dsl_dataset.c

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/*
 * 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 by Delphix. All rights reserved.
 * Copyright (c) 2012, Joyent, Inc. All rights reserved.
 * Copyright (c) 2011 Pawel Jakub Dawidek <pawel@dawidek.net>.
 * All rights reserved.
 * Portions Copyright (c) 2011 Martin Matuska <mm@FreeBSD.org>
 */

#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_prop.h>
#include <sys/dsl_synctask.h>
#include <sys/dmu_traverse.h>
#include <sys/dmu_impl.h>
#include <sys/dmu_tx.h>
#include <sys/arc.h>
#include <sys/zio.h>
#include <sys/zap.h>
#include <sys/zfeature.h>
#include <sys/unique.h>
#include <sys/zfs_context.h>
#include <sys/zfs_ioctl.h>
#include <sys/spa.h>
#include <sys/zfs_znode.h>
#include <sys/zfs_onexit.h>
#include <sys/zvol.h>
#include <sys/dsl_scan.h>
#include <sys/dsl_deadlist.h>

static char *dsl_reaper = "the grim reaper";

static dsl_checkfunc_t dsl_dataset_destroy_begin_check;
static dsl_syncfunc_t dsl_dataset_destroy_begin_sync;
static dsl_syncfunc_t dsl_dataset_set_reservation_sync;

#define SWITCH64(x, y) \
        { \
                uint64_t __tmp = (x); \
                (x) = (y); \
                (y) = __tmp; \
        }

#define DS_REF_MAX      (1ULL << 62)

#define DSL_DEADLIST_BLOCKSIZE  SPA_MAXBLOCKSIZE

#define DSL_DATASET_IS_DESTROYED(ds)    ((ds)->ds_owner == dsl_reaper)


static int64_t
parent_delta(dsl_dataset_t *ds, int64_t delta)
{
        uint64_t old_bytes, new_bytes;

        if (ds->ds_reserved == 0)
                return (delta);

        old_bytes = MAX(ds->ds_phys->ds_unique_bytes, ds->ds_reserved);
        new_bytes = MAX(ds->ds_phys->ds_unique_bytes + delta, ds->ds_reserved);

        ASSERT3U(ABS((int64_t)(new_bytes - old_bytes)), <=, ABS(delta));
        return (new_bytes - old_bytes);
}

void
dsl_dataset_block_born(dsl_dataset_t *ds, const blkptr_t *bp, dmu_tx_t *tx)
{
        int used = bp_get_dsize_sync(tx->tx_pool->dp_spa, bp);
        int compressed = BP_GET_PSIZE(bp);
        int uncompressed = BP_GET_UCSIZE(bp);
        int64_t delta;

        dprintf_bp(bp, "ds=%p", ds);

        ASSERT(dmu_tx_is_syncing(tx));
        /* It could have been compressed away to nothing */
        if (BP_IS_HOLE(bp))
                return;
        ASSERT(BP_GET_TYPE(bp) != DMU_OT_NONE);
        ASSERT(DMU_OT_IS_VALID(BP_GET_TYPE(bp)));
        if (ds == NULL) {
                dsl_pool_mos_diduse_space(tx->tx_pool,
                    used, compressed, uncompressed);
                return;
        }
        dmu_buf_will_dirty(ds->ds_dbuf, tx);

        mutex_enter(&ds->ds_dir->dd_lock);
        mutex_enter(&ds->ds_lock);
        delta = parent_delta(ds, used);
        ds->ds_phys->ds_referenced_bytes += used;
        ds->ds_phys->ds_compressed_bytes += compressed;
        ds->ds_phys->ds_uncompressed_bytes += uncompressed;
        ds->ds_phys->ds_unique_bytes += used;
        mutex_exit(&ds->ds_lock);
        dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD, delta,
            compressed, uncompressed, tx);
        dsl_dir_transfer_space(ds->ds_dir, used - delta,
            DD_USED_REFRSRV, DD_USED_HEAD, tx);
        mutex_exit(&ds->ds_dir->dd_lock);
}

int
dsl_dataset_block_kill(dsl_dataset_t *ds, const blkptr_t *bp, dmu_tx_t *tx,
    boolean_t async)
{
        if (BP_IS_HOLE(bp))
                return (0);

        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(bp->blk_birth <= tx->tx_txg);

        int used = bp_get_dsize_sync(tx->tx_pool->dp_spa, bp);
        int compressed = BP_GET_PSIZE(bp);
        int uncompressed = BP_GET_UCSIZE(bp);

        ASSERT(used > 0);
        if (ds == NULL) {
                dsl_free(tx->tx_pool, tx->tx_txg, bp);
                dsl_pool_mos_diduse_space(tx->tx_pool,
                    -used, -compressed, -uncompressed);
                return (used);
        }
        ASSERT3P(tx->tx_pool, ==, ds->ds_dir->dd_pool);

        ASSERT(!dsl_dataset_is_snapshot(ds));
        dmu_buf_will_dirty(ds->ds_dbuf, tx);

        if (bp->blk_birth > ds->ds_phys->ds_prev_snap_txg) {
                int64_t delta;

                dprintf_bp(bp, "freeing ds=%llu", ds->ds_object);
                dsl_free(tx->tx_pool, tx->tx_txg, bp);

                mutex_enter(&ds->ds_dir->dd_lock);
                mutex_enter(&ds->ds_lock);
                ASSERT(ds->ds_phys->ds_unique_bytes >= used ||
                    !DS_UNIQUE_IS_ACCURATE(ds));
                delta = parent_delta(ds, -used);
                ds->ds_phys->ds_unique_bytes -= used;
                mutex_exit(&ds->ds_lock);
                dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD,
                    delta, -compressed, -uncompressed, tx);
                dsl_dir_transfer_space(ds->ds_dir, -used - delta,
                    DD_USED_REFRSRV, DD_USED_HEAD, tx);
                mutex_exit(&ds->ds_dir->dd_lock);
        } else {
                dprintf_bp(bp, "putting on dead list: %s", "");
                if (async) {
                        /*
                         * We are here as part of zio's write done callback,
                         * which means we're a zio interrupt thread.  We can't
                         * call dsl_deadlist_insert() now because it may block
                         * waiting for I/O.  Instead, put bp on the deferred
                         * queue and let dsl_pool_sync() finish the job.
                         */
                        bplist_append(&ds->ds_pending_deadlist, bp);
                } else {
                        dsl_deadlist_insert(&ds->ds_deadlist, bp, tx);
                }
                ASSERT3U(ds->ds_prev->ds_object, ==,
                    ds->ds_phys->ds_prev_snap_obj);
                ASSERT(ds->ds_prev->ds_phys->ds_num_children > 0);
                /* if (bp->blk_birth > prev prev snap txg) prev unique += bs */
                if (ds->ds_prev->ds_phys->ds_next_snap_obj ==
                    ds->ds_object && bp->blk_birth >
                    ds->ds_prev->ds_phys->ds_prev_snap_txg) {
                        dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
                        mutex_enter(&ds->ds_prev->ds_lock);
                        ds->ds_prev->ds_phys->ds_unique_bytes += used;
                        mutex_exit(&ds->ds_prev->ds_lock);
                }
                if (bp->blk_birth > ds->ds_dir->dd_origin_txg) {
                        dsl_dir_transfer_space(ds->ds_dir, used,
                            DD_USED_HEAD, DD_USED_SNAP, tx);
                }
        }
        mutex_enter(&ds->ds_lock);
        ASSERT3U(ds->ds_phys->ds_referenced_bytes, >=, used);
        ds->ds_phys->ds_referenced_bytes -= used;
        ASSERT3U(ds->ds_phys->ds_compressed_bytes, >=, compressed);
        ds->ds_phys->ds_compressed_bytes -= compressed;
        ASSERT3U(ds->ds_phys->ds_uncompressed_bytes, >=, uncompressed);
        ds->ds_phys->ds_uncompressed_bytes -= uncompressed;
        mutex_exit(&ds->ds_lock);

        return (used);
}

uint64_t
dsl_dataset_prev_snap_txg(dsl_dataset_t *ds)
{
        uint64_t trysnap = 0;

        if (ds == NULL)
                return (0);
        /*
         * The snapshot creation could fail, but that would cause an
         * incorrect FALSE return, which would only result in an
         * overestimation of the amount of space that an operation would
         * consume, which is OK.
         *
         * There's also a small window where we could miss a pending
         * snapshot, because we could set the sync task in the quiescing
         * phase.  So this should only be used as a guess.
         */
        if (ds->ds_trysnap_txg >
            spa_last_synced_txg(ds->ds_dir->dd_pool->dp_spa))
                trysnap = ds->ds_trysnap_txg;
        return (MAX(ds->ds_phys->ds_prev_snap_txg, trysnap));
}

boolean_t
dsl_dataset_block_freeable(dsl_dataset_t *ds, const blkptr_t *bp,
    uint64_t blk_birth)
{
        if (blk_birth <= dsl_dataset_prev_snap_txg(ds))
                return (B_FALSE);

        ddt_prefetch(dsl_dataset_get_spa(ds), bp);

        return (B_TRUE);
}

/* ARGSUSED */
static void
dsl_dataset_evict(dmu_buf_t *db, void *dsv)
{
        dsl_dataset_t *ds = dsv;

        ASSERT(ds->ds_owner == NULL || DSL_DATASET_IS_DESTROYED(ds));

        unique_remove(ds->ds_fsid_guid);

        if (ds->ds_objset != NULL)
                dmu_objset_evict(ds->ds_objset);

        if (ds->ds_prev) {
                dsl_dataset_drop_ref(ds->ds_prev, ds);
                ds->ds_prev = NULL;
        }

        bplist_destroy(&ds->ds_pending_deadlist);
        if (db != NULL) {
                dsl_deadlist_close(&ds->ds_deadlist);
        } else {
                ASSERT(ds->ds_deadlist.dl_dbuf == NULL);
                ASSERT(!ds->ds_deadlist.dl_oldfmt);
        }
        if (ds->ds_dir)
                dsl_dir_close(ds->ds_dir, ds);

        ASSERT(!list_link_active(&ds->ds_synced_link));

        if (mutex_owned(&ds->ds_lock))
                mutex_exit(&ds->ds_lock);
        mutex_destroy(&ds->ds_lock);
        mutex_destroy(&ds->ds_recvlock);
        if (mutex_owned(&ds->ds_opening_lock))
                mutex_exit(&ds->ds_opening_lock);
        mutex_destroy(&ds->ds_opening_lock);
        rw_destroy(&ds->ds_rwlock);
        cv_destroy(&ds->ds_exclusive_cv);

        kmem_free(ds, sizeof (dsl_dataset_t));
}

static int
dsl_dataset_get_snapname(dsl_dataset_t *ds)
{
        dsl_dataset_phys_t *headphys;
        int err;
        dmu_buf_t *headdbuf;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        objset_t *mos = dp->dp_meta_objset;

        if (ds->ds_snapname[0])
                return (0);
        if (ds->ds_phys->ds_next_snap_obj == 0)
                return (0);

        err = dmu_bonus_hold(mos, ds->ds_dir->dd_phys->dd_head_dataset_obj,
            FTAG, &headdbuf);
        if (err)
                return (err);
        headphys = headdbuf->db_data;
        err = zap_value_search(dp->dp_meta_objset,
            headphys->ds_snapnames_zapobj, ds->ds_object, 0, ds->ds_snapname);
        dmu_buf_rele(headdbuf, FTAG);
        return (err);
}

static int
dsl_dataset_snap_lookup(dsl_dataset_t *ds, const char *name, uint64_t *value)
{
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        uint64_t snapobj = ds->ds_phys->ds_snapnames_zapobj;
        matchtype_t mt;
        int err;

        if (ds->ds_phys->ds_flags & DS_FLAG_CI_DATASET)
                mt = MT_FIRST;
        else
                mt = MT_EXACT;

        err = zap_lookup_norm(mos, snapobj, name, 8, 1,
            value, mt, NULL, 0, NULL);
        if (err == ENOTSUP && mt == MT_FIRST)
                err = zap_lookup(mos, snapobj, name, 8, 1, value);
        return (err);
}

static int
dsl_dataset_snap_remove(dsl_dataset_t *ds, char *name, dmu_tx_t *tx)
{
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        uint64_t snapobj = ds->ds_phys->ds_snapnames_zapobj;
        matchtype_t mt;
        int err;

        dsl_dir_snap_cmtime_update(ds->ds_dir);

        if (ds->ds_phys->ds_flags & DS_FLAG_CI_DATASET)
                mt = MT_FIRST;
        else
                mt = MT_EXACT;

        err = zap_remove_norm(mos, snapobj, name, mt, tx);
        if (err == ENOTSUP && mt == MT_FIRST)
                err = zap_remove(mos, snapobj, name, tx);
        return (err);
}

static int
dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
    dsl_dataset_t **dsp)
{
        objset_t *mos = dp->dp_meta_objset;
        dmu_buf_t *dbuf;
        dsl_dataset_t *ds;
        int err;
        dmu_object_info_t doi;

        ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
            dsl_pool_sync_context(dp));

        err = dmu_bonus_hold(mos, dsobj, tag, &dbuf);
        if (err)
                return (err);

        /* Make sure dsobj has the correct object type. */
        dmu_object_info_from_db(dbuf, &doi);
        if (doi.doi_type != DMU_OT_DSL_DATASET)
                return (EINVAL);

        ds = dmu_buf_get_user(dbuf);
        if (ds == NULL) {
                dsl_dataset_t *winner;

                ds = kmem_zalloc(sizeof (dsl_dataset_t), KM_SLEEP);
                ds->ds_dbuf = dbuf;
                ds->ds_object = dsobj;
                ds->ds_phys = dbuf->db_data;

                mutex_init(&ds->ds_lock, NULL, MUTEX_DEFAULT, NULL);
                mutex_init(&ds->ds_recvlock, NULL, MUTEX_DEFAULT, NULL);
                mutex_init(&ds->ds_opening_lock, NULL, MUTEX_DEFAULT, NULL);
                mutex_init(&ds->ds_sendstream_lock, NULL, MUTEX_DEFAULT, NULL);

                rw_init(&ds->ds_rwlock, 0, 0, 0);
                cv_init(&ds->ds_exclusive_cv, NULL, CV_DEFAULT, NULL);

                bplist_create(&ds->ds_pending_deadlist);
                dsl_deadlist_open(&ds->ds_deadlist,
                    mos, ds->ds_phys->ds_deadlist_obj);

                list_create(&ds->ds_sendstreams, sizeof (dmu_sendarg_t),
                    offsetof(dmu_sendarg_t, dsa_link));

                if (err == 0) {
                        err = dsl_dir_open_obj(dp,
                            ds->ds_phys->ds_dir_obj, NULL, ds, &ds->ds_dir);
                }
                if (err) {
                        mutex_destroy(&ds->ds_lock);
                        mutex_destroy(&ds->ds_recvlock);
                        mutex_destroy(&ds->ds_opening_lock);
                        rw_destroy(&ds->ds_rwlock);
                        cv_destroy(&ds->ds_exclusive_cv);
                        bplist_destroy(&ds->ds_pending_deadlist);
                        dsl_deadlist_close(&ds->ds_deadlist);
                        kmem_free(ds, sizeof (dsl_dataset_t));
                        dmu_buf_rele(dbuf, tag);
                        return (err);
                }

                if (!dsl_dataset_is_snapshot(ds)) {
                        ds->ds_snapname[0] = '\0';
                        if (ds->ds_phys->ds_prev_snap_obj) {
                                err = dsl_dataset_get_ref(dp,
                                    ds->ds_phys->ds_prev_snap_obj,
                                    ds, &ds->ds_prev);
                        }
                } else {
                        if (zfs_flags & ZFS_DEBUG_SNAPNAMES)
                                err = dsl_dataset_get_snapname(ds);
                        if (err == 0 && ds->ds_phys->ds_userrefs_obj != 0) {
                                err = zap_count(
                                    ds->ds_dir->dd_pool->dp_meta_objset,
                                    ds->ds_phys->ds_userrefs_obj,
                                    &ds->ds_userrefs);
                        }
                }

                if (err == 0 && !dsl_dataset_is_snapshot(ds)) {
                        /*
                         * In sync context, we're called with either no lock
                         * or with the write lock.  If we're not syncing,
                         * we're always called with the read lock held.
                         */
                        boolean_t need_lock =
                            !RW_WRITE_HELD(&dp->dp_config_rwlock) &&
                            dsl_pool_sync_context(dp);

                        if (need_lock)
                                rw_enter(&dp->dp_config_rwlock, RW_READER);

                        err = dsl_prop_get_ds(ds,
                            "refreservation", sizeof (uint64_t), 1,
                            &ds->ds_reserved, NULL);
                        if (err == 0) {
                                err = dsl_prop_get_ds(ds,
                                    "refquota", sizeof (uint64_t), 1,
                                    &ds->ds_quota, NULL);
                        }

                        if (need_lock)
                                rw_exit(&dp->dp_config_rwlock);
                } else {
                        ds->ds_reserved = ds->ds_quota = 0;
                }

                if (err == 0) {
                        winner = dmu_buf_set_user_ie(dbuf, ds, &ds->ds_phys,
                            dsl_dataset_evict);
                }
                if (err || winner) {
                        bplist_destroy(&ds->ds_pending_deadlist);
                        dsl_deadlist_close(&ds->ds_deadlist);
                        if (ds->ds_prev)
                                dsl_dataset_drop_ref(ds->ds_prev, ds);
                        dsl_dir_close(ds->ds_dir, ds);
                        mutex_destroy(&ds->ds_lock);
                        mutex_destroy(&ds->ds_recvlock);
                        mutex_destroy(&ds->ds_opening_lock);
                        rw_destroy(&ds->ds_rwlock);
                        cv_destroy(&ds->ds_exclusive_cv);
                        kmem_free(ds, sizeof (dsl_dataset_t));
                        if (err) {
                                dmu_buf_rele(dbuf, tag);
                                return (err);
                        }
                        ds = winner;
                } else {
                        ds->ds_fsid_guid =
                            unique_insert(ds->ds_phys->ds_fsid_guid);
                }
        }
        ASSERT3P(ds->ds_dbuf, ==, dbuf);
        ASSERT3P(ds->ds_phys, ==, dbuf->db_data);
        ASSERT(ds->ds_phys->ds_prev_snap_obj != 0 ||
            spa_version(dp->dp_spa) < SPA_VERSION_ORIGIN ||
            dp->dp_origin_snap == NULL || ds == dp->dp_origin_snap);
        mutex_enter(&ds->ds_lock);
        if (!dsl_pool_sync_context(dp) && DSL_DATASET_IS_DESTROYED(ds)) {
                mutex_exit(&ds->ds_lock);
                dmu_buf_rele(ds->ds_dbuf, tag);
                return (ENOENT);
        }
        mutex_exit(&ds->ds_lock);
        *dsp = ds;
        return (0);
}

static int
dsl_dataset_hold_ref(dsl_dataset_t *ds, void *tag)
{
        dsl_pool_t *dp = ds->ds_dir->dd_pool;

