Merge commit 'refs/top-bases/gcc-missing-case' into gcc-missing-case

1 files changed, 3103 insertions, 0 deletions

diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
new file mode 100644
index 000000000..93ea8aa11
--- /dev/null
+++ b/module/zfs/dsl_dataset.c
@@ -0,0 +1,3103 @@
+/*
+ * 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 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#include <sys/dmu_objset.h>
+#include <sys/dsl_dataset.h>
+#include <sys/dsl_dir.h>
+#include <sys/dsl_prop.h>
+#include <sys/dsl_synctask.h>
+#include <sys/dmu_traverse.h>
+#include <sys/dmu_tx.h>
+#include <sys/arc.h>
+#include <sys/zio.h>
+#include <sys/zap.h>
+#include <sys/unique.h>
+#include <sys/zfs_context.h>
+#include <sys/zfs_ioctl.h>
+#include <sys/spa.h>
+#include <sys/zfs_znode.h>
+#include <sys/sunddi.h>
+
+static char *dsl_reaper = "the grim reaper";
+
+static dsl_checkfunc_t dsl_dataset_destroy_begin_check;
+static dsl_syncfunc_t dsl_dataset_destroy_begin_sync;
+static dsl_checkfunc_t dsl_dataset_rollback_check;
+static dsl_syncfunc_t dsl_dataset_rollback_sync;
+static dsl_syncfunc_t dsl_dataset_set_reservation_sync;
+
+#define	DS_REF_MAX	(1ULL << 62)
+
+#define	DSL_DEADLIST_BLOCKSIZE	SPA_MAXBLOCKSIZE
+
+#define	DSL_DATASET_IS_DESTROYED(ds)	((ds)->ds_owner == dsl_reaper)
+
+
+/*
+ * Figure out how much of this delta should be propogated to the dsl_dir
+ * layer.  If there's a refreservation, that space has already been
+ * partially accounted for in our ancestors.
+ */
+static int64_t
+parent_delta(dsl_dataset_t *ds, int64_t delta)
+{
+	uint64_t old_bytes, new_bytes;
+
+	if (ds->ds_reserved == 0)
+		return (delta);
+
+	old_bytes = MAX(ds->ds_phys->ds_unique_bytes, ds->ds_reserved);
+	new_bytes = MAX(ds->ds_phys->ds_unique_bytes + delta, ds->ds_reserved);
+
+	ASSERT3U(ABS((int64_t)(new_bytes - old_bytes)), <=, ABS(delta));
+	return (new_bytes - old_bytes);
+}
+
+void
+dsl_dataset_block_born(dsl_dataset_t *ds, blkptr_t *bp, dmu_tx_t *tx)
+{
+	int used = bp_get_dasize(tx->tx_pool->dp_spa, bp);
+	int compressed = BP_GET_PSIZE(bp);
+	int uncompressed = BP_GET_UCSIZE(bp);
+	int64_t delta;
+
+	dprintf_bp(bp, "born, ds=%p\n", ds);
+
+	ASSERT(dmu_tx_is_syncing(tx));
+	/* It could have been compressed away to nothing */
+	if (BP_IS_HOLE(bp))
+		return;
+	ASSERT(BP_GET_TYPE(bp) != DMU_OT_NONE);
+	ASSERT3U(BP_GET_TYPE(bp), <, DMU_OT_NUMTYPES);
+	if (ds == NULL) {
+		/*
+		 * Account for the meta-objset space in its placeholder
+		 * dsl_dir.
+		 */
+		ASSERT3U(compressed, ==, uncompressed); /* it's all metadata */
+		dsl_dir_diduse_space(tx->tx_pool->dp_mos_dir, DD_USED_HEAD,
+		    used, compressed, uncompressed, tx);
+		dsl_dir_dirty(tx->tx_pool->dp_mos_dir, tx);
+		return;
+	}
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	mutex_enter(&ds->ds_dir->dd_lock);
+	mutex_enter(&ds->ds_lock);
+	delta = parent_delta(ds, used);
+	ds->ds_phys->ds_used_bytes += used;
+	ds->ds_phys->ds_compressed_bytes += compressed;
+	ds->ds_phys->ds_uncompressed_bytes += uncompressed;
+	ds->ds_phys->ds_unique_bytes += used;
+	mutex_exit(&ds->ds_lock);
+	dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD, delta,
+	    compressed, uncompressed, tx);
+	dsl_dir_transfer_space(ds->ds_dir, used - delta,
+	    DD_USED_REFRSRV, DD_USED_HEAD, tx);
+	mutex_exit(&ds->ds_dir->dd_lock);
+}
+
+int
+dsl_dataset_block_kill(dsl_dataset_t *ds, blkptr_t *bp, zio_t *pio,
+    dmu_tx_t *tx)
+{
+	int used = bp_get_dasize(tx->tx_pool->dp_spa, bp);
+	int compressed = BP_GET_PSIZE(bp);
+	int uncompressed = BP_GET_UCSIZE(bp);
+
+	ASSERT(pio != NULL);
+	ASSERT(dmu_tx_is_syncing(tx));
+	/* No block pointer => nothing to free */
+	if (BP_IS_HOLE(bp))
+		return (0);
+
+	ASSERT(used > 0);
+	if (ds == NULL) {
+		int err;
+		/*
+		 * Account for the meta-objset space in its placeholder
+		 * dataset.
+		 */
+		err = dsl_free(pio, tx->tx_pool,
+		    tx->tx_txg, bp, NULL, NULL, ARC_NOWAIT);
+		ASSERT(err == 0);
+
+		dsl_dir_diduse_space(tx->tx_pool->dp_mos_dir, DD_USED_HEAD,
+		    -used, -compressed, -uncompressed, tx);
+		dsl_dir_dirty(tx->tx_pool->dp_mos_dir, tx);
+		return (used);
+	}
+	ASSERT3P(tx->tx_pool, ==, ds->ds_dir->dd_pool);
+
+	ASSERT(!dsl_dataset_is_snapshot(ds));
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+
+	if (bp->blk_birth > ds->ds_phys->ds_prev_snap_txg) {
+		int err;
+		int64_t delta;
+
+		dprintf_bp(bp, "freeing: %s", "");
+		err = dsl_free(pio, tx->tx_pool,
+		    tx->tx_txg, bp, NULL, NULL, ARC_NOWAIT);
+		ASSERT(err == 0);
+
+		mutex_enter(&ds->ds_dir->dd_lock);
+		mutex_enter(&ds->ds_lock);
+		ASSERT(ds->ds_phys->ds_unique_bytes >= used ||
+		    !DS_UNIQUE_IS_ACCURATE(ds));
+		delta = parent_delta(ds, -used);
+		ds->ds_phys->ds_unique_bytes -= used;
+		mutex_exit(&ds->ds_lock);
+		dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD,
+		    delta, -compressed, -uncompressed, tx);
+		dsl_dir_transfer_space(ds->ds_dir, -used - delta,
+		    DD_USED_REFRSRV, DD_USED_HEAD, tx);
+		mutex_exit(&ds->ds_dir->dd_lock);
+	} else {
+		dprintf_bp(bp, "putting on dead list: %s", "");
+		VERIFY(0 == bplist_enqueue(&ds->ds_deadlist, bp, tx));
+		ASSERT3U(ds->ds_prev->ds_object, ==,
+		    ds->ds_phys->ds_prev_snap_obj);
+		ASSERT(ds->ds_prev->ds_phys->ds_num_children > 0);
+		/* if (bp->blk_birth > prev prev snap txg) prev unique += bs */
+		if (ds->ds_prev->ds_phys->ds_next_snap_obj ==
+		    ds->ds_object && bp->blk_birth >
+		    ds->ds_prev->ds_phys->ds_prev_snap_txg) {
+			dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
+			mutex_enter(&ds->ds_prev->ds_lock);
+			ds->ds_prev->ds_phys->ds_unique_bytes += used;
+			mutex_exit(&ds->ds_prev->ds_lock);
+		}
+		if (bp->blk_birth > ds->ds_origin_txg) {
+			dsl_dir_transfer_space(ds->ds_dir, used,
+			    DD_USED_HEAD, DD_USED_SNAP, tx);
+		}
+	}
+	mutex_enter(&ds->ds_lock);
+	ASSERT3U(ds->ds_phys->ds_used_bytes, >=, used);
+	ds->ds_phys->ds_used_bytes -= used;
+	ASSERT3U(ds->ds_phys->ds_compressed_bytes, >=, compressed);
+	ds->ds_phys->ds_compressed_bytes -= compressed;
+	ASSERT3U(ds->ds_phys->ds_uncompressed_bytes, >=, uncompressed);
+	ds->ds_phys->ds_uncompressed_bytes -= uncompressed;
+	mutex_exit(&ds->ds_lock);
+
+	return (used);
+}
+
+uint64_t
+dsl_dataset_prev_snap_txg(dsl_dataset_t *ds)
+{
+	uint64_t trysnap = 0;
+
+	if (ds == NULL)
+		return (0);
+	/*
+	 * The snapshot creation could fail, but that would cause an
+	 * incorrect FALSE return, which would only result in an
+	 * overestimation of the amount of space that an operation would
+	 * consume, which is OK.
+	 *
+	 * There's also a small window where we could miss a pending
+	 * snapshot, because we could set the sync task in the quiescing
+	 * phase.  So this should only be used as a guess.
+	 */
+	if (ds->ds_trysnap_txg >
+	    spa_last_synced_txg(ds->ds_dir->dd_pool->dp_spa))
+		trysnap = ds->ds_trysnap_txg;
+	return (MAX(ds->ds_phys->ds_prev_snap_txg, trysnap));
+}
+
+int
+dsl_dataset_block_freeable(dsl_dataset_t *ds, uint64_t blk_birth)
+{
+	return (blk_birth > dsl_dataset_prev_snap_txg(ds));
+}
+
+/* ARGSUSED */
+static void
+dsl_dataset_evict(dmu_buf_t *db, void *dsv)
+{
+	dsl_dataset_t *ds = dsv;
+
+	ASSERT(ds->ds_owner == NULL || DSL_DATASET_IS_DESTROYED(ds));
+
+	dprintf_ds(ds, "evicting %s\n", "");
+
+	unique_remove(ds->ds_fsid_guid);
+
+	if (ds->ds_user_ptr != NULL)
+		ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+
+	if (ds->ds_prev) {
+		dsl_dataset_drop_ref(ds->ds_prev, ds);
+		ds->ds_prev = NULL;
+	}
+
+	bplist_close(&ds->ds_deadlist);
+	if (ds->ds_dir)
+		dsl_dir_close(ds->ds_dir, ds);
+
+	ASSERT(!list_link_active(&ds->ds_synced_link));
+
+	mutex_destroy(&ds->ds_lock);
+	mutex_destroy(&ds->ds_opening_lock);
+	mutex_destroy(&ds->ds_deadlist.bpl_lock);
+	rw_destroy(&ds->ds_rwlock);
+	cv_destroy(&ds->ds_exclusive_cv);
+
+	kmem_free(ds, sizeof (dsl_dataset_t));
+}
+
+static int
+dsl_dataset_get_snapname(dsl_dataset_t *ds)
+{
+	dsl_dataset_phys_t *headphys;
+	int err;
+	dmu_buf_t *headdbuf;
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	objset_t *mos = dp->dp_meta_objset;
+
+	if (ds->ds_snapname[0])
+		return (0);
+	if (ds->ds_phys->ds_next_snap_obj == 0)
+		return (0);
+
+	err = dmu_bonus_hold(mos, ds->ds_dir->dd_phys->dd_head_dataset_obj,
+	    FTAG, &headdbuf);
+	if (err)
+		return (err);
+	headphys = headdbuf->db_data;
+	err = zap_value_search(dp->dp_meta_objset,
+	    headphys->ds_snapnames_zapobj, ds->ds_object, 0, ds->ds_snapname);
+	dmu_buf_rele(headdbuf, FTAG);
+	return (err);
+}
+
+static int
+dsl_dataset_snap_lookup(dsl_dataset_t *ds, const char *name, uint64_t *value)
+{
+	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
+	uint64_t snapobj = ds->ds_phys->ds_snapnames_zapobj;
+	matchtype_t mt;
+	int err;
+
+	if (ds->ds_phys->ds_flags & DS_FLAG_CI_DATASET)
+		mt = MT_FIRST;
+	else
+		mt = MT_EXACT;
+
+	err = zap_lookup_norm(mos, snapobj, name, 8, 1,
+	    value, mt, NULL, 0, NULL);
+	if (err == ENOTSUP && mt == MT_FIRST)
+		err = zap_lookup(mos, snapobj, name, 8, 1, value);
+	return (err);
+}
+
+static int
+dsl_dataset_snap_remove(dsl_dataset_t *ds, char *name, dmu_tx_t *tx)
+{
+	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
+	uint64_t snapobj = ds->ds_phys->ds_snapnames_zapobj;
+	matchtype_t mt;
+	int err;
+
+	if (ds->ds_phys->ds_flags & DS_FLAG_CI_DATASET)
+		mt = MT_FIRST;
+	else
+		mt = MT_EXACT;
+
+	err = zap_remove_norm(mos, snapobj, name, mt, tx);
+	if (err == ENOTSUP && mt == MT_FIRST)
+		err = zap_remove(mos, snapobj, name, tx);
+	return (err);
+}
+
+static int
+dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
+    dsl_dataset_t **dsp)
+{
+	objset_t *mos = dp->dp_meta_objset;
+	dmu_buf_t *dbuf;
+	dsl_dataset_t *ds;
+	int err;
+
+	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
+	    dsl_pool_sync_context(dp));
+
+	err = dmu_bonus_hold(mos, dsobj, tag, &dbuf);
+	if (err)
+		return (err);
+	ds = dmu_buf_get_user(dbuf);
+	if (ds == NULL) {
+		dsl_dataset_t *winner;
+
+		ds = kmem_zalloc(sizeof (dsl_dataset_t), KM_SLEEP);
+		ds->ds_dbuf = dbuf;
+		ds->ds_object = dsobj;
+		ds->ds_phys = dbuf->db_data;
+
+		mutex_init(&ds->ds_lock, NULL, MUTEX_DEFAULT, NULL);
+		mutex_init(&ds->ds_opening_lock, NULL, MUTEX_DEFAULT, NULL);
+		mutex_init(&ds->ds_deadlist.bpl_lock, NULL, MUTEX_DEFAULT,
+		    NULL);
+		rw_init(&ds->ds_rwlock, 0, 0, 0);
+		cv_init(&ds->ds_exclusive_cv, NULL, CV_DEFAULT, NULL);
+
+		err = bplist_open(&ds->ds_deadlist,
+		    mos, ds->ds_phys->ds_deadlist_obj);
+		if (err == 0) {
+			err = dsl_dir_open_obj(dp,
+			    ds->ds_phys->ds_dir_obj, NULL, ds, &ds->ds_dir);
+		}
+		if (err) {
+			/*
+			 * we don't really need to close the blist if we
+			 * just opened it.
