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, 1125 insertions, 2486 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
index 71c749c..aee5407 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
@@ -20,10 +20,8 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
- * Copyright (c) 2011 Pawel Jakub Dawidek <pawel@dawidek.net>.
- * All rights reserved.
  * Portions Copyright (c) 2011 Martin Matuska <mm@FreeBSD.org>
  */
 
@@ -48,12 +46,8 @@
 #include <sys/zvol.h>
 #include <sys/dsl_scan.h>
 #include <sys/dsl_deadlist.h>
-
-static char *dsl_reaper = "the grim reaper";
-
-static dsl_checkfunc_t dsl_dataset_destroy_begin_check;
-static dsl_syncfunc_t dsl_dataset_destroy_begin_sync;
-static dsl_syncfunc_t dsl_dataset_set_reservation_sync;
+#include <sys/dsl_destroy.h>
+#include <sys/dsl_userhold.h>
 
 #define	SWITCH64(x, y) \
 	{ \
@@ -66,9 +60,6 @@ static dsl_syncfunc_t dsl_dataset_set_reservation_sync;
 
 #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
@@ -255,7 +246,7 @@ dsl_dataset_evict(dmu_buf_t *db, void *dsv)
 {
 	dsl_dataset_t *ds = dsv;
 
-	ASSERT(ds->ds_owner == NULL || DSL_DATASET_IS_DESTROYED(ds));
+	ASSERT(ds->ds_owner == NULL);
 
 	unique_remove(ds->ds_fsid_guid);
 
@@ -263,36 +254,30 @@ dsl_dataset_evict(dmu_buf_t *db, void *dsv)
 		dmu_objset_evict(ds->ds_objset);
 
 	if (ds->ds_prev) {
-		dsl_dataset_drop_ref(ds->ds_prev, ds);
+		dsl_dataset_rele(ds->ds_prev, ds);
 		ds->ds_prev = NULL;
 	}
 
 	bplist_destroy(&ds->ds_pending_deadlist);
-	if (db != NULL) {
+	if (ds->ds_phys->ds_deadlist_obj != 0)
 		dsl_deadlist_close(&ds->ds_deadlist);
-	} else {
-		ASSERT(ds->ds_deadlist.dl_dbuf == NULL);
-		ASSERT(!ds->ds_deadlist.dl_oldfmt);
-	}
 	if (ds->ds_dir)
-		dsl_dir_close(ds->ds_dir, ds);
+		dsl_dir_rele(ds->ds_dir, ds);
 
 	ASSERT(!list_link_active(&ds->ds_synced_link));
 
 	if (mutex_owned(&ds->ds_lock))
 		mutex_exit(&ds->ds_lock);
 	mutex_destroy(&ds->ds_lock);
-	mutex_destroy(&ds->ds_recvlock);
 	if (mutex_owned(&ds->ds_opening_lock))
 		mutex_exit(&ds->ds_opening_lock);
 	mutex_destroy(&ds->ds_opening_lock);
-	rw_destroy(&ds->ds_rwlock);
-	cv_destroy(&ds->ds_exclusive_cv);
+	refcount_destroy(&ds->ds_longholds);
 
 	kmem_free(ds, sizeof (dsl_dataset_t));
 }
 
-static int
+int
 dsl_dataset_get_snapname(dsl_dataset_t *ds)
 {
 	dsl_dataset_phys_t *headphys;
@@ -308,7 +293,7 @@ dsl_dataset_get_snapname(dsl_dataset_t *ds)
 
 	err = dmu_bonus_hold(mos, ds->ds_dir->dd_phys->dd_head_dataset_obj,
 	    FTAG, &headdbuf);
-	if (err)
+	if (err != 0)
 		return (err);
 	headphys = headdbuf->db_data;
 	err = zap_value_search(dp->dp_meta_objset,
@@ -317,7 +302,7 @@ dsl_dataset_get_snapname(dsl_dataset_t *ds)
 	return (err);
 }
 
-static int
+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;
@@ -337,8 +322,8 @@ dsl_dataset_snap_lookup(dsl_dataset_t *ds, const char *name, uint64_t *value)
 	return (err);
 }
 
-static int
-dsl_dataset_snap_remove(dsl_dataset_t *ds, char *name, dmu_tx_t *tx)
+int
+dsl_dataset_snap_remove(dsl_dataset_t *ds, const 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;
@@ -358,8 +343,8 @@ dsl_dataset_snap_remove(dsl_dataset_t *ds, char *name, dmu_tx_t *tx)
 	return (err);
 }
 
-static int
-dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
+int
+dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
     dsl_dataset_t **dsp)
 {
 	objset_t *mos = dp->dp_meta_objset;
@@ -368,11 +353,10 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 	int err;
 	dmu_object_info_t doi;
 
-	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
-	    dsl_pool_sync_context(dp));
+	ASSERT(dsl_pool_config_held(dp));
 
 	err = dmu_bonus_hold(mos, dsobj, tag, &dbuf);
-	if (err)
+	if (err != 0)
 		return (err);
 
 	/* Make sure dsobj has the correct object type. */
@@ -390,12 +374,9 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		ds->ds_phys = dbuf->db_data;
 
 		mutex_init(&ds->ds_lock, NULL, MUTEX_DEFAULT, NULL);
-		mutex_init(&ds->ds_recvlock, NULL, MUTEX_DEFAULT, NULL);
 		mutex_init(&ds->ds_opening_lock, NULL, MUTEX_DEFAULT, NULL);
 		mutex_init(&ds->ds_sendstream_lock, NULL, MUTEX_DEFAULT, NULL);
-
-		rw_init(&ds->ds_rwlock, 0, 0, 0);
-		cv_init(&ds->ds_exclusive_cv, NULL, CV_DEFAULT, NULL);
+		refcount_create(&ds->ds_longholds);
 
 		bplist_create(&ds->ds_pending_deadlist);
 		dsl_deadlist_open(&ds->ds_deadlist,
@@ -405,15 +386,13 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		    offsetof(dmu_sendarg_t, dsa_link));
 
 		if (err == 0) {
-			err = dsl_dir_open_obj(dp,
+			err = dsl_dir_hold_obj(dp,
 			    ds->ds_phys->ds_dir_obj, NULL, ds, &ds->ds_dir);
 		}
-		if (err) {
+		if (err != 0) {
 			mutex_destroy(&ds->ds_lock);
-			mutex_destroy(&ds->ds_recvlock);
 			mutex_destroy(&ds->ds_opening_lock);
-			rw_destroy(&ds->ds_rwlock);
-			cv_destroy(&ds->ds_exclusive_cv);
+			refcount_destroy(&ds->ds_longholds);
 			bplist_destroy(&ds->ds_pending_deadlist);
 			dsl_deadlist_close(&ds->ds_deadlist);
 			kmem_free(ds, sizeof (dsl_dataset_t));
@@ -423,8 +402,8 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 
 		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,
+			if (ds->ds_phys->ds_prev_snap_obj != 0) {
+				err = dsl_dataset_hold_obj(dp,
 				    ds->ds_phys->ds_prev_snap_obj,
 				    ds, &ds->ds_prev);
 			}
@@ -440,29 +419,14 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		}
 
 		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);
+			err = dsl_prop_get_int_ds(ds,
+			    zfs_prop_to_name(ZFS_PROP_REFRESERVATION),
+			    &ds->ds_reserved);
 			if (err == 0) {
-				err = dsl_prop_get_ds(ds,
-				    "refquota", sizeof (uint64_t), 1,
-				    &ds->ds_quota, NULL);
+				err = dsl_prop_get_int_ds(ds,
+				    zfs_prop_to_name(ZFS_PROP_REFQUOTA),
+				    &ds->ds_quota);
 			}
-
-			if (need_lock)
-				rw_exit(&dp->dp_config_rwlock);
 		} else {
 			ds->ds_reserved = ds->ds_quota = 0;
 		}
@@ -472,15 +436,13 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 			bplist_destroy(&ds->ds_pending_deadlist);
 			dsl_deadlist_close(&ds->ds_deadlist);
 			if (ds->ds_prev)
-				dsl_dataset_drop_ref(ds->ds_prev, ds);
-			dsl_dir_close(ds->ds_dir, ds);
+				dsl_dataset_rele(ds->ds_prev, ds);
+			dsl_dir_rele(ds->ds_dir, ds);
 			mutex_destroy(&ds->ds_lock);
-			mutex_destroy(&ds->ds_recvlock);
 			mutex_destroy(&ds->ds_opening_lock);
-			rw_destroy(&ds->ds_rwlock);
-			cv_destroy(&ds->ds_exclusive_cv);
+			refcount_destroy(&ds->ds_longholds);
 			kmem_free(ds, sizeof (dsl_dataset_t));
-			if (err) {
+			if (err != 0) {
 				dmu_buf_rele(dbuf, tag);
 				return (err);
 			}
@@ -495,170 +457,118 @@ dsl_dataset_get_ref(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 	ASSERT(ds->ds_phys->ds_prev_snap_obj != 0 ||
 	    spa_version(dp->dp_spa) < SPA_VERSION_ORIGIN ||
 	    dp->dp_origin_snap == NULL || ds == dp->dp_origin_snap);
-	mutex_enter(&ds->ds_lock);
-	if (!dsl_pool_sync_context(dp) && DSL_DATASET_IS_DESTROYED(ds)) {
-		mutex_exit(&ds->ds_lock);
-		dmu_buf_rele(ds->ds_dbuf, tag);
-		return (ENOENT);
-	}
-	mutex_exit(&ds->ds_lock);
 	*dsp = ds;
 	return (0);
 }
 
-static int
-dsl_dataset_hold_ref(dsl_dataset_t *ds, void *tag)
-{
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
-
-	/*
-	 * In syncing context we don't want the rwlock lock: there
-	 * may be an existing writer waiting for sync phase to
-	 * finish.  We don't need to worry about such writers, since
-	 * sync phase is single-threaded, so the writer can't be
-	 * doing anything while we are active.
-	 */
-	if (dsl_pool_sync_context(dp)) {
-		ASSERT(!DSL_DATASET_IS_DESTROYED(ds));
-		return (0);
-	}
-
-	/*
-	 * Normal users will hold the ds_rwlock as a READER until they
-	 * are finished (i.e., call dsl_dataset_rele()).  "Owners" will
-	 * drop their READER lock after they set the ds_owner field.
-	 *
-	 * If the dataset is being destroyed, the destroy thread will
-	 * obtain a WRITER lock for exclusive access after it's done its
-	 * open-context work and then change the ds_owner to
-	 * dsl_reaper once destruction is assured.  So threads
-	 * may block here temporarily, until the "destructability" of
-	 * the dataset is determined.
-	 */
-	ASSERT(!RW_WRITE_HELD(&dp->dp_config_rwlock));
-	mutex_enter(&ds->ds_lock);
-	while (!rw_tryenter(&ds->ds_rwlock, RW_READER)) {
-		rw_exit(&dp->dp_config_rwlock);
-		cv_wait(&ds->ds_exclusive_cv, &ds->ds_lock);
-		if (DSL_DATASET_IS_DESTROYED(ds)) {
-			mutex_exit(&ds->ds_lock);
-			dsl_dataset_drop_ref(ds, tag);
-			rw_enter(&dp->dp_config_rwlock, RW_READER);
-			return (ENOENT);
-		}
-		/*
-		 * The dp_config_rwlock lives above the ds_lock. And
-		 * we need to check DSL_DATASET_IS_DESTROYED() while
-		 * holding the ds_lock, so we have to drop and reacquire
-		 * the ds_lock here.
-		 */
-		mutex_exit(&ds->ds_lock);
-		rw_enter(&dp->dp_config_rwlock, RW_READER);
-		mutex_enter(&ds->ds_lock);
-	}
-	mutex_exit(&ds->ds_lock);
-	return (0);
-}
-
 int
-dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
-    dsl_dataset_t **dsp)
-{
-	int err = dsl_dataset_get_ref(dp, dsobj, tag, dsp);
-
-	if (err)
-		return (err);
-	return (dsl_dataset_hold_ref(*dsp, tag));
-}
-
-int
-dsl_dataset_own_obj(dsl_pool_t *dp, uint64_t dsobj, boolean_t inconsistentok,
+dsl_dataset_hold(dsl_pool_t *dp, const char *name,
     void *tag, dsl_dataset_t **dsp)
 {
-	int err = dsl_dataset_hold_obj(dp, dsobj, tag, dsp);
-	if (err)
-		return (err);
-	if (!dsl_dataset_tryown(*dsp, inconsistentok, tag)) {
-		dsl_dataset_rele(*dsp, tag);
-		*dsp = NULL;
-		return (EBUSY);
-	}
-	return (0);
-}
-
-int
-dsl_dataset_hold(const char *name, void *tag, dsl_dataset_t **dsp)
-{
 	dsl_dir_t *dd;
-	dsl_pool_t *dp;
 	const char *snapname;
 	uint64_t obj;
 	int err = 0;
 