        /*
         * In syncing context we don't want the rwlock lock: there
         * may be an existing writer waiting for sync phase to
         * finish.  We don't need to worry about such writers, since
         * sync phase is single-threaded, so the writer can't be
         * doing anything while we are active.
         */
        if (dsl_pool_sync_context(dp)) {
                ASSERT(!DSL_DATASET_IS_DESTROYED(ds));
                return (0);
        }

        /*
         * Normal users will hold the ds_rwlock as a READER until they
         * are finished (i.e., call dsl_dataset_rele()).  "Owners" will
         * drop their READER lock after they set the ds_owner field.
         *
         * If the dataset is being destroyed, the destroy thread will
         * obtain a WRITER lock for exclusive access after it's done its
         * open-context work and then change the ds_owner to
         * dsl_reaper once destruction is assured.  So threads
         * may block here temporarily, until the "destructability" of
         * the dataset is determined.
         */
        ASSERT(!RW_WRITE_HELD(&dp->dp_config_rwlock));
        mutex_enter(&ds->ds_lock);
        while (!rw_tryenter(&ds->ds_rwlock, RW_READER)) {
                rw_exit(&dp->dp_config_rwlock);
                cv_wait(&ds->ds_exclusive_cv, &ds->ds_lock);
                if (DSL_DATASET_IS_DESTROYED(ds)) {
                        mutex_exit(&ds->ds_lock);
                        dsl_dataset_drop_ref(ds, tag);
                        rw_enter(&dp->dp_config_rwlock, RW_READER);
                        return (ENOENT);
                }
                /*
                 * The dp_config_rwlock lives above the ds_lock. And
                 * we need to check DSL_DATASET_IS_DESTROYED() while
                 * holding the ds_lock, so we have to drop and reacquire
                 * the ds_lock here.
                 */
                mutex_exit(&ds->ds_lock);
                rw_enter(&dp->dp_config_rwlock, RW_READER);
                mutex_enter(&ds->ds_lock);
        }
        mutex_exit(&ds->ds_lock);
        return (0);
}

int
dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
    dsl_dataset_t **dsp)
{
        int err = dsl_dataset_get_ref(dp, dsobj, tag, dsp);

        if (err)
                return (err);
        return (dsl_dataset_hold_ref(*dsp, tag));
}

int
dsl_dataset_own_obj(dsl_pool_t *dp, uint64_t dsobj, boolean_t inconsistentok,
    void *tag, dsl_dataset_t **dsp)
{
        int err = dsl_dataset_hold_obj(dp, dsobj, tag, dsp);
        if (err)
                return (err);
        if (!dsl_dataset_tryown(*dsp, inconsistentok, tag)) {
                dsl_dataset_rele(*dsp, tag);
                *dsp = NULL;
                return (EBUSY);
        }
        return (0);
}

int
dsl_dataset_hold(const char *name, void *tag, dsl_dataset_t **dsp)
{
        dsl_dir_t *dd;
        dsl_pool_t *dp;
        const char *snapname;
        uint64_t obj;
        int err = 0;

        err = dsl_dir_open_spa(NULL, name, FTAG, &dd, &snapname);
        if (err)
                return (err);

        dp = dd->dd_pool;
        obj = dd->dd_phys->dd_head_dataset_obj;
        rw_enter(&dp->dp_config_rwlock, RW_READER);
        if (obj)
                err = dsl_dataset_get_ref(dp, obj, tag, dsp);
        else
                err = ENOENT;
        if (err)
                goto out;

        err = dsl_dataset_hold_ref(*dsp, tag);

        /* we may be looking for a snapshot */
        if (err == 0 && snapname != NULL) {
                dsl_dataset_t *ds = NULL;

                if (*snapname++ != '@') {
                        dsl_dataset_rele(*dsp, tag);
                        err = ENOENT;
                        goto out;
                }

                dprintf("looking for snapshot '%s'\n", snapname);
                err = dsl_dataset_snap_lookup(*dsp, snapname, &obj);
                if (err == 0)
                        err = dsl_dataset_get_ref(dp, obj, tag, &ds);
                dsl_dataset_rele(*dsp, tag);

                ASSERT3U((err == 0), ==, (ds != NULL));

                if (ds) {
                        mutex_enter(&ds->ds_lock);
                        if (ds->ds_snapname[0] == 0)
                                (void) strlcpy(ds->ds_snapname, snapname,
                                    sizeof (ds->ds_snapname));
                        mutex_exit(&ds->ds_lock);
                        err = dsl_dataset_hold_ref(ds, tag);
                        *dsp = err ? NULL : ds;
                }
        }
out:
        rw_exit(&dp->dp_config_rwlock);
        dsl_dir_close(dd, FTAG);
        return (err);
}

int
dsl_dataset_own(const char *name, boolean_t inconsistentok,
    void *tag, dsl_dataset_t **dsp)
{
        int err = dsl_dataset_hold(name, tag, dsp);
        if (err)
                return (err);
        if (!dsl_dataset_tryown(*dsp, inconsistentok, tag)) {
                dsl_dataset_rele(*dsp, tag);
                return (EBUSY);
        }
        return (0);
}

void
dsl_dataset_name(dsl_dataset_t *ds, char *name)
{
        if (ds == NULL) {
                (void) strcpy(name, "mos");
        } else {
                dsl_dir_name(ds->ds_dir, name);
                VERIFY(0 == dsl_dataset_get_snapname(ds));
                if (ds->ds_snapname[0]) {
                        (void) strcat(name, "@");
                        /*
                         * We use a "recursive" mutex so that we
                         * can call dprintf_ds() with ds_lock held.
                         */
                        if (!MUTEX_HELD(&ds->ds_lock)) {
                                mutex_enter(&ds->ds_lock);
                                (void) strcat(name, ds->ds_snapname);
                                mutex_exit(&ds->ds_lock);
                        } else {
                                (void) strcat(name, ds->ds_snapname);
                        }
                }
        }
}

static int
dsl_dataset_namelen(dsl_dataset_t *ds)
{
        int result;

        if (ds == NULL) {
                result = 3;     /* "mos" */
        } else {
                result = dsl_dir_namelen(ds->ds_dir);
                VERIFY(0 == dsl_dataset_get_snapname(ds));
                if (ds->ds_snapname[0]) {
                        ++result;       /* adding one for the @-sign */
                        if (!MUTEX_HELD(&ds->ds_lock)) {
                                mutex_enter(&ds->ds_lock);
                                result += strlen(ds->ds_snapname);
                                mutex_exit(&ds->ds_lock);
                        } else {
                                result += strlen(ds->ds_snapname);
                        }
                }
        }

        return (result);
}

void
dsl_dataset_drop_ref(dsl_dataset_t *ds, void *tag)
{
        dmu_buf_rele(ds->ds_dbuf, tag);
}

void
dsl_dataset_rele(dsl_dataset_t *ds, void *tag)
{
        if (!dsl_pool_sync_context(ds->ds_dir->dd_pool)) {
                rw_exit(&ds->ds_rwlock);
        }
        dsl_dataset_drop_ref(ds, tag);
}

void
dsl_dataset_disown(dsl_dataset_t *ds, void *tag)
{
        ASSERT((ds->ds_owner == tag && ds->ds_dbuf) ||
            (DSL_DATASET_IS_DESTROYED(ds) && ds->ds_dbuf == NULL));

        mutex_enter(&ds->ds_lock);
        ds->ds_owner = NULL;
        if (RW_WRITE_HELD(&ds->ds_rwlock)) {
                rw_exit(&ds->ds_rwlock);
                cv_broadcast(&ds->ds_exclusive_cv);
        }
        mutex_exit(&ds->ds_lock);
        if (ds->ds_dbuf)
                dsl_dataset_drop_ref(ds, tag);
        else
                dsl_dataset_evict(NULL, ds);
}

boolean_t
dsl_dataset_tryown(dsl_dataset_t *ds, boolean_t inconsistentok, void *tag)
{
        boolean_t gotit = FALSE;

        mutex_enter(&ds->ds_lock);
        if (ds->ds_owner == NULL &&
            (!DS_IS_INCONSISTENT(ds) || inconsistentok)) {
                ds->ds_owner = tag;
                if (!dsl_pool_sync_context(ds->ds_dir->dd_pool))
                        rw_exit(&ds->ds_rwlock);
                gotit = TRUE;
        }
        mutex_exit(&ds->ds_lock);
        return (gotit);
}

void
dsl_dataset_make_exclusive(dsl_dataset_t *ds, void *owner)
{
        ASSERT3P(owner, ==, ds->ds_owner);
        if (!RW_WRITE_HELD(&ds->ds_rwlock))
                rw_enter(&ds->ds_rwlock, RW_WRITER);
}

uint64_t
dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
    uint64_t flags, dmu_tx_t *tx)
{
        dsl_pool_t *dp = dd->dd_pool;
        dmu_buf_t *dbuf;
        dsl_dataset_phys_t *dsphys;
        uint64_t dsobj;
        objset_t *mos = dp->dp_meta_objset;

        if (origin == NULL)
                origin = dp->dp_origin_snap;

        ASSERT(origin == NULL || origin->ds_dir->dd_pool == dp);
        ASSERT(origin == NULL || origin->ds_phys->ds_num_children > 0);
        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(dd->dd_phys->dd_head_dataset_obj == 0);

        dsobj = dmu_object_alloc(mos, DMU_OT_DSL_DATASET, 0,
            DMU_OT_DSL_DATASET, sizeof (dsl_dataset_phys_t), tx);
        VERIFY(0 == dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
        dmu_buf_will_dirty(dbuf, tx);
        dsphys = dbuf->db_data;
        bzero(dsphys, sizeof (dsl_dataset_phys_t));
        dsphys->ds_dir_obj = dd->dd_object;
        dsphys->ds_flags = flags;
        dsphys->ds_fsid_guid = unique_create();
        do {
                (void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
                    sizeof (dsphys->ds_guid));
        } while (dsphys->ds_guid == 0);
        dsphys->ds_snapnames_zapobj =
            zap_create_norm(mos, U8_TEXTPREP_TOUPPER, DMU_OT_DSL_DS_SNAP_MAP,
            DMU_OT_NONE, 0, tx);
        dsphys->ds_creation_time = gethrestime_sec();
        dsphys->ds_creation_txg = tx->tx_txg == TXG_INITIAL ? 1 : tx->tx_txg;

        if (origin == NULL) {
                dsphys->ds_deadlist_obj = dsl_deadlist_alloc(mos, tx);
        } else {
                dsl_dataset_t *ohds;

                dsphys->ds_prev_snap_obj = origin->ds_object;
                dsphys->ds_prev_snap_txg =
                    origin->ds_phys->ds_creation_txg;
                dsphys->ds_referenced_bytes =
                    origin->ds_phys->ds_referenced_bytes;
                dsphys->ds_compressed_bytes =
                    origin->ds_phys->ds_compressed_bytes;
                dsphys->ds_uncompressed_bytes =
                    origin->ds_phys->ds_uncompressed_bytes;
                dsphys->ds_bp = origin->ds_phys->ds_bp;
                dsphys->ds_flags |= origin->ds_phys->ds_flags;

                dmu_buf_will_dirty(origin->ds_dbuf, tx);
                origin->ds_phys->ds_num_children++;

                VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
                    origin->ds_dir->dd_phys->dd_head_dataset_obj, FTAG, &ohds));
                dsphys->ds_deadlist_obj = dsl_deadlist_clone(&ohds->ds_deadlist,
                    dsphys->ds_prev_snap_txg, dsphys->ds_prev_snap_obj, tx);
                dsl_dataset_rele(ohds, FTAG);

                if (spa_version(dp->dp_spa) >= SPA_VERSION_NEXT_CLONES) {
                        if (origin->ds_phys->ds_next_clones_obj == 0) {
                                origin->ds_phys->ds_next_clones_obj =
                                    zap_create(mos,
                                    DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
                        }
                        VERIFY(0 == zap_add_int(mos,
                            origin->ds_phys->ds_next_clones_obj,
                            dsobj, tx));
                }

                dmu_buf_will_dirty(dd->dd_dbuf, tx);
                dd->dd_phys->dd_origin_obj = origin->ds_object;
                if (spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
                        if (origin->ds_dir->dd_phys->dd_clones == 0) {
                                dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
                                origin->ds_dir->dd_phys->dd_clones =
                                    zap_create(mos,
                                    DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
                        }
                        VERIFY3U(0, ==, zap_add_int(mos,
                            origin->ds_dir->dd_phys->dd_clones, dsobj, tx));
                }
        }

        if (spa_version(dp->dp_spa) >= SPA_VERSION_UNIQUE_ACCURATE)
                dsphys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;

        dmu_buf_rele(dbuf, FTAG);

        dmu_buf_will_dirty(dd->dd_dbuf, tx);
        dd->dd_phys->dd_head_dataset_obj = dsobj;

        return (dsobj);
}

uint64_t
dsl_dataset_create_sync(dsl_dir_t *pdd, const char *lastname,
    dsl_dataset_t *origin, uint64_t flags, cred_t *cr, dmu_tx_t *tx)
{
        dsl_pool_t *dp = pdd->dd_pool;
        uint64_t dsobj, ddobj;
        dsl_dir_t *dd;

        ASSERT(lastname[0] != '@');

        ddobj = dsl_dir_create_sync(dp, pdd, lastname, tx);
        VERIFY(0 == dsl_dir_open_obj(dp, ddobj, lastname, FTAG, &dd));

        dsobj = dsl_dataset_create_sync_dd(dd, origin, flags, tx);

        dsl_deleg_set_create_perms(dd, tx, cr);

        dsl_dir_close(dd, FTAG);

        /*
         * If we are creating a clone, make sure we zero out any stale
         * data from the origin snapshots zil header.
         */
        if (origin != NULL) {
                dsl_dataset_t *ds;
                objset_t *os;

                VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
                VERIFY3U(0, ==, dmu_objset_from_ds(ds, &os));
                bzero(&os->os_zil_header, sizeof (os->os_zil_header));
                dsl_dataset_dirty(ds, tx);
                dsl_dataset_rele(ds, FTAG);
        }

        return (dsobj);
}

#ifdef __FreeBSD__
/* FreeBSD ioctl compat begin */
struct destroyarg {
        nvlist_t *nvl;
        const char *snapname;
};

static int
dsl_check_snap_cb(const char *name, void *arg)
{
        struct destroyarg *da = arg;
        dsl_dataset_t *ds;
        char *dsname;

        dsname = kmem_asprintf("%s@%s", name, da->snapname);
        VERIFY(nvlist_add_boolean(da->nvl, dsname) == 0);

        return (0);
}

int
dmu_get_recursive_snaps_nvl(const char *fsname, const char *snapname,
    nvlist_t *snaps)
{
        struct destroyarg *da;
        int err;

        da = kmem_zalloc(sizeof (struct destroyarg), KM_SLEEP);
        da->nvl = snaps;
        da->snapname = snapname;
        err = dmu_objset_find(fsname, dsl_check_snap_cb, da,
            DS_FIND_CHILDREN);
        kmem_free(da, sizeof (struct destroyarg));

        return (err);
}
/* FreeBSD ioctl compat end */
#endif /* __FreeBSD__ */

int
dmu_snapshots_destroy_nvl(nvlist_t *snaps, boolean_t defer, char *failed)
{
        int err;
        dsl_sync_task_t *dst;
        spa_t *spa;
        nvpair_t *pair;
        dsl_sync_task_group_t *dstg;

        pair = nvlist_next_nvpair(snaps, NULL);
        if (pair == NULL)
                return (0);

        err = spa_open(nvpair_name(pair), &spa, FTAG);
        if (err)
                return (err);
        dstg = dsl_sync_task_group_create(spa_get_dsl(spa));

        for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
            pair = nvlist_next_nvpair(snaps, pair)) {
                dsl_dataset_t *ds;

                err = dsl_dataset_own(nvpair_name(pair), B_TRUE, dstg, &ds);
                if (err == 0) {
                        struct dsl_ds_destroyarg *dsda;

                        dsl_dataset_make_exclusive(ds, dstg);
                        dsda = kmem_zalloc(sizeof (struct dsl_ds_destroyarg),
                            KM_SLEEP);
                        dsda->ds = ds;
                        dsda->defer = defer;
                        dsl_sync_task_create(dstg, dsl_dataset_destroy_check,
                            dsl_dataset_destroy_sync, dsda, dstg, 0);
                } else if (err == ENOENT) {
                        err = 0;
                } else {
                        (void) strcpy(failed, nvpair_name(pair));
                        break;
                }
        }

        if (err == 0)
                err = dsl_sync_task_group_wait(dstg);

        for (dst = list_head(&dstg->dstg_tasks); dst;
            dst = list_next(&dstg->dstg_tasks, dst)) {
                struct dsl_ds_destroyarg *dsda = dst->dst_arg1;
                dsl_dataset_t *ds = dsda->ds;

                /*
                 * Return the file system name that triggered the error
                 */
                if (dst->dst_err) {
                        dsl_dataset_name(ds, failed);
                }
                ASSERT3P(dsda->rm_origin, ==, NULL);
                dsl_dataset_disown(ds, dstg);
                kmem_free(dsda, sizeof (struct dsl_ds_destroyarg));
        }

        dsl_sync_task_group_destroy(dstg);
        spa_close(spa, FTAG);
        return (err);

}

static boolean_t
dsl_dataset_might_destroy_origin(dsl_dataset_t *ds)
{
        boolean_t might_destroy = B_FALSE;

        mutex_enter(&ds->ds_lock);
        if (ds->ds_phys->ds_num_children == 2 && ds->ds_userrefs == 0 &&
            DS_IS_DEFER_DESTROY(ds))
                might_destroy = B_TRUE;
        mutex_exit(&ds->ds_lock);

        return (might_destroy);
}

static int
dsl_dataset_origin_rm_prep(struct dsl_ds_destroyarg *dsda, void *tag)
{
        dsl_dataset_t *ds = dsda->ds;
        dsl_dataset_t *origin = ds->ds_prev;

        if (dsl_dataset_might_destroy_origin(origin)) {
                char *name;
                int namelen;
                int error;

                namelen = dsl_dataset_namelen(origin) + 1;
                name = kmem_alloc(namelen, KM_SLEEP);
                dsl_dataset_name(origin, name);
#ifdef _KERNEL
                error = zfs_unmount_snap(name, NULL);
                if (error) {
                        kmem_free(name, namelen);
                        return (error);
                }
#endif
                error = dsl_dataset_own(name, B_TRUE, tag, &origin);
                kmem_free(name, namelen);
                if (error)
                        return (error);
                dsda->rm_origin = origin;
                dsl_dataset_make_exclusive(origin, tag);
        }

        return (0);
}

int
dsl_dataset_destroy(dsl_dataset_t *ds, void *tag, boolean_t defer)
{
        int err;
        dsl_sync_task_group_t *dstg;
        objset_t *os;
        dsl_dir_t *dd;
        uint64_t obj;
        struct dsl_ds_destroyarg dsda = { 0 };
        dsl_dataset_t dummy_ds = { 0 };

        dsda.ds = ds;

        if (dsl_dataset_is_snapshot(ds)) {
                /* Destroying a snapshot is simpler */
                dsl_dataset_make_exclusive(ds, tag);

                dsda.defer = defer;
                err = dsl_sync_task_do(ds->ds_dir->dd_pool,
                    dsl_dataset_destroy_check, dsl_dataset_destroy_sync,
                    &dsda, tag, 0);
                ASSERT3P(dsda.rm_origin, ==, NULL);
                goto out;
        } else if (defer) {
                err = EINVAL;
                goto out;
        }

        dd = ds->ds_dir;
        dummy_ds.ds_dir = dd;
        dummy_ds.ds_object = ds->ds_object;

        if (!spa_feature_is_enabled(dsl_dataset_get_spa(ds),
            &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
                /*
                 * Check for errors and mark this ds as inconsistent, in
                 * case we crash while freeing the objects.
                 */
                err = dsl_sync_task_do(dd->dd_pool,
                    dsl_dataset_destroy_begin_check,
                    dsl_dataset_destroy_begin_sync, ds, NULL, 0);
                if (err)
                        goto out;

                err = dmu_objset_from_ds(ds, &os);
                if (err)
                        goto out;

