Improve speculative prefetcher for block cloning

[zfs.git] / module / 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 https://opensource.org/licenses/CDDL-1.0.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2018 by Delphix. All rights reserved.
 * Copyright (c) 2013 Steven Hartland. All rights reserved.
 * Copyright (c) 2013 by Joyent, Inc. All rights reserved.
 * Copyright (c) 2016 Actifio, 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/dsl_destroy.h>
#include <sys/dsl_bookmark.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>
#include <sys/zvol.h>
#include <sys/zcp.h>
#include <sys/dsl_deadlist.h>
#include <sys/zthr.h>
#include <sys/spa_impl.h>

extern int zfs_snapshot_history_enabled;

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);
}

int
dsl_destroy_snapshot_check(void *arg, dmu_tx_t *tx)
{
        dsl_destroy_snapshot_arg_t *ddsa = arg;
        const char *dsname = ddsa->ddsa_name;
        boolean_t defer = ddsa->ddsa_defer;

        dsl_pool_t *dp = dmu_tx_pool(tx);
        int error = 0;
        dsl_dataset_t *ds;

        error = dsl_dataset_hold(dp, dsname, FTAG, &ds);

        /*
         * If the snapshot does not exist, silently ignore it, and
         * dsl_destroy_snapshot_sync() will be a no-op
         * (it's "already destroyed").
         */
        if (error == ENOENT)
                return (0);

        if (error == 0) {
                error = dsl_destroy_snapshot_check_impl(ds, defer);
                dsl_dataset_rele(ds, FTAG);
        }

        return (error);
}

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, boolean_t bp_freed, 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_GET_LOGICAL_BIRTH(bp) <=
            dsl_dataset_phys(poa->ds)->ds_prev_snap_txg) {
                dsl_deadlist_insert(&poa->ds->ds_deadlist, bp, bp_freed, tx);
                if (poa->ds_prev && !poa->after_branch_point &&
                    BP_GET_LOGICAL_BIRTH(bp) >
                    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;
        VERIFY0(dsl_deadlist_open(&ds->ds_deadlist, mos,
            dsl_dataset_phys(ds)->ds_deadlist_obj));
        VERIFY0(dsl_deadlist_open(&ds_next->ds_deadlist, mos,
            dsl_dataset_phys(ds_next)->ds_deadlist_obj));
}

typedef struct remaining_clones_key {
        dsl_dataset_t *rck_clone;
        list_node_t rck_node;
} remaining_clones_key_t;

static remaining_clones_key_t *
rck_alloc(dsl_dataset_t *clone)
{
        remaining_clones_key_t *rck = kmem_alloc(sizeof (*rck), KM_SLEEP);
        rck->rck_clone = clone;
        return (rck);
}

static void
dsl_dir_remove_clones_key_impl(dsl_dir_t *dd, uint64_t mintxg, dmu_tx_t *tx,
    list_t *stack, const void *tag)
{
        objset_t *mos = dd->dd_pool->dp_meta_objset;

        /*
         * 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(dd)->dd_clones == 0)
                return;

        zap_cursor_t *zc = kmem_alloc(sizeof (zap_cursor_t), KM_SLEEP);
        zap_attribute_t *za = zap_attribute_alloc();

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

                VERIFY0(dsl_dataset_hold_obj(dd->dd_pool,
                    za->za_first_integer, tag, &clone));

                if (clone->ds_dir->dd_origin_txg > mintxg) {
                        dsl_deadlist_remove_key(&clone->ds_deadlist,
                            mintxg, tx);

                        if (dsl_dataset_remap_deadlist_exists(clone)) {
                                dsl_deadlist_remove_key(
                                    &clone->ds_remap_deadlist, mintxg, tx);
                        }

                        list_insert_head(stack, rck_alloc(clone));
                } else {
                        dsl_dataset_rele(clone, tag);
                }
        }
        zap_cursor_fini(zc);

        zap_attribute_free(za);
        kmem_free(zc, sizeof (zap_cursor_t));
}

void
dsl_dir_remove_clones_key(dsl_dir_t *top_dd, uint64_t mintxg, dmu_tx_t *tx)
{
        list_t stack;

        list_create(&stack, sizeof (remaining_clones_key_t),
            offsetof(remaining_clones_key_t, rck_node));

        dsl_dir_remove_clones_key_impl(top_dd, mintxg, tx, &stack, FTAG);
        for (remaining_clones_key_t *rck = list_remove_head(&stack);
            rck != NULL; rck = list_remove_head(&stack)) {
                dsl_dataset_t *clone = rck->rck_clone;
                dsl_dir_t *clone_dir = clone->ds_dir;

                kmem_free(rck, sizeof (*rck));

                dsl_dir_remove_clones_key_impl(clone_dir, mintxg, tx,
                    &stack, FTAG);
                dsl_dataset_rele(clone, FTAG);
        }

        list_destroy(&stack);
}

static void
dsl_destroy_snapshot_handle_remaps(dsl_dataset_t *ds, dsl_dataset_t *ds_next,
    dmu_tx_t *tx)
{
        dsl_pool_t *dp = ds->ds_dir->dd_pool;