-	err = dsl_dir_open_spa(NULL, name, FTAG, &dd, &snapname);
-	if (err)
+	err = dsl_dir_hold(dp, name, FTAG, &dd, &snapname);
+	if (err != 0)
 		return (err);
 
-	dp = dd->dd_pool;
+	ASSERT(dsl_pool_config_held(dp));
 	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);
+	if (obj != 0)
+		err = dsl_dataset_hold_obj(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;
+		dsl_dataset_t *ds;
 
 		if (*snapname++ != '@') {
 			dsl_dataset_rele(*dsp, tag);
-			err = ENOENT;
-			goto out;
+			dsl_dir_rele(dd, FTAG);
+			return (ENOENT);
 		}
 
 		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);
+			err = dsl_dataset_hold_obj(dp, obj, tag, &ds);
 		dsl_dataset_rele(*dsp, tag);
 
-		ASSERT3U((err == 0), ==, (ds != NULL));
-
-		if (ds) {
+		if (err == 0) {
 			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;
+			*dsp = ds;
 		}
 	}
-out:
-	rw_exit(&dp->dp_config_rwlock);
-	dsl_dir_close(dd, FTAG);
+
+	dsl_dir_rele(dd, FTAG);
 	return (err);
 }
 
 int
-dsl_dataset_own(const char *name, boolean_t inconsistentok,
+dsl_dataset_own_obj(dsl_pool_t *dp, uint64_t dsobj,
     void *tag, dsl_dataset_t **dsp)
 {
-	int err = dsl_dataset_hold(name, tag, dsp);
-	if (err)
+	int err = dsl_dataset_hold_obj(dp, dsobj, tag, dsp);
+	if (err != 0)
 		return (err);
-	if (!dsl_dataset_tryown(*dsp, inconsistentok, tag)) {
+	if (!dsl_dataset_tryown(*dsp, tag)) {
 		dsl_dataset_rele(*dsp, tag);
+		*dsp = NULL;
 		return (EBUSY);
 	}
 	return (0);
 }
 
+int
+dsl_dataset_own(dsl_pool_t *dp, const char *name,
+    void *tag, dsl_dataset_t **dsp)
+{
+	int err = dsl_dataset_hold(dp, name, tag, dsp);
+	if (err != 0)
+		return (err);
+	if (!dsl_dataset_tryown(*dsp, tag)) {
+		dsl_dataset_rele(*dsp, tag);
+		return (EBUSY);
+	}
+	return (0);
+}
+
+/*
+ * See the comment above dsl_pool_hold() for details.  In summary, a long
+ * hold is used to prevent destruction of a dataset while the pool hold
+ * is dropped, allowing other concurrent operations (e.g. spa_sync()).
+ *
+ * The dataset and pool must be held when this function is called.  After it
+ * is called, the pool hold may be released while the dataset is still held
+ * and accessed.
+ */
+void
+dsl_dataset_long_hold(dsl_dataset_t *ds, void *tag)
+{
+	ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool));
+	(void) refcount_add(&ds->ds_longholds, tag);
+}
+
+void
+dsl_dataset_long_rele(dsl_dataset_t *ds, void *tag)
+{
+	(void) refcount_remove(&ds->ds_longholds, tag);
+}
+
+/* Return B_TRUE if there are any long holds on this dataset. */
+boolean_t
+dsl_dataset_long_held(dsl_dataset_t *ds)
+{
+	return (!refcount_is_zero(&ds->ds_longholds));
+}
+
 void
 dsl_dataset_name(dsl_dataset_t *ds, char *name)
 {
@@ -666,7 +576,7 @@ dsl_dataset_name(dsl_dataset_t *ds, char *name)
 		(void) strcpy(name, "mos");
 	} else {
 		dsl_dir_name(ds->ds_dir, name);
-		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		VERIFY0(dsl_dataset_get_snapname(ds));
 		if (ds->ds_snapname[0]) {
 			(void) strcat(name, "@");
 			/*
@@ -693,7 +603,7 @@ dsl_dataset_namelen(dsl_dataset_t *ds)
 		result = 3;	/* "mos" */
 	} else {
 		result = dsl_dir_namelen(ds->ds_dir);
-		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		VERIFY0(dsl_dataset_get_snapname(ds));
 		if (ds->ds_snapname[0]) {
 			++result;	/* adding one for the @-sign */
 			if (!MUTEX_HELD(&ds->ds_lock)) {
@@ -710,64 +620,41 @@ dsl_dataset_namelen(dsl_dataset_t *ds)
 }
 
 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);
+	dmu_buf_rele(ds->ds_dbuf, tag);
 }
 
 void
 dsl_dataset_disown(dsl_dataset_t *ds, void *tag)
 {
-	ASSERT((ds->ds_owner == tag && ds->ds_dbuf) ||
-	    (DSL_DATASET_IS_DESTROYED(ds) && ds->ds_dbuf == NULL));
+	ASSERT(ds->ds_owner == tag && ds->ds_dbuf != NULL);
 
 	mutex_enter(&ds->ds_lock);
 	ds->ds_owner = NULL;
-	if (RW_WRITE_HELD(&ds->ds_rwlock)) {
-		rw_exit(&ds->ds_rwlock);
-		cv_broadcast(&ds->ds_exclusive_cv);
-	}
 	mutex_exit(&ds->ds_lock);
-	if (ds->ds_dbuf)
-		dsl_dataset_drop_ref(ds, tag);
+	dsl_dataset_long_rele(ds, tag);
+	if (ds->ds_dbuf != NULL)
+		dsl_dataset_rele(ds, tag);
 	else
 		dsl_dataset_evict(NULL, ds);
 }
 
 boolean_t
-dsl_dataset_tryown(dsl_dataset_t *ds, boolean_t inconsistentok, void *tag)
+dsl_dataset_tryown(dsl_dataset_t *ds, void *tag)
 {
 	boolean_t gotit = FALSE;
 
 	mutex_enter(&ds->ds_lock);
-	if (ds->ds_owner == NULL &&
-	    (!DS_IS_INCONSISTENT(ds) || inconsistentok)) {
+	if (ds->ds_owner == NULL && !DS_IS_INCONSISTENT(ds)) {
 		ds->ds_owner = tag;
-		if (!dsl_pool_sync_context(ds->ds_dir->dd_pool))
-			rw_exit(&ds->ds_rwlock);
+		dsl_dataset_long_hold(ds, tag);
 		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)
@@ -788,7 +675,7 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 
 	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));
+	VERIFY0(dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
 	dmu_buf_will_dirty(dbuf, tx);
 	dsphys = dbuf->db_data;
 	bzero(dsphys, sizeof (dsl_dataset_phys_t));
@@ -808,7 +695,7 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 	if (origin == NULL) {
 		dsphys->ds_deadlist_obj = dsl_deadlist_alloc(mos, tx);
 	} else {
-		dsl_dataset_t *ohds;
+		dsl_dataset_t *ohds; /* head of the origin snapshot */
 
 		dsphys->ds_prev_snap_obj = origin->ds_object;
 		dsphys->ds_prev_snap_txg =
@@ -825,7 +712,7 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 		dmu_buf_will_dirty(origin->ds_dbuf, tx);
 		origin->ds_phys->ds_num_children++;
 
-		VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
+		VERIFY0(dsl_dataset_hold_obj(dp,
 		    origin->ds_dir->dd_phys->dd_head_dataset_obj, FTAG, &ohds));
 		dsphys->ds_deadlist_obj = dsl_deadlist_clone(&ohds->ds_deadlist,
 		    dsphys->ds_prev_snap_txg, dsphys->ds_prev_snap_obj, tx);
@@ -837,9 +724,8 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 				    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));
+			VERIFY0(zap_add_int(mos,
+			    origin->ds_phys->ds_next_clones_obj, dsobj, tx));
 		}
 
 		dmu_buf_will_dirty(dd->dd_dbuf, tx);
@@ -851,7 +737,7 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 				    zap_create(mos,
 				    DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
 			}
-			VERIFY3U(0, ==, zap_add_int(mos,
+			VERIFY0(zap_add_int(mos,
 			    origin->ds_dir->dd_phys->dd_clones, dsobj, tx));
 		}
 	}
@@ -867,6 +753,16 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 	return (dsobj);
 }
 
+static void
+dsl_dataset_zero_zil(dsl_dataset_t *ds, dmu_tx_t *tx)
+{
+	objset_t *os;
+
+	VERIFY0(dmu_objset_from_ds(ds, &os));
+	bzero(&os->os_zil_header, sizeof (os->os_zil_header));
+	dsl_dataset_dirty(ds, tx);
+}
+
 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)
@@ -875,29 +771,28 @@ dsl_dataset_create_sync(dsl_dir_t *pdd, const char *lastname,
 	uint64_t dsobj, ddobj;
 	dsl_dir_t *dd;
 
+	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT(lastname[0] != '@');
 
 	ddobj = dsl_dir_create_sync(dp, pdd, lastname, tx);
-	VERIFY(0 == dsl_dir_open_obj(dp, ddobj, lastname, FTAG, &dd));
+	VERIFY0(dsl_dir_hold_obj(dp, ddobj, lastname, FTAG, &dd));
 
-	dsobj = dsl_dataset_create_sync_dd(dd, origin, flags, tx);
+	dsobj = dsl_dataset_create_sync_dd(dd, origin,
+	    flags & ~DS_CREATE_FLAG_NODIRTY, tx);
 
 	dsl_deleg_set_create_perms(dd, tx, cr);
 
-	dsl_dir_close(dd, FTAG);
+	dsl_dir_rele(dd, FTAG);
 