                /*
                 * Remove all objects while in the open context so that
                 * there is less work to do in the syncing context.
                 */
                for (obj = 0; err == 0; err = dmu_object_next(os, &obj, FALSE,
                    ds->ds_phys->ds_prev_snap_txg)) {
                        /*
                         * Ignore errors, if there is not enough disk space
                         * we will deal with it in dsl_dataset_destroy_sync().
                         */
                        (void) dmu_free_object(os, obj);
                }
                if (err != ESRCH)
                        goto out;

                /*
                 * Sync out all in-flight IO.
                 */
                txg_wait_synced(dd->dd_pool, 0);

                /*
                 * If we managed to free all the objects in open
                 * context, the user space accounting should be zero.
                 */
                if (ds->ds_phys->ds_bp.blk_fill == 0 &&
                    dmu_objset_userused_enabled(os)) {
                        uint64_t count;

                        ASSERT(zap_count(os, DMU_USERUSED_OBJECT,
                            &count) != 0 || count == 0);
                        ASSERT(zap_count(os, DMU_GROUPUSED_OBJECT,
                            &count) != 0 || count == 0);
                }
        }

        rw_enter(&dd->dd_pool->dp_config_rwlock, RW_READER);
        err = dsl_dir_open_obj(dd->dd_pool, dd->dd_object, NULL, FTAG, &dd);
        rw_exit(&dd->dd_pool->dp_config_rwlock);

        if (err)
                goto out;

        /*
         * Blow away the dsl_dir + head dataset.
         */
        dsl_dataset_make_exclusive(ds, tag);
        /*
         * If we're removing a clone, we might also need to remove its
         * origin.
         */
        do {
                dsda.need_prep = B_FALSE;
                if (dsl_dir_is_clone(dd)) {
                        err = dsl_dataset_origin_rm_prep(&dsda, tag);
                        if (err) {
                                dsl_dir_close(dd, FTAG);
                                goto out;
                        }
                }

                dstg = dsl_sync_task_group_create(ds->ds_dir->dd_pool);
                dsl_sync_task_create(dstg, dsl_dataset_destroy_check,
                    dsl_dataset_destroy_sync, &dsda, tag, 0);
                dsl_sync_task_create(dstg, dsl_dir_destroy_check,
                    dsl_dir_destroy_sync, &dummy_ds, FTAG, 0);
                err = dsl_sync_task_group_wait(dstg);
                dsl_sync_task_group_destroy(dstg);

                /*
                 * We could be racing against 'zfs release' or 'zfs destroy -d'
                 * on the origin snap, in which case we can get EBUSY if we
                 * needed to destroy the origin snap but were not ready to
                 * do so.
                 */
                if (dsda.need_prep) {
                        ASSERT(err == EBUSY);
                        ASSERT(dsl_dir_is_clone(dd));
                        ASSERT(dsda.rm_origin == NULL);
                }
        } while (dsda.need_prep);

        if (dsda.rm_origin != NULL)
                dsl_dataset_disown(dsda.rm_origin, tag);

        /* if it is successful, dsl_dir_destroy_sync will close the dd */
        if (err)
                dsl_dir_close(dd, FTAG);
out:
        dsl_dataset_disown(ds, tag);
        return (err);
}

blkptr_t *
dsl_dataset_get_blkptr(dsl_dataset_t *ds)
{
        return (&ds->ds_phys->ds_bp);
}

void
dsl_dataset_set_blkptr(dsl_dataset_t *ds, blkptr_t *bp, dmu_tx_t *tx)
{
        ASSERT(dmu_tx_is_syncing(tx));
        /* If it's the meta-objset, set dp_meta_rootbp */
        if (ds == NULL) {
                tx->tx_pool->dp_meta_rootbp = *bp;
        } else {
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                ds->ds_phys->ds_bp = *bp;
        }
}

spa_t *
dsl_dataset_get_spa(dsl_dataset_t *ds)
{
        return (ds->ds_dir->dd_pool->dp_spa);
}

void
dsl_dataset_dirty(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        dsl_pool_t *dp;

        if (ds == NULL) /* this is the meta-objset */
                return;

        ASSERT(ds->ds_objset != NULL);

        if (ds->ds_phys->ds_next_snap_obj != 0)
                panic("dirtying snapshot!");

        dp = ds->ds_dir->dd_pool;

        if (txg_list_add(&dp->dp_dirty_datasets, ds, tx->tx_txg) == 0) {
                /* up the hold count until we can be written out */
                dmu_buf_add_ref(ds->ds_dbuf, ds);
        }
}

boolean_t
dsl_dataset_is_dirty(dsl_dataset_t *ds)
{
        for (int t = 0; t < TXG_SIZE; t++) {
                if (txg_list_member(&ds->ds_dir->dd_pool->dp_dirty_datasets,
                    ds, t))
                        return (B_TRUE);
        }
        return (B_FALSE);
}

static void
dsl_dataset_recalc_head_uniq(dsl_dataset_t *ds)
{
        uint64_t mrs_used;
        uint64_t dlused, dlcomp, dluncomp;

        ASSERT(!dsl_dataset_is_snapshot(ds));

        if (ds->ds_phys->ds_prev_snap_obj != 0)
                mrs_used = ds->ds_prev->ds_phys->ds_referenced_bytes;
        else
                mrs_used = 0;

        dsl_deadlist_space(&ds->ds_deadlist, &dlused, &dlcomp, &dluncomp);

        ASSERT3U(dlused, <=, mrs_used);
        ds->ds_phys->ds_unique_bytes =
            ds->ds_phys->ds_referenced_bytes - (mrs_used - dlused);

        if (spa_version(ds->ds_dir->dd_pool->dp_spa) >=
            SPA_VERSION_UNIQUE_ACCURATE)
                ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
}

struct killarg {
        dsl_dataset_t *ds;
        dmu_tx_t *tx;
};

/* ARGSUSED */
static int
kill_blkptr(spa_t *spa, zilog_t *zilog, const blkptr_t *bp, arc_buf_t *pbuf,
    const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
{
        struct killarg *ka = arg;
        dmu_tx_t *tx = ka->tx;

        if (bp == NULL)
                return (0);

        if (zb->zb_level == ZB_ZIL_LEVEL) {
                ASSERT(zilog != NULL);
                /*
                 * It's a block in the intent log.  It has no
                 * accounting, so just free it.
                 */
                dsl_free(ka->tx->tx_pool, ka->tx->tx_txg, bp);
        } else {
                ASSERT(zilog == NULL);
                ASSERT3U(bp->blk_birth, >, ka->ds->ds_phys->ds_prev_snap_txg);
                (void) dsl_dataset_block_kill(ka->ds, bp, tx, B_FALSE);
        }

        return (0);
}

/* ARGSUSED */
static int
dsl_dataset_destroy_begin_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        uint64_t count;
        int err;

        /*
         * Can't delete a head dataset if there are snapshots of it.
         * (Except if the only snapshots are from the branch we cloned
         * from.)
         */
        if (ds->ds_prev != NULL &&
            ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
                return (EBUSY);

        /*
         * This is really a dsl_dir thing, but check it here so that
         * we'll be less likely to leave this dataset inconsistent &
         * nearly destroyed.
         */
        err = zap_count(mos, ds->ds_dir->dd_phys->dd_child_dir_zapobj, &count);
        if (err)
                return (err);
        if (count != 0)
                return (EEXIST);

        return (0);
}

/* ARGSUSED */
static void
dsl_dataset_destroy_begin_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;

        /* Mark it as inconsistent on-disk, in case we crash */
        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        ds->ds_phys->ds_flags |= DS_FLAG_INCONSISTENT;

        spa_history_log_internal(LOG_DS_DESTROY_BEGIN, dp->dp_spa, tx,
            "dataset = %llu", ds->ds_object);
}

static int
dsl_dataset_origin_check(struct dsl_ds_destroyarg *dsda, void *tag,
    dmu_tx_t *tx)
{
        dsl_dataset_t *ds = dsda->ds;
        dsl_dataset_t *ds_prev = ds->ds_prev;

        if (dsl_dataset_might_destroy_origin(ds_prev)) {
                struct dsl_ds_destroyarg ndsda = {0};

                /*
                 * If we're not prepared to remove the origin, don't remove
                 * the clone either.
                 */
                if (dsda->rm_origin == NULL) {
                        dsda->need_prep = B_TRUE;
                        return (EBUSY);
                }

                ndsda.ds = ds_prev;
                ndsda.is_origin_rm = B_TRUE;
                return (dsl_dataset_destroy_check(&ndsda, tag, tx));
        }

        /*
         * If we're not going to remove the origin after all,
         * undo the open context setup.
         */
        if (dsda->rm_origin != NULL) {
                dsl_dataset_disown(dsda->rm_origin, tag);
                dsda->rm_origin = NULL;
        }

        return (0);
}

/* ARGSUSED */
int
dsl_dataset_destroy_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        struct dsl_ds_destroyarg *dsda = arg1;
        dsl_dataset_t *ds = dsda->ds;

        /* we have an owner hold, so noone else can destroy us */
        ASSERT(!DSL_DATASET_IS_DESTROYED(ds));

        /*
         * Only allow deferred destroy on pools that support it.
         * NOTE: deferred destroy is only supported on snapshots.
         */
        if (dsda->defer) {
                if (spa_version(ds->ds_dir->dd_pool->dp_spa) <
                    SPA_VERSION_USERREFS)
                        return (ENOTSUP);
                ASSERT(dsl_dataset_is_snapshot(ds));
                return (0);
        }

        /*
         * Can't delete a head dataset if there are snapshots of it.
         * (Except if the only snapshots are from the branch we cloned
         * from.)
         */
        if (ds->ds_prev != NULL &&
            ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
                return (EBUSY);

        /*
         * If we made changes this txg, traverse_dsl_dataset won't find
         * them.  Try again.
         */
        if (ds->ds_phys->ds_bp.blk_birth >= tx->tx_txg)
                return (EAGAIN);

        if (dsl_dataset_is_snapshot(ds)) {
                /*
                 * If this snapshot has an elevated user reference count,
                 * we can't destroy it yet.
                 */
                if (ds->ds_userrefs > 0 && !dsda->releasing)
                        return (EBUSY);

                mutex_enter(&ds->ds_lock);
                /*
                 * Can't delete a branch point. However, if we're destroying
                 * a clone and removing its origin due to it having a user
                 * hold count of 0 and having been marked for deferred destroy,
                 * it's OK for the origin to have a single clone.
                 */
                if (ds->ds_phys->ds_num_children >
                    (dsda->is_origin_rm ? 2 : 1)) {
                        mutex_exit(&ds->ds_lock);
                        return (EEXIST);
                }
                mutex_exit(&ds->ds_lock);
        } else if (dsl_dir_is_clone(ds->ds_dir)) {
                return (dsl_dataset_origin_check(dsda, arg2, tx));
        }

        /* XXX we should do some i/o error checking... */
        return (0);
}

struct refsarg {
        kmutex_t lock;
        boolean_t gone;
        kcondvar_t cv;
};

/* ARGSUSED */
static void
dsl_dataset_refs_gone(dmu_buf_t *db, void *argv)
{
        struct refsarg *arg = argv;

        mutex_enter(&arg->lock);
        arg->gone = TRUE;
        cv_signal(&arg->cv);
        mutex_exit(&arg->lock);
}

static void
dsl_dataset_drain_refs(dsl_dataset_t *ds, void *tag)
{
        struct refsarg arg;

        bzero(&arg, sizeof(arg));
        mutex_init(&arg.lock, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&arg.cv, NULL, CV_DEFAULT, NULL);
        arg.gone = FALSE;
        (void) dmu_buf_update_user(ds->ds_dbuf, ds, &arg, &ds->ds_phys,
            dsl_dataset_refs_gone);
        dmu_buf_rele(ds->ds_dbuf, tag);
        mutex_enter(&arg.lock);
        while (!arg.gone)
                cv_wait(&arg.cv, &arg.lock);
        ASSERT(arg.gone);
        mutex_exit(&arg.lock);
        ds->ds_dbuf = NULL;
        ds->ds_phys = NULL;
        mutex_destroy(&arg.lock);
        cv_destroy(&arg.cv);
}

static void
remove_from_next_clones(dsl_dataset_t *ds, uint64_t obj, dmu_tx_t *tx)
{
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        uint64_t count;
        int err;

        ASSERT(ds->ds_phys->ds_num_children >= 2);
        err = zap_remove_int(mos, ds->ds_phys->ds_next_clones_obj, obj, tx);
        /*
         * The err should not be ENOENT, but a bug in a previous version
         * of the code could cause upgrade_clones_cb() to not set
         * ds_next_snap_obj when it should, leading to a missing entry.
         * If we knew that the pool was created after
         * SPA_VERSION_NEXT_CLONES, we could assert that it isn't
         * ENOENT.  However, at least we can check that we don't have
         * too many entries in the next_clones_obj even after failing to
         * remove this one.
         */
        if (err != ENOENT) {
                VERIFY0(err);
        }
        ASSERT3U(0, ==, zap_count(mos, ds->ds_phys->ds_next_clones_obj,
            &count));
        ASSERT3U(count, <=, ds->ds_phys->ds_num_children - 2);
}

static void
dsl_dataset_remove_clones_key(dsl_dataset_t *ds, uint64_t mintxg, dmu_tx_t *tx)
{
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        zap_cursor_t zc;
        zap_attribute_t za;

        /*
         * If it is the old version, dd_clones doesn't exist so we can't
         * find the clones, but deadlist_remove_key() is a no-op so it
         * doesn't matter.
         */
        if (ds->ds_dir->dd_phys->dd_clones == 0)
                return;

        for (zap_cursor_init(&zc, mos, ds->ds_dir->dd_phys->dd_clones);
            zap_cursor_retrieve(&zc, &za) == 0;
            zap_cursor_advance(&zc)) {
                dsl_dataset_t *clone;

                VERIFY3U(0, ==, dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
                    za.za_first_integer, FTAG, &clone));
                if (clone->ds_dir->dd_origin_txg > mintxg) {
                        dsl_deadlist_remove_key(&clone->ds_deadlist,
                            mintxg, tx);
                        dsl_dataset_remove_clones_key(clone, mintxg, tx);
                }
                dsl_dataset_rele(clone, FTAG);
        }
        zap_cursor_fini(&zc);
}

struct process_old_arg {
        dsl_dataset_t *ds;
        dsl_dataset_t *ds_prev;
        boolean_t after_branch_point;
        zio_t *pio;
        uint64_t used, comp, uncomp;
};

static int
process_old_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
{
        struct process_old_arg *poa = arg;
        dsl_pool_t *dp = poa->ds->ds_dir->dd_pool;

        if (bp->blk_birth <= poa->ds->ds_phys->ds_prev_snap_txg) {
                dsl_deadlist_insert(&poa->ds->ds_deadlist, bp, tx);
                if (poa->ds_prev && !poa->after_branch_point &&
                    bp->blk_birth >
                    poa->ds_prev->ds_phys->ds_prev_snap_txg) {
                        poa->ds_prev->ds_phys->ds_unique_bytes +=
                            bp_get_dsize_sync(dp->dp_spa, bp);
                }
        } else {
                poa->used += bp_get_dsize_sync(dp->dp_spa, bp);
                poa->comp += BP_GET_PSIZE(bp);
                poa->uncomp += BP_GET_UCSIZE(bp);
                dsl_free_sync(poa->pio, dp, tx->tx_txg, bp);
        }
        return (0);
}

static void
process_old_deadlist(dsl_dataset_t *ds, dsl_dataset_t *ds_prev,
    dsl_dataset_t *ds_next, boolean_t after_branch_point, dmu_tx_t *tx)
{
        struct process_old_arg poa = { 0 };
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        objset_t *mos = dp->dp_meta_objset;

        ASSERT(ds->ds_deadlist.dl_oldfmt);
        ASSERT(ds_next->ds_deadlist.dl_oldfmt);

        poa.ds = ds;
        poa.ds_prev = ds_prev;
        poa.after_branch_point = after_branch_point;
        poa.pio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
        VERIFY3U(0, ==, bpobj_iterate(&ds_next->ds_deadlist.dl_bpobj,
            process_old_cb, &poa, tx));
        VERIFY0(zio_wait(poa.pio));
        ASSERT3U(poa.used, ==, ds->ds_phys->ds_unique_bytes);

        /* change snapused */
        dsl_dir_diduse_space(ds->ds_dir, DD_USED_SNAP,
            -poa.used, -poa.comp, -poa.uncomp, tx);

        /* swap next's deadlist to our deadlist */
        dsl_deadlist_close(&ds->ds_deadlist);
        dsl_deadlist_close(&ds_next->ds_deadlist);
        SWITCH64(ds_next->ds_phys->ds_deadlist_obj,
            ds->ds_phys->ds_deadlist_obj);
        dsl_deadlist_open(&ds->ds_deadlist, mos, ds->ds_phys->ds_deadlist_obj);
        dsl_deadlist_open(&ds_next->ds_deadlist, mos,
            ds_next->ds_phys->ds_deadlist_obj);
}

static int
old_synchronous_dataset_destroy(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        int err;
        struct killarg ka;