        /* Move blocks to be obsoleted to pool's obsolete list. */
        if (dsl_dataset_remap_deadlist_exists(ds_next)) {
                if (!bpobj_is_open(&dp->dp_obsolete_bpobj))
                        dsl_pool_create_obsolete_bpobj(dp, tx);

                dsl_deadlist_move_bpobj(&ds_next->ds_remap_deadlist,
                    &dp->dp_obsolete_bpobj,
                    dsl_dataset_phys(ds)->ds_prev_snap_txg, tx);
        }

        /* Merge our deadlist into next's and free it. */
        if (dsl_dataset_remap_deadlist_exists(ds)) {
                uint64_t remap_deadlist_object =
                    dsl_dataset_get_remap_deadlist_object(ds);
                ASSERT(remap_deadlist_object != 0);

                mutex_enter(&ds_next->ds_remap_deadlist_lock);
                if (!dsl_dataset_remap_deadlist_exists(ds_next))
                        dsl_dataset_create_remap_deadlist(ds_next, tx);
                mutex_exit(&ds_next->ds_remap_deadlist_lock);

                dsl_deadlist_merge(&ds_next->ds_remap_deadlist,
                    remap_deadlist_object, tx);
                dsl_dataset_destroy_remap_deadlist(ds, tx);
        }
}

void
dsl_destroy_snapshot_sync_impl(dsl_dataset_t *ds, boolean_t defer, dmu_tx_t *tx)
{
        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));
        rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
        ASSERT3U(BP_GET_LOGICAL_BIRTH(&dsl_dataset_phys(ds)->ds_bp), <=,
            tx->tx_txg);
        rrw_exit(&ds->ds_bp_rwlock, FTAG);
        ASSERT(zfs_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;
                if (zfs_snapshot_history_enabled) {
                        spa_history_log_internal_ds(ds, "defer_destroy", tx,
                            " ");
                }
                return;
        }

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

        if (zfs_snapshot_history_enabled) {
                /* 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;

        boolean_t book_exists = dsl_bookmark_ds_destroyed(ds, tx);

        for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
                if (dsl_dataset_feature_is_active(ds, f))
                        dsl_dataset_deactivate_feature(ds, f, 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);

                /*
                 * We are done with the deadlist tree (generated/used
                 * by dsl_deadlist_move_bpobj() and dsl_deadlist_merge()).
                 * Discard it to save memory.
                 */
                dsl_deadlist_discard_tree(&ds_next->ds_deadlist);
        }

        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;

        dsl_destroy_snapshot_handle_remaps(ds, ds_next, tx);

        if (!book_exists) {
                /* Collapse range in clone heads */
                dsl_dir_remove_clones_key(ds->ds_dir,
                    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));
                if (!book_exists) {
                        /* Collapse range in this head. */
                        dsl_deadlist_remove_key(&hds->ds_deadlist,
                            dsl_dataset_phys(ds)->ds_creation_txg, tx);
                }
                if (dsl_dataset_remap_deadlist_exists(hds)) {
                        dsl_deadlist_remove_key(&hds->ds_remap_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;
                int err;

                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 __maybe_unused;
                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);
}

void
dsl_destroy_snapshot_sync(void *arg, dmu_tx_t *tx)
{
        dsl_destroy_snapshot_arg_t *ddsa = arg;
        const char *dsname = ddsa->ddsa_name;
        boolean_t defer = ddsa->ddsa_defer;

        dsl_pool_t *dp = dmu_tx_pool(tx);
        dsl_dataset_t *ds;

        int error = dsl_dataset_hold(dp, dsname, FTAG, &ds);
        if (error == ENOENT)
                return;
        ASSERT0(error);
        dsl_destroy_snapshot_sync_impl(ds, defer, tx);
        zvol_remove_minors(dp->dp_spa, dsname, B_TRUE);
        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)
{
        if (nvlist_next_nvpair(snaps, NULL) == NULL)
                return (0);

