5960 zfs recv should prefetch indirect blocks

[illumos-gate.git] / usr / src / uts / common / fs / zfs / dsl_destroy.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
 * Copyright (c) 2013 Steven Hartland. All rights reserved.
 * Copyright (c) 2013 by Joyent, Inc. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/dsl_userhold.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_synctask.h>
#include <sys/dmu_tx.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_dir.h>
#include <sys/dmu_traverse.h>
#include <sys/dsl_scan.h>
#include <sys/dmu_objset.h>
#include <sys/zap.h>
#include <sys/zfeature.h>
#include <sys/zfs_ioctl.h>
#include <sys/dsl_deleg.h>
#include <sys/dmu_impl.h>

typedef struct dmu_snapshots_destroy_arg {
        nvlist_t *dsda_snaps;
        nvlist_t *dsda_successful_snaps;
        boolean_t dsda_defer;
        nvlist_t *dsda_errlist;
} dmu_snapshots_destroy_arg_t;

int
dsl_destroy_snapshot_check_impl(dsl_dataset_t *ds, boolean_t defer)
{
        if (!ds->ds_is_snapshot)
                return (SET_ERROR(EINVAL));

        if (dsl_dataset_long_held(ds))
                return (SET_ERROR(EBUSY));

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

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

        /*
         * Can't delete a branch point.
         */
        if (dsl_dataset_phys(ds)->ds_num_children > 1)
                return (SET_ERROR(EEXIST));

        return (0);
}

static int
dsl_destroy_snapshot_check(void *arg, dmu_tx_t *tx)
{
        dmu_snapshots_destroy_arg_t *dsda = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        nvpair_t *pair;
        int error = 0;

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

        for (pair = nvlist_next_nvpair(dsda->dsda_snaps, NULL);
            pair != NULL; pair = nvlist_next_nvpair(dsda->dsda_snaps, pair)) {
                dsl_dataset_t *ds;

                error = dsl_dataset_hold(dp, nvpair_name(pair),
                    FTAG, &ds);

                /*
                 * If the snapshot does not exist, silently ignore it
                 * (it's "already destroyed").
                 */
                if (error == ENOENT)
                        continue;

                if (error == 0) {
                        error = dsl_destroy_snapshot_check_impl(ds,
                            dsda->dsda_defer);
                        dsl_dataset_rele(ds, FTAG);
                }

                if (error == 0) {
                        fnvlist_add_boolean(dsda->dsda_successful_snaps,
                            nvpair_name(pair));
                } else {
                        fnvlist_add_int32(dsda->dsda_errlist,
                            nvpair_name(pair), error);
                }
        }

        pair = nvlist_next_nvpair(dsda->dsda_errlist, NULL);
        if (pair != NULL)
                return (fnvpair_value_int32(pair));

        return (0);
}

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;

        ASSERT(!BP_IS_HOLE(bp));

        if (bp->blk_birth <= dsl_dataset_phys(poa->ds)->ds_prev_snap_txg) {
                dsl_deadlist_insert(&poa->ds->ds_deadlist, bp, tx);
                if (poa->ds_prev && !poa->after_branch_point &&
                    bp->blk_birth >
                    dsl_dataset_phys(poa->ds_prev)->ds_prev_snap_txg) {
                        dsl_dataset_phys(poa->ds_prev)->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;
        uint64_t deadlist_obj;

        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);
        VERIFY0(bpobj_iterate(&ds_next->ds_deadlist.dl_bpobj,
            process_old_cb, &poa, tx));
        VERIFY0(zio_wait(poa.pio));
        ASSERT3U(poa.used, ==, dsl_dataset_phys(ds)->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);
        deadlist_obj = dsl_dataset_phys(ds)->ds_deadlist_obj;
        dsl_dataset_phys(ds)->ds_deadlist_obj =
            dsl_dataset_phys(ds_next)->ds_deadlist_obj;
        dsl_dataset_phys(ds_next)->ds_deadlist_obj = deadlist_obj;
        dsl_deadlist_open(&ds->ds_deadlist, mos,
            dsl_dataset_phys(ds)->ds_deadlist_obj);
        dsl_deadlist_open(&ds_next->ds_deadlist, mos,
            dsl_dataset_phys(ds_next)->ds_deadlist_obj);
}