 	/*
 	 * If we are creating a clone, make sure we zero out any stale
 	 * data from the origin snapshots zil header.
 	 */
-	if (origin != NULL) {
+	if (origin != NULL && !(flags & DS_CREATE_FLAG_NODIRTY)) {
 		dsl_dataset_t *ds;
-		objset_t *os;
 
-		VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
-		VERIFY3U(0, ==, dmu_objset_from_ds(ds, &os));
-		bzero(&os->os_zil_header, sizeof (os->os_zil_header));
-		dsl_dataset_dirty(ds, tx);
+		VERIFY0(dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
+		dsl_dataset_zero_zil(ds, tx);
 		dsl_dataset_rele(ds, FTAG);
 	}
 
@@ -926,7 +821,7 @@ dsl_check_snap_cb(const char *name, void *arg)
 }
 
 int
-dmu_get_recursive_snaps_nvl(const char *fsname, const char *snapname,
+dmu_get_recursive_snaps_nvl(char *fsname, const char *snapname,
     nvlist_t *snaps)
 {
 	struct destroyarg *da;
@@ -945,329 +840,6 @@ dmu_get_recursive_snaps_nvl(const char *fsname, const char *snapname,
 #endif /* __FreeBSD__ */
 
 /*
- * The snapshots must all be in the same pool.
- */
-int
-dmu_snapshots_destroy_nvl(nvlist_t *snaps, boolean_t defer,
-    nvlist_t *errlist)
-{
-	int err;
-	dsl_sync_task_t *dst;
-	spa_t *spa;
-	nvpair_t *pair;
-	dsl_sync_task_group_t *dstg;
-
-	pair = nvlist_next_nvpair(snaps, NULL);
-	if (pair == NULL)
-		return (0);
-
-	err = spa_open(nvpair_name(pair), &spa, FTAG);
-	if (err)
-		return (err);
-	dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
-
-	for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
-	    pair = nvlist_next_nvpair(snaps, pair)) {
-		dsl_dataset_t *ds;
-
-		err = dsl_dataset_own(nvpair_name(pair), B_TRUE, dstg, &ds);
-		if (err == 0) {
-			struct dsl_ds_destroyarg *dsda;
-
-			dsl_dataset_make_exclusive(ds, dstg);
-			dsda = kmem_zalloc(sizeof (struct dsl_ds_destroyarg),
-			    KM_SLEEP);
-			dsda->ds = ds;
-			dsda->defer = defer;
-			dsl_sync_task_create(dstg, dsl_dataset_destroy_check,
-			    dsl_dataset_destroy_sync, dsda, dstg, 0);
-		} else if (err == ENOENT) {
-			err = 0;
-		} else {
-			fnvlist_add_int32(errlist, nvpair_name(pair), err);
-			break;
-		}
-	}
-
-	if (err == 0)
-		err = dsl_sync_task_group_wait(dstg);
-
-	for (dst = list_head(&dstg->dstg_tasks); dst;
-	    dst = list_next(&dstg->dstg_tasks, dst)) {
-		struct dsl_ds_destroyarg *dsda = dst->dst_arg1;
-		dsl_dataset_t *ds = dsda->ds;
-
-		/*
-		 * Return the snapshots that triggered the error.
-		 */
-		if (dst->dst_err != 0) {
-			char name[ZFS_MAXNAMELEN];
-			dsl_dataset_name(ds, name);
-			fnvlist_add_int32(errlist, name, dst->dst_err);
-		}
-		ASSERT3P(dsda->rm_origin, ==, NULL);
-		dsl_dataset_disown(ds, dstg);
-		kmem_free(dsda, sizeof (struct dsl_ds_destroyarg));
-	}
-
-	dsl_sync_task_group_destroy(dstg);
-	spa_close(spa, FTAG);
-	return (err);
-
-}
-
-static boolean_t
-dsl_dataset_might_destroy_origin(dsl_dataset_t *ds)
-{
-	boolean_t might_destroy = B_FALSE;
-
-	mutex_enter(&ds->ds_lock);
-	if (ds->ds_phys->ds_num_children == 2 && ds->ds_userrefs == 0 &&
-	    DS_IS_DEFER_DESTROY(ds))
-		might_destroy = B_TRUE;
-	mutex_exit(&ds->ds_lock);
-
-	return (might_destroy);
-}
-
-/*
- * If we're removing a clone, and these three conditions are true:
- *	1) the clone's origin has no other children
- *	2) the clone's origin has no user references
- *	3) the clone's origin has been marked for deferred destruction
- * Then, prepare to remove the origin as part of this sync task group.
- */
-static int
-dsl_dataset_origin_rm_prep(struct dsl_ds_destroyarg *dsda, void *tag)
-{
-	dsl_dataset_t *ds = dsda->ds;
-	dsl_dataset_t *origin = ds->ds_prev;
-
-	if (dsl_dataset_might_destroy_origin(origin)) {
-		char *name;
-		int namelen;
-		int error;
-
-		namelen = dsl_dataset_namelen(origin) + 1;
-		name = kmem_alloc(namelen, KM_SLEEP);
-		dsl_dataset_name(origin, name);
-#ifdef _KERNEL
-		error = zfs_unmount_snap(name, NULL);
-		if (error) {
-			kmem_free(name, namelen);
-			return (error);
-		}
-#endif
-		error = dsl_dataset_own(name, B_TRUE, tag, &origin);
-		kmem_free(name, namelen);
-		if (error)
-			return (error);
-		dsda->rm_origin = origin;
-		dsl_dataset_make_exclusive(origin, tag);
-	}
-
-	return (0);
-}
-
-/*
- * 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, boolean_t defer)
-{
-	int err;
-	dsl_sync_task_group_t *dstg;
-	objset_t *os;
-	dsl_dir_t *dd;
-	uint64_t obj;
-	struct dsl_ds_destroyarg dsda = { 0 };
-
-	dsda.ds = ds;
-
-	if (dsl_dataset_is_snapshot(ds)) {
-		/* Destroying a snapshot is simpler */
-		dsl_dataset_make_exclusive(ds, tag);
-
-		dsda.defer = defer;
-		err = dsl_sync_task_do(ds->ds_dir->dd_pool,
-		    dsl_dataset_destroy_check, dsl_dataset_destroy_sync,
-		    &dsda, tag, 0);
-		ASSERT3P(dsda.rm_origin, ==, NULL);
-		goto out;
-	} else if (defer) {
-		err = EINVAL;
-		goto out;
-	}
-
-	dd = ds->ds_dir;
-
-	if (!spa_feature_is_enabled(dsl_dataset_get_spa(ds),
-	    &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
-		/*
-		 * Check for errors and mark this ds as inconsistent, in
-		 * case we crash while freeing the objects.
-		 */
-		err = dsl_sync_task_do(dd->dd_pool,
-		    dsl_dataset_destroy_begin_check,
-		    dsl_dataset_destroy_begin_sync, ds, NULL, 0);
-		if (err)
-			goto out;
-
-		err = dmu_objset_from_ds(ds, &os);
-		if (err)
-			goto out;
-
-		/*
-		 * Remove all objects while in the open context so that
-		 * there is less work to do in the syncing context.
-		 */
-		for (obj = 0; err == 0; err = dmu_object_next(os, &obj, FALSE,
-		    ds->ds_phys->ds_prev_snap_txg)) {
-			/*
-			 * Ignore errors, if there is not enough disk space
-			 * we will deal with it in dsl_dataset_destroy_sync().
-			 */
-			(void) dmu_free_object(os, obj);
-		}
-		if (err != ESRCH)
-			goto out;
-
-		/*
-		 * Sync out all in-flight IO.
-		 */
-		txg_wait_synced(dd->dd_pool, 0);
-
-		/*
-		 * If we managed to free all the objects in open
-		 * context, the user space accounting should be zero.
-		 */
-		if (ds->ds_phys->ds_bp.blk_fill == 0 &&
-		    dmu_objset_userused_enabled(os)) {
-			uint64_t count;
-
-			ASSERT(zap_count(os, DMU_USERUSED_OBJECT,
-			    &count) != 0 || count == 0);
-			ASSERT(zap_count(os, DMU_GROUPUSED_OBJECT,
-			    &count) != 0 || count == 0);
-		}
-	}
-
-	rw_enter(&dd->dd_pool->dp_config_rwlock, RW_READER);
-	err = dsl_dir_open_obj(dd->dd_pool, dd->dd_object, NULL, FTAG, &dd);
-	rw_exit(&dd->dd_pool->dp_config_rwlock);
-
-	if (err)
-		goto out;
-
-	/*
-	 * Blow away the dsl_dir + head dataset.
-	 */
-	dsl_dataset_make_exclusive(ds, tag);
-	/*
-	 * If we're removing a clone, we might also need to remove its
-	 * origin.
-	 */
-	do {
-		dsda.need_prep = B_FALSE;
-		if (dsl_dir_is_clone(dd)) {
-			err = dsl_dataset_origin_rm_prep(&dsda, tag);
-			if (err) {
-				dsl_dir_close(dd, FTAG);
-				goto out;
-			}
-		}
-
-		dstg = dsl_sync_task_group_create(ds->ds_dir->dd_pool);
-		dsl_sync_task_create(dstg, dsl_dataset_destroy_check,
-		    dsl_dataset_destroy_sync, &dsda, tag, 0);
-		dsl_sync_task_create(dstg, dsl_dir_destroy_check,
-		    dsl_dir_destroy_sync, dd, FTAG, 0);
-		err = dsl_sync_task_group_wait(dstg);
-		dsl_sync_task_group_destroy(dstg);
-
-		/*
-		 * We could be racing against 'zfs release' or 'zfs destroy -d'
-		 * on the origin snap, in which case we can get EBUSY if we
-		 * needed to destroy the origin snap but were not ready to
-		 * do so.
-		 */
-		if (dsda.need_prep) {
-			ASSERT(err == EBUSY);
-			ASSERT(dsl_dir_is_clone(dd));
-			ASSERT(dsda.rm_origin == NULL);
-		}
-	} while (dsda.need_prep);
-
-	if (dsda.rm_origin != NULL)
-		dsl_dataset_disown(dsda.rm_origin, tag);
-
-	/* if it is successful, dsl_dir_destroy_sync will close the dd */
-	if (err)
-		dsl_dir_close(dd, FTAG);
-out:
-	dsl_dataset_disown(ds, tag);
-	return (err);
-}
-
-blkptr_t *
-dsl_dataset_get_blkptr(dsl_dataset_t *ds)
-{
-	return (&ds->ds_phys->ds_bp);
-}
-
-void
-dsl_dataset_set_blkptr(dsl_dataset_t *ds, blkptr_t *bp, dmu_tx_t *tx)
-{
-	ASSERT(dmu_tx_is_syncing(tx));
-	/* If it's the meta-objset, set dp_meta_rootbp */
-	if (ds == NULL) {
-		tx->tx_pool->dp_meta_rootbp = *bp;
-	} else {
-		dmu_buf_will_dirty(ds->ds_dbuf, tx);
-		ds->ds_phys->ds_bp = *bp;
-	}
-}
-
-spa_t *
-dsl_dataset_get_spa(dsl_dataset_t *ds)
-{
-	return (ds->ds_dir->dd_pool->dp_spa);
-}
-
-void
-dsl_dataset_dirty(dsl_dataset_t *ds, dmu_tx_t *tx)
-{
-	dsl_pool_t *dp;
-
-	if (ds == NULL) /* this is the meta-objset */
-		return;
-
-	ASSERT(ds->ds_objset != NULL);
-
-	if (ds->ds_phys->ds_next_snap_obj != 0)
-		panic("dirtying snapshot!");
-
-	dp = ds->ds_dir->dd_pool;
-
-	if (txg_list_add(&dp->dp_dirty_datasets, ds, tx->tx_txg) == 0) {
-		/* up the hold count until we can be written out */
-		dmu_buf_add_ref(ds->ds_dbuf, ds);
-	}
-}
-
-boolean_t
-dsl_dataset_is_dirty(dsl_dataset_t *ds)
-{
-	for (int t = 0; t < TXG_SIZE; t++) {
-		if (txg_list_member(&ds->ds_dir->dd_pool->dp_dirty_datasets,
-		    ds, t))
-			return (B_TRUE);
-	}
-	return (B_FALSE);
-}
-
-/*
  * 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
@@ -1275,7 +847,7 @@ dsl_dataset_is_dirty(dsl_dataset_t *ds)
  * the total space used in the snapshot and subtract out the space that
  * has been freed up since the snapshot was taken.
  */
-static void
+void
 dsl_dataset_recalc_head_uniq(dsl_dataset_t *ds)
 {
 	uint64_t mrs_used;
@@ -1299,235 +871,10 @@ dsl_dataset_recalc_head_uniq(dsl_dataset_t *ds)
 		ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
 }
 