+			 */
+			mutex_destroy(&ds->ds_lock);
+			mutex_destroy(&ds->ds_opening_lock);
+			mutex_destroy(&ds->ds_deadlist.bpl_lock);
+			rw_destroy(&ds->ds_rwlock);
+			cv_destroy(&ds->ds_exclusive_cv);
+			kmem_free(ds, sizeof (dsl_dataset_t));
+			dmu_buf_rele(dbuf, tag);
+			return (err);
+		}
+
+		if (!dsl_dataset_is_snapshot(ds)) {
+			ds->ds_snapname[0] = '\0';
+			if (ds->ds_phys->ds_prev_snap_obj) {
+				err = dsl_dataset_get_ref(dp,
+				    ds->ds_phys->ds_prev_snap_obj,
+				    ds, &ds->ds_prev);
+			}
+
+			if (err == 0 && dsl_dir_is_clone(ds->ds_dir)) {
+				dsl_dataset_t *origin;
+
+				err = dsl_dataset_hold_obj(dp,
+				    ds->ds_dir->dd_phys->dd_origin_obj,
+				    FTAG, &origin);
+				if (err == 0) {
+					ds->ds_origin_txg =
+					    origin->ds_phys->ds_creation_txg;
+					dsl_dataset_rele(origin, FTAG);
+				}
+			}
+		} else if (zfs_flags & ZFS_DEBUG_SNAPNAMES) {
+			err = dsl_dataset_get_snapname(ds);
+		}
+
+		if (err == 0 && !dsl_dataset_is_snapshot(ds)) {
+			/*
+			 * In sync context, we're called with either no lock
+			 * or with the write lock.  If we're not syncing,
+			 * we're always called with the read lock held.
+			 */
+			boolean_t need_lock =
+			    !RW_WRITE_HELD(&dp->dp_config_rwlock) &&
+			    dsl_pool_sync_context(dp);
+
+			if (need_lock)
+				rw_enter(&dp->dp_config_rwlock, RW_READER);
+
+			err = dsl_prop_get_ds(ds,
+			    "refreservation", sizeof (uint64_t), 1,
+			    &ds->ds_reserved, NULL);
+			if (err == 0) {
+				err = dsl_prop_get_ds(ds,
+				    "refquota", sizeof (uint64_t), 1,
+				    &ds->ds_quota, NULL);
+			}
+
+			if (need_lock)
+				rw_exit(&dp->dp_config_rwlock);
+		} else {
+			ds->ds_reserved = ds->ds_quota = 0;
+		}
+
+		if (err == 0) {
+			winner = dmu_buf_set_user_ie(dbuf, ds, &ds->ds_phys,
+			    dsl_dataset_evict);
+		}
+		if (err || winner) {
+			bplist_close(&ds->ds_deadlist);
+			if (ds->ds_prev)
+				dsl_dataset_drop_ref(ds->ds_prev, ds);
+			dsl_dir_close(ds->ds_dir, ds);
+			mutex_destroy(&ds->ds_lock);
+			mutex_destroy(&ds->ds_opening_lock);
+			mutex_destroy(&ds->ds_deadlist.bpl_lock);
+			rw_destroy(&ds->ds_rwlock);
+			cv_destroy(&ds->ds_exclusive_cv);
+			kmem_free(ds, sizeof (dsl_dataset_t));
+			if (err) {
+				dmu_buf_rele(dbuf, tag);
+				return (err);
+			}
+			ds = winner;
+		} else {
+			ds->ds_fsid_guid =
+			    unique_insert(ds->ds_phys->ds_fsid_guid);
+		}
+	}
+	ASSERT3P(ds->ds_dbuf, ==, dbuf);
+	ASSERT3P(ds->ds_phys, ==, dbuf->db_data);
+	ASSERT(ds->ds_phys->ds_prev_snap_obj != 0 ||
+	    spa_version(dp->dp_spa) < SPA_VERSION_ORIGIN ||
+	    dp->dp_origin_snap == NULL || ds == dp->dp_origin_snap);
+	mutex_enter(&ds->ds_lock);
+	if (!dsl_pool_sync_context(dp) && DSL_DATASET_IS_DESTROYED(ds)) {
+		mutex_exit(&ds->ds_lock);
+		dmu_buf_rele(ds->ds_dbuf, tag);
+		return (ENOENT);
+	}
+	mutex_exit(&ds->ds_lock);
+	*dsp = ds;
+	return (0);
+}
+
+static int
+dsl_dataset_hold_ref(dsl_dataset_t *ds, void *tag)
+{
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+
+	/*
+	 * In syncing context we don't want the rwlock lock: there
+	 * may be an existing writer waiting for sync phase to
+	 * finish.  We don't need to worry about such writers, since
+	 * sync phase is single-threaded, so the writer can't be
+	 * doing anything while we are active.
+	 */
+	if (dsl_pool_sync_context(dp)) {
+		ASSERT(!DSL_DATASET_IS_DESTROYED(ds));
+		return (0);
+	}
+
+	/*
+	 * Normal users will hold the ds_rwlock as a READER until they
+	 * are finished (i.e., call dsl_dataset_rele()).  "Owners" will
+	 * drop their READER lock after they set the ds_owner field.
+	 *
+	 * If the dataset is being destroyed, the destroy thread will
+	 * obtain a WRITER lock for exclusive access after it's done its
+	 * open-context work and then change the ds_owner to
+	 * dsl_reaper once destruction is assured.  So threads
+	 * may block here temporarily, until the "destructability" of
+	 * the dataset is determined.
+	 */
+	ASSERT(!RW_WRITE_HELD(&dp->dp_config_rwlock));
+	mutex_enter(&ds->ds_lock);
+	while (!rw_tryenter(&ds->ds_rwlock, RW_READER)) {
+		rw_exit(&dp->dp_config_rwlock);
+		cv_wait(&ds->ds_exclusive_cv, &ds->ds_lock);
+		if (DSL_DATASET_IS_DESTROYED(ds)) {
+			mutex_exit(&ds->ds_lock);
+			dsl_dataset_drop_ref(ds, tag);
+			rw_enter(&dp->dp_config_rwlock, RW_READER);
+			return (ENOENT);
+		}
+		rw_enter(&dp->dp_config_rwlock, RW_READER);
+	}
+	mutex_exit(&ds->ds_lock);
+	return (0);
+}
+
+int
+dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
+    dsl_dataset_t **dsp)
+{
+	int err = dsl_dataset_get_ref(dp, dsobj, tag, dsp);
+
+	if (err)
+		return (err);
+	return (dsl_dataset_hold_ref(*dsp, tag));
+}
+
+int
+dsl_dataset_own_obj(dsl_pool_t *dp, uint64_t dsobj, int flags, void *owner,
+    dsl_dataset_t **dsp)
+{
+	int err = dsl_dataset_hold_obj(dp, dsobj, owner, dsp);
+
+	ASSERT(DS_MODE_TYPE(flags) != DS_MODE_USER);
+
+	if (err)
+		return (err);
+	if (!dsl_dataset_tryown(*dsp, DS_MODE_IS_INCONSISTENT(flags), owner)) {
+		dsl_dataset_rele(*dsp, owner);
+		return (EBUSY);
+	}
+	return (0);
+}
+
+int
+dsl_dataset_hold(const char *name, void *tag, dsl_dataset_t **dsp)
+{
+	dsl_dir_t *dd;
+	dsl_pool_t *dp;
+	const char *snapname;
+	uint64_t obj;
+	int err = 0;
+
+	err = dsl_dir_open_spa(NULL, name, FTAG, &dd, &snapname);
+	if (err)
+		return (err);
+
+	dp = dd->dd_pool;
+	obj = dd->dd_phys->dd_head_dataset_obj;
+	rw_enter(&dp->dp_config_rwlock, RW_READER);
+	if (obj)
+		err = dsl_dataset_get_ref(dp, obj, tag, dsp);
+	else
+		err = ENOENT;
+	if (err)
+		goto out;
+
+	err = dsl_dataset_hold_ref(*dsp, tag);
+
+	/* we may be looking for a snapshot */
+	if (err == 0 && snapname != NULL) {
+		dsl_dataset_t *ds = NULL;
+
+		if (*snapname++ != '@') {
+			dsl_dataset_rele(*dsp, tag);
+			err = ENOENT;
+			goto out;
+		}
+
+		dprintf("looking for snapshot '%s'\n", snapname);
+		err = dsl_dataset_snap_lookup(*dsp, snapname, &obj);
+		if (err == 0)
+			err = dsl_dataset_get_ref(dp, obj, tag, &ds);
+		dsl_dataset_rele(*dsp, tag);
+
+		ASSERT3U((err == 0), ==, (ds != NULL));
+
+		if (ds) {
+			mutex_enter(&ds->ds_lock);
+			if (ds->ds_snapname[0] == 0)
+				(void) strlcpy(ds->ds_snapname, snapname,
+				    sizeof (ds->ds_snapname));
+			mutex_exit(&ds->ds_lock);
+			err = dsl_dataset_hold_ref(ds, tag);
+			*dsp = err ? NULL : ds;
+		}
+	}
+out:
+	rw_exit(&dp->dp_config_rwlock);
+	dsl_dir_close(dd, FTAG);
+	return (err);
+}
+
+int
+dsl_dataset_own(const char *name, int flags, void *owner, dsl_dataset_t **dsp)
+{
+	int err = dsl_dataset_hold(name, owner, dsp);
+	if (err)
+		return (err);
+	if ((*dsp)->ds_phys->ds_num_children > 0 &&
+	    !DS_MODE_IS_READONLY(flags)) {
+		dsl_dataset_rele(*dsp, owner);
+		return (EROFS);
+	}
+	if (!dsl_dataset_tryown(*dsp, DS_MODE_IS_INCONSISTENT(flags), owner)) {
+		dsl_dataset_rele(*dsp, owner);
+		return (EBUSY);
+	}
+	return (0);
+}
+
+void
+dsl_dataset_name(dsl_dataset_t *ds, char *name)
+{
+	if (ds == NULL) {
+		(void) strcpy(name, "mos");
+	} else {
+		dsl_dir_name(ds->ds_dir, name);
+		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		if (ds->ds_snapname[0]) {
+			(void) strcat(name, "@");
+			/*
+			 * We use a "recursive" mutex so that we
+			 * can call dprintf_ds() with ds_lock held.
