MFV r247580:

Merge synctask code restructuring from vendor.

Modify forward and backward compatibility to support new change.

Illumos ZFS issues:
  3464 zfs synctask code needs restructuring

Sponsored by:	Hybrid Logic Ltd.

1 files changed, 926 insertions, 0 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c
new file mode 100644
index 0000000..20d401f
--- /dev/null
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c
@@ -0,0 +1,926 @@
+/*
+ * 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.
+ */
+
+#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>
+
+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;
+
+/*
+ * ds must be owned.
+ */
+static int
+dsl_destroy_snapshot_check_impl(dsl_dataset_t *ds, boolean_t defer)
+{
+	if (!dsl_dataset_is_snapshot(ds))
+		return (EINVAL);
+
+	if (dsl_dataset_long_held(ds))
+		return (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 (ENOTSUP);
+		return (0);
+	}
+
+	/*
+	 * If this snapshot has an elevated user reference count,
+	 * we can't destroy it yet.
+	 */
+	if (ds->ds_userrefs > 0)
+		return (EBUSY);
+
+	/*
+	 * Can't delete a branch point.
+	 */
+	if (ds->ds_phys->ds_num_children > 1)
+		return (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;
+
+	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;
+	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, ==, 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);
+	deadlist_obj = ds->ds_phys->ds_deadlist_obj;
+	ds->ds_phys->ds_deadlist_obj = ds_next->ds_phys->ds_deadlist_obj;
+	ds_next->ds_phys->ds_deadlist_obj = 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 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 (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;
+
+		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(ds->ds_phys->ds_bp.blk_birth, <=, tx->tx_txg);
+	ASSERT(refcount_is_zero(&ds->ds_longholds));
+
+	if (defer &&
+	    (ds->ds_userrefs > 0 || ds->ds_phys->ds_num_children > 1)) {
+		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;
+		spa_history_log_internal_ds(ds, "defer_destroy", tx, "");
+		return;
+	}
+
+	ASSERT3U(ds->ds_phys->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_phys->ds_prev_snap_obj != 0) {
+		ASSERT3P(ds->ds_prev, ==, NULL);
+		VERIFY0(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) {
+			dsl_dataset_remove_from_next_clones(ds_prev, obj, tx);
+			if (ds->ds_phys->ds_next_snap_obj != 0) {
+				VERIFY0(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_prev->ds_phys->ds_next_snap_obj =
+			    ds->ds_phys->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,
+	    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);
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	ds->ds_phys->ds_deadlist_obj = 0;
+
+	/* 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).
+		 */
+		VERIFY0(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;
+		VERIFY0(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_rele(ds_next->ds_prev, ds_next);
+		ds_next->ds_prev = NULL;
+		if (ds_prev) {
+			VERIFY0(dsl_dataset_hold_obj(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 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 =
+			    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);
+
+	/*
+	 * 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(ds->ds_phys->ds_snapnames_zapobj == 0);
+	VERIFY0(dsl_dataset_hold_obj(dp,
+	    ds->ds_dir->dd_phys->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));
+	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 (ds->ds_phys->ds_next_clones_obj != 0) {
+		uint64_t count;
+		ASSERT0(zap_count(mos,
+		    ds->ds_phys->ds_next_clones_obj, &count) && count == 0);
+		VERIFY0(dmu_object_free(mos,
+		    ds->ds_phys->ds_next_clones_obj, tx));
+	}
+	if (ds->ds_phys->ds_props_obj != 0)
+		VERIFY0(zap_destroy(mos, ds->ds_phys->ds_props_obj, tx));
+	if (ds->ds_phys->ds_userrefs_obj != 0)
+		VERIFY0(zap_destroy(mos, ds->ds_phys->ds_userrefs_obj, tx));
+	dsl_dir_rele(ds->ds_dir, ds);
+	ds->ds_dir = NULL;
+	VERIFY0(dmu_object_free(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);
+	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_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);