        /*
         * Free everything that we point to (that's born after
         * the previous snapshot, if we are a clone)
         *
         * NB: this should be very quick, because we already
         * freed all the objects in open context.
         */
        ka.ds = ds;
        ka.tx = tx;
        err = traverse_dataset(ds,
            ds->ds_phys->ds_prev_snap_txg, TRAVERSE_POST,
            kill_blkptr, &ka);
        ASSERT0(err);
        ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) || ds->ds_phys->ds_unique_bytes == 0);

        return (err);
}

void
dsl_dataset_destroy_sync(void *arg1, void *tag, dmu_tx_t *tx)
{
        struct dsl_ds_destroyarg *dsda = arg1;
        dsl_dataset_t *ds = dsda->ds;
        int err;
        int after_branch_point = FALSE;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        objset_t *mos = dp->dp_meta_objset;
        dsl_dataset_t *ds_prev = NULL;
        boolean_t wont_destroy;
        uint64_t obj;

        wont_destroy = (dsda->defer &&
            (ds->ds_userrefs > 0 || ds->ds_phys->ds_num_children > 1));

        ASSERT(ds->ds_owner || wont_destroy);
        ASSERT(dsda->defer || ds->ds_phys->ds_num_children <= 1);
        ASSERT(ds->ds_prev == NULL ||
            ds->ds_prev->ds_phys->ds_next_snap_obj != ds->ds_object);
        ASSERT3U(ds->ds_phys->ds_bp.blk_birth, <=, tx->tx_txg);

        if (wont_destroy) {
                ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                ds->ds_phys->ds_flags |= DS_FLAG_DEFER_DESTROY;
                return;
        }

        /* signal any waiters that this dataset is going away */
        mutex_enter(&ds->ds_lock);
        ds->ds_owner = dsl_reaper;
        cv_broadcast(&ds->ds_exclusive_cv);
        mutex_exit(&ds->ds_lock);

        /* Remove our reservation */
        if (ds->ds_reserved != 0) {
                dsl_prop_setarg_t psa;
                uint64_t value = 0;

                dsl_prop_setarg_init_uint64(&psa, "refreservation",
                    (ZPROP_SRC_NONE | ZPROP_SRC_LOCAL | ZPROP_SRC_RECEIVED),
                    &value);
                psa.psa_effective_value = 0;    /* predict default value */

                dsl_dataset_set_reservation_sync(ds, &psa, tx);
                ASSERT0(ds->ds_reserved);
        }

        ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));

        dsl_scan_ds_destroyed(ds, tx);

        obj = ds->ds_object;

        if (ds->ds_phys->ds_prev_snap_obj != 0) {
                if (ds->ds_prev) {
                        ds_prev = ds->ds_prev;
                } else {
                        VERIFY(0 == dsl_dataset_hold_obj(dp,
                            ds->ds_phys->ds_prev_snap_obj, FTAG, &ds_prev));
                }
                after_branch_point =
                    (ds_prev->ds_phys->ds_next_snap_obj != obj);

                dmu_buf_will_dirty(ds_prev->ds_dbuf, tx);
                if (after_branch_point &&
                    ds_prev->ds_phys->ds_next_clones_obj != 0) {
                        remove_from_next_clones(ds_prev, obj, tx);
                        if (ds->ds_phys->ds_next_snap_obj != 0) {
                                VERIFY(0 == zap_add_int(mos,
                                    ds_prev->ds_phys->ds_next_clones_obj,
                                    ds->ds_phys->ds_next_snap_obj, tx));
                        }
                }
                if (after_branch_point &&
                    ds->ds_phys->ds_next_snap_obj == 0) {
                        /* This clone is toast. */
                        ASSERT(ds_prev->ds_phys->ds_num_children > 1);
                        ds_prev->ds_phys->ds_num_children--;

                        /*
                         * If the clone's origin has no other clones, no
                         * user holds, and has been marked for deferred
                         * deletion, then we should have done the necessary
                         * destroy setup for it.
                         */
                        if (ds_prev->ds_phys->ds_num_children == 1 &&
                            ds_prev->ds_userrefs == 0 &&
                            DS_IS_DEFER_DESTROY(ds_prev)) {
                                ASSERT3P(dsda->rm_origin, !=, NULL);
                        } else {
                                ASSERT3P(dsda->rm_origin, ==, NULL);
                        }
                } else if (!after_branch_point) {
                        ds_prev->ds_phys->ds_next_snap_obj =
                            ds->ds_phys->ds_next_snap_obj;
                }
        }

        if (dsl_dataset_is_snapshot(ds)) {
                dsl_dataset_t *ds_next;
                uint64_t old_unique;
                uint64_t used = 0, comp = 0, uncomp = 0;

                VERIFY(0 == dsl_dataset_hold_obj(dp,
                    ds->ds_phys->ds_next_snap_obj, FTAG, &ds_next));
                ASSERT3U(ds_next->ds_phys->ds_prev_snap_obj, ==, obj);

                old_unique = ds_next->ds_phys->ds_unique_bytes;

                dmu_buf_will_dirty(ds_next->ds_dbuf, tx);
                ds_next->ds_phys->ds_prev_snap_obj =
                    ds->ds_phys->ds_prev_snap_obj;
                ds_next->ds_phys->ds_prev_snap_txg =
                    ds->ds_phys->ds_prev_snap_txg;
                ASSERT3U(ds->ds_phys->ds_prev_snap_txg, ==,
                    ds_prev ? ds_prev->ds_phys->ds_creation_txg : 0);


                if (ds_next->ds_deadlist.dl_oldfmt) {
                        process_old_deadlist(ds, ds_prev, ds_next,
                            after_branch_point, tx);
                } else {
                        /* Adjust prev's unique space. */
                        if (ds_prev && !after_branch_point) {
                                dsl_deadlist_space_range(&ds_next->ds_deadlist,
                                    ds_prev->ds_phys->ds_prev_snap_txg,
                                    ds->ds_phys->ds_prev_snap_txg,
                                    &used, &comp, &uncomp);
                                ds_prev->ds_phys->ds_unique_bytes += used;
                        }

                        /* Adjust snapused. */
                        dsl_deadlist_space_range(&ds_next->ds_deadlist,
                            ds->ds_phys->ds_prev_snap_txg, UINT64_MAX,
                            &used, &comp, &uncomp);
                        dsl_dir_diduse_space(ds->ds_dir, DD_USED_SNAP,
                            -used, -comp, -uncomp, tx);

                        /* Move blocks to be freed to pool's free list. */
                        dsl_deadlist_move_bpobj(&ds_next->ds_deadlist,
                            &dp->dp_free_bpobj, ds->ds_phys->ds_prev_snap_txg,
                            tx);
                        dsl_dir_diduse_space(tx->tx_pool->dp_free_dir,
                            DD_USED_HEAD, used, comp, uncomp, tx);

                        /* Merge our deadlist into next's and free it. */
                        dsl_deadlist_merge(&ds_next->ds_deadlist,
                            ds->ds_phys->ds_deadlist_obj, tx);
                }
                dsl_deadlist_close(&ds->ds_deadlist);
                dsl_deadlist_free(mos, ds->ds_phys->ds_deadlist_obj, tx);

                /* Collapse range in clone heads */
                dsl_dataset_remove_clones_key(ds,
                    ds->ds_phys->ds_creation_txg, tx);

                if (dsl_dataset_is_snapshot(ds_next)) {
                        dsl_dataset_t *ds_nextnext;

                        /*
                         * Update next's unique to include blocks which
                         * were previously shared by only this snapshot
                         * and it.  Those blocks will be born after the
                         * prev snap and before this snap, and will have
                         * died after the next snap and before the one
                         * after that (ie. be on the snap after next's
                         * deadlist).
                         */
                        VERIFY(0 == dsl_dataset_hold_obj(dp,
                            ds_next->ds_phys->ds_next_snap_obj,
                            FTAG, &ds_nextnext));
                        dsl_deadlist_space_range(&ds_nextnext->ds_deadlist,
                            ds->ds_phys->ds_prev_snap_txg,
                            ds->ds_phys->ds_creation_txg,
                            &used, &comp, &uncomp);
                        ds_next->ds_phys->ds_unique_bytes += used;
                        dsl_dataset_rele(ds_nextnext, FTAG);
                        ASSERT3P(ds_next->ds_prev, ==, NULL);

                        /* Collapse range in this head. */
                        dsl_dataset_t *hds;
                        VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
                            ds->ds_dir->dd_phys->dd_head_dataset_obj,
                            FTAG, &hds));
                        dsl_deadlist_remove_key(&hds->ds_deadlist,
                            ds->ds_phys->ds_creation_txg, tx);
                        dsl_dataset_rele(hds, FTAG);

                } else {
                        ASSERT3P(ds_next->ds_prev, ==, ds);
                        dsl_dataset_drop_ref(ds_next->ds_prev, ds_next);
                        ds_next->ds_prev = NULL;
                        if (ds_prev) {
                                VERIFY(0 == dsl_dataset_get_ref(dp,
                                    ds->ds_phys->ds_prev_snap_obj,
                                    ds_next, &ds_next->ds_prev));
                        }

                        dsl_dataset_recalc_head_uniq(ds_next);

                        /*
                         * Reduce the amount of our unconsmed refreservation
                         * being charged to our parent by the amount of
                         * new unique data we have gained.
                         */
                        if (old_unique < ds_next->ds_reserved) {
                                int64_t mrsdelta;
                                uint64_t new_unique =
                                    ds_next->ds_phys->ds_unique_bytes;

                                ASSERT(old_unique <= new_unique);
                                mrsdelta = MIN(new_unique - old_unique,
                                    ds_next->ds_reserved - old_unique);
                                dsl_dir_diduse_space(ds->ds_dir,
                                    DD_USED_REFRSRV, -mrsdelta, 0, 0, tx);
                        }
                }
                dsl_dataset_rele(ds_next, FTAG);
        } else {
                zfeature_info_t *async_destroy =
                    &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY];
                objset_t *os;

                /*
                 * There's no next snapshot, so this is a head dataset.
                 * Destroy the deadlist.  Unless it's a clone, the
                 * deadlist should be empty.  (If it's a clone, it's
                 * safe to ignore the deadlist contents.)
                 */
                dsl_deadlist_close(&ds->ds_deadlist);
                dsl_deadlist_free(mos, ds->ds_phys->ds_deadlist_obj, tx);
                ds->ds_phys->ds_deadlist_obj = 0;

                VERIFY3U(0, ==, dmu_objset_from_ds(ds, &os));

                if (!spa_feature_is_enabled(dp->dp_spa, async_destroy)) {
                        err = old_synchronous_dataset_destroy(ds, tx);
                } else {
                        /*
                         * Move the bptree into the pool's list of trees to
                         * clean up and update space accounting information.
                         */
                        uint64_t used, comp, uncomp;

                        zil_destroy_sync(dmu_objset_zil(os), tx);

                        if (!spa_feature_is_active(dp->dp_spa, async_destroy)) {
                                spa_feature_incr(dp->dp_spa, async_destroy, tx);
                                dp->dp_bptree_obj = bptree_alloc(mos, tx);
                                VERIFY(zap_add(mos,
                                    DMU_POOL_DIRECTORY_OBJECT,
                                    DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
                                    &dp->dp_bptree_obj, tx) == 0);
                        }

                        used = ds->ds_dir->dd_phys->dd_used_bytes;
                        comp = ds->ds_dir->dd_phys->dd_compressed_bytes;
                        uncomp = ds->ds_dir->dd_phys->dd_uncompressed_bytes;

                        ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) ||
                            ds->ds_phys->ds_unique_bytes == used);

                        bptree_add(mos, dp->dp_bptree_obj,
                            &ds->ds_phys->ds_bp, ds->ds_phys->ds_prev_snap_txg,
                            used, comp, uncomp, tx);
                        dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD,
                            -used, -comp, -uncomp, tx);
                        dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
                            used, comp, uncomp, tx);
                }

                if (ds->ds_prev != NULL) {
                        if (spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
                                VERIFY3U(0, ==, zap_remove_int(mos,
                                    ds->ds_prev->ds_dir->dd_phys->dd_clones,
                                    ds->ds_object, tx));
                        }
                        dsl_dataset_rele(ds->ds_prev, ds);
                        ds->ds_prev = ds_prev = NULL;
                }
        }

        /*
         * This must be done after the dsl_traverse(), because it will
         * re-open the objset.
         */
        if (ds->ds_objset) {
                dmu_objset_evict(ds->ds_objset);
                ds->ds_objset = NULL;
        }

        if (ds->ds_dir->dd_phys->dd_head_dataset_obj == ds->ds_object) {
                /* Erase the link in the dir */
                dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
                ds->ds_dir->dd_phys->dd_head_dataset_obj = 0;
                ASSERT(ds->ds_phys->ds_snapnames_zapobj != 0);
                err = zap_destroy(mos, ds->ds_phys->ds_snapnames_zapobj, tx);
                ASSERT(err == 0);
        } else {
                /* remove from snapshot namespace */
                dsl_dataset_t *ds_head;
                ASSERT(ds->ds_phys->ds_snapnames_zapobj == 0);
                VERIFY(0 == dsl_dataset_hold_obj(dp,
                    ds->ds_dir->dd_phys->dd_head_dataset_obj, FTAG, &ds_head));
                VERIFY(0 == dsl_dataset_get_snapname(ds));
#ifdef ZFS_DEBUG
                {
                        uint64_t val;

                        err = dsl_dataset_snap_lookup(ds_head,
                            ds->ds_snapname, &val);
                        ASSERT0(err);
                        ASSERT3U(val, ==, obj);
                }
#endif
                err = dsl_dataset_snap_remove(ds_head, ds->ds_snapname, tx);
                ASSERT(err == 0);
                dsl_dataset_rele(ds_head, FTAG);
        }

        if (ds_prev && ds->ds_prev != ds_prev)
                dsl_dataset_rele(ds_prev, FTAG);

        spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);
        spa_history_log_internal(LOG_DS_DESTROY, dp->dp_spa, tx,
            "dataset = %llu", ds->ds_object);

        if (ds->ds_phys->ds_next_clones_obj != 0) {
                uint64_t count;
                ASSERT(0 == zap_count(mos,
                    ds->ds_phys->ds_next_clones_obj, &count) && count == 0);
                VERIFY(0 == dmu_object_free(mos,
                    ds->ds_phys->ds_next_clones_obj, tx));
        }
        if (ds->ds_phys->ds_props_obj != 0)
                VERIFY(0 == zap_destroy(mos, ds->ds_phys->ds_props_obj, tx));
        if (ds->ds_phys->ds_userrefs_obj != 0)
                VERIFY(0 == zap_destroy(mos, ds->ds_phys->ds_userrefs_obj, tx));
        dsl_dir_close(ds->ds_dir, ds);
        ds->ds_dir = NULL;
        dsl_dataset_drain_refs(ds, tag);
        VERIFY(0 == dmu_object_free(mos, obj, tx));

        if (dsda->rm_origin) {
                /*
                 * Remove the origin of the clone we just destroyed.
                 */
                struct dsl_ds_destroyarg ndsda = {0};

                ndsda.ds = dsda->rm_origin;
                dsl_dataset_destroy_sync(&ndsda, tag, tx);
        }
}

static int
dsl_dataset_snapshot_reserve_space(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        uint64_t asize;

        if (!dmu_tx_is_syncing(tx))
                return (0);

        /*
         * If there's an fs-only reservation, any blocks that might become
         * owned by the snapshot dataset must be accommodated by space
         * outside of the reservation.
         */
        ASSERT(ds->ds_reserved == 0 || DS_UNIQUE_IS_ACCURATE(ds));
        asize = MIN(ds->ds_phys->ds_unique_bytes, ds->ds_reserved);
        if (asize > dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE))
                return (ENOSPC);

        /*
         * Propogate any reserved space for this snapshot to other
         * snapshot checks in this sync group.
         */
        if (asize > 0)
                dsl_dir_willuse_space(ds->ds_dir, asize, tx);

        return (0);
}

int
dsl_dataset_snapshot_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        const char *snapname = arg2;
        int err;
        uint64_t value;

        /*
         * We don't allow multiple snapshots of the same txg.  If there
         * is already one, try again.
         */
        if (ds->ds_phys->ds_prev_snap_txg >= tx->tx_txg)
                return (EAGAIN);

        /*
         * Check for conflicting name snapshot name.
         */
        err = dsl_dataset_snap_lookup(ds, snapname, &value);
        if (err == 0)
                return (EEXIST);
        if (err != ENOENT)
                return (err);

        /*
         * Check that the dataset's name is not too long.  Name consists
         * of the dataset's length + 1 for the @-sign + snapshot name's length
         */
        if (dsl_dataset_namelen(ds) + 1 + strlen(snapname) >= MAXNAMELEN)
                return (ENAMETOOLONG);

        err = dsl_dataset_snapshot_reserve_space(ds, tx);
        if (err)
                return (err);

        ds->ds_trysnap_txg = tx->tx_txg;
        return (0);
}

void
dsl_dataset_snapshot_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        const char *snapname = arg2;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        dmu_buf_t *dbuf;
        dsl_dataset_phys_t *dsphys;
        uint64_t dsobj, crtxg;
        objset_t *mos = dp->dp_meta_objset;
        int err;

        ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));

        /*
         * The origin's ds_creation_txg has to be < TXG_INITIAL
         */
        if (strcmp(snapname, ORIGIN_DIR_NAME) == 0)
                crtxg = 1;
        else
                crtxg = tx->tx_txg;

        dsobj = dmu_object_alloc(mos, DMU_OT_DSL_DATASET, 0,
            DMU_OT_DSL_DATASET, sizeof (dsl_dataset_phys_t), tx);
        VERIFY(0 == dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
        dmu_buf_will_dirty(dbuf, tx);
        dsphys = dbuf->db_data;
        bzero(dsphys, sizeof (dsl_dataset_phys_t));
        dsphys->ds_dir_obj = ds->ds_dir->dd_object;
        dsphys->ds_fsid_guid = unique_create();
        do {
                (void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
                    sizeof (dsphys->ds_guid));
        } while (dsphys->ds_guid == 0);
        dsphys->ds_prev_snap_obj = ds->ds_phys->ds_prev_snap_obj;
        dsphys->ds_prev_snap_txg = ds->ds_phys->ds_prev_snap_txg;
        dsphys->ds_next_snap_obj = ds->ds_object;
        dsphys->ds_num_children = 1;
        dsphys->ds_creation_time = gethrestime_sec();
        dsphys->ds_creation_txg = crtxg;
        dsphys->ds_deadlist_obj = ds->ds_phys->ds_deadlist_obj;
        dsphys->ds_referenced_bytes = ds->ds_phys->ds_referenced_bytes;
        dsphys->ds_compressed_bytes = ds->ds_phys->ds_compressed_bytes;
        dsphys->ds_uncompressed_bytes = ds->ds_phys->ds_uncompressed_bytes;
        dsphys->ds_flags = ds->ds_phys->ds_flags;
        dsphys->ds_bp = ds->ds_phys->ds_bp;
        dmu_buf_rele(dbuf, FTAG);