+			 */
+			if (!MUTEX_HELD(&ds->ds_lock)) {
+				mutex_enter(&ds->ds_lock);
+				(void) strcat(name, ds->ds_snapname);
+				mutex_exit(&ds->ds_lock);
+			} else {
+				(void) strcat(name, ds->ds_snapname);
+			}
+		}
+	}
+}
+
+static int
+dsl_dataset_namelen(dsl_dataset_t *ds)
+{
+	int result;
+
+	if (ds == NULL) {
+		result = 3;	/* "mos" */
+	} else {
+		result = dsl_dir_namelen(ds->ds_dir);
+		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		if (ds->ds_snapname[0]) {
+			++result;	/* adding one for the @-sign */
+			if (!MUTEX_HELD(&ds->ds_lock)) {
+				mutex_enter(&ds->ds_lock);
+				result += strlen(ds->ds_snapname);
+				mutex_exit(&ds->ds_lock);
+			} else {
+				result += strlen(ds->ds_snapname);
+			}
+		}
+	}
+
+	return (result);
+}
+
+void
+dsl_dataset_drop_ref(dsl_dataset_t *ds, void *tag)
+{
+	dmu_buf_rele(ds->ds_dbuf, tag);
+}
+
+void
+dsl_dataset_rele(dsl_dataset_t *ds, void *tag)
+{
+	if (!dsl_pool_sync_context(ds->ds_dir->dd_pool)) {
+		rw_exit(&ds->ds_rwlock);
+	}
+	dsl_dataset_drop_ref(ds, tag);
+}
+
+void
+dsl_dataset_disown(dsl_dataset_t *ds, void *owner)
+{
+	ASSERT((ds->ds_owner == owner && ds->ds_dbuf) ||
+	    (DSL_DATASET_IS_DESTROYED(ds) && ds->ds_dbuf == NULL));
+
+	mutex_enter(&ds->ds_lock);
+	ds->ds_owner = NULL;
+	if (RW_WRITE_HELD(&ds->ds_rwlock)) {
+		rw_exit(&ds->ds_rwlock);
+		cv_broadcast(&ds->ds_exclusive_cv);
+	}
+	mutex_exit(&ds->ds_lock);
+	if (ds->ds_dbuf)
+		dsl_dataset_drop_ref(ds, owner);
+	else
+		dsl_dataset_evict(ds->ds_dbuf, ds);
+}
+
+boolean_t
+dsl_dataset_tryown(dsl_dataset_t *ds, boolean_t inconsistentok, void *owner)
+{
+	boolean_t gotit = FALSE;
+
+	mutex_enter(&ds->ds_lock);
+	if (ds->ds_owner == NULL &&
+	    (!DS_IS_INCONSISTENT(ds) || inconsistentok)) {
+		ds->ds_owner = owner;
+		if (!dsl_pool_sync_context(ds->ds_dir->dd_pool))
+			rw_exit(&ds->ds_rwlock);
+		gotit = TRUE;
+	}
+	mutex_exit(&ds->ds_lock);
+	return (gotit);
+}
+
+void
+dsl_dataset_make_exclusive(dsl_dataset_t *ds, void *owner)
+{
+	ASSERT3P(owner, ==, ds->ds_owner);
+	if (!RW_WRITE_HELD(&ds->ds_rwlock))
+		rw_enter(&ds->ds_rwlock, RW_WRITER);
+}
+
+uint64_t
+dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
+    uint64_t flags, dmu_tx_t *tx)
+{
+	dsl_pool_t *dp = dd->dd_pool;
+	dmu_buf_t *dbuf;
+	dsl_dataset_phys_t *dsphys;
+	uint64_t dsobj;
+	objset_t *mos = dp->dp_meta_objset;
+
+	if (origin == NULL)
+		origin = dp->dp_origin_snap;
+
+	ASSERT(origin == NULL || origin->ds_dir->dd_pool == dp);
+	ASSERT(origin == NULL || origin->ds_phys->ds_num_children > 0);
+	ASSERT(dmu_tx_is_syncing(tx));
+	ASSERT(dd->dd_phys->dd_head_dataset_obj == 0);
+
+	dsobj = dmu_object_alloc(mos, DMU_OT_DSL_DATASET, 0,
+	    DMU_OT_DSL_DATASET, sizeof (dsl_dataset_phys_t), tx);
+	VERIFY(0 == dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
+	dmu_buf_will_dirty(dbuf, tx);
+	dsphys = dbuf->db_data;
+	bzero(dsphys, sizeof (dsl_dataset_phys_t));
+	dsphys->ds_dir_obj = dd->dd_object;
+	dsphys->ds_flags = flags;
+	dsphys->ds_fsid_guid = unique_create();
+	(void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
+	    sizeof (dsphys->ds_guid));
+	dsphys->ds_snapnames_zapobj =
+	    zap_create_norm(mos, U8_TEXTPREP_TOUPPER, DMU_OT_DSL_DS_SNAP_MAP,
+	    DMU_OT_NONE, 0, tx);
+	dsphys->ds_creation_time = gethrestime_sec();
+	dsphys->ds_creation_txg = tx->tx_txg == TXG_INITIAL ? 1 : tx->tx_txg;
+	dsphys->ds_deadlist_obj =
+	    bplist_create(mos, DSL_DEADLIST_BLOCKSIZE, tx);
+
+	if (origin) {
+		dsphys->ds_prev_snap_obj = origin->ds_object;
+		dsphys->ds_prev_snap_txg =
+		    origin->ds_phys->ds_creation_txg;
+		dsphys->ds_used_bytes =
+		    origin->ds_phys->ds_used_bytes;
+		dsphys->ds_compressed_bytes =
+		    origin->ds_phys->ds_compressed_bytes;
+		dsphys->ds_uncompressed_bytes =
+		    origin->ds_phys->ds_uncompressed_bytes;
+		dsphys->ds_bp = origin->ds_phys->ds_bp;
+		dsphys->ds_flags |= origin->ds_phys->ds_flags;
+
+		dmu_buf_will_dirty(origin->ds_dbuf, tx);
+		origin->ds_phys->ds_num_children++;
+
+		if (spa_version(dp->dp_spa) >= SPA_VERSION_NEXT_CLONES) {
+			if (origin->ds_phys->ds_next_clones_obj == 0) {
+				origin->ds_phys->ds_next_clones_obj =
+				    zap_create(mos,
+				    DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
+			}
+			VERIFY(0 == zap_add_int(mos,
+			    origin->ds_phys->ds_next_clones_obj,
+			    dsobj, tx));
+		}
+
+		dmu_buf_will_dirty(dd->dd_dbuf, tx);
+		dd->dd_phys->dd_origin_obj = origin->ds_object;
+	}
+
+	if (spa_version(dp->dp_spa) >= SPA_VERSION_UNIQUE_ACCURATE)
+		dsphys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
+
+	dmu_buf_rele(dbuf, FTAG);
+
+	dmu_buf_will_dirty(dd->dd_dbuf, tx);
+	dd->dd_phys->dd_head_dataset_obj = dsobj;
+
+	return (dsobj);
+}
+
+uint64_t
+dsl_dataset_create_sync(dsl_dir_t *pdd, const char *lastname,
+    dsl_dataset_t *origin, uint64_t flags, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_pool_t *dp = pdd->dd_pool;
+	uint64_t dsobj, ddobj;
+	dsl_dir_t *dd;
+
+	ASSERT(lastname[0] != '@');
+
+	ddobj = dsl_dir_create_sync(dp, pdd, lastname, tx);
+	VERIFY(0 == dsl_dir_open_obj(dp, ddobj, lastname, FTAG, &dd));
+
+	dsobj = dsl_dataset_create_sync_dd(dd, origin, flags, tx);
+
+	dsl_deleg_set_create_perms(dd, tx, cr);
+
+	dsl_dir_close(dd, FTAG);
+
+	return (dsobj);
+}
+
+struct destroyarg {
+	dsl_sync_task_group_t *dstg;
+	char *snapname;
+	char *failed;
+};
+
+static int
+dsl_snapshot_destroy_one(char *name, void *arg)
+{
+	struct destroyarg *da = arg;
+	dsl_dataset_t *ds;
+	char *cp;
+	int err;
+
+	(void) strcat(name, "@");
+	(void) strcat(name, da->snapname);
+	err = dsl_dataset_own(name, DS_MODE_READONLY | DS_MODE_INCONSISTENT,
+	    da->dstg, &ds);
+	cp = strchr(name, '@');
+	*cp = '\0';
+	if (err == 0) {
+		dsl_dataset_make_exclusive(ds, da->dstg);
+		if (ds->ds_user_ptr) {
+			ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+			ds->ds_user_ptr = NULL;
+		}
+		dsl_sync_task_create(da->dstg, dsl_dataset_destroy_check,
+		    dsl_dataset_destroy_sync, ds, da->dstg, 0);
+	} else if (err == ENOENT) {
+		err = 0;
+	} else {
+		(void) strcpy(da->failed, name);
+	}
+	return (err);
+}
+
+/*
+ * Destroy 'snapname' in all descendants of 'fsname'.
+ */
+#pragma weak dmu_snapshots_destroy = dsl_snapshots_destroy
+int
+dsl_snapshots_destroy(char *fsname, char *snapname)
+{
+	int err;
+	struct destroyarg da;
+	dsl_sync_task_t *dst;
+	spa_t *spa;
+
+	err = spa_open(fsname, &spa, FTAG);
+	if (err)
+		return (err);
+	da.dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
+	da.snapname = snapname;
+	da.failed = fsname;
+
+	err = dmu_objset_find(fsname,
+	    dsl_snapshot_destroy_one, &da, DS_FIND_CHILDREN);
+
+	if (err == 0)
+		err = dsl_sync_task_group_wait(da.dstg);
+
+	for (dst = list_head(&da.dstg->dstg_tasks); dst;
+	    dst = list_next(&da.dstg->dstg_tasks, dst)) {
+		dsl_dataset_t *ds = dst->dst_arg1;
+		/*
+		 * Return the file system name that triggered the error
+		 */
+		if (dst->dst_err) {
+			dsl_dataset_name(ds, fsname);
+			*strchr(fsname, '@') = '\0';
+		}
+		dsl_dataset_disown(ds, da.dstg);
+	}
+
+	dsl_sync_task_group_destroy(da.dstg);
+	spa_close(spa, FTAG);
+	return (err);
+}
+
+/*
+ * ds must be opened as OWNER.  On return (whether successful or not),
+ * ds will be closed and caller can no longer dereference it.
+ */
+int
+dsl_dataset_destroy(dsl_dataset_t *ds, void *tag)
+{
+	int err;
+	dsl_sync_task_group_t *dstg;
+	objset_t *os;
+	dsl_dir_t *dd;
+	uint64_t obj;
+
+	if (dsl_dataset_is_snapshot(ds)) {
+		/* Destroying a snapshot is simpler */
+		dsl_dataset_make_exclusive(ds, tag);
+
+		if (ds->ds_user_ptr) {
+			ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+			ds->ds_user_ptr = NULL;
+		}
+		err = dsl_sync_task_do(ds->ds_dir->dd_pool,
+		    dsl_dataset_destroy_check, dsl_dataset_destroy_sync,
+		    ds, tag, 0);
+		goto out;
+	}
+
+	dd = ds->ds_dir;
+
+	/*
+	 * Check for errors and mark this ds as inconsistent, in
+	 * case we crash while freeing the objects.
+	 */
+	err = dsl_sync_task_do(dd->dd_pool, dsl_dataset_destroy_begin_check,
+	    dsl_dataset_destroy_begin_sync, ds, NULL, 0);
+	if (err)
+		goto out;
+
+	err = dmu_objset_open_ds(ds, DMU_OST_ANY, &os);
+	if (err)
+		goto out;
+
+	/*
+	 * remove the objects in open context, so that we won't
+	 * have too much to do in syncing context.
+	 */
+	for (obj = 0; err == 0; err = dmu_object_next(os, &obj, FALSE,
+	    ds->ds_phys->ds_prev_snap_txg)) {
+		/*
+		 * Ignore errors, if there is not enough disk space
+		 * we will deal with it in dsl_dataset_destroy_sync().
+		 */
+		(void) dmu_free_object(os, obj);
+	}
+
+	dmu_objset_close(os);
+	if (err != ESRCH)
+		goto out;
+
+	rw_enter(&dd->dd_pool->dp_config_rwlock, RW_READER);
+	err = dsl_dir_open_obj(dd->dd_pool, dd->dd_object, NULL, FTAG, &dd);
+	rw_exit(&dd->dd_pool->dp_config_rwlock);
+
+	if (err)
+		goto out;
+
+	if (ds->ds_user_ptr) {
+		/*
+		 * We need to sync out all in-flight IO before we try
+		 * to evict (the dataset evict func is trying to clear
+		 * the cached entries for this dataset in the ARC).
+		 */
+		txg_wait_synced(dd->dd_pool, 0);
+	}
+
+	/*
+	 * Blow away the dsl_dir + head dataset.
+	 */
+	dsl_dataset_make_exclusive(ds, tag);
+	if (ds->ds_user_ptr) {
+		ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+		ds->ds_user_ptr = NULL;
+	}
+	dstg = dsl_sync_task_group_create(ds->ds_dir->dd_pool);
+	dsl_sync_task_create(dstg, dsl_dataset_destroy_check,
+	    dsl_dataset_destroy_sync, ds, tag, 0);
+	dsl_sync_task_create(dstg, dsl_dir_destroy_check,
+	    dsl_dir_destroy_sync, dd, FTAG, 0);
+	err = dsl_sync_task_group_wait(dstg);
+	dsl_sync_task_group_destroy(dstg);
+	/* if it is successful, dsl_dir_destroy_sync will close the dd */
+	if (err)
+		dsl_dir_close(dd, FTAG);
+out:
+	dsl_dataset_disown(ds, tag);
+	return (err);
+}
+
+int
+dsl_dataset_rollback(dsl_dataset_t *ds, dmu_objset_type_t ost)
+{
+	int err;
+
+	ASSERT(ds->ds_owner);
+
+	dsl_dataset_make_exclusive(ds, ds->ds_owner);
+	err = dsl_sync_task_do(ds->ds_dir->dd_pool,
+	    dsl_dataset_rollback_check, dsl_dataset_rollback_sync,
+	    ds, &ost, 0);
+	/* drop exclusive access */
+	mutex_enter(&ds->ds_lock);
+	rw_exit(&ds->ds_rwlock);
+	cv_broadcast(&ds->ds_exclusive_cv);
+	mutex_exit(&ds->ds_lock);
+	return (err);
+}
+
+void *
+dsl_dataset_set_user_ptr(dsl_dataset_t *ds,
+    void *p, dsl_dataset_evict_func_t func)
+{
+	void *old;
+
+	mutex_enter(&ds->ds_lock);
+	old = ds->ds_user_ptr;
+	if (old == NULL) {
+		ds->ds_user_ptr = p;
+		ds->ds_user_evict_func = func;
+	}
+	mutex_exit(&ds->ds_lock);
+	return (old);
+}
+
+void *
+dsl_dataset_get_user_ptr(dsl_dataset_t *ds)
+{
+	return (ds->ds_user_ptr);
+}
+
+
+blkptr_t *
+dsl_dataset_get_blkptr(dsl_dataset_t *ds)
+{
+	return (&ds->ds_phys->ds_bp);
+}
+
+void
+dsl_dataset_set_blkptr(dsl_dataset_t *ds, blkptr_t *bp, dmu_tx_t *tx)
+{
+	ASSERT(dmu_tx_is_syncing(tx));
+	/* If it's the meta-objset, set dp_meta_rootbp */
+	if (ds == NULL) {
+		tx->tx_pool->dp_meta_rootbp = *bp;
+	} else {
+		dmu_buf_will_dirty(ds->ds_dbuf, tx);
+		ds->ds_phys->ds_bp = *bp;
+	}
+}
+
+spa_t *
+dsl_dataset_get_spa(dsl_dataset_t *ds)
+{
+	return (ds->ds_dir->dd_pool->dp_spa);
+}
+
+void
+dsl_dataset_dirty(dsl_dataset_t *ds, dmu_tx_t *tx)
+{
+	dsl_pool_t *dp;
+
+	if (ds == NULL) /* this is the meta-objset */
+		return;
+
+	ASSERT(ds->ds_user_ptr != NULL);
+
+	if (ds->ds_phys->ds_next_snap_obj != 0)
+		panic("dirtying snapshot!");
+
+	dp = ds->ds_dir->dd_pool;
+
+	if (txg_list_add(&dp->dp_dirty_datasets, ds, tx->tx_txg) == 0) {
+		/* up the hold count until we can be written out */
+		dmu_buf_add_ref(ds->ds_dbuf, ds);
+	}
+}
+
+/*
+ * The unique space in the head dataset can be calculated by subtracting
+ * the space used in the most recent snapshot, that is still being used
+ * in this file system, from the space currently in use.  To figure out
+ * the space in the most recent snapshot still in use, we need to take
+ * the total space used in the snapshot and subtract out the space that
+ * has been freed up since the snapshot was taken.
+ */
+static void
+dsl_dataset_recalc_head_uniq(dsl_dataset_t *ds)
+{
+	uint64_t mrs_used;
+	uint64_t dlused, dlcomp, dluncomp;
+
+	ASSERT(ds->ds_object == ds->ds_dir->dd_phys->dd_head_dataset_obj);
+
+	if (ds->ds_phys->ds_prev_snap_obj != 0)
+		mrs_used = ds->ds_prev->ds_phys->ds_used_bytes;
+	else
+		mrs_used = 0;
+
+	VERIFY(0 == bplist_space(&ds->ds_deadlist, &dlused, &dlcomp,
+	    &dluncomp));
+
+	ASSERT3U(dlused, <=, mrs_used);
+	ds->ds_phys->ds_unique_bytes =
+	    ds->ds_phys->ds_used_bytes - (mrs_used - dlused);
+
+	if (!DS_UNIQUE_IS_ACCURATE(ds) &&
+	    spa_version(ds->ds_dir->dd_pool->dp_spa) >=
+	    SPA_VERSION_UNIQUE_ACCURATE)
+		ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
+}
+
+static uint64_t
+dsl_dataset_unique(dsl_dataset_t *ds)
+{
+	if (!DS_UNIQUE_IS_ACCURATE(ds) && !dsl_dataset_is_snapshot(ds))
+		dsl_dataset_recalc_head_uniq(ds);
+
+	return (ds->ds_phys->ds_unique_bytes);
+}
+
+struct killarg {
+	dsl_dataset_t *ds;
+	zio_t *zio;
+	dmu_tx_t *tx;
+};
+
+/* ARGSUSED */
+static int
+kill_blkptr(spa_t *spa, blkptr_t *bp, const zbookmark_t *zb,
+    const dnode_phys_t *dnp, void *arg)
+{
+	struct killarg *ka = arg;
+
+	if (bp == NULL)
+		return (0);
+
+	ASSERT3U(bp->blk_birth, >, ka->ds->ds_phys->ds_prev_snap_txg);
+	(void) dsl_dataset_block_kill(ka->ds, bp, ka->zio, ka->tx);
+
+	return (0);
+}
+
+/* ARGSUSED */
+static int
+dsl_dataset_rollback_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	dmu_objset_type_t *ost = arg2;
+
+	/*
+	 * We can only roll back to emptyness if it is a ZPL objset.