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 dsl_deadlist_remove_key() is a no-op so it
         * doesn't matter.
         */
        if (dsl_dir_phys(ds->ds_dir)->dd_clones == 0)
                return;

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

                VERIFY0(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);
}

void
dsl_destroy_snapshot_sync_impl(dsl_dataset_t *ds, boolean_t defer, dmu_tx_t *tx)
{
        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;
        uint64_t obj;

        ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));
        ASSERT3U(dsl_dataset_phys(ds)->ds_bp.blk_birth, <=, tx->tx_txg);
        ASSERT(refcount_is_zero(&ds->ds_longholds));

        if (defer &&
            (ds->ds_userrefs > 0 ||
            dsl_dataset_phys(ds)->ds_num_children > 1)) {
                ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                dsl_dataset_phys(ds)->ds_flags |= DS_FLAG_DEFER_DESTROY;
                spa_history_log_internal_ds(ds, "defer_destroy", tx, "");
                return;
        }

        ASSERT3U(dsl_dataset_phys(ds)->ds_num_children, <=, 1);

        /* We need to log before removing it from the namespace. */
        spa_history_log_internal_ds(ds, "destroy", tx, "");

        dsl_scan_ds_destroyed(ds, tx);

        obj = ds->ds_object;

        if (ds->ds_large_blocks) {
                ASSERT0(zap_contains(mos, obj, DS_FIELD_LARGE_BLOCKS));
                spa_feature_decr(dp->dp_spa, SPA_FEATURE_LARGE_BLOCKS, tx);
        }
        if (dsl_dataset_phys(ds)->ds_prev_snap_obj != 0) {
                ASSERT3P(ds->ds_prev, ==, NULL);
                VERIFY0(dsl_dataset_hold_obj(dp,
                    dsl_dataset_phys(ds)->ds_prev_snap_obj, FTAG, &ds_prev));
                after_branch_point =
                    (dsl_dataset_phys(ds_prev)->ds_next_snap_obj != obj);

                dmu_buf_will_dirty(ds_prev->ds_dbuf, tx);
                if (after_branch_point &&
                    dsl_dataset_phys(ds_prev)->ds_next_clones_obj != 0) {
                        dsl_dataset_remove_from_next_clones(ds_prev, obj, tx);
                        if (dsl_dataset_phys(ds)->ds_next_snap_obj != 0) {
                                VERIFY0(zap_add_int(mos,
                                    dsl_dataset_phys(ds_prev)->
                                    ds_next_clones_obj,
                                    dsl_dataset_phys(ds)->ds_next_snap_obj,
                                    tx));
                        }
                }
                if (!after_branch_point) {
                        dsl_dataset_phys(ds_prev)->ds_next_snap_obj =
                            dsl_dataset_phys(ds)->ds_next_snap_obj;
                }
        }

        dsl_dataset_t *ds_next;
        uint64_t old_unique;
        uint64_t used = 0, comp = 0, uncomp = 0;

        VERIFY0(dsl_dataset_hold_obj(dp,
            dsl_dataset_phys(ds)->ds_next_snap_obj, FTAG, &ds_next));
        ASSERT3U(dsl_dataset_phys(ds_next)->ds_prev_snap_obj, ==, obj);

        old_unique = dsl_dataset_phys(ds_next)->ds_unique_bytes;

        dmu_buf_will_dirty(ds_next->ds_dbuf, tx);
        dsl_dataset_phys(ds_next)->ds_prev_snap_obj =
            dsl_dataset_phys(ds)->ds_prev_snap_obj;
        dsl_dataset_phys(ds_next)->ds_prev_snap_txg =
            dsl_dataset_phys(ds)->ds_prev_snap_txg;
        ASSERT3U(dsl_dataset_phys(ds)->ds_prev_snap_txg, ==,
            ds_prev ? dsl_dataset_phys(ds_prev)->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,
                            dsl_dataset_phys(ds_prev)->ds_prev_snap_txg,
                            dsl_dataset_phys(ds)->ds_prev_snap_txg,
                            &used, &comp, &uncomp);
                        dsl_dataset_phys(ds_prev)->ds_unique_bytes += used;
                }