-struct killarg {
-	dsl_dataset_t *ds;
-	dmu_tx_t *tx;
-};
-
-/* ARGSUSED */
-static int
-kill_blkptr(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
-    const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
-{
-	struct killarg *ka = arg;
-	dmu_tx_t *tx = ka->tx;
-
-	if (bp == NULL)
-		return (0);
-
-	if (zb->zb_level == ZB_ZIL_LEVEL) {
-		ASSERT(zilog != NULL);
-		/*
-		 * It's a block in the intent log.  It has no
-		 * accounting, so just free it.
-		 */
-		dsl_free(ka->tx->tx_pool, ka->tx->tx_txg, bp);
-	} else {
-		ASSERT(zilog == NULL);
-		ASSERT3U(bp->blk_birth, >, ka->ds->ds_phys->ds_prev_snap_txg);
-		(void) dsl_dataset_block_kill(ka->ds, bp, tx, B_FALSE);
-	}
-
-	return (0);
-}
-
-/* ARGSUSED */
-static int
-dsl_dataset_destroy_begin_check(void *arg1, void *arg2, dmu_tx_t *tx)
-{
-	dsl_dataset_t *ds = arg1;
-	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
-	uint64_t count;
-	int err;
-
-	/*
-	 * Can't delete a head dataset if there are snapshots of it.
-	 * (Except if the only snapshots are from the branch we cloned
-	 * from.)
-	 */
-	if (ds->ds_prev != NULL &&
-	    ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
-		return (EBUSY);
-
-	/*
-	 * This is really a dsl_dir thing, but check it here so that
-	 * we'll be less likely to leave this dataset inconsistent &
-	 * nearly destroyed.
-	 */
-	err = zap_count(mos, ds->ds_dir->dd_phys->dd_child_dir_zapobj, &count);
-	if (err)
-		return (err);
-	if (count != 0)
-		return (EEXIST);
-
-	return (0);
-}
-
-/* ARGSUSED */
-static void
-dsl_dataset_destroy_begin_sync(void *arg1, void *arg2, dmu_tx_t *tx)
-{
-	dsl_dataset_t *ds = arg1;
-
-	/* 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, "");
-}
-
-static int
-dsl_dataset_origin_check(struct dsl_ds_destroyarg *dsda, void *tag,
+void
+dsl_dataset_remove_from_next_clones(dsl_dataset_t *ds, uint64_t obj,
     dmu_tx_t *tx)
 {
-	dsl_dataset_t *ds = dsda->ds;
-	dsl_dataset_t *ds_prev = ds->ds_prev;
-
-	if (dsl_dataset_might_destroy_origin(ds_prev)) {
-		struct dsl_ds_destroyarg ndsda = {0};
-
-		/*
-		 * If we're not prepared to remove the origin, don't remove
-		 * the clone either.
-		 */
-		if (dsda->rm_origin == NULL) {
-			dsda->need_prep = B_TRUE;
-			return (EBUSY);
-		}
-
-		ndsda.ds = ds_prev;
-		ndsda.is_origin_rm = B_TRUE;
-		return (dsl_dataset_destroy_check(&ndsda, tag, tx));
-	}
-
-	/*
-	 * If we're not going to remove the origin after all,
-	 * undo the open context setup.
-	 */
-	if (dsda->rm_origin != NULL) {
-		dsl_dataset_disown(dsda->rm_origin, tag);
-		dsda->rm_origin = NULL;
-	}
-
-	return (0);
-}
-
-/*
- * If you add new checks here, you may need to add
- * additional checks to the "temporary" case in
- * snapshot_check() in dmu_objset.c.
- */
-/* ARGSUSED */
-int
-dsl_dataset_destroy_check(void *arg1, void *arg2, dmu_tx_t *tx)
-{
-	struct dsl_ds_destroyarg *dsda = arg1;
-	dsl_dataset_t *ds = dsda->ds;
-
-	/* we have an owner hold, so noone else can destroy us */
-	ASSERT(!DSL_DATASET_IS_DESTROYED(ds));
-
-	/*
-	 * Only allow deferred destroy on pools that support it.
-	 * NOTE: deferred destroy is only supported on snapshots.
-	 */
-	if (dsda->defer) {
-		if (spa_version(ds->ds_dir->dd_pool->dp_spa) <
-		    SPA_VERSION_USERREFS)
-			return (ENOTSUP);
-		ASSERT(dsl_dataset_is_snapshot(ds));
-		return (0);
-	}
-
-	/*
-	 * Can't delete a head dataset if there are snapshots of it.
-	 * (Except if the only snapshots are from the branch we cloned
-	 * from.)
-	 */
-	if (ds->ds_prev != NULL &&
-	    ds->ds_prev->ds_phys->ds_next_snap_obj == ds->ds_object)
-		return (EBUSY);
-
-	/*
-	 * If we made changes this txg, traverse_dsl_dataset won't find
-	 * them.  Try again.
-	 */
-	if (ds->ds_phys->ds_bp.blk_birth >= tx->tx_txg)
-		return (EAGAIN);
-
-	if (dsl_dataset_is_snapshot(ds)) {
-		/*
-		 * If this snapshot has an elevated user reference count,
-		 * we can't destroy it yet.
-		 */
-		if (ds->ds_userrefs > 0 && !dsda->releasing)
-			return (EBUSY);
-
-		mutex_enter(&ds->ds_lock);
-		/*
-		 * Can't delete a branch point. However, if we're destroying
-		 * a clone and removing its origin due to it having a user
-		 * hold count of 0 and having been marked for deferred destroy,
-		 * it's OK for the origin to have a single clone.
-		 */
-		if (ds->ds_phys->ds_num_children >
-		    (dsda->is_origin_rm ? 2 : 1)) {
-			mutex_exit(&ds->ds_lock);
-			return (EEXIST);
-		}
-		mutex_exit(&ds->ds_lock);
-	} else if (dsl_dir_is_clone(ds->ds_dir)) {
-		return (dsl_dataset_origin_check(dsda, arg2, tx));
-	}
-
-	/* XXX we should do some i/o error checking... */
-	return (0);
-}
-
-struct refsarg {
-	kmutex_t lock;
-	boolean_t gone;
-	kcondvar_t cv;
-};
-
-/* ARGSUSED */
-static void
-dsl_dataset_refs_gone(dmu_buf_t *db, void *argv)
-{
-	struct refsarg *arg = argv;
-
-	mutex_enter(&arg->lock);
-	arg->gone = TRUE;
-	cv_signal(&arg->cv);
-	mutex_exit(&arg->lock);
-}
-
-static void
-dsl_dataset_drain_refs(dsl_dataset_t *ds, void *tag)
-{
-	struct refsarg arg;
-
-	bzero(&arg, sizeof(arg));
-	mutex_init(&arg.lock, NULL, MUTEX_DEFAULT, NULL);
-	cv_init(&arg.cv, NULL, CV_DEFAULT, NULL);
-	arg.gone = FALSE;
-	(void) dmu_buf_update_user(ds->ds_dbuf, ds, &arg, &ds->ds_phys,
-	    dsl_dataset_refs_gone);
-	dmu_buf_rele(ds->ds_dbuf, tag);
-	mutex_enter(&arg.lock);
-	while (!arg.gone)
-		cv_wait(&arg.cv, &arg.lock);
-	ASSERT(arg.gone);
-	mutex_exit(&arg.lock);
-	ds->ds_dbuf = NULL;
-	ds->ds_phys = NULL;
-	mutex_destroy(&arg.lock);
-	cv_destroy(&arg.cv);
-}
-
-static void
-remove_from_next_clones(dsl_dataset_t *ds, uint64_t obj, dmu_tx_t *tx)
-{
 	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
 	uint64_t count;
 	int err;
@@ -1544,491 +891,69 @@ remove_from_next_clones(dsl_dataset_t *ds, uint64_t obj, dmu_tx_t *tx)
 	 * too many entries in the next_clones_obj even after failing to
 	 * remove this one.
 	 */
-	if (err != ENOENT) {
+	if (err != ENOENT)
 		VERIFY0(err);
-	}
-	ASSERT3U(0, ==, zap_count(mos, ds->ds_phys->ds_next_clones_obj,
+	ASSERT0(zap_count(mos, ds->ds_phys->ds_next_clones_obj,
 	    &count));
 	ASSERT3U(count, <=, ds->ds_phys->ds_num_children - 2);
 }
 
-static void
-dsl_dataset_remove_clones_key(dsl_dataset_t *ds, uint64_t mintxg, dmu_tx_t *tx)
-{
-	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
-	zap_cursor_t zc;
-	zap_attribute_t za;
-
-	/*
-	 * If it is the old version, dd_clones doesn't exist so we can't
-	 * find the clones, but deadlist_remove_key() is a no-op so it
-	 * doesn't matter.
-	 */
-	if (ds->ds_dir->dd_phys->dd_clones == 0)
-		return;
 
-	for (zap_cursor_init(&zc, mos, ds->ds_dir->dd_phys->dd_clones);
-	    zap_cursor_retrieve(&zc, &za) == 0;
-	    zap_cursor_advance(&zc)) {
-		dsl_dataset_t *clone;
-
-		VERIFY3U(0, ==, dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
-		    za.za_first_integer, FTAG, &clone));
-		if (clone->ds_dir->dd_origin_txg > mintxg) {
-			dsl_deadlist_remove_key(&clone->ds_deadlist,
-			    mintxg, tx);
-			dsl_dataset_remove_clones_key(clone, mintxg, tx);
-		}
-		dsl_dataset_rele(clone, FTAG);
-	}
-	zap_cursor_fini(&zc);
+blkptr_t *
+dsl_dataset_get_blkptr(dsl_dataset_t *ds)
+{
+	return (&ds->ds_phys->ds_bp);
 }
 