+	 */
+	if (*ost != DMU_OST_ZFS && ds->ds_phys->ds_prev_snap_txg == 0)
+		return (EINVAL);
+
+	/*
+	 * This must not be a snapshot.
+	 */
+	if (ds->ds_phys->ds_next_snap_obj != 0)
+		return (EINVAL);
+
+	/*
+	 * If we made changes this txg, traverse_dataset won't find
+	 * them.  Try again.
+	 */
+	if (ds->ds_phys->ds_bp.blk_birth >= tx->tx_txg)
+		return (EAGAIN);
+
+	return (0);
+}
+
+/* ARGSUSED */
+static void
+dsl_dataset_rollback_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	dmu_objset_type_t *ost = arg2;
+	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
+
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+
+	/*
+	 * Before the roll back destroy the zil.
+	 */
+	if (ds->ds_user_ptr != NULL) {
+		zil_rollback_destroy(
+		    ((objset_impl_t *)ds->ds_user_ptr)->os_zil, tx);
+
+		/*
+		 * We need to make sure that the objset_impl_t is reopened after
+		 * we do the rollback, otherwise it will have the wrong
+		 * objset_phys_t.  Normally this would happen when this
+		 * dataset-open is closed, thus causing the
+		 * dataset to be immediately evicted.  But when doing "zfs recv
+		 * -F", we reopen the objset before that, so that there is no
+		 * window where the dataset is closed and inconsistent.
+		 */
+		ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+		ds->ds_user_ptr = NULL;
+	}
+
+	/* Transfer space that was freed since last snap back to the head. */
+	{
+		uint64_t used;
+
+		VERIFY(0 == bplist_space_birthrange(&ds->ds_deadlist,
+		    ds->ds_origin_txg, UINT64_MAX, &used));
+		dsl_dir_transfer_space(ds->ds_dir, used,
+		    DD_USED_SNAP, DD_USED_HEAD, tx);
+	}
+
+	/* Zero out the deadlist. */
+	bplist_close(&ds->ds_deadlist);
+	bplist_destroy(mos, ds->ds_phys->ds_deadlist_obj, tx);
+	ds->ds_phys->ds_deadlist_obj =
+	    bplist_create(mos, DSL_DEADLIST_BLOCKSIZE, tx);
+	VERIFY(0 == bplist_open(&ds->ds_deadlist, mos,
+	    ds->ds_phys->ds_deadlist_obj));
+
+	{
+		/* Free blkptrs that we gave birth to */
+		zio_t *zio;
+		struct killarg ka;
+
+		zio = zio_root(tx->tx_pool->dp_spa, NULL, NULL,
+		    ZIO_FLAG_MUSTSUCCEED);
+		ka.ds = ds;
+		ka.zio = zio;
+		ka.tx = tx;
+		(void) traverse_dataset(ds, ds->ds_phys->ds_prev_snap_txg,
+		    TRAVERSE_POST, kill_blkptr, &ka);
+		(void) zio_wait(zio);
+	}
+
+	ASSERT(!(ds->ds_phys->ds_flags & DS_FLAG_UNIQUE_ACCURATE) ||
+	    ds->ds_phys->ds_unique_bytes == 0);
+
+	if (ds->ds_prev && ds->ds_prev != ds->ds_dir->dd_pool->dp_origin_snap) {
+		/* Change our contents to that of the prev snapshot */
+
+		ASSERT3U(ds->ds_prev->ds_object, ==,
+		    ds->ds_phys->ds_prev_snap_obj);
+		ASSERT3U(ds->ds_phys->ds_used_bytes, <=,
+		    ds->ds_prev->ds_phys->ds_used_bytes);
+
+		ds->ds_phys->ds_bp = ds->ds_prev->ds_phys->ds_bp;
+		ds->ds_phys->ds_used_bytes =
+		    ds->ds_prev->ds_phys->ds_used_bytes;
+		ds->ds_phys->ds_compressed_bytes =
+		    ds->ds_prev->ds_phys->ds_compressed_bytes;
+		ds->ds_phys->ds_uncompressed_bytes =
+		    ds->ds_prev->ds_phys->ds_uncompressed_bytes;
+		ds->ds_phys->ds_flags = ds->ds_prev->ds_phys->ds_flags;
+
+		if (ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object) {
+			dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
+			ds->ds_prev->ds_phys->ds_unique_bytes = 0;
+		}
+	} else {
+		objset_impl_t *osi;
+
+		ASSERT3U(ds->ds_phys->ds_used_bytes, ==, 0);
+		ASSERT3U(ds->ds_phys->ds_compressed_bytes, ==, 0);
+		ASSERT3U(ds->ds_phys->ds_uncompressed_bytes, ==, 0);
+
+		bzero(&ds->ds_phys->ds_bp, sizeof (blkptr_t));
+		ds->ds_phys->ds_flags = 0;
+		ds->ds_phys->ds_unique_bytes = 0;
+		if (spa_version(ds->ds_dir->dd_pool->dp_spa) >=
+		    SPA_VERSION_UNIQUE_ACCURATE)
+			ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
+
+		osi = dmu_objset_create_impl(ds->ds_dir->dd_pool->dp_spa, ds,
+		    &ds->ds_phys->ds_bp, *ost, tx);
+#ifdef _KERNEL
+		zfs_create_fs(&osi->os, kcred, NULL, tx);
+#endif
+	}
+
+	spa_history_internal_log(LOG_DS_ROLLBACK, ds->ds_dir->dd_pool->dp_spa,
+	    tx, cr, "dataset = %llu", ds->ds_object);
+}
+
+/* ARGSUSED */
+static int
+dsl_dataset_destroy_begin_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
+	uint64_t count;
+	int err;
+
+	/*
+	 * Can't delete a head dataset if there are snapshots of it.
+	 * (Except if the only snapshots are from the branch we cloned
+	 * from.)
+	 */
+	if (ds->ds_prev != NULL &&
+	    ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
+		return (EINVAL);
+
+	/*
+	 * This is really a dsl_dir thing, but check it here so that
+	 * we'll be less likely to leave this dataset inconsistent &
+	 * nearly destroyed.
+	 */
+	err = zap_count(mos, ds->ds_dir->dd_phys->dd_child_dir_zapobj, &count);
+	if (err)
+		return (err);
+	if (count != 0)
+		return (EEXIST);
+
+	return (0);
+}
+
+/* ARGSUSED */
+static void
+dsl_dataset_destroy_begin_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+
+	/* Mark it as inconsistent on-disk, in case we crash */
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	ds->ds_phys->ds_flags |= DS_FLAG_INCONSISTENT;
+
+	spa_history_internal_log(LOG_DS_DESTROY_BEGIN, dp->dp_spa, tx,
+	    cr, "dataset = %llu", ds->ds_object);
+}
+
+/* ARGSUSED */
+int
+dsl_dataset_destroy_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+
+	/* we have an owner hold, so noone else can destroy us */
+	ASSERT(!DSL_DATASET_IS_DESTROYED(ds));
+
+	/* Can't delete a branch point. */
+	if (ds->ds_phys->ds_num_children > 1)
+		return (EEXIST);
+
+	/*
+	 * 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 (EINVAL);
+
+	/*
+	 * If we made changes this txg, traverse_dsl_dataset won't find
+	 * them.  Try again.
+	 */
+	if (ds->ds_phys->ds_bp.blk_birth >= tx->tx_txg)
+		return (EAGAIN);
+
+	/* XXX we should do some i/o error checking... */
+	return (0);
+}
+
+struct refsarg {
+	kmutex_t lock;
+	boolean_t gone;
+	kcondvar_t cv;
+};
+
+/* ARGSUSED */
+static void
+dsl_dataset_refs_gone(dmu_buf_t *db, void *argv)
+{
+	struct refsarg *arg = argv;
+
+	mutex_enter(&arg->lock);
+	arg->gone = TRUE;
+	cv_signal(&arg->cv);
+	mutex_exit(&arg->lock);
+}
+
+static void
+dsl_dataset_drain_refs(dsl_dataset_t *ds, void *tag)
+{
+	struct refsarg arg;
+
+	mutex_init(&arg.lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&arg.cv, NULL, CV_DEFAULT, NULL);
+	arg.gone = FALSE;
+	(void) dmu_buf_update_user(ds->ds_dbuf, ds, &arg, &ds->ds_phys,
+	    dsl_dataset_refs_gone);
+	dmu_buf_rele(ds->ds_dbuf, tag);
+	mutex_enter(&arg.lock);
+	while (!arg.gone)
+		cv_wait(&arg.cv, &arg.lock);
+	ASSERT(arg.gone);
+	mutex_exit(&arg.lock);
+	ds->ds_dbuf = NULL;
+	ds->ds_phys = NULL;
+	mutex_destroy(&arg.lock);
+	cv_destroy(&arg.cv);
+}
+
+void
+dsl_dataset_destroy_sync(void *arg1, void *tag, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	zio_t *zio;
+	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(ds->ds_owner);
+	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);
+
+	/* signal any waiters that this dataset is going away */
+	mutex_enter(&ds->ds_lock);
+	ds->ds_owner = dsl_reaper;
+	cv_broadcast(&ds->ds_exclusive_cv);
+	mutex_exit(&ds->ds_lock);
+
+	/* Remove our reservation */
+	if (ds->ds_reserved != 0) {
+		uint64_t val = 0;
+		dsl_dataset_set_reservation_sync(ds, &val, cr, tx);
+		ASSERT3U(ds->ds_reserved, ==, 0);
+	}
+
+	ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));
+
+	dsl_pool_ds_destroyed(ds, tx);
+
+	obj = ds->ds_object;
+
+	if (ds->ds_phys->ds_prev_snap_obj != 0) {
+		if (ds->ds_prev) {
+			ds_prev = ds->ds_prev;
+		} else {
+			VERIFY(0 == dsl_dataset_hold_obj(dp,
+			    ds->ds_phys->ds_prev_snap_obj, FTAG, &ds_prev));
+		}
+		after_branch_point =
+		    (ds_prev->ds_phys->ds_next_snap_obj != obj);
+
+		dmu_buf_will_dirty(ds_prev->ds_dbuf, tx);
+		if (after_branch_point &&
+		    ds_prev->ds_phys->ds_next_clones_obj != 0) {
+			VERIFY(0 == zap_remove_int(mos,
+			    ds_prev->ds_phys->ds_next_clones_obj, obj, tx));
+			if (ds->ds_phys->ds_next_snap_obj != 0) {
+				VERIFY(0 == zap_add_int(mos,
+				    ds_prev->ds_phys->ds_next_clones_obj,
+				    ds->ds_phys->ds_next_snap_obj, tx));
+			}
+		}
+		if (after_branch_point &&
+		    ds->ds_phys->ds_next_snap_obj == 0) {
+			/* This clone is toast. */
+			ASSERT(ds_prev->ds_phys->ds_num_children > 1);
+			ds_prev->ds_phys->ds_num_children--;
+		} else if (!after_branch_point) {
+			ds_prev->ds_phys->ds_next_snap_obj =
+			    ds->ds_phys->ds_next_snap_obj;
+		}
+	}
+
+	zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
+
+	if (ds->ds_phys->ds_next_snap_obj != 0) {
+		blkptr_t bp;
+		dsl_dataset_t *ds_next;
+		uint64_t itor = 0;
+		uint64_t old_unique;
+		int64_t used = 0, compressed = 0, uncompressed = 0;
+
+		VERIFY(0 == dsl_dataset_hold_obj(dp,
+		    ds->ds_phys->ds_next_snap_obj, FTAG, &ds_next));
+		ASSERT3U(ds_next->ds_phys->ds_prev_snap_obj, ==, obj);
+
+		old_unique = dsl_dataset_unique(ds_next);
+
+		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);
+
+		/*
+		 * Transfer to our deadlist (which will become next's
+		 * new deadlist) any entries from next's current
+		 * deadlist which were born before prev, and free the
+		 * other entries.
+		 *
+		 * XXX we're doing this long task with the config lock held
+		 */
+		while (bplist_iterate(&ds_next->ds_deadlist, &itor, &bp) == 0) {
+			if (bp.blk_birth <= ds->ds_phys->ds_prev_snap_txg) {
+				VERIFY(0 == bplist_enqueue(&ds->ds_deadlist,
+				    &bp, tx));
+				if (ds_prev && !after_branch_point &&
+				    bp.blk_birth >
+				    ds_prev->ds_phys->ds_prev_snap_txg) {
+					ds_prev->ds_phys->ds_unique_bytes +=
+					    bp_get_dasize(dp->dp_spa, &bp);
+				}
+			} else {
+				used += bp_get_dasize(dp->dp_spa, &bp);
+				compressed += BP_GET_PSIZE(&bp);
+				uncompressed += BP_GET_UCSIZE(&bp);
+				/* XXX check return value? */
+				(void) dsl_free(zio, dp, tx->tx_txg,
+				    &bp, NULL, NULL, ARC_NOWAIT);
+			}
+		}
+
+		ASSERT3U(used, ==, ds->ds_phys->ds_unique_bytes);
+
+		/* change snapused */
+		dsl_dir_diduse_space(ds->ds_dir, DD_USED_SNAP,
+		    -used, -compressed, -uncompressed, tx);
+
+		/* free next's deadlist */
+		bplist_close(&ds_next->ds_deadlist);
+		bplist_destroy(mos, ds_next->ds_phys->ds_deadlist_obj, tx);
+
+		/* set next's deadlist to our deadlist */
+		bplist_close(&ds->ds_deadlist);
+		ds_next->ds_phys->ds_deadlist_obj =
+		    ds->ds_phys->ds_deadlist_obj;
+		VERIFY(0 == bplist_open(&ds_next->ds_deadlist, mos,
+		    ds_next->ds_phys->ds_deadlist_obj));
+		ds->ds_phys->ds_deadlist_obj = 0;
+
+		if (ds_next->ds_phys->ds_next_snap_obj != 0) {
+			/*
+			 * 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).