                /* Adjust snapused. */
                dsl_deadlist_space_range(&ds_next->ds_deadlist,
                    dsl_dataset_phys(ds)->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, dsl_dataset_phys(ds)->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,
                    dsl_dataset_phys(ds)->ds_deadlist_obj, tx);
        }
        dsl_deadlist_close(&ds->ds_deadlist);
        dsl_deadlist_free(mos, dsl_dataset_phys(ds)->ds_deadlist_obj, tx);
        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        dsl_dataset_phys(ds)->ds_deadlist_obj = 0;

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

        if (ds_next->ds_is_snapshot) {
                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).
                 */
                VERIFY0(dsl_dataset_hold_obj(dp,
                    dsl_dataset_phys(ds_next)->ds_next_snap_obj,
                    FTAG, &ds_nextnext));
                dsl_deadlist_space_range(&ds_nextnext->ds_deadlist,
                    dsl_dataset_phys(ds)->ds_prev_snap_txg,
                    dsl_dataset_phys(ds)->ds_creation_txg,
                    &used, &comp, &uncomp);
                dsl_dataset_phys(ds_next)->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;
                VERIFY0(dsl_dataset_hold_obj(dp,
                    dsl_dir_phys(ds->ds_dir)->dd_head_dataset_obj, FTAG, &hds));
                dsl_deadlist_remove_key(&hds->ds_deadlist,
                    dsl_dataset_phys(ds)->ds_creation_txg, tx);
                dsl_dataset_rele(hds, FTAG);

        } else {
                ASSERT3P(ds_next->ds_prev, ==, ds);
                dsl_dataset_rele(ds_next->ds_prev, ds_next);
                ds_next->ds_prev = NULL;
                if (ds_prev) {
                        VERIFY0(dsl_dataset_hold_obj(dp,
                            dsl_dataset_phys(ds)->ds_prev_snap_obj,
                            ds_next, &ds_next->ds_prev));
                }

                dsl_dataset_recalc_head_uniq(ds_next);

                /*
                 * Reduce the amount of our unconsumed 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 =
                            dsl_dataset_phys(ds_next)->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);

        /*
         * 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;
        }

        /* remove from snapshot namespace */
        dsl_dataset_t *ds_head;
        ASSERT(dsl_dataset_phys(ds)->ds_snapnames_zapobj == 0);
        VERIFY0(dsl_dataset_hold_obj(dp,
            dsl_dir_phys(ds->ds_dir)->dd_head_dataset_obj, FTAG, &ds_head));
        VERIFY0(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
        VERIFY0(dsl_dataset_snap_remove(ds_head, ds->ds_snapname, tx, B_TRUE));
        dsl_dataset_rele(ds_head, FTAG);

        if (ds_prev != NULL)
                dsl_dataset_rele(ds_prev, FTAG);

        spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);

        if (dsl_dataset_phys(ds)->ds_next_clones_obj != 0) {
                uint64_t count;
                ASSERT0(zap_count(mos,
                    dsl_dataset_phys(ds)->ds_next_clones_obj, &count) &&
                    count == 0);
                VERIFY0(dmu_object_free(mos,
                    dsl_dataset_phys(ds)->ds_next_clones_obj, tx));
        }
        if (dsl_dataset_phys(ds)->ds_props_obj != 0)
                VERIFY0(zap_destroy(mos, dsl_dataset_phys(ds)->ds_props_obj,
                    tx));
        if (dsl_dataset_phys(ds)->ds_userrefs_obj != 0)
                VERIFY0(zap_destroy(mos, dsl_dataset_phys(ds)->ds_userrefs_obj,
                    tx));
        dsl_dir_rele(ds->ds_dir, ds);
        ds->ds_dir = NULL;
        dmu_object_free_zapified(mos, obj, tx);
}

static void
dsl_destroy_snapshot_sync(void *arg, dmu_tx_t *tx)
{
        dmu_snapshots_destroy_arg_t *dsda = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        nvpair_t *pair;

        for (pair = nvlist_next_nvpair(dsda->dsda_successful_snaps, NULL);
            pair != NULL;
            pair = nvlist_next_nvpair(dsda->dsda_successful_snaps, pair)) {
                dsl_dataset_t *ds;