        ASSERT3U(ds->ds_prev != 0, ==, ds->ds_phys->ds_prev_snap_obj != 0);
        if (ds->ds_prev) {
                uint64_t next_clones_obj =
                    ds->ds_prev->ds_phys->ds_next_clones_obj;
                ASSERT(ds->ds_prev->ds_phys->ds_next_snap_obj ==
                    ds->ds_object ||
                    ds->ds_prev->ds_phys->ds_num_children > 1);
                if (ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object) {
                        dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
                        ASSERT3U(ds->ds_phys->ds_prev_snap_txg, ==,
                            ds->ds_prev->ds_phys->ds_creation_txg);
                        ds->ds_prev->ds_phys->ds_next_snap_obj = dsobj;
                } else if (next_clones_obj != 0) {
                        remove_from_next_clones(ds->ds_prev,
                            dsphys->ds_next_snap_obj, tx);
                        VERIFY3U(0, ==, zap_add_int(mos,
                            next_clones_obj, dsobj, tx));
                }
        }

        /*
         * If we have a reference-reservation on this dataset, we will
         * need to increase the amount of refreservation being charged
         * since our unique space is going to zero.
         */
        if (ds->ds_reserved) {
                int64_t delta;
                ASSERT(DS_UNIQUE_IS_ACCURATE(ds));
                delta = MIN(ds->ds_phys->ds_unique_bytes, ds->ds_reserved);
                dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV,
                    delta, 0, 0, tx);
        }

        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        zfs_dbgmsg("taking snapshot %s@%s/%llu; newkey=%llu",
            ds->ds_dir->dd_myname, snapname, dsobj,
            ds->ds_phys->ds_prev_snap_txg);
        ds->ds_phys->ds_deadlist_obj = dsl_deadlist_clone(&ds->ds_deadlist,
            UINT64_MAX, ds->ds_phys->ds_prev_snap_obj, tx);
        dsl_deadlist_close(&ds->ds_deadlist);
        dsl_deadlist_open(&ds->ds_deadlist, mos, ds->ds_phys->ds_deadlist_obj);
        dsl_deadlist_add_key(&ds->ds_deadlist,
            ds->ds_phys->ds_prev_snap_txg, tx);

        ASSERT3U(ds->ds_phys->ds_prev_snap_txg, <, tx->tx_txg);
        ds->ds_phys->ds_prev_snap_obj = dsobj;
        ds->ds_phys->ds_prev_snap_txg = crtxg;
        ds->ds_phys->ds_unique_bytes = 0;
        if (spa_version(dp->dp_spa) >= SPA_VERSION_UNIQUE_ACCURATE)
                ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;

        err = zap_add(mos, ds->ds_phys->ds_snapnames_zapobj,
            snapname, 8, 1, &dsobj, tx);
        ASSERT(err == 0);

        if (ds->ds_prev)
                dsl_dataset_drop_ref(ds->ds_prev, ds);
        VERIFY(0 == dsl_dataset_get_ref(dp,
            ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));

        dsl_scan_ds_snapshotted(ds, tx);

        dsl_dir_snap_cmtime_update(ds->ds_dir);

        spa_history_log_internal(LOG_DS_SNAPSHOT, dp->dp_spa, tx,
            "dataset = %llu", dsobj);
}

void
dsl_dataset_sync(dsl_dataset_t *ds, zio_t *zio, dmu_tx_t *tx)
{
        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(ds->ds_objset != NULL);
        ASSERT(ds->ds_phys->ds_next_snap_obj == 0);

        /*
         * in case we had to change ds_fsid_guid when we opened it,
         * sync it out now.
         */
        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        ds->ds_phys->ds_fsid_guid = ds->ds_fsid_guid;

        dmu_objset_sync(ds->ds_objset, zio, tx);
}

static void
get_clones_stat(dsl_dataset_t *ds, nvlist_t *nv)
{
        uint64_t count = 0;
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        zap_cursor_t zc;
        zap_attribute_t za;
        nvlist_t *propval;
        nvlist_t *val;

        rw_enter(&ds->ds_dir->dd_pool->dp_config_rwlock, RW_READER);
        VERIFY(nvlist_alloc(&propval, NV_UNIQUE_NAME, KM_SLEEP) == 0);
        VERIFY(nvlist_alloc(&val, NV_UNIQUE_NAME, KM_SLEEP) == 0);

        /*
         * There may me missing entries in ds_next_clones_obj
         * due to a bug in a previous version of the code.
         * Only trust it if it has the right number of entries.
         */
        if (ds->ds_phys->ds_next_clones_obj != 0) {
                ASSERT3U(0, ==, zap_count(mos, ds->ds_phys->ds_next_clones_obj,
                    &count));
        }
        if (count != ds->ds_phys->ds_num_children - 1) {
                goto fail;
        }
        for (zap_cursor_init(&zc, mos, ds->ds_phys->ds_next_clones_obj);
            zap_cursor_retrieve(&zc, &za) == 0;
            zap_cursor_advance(&zc)) {
                dsl_dataset_t *clone;
                char buf[ZFS_MAXNAMELEN];
                /*
                 * Even though we hold the dp_config_rwlock, the dataset
                 * may fail to open, returning ENOENT.  If there is a
                 * thread concurrently attempting to destroy this
                 * dataset, it will have the ds_rwlock held for
                 * RW_WRITER.  Our call to dsl_dataset_hold_obj() ->
                 * dsl_dataset_hold_ref() will fail its
                 * rw_tryenter(&ds->ds_rwlock, RW_READER), drop the
                 * dp_config_rwlock, and wait for the destroy progress
                 * and signal ds_exclusive_cv.  If the destroy was
                 * successful, we will see that
                 * DSL_DATASET_IS_DESTROYED(), and return ENOENT.
                 */
                if (dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
                    za.za_first_integer, FTAG, &clone) != 0)
                        continue;
                dsl_dir_name(clone->ds_dir, buf);
                VERIFY(nvlist_add_boolean(val, buf) == 0);
                dsl_dataset_rele(clone, FTAG);
        }
        zap_cursor_fini(&zc);
        VERIFY(nvlist_add_nvlist(propval, ZPROP_VALUE, val) == 0);
        VERIFY(nvlist_add_nvlist(nv, zfs_prop_to_name(ZFS_PROP_CLONES),
            propval) == 0);
fail:
        nvlist_free(val);
        nvlist_free(propval);
        rw_exit(&ds->ds_dir->dd_pool->dp_config_rwlock);
}

void
dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
{
        uint64_t refd, avail, uobjs, aobjs, ratio;

        dsl_dir_stats(ds->ds_dir, nv);

        dsl_dataset_space(ds, &refd, &avail, &uobjs, &aobjs);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_AVAILABLE, avail);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFERENCED, refd);

        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_CREATION,
            ds->ds_phys->ds_creation_time);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_CREATETXG,
            ds->ds_phys->ds_creation_txg);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFQUOTA,
            ds->ds_quota);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFRESERVATION,
            ds->ds_reserved);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_GUID,
            ds->ds_phys->ds_guid);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_UNIQUE,
            ds->ds_phys->ds_unique_bytes);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_OBJSETID,
            ds->ds_object);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_USERREFS,
            ds->ds_userrefs);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_DEFER_DESTROY,
            DS_IS_DEFER_DESTROY(ds) ? 1 : 0);

        if (ds->ds_phys->ds_prev_snap_obj != 0) {
                uint64_t written, comp, uncomp;
                dsl_pool_t *dp = ds->ds_dir->dd_pool;
                dsl_dataset_t *prev;

                rw_enter(&dp->dp_config_rwlock, RW_READER);
                int err = dsl_dataset_hold_obj(dp,
                    ds->ds_phys->ds_prev_snap_obj, FTAG, &prev);
                rw_exit(&dp->dp_config_rwlock);
                if (err == 0) {
                        err = dsl_dataset_space_written(prev, ds, &written,
                            &comp, &uncomp);
                        dsl_dataset_rele(prev, FTAG);
                        if (err == 0) {
                                dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_WRITTEN,
                                    written);
                        }
                }
        }
        ratio = ds->ds_phys->ds_compressed_bytes == 0 ? 100 :
            (ds->ds_phys->ds_uncompressed_bytes * 100 /
            ds->ds_phys->ds_compressed_bytes);
        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFRATIO, ratio);

        if (ds->ds_phys->ds_next_snap_obj) {
                /*
                 * This is a snapshot; override the dd's space used with
                 * our unique space and compression ratio.
                 */
                dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_USED,
                    ds->ds_phys->ds_unique_bytes);
                dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_COMPRESSRATIO, ratio);

                get_clones_stat(ds, nv);
        }
}

void
dsl_dataset_fast_stat(dsl_dataset_t *ds, dmu_objset_stats_t *stat)
{
        stat->dds_creation_txg = ds->ds_phys->ds_creation_txg;
        stat->dds_inconsistent = ds->ds_phys->ds_flags & DS_FLAG_INCONSISTENT;
        stat->dds_guid = ds->ds_phys->ds_guid;
        if (ds->ds_phys->ds_next_snap_obj) {
                stat->dds_is_snapshot = B_TRUE;
                stat->dds_num_clones = ds->ds_phys->ds_num_children - 1;
        } else {
                stat->dds_is_snapshot = B_FALSE;
                stat->dds_num_clones = 0;
        }

        /* clone origin is really a dsl_dir thing... */
        rw_enter(&ds->ds_dir->dd_pool->dp_config_rwlock, RW_READER);
        if (dsl_dir_is_clone(ds->ds_dir)) {
                dsl_dataset_t *ods;

                VERIFY(0 == dsl_dataset_get_ref(ds->ds_dir->dd_pool,
                    ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &ods));
                dsl_dataset_name(ods, stat->dds_origin);
                dsl_dataset_drop_ref(ods, FTAG);
        } else {
                stat->dds_origin[0] = '\0';
        }
        rw_exit(&ds->ds_dir->dd_pool->dp_config_rwlock);
}

uint64_t
dsl_dataset_fsid_guid(dsl_dataset_t *ds)
{
        return (ds->ds_fsid_guid);
}

void
dsl_dataset_space(dsl_dataset_t *ds,
    uint64_t *refdbytesp, uint64_t *availbytesp,
    uint64_t *usedobjsp, uint64_t *availobjsp)
{
        *refdbytesp = ds->ds_phys->ds_referenced_bytes;
        *availbytesp = dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE);
        if (ds->ds_reserved > ds->ds_phys->ds_unique_bytes)
                *availbytesp += ds->ds_reserved - ds->ds_phys->ds_unique_bytes;
        if (ds->ds_quota != 0) {
                /*
                 * Adjust available bytes according to refquota
                 */
                if (*refdbytesp < ds->ds_quota)
                        *availbytesp = MIN(*availbytesp,
                            ds->ds_quota - *refdbytesp);
                else
                        *availbytesp = 0;
        }
        *usedobjsp = ds->ds_phys->ds_bp.blk_fill;
        *availobjsp = DN_MAX_OBJECT - *usedobjsp;
}

boolean_t
dsl_dataset_modified_since_lastsnap(dsl_dataset_t *ds)
{
        dsl_pool_t *dp = ds->ds_dir->dd_pool;

        ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
            dsl_pool_sync_context(dp));
        if (ds->ds_prev == NULL)
                return (B_FALSE);
        if (ds->ds_phys->ds_bp.blk_birth >
            ds->ds_prev->ds_phys->ds_creation_txg) {
                objset_t *os, *os_prev;
                /*
                 * It may be that only the ZIL differs, because it was
                 * reset in the head.  Don't count that as being
                 * modified.
                 */
                if (dmu_objset_from_ds(ds, &os) != 0)
                        return (B_TRUE);
                if (dmu_objset_from_ds(ds->ds_prev, &os_prev) != 0)
                        return (B_TRUE);
                return (bcmp(&os->os_phys->os_meta_dnode,
                    &os_prev->os_phys->os_meta_dnode,
                    sizeof (os->os_phys->os_meta_dnode)) != 0);
        }
        return (B_FALSE);
}

/* ARGSUSED */
static int
dsl_dataset_snapshot_rename_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        char *newsnapname = arg2;
        dsl_dir_t *dd = ds->ds_dir;
        dsl_dataset_t *hds;
        uint64_t val;
        int err;

        err = dsl_dataset_hold_obj(dd->dd_pool,
            dd->dd_phys->dd_head_dataset_obj, FTAG, &hds);
        if (err)
                return (err);

        /* new name better not be in use */
        err = dsl_dataset_snap_lookup(hds, newsnapname, &val);
        dsl_dataset_rele(hds, FTAG);

        if (err == 0)
                err = EEXIST;
        else if (err == ENOENT)
                err = 0;

        /* dataset name + 1 for the "@" + the new snapshot name must fit */
        if (dsl_dir_namelen(ds->ds_dir) + 1 + strlen(newsnapname) >= MAXNAMELEN)
                err = ENAMETOOLONG;

        return (err);
}

static void
dsl_dataset_snapshot_rename_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        char oldname[MAXPATHLEN], newname[MAXPATHLEN];
        dsl_dataset_t *ds = arg1;
        const char *newsnapname = arg2;
        dsl_dir_t *dd = ds->ds_dir;
        objset_t *mos = dd->dd_pool->dp_meta_objset;
        dsl_dataset_t *hds;
        int err;

        ASSERT(ds->ds_phys->ds_next_snap_obj != 0);

        VERIFY(0 == dsl_dataset_hold_obj(dd->dd_pool,
            dd->dd_phys->dd_head_dataset_obj, FTAG, &hds));

        VERIFY(0 == dsl_dataset_get_snapname(ds));
        err = dsl_dataset_snap_remove(hds, ds->ds_snapname, tx);
        ASSERT0(err);
        dsl_dataset_name(ds, oldname);
        mutex_enter(&ds->ds_lock);
        (void) strcpy(ds->ds_snapname, newsnapname);
        mutex_exit(&ds->ds_lock);
        err = zap_add(mos, hds->ds_phys->ds_snapnames_zapobj,
            ds->ds_snapname, 8, 1, &ds->ds_object, tx);
        ASSERT0(err);
        dsl_dataset_name(ds, newname);
#ifdef _KERNEL
        zvol_rename_minors(oldname, newname);
#endif

        spa_history_log_internal(LOG_DS_RENAME, dd->dd_pool->dp_spa, tx,
            "dataset = %llu", ds->ds_object);
        dsl_dataset_rele(hds, FTAG);
}

struct renamesnaparg {
        dsl_sync_task_group_t *dstg;
        char failed[MAXPATHLEN];
        char *oldsnap;
        char *newsnap;
        int error;
};

static int
dsl_snapshot_rename_one(const char *name, void *arg)
{
        struct renamesnaparg *ra = arg;
        dsl_dataset_t *ds = NULL;
        char *snapname;
        int err;

        snapname = kmem_asprintf("%s@%s", name, ra->oldsnap);
        (void) strlcpy(ra->failed, snapname, sizeof (ra->failed));

        /*
         * For recursive snapshot renames the parent won't be changing
         * so we just pass name for both the to/from argument.
         */
        err = zfs_secpolicy_rename_perms(snapname, snapname, CRED());
        if (err != 0) {
                strfree(snapname);
                return (err == ENOENT ? 0 : err);
        }

#ifdef _KERNEL
        /*
         * For all filesystems undergoing rename, we'll need to unmount it.
         */
        (void) zfs_unmount_snap(snapname, NULL);
#endif
        err = dsl_dataset_hold(snapname, ra->dstg, &ds);
        strfree(snapname);
        if (err != 0)
                return (err == ENOENT ? 0 : err);

        dsl_sync_task_create(ra->dstg, dsl_dataset_snapshot_rename_check,
            dsl_dataset_snapshot_rename_sync, ds, ra->newsnap, 0);

        /* First successful rename clears the error. */
        ra->error = 0;

        return (0);
}

static int
dsl_recursive_rename(char *oldname, const char *newname)
{
        int err;
        struct renamesnaparg *ra;
        dsl_sync_task_t *dst;
        spa_t *spa;
        char *cp, *fsname = spa_strdup(oldname);
        int len = strlen(oldname) + 1;

        /* truncate the snapshot name to get the fsname */
        cp = strchr(fsname, '@');
        *cp = '\0';

        err = spa_open(fsname, &spa, FTAG);
        if (err) {
                kmem_free(fsname, len);
                return (err);
        }
        ra = kmem_alloc(sizeof (struct renamesnaparg), KM_SLEEP);
        ra->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));

        ra->oldsnap = strchr(oldname, '@') + 1;
        ra->newsnap = strchr(newname, '@') + 1;
        *ra->failed = '\0';
        ra->error = ENOENT;

        err = dmu_objset_find(fsname, dsl_snapshot_rename_one, ra,
            DS_FIND_CHILDREN);
        kmem_free(fsname, len);
        if (err == 0)
                err = ra->error;

        if (err == 0)
                err = dsl_sync_task_group_wait(ra->dstg);

        for (dst = list_head(&ra->dstg->dstg_tasks); dst;
            dst = list_next(&ra->dstg->dstg_tasks, dst)) {
                dsl_dataset_t *ds = dst->dst_arg1;
                if (dst->dst_err) {
                        dsl_dir_name(ds->ds_dir, ra->failed);
                        (void) strlcat(ra->failed, "@", sizeof (ra->failed));
                        (void) strlcat(ra->failed, ra->newsnap,
                            sizeof (ra->failed));
                }
                dsl_dataset_rele(ds, ra->dstg);
        }

        if (err)
                (void) strlcpy(oldname, ra->failed, sizeof (ra->failed));

        dsl_sync_task_group_destroy(ra->dstg);
        kmem_free(ra, sizeof (struct renamesnaparg));
        spa_close(spa, FTAG);
        return (err);
}

static int
dsl_valid_rename(const char *oldname, void *arg)
{
        int delta = *(int *)arg;

        if (strlen(oldname) + delta >= MAXNAMELEN)
                return (ENAMETOOLONG);

        return (0);
}

#pragma weak dmu_objset_rename = dsl_dataset_rename
int
dsl_dataset_rename(char *oldname, const char *newname, int flags)
{
        dsl_dir_t *dd;
        dsl_dataset_t *ds;
        const char *tail;
        int err;

        err = dsl_dir_open(oldname, FTAG, &dd, &tail);
        if (err)
                return (err);

        if (tail == NULL) {
                int delta = strlen(newname) - strlen(oldname);

                /* if we're growing, validate child name lengths */
                if (delta > 0)
                        err = dmu_objset_find(oldname, dsl_valid_rename,
                            &delta, DS_FIND_CHILDREN | DS_FIND_SNAPSHOTS);

                if (err == 0)
                        err = dsl_dir_rename(dd, newname, flags);
                dsl_dir_close(dd, FTAG);
                return (err);
        }

        if (tail[0] != '@') {
                /* the name ended in a nonexistent component */
                dsl_dir_close(dd, FTAG);
                return (ENOENT);
        }

        dsl_dir_close(dd, FTAG);