+}
+
+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,
+	    ds->ds_phys->ds_prev_snap_txg, TRAVERSE_POST,
+	    kill_blkptr, &ka));
+	ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) || ds->ds_phys->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;
+
+	if (dsl_dataset_is_snapshot(ds))
+		return (EINVAL);
+
+	if (refcount_count(&ds->ds_longholds) != expected_holds)
+		return (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 &&
+	    ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
+		return (EBUSY);
+
+	/*
+	 * Can't delete if there are children of this fs.
+	 */
+	error = zap_count(mos,
+	    ds->ds_dir->dd_phys->dd_child_dir_zapobj, &count);
+	if (error != 0)
+		return (error);
+	if (count != 0)
+		return (EEXIST);
+
+	if (dsl_dir_is_clone(ds->ds_dir) && DS_IS_DEFER_DESTROY(ds->ds_prev) &&
+	    ds->ds_prev->ds_phys->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 (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(dd->dd_phys->dd_head_dataset_obj);
+
+	/*
+	 * 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(dd->dd_phys->dd_used_bytes);
+	ASSERT0(dd->dd_phys->dd_reserved);
+	for (t = 0; t < DD_USED_NUM; t++)
+		ASSERT0(dd->dd_phys->dd_used_breakdown[t]);
+
+	VERIFY0(zap_destroy(mos, dd->dd_phys->dd_child_dir_zapobj, tx));
+	VERIFY0(zap_destroy(mos, dd->dd_phys->dd_props_zapobj, tx));
+	VERIFY0(dsl_deleg_destroy(mos, dd->dd_phys->dd_deleg_zapobj, tx));
+	VERIFY0(zap_remove(mos,
+	    dd->dd_parent->dd_phys->dd_child_dir_zapobj, dd->dd_myname, tx));
+
+	dsl_dir_rele(dd, FTAG);
+	VERIFY0(dmu_object_free(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(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);
+	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) &&
+	    ds->ds_prev->ds_phys->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);
+	}
+
+	dsl_scan_ds_destroyed(ds, tx);
+
+	obj = ds->ds_object;
+
+	if (ds->ds_phys->ds_prev_snap_obj != 0) {
+		/* This is a clone */
+		ASSERT(ds->ds_prev != NULL);
+		ASSERT3U(ds->ds_prev->ds_phys->ds_next_snap_obj, !=, obj);
+		ASSERT0(ds->ds_phys->ds_next_snap_obj);
+
+		dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
+		if (ds->ds_prev->ds_phys->ds_next_clones_obj != 0) {
+			dsl_dataset_remove_from_next_clones(ds->ds_prev,
+			    obj, tx);
+		}
+
+		ASSERT3U(ds->ds_prev->ds_phys->ds_num_children, >, 1);
+		ds->ds_prev->ds_phys->ds_num_children--;
+	}
+
+	zfeature_info_t *async_destroy =
+	    &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY];
+	objset_t *os;
+
+	/*
+	 * 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);
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	ds->ds_phys->ds_deadlist_obj = 0;
+
+	VERIFY0(dmu_objset_from_ds(ds, &os));
+
+	if (!spa_feature_is_enabled(dp->dp_spa, 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, async_destroy)) {
+			spa_feature_incr(dp->dp_spa, 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));
+		}
+
+		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) {
+			VERIFY0(zap_remove_int(mos,
+			    ds->ds_prev->ds_dir->dd_phys->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);
+	ds->ds_dir->dd_phys->dd_head_dataset_obj = 0;
+	ddobj = ds->ds_dir->dd_object;
+	ASSERT(ds->ds_phys->ds_snapnames_zapobj != 0);
+	VERIFY0(zap_destroy(mos, ds->ds_phys->ds_snapnames_zapobj, tx));
+
+	spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);
+
+	ASSERT0(ds->ds_phys->ds_next_clones_obj);
+	ASSERT0(ds->ds_phys->ds_props_obj);
+	ASSERT0(ds->ds_phys->ds_userrefs_obj);
+	dsl_dir_rele(ds->ds_dir, ds);
+	ds->ds_dir = NULL;
+	VERIFY0(dmu_object_free(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);
+	ds->ds_phys->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_table[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);
+		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 =
+			    dmu_objset_ds(os)->ds_phys->ds_prev_snap_txg;
+			for (uint64_t obj = 0; error == 0;
+			    error = dmu_object_next(os, &obj, FALSE,
+			    prev_snap_txg))
+				(void) dmu_free_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));
+}
+
+/*
+ * 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);
+}