+			 *
+			 * XXX we're doing this long task with the
+			 * config lock held
+			 */
+			dsl_dataset_t *ds_after_next;
+			uint64_t space;
+
+			VERIFY(0 == dsl_dataset_hold_obj(dp,
+			    ds_next->ds_phys->ds_next_snap_obj,
+			    FTAG, &ds_after_next));
+
+			VERIFY(0 ==
+			    bplist_space_birthrange(&ds_after_next->ds_deadlist,
+			    ds->ds_phys->ds_prev_snap_txg,
+			    ds->ds_phys->ds_creation_txg, &space));
+			ds_next->ds_phys->ds_unique_bytes += space;
+
+			dsl_dataset_rele(ds_after_next, FTAG);
+			ASSERT3P(ds_next->ds_prev, ==, NULL);
+		} else {
+			ASSERT3P(ds_next->ds_prev, ==, ds);
+			dsl_dataset_drop_ref(ds_next->ds_prev, ds_next);
+			ds_next->ds_prev = NULL;
+			if (ds_prev) {
+				VERIFY(0 == dsl_dataset_get_ref(dp,
+				    ds->ds_phys->ds_prev_snap_obj,
+				    ds_next, &ds_next->ds_prev));
+			}
+
+			dsl_dataset_recalc_head_uniq(ds_next);
+
+			/*
+			 * Reduce the amount of our unconsmed refreservation
+			 * being charged to our parent by the amount of
+			 * new unique data we have gained.
+			 */
+			if (old_unique < ds_next->ds_reserved) {
+				int64_t mrsdelta;
+				uint64_t new_unique =
+				    ds_next->ds_phys->ds_unique_bytes;
+
+				ASSERT(old_unique <= new_unique);
+				mrsdelta = MIN(new_unique - old_unique,
+				    ds_next->ds_reserved - old_unique);
+				dsl_dir_diduse_space(ds->ds_dir,
+				    DD_USED_REFRSRV, -mrsdelta, 0, 0, tx);
+			}
+		}
+		dsl_dataset_rele(ds_next, FTAG);
+	} else {
+		/*
+		 * There's no next snapshot, so this is a head dataset.
+		 * Destroy the deadlist.  Unless it's a clone, the
+		 * deadlist should be empty.  (If it's a clone, it's
+		 * safe to ignore the deadlist contents.)
+		 */
+		struct killarg ka;
+
+		ASSERT(after_branch_point || bplist_empty(&ds->ds_deadlist));
+		bplist_close(&ds->ds_deadlist);
+		bplist_destroy(mos, ds->ds_phys->ds_deadlist_obj, tx);
+		ds->ds_phys->ds_deadlist_obj = 0;
+
+		/*
+		 * 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.zio = zio;
+		ka.tx = tx;
+		err = traverse_dataset(ds, ds->ds_phys->ds_prev_snap_txg,
+		    TRAVERSE_POST, kill_blkptr, &ka);
+		ASSERT3U(err, ==, 0);
+		ASSERT(spa_version(dp->dp_spa) < SPA_VERSION_UNIQUE_ACCURATE ||
+		    ds->ds_phys->ds_unique_bytes == 0);
+	}
+
+	err = zio_wait(zio);
+	ASSERT3U(err, ==, 0);
+
+	if (ds->ds_dir->dd_phys->dd_head_dataset_obj == ds->ds_object) {
+		/* Erase the link in the dir */
+		dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
+		ds->ds_dir->dd_phys->dd_head_dataset_obj = 0;
+		ASSERT(ds->ds_phys->ds_snapnames_zapobj != 0);
+		err = zap_destroy(mos, ds->ds_phys->ds_snapnames_zapobj, tx);
+		ASSERT(err == 0);
+	} else {
+		/* remove from snapshot namespace */
+		dsl_dataset_t *ds_head;
+		ASSERT(ds->ds_phys->ds_snapnames_zapobj == 0);
+		VERIFY(0 == dsl_dataset_hold_obj(dp,
+		    ds->ds_dir->dd_phys->dd_head_dataset_obj, FTAG, &ds_head));
+		VERIFY(0 == dsl_dataset_get_snapname(ds));
+#ifdef ZFS_DEBUG
+		{
+			uint64_t val;
+
+			err = dsl_dataset_snap_lookup(ds_head,
+			    ds->ds_snapname, &val);
+			ASSERT3U(err, ==, 0);
+			ASSERT3U(val, ==, obj);
+		}
+#endif
+		err = dsl_dataset_snap_remove(ds_head, ds->ds_snapname, tx);
+		ASSERT(err == 0);
+		dsl_dataset_rele(ds_head, FTAG);
+	}
+
+	if (ds_prev && ds->ds_prev != ds_prev)
+		dsl_dataset_rele(ds_prev, FTAG);
+
+	spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);
+	spa_history_internal_log(LOG_DS_DESTROY, dp->dp_spa, tx,
+	    cr, "dataset = %llu", ds->ds_object);
+
+	if (ds->ds_phys->ds_next_clones_obj != 0) {
+		uint64_t count;
+		ASSERT(0 == zap_count(mos,
+		    ds->ds_phys->ds_next_clones_obj, &count) && count == 0);
+		VERIFY(0 == dmu_object_free(mos,
+		    ds->ds_phys->ds_next_clones_obj, tx));
+	}
+	if (ds->ds_phys->ds_props_obj != 0)
+		VERIFY(0 == zap_destroy(mos, ds->ds_phys->ds_props_obj, tx));
+	dsl_dir_close(ds->ds_dir, ds);
+	ds->ds_dir = NULL;
+	dsl_dataset_drain_refs(ds, tag);
+	VERIFY(0 == dmu_object_free(mos, obj, tx));
+}
+
+static int
+dsl_dataset_snapshot_reserve_space(dsl_dataset_t *ds, dmu_tx_t *tx)
+{
+	uint64_t asize;
+
+	if (!dmu_tx_is_syncing(tx))
+		return (0);
+
+	/*
+	 * If there's an fs-only reservation, any blocks that might become
+	 * owned by the snapshot dataset must be accommodated by space
+	 * outside of the reservation.
+	 */
+	asize = MIN(dsl_dataset_unique(ds), ds->ds_reserved);
+	if (asize > dsl_dir_space_available(ds->ds_dir, NULL, 0, FALSE))
+		return (ENOSPC);
+
+	/*
+	 * Propogate any reserved space for this snapshot to other
+	 * snapshot checks in this sync group.
+	 */
+	if (asize > 0)
+		dsl_dir_willuse_space(ds->ds_dir, asize, tx);
+
+	return (0);
+}
+
+/* ARGSUSED */
+int
+dsl_dataset_snapshot_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	const char *snapname = arg2;
+	int err;
+	uint64_t value;
+
+	/*
+	 * We don't allow multiple snapshots of the same txg.  If there
+	 * is already one, try again.
+	 */
+	if (ds->ds_phys->ds_prev_snap_txg >= tx->tx_txg)
+		return (EAGAIN);
+
+	/*
+	 * Check for conflicting name snapshot name.
+	 */
+	err = dsl_dataset_snap_lookup(ds, snapname, &value);
+	if (err == 0)
+		return (EEXIST);
+	if (err != ENOENT)
+		return (err);
+
+	/*
+	 * Check that the dataset's name is not too long.  Name consists
+	 * of the dataset's length + 1 for the @-sign + snapshot name's length
+	 */
+	if (dsl_dataset_namelen(ds) + 1 + strlen(snapname) >= MAXNAMELEN)
+		return (ENAMETOOLONG);
+
+	err = dsl_dataset_snapshot_reserve_space(ds, tx);
+	if (err)
+		return (err);
+
+	ds->ds_trysnap_txg = tx->tx_txg;
+	return (0);
+}
+
+void
+dsl_dataset_snapshot_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	const char *snapname = arg2;
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	dmu_buf_t *dbuf;
+	dsl_dataset_phys_t *dsphys;
+	uint64_t dsobj, crtxg;
+	objset_t *mos = dp->dp_meta_objset;
+	int err;
+
+	ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));
+
+	/*
+	 * The origin's ds_creation_txg has to be < TXG_INITIAL
+	 */
+	if (strcmp(snapname, ORIGIN_DIR_NAME) == 0)
+		crtxg = 1;
+	else
+		crtxg = tx->tx_txg;
+
+	dsobj = dmu_object_alloc(mos, DMU_OT_DSL_DATASET, 0,
+	    DMU_OT_DSL_DATASET, sizeof (dsl_dataset_phys_t), tx);
+	VERIFY(0 == dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
+	dmu_buf_will_dirty(dbuf, tx);
+	dsphys = dbuf->db_data;
+	bzero(dsphys, sizeof (dsl_dataset_phys_t));
+	dsphys->ds_dir_obj = ds->ds_dir->dd_object;
+	dsphys->ds_fsid_guid = unique_create();
+	(void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
+	    sizeof (dsphys->ds_guid));
+	dsphys->ds_prev_snap_obj = ds->ds_phys->ds_prev_snap_obj;
+	dsphys->ds_prev_snap_txg = ds->ds_phys->ds_prev_snap_txg;
+	dsphys->ds_next_snap_obj = ds->ds_object;
+	dsphys->ds_num_children = 1;
+	dsphys->ds_creation_time = gethrestime_sec();
+	dsphys->ds_creation_txg = crtxg;
+	dsphys->ds_deadlist_obj = ds->ds_phys->ds_deadlist_obj;
+	dsphys->ds_used_bytes = ds->ds_phys->ds_used_bytes;
+	dsphys->ds_compressed_bytes = ds->ds_phys->ds_compressed_bytes;
+	dsphys->ds_uncompressed_bytes = ds->ds_phys->ds_uncompressed_bytes;
+	dsphys->ds_flags = ds->ds_phys->ds_flags;
+	dsphys->ds_bp = ds->ds_phys->ds_bp;
+	dmu_buf_rele(dbuf, FTAG);
+
+	ASSERT3U(ds->ds_prev != 0, ==, ds->ds_phys->ds_prev_snap_obj != 0);
+	if (ds->ds_prev) {
+		uint64_t next_clones_obj =
+		    ds->ds_prev->ds_phys->ds_next_clones_obj;
+		ASSERT(ds->ds_prev->ds_phys->ds_next_snap_obj ==
+		    ds->ds_object ||
+		    ds->ds_prev->ds_phys->ds_num_children > 1);
+		if (ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object) {
+			dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
+			ASSERT3U(ds->ds_phys->ds_prev_snap_txg, ==,
+			    ds->ds_prev->ds_phys->ds_creation_txg);
+			ds->ds_prev->ds_phys->ds_next_snap_obj = dsobj;
+		} else if (next_clones_obj != 0) {
+			VERIFY3U(0, ==, zap_remove_int(mos,
+			    next_clones_obj, dsphys->ds_next_snap_obj, tx));
+			VERIFY3U(0, ==, zap_add_int(mos,
+			    next_clones_obj, dsobj, tx));
+		}
+	}
+
+	/*
+	 * If we have a reference-reservation on this dataset, we will
+	 * need to increase the amount of refreservation being charged
+	 * since our unique space is going to zero.
+	 */
+	if (ds->ds_reserved) {
+		int64_t add = MIN(dsl_dataset_unique(ds), ds->ds_reserved);
+		dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV,
+		    add, 0, 0, tx);
+	}
+
+	bplist_close(&ds->ds_deadlist);
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	ASSERT3U(ds->ds_phys->ds_prev_snap_txg, <, tx->tx_txg);
+	ds->ds_phys->ds_prev_snap_obj = dsobj;
+	ds->ds_phys->ds_prev_snap_txg = crtxg;
+	ds->ds_phys->ds_unique_bytes = 0;
+	if (spa_version(dp->dp_spa) >= SPA_VERSION_UNIQUE_ACCURATE)
+		ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
+	ds->ds_phys->ds_deadlist_obj =
+	    bplist_create(mos, DSL_DEADLIST_BLOCKSIZE, tx);
+	VERIFY(0 == bplist_open(&ds->ds_deadlist, mos,
+	    ds->ds_phys->ds_deadlist_obj));
+
+	dprintf("snap '%s' -> obj %llu\n", snapname, dsobj);
+	err = zap_add(mos, ds->ds_phys->ds_snapnames_zapobj,
+	    snapname, 8, 1, &dsobj, tx);
+	ASSERT(err == 0);
+
+	if (ds->ds_prev)
+		dsl_dataset_drop_ref(ds->ds_prev, ds);
+	VERIFY(0 == dsl_dataset_get_ref(dp,
+	    ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));
+
+	dsl_pool_ds_snapshotted(ds, tx);
+
+	spa_history_internal_log(LOG_DS_SNAPSHOT, dp->dp_spa, tx, cr,
+	    "dataset = %llu", dsobj);
+}
+
+void
+dsl_dataset_sync(dsl_dataset_t *ds, zio_t *zio, dmu_tx_t *tx)
+{
+	ASSERT(dmu_tx_is_syncing(tx));
+	ASSERT(ds->ds_user_ptr != NULL);
+	ASSERT(ds->ds_phys->ds_next_snap_obj == 0);
+
+	/*
+	 * in case we had to change ds_fsid_guid when we opened it,
+	 * sync it out now.
+	 */
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	ds->ds_phys->ds_fsid_guid = ds->ds_fsid_guid;
+
+	dsl_dir_dirty(ds->ds_dir, tx);
+	dmu_objset_sync(ds->ds_user_ptr, zio, tx);
+}
+
+void
+dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
+{
+	uint64_t refd, avail, uobjs, aobjs;
+
+	dsl_dir_stats(ds->ds_dir, nv);
+
+	dsl_dataset_space(ds, &refd, &avail, &uobjs, &aobjs);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_AVAILABLE, avail);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFERENCED, refd);
+
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_CREATION,
+	    ds->ds_phys->ds_creation_time);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_CREATETXG,
+	    ds->ds_phys->ds_creation_txg);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFQUOTA,
+	    ds->ds_quota);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFRESERVATION,
+	    ds->ds_reserved);
+	dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_GUID,
+	    ds->ds_phys->ds_guid);
+
+	if (ds->ds_phys->ds_next_snap_obj) {
+		/*
+		 * This is a snapshot; override the dd's space used with
+		 * our unique space and compression ratio.