-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)
+void
+dsl_dataset_set_blkptr(dsl_dataset_t *ds, 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);
-		}
+	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 {
-		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);
+		dmu_buf_will_dirty(ds->ds_dbuf, tx);
+		ds->ds_phys->ds_bp = *bp;
 	}
-	return (0);
-}
-
-static void
-process_old_deadlist(dsl_dataset_t *ds, dsl_dataset_t *ds_prev,
-    dsl_dataset_t *ds_next, boolean_t after_branch_point, dmu_tx_t *tx)
-{
-	struct process_old_arg poa = { 0 };
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
-	objset_t *mos = dp->dp_meta_objset;
-
-	ASSERT(ds->ds_deadlist.dl_oldfmt);
-	ASSERT(ds_next->ds_deadlist.dl_oldfmt);
-
-	poa.ds = ds;
-	poa.ds_prev = ds_prev;
-	poa.after_branch_point = after_branch_point;
-	poa.pio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
-	VERIFY3U(0, ==, bpobj_iterate(&ds_next->ds_deadlist.dl_bpobj,
-	    process_old_cb, &poa, tx));
-	VERIFY0(zio_wait(poa.pio));
-	ASSERT3U(poa.used, ==, ds->ds_phys->ds_unique_bytes);
-
-	/* change snapused */
-	dsl_dir_diduse_space(ds->ds_dir, DD_USED_SNAP,
-	    -poa.used, -poa.comp, -poa.uncomp, tx);
-
-	/* swap next's deadlist to our deadlist */
-	dsl_deadlist_close(&ds->ds_deadlist);
-	dsl_deadlist_close(&ds_next->ds_deadlist);
-	SWITCH64(ds_next->ds_phys->ds_deadlist_obj,
-	    ds->ds_phys->ds_deadlist_obj);
-	dsl_deadlist_open(&ds->ds_deadlist, mos, ds->ds_phys->ds_deadlist_obj);
-	dsl_deadlist_open(&ds_next->ds_deadlist, mos,
-	    ds_next->ds_phys->ds_deadlist_obj);
 }
 
-static int
-old_synchronous_dataset_destroy(dsl_dataset_t *ds, dmu_tx_t *tx)
+spa_t *
+dsl_dataset_get_spa(dsl_dataset_t *ds)
 {
-	int err;
-	struct killarg ka;
-
-	/*
-	 * Free everything that we point to (that's born after
-	 * the previous snapshot, if we are a clone)
-	 *
-	 * NB: this should be very quick, because we already
-	 * freed all the objects in open context.
-	 */
-	ka.ds = ds;
-	ka.tx = tx;
-	err = traverse_dataset(ds,
-	    ds->ds_phys->ds_prev_snap_txg, TRAVERSE_POST,
-	    kill_blkptr, &ka);
-	ASSERT0(err);
-	ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) || ds->ds_phys->ds_unique_bytes == 0);
-
-	return (err);
+	return (ds->ds_dir->dd_pool->dp_spa);
 }
 
 void
-dsl_dataset_destroy_sync(void *arg1, void *tag, dmu_tx_t *tx)
+dsl_dataset_dirty(dsl_dataset_t *ds, dmu_tx_t *tx)
 {
-	struct dsl_ds_destroyarg *dsda = arg1;
-	dsl_dataset_t *ds = dsda->ds;
-	int err;
-	int after_branch_point = FALSE;
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
-	objset_t *mos = dp->dp_meta_objset;
-	dsl_dataset_t *ds_prev = NULL;
-	boolean_t wont_destroy;
-	uint64_t obj;
-
-	wont_destroy = (dsda->defer &&
-	    (ds->ds_userrefs > 0 || ds->ds_phys->ds_num_children > 1));
-
-	ASSERT(ds->ds_owner || wont_destroy);
-	ASSERT(dsda->defer || ds->ds_phys->ds_num_children <= 1);
-	ASSERT(ds->ds_prev == NULL ||
-	    ds->ds_prev->ds_phys->ds_next_snap_obj != ds->ds_object);
-	ASSERT3U(ds->ds_phys->ds_bp.blk_birth, <=, tx->tx_txg);
+	dsl_pool_t *dp;
 
-	if (wont_destroy) {
-		ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
-		dmu_buf_will_dirty(ds->ds_dbuf, tx);
-		ds->ds_phys->ds_flags |= DS_FLAG_DEFER_DESTROY;
-		spa_history_log_internal_ds(ds, "defer_destroy", tx, "");
+	if (ds == NULL) /* this is the meta-objset */
 		return;
-	}
 
-	/* We need to log before removing it from the namespace. */
-	spa_history_log_internal_ds(ds, "destroy", tx, "");
-
-	/* signal any waiters that this dataset is going away */
-	mutex_enter(&ds->ds_lock);
-	ds->ds_owner = dsl_reaper;
-	cv_broadcast(&ds->ds_exclusive_cv);
-	mutex_exit(&ds->ds_lock);
-
-	/* Remove our reservation */
-	if (ds->ds_reserved != 0) {
-		dsl_prop_setarg_t psa;
-		uint64_t value = 0;
-
-		dsl_prop_setarg_init_uint64(&psa, "refreservation",
-		    (ZPROP_SRC_NONE | ZPROP_SRC_LOCAL | ZPROP_SRC_RECEIVED),
-		    &value);
-		psa.psa_effective_value = 0;	/* predict default value */
-
-		dsl_dataset_set_reservation_sync(ds, &psa, tx);
-		ASSERT0(ds->ds_reserved);
-	}
-
-	ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));
-
-	dsl_scan_ds_destroyed(ds, tx);
-
-	obj = ds->ds_object;
-
-	if (ds->ds_phys->ds_prev_snap_obj != 0) {
-		if (ds->ds_prev) {
-			ds_prev = ds->ds_prev;
-		} else {
-			VERIFY(0 == dsl_dataset_hold_obj(dp,
-			    ds->ds_phys->ds_prev_snap_obj, FTAG, &ds_prev));
-		}
-		after_branch_point =
-		    (ds_prev->ds_phys->ds_next_snap_obj != obj);
-
-		dmu_buf_will_dirty(ds_prev->ds_dbuf, tx);
-		if (after_branch_point &&
-		    ds_prev->ds_phys->ds_next_clones_obj != 0) {
-			remove_from_next_clones(ds_prev, obj, tx);
-			if (ds->ds_phys->ds_next_snap_obj != 0) {
-				VERIFY(0 == zap_add_int(mos,
-				    ds_prev->ds_phys->ds_next_clones_obj,
-				    ds->ds_phys->ds_next_snap_obj, tx));
-			}
-		}
-		if (after_branch_point &&
-		    ds->ds_phys->ds_next_snap_obj == 0) {
-			/* This clone is toast. */
-			ASSERT(ds_prev->ds_phys->ds_num_children > 1);
-			ds_prev->ds_phys->ds_num_children--;
-
-			/*
-			 * If the clone's origin has no other clones, no
-			 * user holds, and has been marked for deferred
-			 * deletion, then we should have done the necessary
-			 * destroy setup for it.
-			 */
-			if (ds_prev->ds_phys->ds_num_children == 1 &&
-			    ds_prev->ds_userrefs == 0 &&
-			    DS_IS_DEFER_DESTROY(ds_prev)) {
-				ASSERT3P(dsda->rm_origin, !=, NULL);
-			} else {
-				ASSERT3P(dsda->rm_origin, ==, NULL);
-			}
-		} else if (!after_branch_point) {
-			ds_prev->ds_phys->ds_next_snap_obj =
-			    ds->ds_phys->ds_next_snap_obj;
-		}
-	}
-
-	if (dsl_dataset_is_snapshot(ds)) {
-		dsl_dataset_t *ds_next;
-		uint64_t old_unique;
-		uint64_t used = 0, comp = 0, uncomp = 0;
-
-		VERIFY(0 == dsl_dataset_hold_obj(dp,
-		    ds->ds_phys->ds_next_snap_obj, FTAG, &ds_next));
-		ASSERT3U(ds_next->ds_phys->ds_prev_snap_obj, ==, obj);
-
-		old_unique = ds_next->ds_phys->ds_unique_bytes;
-
-		dmu_buf_will_dirty(ds_next->ds_dbuf, tx);
-		ds_next->ds_phys->ds_prev_snap_obj =
-		    ds->ds_phys->ds_prev_snap_obj;
-		ds_next->ds_phys->ds_prev_snap_txg =
-		    ds->ds_phys->ds_prev_snap_txg;
-		ASSERT3U(ds->ds_phys->ds_prev_snap_txg, ==,
-		    ds_prev ? ds_prev->ds_phys->ds_creation_txg : 0);
-
-
-		if (ds_next->ds_deadlist.dl_oldfmt) {
-			process_old_deadlist(ds, ds_prev, ds_next,
-			    after_branch_point, tx);
-		} else {
-			/* Adjust prev's unique space. */
-			if (ds_prev && !after_branch_point) {
-				dsl_deadlist_space_range(&ds_next->ds_deadlist,
-				    ds_prev->ds_phys->ds_prev_snap_txg,
-				    ds->ds_phys->ds_prev_snap_txg,
-				    &used, &comp, &uncomp);
-				ds_prev->ds_phys->ds_unique_bytes += used;
-			}
-
-			/* Adjust snapused. */
-			dsl_deadlist_space_range(&ds_next->ds_deadlist,
-			    ds->ds_phys->ds_prev_snap_txg, UINT64_MAX,
-			    &used, &comp, &uncomp);
-			dsl_dir_diduse_space(ds->ds_dir, DD_USED_SNAP,
-			    -used, -comp, -uncomp, tx);
-
-			/* Move blocks to be freed to pool's free list. */
-			dsl_deadlist_move_bpobj(&ds_next->ds_deadlist,
-			    &dp->dp_free_bpobj, ds->ds_phys->ds_prev_snap_txg,
-			    tx);
-			dsl_dir_diduse_space(tx->tx_pool->dp_free_dir,
-			    DD_USED_HEAD, used, comp, uncomp, tx);
-
-			/* Merge our deadlist into next's and free it. */
-			dsl_deadlist_merge(&ds_next->ds_deadlist,
-			    ds->ds_phys->ds_deadlist_obj, tx);
-		}
-		dsl_deadlist_close(&ds->ds_deadlist);
-		dsl_deadlist_free(mos, ds->ds_phys->ds_deadlist_obj, tx);
-
-		/* Collapse range in clone heads */
-		dsl_dataset_remove_clones_key(ds,
-		    ds->ds_phys->ds_creation_txg, tx);
-
-		if (dsl_dataset_is_snapshot(ds_next)) {
-			dsl_dataset_t *ds_nextnext;
-
-			/*
-			 * Update next's unique to include blocks which
-			 * were previously shared by only this snapshot
-			 * and it.  Those blocks will be born after the
-			 * prev snap and before this snap, and will have
-			 * died after the next snap and before the one
-			 * after that (ie. be on the snap after next's
-			 * deadlist).
-			 */
-			VERIFY(0 == dsl_dataset_hold_obj(dp,
-			    ds_next->ds_phys->ds_next_snap_obj,
-			    FTAG, &ds_nextnext));
-			dsl_deadlist_space_range(&ds_nextnext->ds_deadlist,
-			    ds->ds_phys->ds_prev_snap_txg,
-			    ds->ds_phys->ds_creation_txg,
-			    &used, &comp, &uncomp);
-			ds_next->ds_phys->ds_unique_bytes += used;
-			dsl_dataset_rele(ds_nextnext, FTAG);
-			ASSERT3P(ds_next->ds_prev, ==, NULL);
-
-			/* Collapse range in this head. */
-			dsl_dataset_t *hds;
-			VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
-			    ds->ds_dir->dd_phys->dd_head_dataset_obj,
-			    FTAG, &hds));
-			dsl_deadlist_remove_key(&hds->ds_deadlist,
-			    ds->ds_phys->ds_creation_txg, tx);
-			dsl_dataset_rele(hds, FTAG);
-
-		} else {
-			ASSERT3P(ds_next->ds_prev, ==, ds);
-			dsl_dataset_drop_ref(ds_next->ds_prev, ds_next);
-			ds_next->ds_prev = NULL;
-			if (ds_prev) {
-				VERIFY(0 == dsl_dataset_get_ref(dp,
-				    ds->ds_phys->ds_prev_snap_obj,
-				    ds_next, &ds_next->ds_prev));
-			}
-
-			dsl_dataset_recalc_head_uniq(ds_next);
-
-			/*
-			 * Reduce the amount of our unconsmed refreservation
-			 * being charged to our parent by the amount of
-			 * new unique data we have gained.
-			 */
-			if (old_unique < ds_next->ds_reserved) {
-				int64_t mrsdelta;
-				uint64_t new_unique =
-				    ds_next->ds_phys->ds_unique_bytes;
-
-				ASSERT(old_unique <= new_unique);
-				mrsdelta = MIN(new_unique - old_unique,
-				    ds_next->ds_reserved - old_unique);
-				dsl_dir_diduse_space(ds->ds_dir,
-				    DD_USED_REFRSRV, -mrsdelta, 0, 0, tx);
-			}
-		}
-		dsl_dataset_rele(ds_next, FTAG);
-	} else {
-		zfeature_info_t *async_destroy =
-		    &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY];
-		objset_t *os;
-
-		/*
-		 * There's no next snapshot, so this is a head dataset.
-		 * Destroy the deadlist.  Unless it's a clone, the
-		 * deadlist should be empty.  (If it's a clone, it's
-		 * safe to ignore the deadlist contents.)
-		 */
-		dsl_deadlist_close(&ds->ds_deadlist);
-		dsl_deadlist_free(mos, ds->ds_phys->ds_deadlist_obj, tx);
-		ds->ds_phys->ds_deadlist_obj = 0;
-
-		VERIFY3U(0, ==, dmu_objset_from_ds(ds, &os));
-
-		if (!spa_feature_is_enabled(dp->dp_spa, async_destroy)) {
-			err = old_synchronous_dataset_destroy(ds, tx);
-		} else {
-			/*
-			 * Move the bptree into the pool's list of trees to
-			 * clean up and update space accounting information.
-			 */
-			uint64_t used, comp, uncomp;
-
-			zil_destroy_sync(dmu_objset_zil(os), tx);
-
-			if (!spa_feature_is_active(dp->dp_spa, async_destroy)) {
-				spa_feature_incr(dp->dp_spa, async_destroy, tx);
-				dp->dp_bptree_obj = bptree_alloc(mos, tx);
-				VERIFY(zap_add(mos,
-				    DMU_POOL_DIRECTORY_OBJECT,
-				    DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
-				    &dp->dp_bptree_obj, tx) == 0);
-			}
-
-			used = ds->ds_dir->dd_phys->dd_used_bytes;
-			comp = ds->ds_dir->dd_phys->dd_compressed_bytes;
-			uncomp = ds->ds_dir->dd_phys->dd_uncompressed_bytes;
-
-			ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) ||
-			    ds->ds_phys->ds_unique_bytes == used);
-
-			bptree_add(mos, dp->dp_bptree_obj,
-			    &ds->ds_phys->ds_bp, ds->ds_phys->ds_prev_snap_txg,
-			    used, comp, uncomp, tx);
-			dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD,
-			    -used, -comp, -uncomp, tx);
-			dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
-			    used, comp, uncomp, tx);
-		}
-
-		if (ds->ds_prev != NULL) {
-			if (spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
-				VERIFY3U(0, ==, zap_remove_int(mos,
-				    ds->ds_prev->ds_dir->dd_phys->dd_clones,
-				    ds->ds_object, tx));
-			}
-			dsl_dataset_rele(ds->ds_prev, ds);
-			ds->ds_prev = ds_prev = NULL;
-		}
-	}
-
-	/*
-	 * This must be done after the dsl_traverse(), because it will
-	 * re-open the objset.
-	 */
-	if (ds->ds_objset) {
-		dmu_objset_evict(ds->ds_objset);
-		ds->ds_objset = NULL;
-	}
-
-	if (ds->ds_dir->dd_phys->dd_head_dataset_obj == ds->ds_object) {
-		/* Erase the link in the dir */
-		dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
-		ds->ds_dir->dd_phys->dd_head_dataset_obj = 0;
-		ASSERT(ds->ds_phys->ds_snapnames_zapobj != 0);
-		err = zap_destroy(mos, ds->ds_phys->ds_snapnames_zapobj, tx);
-		ASSERT(err == 0);
-	} else {
-		/* remove from snapshot namespace */
-		dsl_dataset_t *ds_head;
-		ASSERT(ds->ds_phys->ds_snapnames_zapobj == 0);
-		VERIFY(0 == dsl_dataset_hold_obj(dp,
-		    ds->ds_dir->dd_phys->dd_head_dataset_obj, FTAG, &ds_head));
-		VERIFY(0 == dsl_dataset_get_snapname(ds));
-#ifdef ZFS_DEBUG
-		{
-			uint64_t val;
-
-			err = dsl_dataset_snap_lookup(ds_head,
-			    ds->ds_snapname, &val);
-			ASSERT0(err);
-			ASSERT3U(val, ==, obj);
-		}
-#endif
-		err = dsl_dataset_snap_remove(ds_head, ds->ds_snapname, tx);
-		ASSERT(err == 0);
-		dsl_dataset_rele(ds_head, FTAG);
-	}
+	ASSERT(ds->ds_objset != NULL);
 