        /*
         * lzc_destroy_snaps() is documented to take an nvlist whose
         * values "don't matter".  We need to convert that nvlist to
         * one that we know can be converted to LUA.
         */
        nvlist_t *snaps_normalized = fnvlist_alloc();
        for (nvpair_t *pair = nvlist_next_nvpair(snaps, NULL);
            pair != NULL; pair = nvlist_next_nvpair(snaps, pair)) {
                fnvlist_add_boolean_value(snaps_normalized,
                    nvpair_name(pair), B_TRUE);
        }

        nvlist_t *arg = fnvlist_alloc();
        fnvlist_add_nvlist(arg, "snaps", snaps_normalized);
        fnvlist_free(snaps_normalized);
        fnvlist_add_boolean_value(arg, "defer", defer);

        nvlist_t *wrapper = fnvlist_alloc();
        fnvlist_add_nvlist(wrapper, ZCP_ARG_ARGLIST, arg);
        fnvlist_free(arg);

        const char *program =
            "arg = ...\n"
            "snaps = arg['snaps']\n"
            "defer = arg['defer']\n"
            "errors = { }\n"
            "has_errors = false\n"
            "for snap, v in pairs(snaps) do\n"
            "    errno = zfs.check.destroy{snap, defer=defer}\n"
            "    zfs.debug('snap: ' .. snap .. ' errno: ' .. errno)\n"
            "    if errno == ENOENT then\n"
            "        snaps[snap] = nil\n"
            "    elseif errno ~= 0 then\n"
            "        errors[snap] = errno\n"
            "        has_errors = true\n"
            "    end\n"
            "end\n"
            "if has_errors then\n"
            "    return errors\n"
            "end\n"
            "for snap, v in pairs(snaps) do\n"
            "    errno = zfs.sync.destroy{snap, defer=defer}\n"
            "    assert(errno == 0)\n"
            "end\n"
            "return { }\n";

        nvlist_t *result = fnvlist_alloc();
        int error = zcp_eval(nvpair_name(nvlist_next_nvpair(snaps, NULL)),
            program,
            B_TRUE,
            0,
            zfs_lua_max_memlimit,
            fnvlist_lookup_nvpair(wrapper, ZCP_ARG_ARGLIST), result);
        if (error != 0) {
                const char *errorstr = NULL;
                (void) nvlist_lookup_string(result, ZCP_RET_ERROR, &errorstr);
                if (errorstr != NULL) {
                        zfs_dbgmsg("%s", errorstr);
                }
                fnvlist_free(wrapper);
                fnvlist_free(result);
                return (error);
        }
        fnvlist_free(wrapper);

        /*
         * lzc_destroy_snaps() is documented to fill the errlist with
         * int32 values, so we need to convert the int64 values that are
         * returned from LUA.
         */
        int rv = 0;
        nvlist_t *errlist_raw = fnvlist_lookup_nvlist(result, ZCP_RET_RETURN);
        for (nvpair_t *pair = nvlist_next_nvpair(errlist_raw, NULL);
            pair != NULL; pair = nvlist_next_nvpair(errlist_raw, pair)) {
                int32_t val = (int32_t)fnvpair_value_int64(pair);
                if (rv == 0)
                        rv = val;
                fnvlist_add_int32(errlist, nvpair_name(pair), val);
        }
        fnvlist_free(result);
        return (rv);
}

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;
};

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)
{
        (void) spa, (void) dnp;
        struct killarg *ka = arg;
        dmu_tx_t *tx = ka->tx;

        if (zb->zb_level == ZB_DNODE_LEVEL || 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_GET_LOGICAL_BIRTH(bp), >,
                    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;

        spa_history_log_internal_ds(ds, "destroy", tx,
            "(synchronous, mintxg=%llu)",
            (long long)dsl_dataset_phys(ds)->ds_prev_snap_txg);

        /*
         * 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 |
            TRAVERSE_NO_DECRYPT, kill_blkptr, &ka));
        ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) ||
            dsl_dataset_phys(ds)->ds_unique_bytes == 0);
}

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

        ASSERT0(ds->ds_dir->dd_activity_waiters);

        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 (!zfs_refcount_is_zero(&ds->ds_prev->ds_longholds))
                        return (SET_ERROR(EBUSY));
        }
        return (0);
}

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. */
        if (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]);

        if (dd->dd_crypto_obj != 0) {
                dsl_crypto_key_destroy_sync(dd->dd_crypto_obj, tx);
                (void) spa_keystore_unload_wkey_impl(dp->dp_spa, dd->dd_object);
        }

        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));
        if (dsl_dir_phys(dd)->dd_clones != 0)
                VERIFY0(zap_destroy(mos, dsl_dir_phys(dd)->dd_clones, 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);
}

static void
dsl_clone_destroy_assert(dsl_dir_t *dd)
{
        uint64_t used, comp, uncomp;