+		 */
+		dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_USED,
+		    ds->ds_phys->ds_unique_bytes);
+		dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_COMPRESSRATIO,
+		    ds->ds_phys->ds_compressed_bytes == 0 ? 100 :
+		    (ds->ds_phys->ds_uncompressed_bytes * 100 /
+		    ds->ds_phys->ds_compressed_bytes));
+	}
+}
+
+void
+dsl_dataset_fast_stat(dsl_dataset_t *ds, dmu_objset_stats_t *stat)
+{
+	stat->dds_creation_txg = ds->ds_phys->ds_creation_txg;
+	stat->dds_inconsistent = ds->ds_phys->ds_flags & DS_FLAG_INCONSISTENT;
+	stat->dds_guid = ds->ds_phys->ds_guid;
+	if (ds->ds_phys->ds_next_snap_obj) {
+		stat->dds_is_snapshot = B_TRUE;
+		stat->dds_num_clones = ds->ds_phys->ds_num_children - 1;
+	}
+
+	/* clone origin is really a dsl_dir thing... */
+	rw_enter(&ds->ds_dir->dd_pool->dp_config_rwlock, RW_READER);
+	if (dsl_dir_is_clone(ds->ds_dir)) {
+		dsl_dataset_t *ods;
+
+		VERIFY(0 == dsl_dataset_get_ref(ds->ds_dir->dd_pool,
+		    ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &ods));
+		dsl_dataset_name(ods, stat->dds_origin);
+		dsl_dataset_drop_ref(ods, FTAG);
+	}
+	rw_exit(&ds->ds_dir->dd_pool->dp_config_rwlock);
+}
+
+uint64_t
+dsl_dataset_fsid_guid(dsl_dataset_t *ds)
+{
+	return (ds->ds_fsid_guid);
+}
+
+void
+dsl_dataset_space(dsl_dataset_t *ds,
+    uint64_t *refdbytesp, uint64_t *availbytesp,
+    uint64_t *usedobjsp, uint64_t *availobjsp)
+{
+	*refdbytesp = ds->ds_phys->ds_used_bytes;
+	*availbytesp = dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE);
+	if (ds->ds_reserved > ds->ds_phys->ds_unique_bytes)
+		*availbytesp += ds->ds_reserved - ds->ds_phys->ds_unique_bytes;
+	if (ds->ds_quota != 0) {
+		/*
+		 * Adjust available bytes according to refquota
+		 */
+		if (*refdbytesp < ds->ds_quota)
+			*availbytesp = MIN(*availbytesp,
+			    ds->ds_quota - *refdbytesp);
+		else
+			*availbytesp = 0;
+	}
+	*usedobjsp = ds->ds_phys->ds_bp.blk_fill;
+	*availobjsp = DN_MAX_OBJECT - *usedobjsp;
+}
+
+boolean_t
+dsl_dataset_modified_since_lastsnap(dsl_dataset_t *ds)
+{
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+
+	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
+	    dsl_pool_sync_context(dp));
+	if (ds->ds_prev == NULL)
+		return (B_FALSE);
+	if (ds->ds_phys->ds_bp.blk_birth >
+	    ds->ds_prev->ds_phys->ds_creation_txg)
+		return (B_TRUE);
+	return (B_FALSE);
+}
+
+/* ARGSUSED */
+static int
+dsl_dataset_snapshot_rename_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	char *newsnapname = arg2;
+	dsl_dir_t *dd = ds->ds_dir;
+	dsl_dataset_t *hds;
+	uint64_t val;
+	int err;
+
+	err = dsl_dataset_hold_obj(dd->dd_pool,
+	    dd->dd_phys->dd_head_dataset_obj, FTAG, &hds);
+	if (err)
+		return (err);
+
+	/* new name better not be in use */
+	err = dsl_dataset_snap_lookup(hds, newsnapname, &val);
+	dsl_dataset_rele(hds, FTAG);
+
+	if (err == 0)
+		err = EEXIST;
+	else if (err == ENOENT)
+		err = 0;
+
+	/* dataset name + 1 for the "@" + the new snapshot name must fit */
+	if (dsl_dir_namelen(ds->ds_dir) + 1 + strlen(newsnapname) >= MAXNAMELEN)
+		err = ENAMETOOLONG;
+
+	return (err);
+}
+
+static void
+dsl_dataset_snapshot_rename_sync(void *arg1, void *arg2,
+    cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	const char *newsnapname = arg2;
+	dsl_dir_t *dd = ds->ds_dir;
+	objset_t *mos = dd->dd_pool->dp_meta_objset;
+	dsl_dataset_t *hds;
+	int err;
+
+	ASSERT(ds->ds_phys->ds_next_snap_obj != 0);
+
+	VERIFY(0 == dsl_dataset_hold_obj(dd->dd_pool,
+	    dd->dd_phys->dd_head_dataset_obj, FTAG, &hds));
+
+	VERIFY(0 == dsl_dataset_get_snapname(ds));
+	err = dsl_dataset_snap_remove(hds, ds->ds_snapname, tx);
+	ASSERT3U(err, ==, 0);
+	mutex_enter(&ds->ds_lock);
+	(void) strcpy(ds->ds_snapname, newsnapname);
+	mutex_exit(&ds->ds_lock);
+	err = zap_add(mos, hds->ds_phys->ds_snapnames_zapobj,
+	    ds->ds_snapname, 8, 1, &ds->ds_object, tx);
+	ASSERT3U(err, ==, 0);
+
+	spa_history_internal_log(LOG_DS_RENAME, dd->dd_pool->dp_spa, tx,
+	    cr, "dataset = %llu", ds->ds_object);
+	dsl_dataset_rele(hds, FTAG);
+}
+
+struct renamesnaparg {
+	dsl_sync_task_group_t *dstg;
+	char failed[MAXPATHLEN];
+	char *oldsnap;
+	char *newsnap;
+};
+
+static int
+dsl_snapshot_rename_one(char *name, void *arg)
+{
+	struct renamesnaparg *ra = arg;
+	dsl_dataset_t *ds = NULL;
+	char *cp;
+	int err;
+
+	cp = name + strlen(name);
+	*cp = '@';
+	(void) strcpy(cp + 1, ra->oldsnap);
+
+	/*
+	 * For recursive snapshot renames the parent won't be changing
+	 * so we just pass name for both the to/from argument.
+	 */
+	err = zfs_secpolicy_rename_perms(name, name, CRED());
+	if (err == ENOENT) {
+		return (0);
+	} else if (err) {
+		(void) strcpy(ra->failed, name);
+		return (err);
+	}
+
+#ifdef _KERNEL
+	/*
+	 * For all filesystems undergoing rename, we'll need to unmount it.
+	 */
+	(void) zfs_unmount_snap(name, NULL);
+#endif
+	err = dsl_dataset_hold(name, ra->dstg, &ds);
+	*cp = '\0';
+	if (err == ENOENT) {
+		return (0);
+	} else if (err) {
+		(void) strcpy(ra->failed, name);
+		return (err);
+	}
+
+	dsl_sync_task_create(ra->dstg, dsl_dataset_snapshot_rename_check,
+	    dsl_dataset_snapshot_rename_sync, ds, ra->newsnap, 0);
+
+	return (0);
+}
+
+static int
+dsl_recursive_rename(char *oldname, const char *newname)
+{
+	int err;
+	struct renamesnaparg *ra;
+	dsl_sync_task_t *dst;
+	spa_t *spa;
+	char *cp, *fsname = spa_strdup(oldname);
+	int len = strlen(oldname);
+
+	/* truncate the snapshot name to get the fsname */
+	cp = strchr(fsname, '@');
+	*cp = '\0';
+
+	err = spa_open(fsname, &spa, FTAG);
+	if (err) {
+		kmem_free(fsname, len + 1);
+		return (err);
+	}
+	ra = kmem_alloc(sizeof (struct renamesnaparg), KM_SLEEP);
+	ra->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
+
+	ra->oldsnap = strchr(oldname, '@') + 1;
+	ra->newsnap = strchr(newname, '@') + 1;
+	*ra->failed = '\0';
+
+	err = dmu_objset_find(fsname, dsl_snapshot_rename_one, ra,
+	    DS_FIND_CHILDREN);
+	kmem_free(fsname, len + 1);
+
+	if (err == 0) {
+		err = dsl_sync_task_group_wait(ra->dstg);
+	}
+
+	for (dst = list_head(&ra->dstg->dstg_tasks); dst;
+	    dst = list_next(&ra->dstg->dstg_tasks, dst)) {
+		dsl_dataset_t *ds = dst->dst_arg1;
+		if (dst->dst_err) {
+			dsl_dir_name(ds->ds_dir, ra->failed);
+			(void) strcat(ra->failed, "@");
+			(void) strcat(ra->failed, ra->newsnap);
+		}
+		dsl_dataset_rele(ds, ra->dstg);
+	}
+
+	if (err)
+		(void) strcpy(oldname, ra->failed);
+
+	dsl_sync_task_group_destroy(ra->dstg);
+	kmem_free(ra, sizeof (struct renamesnaparg));
+	spa_close(spa, FTAG);
+	return (err);
+}
+
+static int
+dsl_valid_rename(char *oldname, void *arg)
+{
+	int delta = *(int *)arg;
+
+	if (strlen(oldname) + delta >= MAXNAMELEN)
+		return (ENAMETOOLONG);
+
+	return (0);
+}
+
+#pragma weak dmu_objset_rename = dsl_dataset_rename
+int
+dsl_dataset_rename(char *oldname, const char *newname, boolean_t recursive)
+{
+	dsl_dir_t *dd;
+	dsl_dataset_t *ds;
+	const char *tail;
+	int err;
+
+	err = dsl_dir_open(oldname, FTAG, &dd, &tail);
+	if (err)
+		return (err);
+	if (tail == NULL) {
+		int delta = strlen(newname) - strlen(oldname);
+
+		/* if we're growing, validate child name lengths */
+		if (delta > 0)
+			err = dmu_objset_find(oldname, dsl_valid_rename,
+			    &delta, DS_FIND_CHILDREN | DS_FIND_SNAPSHOTS);
+
+		if (!err)
+			err = dsl_dir_rename(dd, newname);
+		dsl_dir_close(dd, FTAG);
+		return (err);
+	}
+	if (tail[0] != '@') {
+		/* the name ended in a nonexistant component */
+		dsl_dir_close(dd, FTAG);
+		return (ENOENT);
+	}
+
+	dsl_dir_close(dd, FTAG);
+
+	/* new name must be snapshot in same filesystem */
+	tail = strchr(newname, '@');
+	if (tail == NULL)
+		return (EINVAL);
+	tail++;
+	if (strncmp(oldname, newname, tail - newname) != 0)
+		return (EXDEV);
+
+	if (recursive) {
+		err = dsl_recursive_rename(oldname, newname);
+	} else {
+		err = dsl_dataset_hold(oldname, FTAG, &ds);
+		if (err)
+			return (err);
+
+		err = dsl_sync_task_do(ds->ds_dir->dd_pool,
+		    dsl_dataset_snapshot_rename_check,
+		    dsl_dataset_snapshot_rename_sync, ds, (char *)tail, 1);
+
+		dsl_dataset_rele(ds, FTAG);
+	}
+
+	return (err);
+}
+
+struct promotenode {
+	list_node_t link;
+	dsl_dataset_t *ds;
+};
+
+struct promotearg {
+	list_t shared_snaps, origin_snaps, clone_snaps;
+	dsl_dataset_t *origin_origin, *origin_head;
+	uint64_t used, comp, uncomp, unique, cloneusedsnap, originusedsnap;
+};
+
+static int snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep);
+
+/* ARGSUSED */
+static int
+dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *hds = arg1;
+	struct promotearg *pa = arg2;
+	struct promotenode *snap = list_head(&pa->shared_snaps);
+	dsl_dataset_t *origin_ds = snap->ds;
+	int err;
+
+	/* Check that it is a real clone */
+	if (!dsl_dir_is_clone(hds->ds_dir))
+		return (EINVAL);
+
+	/* Since this is so expensive, don't do the preliminary check */
+	if (!dmu_tx_is_syncing(tx))
+		return (0);
+
+	if (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE)
+		return (EXDEV);
+
+	/* compute origin's new unique space */
+	snap = list_tail(&pa->clone_snaps);
+	ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
+	err = bplist_space_birthrange(&snap->ds->ds_deadlist,
+	    origin_ds->ds_phys->ds_prev_snap_txg, UINT64_MAX, &pa->unique);
+	if (err)
+		return (err);
+
+	/*
+	 * Walk the snapshots that we are moving
+	 *
+	 * Compute space to transfer.  Consider the incremental changes
+	 * to used for each snapshot:
+	 * (my used) = (prev's used) + (blocks born) - (blocks killed)
+	 * So each snapshot gave birth to:
+	 * (blocks born) = (my used) - (prev's used) + (blocks killed)
+	 * So a sequence would look like:
+	 * (uN - u(N-1) + kN) + ... + (u1 - u0 + k1) + (u0 - 0 + k0)
+	 * Which simplifies to:
+	 * uN + kN + kN-1 + ... + k1 + k0
+	 * Note however, if we stop before we reach the ORIGIN we get:
+	 * uN + kN + kN-1 + ... + kM - uM-1
+	 */
+	pa->used = origin_ds->ds_phys->ds_used_bytes;
+	pa->comp = origin_ds->ds_phys->ds_compressed_bytes;
+	pa->uncomp = origin_ds->ds_phys->ds_uncompressed_bytes;
+	for (snap = list_head(&pa->shared_snaps); snap;
+	    snap = list_next(&pa->shared_snaps, snap)) {
+		uint64_t val, dlused, dlcomp, dluncomp;
+		dsl_dataset_t *ds = snap->ds;
+
+		/* Check that the snapshot name does not conflict */
+		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		err = dsl_dataset_snap_lookup(hds, ds->ds_snapname, &val);
+		if (err == 0)
+			return (EEXIST);
+		if (err != ENOENT)
+			return (err);
+
+		/* The very first snapshot does not have a deadlist */
+		if (ds->ds_phys->ds_prev_snap_obj == 0)
+			continue;
+
+		if (err = bplist_space(&ds->ds_deadlist,
+		    &dlused, &dlcomp, &dluncomp))
+			return (err);
+		pa->used += dlused;
+		pa->comp += dlcomp;
+		pa->uncomp += dluncomp;
+	}
+
+	/*
+	 * If we are a clone of a clone then we never reached ORIGIN,
+	 * so we need to subtract out the clone origin's used space.
+	 */
+	if (pa->origin_origin) {
+		pa->used -= pa->origin_origin->ds_phys->ds_used_bytes;
+		pa->comp -= pa->origin_origin->ds_phys->ds_compressed_bytes;
+		pa->uncomp -= pa->origin_origin->ds_phys->ds_uncompressed_bytes;
+	}
+
+	/* Check that there is enough space here */
+	err = dsl_dir_transfer_possible(origin_ds->ds_dir, hds->ds_dir,
+	    pa->used);
+	if (err)
+		return (err);
+
+	/*
+	 * Compute the amounts of space that will be used by snapshots
+	 * after the promotion (for both origin and clone).  For each,
+	 * it is the amount of space that will be on all of their
+	 * deadlists (that was not born before their new origin).