-	if (ds_prev && ds->ds_prev != ds_prev)
-		dsl_dataset_rele(ds_prev, FTAG);
+	if (ds->ds_phys->ds_next_snap_obj != 0)
+		panic("dirtying snapshot!");
 
-	spa_prop_clear_bootfs(dp->dp_spa, ds->ds_object, tx);
+	dp = ds->ds_dir->dd_pool;
 
-	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 (txg_list_add(&dp->dp_dirty_datasets, ds, tx->tx_txg)) {
+		/* up the hold count until we can be written out */
+		dmu_buf_add_ref(ds->ds_dbuf, ds);
 	}
-	if (ds->ds_phys->ds_props_obj != 0)
-		VERIFY(0 == zap_destroy(mos, ds->ds_phys->ds_props_obj, tx));
-	if (ds->ds_phys->ds_userrefs_obj != 0)
-		VERIFY(0 == zap_destroy(mos, ds->ds_phys->ds_userrefs_obj, tx));
-	dsl_dir_close(ds->ds_dir, ds);
-	ds->ds_dir = NULL;
-	dsl_dataset_drain_refs(ds, tag);
-	VERIFY(0 == dmu_object_free(mos, obj, tx));
-
-	if (dsda->rm_origin) {
-		/*
-		 * Remove the origin of the clone we just destroyed.
-		 */
-		struct dsl_ds_destroyarg ndsda = {0};
+}
 
-		ndsda.ds = dsda->rm_origin;
-		dsl_dataset_destroy_sync(&ndsda, tag, tx);
+boolean_t
+dsl_dataset_is_dirty(dsl_dataset_t *ds)
+{
+	for (int t = 0; t < TXG_SIZE; t++) {
+		if (txg_list_member(&ds->ds_dir->dd_pool->dp_dirty_datasets,
+		    ds, t))
+			return (B_TRUE);
 	}
+	return (B_FALSE);
 }
 
 static int
@@ -2059,13 +984,24 @@ dsl_dataset_snapshot_reserve_space(dsl_dataset_t *ds, dmu_tx_t *tx)
 	return (0);
 }
 
+typedef struct dsl_dataset_snapshot_arg {
+	nvlist_t *ddsa_snaps;
+	nvlist_t *ddsa_props;
+	nvlist_t *ddsa_errors;
+} dsl_dataset_snapshot_arg_t;
+
 int
-dsl_dataset_snapshot_check(dsl_dataset_t *ds, const char *snapname,
+dsl_dataset_snapshot_check_impl(dsl_dataset_t *ds, const char *snapname,
     dmu_tx_t *tx)
 {
-	int err;
+	int error;
 	uint64_t value;
 
+	ds->ds_trysnap_txg = tx->tx_txg;
+
+	if (!dmu_tx_is_syncing(tx))
+		return (0);
+
 	/*
 	 * We don't allow multiple snapshots of the same txg.  If there
 	 * is already one, try again.
@@ -2076,39 +1012,87 @@ dsl_dataset_snapshot_check(dsl_dataset_t *ds, const char *snapname,
 	/*
 	 * Check for conflicting snapshot name.
 	 */
-	err = dsl_dataset_snap_lookup(ds, snapname, &value);
-	if (err == 0)
+	error = dsl_dataset_snap_lookup(ds, snapname, &value);
+	if (error == 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);
+	if (error != ENOENT)
+		return (error);
 
-	err = dsl_dataset_snapshot_reserve_space(ds, tx);
-	if (err)
-		return (err);
+	error = dsl_dataset_snapshot_reserve_space(ds, tx);
+	if (error != 0)
+		return (error);
 
-	ds->ds_trysnap_txg = tx->tx_txg;
 	return (0);
 }
 
+static int
+dsl_dataset_snapshot_check(void *arg, dmu_tx_t *tx)
+{
+	dsl_dataset_snapshot_arg_t *ddsa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	nvpair_t *pair;
+	int rv = 0;
+
+	for (pair = nvlist_next_nvpair(ddsa->ddsa_snaps, NULL);
+	    pair != NULL; pair = nvlist_next_nvpair(ddsa->ddsa_snaps, pair)) {
+		int error = 0;
+		dsl_dataset_t *ds;
+		char *name, *atp;
+		char dsname[MAXNAMELEN];
+
+		name = nvpair_name(pair);
+		if (strlen(name) >= MAXNAMELEN)
+			error = ENAMETOOLONG;
+		if (error == 0) {
+			atp = strchr(name, '@');
+			if (atp == NULL)
+				error = EINVAL;
+			if (error == 0)
+				(void) strlcpy(dsname, name, atp - name + 1);
+		}
+		if (error == 0)
+			error = dsl_dataset_hold(dp, dsname, FTAG, &ds);
+		if (error == 0) {
+			error = dsl_dataset_snapshot_check_impl(ds,
+			    atp + 1, tx);
+			dsl_dataset_rele(ds, FTAG);
+		}
+
+		if (error != 0) {
+			if (ddsa->ddsa_errors != NULL) {
+				fnvlist_add_int32(ddsa->ddsa_errors,
+				    name, error);
+			}
+			rv = error;
+		}
+	}
+	return (rv);
+}
+
 void
-dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
+dsl_dataset_snapshot_sync_impl(dsl_dataset_t *ds, const char *snapname,
     dmu_tx_t *tx)
 {
+	static zil_header_t zero_zil;
+
 	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;
+	objset_t *os;
+
+	ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));
+
+	/*
+	 * If we are on an old pool, the zil must not be active, in which
+	 * case it will be zeroed.  Usually zil_suspend() accomplishes this.
+	 */
+	ASSERT(spa_version(dmu_tx_pool(tx)->dp_spa) >= SPA_VERSION_FAST_SNAP ||
+	    dmu_objset_from_ds(ds, &os) != 0 ||
+	    bcmp(&os->os_phys->os_zil_header, &zero_zil,
+	    sizeof (zero_zil)) == 0);
 