        ASSERT(dsl_dir_is_clone(dd));
        dsl_deadlist_space(&dd->dd_livelist, &used, &comp, &uncomp);

        ASSERT3U(dsl_dir_phys(dd)->dd_used_bytes, ==, used);
        ASSERT3U(dsl_dir_phys(dd)->dd_compressed_bytes, ==, comp);
        /*
         * Greater than because we do not track embedded block pointers in
         * the livelist
         */
        ASSERT3U(dsl_dir_phys(dd)->dd_uncompressed_bytes, >=, uncomp);

        ASSERT(list_is_empty(&dd->dd_pending_allocs.bpl_list));
        ASSERT(list_is_empty(&dd->dd_pending_frees.bpl_list));
}

/*
 * Start the delete process for a clone. Free its zil, verify the space usage
 * and queue the blkptrs for deletion by adding the livelist to the pool-wide
 * delete queue.
 */
static void
dsl_async_clone_destroy(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        uint64_t zap_obj, to_delete, used, comp, uncomp;
        objset_t *os;
        dsl_dir_t *dd = ds->ds_dir;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        objset_t *mos = dp->dp_meta_objset;
        spa_t *spa = dmu_tx_pool(tx)->dp_spa;
        VERIFY0(dmu_objset_from_ds(ds, &os));

        uint64_t mintxg = 0;
        dsl_deadlist_entry_t *dle = dsl_deadlist_first(&dd->dd_livelist);
        if (dle != NULL)
                mintxg = dle->dle_mintxg;

        spa_history_log_internal_ds(ds, "destroy", tx,
            "(livelist, mintxg=%llu)", (long long)mintxg);

        /* Check that the clone is in a correct state to be deleted */
        dsl_clone_destroy_assert(dd);

        /* Destroy the zil */
        zil_destroy_sync(dmu_objset_zil(os), tx);

        VERIFY0(zap_lookup(mos, dd->dd_object,
            DD_FIELD_LIVELIST, sizeof (uint64_t), 1, &to_delete));
        /* Initialize deleted_clones entry to track livelists to cleanup */
        int error = zap_lookup(mos, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_DELETED_CLONES, sizeof (uint64_t), 1, &zap_obj);
        if (error == ENOENT) {
                zap_obj = zap_create(mos, DMU_OTN_ZAP_METADATA,
                    DMU_OT_NONE, 0, tx);
                VERIFY0(zap_add(mos, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_DELETED_CLONES, sizeof (uint64_t), 1,
                    &(zap_obj), tx));
                spa->spa_livelists_to_delete = zap_obj;
        } else if (error != 0) {
                zfs_panic_recover("zfs: error %d was returned while looking "
                    "up DMU_POOL_DELETED_CLONES in the zap", error);
                return;
        }
        VERIFY0(zap_add_int(mos, zap_obj, to_delete, tx));

        /* Clone is no longer using space, now tracked by dp_free_dir */
        dsl_deadlist_space(&dd->dd_livelist, &used, &comp, &uncomp);
        dsl_dir_diduse_space(dd, DD_USED_HEAD,
            -used, -comp, -dsl_dir_phys(dd)->dd_uncompressed_bytes,
            tx);
        dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
            used, comp, uncomp, tx);
        dsl_dir_remove_livelist(dd, tx, B_FALSE);
        zthr_wakeup(spa->spa_livelist_delete_zthr);
}

/*
 * Move the bptree into the pool's list of trees to clean up, update space
 * accounting information and destroy the zil.
 */
static void
dsl_async_dataset_destroy(dsl_dataset_t *ds, dmu_tx_t *tx)
{
        uint64_t used, comp, uncomp;
        objset_t *os;

        VERIFY0(dmu_objset_from_ds(ds, &os));
        dsl_pool_t *dp = dmu_tx_pool(tx);
        objset_t *mos = dp->dp_meta_objset;

        spa_history_log_internal_ds(ds, "destroy", tx,
            "(bptree, mintxg=%llu)",
            (long long)dsl_dataset_phys(ds)->ds_prev_snap_txg);

        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);

        rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
        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);
        rrw_exit(&ds->ds_bp_rwlock, FTAG);
        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);
}

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);
        rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
        ASSERT3U(BP_GET_LOGICAL_BIRTH(&dsl_dataset_phys(ds)->ds_bp), <=,
            tx->tx_txg);
        rrw_exit(&ds->ds_bp_rwlock, FTAG);
        ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));

        dsl_dir_cancel_waiters(ds->ds_dir);