+	 */
+	if (hds->ds_dir->dd_phys->dd_flags & DD_FLAG_USED_BREAKDOWN) {
+		uint64_t space;
+
+		/*
+		 * Note, typically this will not be a clone of a clone,
+		 * so snap->ds->ds_origin_txg will be < TXG_INITIAL, so
+		 * these snaplist_space() -> bplist_space_birthrange()
+		 * calls will be fast because they do not have to
+		 * iterate over all bps.
+		 */
+		snap = list_head(&pa->origin_snaps);
+		err = snaplist_space(&pa->shared_snaps,
+		    snap->ds->ds_origin_txg, &pa->cloneusedsnap);
+		if (err)
+			return (err);
+
+		err = snaplist_space(&pa->clone_snaps,
+		    snap->ds->ds_origin_txg, &space);
+		if (err)
+			return (err);
+		pa->cloneusedsnap += space;
+	}
+	if (origin_ds->ds_dir->dd_phys->dd_flags & DD_FLAG_USED_BREAKDOWN) {
+		err = snaplist_space(&pa->origin_snaps,
+		    origin_ds->ds_phys->ds_creation_txg, &pa->originusedsnap);
+		if (err)
+			return (err);
+	}
+
+	return (0);
+}
+
+static void
+dsl_dataset_promote_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *hds = arg1;
+	struct promotearg *pa = arg2;
+	struct promotenode *snap = list_head(&pa->shared_snaps);
+	dsl_dataset_t *origin_ds = snap->ds;
+	dsl_dataset_t *origin_head;
+	dsl_dir_t *dd = hds->ds_dir;
+	dsl_pool_t *dp = hds->ds_dir->dd_pool;
+	dsl_dir_t *odd = NULL;
+	uint64_t oldnext_obj;
+	int64_t delta;
+
+	ASSERT(0 == (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE));
+
+	snap = list_head(&pa->origin_snaps);
+	origin_head = snap->ds;
+
+	/*
+	 * We need to explicitly open odd, since origin_ds's dd will be
+	 * changing.
+	 */
+	VERIFY(0 == dsl_dir_open_obj(dp, origin_ds->ds_dir->dd_object,
+	    NULL, FTAG, &odd));
+
+	/* change origin's next snap */
+	dmu_buf_will_dirty(origin_ds->ds_dbuf, tx);
+	oldnext_obj = origin_ds->ds_phys->ds_next_snap_obj;
+	snap = list_tail(&pa->clone_snaps);
+	ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
+	origin_ds->ds_phys->ds_next_snap_obj = snap->ds->ds_object;
+
+	/* change the origin's next clone */
+	if (origin_ds->ds_phys->ds_next_clones_obj) {
+		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
+		    origin_ds->ds_phys->ds_next_clones_obj,
+		    origin_ds->ds_phys->ds_next_snap_obj, tx));
+		VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
+		    origin_ds->ds_phys->ds_next_clones_obj,
+		    oldnext_obj, tx));
+	}
+
+	/* change origin */
+	dmu_buf_will_dirty(dd->dd_dbuf, tx);
+	ASSERT3U(dd->dd_phys->dd_origin_obj, ==, origin_ds->ds_object);
+	dd->dd_phys->dd_origin_obj = odd->dd_phys->dd_origin_obj;
+	hds->ds_origin_txg = origin_head->ds_origin_txg;
+	dmu_buf_will_dirty(odd->dd_dbuf, tx);
+	odd->dd_phys->dd_origin_obj = origin_ds->ds_object;
+	origin_head->ds_origin_txg = origin_ds->ds_phys->ds_creation_txg;
+
+	/* move snapshots to this dir */
+	for (snap = list_head(&pa->shared_snaps); snap;
+	    snap = list_next(&pa->shared_snaps, snap)) {
+		dsl_dataset_t *ds = snap->ds;
+
+		/* unregister props as dsl_dir is changing */
+		if (ds->ds_user_ptr) {
+			ds->ds_user_evict_func(ds, ds->ds_user_ptr);
+			ds->ds_user_ptr = NULL;
+		}
+		/* move snap name entry */
+		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		VERIFY(0 == dsl_dataset_snap_remove(origin_head,
+		    ds->ds_snapname, tx));
+		VERIFY(0 == zap_add(dp->dp_meta_objset,
+		    hds->ds_phys->ds_snapnames_zapobj, ds->ds_snapname,
+		    8, 1, &ds->ds_object, tx));
+		/* change containing dsl_dir */
+		dmu_buf_will_dirty(ds->ds_dbuf, tx);
+		ASSERT3U(ds->ds_phys->ds_dir_obj, ==, odd->dd_object);
+		ds->ds_phys->ds_dir_obj = dd->dd_object;
+		ASSERT3P(ds->ds_dir, ==, odd);
+		dsl_dir_close(ds->ds_dir, ds);
+		VERIFY(0 == dsl_dir_open_obj(dp, dd->dd_object,
+		    NULL, ds, &ds->ds_dir));
+
+		ASSERT3U(dsl_prop_numcb(ds), ==, 0);
+	}
+
+	/*
+	 * Change space accounting.
+	 * Note, pa->*usedsnap and dd_used_breakdown[SNAP] will either
+	 * both be valid, or both be 0 (resulting in delta == 0).  This
+	 * is true for each of {clone,origin} independently.
+	 */
+
+	delta = pa->cloneusedsnap -
+	    dd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
+	ASSERT3S(delta, >=, 0);
+	ASSERT3U(pa->used, >=, delta);
+	dsl_dir_diduse_space(dd, DD_USED_SNAP, delta, 0, 0, tx);
+	dsl_dir_diduse_space(dd, DD_USED_HEAD,
+	    pa->used - delta, pa->comp, pa->uncomp, tx);
+
+	delta = pa->originusedsnap -
+	    odd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
+	ASSERT3S(delta, <=, 0);
+	ASSERT3U(pa->used, >=, -delta);
+	dsl_dir_diduse_space(odd, DD_USED_SNAP, delta, 0, 0, tx);
+	dsl_dir_diduse_space(odd, DD_USED_HEAD,
+	    -pa->used - delta, -pa->comp, -pa->uncomp, tx);
+
+	origin_ds->ds_phys->ds_unique_bytes = pa->unique;
+
+	/* log history record */
+	spa_history_internal_log(LOG_DS_PROMOTE, dd->dd_pool->dp_spa, tx,
+	    cr, "dataset = %llu", hds->ds_object);
+
+	dsl_dir_close(odd, FTAG);
+}
+
+static char *snaplist_tag = "snaplist";
+/*
+ * Make a list of dsl_dataset_t's for the snapshots between first_obj
+ * (exclusive) and last_obj (inclusive).  The list will be in reverse
+ * order (last_obj will be the list_head()).  If first_obj == 0, do all
+ * snapshots back to this dataset's origin.
+ */
+static int
+snaplist_make(dsl_pool_t *dp, boolean_t own,
+    uint64_t first_obj, uint64_t last_obj, list_t *l)
+{
+	uint64_t obj = last_obj;
+
+	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock));
+
+	list_create(l, sizeof (struct promotenode),
+	    offsetof(struct promotenode, link));
+
+	while (obj != first_obj) {
+		dsl_dataset_t *ds;
+		struct promotenode *snap;
+		int err;
+
+		if (own) {
+			err = dsl_dataset_own_obj(dp, obj,
+			    0, snaplist_tag, &ds);
+			if (err == 0)
+				dsl_dataset_make_exclusive(ds, snaplist_tag);
+		} else {
+			err = dsl_dataset_hold_obj(dp, obj, snaplist_tag, &ds);
+		}
+		if (err == ENOENT) {
+			/* lost race with snapshot destroy */
+			struct promotenode *last = list_tail(l);
+			ASSERT(obj != last->ds->ds_phys->ds_prev_snap_obj);
+			obj = last->ds->ds_phys->ds_prev_snap_obj;
+			continue;
+		} else if (err) {
+			return (err);
+		}
+
+		if (first_obj == 0)
+			first_obj = ds->ds_dir->dd_phys->dd_origin_obj;
+
+		snap = kmem_alloc(sizeof (struct promotenode), KM_SLEEP);
+		snap->ds = ds;
+		list_insert_tail(l, snap);
+		obj = ds->ds_phys->ds_prev_snap_obj;
+	}
+
+	return (0);
+}
+
+static int
+snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep)
+{
+	struct promotenode *snap;
+
+	*spacep = 0;
+	for (snap = list_head(l); snap; snap = list_next(l, snap)) {
+		uint64_t used;
+		int err = bplist_space_birthrange(&snap->ds->ds_deadlist,
+		    mintxg, UINT64_MAX, &used);
+		if (err)
+			return (err);
+		*spacep += used;
+	}
+	return (0);
+}
+
+static void
+snaplist_destroy(list_t *l, boolean_t own)
+{
+	struct promotenode *snap;
+
+	if (!list_link_active(&l->list_head))
+		return;
+
+	while ((snap = list_tail(l)) != NULL) {
+		list_remove(l, snap);
+		if (own)
+			dsl_dataset_disown(snap->ds, snaplist_tag);
+		else
+			dsl_dataset_rele(snap->ds, snaplist_tag);
+		kmem_free(snap, sizeof (struct promotenode));
+	}
+	list_destroy(l);
+}
+
+/*
+ * Promote a clone.  Nomenclature note:
+ * "clone" or "cds": the original clone which is being promoted
+ * "origin" or "ods": the snapshot which is originally clone's origin
+ * "origin head" or "ohds": the dataset which is the head
+ * (filesystem/volume) for the origin
+ * "origin origin": the origin of the origin's filesystem (typically
+ * NULL, indicating that the clone is not a clone of a clone).
+ */
+int
+dsl_dataset_promote(const char *name)
+{
+	dsl_dataset_t *ds;
+	dsl_dir_t *dd;
+	dsl_pool_t *dp;
+	dmu_object_info_t doi;
+	struct promotearg pa = { 0 };
+	struct promotenode *snap;
+	int err;
+
+	err = dsl_dataset_hold(name, FTAG, &ds);
+	if (err)
+		return (err);
+	dd = ds->ds_dir;
+	dp = dd->dd_pool;
+
+	err = dmu_object_info(dp->dp_meta_objset,
+	    ds->ds_phys->ds_snapnames_zapobj, &doi);
+	if (err) {
+		dsl_dataset_rele(ds, FTAG);
+		return (err);
+	}
+
+	if (dsl_dataset_is_snapshot(ds) || dd->dd_phys->dd_origin_obj == 0) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EINVAL);
+	}
+
+	/*
+	 * We are going to inherit all the snapshots taken before our
+	 * origin (i.e., our new origin will be our parent's origin).
+	 * Take ownership of them so that we can rename them into our
+	 * namespace.
+	 */
+	rw_enter(&dp->dp_config_rwlock, RW_READER);
+
+	err = snaplist_make(dp, B_TRUE, 0, dd->dd_phys->dd_origin_obj,
+	    &pa.shared_snaps);
+	if (err != 0)
+		goto out;
+
+	err = snaplist_make(dp, B_FALSE, 0, ds->ds_object, &pa.clone_snaps);
+	if (err != 0)
+		goto out;
+
+	snap = list_head(&pa.shared_snaps);
+	ASSERT3U(snap->ds->ds_object, ==, dd->dd_phys->dd_origin_obj);
+	err = snaplist_make(dp, B_FALSE, dd->dd_phys->dd_origin_obj,
+	    snap->ds->ds_dir->dd_phys->dd_head_dataset_obj, &pa.origin_snaps);
+	if (err != 0)
+		goto out;
+
+	if (dsl_dir_is_clone(snap->ds->ds_dir)) {
+		err = dsl_dataset_own_obj(dp,
+		    snap->ds->ds_dir->dd_phys->dd_origin_obj,
+		    0, FTAG, &pa.origin_origin);
+		if (err != 0)
+			goto out;
+	}
+
+out:
+	rw_exit(&dp->dp_config_rwlock);
+
+	/*
+	 * Add in 128x the snapnames zapobj size, since we will be moving
+	 * a bunch of snapnames to the promoted ds, and dirtying their
+	 * bonus buffers.
