 0)
                return;

        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)
                        os->os_upgrade_status = ENOMEM;
        }
        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);

                taskq_cancel_id(os->os_spa->spa_upgrade_taskq, id);
        } 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 ouside 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);

                multilist_t *newlist = dn->dn_objset->os_synced_dnodes;
                if (newlist != NULL) {
                        (void) dnode_add_ref(dn, newlist);
                        multilist_insert(newlist, dn);
                }

                dnode_sync(dn, tx);
        }
}

/* ARGSUSED */
static void
dmu_objset_write_ready(zio_t *zio, arc_buf_t *abuf, void *arg)
{
        int i;

        blkptr_t *bp = zio->io_bp;
        objset_t *os = arg;
        dnode_phys_t *dnp = &os->os_phys->os_meta_dnode;

        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 accounting objects).
         */
        bp->blk_fill = 0;
        for (i = 0; i < dnp->dn_nblkptr; i++)
                bp->blk_fill += BP_GET_FILL(&dnp->dn_blkptr[i]);
        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);
}

/* ARGSUSED */
static void
dmu_objset_write_done(zio_t *zio, arc_buf_t *abuf, void *arg)
{
        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;
        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", 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);

        zio = arc_write(pio, os->os_spa, tx->tx_txg,
            blkptr_copy, os->os_phys_buf, 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);
        }

        txgoff = tx->tx_txg & TXG_MASK;

        if (dmu_objset_userused_enabled(os)) {
                /*
                 * 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 == NULL) {
                        os->os_synced_dnodes =
                            multilist_create(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]));
                }
        }

        for (int i = 0;
            i < multilist_get_num_sublists(os->os_dirty_dnodes[txgoff]); i++) {
                sync_dnodes_arg_t *sda = kmem_alloc(sizeof (*sda), KM_SLEEP);
                sda->sda_list = os->os_dirty_dnodes[txgoff];
                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);
                if (dr->dr_zio)
                        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 objset_used_cb_t *used_cbs[DMU_OST_NUMTYPES];

void
dmu_objset_register_type(dmu_objset_type_t ost, objset_used_cb_t *cb)
{
        used_cbs[ost] = cb;
}

boolean_t
dmu_objset_userused_enabled(objset_t *os)
{
        return (spa_version(os->os_spa) >= SPA_VERSION_USERSPACE &&
            used_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));
}

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;
} 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 (AVL_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);
}

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(userquota_cache_t *cache, uint64_t used, uint64_t flags,
    uint64_t user, uint64_t group, boolean_t subtract)
{
        if ((flags & DNODE_FLAG_USERUSED_ACCOUNTED)) {
                int64_t delta = DNODE_MIN_SIZE + used;
                char name[20];

                if (subtract)
                        delta = -delta;

                (void) sprintf(name, "%llx", (longlong_t)user);
                userquota_update_cache(&cache->uqc_user_deltas, name, delta);

                (void) sprintf(name, "%llx", (longlong_t)group);
                userquota_update_cache(&cache->uqc_group_deltas, name, delta);
        }
}

static void
do_userobjquota_update(userquota_cache_t *cache, uint64_t flags,
    uint64_t user, uint64_t group, 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);
        }
}

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));

        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(&cache,
                            dn->dn_oldused, dn->dn_oldflags,
                            dn->dn_olduid, dn->dn_oldgid, B_TRUE);
                        do_userobjquota_update(&cache, dn->dn_oldflags,
                            dn->dn_olduid, dn->dn_oldgid, B_TRUE);
                }
                if (flags & DN_ID_NEW_EXIST) {
                        do_userquota_update(&cache,
                            DN_USED_BYTES(dn->dn_phys), dn->dn_phys->dn_flags,
                            dn->dn_newuid, dn->dn_newgid, B_FALSE);
                        do_userobjquota_update(&cache, dn->dn_phys->dn_flags,
                            dn->dn_newuid, dn->dn_newgid, 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_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));
}

void
dmu_objset_do_userquota_updates(objset_t *os, dmu_tx_t *tx)
{
        if (!dmu_objset_userused_enabled(os))
                return;