-	ASSERT(RW_WRITE_HELD(&dp->dp_config_rwlock));
 
 	/*
 	 * The origin's ds_creation_txg has to be < TXG_INITIAL
@@ -2120,7 +1104,7 @@ dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
 
 	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));
+	VERIFY0(dmu_bonus_hold(mos, dsobj, FTAG, &dbuf));
 	dmu_buf_will_dirty(dbuf, tx);
 	dsphys = dbuf->db_data;
 	bzero(dsphys, sizeof (dsl_dataset_phys_t));
@@ -2157,9 +1141,9 @@ dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
 			    ds->ds_prev->ds_phys->ds_creation_txg);
 			ds->ds_prev->ds_phys->ds_next_snap_obj = dsobj;
 		} else if (next_clones_obj != 0) {
-			remove_from_next_clones(ds->ds_prev,
+			dsl_dataset_remove_from_next_clones(ds->ds_prev,
 			    dsphys->ds_next_snap_obj, tx);
-			VERIFY3U(0, ==, zap_add_int(mos,
+			VERIFY0(zap_add_int(mos,
 			    next_clones_obj, dsobj, tx));
 		}
 	}
@@ -2178,9 +1162,6 @@ dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
 	}
 
 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
-	zfs_dbgmsg("taking snapshot %s@%s/%llu; newkey=%llu",
-	    ds->ds_dir->dd_myname, snapname, dsobj,
-	    ds->ds_phys->ds_prev_snap_txg);
 	ds->ds_phys->ds_deadlist_obj = dsl_deadlist_clone(&ds->ds_deadlist,
 	    UINT64_MAX, ds->ds_phys->ds_prev_snap_obj, tx);
 	dsl_deadlist_close(&ds->ds_deadlist);
@@ -2195,13 +1176,12 @@ dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
 	if (spa_version(dp->dp_spa) >= SPA_VERSION_UNIQUE_ACCURATE)
 		ds->ds_phys->ds_flags |= DS_FLAG_UNIQUE_ACCURATE;
 
-	err = zap_add(mos, ds->ds_phys->ds_snapnames_zapobj,
-	    snapname, 8, 1, &dsobj, tx);
-	ASSERT(err == 0);
+	VERIFY0(zap_add(mos, ds->ds_phys->ds_snapnames_zapobj,
+	    snapname, 8, 1, &dsobj, tx));
 
 	if (ds->ds_prev)
-		dsl_dataset_drop_ref(ds->ds_prev, ds);
-	VERIFY(0 == dsl_dataset_get_ref(dp,
+		dsl_dataset_rele(ds->ds_prev, ds);
+	VERIFY0(dsl_dataset_hold_obj(dp,
 	    ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));
 
 	dsl_scan_ds_snapshotted(ds, tx);
@@ -2211,6 +1191,198 @@ dsl_dataset_snapshot_sync(dsl_dataset_t *ds, const char *snapname,
 	spa_history_log_internal_ds(ds->ds_prev, "snapshot", tx, "");
 }
 
+static void
+dsl_dataset_snapshot_sync(void *arg, dmu_tx_t *tx)
+{
+	dsl_dataset_snapshot_arg_t *ddsa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	nvpair_t *pair;
+
+	for (pair = nvlist_next_nvpair(ddsa->ddsa_snaps, NULL);
+	    pair != NULL; pair = nvlist_next_nvpair(ddsa->ddsa_snaps, pair)) {
+		dsl_dataset_t *ds;
+		char *name, *atp;
+		char dsname[MAXNAMELEN];
+
+		name = nvpair_name(pair);
+		atp = strchr(name, '@');
+		(void) strlcpy(dsname, name, atp - name + 1);
+		VERIFY0(dsl_dataset_hold(dp, dsname, FTAG, &ds));
+
+		dsl_dataset_snapshot_sync_impl(ds, atp + 1, tx);
+		if (ddsa->ddsa_props != NULL) {
+			dsl_props_set_sync_impl(ds->ds_prev,
+			    ZPROP_SRC_LOCAL, ddsa->ddsa_props, tx);
+		}
+		dsl_dataset_rele(ds, FTAG);
+	}
+}
+
+/*
+ * The snapshots must all be in the same pool.
+ * All-or-nothing: if there are any failures, nothing will be modified.
+ */
+int
+dsl_dataset_snapshot(nvlist_t *snaps, nvlist_t *props, nvlist_t *errors)
+{
+	dsl_dataset_snapshot_arg_t ddsa;
+	nvpair_t *pair;
+	boolean_t needsuspend;
+	int error;
+	spa_t *spa;
+	char *firstname;
+	nvlist_t *suspended = NULL;
+
+	pair = nvlist_next_nvpair(snaps, NULL);
+	if (pair == NULL)
+		return (0);
+	firstname = nvpair_name(pair);
+
+	error = spa_open(firstname, &spa, FTAG);
+	if (error != 0)
+		return (error);
+	needsuspend = (spa_version(spa) < SPA_VERSION_FAST_SNAP);
+	spa_close(spa, FTAG);
+
+	if (needsuspend) {
+		suspended = fnvlist_alloc();
+		for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
+		    pair = nvlist_next_nvpair(snaps, pair)) {
+			char fsname[MAXNAMELEN];
+			char *snapname = nvpair_name(pair);
+			char *atp;
+			void *cookie;
+
+			atp = strchr(snapname, '@');
+			if (atp == NULL) {
+				error = EINVAL;
+				break;
+			}
+			(void) strlcpy(fsname, snapname, atp - snapname + 1);
+
+			error = zil_suspend(fsname, &cookie);
+			if (error != 0)
+				break;
+			fnvlist_add_uint64(suspended, fsname,
+			    (uintptr_t)cookie);
+		}
+	}
+
+	ddsa.ddsa_snaps = snaps;
+	ddsa.ddsa_props = props;
+	ddsa.ddsa_errors = errors;
+
+	if (error == 0) {
+		error = dsl_sync_task(firstname, dsl_dataset_snapshot_check,
+		    dsl_dataset_snapshot_sync, &ddsa,
+		    fnvlist_num_pairs(snaps) * 3);
+	}
+
+	if (suspended != NULL) {
+		for (pair = nvlist_next_nvpair(suspended, NULL); pair != NULL;
+		    pair = nvlist_next_nvpair(suspended, pair)) {
+			zil_resume((void *)(uintptr_t)
+			    fnvpair_value_uint64(pair));
+		}
+		fnvlist_free(suspended);
+	}
+
+	return (error);
+}
+
+typedef struct dsl_dataset_snapshot_tmp_arg {
+	const char *ddsta_fsname;
+	const char *ddsta_snapname;
+	minor_t ddsta_cleanup_minor;
+	const char *ddsta_htag;
+} dsl_dataset_snapshot_tmp_arg_t;
+
+static int
+dsl_dataset_snapshot_tmp_check(void *arg, dmu_tx_t *tx)
+{
+	dsl_dataset_snapshot_tmp_arg_t *ddsta = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+	int error;
+
+	error = dsl_dataset_hold(dp, ddsta->ddsta_fsname, FTAG, &ds);
+	if (error != 0)
+		return (error);
+
+	error = dsl_dataset_snapshot_check_impl(ds, ddsta->ddsta_snapname, tx);
+	if (error != 0) {
+		dsl_dataset_rele(ds, FTAG);
+		return (error);
+	}
+
+	if (spa_version(dp->dp_spa) < SPA_VERSION_USERREFS) {
+		dsl_dataset_rele(ds, FTAG);
+		return (ENOTSUP);
+	}
+	error = dsl_dataset_user_hold_check_one(NULL, ddsta->ddsta_htag,
+	    B_TRUE, tx);
+	if (error != 0) {
+		dsl_dataset_rele(ds, FTAG);
+		return (error);
+	}
+
+	dsl_dataset_rele(ds, FTAG);
+	return (0);
+}
+
+static void
+dsl_dataset_snapshot_tmp_sync(void *arg, dmu_tx_t *tx)
+{
+	dsl_dataset_snapshot_tmp_arg_t *ddsta = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+
+	VERIFY0(dsl_dataset_hold(dp, ddsta->ddsta_fsname, FTAG, &ds));
+
+	dsl_dataset_snapshot_sync_impl(ds, ddsta->ddsta_snapname, tx);
+	dsl_dataset_user_hold_sync_one(ds->ds_prev, ddsta->ddsta_htag,
+	    ddsta->ddsta_cleanup_minor, gethrestime_sec(), tx);
+	dsl_destroy_snapshot_sync_impl(ds->ds_prev, B_TRUE, tx);
+
+	dsl_dataset_rele(ds, FTAG);
+}
+
+int
+dsl_dataset_snapshot_tmp(const char *fsname, const char *snapname,
+    minor_t cleanup_minor, const char *htag)
+{
+	dsl_dataset_snapshot_tmp_arg_t ddsta;
+	int error;
+	spa_t *spa;
+	boolean_t needsuspend;
+	void *cookie;
+
+	ddsta.ddsta_fsname = fsname;
+	ddsta.ddsta_snapname = snapname;
+	ddsta.ddsta_cleanup_minor = cleanup_minor;
+	ddsta.ddsta_htag = htag;
+
+	error = spa_open(fsname, &spa, FTAG);
+	if (error != 0)
+		return (error);
+	needsuspend = (spa_version(spa) < SPA_VERSION_FAST_SNAP);
+	spa_close(spa, FTAG);
+
+	if (needsuspend) {
+		error = zil_suspend(fsname, &cookie);
+		if (error != 0)
+			return (error);
+	}
+
+	error = dsl_sync_task(fsname, dsl_dataset_snapshot_tmp_check,
+	    dsl_dataset_snapshot_tmp_sync, &ddsta, 3);
+
+	if (needsuspend)
+		zil_resume(cookie);
+	return (error);
+}
+
+
 void
 dsl_dataset_sync(dsl_dataset_t *ds, zio_t *zio, dmu_tx_t *tx)
 {
@@ -2235,65 +1407,49 @@ get_clones_stat(dsl_dataset_t *ds, nvlist_t *nv)
 	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
 	zap_cursor_t zc;
 	zap_attribute_t za;
-	nvlist_t *propval;
-	nvlist_t *val;
+	nvlist_t *propval = fnvlist_alloc();
+	nvlist_t *val = fnvlist_alloc();
 
-	rw_enter(&ds->ds_dir->dd_pool->dp_config_rwlock, RW_READER);
-	VERIFY(nvlist_alloc(&propval, NV_UNIQUE_NAME, KM_SLEEP) == 0);
-	VERIFY(nvlist_alloc(&val, NV_UNIQUE_NAME, KM_SLEEP) == 0);
+	ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool));
 