        /* new name must be snapshot in same filesystem */
        tail = strchr(newname, '@');
        if (tail == NULL)
                return (EINVAL);
        tail++;
        if (strncmp(oldname, newname, tail - newname) != 0)
                return (EXDEV);

        if (flags & ZFS_RENAME_RECURSIVE) {
                err = dsl_recursive_rename(oldname, newname);
        } else {
                err = dsl_dataset_hold(oldname, FTAG, &ds);
                if (err)
                        return (err);

                err = dsl_sync_task_do(ds->ds_dir->dd_pool,
                    dsl_dataset_snapshot_rename_check,
                    dsl_dataset_snapshot_rename_sync, ds, (char *)tail, 1);

                dsl_dataset_rele(ds, FTAG);
        }

        return (err);
}

struct promotenode {
        list_node_t link;
        dsl_dataset_t *ds;
};

struct promotearg {
        list_t shared_snaps, origin_snaps, clone_snaps;
        dsl_dataset_t *origin_origin;
        uint64_t used, comp, uncomp, unique, cloneusedsnap, originusedsnap;
        char *err_ds;
};

static int snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep);
static boolean_t snaplist_unstable(list_t *l);

static int
dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *hds = arg1;
        struct promotearg *pa = arg2;
        struct promotenode *snap = list_head(&pa->shared_snaps);
        dsl_dataset_t *origin_ds = snap->ds;
        int err;
        uint64_t unused;

        /* Check that it is a real clone */
        if (!dsl_dir_is_clone(hds->ds_dir))
                return (EINVAL);

        /* Since this is so expensive, don't do the preliminary check */
        if (!dmu_tx_is_syncing(tx))
                return (0);

        if (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE)
                return (EXDEV);

        /* compute origin's new unique space */
        snap = list_tail(&pa->clone_snaps);
        ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
        dsl_deadlist_space_range(&snap->ds->ds_deadlist,
            origin_ds->ds_phys->ds_prev_snap_txg, UINT64_MAX,
            &pa->unique, &unused, &unused);

        /*
         * Walk the snapshots that we are moving
         *
         * Compute space to transfer.  Consider the incremental changes
         * to used for each snapshot:
         * (my used) = (prev's used) + (blocks born) - (blocks killed)
         * So each snapshot gave birth to:
         * (blocks born) = (my used) - (prev's used) + (blocks killed)
         * So a sequence would look like:
         * (uN - u(N-1) + kN) + ... + (u1 - u0 + k1) + (u0 - 0 + k0)
         * Which simplifies to:
         * uN + kN + kN-1 + ... + k1 + k0
         * Note however, if we stop before we reach the ORIGIN we get:
         * uN + kN + kN-1 + ... + kM - uM-1
         */
        pa->used = origin_ds->ds_phys->ds_referenced_bytes;
        pa->comp = origin_ds->ds_phys->ds_compressed_bytes;
        pa->uncomp = origin_ds->ds_phys->ds_uncompressed_bytes;
        for (snap = list_head(&pa->shared_snaps); snap;
            snap = list_next(&pa->shared_snaps, snap)) {
                uint64_t val, dlused, dlcomp, dluncomp;
                dsl_dataset_t *ds = snap->ds;

                /* Check that the snapshot name does not conflict */
                VERIFY(0 == dsl_dataset_get_snapname(ds));
                err = dsl_dataset_snap_lookup(hds, ds->ds_snapname, &val);
                if (err == 0) {
                        err = EEXIST;
                        goto out;
                }
                if (err != ENOENT)
                        goto out;

                /* The very first snapshot does not have a deadlist */
                if (ds->ds_phys->ds_prev_snap_obj == 0)
                        continue;

                dsl_deadlist_space(&ds->ds_deadlist,
                    &dlused, &dlcomp, &dluncomp);
                pa->used += dlused;
                pa->comp += dlcomp;
                pa->uncomp += dluncomp;
        }

        /*
         * If we are a clone of a clone then we never reached ORIGIN,
         * so we need to subtract out the clone origin's used space.
         */
        if (pa->origin_origin) {
                pa->used -= pa->origin_origin->ds_phys->ds_referenced_bytes;
                pa->comp -= pa->origin_origin->ds_phys->ds_compressed_bytes;
                pa->uncomp -= pa->origin_origin->ds_phys->ds_uncompressed_bytes;
        }

        /* Check that there is enough space here */
        err = dsl_dir_transfer_possible(origin_ds->ds_dir, hds->ds_dir,
            pa->used);
        if (err)
                return (err);

        /*
         * Compute the amounts of space that will be used by snapshots
         * after the promotion (for both origin and clone).  For each,
         * it is the amount of space that will be on all of their
         * deadlists (that was not born before their new origin).
         */
        if (hds->ds_dir->dd_phys->dd_flags & DD_FLAG_USED_BREAKDOWN) {
                uint64_t space;

                /*
                 * Note, typically this will not be a clone of a clone,
                 * so dd_origin_txg will be < TXG_INITIAL, so
                 * these snaplist_space() -> dsl_deadlist_space_range()
                 * calls will be fast because they do not have to
                 * iterate over all bps.
                 */
                snap = list_head(&pa->origin_snaps);
                err = snaplist_space(&pa->shared_snaps,
                    snap->ds->ds_dir->dd_origin_txg, &pa->cloneusedsnap);
                if (err)
                        return (err);

                err = snaplist_space(&pa->clone_snaps,
                    snap->ds->ds_dir->dd_origin_txg, &space);
                if (err)
                        return (err);
                pa->cloneusedsnap += space;
        }
        if (origin_ds->ds_dir->dd_phys->dd_flags & DD_FLAG_USED_BREAKDOWN) {
                err = snaplist_space(&pa->origin_snaps,
                    origin_ds->ds_phys->ds_creation_txg, &pa->originusedsnap);
                if (err)
                        return (err);
        }

        return (0);
out:
        pa->err_ds =  snap->ds->ds_snapname;
        return (err);
}

static void
dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *hds = arg1;
        struct promotearg *pa = arg2;
        struct promotenode *snap = list_head(&pa->shared_snaps);
        dsl_dataset_t *origin_ds = snap->ds;
        dsl_dataset_t *origin_head;
        dsl_dir_t *dd = hds->ds_dir;
        dsl_pool_t *dp = hds->ds_dir->dd_pool;
        dsl_dir_t *odd = NULL;
        uint64_t oldnext_obj;
        int64_t delta;

        ASSERT(0 == (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE));

        snap = list_head(&pa->origin_snaps);
        origin_head = snap->ds;

        /*
         * We need to explicitly open odd, since origin_ds's dd will be
         * changing.
         */
        VERIFY(0 == dsl_dir_open_obj(dp, origin_ds->ds_dir->dd_object,
            NULL, FTAG, &odd));

        /* change origin's next snap */
        dmu_buf_will_dirty(origin_ds->ds_dbuf, tx);
        oldnext_obj = origin_ds->ds_phys->ds_next_snap_obj;
        snap = list_tail(&pa->clone_snaps);
        ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
        origin_ds->ds_phys->ds_next_snap_obj = snap->ds->ds_object;

        /* change the origin's next clone */
        if (origin_ds->ds_phys->ds_next_clones_obj) {
                remove_from_next_clones(origin_ds, snap->ds->ds_object, tx);
                VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
                    origin_ds->ds_phys->ds_next_clones_obj,
                    oldnext_obj, tx));
        }

        /* change origin */
        dmu_buf_will_dirty(dd->dd_dbuf, tx);
        ASSERT3U(dd->dd_phys->dd_origin_obj, ==, origin_ds->ds_object);
        dd->dd_phys->dd_origin_obj = odd->dd_phys->dd_origin_obj;
        dd->dd_origin_txg = origin_head->ds_dir->dd_origin_txg;
        dmu_buf_will_dirty(odd->dd_dbuf, tx);
        odd->dd_phys->dd_origin_obj = origin_ds->ds_object;
        origin_head->ds_dir->dd_origin_txg =
            origin_ds->ds_phys->ds_creation_txg;

        /* change dd_clone entries */
        if (spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
                VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
                    odd->dd_phys->dd_clones, hds->ds_object, tx));
                VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
                    pa->origin_origin->ds_dir->dd_phys->dd_clones,
                    hds->ds_object, tx));

                VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
                    pa->origin_origin->ds_dir->dd_phys->dd_clones,
                    origin_head->ds_object, tx));
                if (dd->dd_phys->dd_clones == 0) {
                        dd->dd_phys->dd_clones = zap_create(dp->dp_meta_objset,
                            DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
                }
                VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
                    dd->dd_phys->dd_clones, origin_head->ds_object, tx));

        }

        /* move snapshots to this dir */
        for (snap = list_head(&pa->shared_snaps); snap;
            snap = list_next(&pa->shared_snaps, snap)) {
                dsl_dataset_t *ds = snap->ds;

                /* unregister props as dsl_dir is changing */
                if (ds->ds_objset) {
                        dmu_objset_evict(ds->ds_objset);
                        ds->ds_objset = NULL;
                }
                /* move snap name entry */
                VERIFY(0 == dsl_dataset_get_snapname(ds));
                VERIFY(0 == dsl_dataset_snap_remove(origin_head,
                    ds->ds_snapname, tx));
                VERIFY(0 == zap_add(dp->dp_meta_objset,
                    hds->ds_phys->ds_snapnames_zapobj, ds->ds_snapname,
                    8, 1, &ds->ds_object, tx));

                /* change containing dsl_dir */
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                ASSERT3U(ds->ds_phys->ds_dir_obj, ==, odd->dd_object);
                ds->ds_phys->ds_dir_obj = dd->dd_object;
                ASSERT3P(ds->ds_dir, ==, odd);
                dsl_dir_close(ds->ds_dir, ds);
                VERIFY(0 == dsl_dir_open_obj(dp, dd->dd_object,
                    NULL, ds, &ds->ds_dir));

                /* move any clone references */
                if (ds->ds_phys->ds_next_clones_obj &&
                    spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
                        zap_cursor_t zc;
                        zap_attribute_t za;

                        for (zap_cursor_init(&zc, dp->dp_meta_objset,
                            ds->ds_phys->ds_next_clones_obj);
                            zap_cursor_retrieve(&zc, &za) == 0;
                            zap_cursor_advance(&zc)) {
                                dsl_dataset_t *cnds;
                                uint64_t o;

                                if (za.za_first_integer == oldnext_obj) {
                                        /*
                                         * We've already moved the
                                         * origin's reference.
                                         */
                                        continue;
                                }

                                VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
                                    za.za_first_integer, FTAG, &cnds));
                                o = cnds->ds_dir->dd_phys->dd_head_dataset_obj;

                                VERIFY3U(zap_remove_int(dp->dp_meta_objset,
                                    odd->dd_phys->dd_clones, o, tx), ==, 0);
                                VERIFY3U(zap_add_int(dp->dp_meta_objset,
                                    dd->dd_phys->dd_clones, o, tx), ==, 0);
                                dsl_dataset_rele(cnds, FTAG);
                        }
                        zap_cursor_fini(&zc);
                }

                ASSERT0(dsl_prop_numcb(ds));
        }

        /*
         * Change space accounting.
         * Note, pa->*usedsnap and dd_used_breakdown[SNAP] will either
         * both be valid, or both be 0 (resulting in delta == 0).  This
         * is true for each of {clone,origin} independently.
         */

        delta = pa->cloneusedsnap -
            dd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
        ASSERT3S(delta, >=, 0);
        ASSERT3U(pa->used, >=, delta);
        dsl_dir_diduse_space(dd, DD_USED_SNAP, delta, 0, 0, tx);
        dsl_dir_diduse_space(dd, DD_USED_HEAD,
            pa->used - delta, pa->comp, pa->uncomp, tx);

        delta = pa->originusedsnap -
            odd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
        ASSERT3S(delta, <=, 0);
        ASSERT3U(pa->used, >=, -delta);
        dsl_dir_diduse_space(odd, DD_USED_SNAP, delta, 0, 0, tx);
        dsl_dir_diduse_space(odd, DD_USED_HEAD,
            -pa->used - delta, -pa->comp, -pa->uncomp, tx);

        origin_ds->ds_phys->ds_unique_bytes = pa->unique;

        /* log history record */
        spa_history_log_internal(LOG_DS_PROMOTE, dd->dd_pool->dp_spa, tx,
            "dataset = %llu", hds->ds_object);

        dsl_dir_close(odd, FTAG);
}

static char *snaplist_tag = "snaplist";
static int
snaplist_make(dsl_pool_t *dp, boolean_t own,
    uint64_t first_obj, uint64_t last_obj, list_t *l)
{
        uint64_t obj = last_obj;

        ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock));

        list_create(l, sizeof (struct promotenode),
            offsetof(struct promotenode, link));

        while (obj != first_obj) {
                dsl_dataset_t *ds;
                struct promotenode *snap;
                int err;

                if (own) {
                        err = dsl_dataset_own_obj(dp, obj,
                            0, snaplist_tag, &ds);
                        if (err == 0)
                                dsl_dataset_make_exclusive(ds, snaplist_tag);
                } else {
                        err = dsl_dataset_hold_obj(dp, obj, snaplist_tag, &ds);
                }
                if (err == ENOENT) {
                        /* lost race with snapshot destroy */
                        struct promotenode *last = list_tail(l);
                        ASSERT(obj != last->ds->ds_phys->ds_prev_snap_obj);
                        obj = last->ds->ds_phys->ds_prev_snap_obj;
                        continue;
                } else if (err) {
                        return (err);
                }

                if (first_obj == 0)
                        first_obj = ds->ds_dir->dd_phys->dd_origin_obj;

                snap = kmem_alloc(sizeof (struct promotenode), KM_SLEEP);
                snap->ds = ds;
                list_insert_tail(l, snap);
                obj = ds->ds_phys->ds_prev_snap_obj;
        }

        return (0);
}

static int
snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep)
{
        struct promotenode *snap;

        *spacep = 0;
        for (snap = list_head(l); snap; snap = list_next(l, snap)) {
                uint64_t used, comp, uncomp;
                dsl_deadlist_space_range(&snap->ds->ds_deadlist,
                    mintxg, UINT64_MAX, &used, &comp, &uncomp);
                *spacep += used;
        }
        return (0);
}

static void
snaplist_destroy(list_t *l, boolean_t own)
{
        struct promotenode *snap;

        if (!l || !list_link_active(&l->list_head))
                return;

        while ((snap = list_tail(l)) != NULL) {
                list_remove(l, snap);
                if (own)
                        dsl_dataset_disown(snap->ds, snaplist_tag);
                else
                        dsl_dataset_rele(snap->ds, snaplist_tag);
                kmem_free(snap, sizeof (struct promotenode));
        }
        list_destroy(l);
}

int
dsl_dataset_promote(const char *name, char *conflsnap)
{
        dsl_dataset_t *ds;
        dsl_dir_t *dd;
        dsl_pool_t *dp;
        dmu_object_info_t doi;
        struct promotearg pa = { 0 };
        struct promotenode *snap;
        int err;

        err = dsl_dataset_hold(name, FTAG, &ds);
        if (err)
                return (err);
        dd = ds->ds_dir;
        dp = dd->dd_pool;

        err = dmu_object_info(dp->dp_meta_objset,
            ds->ds_phys->ds_snapnames_zapobj, &doi);
        if (err) {
                dsl_dataset_rele(ds, FTAG);
                return (err);
        }

        if (dsl_dataset_is_snapshot(ds) || dd->dd_phys->dd_origin_obj == 0) {
                dsl_dataset_rele(ds, FTAG);
                return (EINVAL);
        }

        /*
         * We are going to inherit all the snapshots taken before our
         * origin (i.e., our new origin will be our parent's origin).
         * Take ownership of them so that we can rename them into our
         * namespace.
         */
        rw_enter(&dp->dp_config_rwlock, RW_READER);

        err = snaplist_make(dp, B_TRUE, 0, dd->dd_phys->dd_origin_obj,
            &pa.shared_snaps);
        if (err != 0)
                goto out;

        err = snaplist_make(dp, B_FALSE, 0, ds->ds_object, &pa.clone_snaps);
        if (err != 0)
                goto out;

        snap = list_head(&pa.shared_snaps);
        ASSERT3U(snap->ds->ds_object, ==, dd->dd_phys->dd_origin_obj);
        err = snaplist_make(dp, B_FALSE, dd->dd_phys->dd_origin_obj,
            snap->ds->ds_dir->dd_phys->dd_head_dataset_obj, &pa.origin_snaps);
        if (err != 0)
                goto out;

        if (snap->ds->ds_dir->dd_phys->dd_origin_obj != 0) {
                err = dsl_dataset_hold_obj(dp,
                    snap->ds->ds_dir->dd_phys->dd_origin_obj,
                    FTAG, &pa.origin_origin);
                if (err != 0)
                        goto out;
        }

out:
        rw_exit(&dp->dp_config_rwlock);

        /*
         * Add in 128x the snapnames zapobj size, since we will be moving
         * a bunch of snapnames to the promoted ds, and dirtying their
         * bonus buffers.
         */
        if (err == 0) {
                err = dsl_sync_task_do(dp, dsl_dataset_promote_check,
                    dsl_dataset_promote_sync, ds, &pa,
                    2 + 2 * doi.doi_physical_blocks_512);
                if (err && pa.err_ds && conflsnap)
                        (void) strncpy(conflsnap, pa.err_ds, MAXNAMELEN);
        }

        snaplist_destroy(&pa.shared_snaps, B_TRUE);
        snaplist_destroy(&pa.clone_snaps, B_FALSE);
        snaplist_destroy(&pa.origin_snaps, B_FALSE);
        if (pa.origin_origin)
                dsl_dataset_rele(pa.origin_origin, FTAG);
        dsl_dataset_rele(ds, FTAG);
        return (err);
}

struct cloneswaparg {
        dsl_dataset_t *cds; /* clone dataset */
        dsl_dataset_t *ohds; /* origin's head dataset */
        boolean_t force;
        int64_t unused_refres_delta; /* change in unconsumed refreservation */
};

/* ARGSUSED */
static int
dsl_dataset_clone_swap_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        struct cloneswaparg *csa = arg1;

        /* they should both be heads */
        if (dsl_dataset_is_snapshot(csa->cds) ||
            dsl_dataset_is_snapshot(csa->ohds))
                return (EINVAL);

        /* the branch point should be just before them */
        if (csa->cds->ds_prev != csa->ohds->ds_prev)
                return (EINVAL);

        /* cds should be the clone (unless they are unrelated) */
        if (csa->cds->ds_prev != NULL &&
            csa->cds->ds_prev != csa->cds->ds_dir->dd_pool->dp_origin_snap &&
            csa->ohds->ds_object !=
            csa->cds->ds_prev->ds_phys->ds_next_snap_obj)
                return (EINVAL);

        /* the clone should be a child of the origin */
        if (csa->cds->ds_dir->dd_parent != csa->ohds->ds_dir)
                return (EINVAL);

        /* ohds shouldn't be modified unless 'force' */
        if (!csa->force && dsl_dataset_modified_since_lastsnap(csa->ohds))
                return (ETXTBSY);