                VERIFY0(dsl_dataset_hold(dp, nvpair_name(pair), FTAG, &ds));

                dsl_destroy_snapshot_sync_impl(ds, dsda->dsda_defer, tx);
                dsl_dataset_rele(ds, FTAG);
        }
}

/*
 * The semantics of this function are described in the comment above
 * lzc_destroy_snaps().  To summarize:
 *
 * The snapshots must all be in the same pool.
 *
 * Snapshots that don't exist will be silently ignored (considered to be
 * "already deleted").
 *
 * On success, all snaps will be destroyed and this will return 0.
 * On failure, no snaps will be destroyed, the errlist will be filled in,
 * and this will return an errno.
 */
int
dsl_destroy_snapshots_nvl(nvlist_t *snaps, boolean_t defer,
    nvlist_t *errlist)
{
        dmu_snapshots_destroy_arg_t dsda;
        int error;
        nvpair_t *pair;

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

        dsda.dsda_snaps = snaps;
        dsda.dsda_successful_snaps = fnvlist_alloc();
        dsda.dsda_defer = defer;
        dsda.dsda_errlist = errlist;

        error = dsl_sync_task(nvpair_name(pair),
            dsl_destroy_snapshot_check, dsl_destroy_snapshot_sync,
            &dsda, 0, ZFS_SPACE_CHECK_NONE);
        fnvlist_free(dsda.dsda_successful_snaps);

        return (error);
}

int
dsl_destroy_snapshot(const char *name, boolean_t defer)
{
        int error;
        nvlist_t *nvl = fnvlist_alloc();
        nvlist_t *errlist = fnvlist_alloc();

        fnvlist_add_boolean(nvl, name);
        error = dsl_destroy_snapshots_nvl(nvl, defer, errlist);
        fnvlist_free(errlist);
        fnvlist_free(nvl);
        return (error);
}

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,
    const zbookmark_phys_t *zb, const dnode_phys_t *dnp, void *arg)
{
        struct killarg *ka = arg;
        dmu_tx_t *tx = ka->tx;

        if (bp == NULL || BP_IS_HOLE(bp) || BP_IS_EMBEDDED(bp))
                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, >,
                    dsl_dataset_phys(ka->ds)->ds_prev_snap_txg);
                (void) dsl_dataset_block_kill(ka->ds, bp, tx, B_FALSE);
        }

        return (0);
}

static void
old_synchronous_dataset_destroy(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        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;
        VERIFY0(traverse_dataset(ds,
            dsl_dataset_phys(ds)->ds_prev_snap_txg, TRAVERSE_POST,
            kill_blkptr, &ka));
        ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) ||
            dsl_dataset_phys(ds)->ds_unique_bytes == 0);
}

typedef struct dsl_destroy_head_arg {
        const char *ddha_name;
} dsl_destroy_head_arg_t;

int
dsl_destroy_head_check_impl(dsl_dataset_t *ds, int expected_holds)
{
        int error;
        uint64_t count;
        objset_t *mos;

        ASSERT(!ds->ds_is_snapshot);
        if (ds->ds_is_snapshot)
                return (SET_ERROR(EINVAL));

        if (refcount_count(&ds->ds_longholds) != expected_holds)
                return (SET_ERROR(EBUSY));

        mos = ds->ds_dir->dd_pool->dp_meta_objset;

        /*
         * 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 &&
            dsl_dataset_phys(ds->ds_prev)->ds_next_snap_obj == ds->ds_object)
                return (SET_ERROR(EBUSY));