        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);
        }

        obj = ds->ds_object;

        for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
                if (dsl_dataset_feature_is_active(ds, f))
                        dsl_dataset_deactivate_feature(ds, f, tx);
        }

        dsl_scan_ds_destroyed(ds, tx);

        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 since the dataset has no snapshots.
         * (If it's a clone, it's safe to ignore the deadlist contents
         * since they are still referenced by the origin snapshot.)
         */
        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;

        if (dsl_dataset_remap_deadlist_exists(ds))
                dsl_dataset_destroy_remap_deadlist(ds, tx);

        /*
         * Each destroy is responsible for both destroying (enqueuing
         * to be destroyed) the blkptrs comprising the dataset as well as
         * those belonging to the zil.
         */
        if (dsl_deadlist_is_open(&ds->ds_dir->dd_livelist)) {
                dsl_async_clone_destroy(ds, tx);
        } else if (spa_feature_is_enabled(dp->dp_spa,
            SPA_FEATURE_ASYNC_DESTROY)) {
                dsl_async_dataset_destroy(ds, tx);
        } else {
                old_synchronous_dataset_destroy(ds, 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_obj != 0) {
                void *cookie = NULL;
                dsl_bookmark_node_t *dbn;

                while ((dbn = avl_destroy_nodes(&ds->ds_bookmarks, &cookie)) !=
                    NULL) {
                        if (dbn->dbn_phys.zbm_redaction_obj != 0) {
                                dnode_t *rl;
                                VERIFY0(dnode_hold(mos,
                                    dbn->dbn_phys.zbm_redaction_obj, FTAG,
                                    &rl));
                                if (rl->dn_have_spill) {
                                        spa_feature_decr(dmu_objset_spa(mos),
                                            SPA_FEATURE_REDACTION_LIST_SPILL,
                                            tx);
                                }
                                dnode_rele(rl, FTAG);
                                VERIFY0(dmu_object_free(mos,
                                    dbn->dbn_phys.zbm_redaction_obj, tx));
                                spa_feature_decr(dmu_objset_spa(mos),
                                    SPA_FEATURE_REDACTION_BOOKMARKS, tx);
                        }
                        if (dbn->dbn_phys.zbm_flags & ZBM_FLAG_HAS_FBN) {
                                spa_feature_decr(dmu_objset_spa(mos),
                                    SPA_FEATURE_BOOKMARK_WRITTEN, tx);
                        }
                        spa_strfree(dbn->dbn_name);
                        mutex_destroy(&dbn->dbn_lock);
                        kmem_free(dbn, sizeof (*dbn));
                }
                avl_destroy(&ds->ds_bookmarks);
                VERIFY0(zap_destroy(mos, ds->ds_bookmarks_obj, 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);
        }
        /* Delete errlog. */
        if (spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_HEAD_ERRLOG))
                spa_delete_dataset_errlog(dp->dp_spa, ds->ds_object, tx);
}

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);
        zvol_remove_minors(dp->dp_spa, ddha->ddha_name, B_TRUE);
        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_DESTROY);
                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. This optimization can only work for
                 * encrypted datasets if the wrapping key is loaded.
                 */
                error = dmu_objset_own(name, DMU_OST_ANY, B_FALSE, B_TRUE,
                    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, B_TRUE, FTAG);
                }
        }

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

/*
 * 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.
 */
int
dsl_destroy_inconsistent(const char *dsname, void *arg)
{
        (void) arg;
        objset_t *os;

        if (dmu_objset_hold(dsname, FTAG, &os) == 0) {
                boolean_t need_destroy = DS_IS_INCONSISTENT(dmu_objset_ds(os));

                /*
                 * If the dataset is inconsistent because a resumable receive
                 * has failed, then do not destroy it.
                 */
                if (dsl_dataset_has_resume_receive_state(dmu_objset_ds(os)))
                        need_destroy = B_FALSE;

                dmu_objset_rele(os, FTAG);
                if (need_destroy)
                        (void) dsl_destroy_head(dsname);
        }
        return (0);
}


#if defined(_KERNEL)
EXPORT_SYMBOL(dsl_destroy_head);
EXPORT_SYMBOL(dsl_destroy_head_sync_impl);
EXPORT_SYMBOL(dsl_dataset_user_hold_check_one);
EXPORT_SYMBOL(dsl_destroy_snapshot_sync_impl);
EXPORT_SYMBOL(dsl_destroy_inconsistent);
EXPORT_SYMBOL(dsl_dataset_user_release_tmp);
EXPORT_SYMBOL(dsl_destroy_head_check_impl);
#endif