+	 */
+	if (err == 0) {
+		err = dsl_sync_task_do(dp, dsl_dataset_promote_check,
+		    dsl_dataset_promote_sync, ds, &pa,
+		    2 + 2 * doi.doi_physical_blks);
+	}
+
+	snaplist_destroy(&pa.shared_snaps, B_TRUE);
+	snaplist_destroy(&pa.clone_snaps, B_FALSE);
+	snaplist_destroy(&pa.origin_snaps, B_FALSE);
+	if (pa.origin_origin)
+		dsl_dataset_disown(pa.origin_origin, FTAG);
+	dsl_dataset_rele(ds, FTAG);
+	return (err);
+}
+
+struct cloneswaparg {
+	dsl_dataset_t *cds; /* clone dataset */
+	dsl_dataset_t *ohds; /* origin's head dataset */
+	boolean_t force;
+	int64_t unused_refres_delta; /* change in unconsumed refreservation */
+};
+
+/* ARGSUSED */
+static int
+dsl_dataset_clone_swap_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	struct cloneswaparg *csa = arg1;
+
+	/* they should both be heads */
+	if (dsl_dataset_is_snapshot(csa->cds) ||
+	    dsl_dataset_is_snapshot(csa->ohds))
+		return (EINVAL);
+
+	/* the branch point should be just before them */
+	if (csa->cds->ds_prev != csa->ohds->ds_prev)
+		return (EINVAL);
+
+	/* cds should be the clone */
+	if (csa->cds->ds_prev->ds_phys->ds_next_snap_obj !=
+	    csa->ohds->ds_object)
+		return (EINVAL);
+
+	/* the clone should be a child of the origin */
+	if (csa->cds->ds_dir->dd_parent != csa->ohds->ds_dir)
+		return (EINVAL);
+
+	/* ohds shouldn't be modified unless 'force' */
+	if (!csa->force && dsl_dataset_modified_since_lastsnap(csa->ohds))
+		return (ETXTBSY);
+
+	/* adjust amount of any unconsumed refreservation */
+	csa->unused_refres_delta =
+	    (int64_t)MIN(csa->ohds->ds_reserved,
+	    csa->ohds->ds_phys->ds_unique_bytes) -
+	    (int64_t)MIN(csa->ohds->ds_reserved,
+	    csa->cds->ds_phys->ds_unique_bytes);
+
+	if (csa->unused_refres_delta > 0 &&
+	    csa->unused_refres_delta >
+	    dsl_dir_space_available(csa->ohds->ds_dir, NULL, 0, TRUE))
+		return (ENOSPC);
+
+	return (0);
+}
+
+/* ARGSUSED */
+static void
+dsl_dataset_clone_swap_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	struct cloneswaparg *csa = arg1;
+	dsl_pool_t *dp = csa->cds->ds_dir->dd_pool;
+
+	ASSERT(csa->cds->ds_reserved == 0);
+	ASSERT(csa->cds->ds_quota == csa->ohds->ds_quota);
+
+	dmu_buf_will_dirty(csa->cds->ds_dbuf, tx);
+	dmu_buf_will_dirty(csa->ohds->ds_dbuf, tx);
+	dmu_buf_will_dirty(csa->cds->ds_prev->ds_dbuf, tx);
+
+	if (csa->cds->ds_user_ptr != NULL) {
+		csa->cds->ds_user_evict_func(csa->cds, csa->cds->ds_user_ptr);
+		csa->cds->ds_user_ptr = NULL;
+	}
+
+	if (csa->ohds->ds_user_ptr != NULL) {
+		csa->ohds->ds_user_evict_func(csa->ohds,
+		    csa->ohds->ds_user_ptr);
+		csa->ohds->ds_user_ptr = NULL;
+	}
+
+	/* reset origin's unique bytes */
+	VERIFY(0 == bplist_space_birthrange(&csa->cds->ds_deadlist,
+	    csa->cds->ds_prev->ds_phys->ds_prev_snap_txg, UINT64_MAX,
+	    &csa->cds->ds_prev->ds_phys->ds_unique_bytes));
+
+	/* swap blkptrs */
+	{
+		blkptr_t tmp;
+		tmp = csa->ohds->ds_phys->ds_bp;
+		csa->ohds->ds_phys->ds_bp = csa->cds->ds_phys->ds_bp;
+		csa->cds->ds_phys->ds_bp = tmp;
+	}
+
+	/* set dd_*_bytes */
+	{
+		int64_t dused, dcomp, duncomp;
+		uint64_t cdl_used, cdl_comp, cdl_uncomp;
+		uint64_t odl_used, odl_comp, odl_uncomp;
+
+		ASSERT3U(csa->cds->ds_dir->dd_phys->
+		    dd_used_breakdown[DD_USED_SNAP], ==, 0);
+
+		VERIFY(0 == bplist_space(&csa->cds->ds_deadlist, &cdl_used,
+		    &cdl_comp, &cdl_uncomp));
+		VERIFY(0 == bplist_space(&csa->ohds->ds_deadlist, &odl_used,
+		    &odl_comp, &odl_uncomp));
+
+		dused = csa->cds->ds_phys->ds_used_bytes + cdl_used -
+		    (csa->ohds->ds_phys->ds_used_bytes + odl_used);
+		dcomp = csa->cds->ds_phys->ds_compressed_bytes + cdl_comp -
+		    (csa->ohds->ds_phys->ds_compressed_bytes + odl_comp);
+		duncomp = csa->cds->ds_phys->ds_uncompressed_bytes +
+		    cdl_uncomp -
+		    (csa->ohds->ds_phys->ds_uncompressed_bytes + odl_uncomp);
+
+		dsl_dir_diduse_space(csa->ohds->ds_dir, DD_USED_HEAD,
+		    dused, dcomp, duncomp, tx);
+		dsl_dir_diduse_space(csa->cds->ds_dir, DD_USED_HEAD,
+		    -dused, -dcomp, -duncomp, tx);
+
+		/*
+		 * The difference in the space used by snapshots is the
+		 * difference in snapshot space due to the head's
+		 * deadlist (since that's the only thing that's
+		 * changing that affects the snapused).
+		 */
+		VERIFY(0 == bplist_space_birthrange(&csa->cds->ds_deadlist,
+		    csa->ohds->ds_origin_txg, UINT64_MAX, &cdl_used));
+		VERIFY(0 == bplist_space_birthrange(&csa->ohds->ds_deadlist,
+		    csa->ohds->ds_origin_txg, UINT64_MAX, &odl_used));
+		dsl_dir_transfer_space(csa->ohds->ds_dir, cdl_used - odl_used,
+		    DD_USED_HEAD, DD_USED_SNAP, tx);
+	}
+
+#define	SWITCH64(x, y) \
+	{ \
+		uint64_t __tmp = (x); \
+		(x) = (y); \
+		(y) = __tmp; \
+	}
+
+	/* swap ds_*_bytes */
+	SWITCH64(csa->ohds->ds_phys->ds_used_bytes,
+	    csa->cds->ds_phys->ds_used_bytes);
+	SWITCH64(csa->ohds->ds_phys->ds_compressed_bytes,
+	    csa->cds->ds_phys->ds_compressed_bytes);
+	SWITCH64(csa->ohds->ds_phys->ds_uncompressed_bytes,
+	    csa->cds->ds_phys->ds_uncompressed_bytes);
+	SWITCH64(csa->ohds->ds_phys->ds_unique_bytes,
+	    csa->cds->ds_phys->ds_unique_bytes);
+
+	/* apply any parent delta for change in unconsumed refreservation */
+	dsl_dir_diduse_space(csa->ohds->ds_dir, DD_USED_REFRSRV,
+	    csa->unused_refres_delta, 0, 0, tx);
+
+	/* swap deadlists */
+	bplist_close(&csa->cds->ds_deadlist);
+	bplist_close(&csa->ohds->ds_deadlist);
+	SWITCH64(csa->ohds->ds_phys->ds_deadlist_obj,
+	    csa->cds->ds_phys->ds_deadlist_obj);
+	VERIFY(0 == bplist_open(&csa->cds->ds_deadlist, dp->dp_meta_objset,
+	    csa->cds->ds_phys->ds_deadlist_obj));
+	VERIFY(0 == bplist_open(&csa->ohds->ds_deadlist, dp->dp_meta_objset,
+	    csa->ohds->ds_phys->ds_deadlist_obj));
+
+	dsl_pool_ds_clone_swapped(csa->ohds, csa->cds, tx);
+}
+
+/*
+ * Swap 'clone' with its origin head file system.  Used at the end
+ * of "online recv" to swizzle the file system to the new version.
+ */
+int
+dsl_dataset_clone_swap(dsl_dataset_t *clone, dsl_dataset_t *origin_head,
+    boolean_t force)
+{
+	struct cloneswaparg csa;
+	int error;
+
+	ASSERT(clone->ds_owner);
+	ASSERT(origin_head->ds_owner);
+retry:
+	/* Need exclusive access for the swap */
+	rw_enter(&clone->ds_rwlock, RW_WRITER);
+	if (!rw_tryenter(&origin_head->ds_rwlock, RW_WRITER)) {
+		rw_exit(&clone->ds_rwlock);
+		rw_enter(&origin_head->ds_rwlock, RW_WRITER);
+		if (!rw_tryenter(&clone->ds_rwlock, RW_WRITER)) {
+			rw_exit(&origin_head->ds_rwlock);
+			goto retry;
+		}
+	}
+	csa.cds = clone;
+	csa.ohds = origin_head;
+	csa.force = force;
+	error = dsl_sync_task_do(clone->ds_dir->dd_pool,
+	    dsl_dataset_clone_swap_check,
+	    dsl_dataset_clone_swap_sync, &csa, NULL, 9);
+	return (error);
+}
+
+/*
+ * Given a pool name and a dataset object number in that pool,
+ * return the name of that dataset.
+ */
+int
+dsl_dsobj_to_dsname(char *pname, uint64_t obj, char *buf)
+{
+	spa_t *spa;
+	dsl_pool_t *dp;
+	dsl_dataset_t *ds;
+	int error;
+
+	if ((error = spa_open(pname, &spa, FTAG)) != 0)
+		return (error);
+	dp = spa_get_dsl(spa);
+	rw_enter(&dp->dp_config_rwlock, RW_READER);
+	if ((error = dsl_dataset_hold_obj(dp, obj, FTAG, &ds)) == 0) {
+		dsl_dataset_name(ds, buf);
+		dsl_dataset_rele(ds, FTAG);
+	}
+	rw_exit(&dp->dp_config_rwlock);
+	spa_close(spa, FTAG);
+
+	return (error);
+}
+
+int
+dsl_dataset_check_quota(dsl_dataset_t *ds, boolean_t check_quota,
+    uint64_t asize, uint64_t inflight, uint64_t *used, uint64_t *ref_rsrv)
+{
+	int error = 0;
+
+	ASSERT3S(asize, >, 0);
+
+	/*
+	 * *ref_rsrv is the portion of asize that will come from any
+	 * unconsumed refreservation space.
+	 */
+	*ref_rsrv = 0;
+
+	mutex_enter(&ds->ds_lock);
+	/*
+	 * Make a space adjustment for reserved bytes.
+	 */
+	if (ds->ds_reserved > ds->ds_phys->ds_unique_bytes) {
+		ASSERT3U(*used, >=,
+		    ds->ds_reserved - ds->ds_phys->ds_unique_bytes);
+		*used -= (ds->ds_reserved - ds->ds_phys->ds_unique_bytes);
+		*ref_rsrv =
+		    asize - MIN(asize, parent_delta(ds, asize + inflight));
+	}
+
+	if (!check_quota || ds->ds_quota == 0) {
+		mutex_exit(&ds->ds_lock);
+		return (0);
+	}
+	/*
+	 * If they are requesting more space, and our current estimate
+	 * is over quota, they get to try again unless the actual
+	 * on-disk is over quota and there are no pending changes (which
+	 * may free up space for us).
+	 */
+	if (ds->ds_phys->ds_used_bytes + inflight >= ds->ds_quota) {
+		if (inflight > 0 || ds->ds_phys->ds_used_bytes < ds->ds_quota)
+			error = ERESTART;
+		else
+			error = EDQUOT;
+	}
+	mutex_exit(&ds->ds_lock);
+
+	return (error);
+}
+
+/* ARGSUSED */
+static int
+dsl_dataset_set_quota_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	uint64_t *quotap = arg2;
+	uint64_t new_quota = *quotap;
+
+	if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_REFQUOTA)
+		return (ENOTSUP);
+
+	if (new_quota == 0)
+		return (0);
+
+	if (new_quota < ds->ds_phys->ds_used_bytes ||
+	    new_quota < ds->ds_reserved)
+		return (ENOSPC);
+
+	return (0);
+}
+
+/* ARGSUSED */
+void
+dsl_dataset_set_quota_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	uint64_t *quotap = arg2;
+	uint64_t new_quota = *quotap;
+
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+
+	ds->ds_quota = new_quota;
+
+	dsl_prop_set_uint64_sync(ds->ds_dir, "refquota", new_quota, cr, tx);
+
+	spa_history_internal_log(LOG_DS_REFQUOTA, ds->ds_dir->dd_pool->dp_spa,
+	    tx, cr, "%lld dataset = %llu ",
+	    (longlong_t)new_quota, ds->ds_object);
+}
+
+int
+dsl_dataset_set_quota(const char *dsname, uint64_t quota)
+{
+	dsl_dataset_t *ds;
+	int err;
+
+	err = dsl_dataset_hold(dsname, FTAG, &ds);
+	if (err)
+		return (err);
+
+	if (quota != ds->ds_quota) {
+		/*
+		 * If someone removes a file, then tries to set the quota, we
+		 * want to make sure the file freeing takes effect.
+		 */
+		txg_wait_open(ds->ds_dir->dd_pool, 0);
+
+		err = dsl_sync_task_do(ds->ds_dir->dd_pool,
+		    dsl_dataset_set_quota_check, dsl_dataset_set_quota_sync,
+		    ds, &quota, 0);
+	}
+	dsl_dataset_rele(ds, FTAG);
+	return (err);
+}
+
+static int
+dsl_dataset_set_reservation_check(void *arg1, void *arg2, dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	uint64_t *reservationp = arg2;
+	uint64_t new_reservation = *reservationp;
+	int64_t delta;
+	uint64_t unique;
+
+	if (new_reservation > INT64_MAX)
+		return (EOVERFLOW);
+
+	if (spa_version(ds->ds_dir->dd_pool->dp_spa) <
+	    SPA_VERSION_REFRESERVATION)
+		return (ENOTSUP);
+
+	if (dsl_dataset_is_snapshot(ds))
+		return (EINVAL);
+
+	/*
+	 * If we are doing the preliminary check in open context, the
+	 * space estimates may be inaccurate.
+	 */
+	if (!dmu_tx_is_syncing(tx))
+		return (0);
+
+	mutex_enter(&ds->ds_lock);
+	unique = dsl_dataset_unique(ds);
+	delta = MAX(unique, new_reservation) - MAX(unique, ds->ds_reserved);
+	mutex_exit(&ds->ds_lock);
+
+	if (delta > 0 &&
+	    delta > dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE))
+		return (ENOSPC);
+	if (delta > 0 && ds->ds_quota > 0 &&
+	    new_reservation > ds->ds_quota)
+		return (ENOSPC);
+
+	return (0);
+}
+
+/* ARGSUSED */
+static void
+dsl_dataset_set_reservation_sync(void *arg1, void *arg2, cred_t *cr,
+    dmu_tx_t *tx)
+{
+	dsl_dataset_t *ds = arg1;
+	uint64_t *reservationp = arg2;
+	uint64_t new_reservation = *reservationp;
+	uint64_t unique;
+	int64_t delta;
+
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+
+	mutex_enter(&ds->ds_dir->dd_lock);
+	mutex_enter(&ds->ds_lock);
+	unique = dsl_dataset_unique(ds);
+	delta = MAX(0, (int64_t)(new_reservation - unique)) -
+	    MAX(0, (int64_t)(ds->ds_reserved - unique));
+	ds->ds_reserved = new_reservation;
+	mutex_exit(&ds->ds_lock);
+
+	dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV, delta, 0, 0, tx);
+	mutex_exit(&ds->ds_dir->dd_lock);
+	dsl_prop_set_uint64_sync(ds->ds_dir, "refreservation",
+	    new_reservation, cr, tx);
+
+	spa_history_internal_log(LOG_DS_REFRESERV,
+	    ds->ds_dir->dd_pool->dp_spa, tx, cr, "%lld dataset = %llu",
+	    (longlong_t)new_reservation, ds->ds_object);
+}
+
+int
+dsl_dataset_set_reservation(const char *dsname, uint64_t reservation)
+{
+	dsl_dataset_t *ds;
+	int err;
+
+	err = dsl_dataset_hold(dsname, FTAG, &ds);
+	if (err)
+		return (err);
+
+	err = dsl_sync_task_do(ds->ds_dir->dd_pool,
+	    dsl_dataset_set_reservation_check,
+	    dsl_dataset_set_reservation_sync, ds, &reservation, 0);
+	dsl_dataset_rele(ds, FTAG);
+	return (err);
+}