        /*
         * Can't delete if there are children of this fs.
         */
        error = zap_count(mos,
            dsl_dir_phys(ds->ds_dir)->dd_child_dir_zapobj, &count);
        if (error != 0)
                return (error);
        if (count != 0)
                return (SET_ERROR(EEXIST));

        if (dsl_dir_is_clone(ds->ds_dir) && DS_IS_DEFER_DESTROY(ds->ds_prev) &&
            dsl_dataset_phys(ds->ds_prev)->ds_num_children == 2 &&
            ds->ds_prev->ds_userrefs == 0) {
                /* We need to remove the origin snapshot as well. */
                if (!refcount_is_zero(&ds->ds_prev->ds_longholds))
                        return (SET_ERROR(EBUSY));
        }
        return (0);
}

static int
dsl_destroy_head_check(void *arg, dmu_tx_t *tx)
{
        dsl_destroy_head_arg_t *ddha = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        dsl_dataset_t *ds;
        int error;

        error = dsl_dataset_hold(dp, ddha->ddha_name, FTAG, &ds);
        if (error != 0)
                return (error);

        error = dsl_destroy_head_check_impl(ds, 0);
        dsl_dataset_rele(ds, FTAG);
        return (error);
}

static void
dsl_dir_destroy_sync(uint64_t ddobj, dmu_tx_t *tx)
{
        dsl_dir_t *dd;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        objset_t *mos = dp->dp_meta_objset;
        dd_used_t t;

        ASSERT(RRW_WRITE_HELD(&dmu_tx_pool(tx)->dp_config_rwlock));

        VERIFY0(dsl_dir_hold_obj(dp, ddobj, NULL, FTAG, &dd));

        ASSERT0(dsl_dir_phys(dd)->dd_head_dataset_obj);

        /*
         * Decrement the filesystem count for all parent filesystems.
         *
         * When we receive an incremental stream into a filesystem that already
         * exists, a temporary clone is created.  We never count this temporary
         * clone, whose name begins with a '%'.
         */
        if (dd->dd_myname[0] != '%' && dd->dd_parent != NULL)
                dsl_fs_ss_count_adjust(dd->dd_parent, -1,
                    DD_FIELD_FILESYSTEM_COUNT, tx);

        /*
         * Remove our reservation. The impl() routine avoids setting the
         * actual property, which would require the (already destroyed) ds.
         */
        dsl_dir_set_reservation_sync_impl(dd, 0, tx);

        ASSERT0(dsl_dir_phys(dd)->dd_used_bytes);
        ASSERT0(dsl_dir_phys(dd)->dd_reserved);
        for (t = 0; t < DD_USED_NUM; t++)
                ASSERT0(dsl_dir_phys(dd)->dd_used_breakdown[t]);

        VERIFY0(zap_destroy(mos, dsl_dir_phys(dd)->dd_child_dir_zapobj, tx));
        VERIFY0(zap_destroy(mos, dsl_dir_phys(dd)->dd_props_zapobj, tx));
        VERIFY0(dsl_deleg_destroy(mos, dsl_dir_phys(dd)->dd_deleg_zapobj, tx));
        VERIFY0(zap_remove(mos,
            dsl_dir_phys(dd->dd_parent)->dd_child_dir_zapobj,
            dd->dd_myname, tx));

        dsl_dir_rele(dd, FTAG);
        dmu_object_free_zapified(mos, ddobj, tx);
}

void
dsl_destroy_head_sync_impl(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        dsl_pool_t *dp = dmu_tx_pool(tx);
        objset_t *mos = dp->dp_meta_objset;
        uint64_t obj, ddobj, prevobj = 0;
        boolean_t rmorigin;

        ASSERT3U(dsl_dataset_phys(ds)->ds_num_children, <=, 1);
        ASSERT(ds->ds_prev == NULL ||
            dsl_dataset_phys(ds->ds_prev)->ds_next_snap_obj != ds->ds_object);
        ASSERT3U(dsl_dataset_phys(ds)->ds_bp.blk_birth, <=, tx->tx_txg);
        ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));