        /* adjust amount of any unconsumed refreservation */
        csa->unused_refres_delta =
            (int64_t)MIN(csa->ohds->ds_reserved,
            csa->ohds->ds_phys->ds_unique_bytes) -
            (int64_t)MIN(csa->ohds->ds_reserved,
            csa->cds->ds_phys->ds_unique_bytes);

        if (csa->unused_refres_delta > 0 &&
            csa->unused_refres_delta >
            dsl_dir_space_available(csa->ohds->ds_dir, NULL, 0, TRUE))
                return (ENOSPC);

        if (csa->ohds->ds_quota != 0 &&
            csa->cds->ds_phys->ds_unique_bytes > csa->ohds->ds_quota)
                return (EDQUOT);

        return (0);
}

/* ARGSUSED */
static void
dsl_dataset_clone_swap_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        struct cloneswaparg *csa = arg1;
        dsl_pool_t *dp = csa->cds->ds_dir->dd_pool;

        ASSERT(csa->cds->ds_reserved == 0);
        ASSERT(csa->ohds->ds_quota == 0 ||
            csa->cds->ds_phys->ds_unique_bytes <= csa->ohds->ds_quota);

        dmu_buf_will_dirty(csa->cds->ds_dbuf, tx);
        dmu_buf_will_dirty(csa->ohds->ds_dbuf, tx);

        if (csa->cds->ds_objset != NULL) {
                dmu_objset_evict(csa->cds->ds_objset);
                csa->cds->ds_objset = NULL;
        }

        if (csa->ohds->ds_objset != NULL) {
                dmu_objset_evict(csa->ohds->ds_objset);
                csa->ohds->ds_objset = NULL;
        }

        /*
         * Reset origin's unique bytes, if it exists.
         */
        if (csa->cds->ds_prev) {
                dsl_dataset_t *origin = csa->cds->ds_prev;
                uint64_t comp, uncomp;

                dmu_buf_will_dirty(origin->ds_dbuf, tx);
                dsl_deadlist_space_range(&csa->cds->ds_deadlist,
                    origin->ds_phys->ds_prev_snap_txg, UINT64_MAX,
                    &origin->ds_phys->ds_unique_bytes, &comp, &uncomp);
        }

        /* swap blkptrs */
        {
                blkptr_t tmp;
                tmp = csa->ohds->ds_phys->ds_bp;
                csa->ohds->ds_phys->ds_bp = csa->cds->ds_phys->ds_bp;
                csa->cds->ds_phys->ds_bp = tmp;
        }

        /* set dd_*_bytes */
        {
                int64_t dused, dcomp, duncomp;
                uint64_t cdl_used, cdl_comp, cdl_uncomp;
                uint64_t odl_used, odl_comp, odl_uncomp;

                ASSERT3U(csa->cds->ds_dir->dd_phys->
                    dd_used_breakdown[DD_USED_SNAP], ==, 0);

                dsl_deadlist_space(&csa->cds->ds_deadlist,
                    &cdl_used, &cdl_comp, &cdl_uncomp);
                dsl_deadlist_space(&csa->ohds->ds_deadlist,
                    &odl_used, &odl_comp, &odl_uncomp);

                dused = csa->cds->ds_phys->ds_referenced_bytes + cdl_used -
                    (csa->ohds->ds_phys->ds_referenced_bytes + odl_used);
                dcomp = csa->cds->ds_phys->ds_compressed_bytes + cdl_comp -
                    (csa->ohds->ds_phys->ds_compressed_bytes + odl_comp);
                duncomp = csa->cds->ds_phys->ds_uncompressed_bytes +
                    cdl_uncomp -
                    (csa->ohds->ds_phys->ds_uncompressed_bytes + odl_uncomp);

                dsl_dir_diduse_space(csa->ohds->ds_dir, DD_USED_HEAD,
                    dused, dcomp, duncomp, tx);
                dsl_dir_diduse_space(csa->cds->ds_dir, DD_USED_HEAD,
                    -dused, -dcomp, -duncomp, tx);

                /*
                 * The difference in the space used by snapshots is the
                 * difference in snapshot space due to the head's
                 * deadlist (since that's the only thing that's
                 * changing that affects the snapused).
                 */
                dsl_deadlist_space_range(&csa->cds->ds_deadlist,
                    csa->ohds->ds_dir->dd_origin_txg, UINT64_MAX,
                    &cdl_used, &cdl_comp, &cdl_uncomp);
                dsl_deadlist_space_range(&csa->ohds->ds_deadlist,
                    csa->ohds->ds_dir->dd_origin_txg, UINT64_MAX,
                    &odl_used, &odl_comp, &odl_uncomp);
                dsl_dir_transfer_space(csa->ohds->ds_dir, cdl_used - odl_used,
                    DD_USED_HEAD, DD_USED_SNAP, tx);
        }

        /* swap ds_*_bytes */
        SWITCH64(csa->ohds->ds_phys->ds_referenced_bytes,
            csa->cds->ds_phys->ds_referenced_bytes);
        SWITCH64(csa->ohds->ds_phys->ds_compressed_bytes,
            csa->cds->ds_phys->ds_compressed_bytes);
        SWITCH64(csa->ohds->ds_phys->ds_uncompressed_bytes,
            csa->cds->ds_phys->ds_uncompressed_bytes);
        SWITCH64(csa->ohds->ds_phys->ds_unique_bytes,
            csa->cds->ds_phys->ds_unique_bytes);

        /* apply any parent delta for change in unconsumed refreservation */
        dsl_dir_diduse_space(csa->ohds->ds_dir, DD_USED_REFRSRV,
            csa->unused_refres_delta, 0, 0, tx);

        /*
         * Swap deadlists.
         */
        dsl_deadlist_close(&csa->cds->ds_deadlist);
        dsl_deadlist_close(&csa->ohds->ds_deadlist);
        SWITCH64(csa->ohds->ds_phys->ds_deadlist_obj,
            csa->cds->ds_phys->ds_deadlist_obj);
        dsl_deadlist_open(&csa->cds->ds_deadlist, dp->dp_meta_objset,
            csa->cds->ds_phys->ds_deadlist_obj);
        dsl_deadlist_open(&csa->ohds->ds_deadlist, dp->dp_meta_objset,
            csa->ohds->ds_phys->ds_deadlist_obj);

        dsl_scan_ds_clone_swapped(csa->ohds, csa->cds, tx);
}

int
dsl_dataset_clone_swap(dsl_dataset_t *clone, dsl_dataset_t *origin_head,
    boolean_t force)
{
        struct cloneswaparg csa;
        int error;

        ASSERT(clone->ds_owner);
        ASSERT(origin_head->ds_owner);
retry:
        /*
         * Need exclusive access for the swap. If we're swapping these
         * datasets back after an error, we already hold the locks.
         */
        if (!RW_WRITE_HELD(&clone->ds_rwlock))
                rw_enter(&clone->ds_rwlock, RW_WRITER);
        if (!RW_WRITE_HELD(&origin_head->ds_rwlock) &&
            !rw_tryenter(&origin_head->ds_rwlock, RW_WRITER)) {
                rw_exit(&clone->ds_rwlock);
                rw_enter(&origin_head->ds_rwlock, RW_WRITER);
                if (!rw_tryenter(&clone->ds_rwlock, RW_WRITER)) {
                        rw_exit(&origin_head->ds_rwlock);
                        goto retry;
                }
        }
        csa.cds = clone;
        csa.ohds = origin_head;
        csa.force = force;
        error = dsl_sync_task_do(clone->ds_dir->dd_pool,
            dsl_dataset_clone_swap_check,
            dsl_dataset_clone_swap_sync, &csa, NULL, 9);
        return (error);
}

int
dsl_dsobj_to_dsname(char *pname, uint64_t obj, char *buf)
{
        spa_t *spa;
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        int error;

        if ((error = spa_open(pname, &spa, FTAG)) != 0)
                return (error);
        dp = spa_get_dsl(spa);
        rw_enter(&dp->dp_config_rwlock, RW_READER);
        if ((error = dsl_dataset_hold_obj(dp, obj, FTAG, &ds)) == 0) {
                dsl_dataset_name(ds, buf);
                dsl_dataset_rele(ds, FTAG);
        }
        rw_exit(&dp->dp_config_rwlock);
        spa_close(spa, FTAG);

        return (error);
}

int
dsl_dataset_check_quota(dsl_dataset_t *ds, boolean_t check_quota,
    uint64_t asize, uint64_t inflight, uint64_t *used, uint64_t *ref_rsrv)
{
        int error = 0;

        ASSERT3S(asize, >, 0);

        /*
         * *ref_rsrv is the portion of asize that will come from any
         * unconsumed refreservation space.
         */
        *ref_rsrv = 0;

        mutex_enter(&ds->ds_lock);
        /*
         * Make a space adjustment for reserved bytes.
         */
        if (ds->ds_reserved > ds->ds_phys->ds_unique_bytes) {
                ASSERT3U(*used, >=,
                    ds->ds_reserved - ds->ds_phys->ds_unique_bytes);
                *used -= (ds->ds_reserved - ds->ds_phys->ds_unique_bytes);
                *ref_rsrv =
                    asize - MIN(asize, parent_delta(ds, asize + inflight));
        }

        if (!check_quota || ds->ds_quota == 0) {
                mutex_exit(&ds->ds_lock);
                return (0);
        }
        /*
         * If they are requesting more space, and our current estimate
         * is over quota, they get to try again unless the actual
         * on-disk is over quota and there are no pending changes (which
         * may free up space for us).
         */
        if (ds->ds_phys->ds_referenced_bytes + inflight >= ds->ds_quota) {
                if (inflight > 0 ||
                    ds->ds_phys->ds_referenced_bytes < ds->ds_quota)
                        error = ERESTART;
                else
                        error = EDQUOT;
        }
        mutex_exit(&ds->ds_lock);

        return (error);
}

/* ARGSUSED */
static int
dsl_dataset_set_quota_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        dsl_prop_setarg_t *psa = arg2;
        int err;

        if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_REFQUOTA)
                return (ENOTSUP);

        if ((err = dsl_prop_predict_sync(ds->ds_dir, psa)) != 0)
                return (err);

        if (psa->psa_effective_value == 0)
                return (0);

        if (psa->psa_effective_value < ds->ds_phys->ds_referenced_bytes ||
            psa->psa_effective_value < ds->ds_reserved)
                return (ENOSPC);

        return (0);
}

extern void dsl_prop_set_sync(void *, void *, dmu_tx_t *);

void
dsl_dataset_set_quota_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        dsl_prop_setarg_t *psa = arg2;
        uint64_t effective_value = psa->psa_effective_value;

        dsl_prop_set_sync(ds, psa, tx);
        DSL_PROP_CHECK_PREDICTION(ds->ds_dir, psa);

        if (ds->ds_quota != effective_value) {
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                ds->ds_quota = effective_value;
        }
}

int
dsl_dataset_set_quota(const char *dsname, zprop_source_t source, uint64_t quota)
{
        dsl_dataset_t *ds;
        dsl_prop_setarg_t psa;
        int err;

        dsl_prop_setarg_init_uint64(&psa, "refquota", source, &quota);

        err = dsl_dataset_hold(dsname, FTAG, &ds);
        if (err)
                return (err);

        /*
         * If someone removes a file, then tries to set the quota, we
         * want to make sure the file freeing takes effect.
         */
        txg_wait_open(ds->ds_dir->dd_pool, 0);

        err = dsl_sync_task_do(ds->ds_dir->dd_pool,
            dsl_dataset_set_quota_check, dsl_dataset_set_quota_sync,
            ds, &psa, 0);

        dsl_dataset_rele(ds, FTAG);
        return (err);
}

static int
dsl_dataset_set_reservation_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        dsl_prop_setarg_t *psa = arg2;
        uint64_t effective_value;
        uint64_t unique;
        int err;

        if (spa_version(ds->ds_dir->dd_pool->dp_spa) <
            SPA_VERSION_REFRESERVATION)
                return (ENOTSUP);

        if (dsl_dataset_is_snapshot(ds))
                return (EINVAL);

        if ((err = dsl_prop_predict_sync(ds->ds_dir, psa)) != 0)
                return (err);

        effective_value = psa->psa_effective_value;

        /*
         * If we are doing the preliminary check in open context, the
         * space estimates may be inaccurate.
         */
        if (!dmu_tx_is_syncing(tx))
                return (0);

        mutex_enter(&ds->ds_lock);
        if (!DS_UNIQUE_IS_ACCURATE(ds))
                dsl_dataset_recalc_head_uniq(ds);
        unique = ds->ds_phys->ds_unique_bytes;
        mutex_exit(&ds->ds_lock);

        if (MAX(unique, effective_value) > MAX(unique, ds->ds_reserved)) {
                uint64_t delta = MAX(unique, effective_value) -
                    MAX(unique, ds->ds_reserved);

                if (delta > dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE))
                        return (ENOSPC);
                if (ds->ds_quota > 0 &&
                    effective_value > ds->ds_quota)
                        return (ENOSPC);
        }

        return (0);
}

static void
dsl_dataset_set_reservation_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        dsl_prop_setarg_t *psa = arg2;
        uint64_t effective_value = psa->psa_effective_value;
        uint64_t unique;
        int64_t delta;

        dsl_prop_set_sync(ds, psa, tx);
        DSL_PROP_CHECK_PREDICTION(ds->ds_dir, psa);

        dmu_buf_will_dirty(ds->ds_dbuf, tx);

        mutex_enter(&ds->ds_dir->dd_lock);
        mutex_enter(&ds->ds_lock);
        ASSERT(DS_UNIQUE_IS_ACCURATE(ds));
        unique = ds->ds_phys->ds_unique_bytes;
        delta = MAX(0, (int64_t)(effective_value - unique)) -
            MAX(0, (int64_t)(ds->ds_reserved - unique));
        ds->ds_reserved = effective_value;
        mutex_exit(&ds->ds_lock);

        dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV, delta, 0, 0, tx);
        mutex_exit(&ds->ds_dir->dd_lock);
}

int
dsl_dataset_set_reservation(const char *dsname, zprop_source_t source,
    uint64_t reservation)
{
        dsl_dataset_t *ds;
        dsl_prop_setarg_t psa;
        int err;

        dsl_prop_setarg_init_uint64(&psa, "refreservation", source,
            &reservation);

        err = dsl_dataset_hold(dsname, FTAG, &ds);
        if (err)
                return (err);

        err = dsl_sync_task_do(ds->ds_dir->dd_pool,
            dsl_dataset_set_reservation_check,
            dsl_dataset_set_reservation_sync, ds, &psa, 0);

        dsl_dataset_rele(ds, FTAG);
        return (err);
}

typedef struct zfs_hold_cleanup_arg {
        dsl_pool_t *dp;
        uint64_t dsobj;
        char htag[MAXNAMELEN];
} zfs_hold_cleanup_arg_t;

static void
dsl_dataset_user_release_onexit(void *arg)
{
        zfs_hold_cleanup_arg_t *ca = arg;

        (void) dsl_dataset_user_release_tmp(ca->dp, ca->dsobj, ca->htag,
            B_TRUE);
        kmem_free(ca, sizeof (zfs_hold_cleanup_arg_t));
}

void
dsl_register_onexit_hold_cleanup(dsl_dataset_t *ds, const char *htag,
    minor_t minor)
{
        zfs_hold_cleanup_arg_t *ca;

        ca = kmem_alloc(sizeof (zfs_hold_cleanup_arg_t), KM_SLEEP);
        ca->dp = ds->ds_dir->dd_pool;
        ca->dsobj = ds->ds_object;
        (void) strlcpy(ca->htag, htag, sizeof (ca->htag));
        VERIFY3U(0, ==, zfs_onexit_add_cb(minor,
            dsl_dataset_user_release_onexit, ca, NULL));
}

static int
dsl_dataset_user_hold_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        struct dsl_ds_holdarg *ha = arg2;
        char *htag = ha->htag;
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        int error = 0;

        if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_USERREFS)
                return (ENOTSUP);

        if (!dsl_dataset_is_snapshot(ds))
                return (EINVAL);

        /* tags must be unique */
        mutex_enter(&ds->ds_lock);
        if (ds->ds_phys->ds_userrefs_obj) {
                error = zap_lookup(mos, ds->ds_phys->ds_userrefs_obj, htag,
                    8, 1, tx);
                if (error == 0)
                        error = EEXIST;
                else if (error == ENOENT)
                        error = 0;
        }
        mutex_exit(&ds->ds_lock);

        if (error == 0 && ha->temphold &&
            strlen(htag) + MAX_TAG_PREFIX_LEN >= MAXNAMELEN)
                error = E2BIG;

        return (error);
}

void
dsl_dataset_user_hold_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = arg1;
        struct dsl_ds_holdarg *ha = arg2;
        char *htag = ha->htag;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        objset_t *mos = dp->dp_meta_objset;
        uint64_t now = gethrestime_sec();
        uint64_t zapobj;

        mutex_enter(&ds->ds_lock);
        if (ds->ds_phys->ds_userrefs_obj == 0) {
                /*
                 * This is the first user hold for this dataset.  Create
                 * the userrefs zap object.
                 */
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                zapobj = ds->ds_phys->ds_userrefs_obj =
                    zap_create(mos, DMU_OT_USERREFS, DMU_OT_NONE, 0, tx);
        } else {
                zapobj = ds->ds_phys->ds_userrefs_obj;
        }
        ds->ds_userrefs++;
        mutex_exit(&ds->ds_lock);

        VERIFY(0 == zap_add(mos, zapobj, htag, 8, 1, &now, tx));

        if (ha->temphold) {
                VERIFY(0 == dsl_pool_user_hold(dp, ds->ds_object,
                    htag, &now, tx));
        }

        spa_history_log_internal(LOG_DS_USER_HOLD,
            dp->dp_spa, tx, "<%s> temp = %d dataset = %llu", htag,
            (int)ha->temphold, ds->ds_object);
}

static int
dsl_dataset_user_hold_one(const char *dsname, void *arg)
{
        struct dsl_ds_holdarg *ha = arg;
        dsl_dataset_t *ds;
        int error;
        char *name;

        /* alloc a buffer to hold dsname@snapname plus terminating NULL */
        name = kmem_asprintf("%s@%s", dsname, ha->snapname);
        error = dsl_dataset_hold(name, ha->dstg, &ds);
        strfree(name);
        if (error == 0) {
                ha->gotone = B_TRUE;
                dsl_sync_task_create(ha->dstg, dsl_dataset_user_hold_check,
                    dsl_dataset_user_hold_sync, ds, ha, 0);
        } else if (error == ENOENT && ha->recursive) {
                error = 0;
        } else {
                (void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
        }
        return (error);
}

int
dsl_dataset_user_hold_for_send(dsl_dataset_t *ds, char *htag,
    boolean_t temphold)
{
        struct dsl_ds_holdarg *ha;
        int error;

        ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);
        ha->htag = htag;
        ha->temphold = temphold;
        error = dsl_sync_task_do(ds->ds_dir->dd_pool,
            dsl_dataset_user_hold_check, dsl_dataset_user_hold_sync,
            ds, ha, 0);
        kmem_free(ha, sizeof (struct dsl_ds_holdarg));

        return (error);
}

int
dsl_dataset_user_hold(char *dsname, char *snapname, char *htag,
    boolean_t recursive, boolean_t temphold, int cleanup_fd)
{
        struct dsl_ds_holdarg *ha;
        dsl_sync_task_t *dst;
        spa_t *spa;
        int error;
        minor_t minor = 0;

        if (cleanup_fd != -1) {
                /* Currently we only support cleanup-on-exit of tempholds. */
                if (!temphold)
                        return (EINVAL);
                error = zfs_onexit_fd_hold(cleanup_fd, &minor);
                if (error)
                        return (error);
        }

        ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);

        (void) strlcpy(ha->failed, dsname, sizeof (ha->failed));

        error = spa_open(dsname, &spa, FTAG);
        if (error) {
                kmem_free(ha, sizeof (struct dsl_ds_holdarg));
                if (cleanup_fd != -1)
                        zfs_onexit_fd_rele(cleanup_fd);
                return (error);
        }

        ha->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
        ha->htag = htag;
        ha->snapname = snapname;
        ha->recursive = recursive;
        ha->temphold = temphold;

        if (recursive) {
                error = dmu_objset_find(dsname, dsl_dataset_user_hold_one,
                    ha, DS_FIND_CHILDREN);
        } else {
                error = dsl_dataset_user_hold_one(dsname, ha);
        }
        if (error == 0)
                error = dsl_sync_task_group_wait(ha->dstg);

        for (dst = list_head(&ha->dstg->dstg_tasks); dst;
            dst = list_next(&ha->dstg->dstg_tasks, dst)) {
                dsl_dataset_t *ds = dst->dst_arg1;

                if (dst->dst_err) {
                        dsl_dataset_name(ds, ha->failed);
                        *strchr(ha->failed, '@') = '\0';
                } else if (error == 0 && minor != 0 && temphold) {
                        /*
                         * If this hold is to be released upon process exit,
                         * register that action now.
                         */
                        dsl_register_onexit_hold_cleanup(ds, htag, minor);
                }
                dsl_dataset_rele(ds, ha->dstg);
        }

        if (error == 0 && recursive && !ha->gotone)
                error = ENOENT;

        if (error)
                (void) strlcpy(dsname, ha->failed, sizeof (ha->failed));

        dsl_sync_task_group_destroy(ha->dstg);

        kmem_free(ha, sizeof (struct dsl_ds_holdarg));
        spa_close(spa, FTAG);
        if (cleanup_fd != -1)
                zfs_onexit_fd_rele(cleanup_fd);
        return (error);
}

struct dsl_ds_releasearg {
        dsl_dataset_t *ds;
        const char *htag;
        boolean_t own;          /* do we own or just hold ds? */
};

static int
dsl_dataset_release_might_destroy(dsl_dataset_t *ds, const char *htag,
    boolean_t *might_destroy)
{
        objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
        uint64_t zapobj;
        uint64_t tmp;
        int error;

        *might_destroy = B_FALSE;

        mutex_enter(&ds->ds_lock);
        zapobj = ds->ds_phys->ds_userrefs_obj;
        if (zapobj == 0) {
                /* The tag can't possibly exist */
                mutex_exit(&ds->ds_lock);
                return (ESRCH);
        }

        /* Make sure the tag exists */
        error = zap_lookup(mos, zapobj, htag, 8, 1, &tmp);
        if (error) {
                mutex_exit(&ds->ds_lock);
                if (error == ENOENT)
                        error = ESRCH;
                return (error);
        }

        if (ds->ds_userrefs == 1 && ds->ds_phys->ds_num_children == 1 &&
            DS_IS_DEFER_DESTROY(ds))
                *might_destroy = B_TRUE;

        mutex_exit(&ds->ds_lock);
        return (0);
}

static int
dsl_dataset_user_release_check(void *arg1, void *tag, dmu_tx_t *tx)
{
        struct dsl_ds_releasearg *ra = arg1;
        dsl_dataset_t *ds = ra->ds;
        boolean_t might_destroy;
        int error;

        if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_USERREFS)
                return (ENOTSUP);

        error = dsl_dataset_release_might_destroy(ds, ra->htag, &might_destroy);
        if (error)
                return (error);

        if (might_destroy) {
                struct dsl_ds_destroyarg dsda = {0};

                if (dmu_tx_is_syncing(tx)) {
                        /*
                         * If we're not prepared to remove the snapshot,
                         * we can't allow the release to happen right now.
                         */
                        if (!ra->own)
                                return (EBUSY);
                }
                dsda.ds = ds;
                dsda.releasing = B_TRUE;
                return (dsl_dataset_destroy_check(&dsda, tag, tx));
        }

        return (0);
}

static void
dsl_dataset_user_release_sync(void *arg1, void *tag, dmu_tx_t *tx)
{
        struct dsl_ds_releasearg *ra = arg1;
        dsl_dataset_t *ds = ra->ds;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        objset_t *mos = dp->dp_meta_objset;
        uint64_t zapobj;
        uint64_t dsobj = ds->ds_object;
        uint64_t refs;
        int error;

        mutex_enter(&ds->ds_lock);
        ds->ds_userrefs--;
        refs = ds->ds_userrefs;
        mutex_exit(&ds->ds_lock);
        error = dsl_pool_user_release(dp, ds->ds_object, ra->htag, tx);
        VERIFY(error == 0 || error == ENOENT);
        zapobj = ds->ds_phys->ds_userrefs_obj;
        VERIFY(0 == zap_remove(mos, zapobj, ra->htag, tx));

        spa_history_log_internal(LOG_DS_USER_RELEASE,
            dp->dp_spa, tx, "<%s> %lld dataset = %llu",
            ra->htag, (longlong_t)refs, dsobj);

        if (ds->ds_userrefs == 0 && ds->ds_phys->ds_num_children == 1 &&
            DS_IS_DEFER_DESTROY(ds)) {
                struct dsl_ds_destroyarg dsda = {0};

                ASSERT(ra->own);
                dsda.ds = ds;
                dsda.releasing = B_TRUE;
                /* We already did the destroy_check */
                dsl_dataset_destroy_sync(&dsda, tag, tx);
        }
}

static int
dsl_dataset_user_release_one(const char *dsname, void *arg)
{
        struct dsl_ds_holdarg *ha = arg;
        struct dsl_ds_releasearg *ra;
        dsl_dataset_t *ds;
        int error;
        void *dtag = ha->dstg;
        char *name;
        boolean_t own = B_FALSE;
        boolean_t might_destroy;

        /* alloc a buffer to hold dsname@snapname, plus the terminating NULL */
        name = kmem_asprintf("%s@%s", dsname, ha->snapname);
        error = dsl_dataset_hold(name, dtag, &ds);
        strfree(name);
        if (error == ENOENT && ha->recursive)
                return (0);
        (void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
        if (error)
                return (error);

        ha->gotone = B_TRUE;

        ASSERT(dsl_dataset_is_snapshot(ds));

        error = dsl_dataset_release_might_destroy(ds, ha->htag, &might_destroy);
        if (error) {
                dsl_dataset_rele(ds, dtag);
                return (error);
        }

        if (might_destroy) {
#ifdef _KERNEL
                name = kmem_asprintf("%s@%s", dsname, ha->snapname);
                error = zfs_unmount_snap(name, NULL);
                strfree(name);
                if (error) {
                        dsl_dataset_rele(ds, dtag);
                        return (error);
                }
#endif
                if (!dsl_dataset_tryown(ds, B_TRUE, dtag)) {
                        dsl_dataset_rele(ds, dtag);
                        return (EBUSY);
                } else {
                        own = B_TRUE;
                        dsl_dataset_make_exclusive(ds, dtag);
                }
        }

        ra = kmem_alloc(sizeof (struct dsl_ds_releasearg), KM_SLEEP);
        ra->ds = ds;
        ra->htag = ha->htag;
        ra->own = own;
        dsl_sync_task_create(ha->dstg, dsl_dataset_user_release_check,
            dsl_dataset_user_release_sync, ra, dtag, 0);

        return (0);
}

int
dsl_dataset_user_release(char *dsname, char *snapname, char *htag,
    boolean_t recursive)
{
        struct dsl_ds_holdarg *ha;
        dsl_sync_task_t *dst;
        spa_t *spa;
        int error;

top:
        ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);

        (void) strlcpy(ha->failed, dsname, sizeof (ha->failed));

        error = spa_open(dsname, &spa, FTAG);
        if (error) {
                kmem_free(ha, sizeof (struct dsl_ds_holdarg));
                return (error);
        }

        ha->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
        ha->htag = htag;
        ha->snapname = snapname;
        ha->recursive = recursive;
        if (recursive) {
                error = dmu_objset_find(dsname, dsl_dataset_user_release_one,
                    ha, DS_FIND_CHILDREN);
        } else {
                error = dsl_dataset_user_release_one(dsname, ha);
        }
        if (error == 0)
                error = dsl_sync_task_group_wait(ha->dstg);

        for (dst = list_head(&ha->dstg->dstg_tasks); dst;
            dst = list_next(&ha->dstg->dstg_tasks, dst)) {
                struct dsl_ds_releasearg *ra = dst->dst_arg1;
                dsl_dataset_t *ds = ra->ds;

                if (dst->dst_err)
                        dsl_dataset_name(ds, ha->failed);

                if (ra->own)
                        dsl_dataset_disown(ds, ha->dstg);
                else
                        dsl_dataset_rele(ds, ha->dstg);

                kmem_free(ra, sizeof (struct dsl_ds_releasearg));
        }

        if (error == 0 && recursive && !ha->gotone)
                error = ENOENT;

        if (error && error != EBUSY)
                (void) strlcpy(dsname, ha->failed, sizeof (ha->failed));

        dsl_sync_task_group_destroy(ha->dstg);
        kmem_free(ha, sizeof (struct dsl_ds_holdarg));
        spa_close(spa, FTAG);

        /*
         * We can get EBUSY if we were racing with deferred destroy and
         * dsl_dataset_user_release_check() hadn't done the necessary
         * open context setup.  We can also get EBUSY if we're racing
         * with destroy and that thread is the ds_owner.  Either way
         * the busy condition should be transient, and we should retry
         * the release operation.
         */
        if (error == EBUSY)
                goto top;

        return (error);
}

int
dsl_dataset_user_release_tmp(dsl_pool_t *dp, uint64_t dsobj, char *htag,
    boolean_t retry)
{
        dsl_dataset_t *ds;
        char *snap;
        char *name;
        int namelen;
        int error;

        do {
                rw_enter(&dp->dp_config_rwlock, RW_READER);
                error = dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds);
                rw_exit(&dp->dp_config_rwlock);
                if (error)
                        return (error);
                namelen = dsl_dataset_namelen(ds)+1;
                name = kmem_alloc(namelen, KM_SLEEP);
                dsl_dataset_name(ds, name);
                dsl_dataset_rele(ds, FTAG);

                snap = strchr(name, '@');
                *snap = '\0';
                ++snap;
                error = dsl_dataset_user_release(name, snap, htag, B_FALSE);
                kmem_free(name, namelen);

                /*
                 * The object can't have been destroyed because we have a hold,
                 * but it might have been renamed, resulting in ENOENT.  Retry
                 * if we've been requested to do so.
                 *
                 * It would be nice if we could use the dsobj all the way
                 * through and avoid ENOENT entirely.  But we might need to
                 * unmount the snapshot, and there's currently no way to lookup
                 * a vfsp using a ZFS object id.
                 */
        } while ((error == ENOENT) && retry);

        return (error);
}

int
dsl_dataset_get_holds(const char *dsname, nvlist_t **nvp)
{
        dsl_dataset_t *ds;
        int err;

        err = dsl_dataset_hold(dsname, FTAG, &ds);
        if (err)
                return (err);

        VERIFY(0 == nvlist_alloc(nvp, NV_UNIQUE_NAME, KM_SLEEP));
        if (ds->ds_phys->ds_userrefs_obj != 0) {
                zap_attribute_t *za;
                zap_cursor_t zc;

                za = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
                for (zap_cursor_init(&zc, ds->ds_dir->dd_pool->dp_meta_objset,
                    ds->ds_phys->ds_userrefs_obj);
                    zap_cursor_retrieve(&zc, za) == 0;
                    zap_cursor_advance(&zc)) {
                        VERIFY(0 == nvlist_add_uint64(*nvp, za->za_name,
                            za->za_first_integer));
                }
                zap_cursor_fini(&zc);
                kmem_free(za, sizeof (zap_attribute_t));
        }
        dsl_dataset_rele(ds, FTAG);
        return (0);
}

/* ARGSUSED */
int
dsl_destroy_inconsistent(const char *dsname, void *arg)
{
        dsl_dataset_t *ds;

        if (dsl_dataset_own(dsname, B_TRUE, FTAG, &ds) == 0) {
                if (DS_IS_INCONSISTENT(ds))
                        (void) dsl_dataset_destroy(ds, FTAG, B_FALSE);
                else
                        dsl_dataset_disown(ds, FTAG);
        }
        return (0);
}

/*
 * Return (in *usedp) the amount of space written in new that is not
 * present in oldsnap.  New may be a snapshot or the head.  Old must be
 * a snapshot before new, in new's filesystem (or its origin).  If not then
 * fail and return EINVAL.
 *
 * The written space is calculated by considering two components:  First, we
 * ignore any freed space, and calculate the written as new's used space
 * minus old's used space.  Next, we add in the amount of space that was freed
 * between the two snapshots, thus reducing new's used space relative to old's.
 * Specifically, this is the space that was born before old->ds_creation_txg,
 * and freed before new (ie. on new's deadlist or a previous deadlist).
 *
 * space freed                         [---------------------]
 * snapshots                       ---O-------O--------O-------O------
 *                                         oldsnap            new
 */
int
dsl_dataset_space_written(dsl_dataset_t *oldsnap, dsl_dataset_t *new,
    uint64_t *usedp, uint64_t *compp, uint64_t *uncompp)
{
        int err = 0;
        uint64_t snapobj;
        dsl_pool_t *dp = new->ds_dir->dd_pool;

        *usedp = 0;
        *usedp += new->ds_phys->ds_referenced_bytes;
        *usedp -= oldsnap->ds_phys->ds_referenced_bytes;

        *compp = 0;
        *compp += new->ds_phys->ds_compressed_bytes;
        *compp -= oldsnap->ds_phys->ds_compressed_bytes;

        *uncompp = 0;
        *uncompp += new->ds_phys->ds_uncompressed_bytes;
        *uncompp -= oldsnap->ds_phys->ds_uncompressed_bytes;

        rw_enter(&dp->dp_config_rwlock, RW_READER);
        snapobj = new->ds_object;
        while (snapobj != oldsnap->ds_object) {
                dsl_dataset_t *snap;
                uint64_t used, comp, uncomp;

                if (snapobj == new->ds_object) {
                        snap = new;
                } else {
                        err = dsl_dataset_hold_obj(dp, snapobj, FTAG, &snap);
                        if (err != 0)
                                break;
                }

                if (snap->ds_phys->ds_prev_snap_txg ==
                    oldsnap->ds_phys->ds_creation_txg) {
                        /*
                         * The blocks in the deadlist can not be born after
                         * ds_prev_snap_txg, so get the whole deadlist space,
                         * which is more efficient (especially for old-format
                         * deadlists).  Unfortunately the deadlist code
                         * doesn't have enough information to make this
                         * optimization itself.
                         */
                        dsl_deadlist_space(&snap->ds_deadlist,
                            &used, &comp, &uncomp);
                } else {
                        dsl_deadlist_space_range(&snap->ds_deadlist,
                            0, oldsnap->ds_phys->ds_creation_txg,
                            &used, &comp, &uncomp);
                }
                *usedp += used;
                *compp += comp;
                *uncompp += uncomp;

                /*
                 * If we get to the beginning of the chain of snapshots
                 * (ds_prev_snap_obj == 0) before oldsnap, then oldsnap
                 * was not a snapshot of/before new.
                 */
                snapobj = snap->ds_phys->ds_prev_snap_obj;
                if (snap != new)
                        dsl_dataset_rele(snap, FTAG);
                if (snapobj == 0) {
                        err = EINVAL;
                        break;
                }

        }
        rw_exit(&dp->dp_config_rwlock);
        return (err);
}

/*
 * Return (in *usedp) the amount of space that will be reclaimed if firstsnap,
 * lastsnap, and all snapshots in between are deleted.
 *
 * blocks that would be freed            [---------------------------]
 * snapshots                       ---O-------O--------O-------O--------O
 *                                        firstsnap        lastsnap
 *
 * This is the set of blocks that were born after the snap before firstsnap,
 * (birth > firstsnap->prev_snap_txg) and died before the snap after the
 * last snap (ie, is on lastsnap->ds_next->ds_deadlist or an earlier deadlist).
 * We calculate this by iterating over the relevant deadlists (from the snap
 * after lastsnap, backward to the snap after firstsnap), summing up the
 * space on the deadlist that was born after the snap before firstsnap.
 */
int
dsl_dataset_space_wouldfree(dsl_dataset_t *firstsnap,
    dsl_dataset_t *lastsnap,
    uint64_t *usedp, uint64_t *compp, uint64_t *uncompp)
{
        int err = 0;
        uint64_t snapobj;
        dsl_pool_t *dp = firstsnap->ds_dir->dd_pool;

        ASSERT(dsl_dataset_is_snapshot(firstsnap));
        ASSERT(dsl_dataset_is_snapshot(lastsnap));

        /*
         * Check that the snapshots are in the same dsl_dir, and firstsnap
         * is before lastsnap.
         */
        if (firstsnap->ds_dir != lastsnap->ds_dir ||
            firstsnap->ds_phys->ds_creation_txg >
            lastsnap->ds_phys->ds_creation_txg)
                return (EINVAL);

        *usedp = *compp = *uncompp = 0;

        rw_enter(&dp->dp_config_rwlock, RW_READER);
        snapobj = lastsnap->ds_phys->ds_next_snap_obj;
        while (snapobj != firstsnap->ds_object) {
                dsl_dataset_t *ds;
                uint64_t used, comp, uncomp;

                err = dsl_dataset_hold_obj(dp, snapobj, FTAG, &ds);
                if (err != 0)
                        break;

                dsl_deadlist_space_range(&ds->ds_deadlist,
                    firstsnap->ds_phys->ds_prev_snap_txg, UINT64_MAX,
                    &used, &comp, &uncomp);
                *usedp += used;
                *compp += comp;
                *uncompp += uncomp;

                snapobj = ds->ds_phys->ds_prev_snap_obj;
                ASSERT3U(snapobj, !=, 0);
                dsl_dataset_rele(ds, FTAG);
        }
        rw_exit(&dp->dp_config_rwlock);
        return (err);
}