        /* Allocate the user/groupused 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));
        }

        for (int i = 0;
            i < multilist_get_num_sublists(os->os_synced_dnodes); 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;
                /* note: caller does taskq_wait() */
                (void) taskq_dispatch(dmu_objset_pool(os)->dp_sync_taskq,
                    userquota_updates_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, **drp;
        void *data;

        if (db->db_dirtycnt == 0)
                return (db->db.db_data);  /* Nothing is changing */

        for (drp = &db->db_last_dirty; (dr = *drp) != NULL; drp = &dr->dr_next)
                if (dr->dr_txg == tx->tx_txg)
                        break;

        if (dr == NULL) {
                data = NULL;
        } else {
                dnode_t *dn;

                DB_DNODE_ENTER(dr->dr_dbuf);
                dn = DB_DNODE(dr->dr_dbuf);

                if (dn->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;

                DB_DNODE_EXIT(dr->dr_dbuf);
        }

        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;
        uint64_t *user = NULL;
        uint64_t *group = NULL;
        int flags = dn->dn_id_flags;
        int error;
        boolean_t have_spill = B_FALSE;

        if (!dmu_objset_userused_enabled(dn->dn_objset))
                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;
        }

        if (before) {
                ASSERT(data);
                user = &dn->dn_olduid;
                group = &dn->dn_oldgid;
        } else if (data) {
                user = &dn->dn_newuid;
                group = &dn->dn_newgid;
        }

        /*
         * Must always call the callback in case the object
         * type has changed and that type isn't an object type to track
         */
        error = used_cbs[os->os_phys->os_type](dn->dn_bonustype, data,
            user, group);

        /*
         * 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;
                } else {
                        dn->dn_newuid = 0;
                        dn->dn_newgid = 0;
                }
                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);
}

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_tx_abort(tx);
                        continue;
                }
                dmu_buf_will_dirty(db, tx);
                dmu_buf_rele(db, FTAG);
                dmu_tx_commit(tx);
        }
        return (0);
}

int
dmu_objset_userspace_upgrade(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);
}

static int
dmu_objset_userobjspace_upgrade_cb(objset_t *os)
{
        int err = 0;

        if (dmu_objset_userobjspace_present(os))
                return (0);
        if (dmu_objset_is_snapshot(os))
                return (SET_ERROR(EINVAL));
        if (!dmu_objset_userobjused_enabled(os))
                return (SET_ERROR(ENOTSUP));

        dmu_objset_ds(os)->ds_feature_activation_needed[
            SPA_FEATURE_USEROBJ_ACCOUNTING] = B_TRUE;

        err = dmu_objset_space_upgrade(os);
        if (err)
                return (err);

        os->os_flags |= OBJSET_FLAG_USEROBJACCOUNTING_COMPLETE;
        txg_wait_synced(dmu_objset_pool(os), 0);
        return (0);
}

void
dmu_objset_userobjspace_upgrade(objset_t *os)
{
        dmu_objset_upgrade(os, dmu_objset_userobjspace_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));
}

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, 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) strcpy(name, attr.za_name);
        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) strcpy(name, attr.za_name);
        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;
        dmu_objset_find_ctx_t *child_dcp;
        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);

                        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
         * asssert(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);
                        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);
                                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(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);
}

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.
 */
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) && defined(HAVE_SPL)
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_own);
EXPORT_SYMBOL(dmu_objset_rele);
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);
EXPORT_SYMBOL(dmu_objset_open_impl);
EXPORT_SYMBOL(dmu_objset_evict);
EXPORT_SYMBOL(dmu_objset_register_type);
EXPORT_SYMBOL(dmu_objset_do_userquota_updates);
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_upgrade);
EXPORT_SYMBOL(dmu_objset_userobjspace_upgradable);
EXPORT_SYMBOL(dmu_objset_userobjspace_present);
#endif