        /* We need to log before removing it from the namespace. */
        spa_history_log_internal_ds(ds, "destroy", tx, "");

        rmorigin = (dsl_dir_is_clone(ds->ds_dir) &&
            DS_IS_DEFER_DESTROY(ds->ds_prev) &&
            dsl_dataset_phys(ds->ds_prev)->ds_num_children == 2 &&
            ds->ds_prev->ds_userrefs == 0);

        /* Remove our reservation. */
        if (ds->ds_reserved != 0) {
                dsl_dataset_set_refreservation_sync_impl(ds,
                    (ZPROP_SRC_NONE | ZPROP_SRC_LOCAL | ZPROP_SRC_RECEIVED),
                    0, tx);
                ASSERT0(ds->ds_reserved);
        }

        if (ds->ds_large_blocks)
                spa_feature_decr(dp->dp_spa, SPA_FEATURE_LARGE_BLOCKS, tx);

        dsl_scan_ds_destroyed(ds, tx);

        obj = ds->ds_object;

        if (dsl_dataset_phys(ds)->ds_prev_snap_obj != 0) {
                /* This is a clone */
                ASSERT(ds->ds_prev != NULL);
                ASSERT3U(dsl_dataset_phys(ds->ds_prev)->ds_next_snap_obj, !=,
                    obj);
                ASSERT0(dsl_dataset_phys(ds)->ds_next_snap_obj);

                dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
                if (dsl_dataset_phys(ds->ds_prev)->ds_next_clones_obj != 0) {
                        dsl_dataset_remove_from_next_clones(ds->ds_prev,
                            obj, tx);
                }

                ASSERT3U(dsl_dataset_phys(ds->ds_prev)->ds_num_children, >, 1);
                dsl_dataset_phys(ds->ds_prev)->ds_num_children--;
        }

        /*
         * 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, dsl_dataset_phys(ds)->ds_deadlist_obj, tx);
        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        dsl_dataset_phys(ds)->ds_deadlist_obj = 0;

        objset_t *os;
        VERIFY0(dmu_objset_from_ds(ds, &os));

        if (!spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_ASYNC_DESTROY)) {
                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,
                    SPA_FEATURE_ASYNC_DESTROY)) {
                        dsl_scan_t *scn = dp->dp_scan;
                        spa_feature_incr(dp->dp_spa, SPA_FEATURE_ASYNC_DESTROY,
                            tx);
                        dp->dp_bptree_obj = bptree_alloc(mos, tx);
                        VERIFY0(zap_add(mos,
                            DMU_POOL_DIRECTORY_OBJECT,
                            DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
                            &dp->dp_bptree_obj, tx));
                        ASSERT(!scn->scn_async_destroying);
                        scn->scn_async_destroying = B_TRUE;
                }

                used = dsl_dir_phys(ds->ds_dir)->dd_used_bytes;
                comp = dsl_dir_phys(ds->ds_dir)->dd_compressed_bytes;
                uncomp = dsl_dir_phys(ds->ds_dir)->dd_uncompressed_bytes;

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

                bptree_add(mos, dp->dp_bptree_obj,
                    &dsl_dataset_phys(ds)->ds_bp,
                    dsl_dataset_phys(ds)->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) {
                        VERIFY0(zap_remove_int(mos,
                            dsl_dir_phys(ds->ds_prev->ds_dir)->dd_clones,
                            ds->ds_object, tx));
                }
                prevobj = ds->ds_prev->ds_object;
                dsl_dataset_rele(ds->ds_prev, ds);
                ds->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;
        }

        /* Erase the link in the dir */
        dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
        dsl_dir_phys(ds->ds_dir)->dd_head_dataset_obj = 0;
        ddobj = ds->ds_dir->dd_object;
        ASSERT(dsl_dataset_phys(ds)->ds_snapnames_zapobj != 0);
        VERIFY0(zap_destroy(mos,
            dsl_dataset_phys(ds)->ds_snapnames_zapobj, tx));

        if (ds->ds_bookmarks != 0) {
                VERIFY0(zap_destroy(mos, ds->ds_bookmarks, tx));
                spa_feature_decr(dp->dp_spa, SPA_FEATURE_BOOKMARKS, tx);
        }

        spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);

        ASSERT0(dsl_dataset_phys(ds)->ds_next_clones_obj);
        ASSERT0(dsl_dataset_phys(ds)->ds_props_obj);
        ASSERT0(dsl_dataset_phys(ds)->ds_userrefs_obj);
        dsl_dir_rele(ds->ds_dir, ds);
        ds->ds_dir = NULL;
        dmu_object_free_zapified(mos, obj, tx);

        dsl_dir_destroy_sync(ddobj, tx);

        if (rmorigin) {
                dsl_dataset_t *prev;
                VERIFY0(dsl_dataset_hold_obj(dp, prevobj, FTAG, &prev));
                dsl_destroy_snapshot_sync_impl(prev, B_FALSE, tx);
                dsl_dataset_rele(prev, FTAG);
        }
}

static void
dsl_destroy_head_sync(void *arg, dmu_tx_t *tx)
{
        dsl_destroy_head_arg_t *ddha = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        dsl_dataset_t *ds;

        VERIFY0(dsl_dataset_hold(dp, ddha->ddha_name, FTAG, &ds));
        dsl_destroy_head_sync_impl(ds, tx);
        dsl_dataset_rele(ds, FTAG);
}

static void
dsl_destroy_head_begin_sync(void *arg, dmu_tx_t *tx)
{
        dsl_destroy_head_arg_t *ddha = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        dsl_dataset_t *ds;

        VERIFY0(dsl_dataset_hold(dp, ddha->ddha_name, FTAG, &ds));

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

        spa_history_log_internal_ds(ds, "destroy begin", tx, "");
        dsl_dataset_rele(ds, FTAG);
}

int
dsl_destroy_head(const char *name)
{
        dsl_destroy_head_arg_t ddha;
        int error;
        spa_t *spa;
        boolean_t isenabled;

#ifdef _KERNEL
        zfs_destroy_unmount_origin(name);
#endif

        error = spa_open(name, &spa, FTAG);
        if (error != 0)
                return (error);
        isenabled = spa_feature_is_enabled(spa, SPA_FEATURE_ASYNC_DESTROY);
        spa_close(spa, FTAG);

        ddha.ddha_name = name;

        if (!isenabled) {
                objset_t *os;

                error = dsl_sync_task(name, dsl_destroy_head_check,
                    dsl_destroy_head_begin_sync, &ddha,
                    0, ZFS_SPACE_CHECK_NONE);
                if (error != 0)
                        return (error);

                /*
                 * Head deletion is processed in one txg on old pools;
                 * remove the objects from open context so that the txg sync
                 * is not too long.
                 */
                error = dmu_objset_own(name, DMU_OST_ANY, B_FALSE, FTAG, &os);
                if (error == 0) {
                        uint64_t prev_snap_txg =
                            dsl_dataset_phys(dmu_objset_ds(os))->
                            ds_prev_snap_txg;
                        for (uint64_t obj = 0; error == 0;
                            error = dmu_object_next(os, &obj, FALSE,
                            prev_snap_txg))
                                (void) dmu_free_long_object(os, obj);
                        /* sync out all frees */
                        txg_wait_synced(dmu_objset_pool(os), 0);
                        dmu_objset_disown(os, FTAG);
                }
        }

        return (dsl_sync_task(name, dsl_destroy_head_check,
            dsl_destroy_head_sync, &ddha, 0, ZFS_SPACE_CHECK_NONE));
}

/*
 * Note, this function is used as the callback for dmu_objset_find().  We
 * always return 0 so that we will continue to find and process
 * inconsistent datasets, even if we encounter an error trying to
 * process one of them.
 */
/* ARGSUSED */
int
dsl_destroy_inconsistent(const char *dsname, void *arg)
{
        objset_t *os;

        if (dmu_objset_hold(dsname, FTAG, &os) == 0) {
                boolean_t inconsistent = DS_IS_INCONSISTENT(dmu_objset_ds(os));
                dmu_objset_rele(os, FTAG);
                if (inconsistent)
                        (void) dsl_destroy_head(dsname);
        }
        return (0);
}