 	/*
-	 * There may me missing entries in ds_next_clones_obj
+	 * There may be missing entries in ds_next_clones_obj
 	 * due to a bug in a previous version of the code.
 	 * Only trust it if it has the right number of entries.
 	 */
 	if (ds->ds_phys->ds_next_clones_obj != 0) {
-		ASSERT3U(0, ==, zap_count(mos, ds->ds_phys->ds_next_clones_obj,
+		ASSERT0(zap_count(mos, ds->ds_phys->ds_next_clones_obj,
 		    &count));
 	}
-	if (count != ds->ds_phys->ds_num_children - 1) {
+	if (count != ds->ds_phys->ds_num_children - 1)
 		goto fail;
-	}
 	for (zap_cursor_init(&zc, mos, ds->ds_phys->ds_next_clones_obj);
 	    zap_cursor_retrieve(&zc, &za) == 0;
 	    zap_cursor_advance(&zc)) {
 		dsl_dataset_t *clone;
 		char buf[ZFS_MAXNAMELEN];
-		/*
-		 * Even though we hold the dp_config_rwlock, the dataset
-		 * may fail to open, returning ENOENT.  If there is a
-		 * thread concurrently attempting to destroy this
-		 * dataset, it will have the ds_rwlock held for
-		 * RW_WRITER.  Our call to dsl_dataset_hold_obj() ->
-		 * dsl_dataset_hold_ref() will fail its
-		 * rw_tryenter(&ds->ds_rwlock, RW_READER), drop the
-		 * dp_config_rwlock, and wait for the destroy progress
-		 * and signal ds_exclusive_cv.  If the destroy was
-		 * successful, we will see that
-		 * DSL_DATASET_IS_DESTROYED(), and return ENOENT.
-		 */
-		if (dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
-		    za.za_first_integer, FTAG, &clone) != 0)
-			continue;
+		VERIFY0(dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
+		    za.za_first_integer, FTAG, &clone));
 		dsl_dir_name(clone->ds_dir, buf);
-		VERIFY(nvlist_add_boolean(val, buf) == 0);
+		fnvlist_add_boolean(val, buf);
 		dsl_dataset_rele(clone, FTAG);
 	}
 	zap_cursor_fini(&zc);
-	VERIFY(nvlist_add_nvlist(propval, ZPROP_VALUE, val) == 0);
-	VERIFY(nvlist_add_nvlist(nv, zfs_prop_to_name(ZFS_PROP_CLONES),
-	    propval) == 0);
+	fnvlist_add_nvlist(propval, ZPROP_VALUE, val);
+	fnvlist_add_nvlist(nv, zfs_prop_to_name(ZFS_PROP_CLONES), propval);
 fail:
 	nvlist_free(val);
 	nvlist_free(propval);
-	rw_exit(&ds->ds_dir->dd_pool->dp_config_rwlock);
 }
 
 void
 dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 {
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
 	uint64_t refd, avail, uobjs, aobjs, ratio;
 
+	ASSERT(dsl_pool_config_held(dp));
+
 	ratio = ds->ds_phys->ds_compressed_bytes == 0 ? 100 :
 	    (ds->ds_phys->ds_uncompressed_bytes * 100 /
 	    ds->ds_phys->ds_compressed_bytes);
@@ -2339,10 +1495,8 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 		dsl_pool_t *dp = ds->ds_dir->dd_pool;
 		dsl_dataset_t *prev;
 
-		rw_enter(&dp->dp_config_rwlock, RW_READER);
 		int err = dsl_dataset_hold_obj(dp,
 		    ds->ds_phys->ds_prev_snap_obj, FTAG, &prev);
-		rw_exit(&dp->dp_config_rwlock);
 		if (err == 0) {
 			err = dsl_dataset_space_written(prev, ds, &written,
 			    &comp, &uncomp);
@@ -2358,6 +1512,9 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 void
 dsl_dataset_fast_stat(dsl_dataset_t *ds, dmu_objset_stats_t *stat)
 {
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	ASSERT(dsl_pool_config_held(dp));
+
 	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;
@@ -2369,16 +1526,14 @@ dsl_dataset_fast_stat(dsl_dataset_t *ds, dmu_objset_stats_t *stat)
 		stat->dds_is_snapshot = B_FALSE;
 		stat->dds_num_clones = 0;
 
-		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,
+			VERIFY0(dsl_dataset_hold_obj(dp,
 			    ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &ods));
 			dsl_dataset_name(ods, stat->dds_origin);
-			dsl_dataset_drop_ref(ods, FTAG);
+			dsl_dataset_rele(ods, FTAG);
 		}
-		rw_exit(&ds->ds_dir->dd_pool->dp_config_rwlock);
 	}
 }
 
@@ -2416,8 +1571,7 @@ 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));
+	ASSERT(dsl_pool_config_held(dp));
 	if (ds->ds_prev == NULL)
 		return (B_FALSE);
 	if (ds->ds_phys->ds_bp.blk_birth >
@@ -2439,249 +1593,245 @@ dsl_dataset_modified_since_lastsnap(dsl_dataset_t *ds)
 	return (B_FALSE);
 }
 
+typedef struct dsl_dataset_rename_snapshot_arg {
+	const char *ddrsa_fsname;
+	const char *ddrsa_oldsnapname;
+	const char *ddrsa_newsnapname;
+	boolean_t ddrsa_recursive;
+	dmu_tx_t *ddrsa_tx;
+} dsl_dataset_rename_snapshot_arg_t;
+
 /* ARGSUSED */
 static int
-dsl_dataset_snapshot_rename_check(void *arg1, void *arg2, dmu_tx_t *tx)
+dsl_dataset_rename_snapshot_check_impl(dsl_pool_t *dp,
+    dsl_dataset_t *hds, void *arg)
 {
-	dsl_dataset_t *ds = arg1;
-	char *newsnapname = arg2;
-	dsl_dir_t *dd = ds->ds_dir;
-	dsl_dataset_t *hds;
+	dsl_dataset_rename_snapshot_arg_t *ddrsa = arg;
+	int error;
 	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);
+	error = dsl_dataset_snap_lookup(hds, ddrsa->ddrsa_oldsnapname, &val);
+	if (error != 0) {
+		/* ignore nonexistent snapshots */
+		return (error == ENOENT ? 0 : error);
+	}
 
-	if (err == 0)
-		err = EEXIST;
-	else if (err == ENOENT)
-		err = 0;
+	/* new name should not exist */
+	error = dsl_dataset_snap_lookup(hds, ddrsa->ddrsa_newsnapname, &val);
+	if (error == 0)
+		error = EEXIST;
+	else if (error == ENOENT)
+		error = 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;
+	if (dsl_dir_namelen(hds->ds_dir) + 1 +
+	    strlen(ddrsa->ddrsa_newsnapname) >= MAXNAMELEN)
+		error = ENAMETOOLONG;
 
-	return (err);
+	return (error);
 }
 
-static void
-dsl_dataset_snapshot_rename_sync(void *arg1, void *arg2, dmu_tx_t *tx)
+static int
+dsl_dataset_rename_snapshot_check(void *arg, dmu_tx_t *tx)
 {
-	char oldname[MAXPATHLEN], newname[MAXPATHLEN];
-	dsl_dataset_t *ds = arg1;
-	const char *newsnapname = arg2;
-	dsl_dir_t *dd = ds->ds_dir;
-	objset_t *mos = dd->dd_pool->dp_meta_objset;
+	dsl_dataset_rename_snapshot_arg_t *ddrsa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
 	dsl_dataset_t *hds;
-	int err;
+	int error;
 
-	ASSERT(ds->ds_phys->ds_next_snap_obj != 0);
+	error = dsl_dataset_hold(dp, ddrsa->ddrsa_fsname, FTAG, &hds);
+	if (error != 0)
+		return (error);
 
-	VERIFY(0 == dsl_dataset_hold_obj(dd->dd_pool,
-	    dd->dd_phys->dd_head_dataset_obj, FTAG, &hds));
+	if (ddrsa->ddrsa_recursive) {
+		error = dmu_objset_find_dp(dp, hds->ds_dir->dd_object,
+		    dsl_dataset_rename_snapshot_check_impl, ddrsa,
+		    DS_FIND_CHILDREN);
+	} else {
+		error = dsl_dataset_rename_snapshot_check_impl(dp, hds, ddrsa);
+	}
+	dsl_dataset_rele(hds, FTAG);
+	return (error);
+}
 
-	VERIFY(0 == dsl_dataset_get_snapname(ds));
-	err = dsl_dataset_snap_remove(hds, ds->ds_snapname, tx);
-	ASSERT0(err);
-	dsl_dataset_name(ds, oldname);
+static int
+dsl_dataset_rename_snapshot_sync_impl(dsl_pool_t *dp,
+    dsl_dataset_t *hds, void *arg)
+{
+#ifdef __FreeBSD__
+#ifdef _KERNEL
+	char *oldname, *newname;
+#endif
+#endif
+	dsl_dataset_rename_snapshot_arg_t *ddrsa = arg;
+	dsl_dataset_t *ds;
+	uint64_t val;
+	dmu_tx_t *tx = ddrsa->ddrsa_tx;
+	int error;
+
+	error = dsl_dataset_snap_lookup(hds, ddrsa->ddrsa_oldsnapname, &val);
+	ASSERT(error == 0 || error == ENOENT);
+	if (error == ENOENT) {
+		/* ignore nonexistent snapshots */
+		return (0);
+	}
+
+	VERIFY0(dsl_dataset_hold_obj(dp, val, FTAG, &ds));
+
+	/* log before we change the name */
+	spa_history_log_internal_ds(ds, "rename", tx,
+	    "-> @%s", ddrsa->ddrsa_newsnapname);
+
+	VERIFY0(dsl_dataset_snap_remove(hds, ddrsa->ddrsa_oldsnapname, tx));
 	mutex_enter(&ds->ds_lock);
-	(void) strcpy(ds->ds_snapname, newsnapname);
+	(void) strcpy(ds->ds_snapname, ddrsa->ddrsa_newsnapname);
 	mutex_exit(&ds->ds_lock);
-	err = zap_add(mos, hds->ds_phys->ds_snapnames_zapobj,
-	    ds->ds_snapname, 8, 1, &ds->ds_object, tx);
-	ASSERT0(err);
-	dsl_dataset_name(ds, newname);
+	VERIFY0(zap_add(dp->dp_meta_objset, hds->ds_phys->ds_snapnames_zapobj,
+	    ds->ds_snapname, 8, 1, &ds->ds_object, tx));
+
+#ifdef __FreeBSD__
 #ifdef _KERNEL
+	oldname = kmem_alloc(MAXPATHLEN, KM_SLEEP);
+	newname = kmem_alloc(MAXPATHLEN, KM_SLEEP);
+	snprintf(oldname, MAXPATHLEN, "%s@%s", ddrsa->ddrsa_fsname,
+	    ddrsa->ddrsa_oldsnapname);
+	snprintf(newname, MAXPATHLEN, "%s@%s", ddrsa->ddrsa_fsname,
+	    ddrsa->ddrsa_newsnapname);
+	zfsvfs_update_fromname(oldname, newname);
 	zvol_rename_minors(oldname, newname);
+	kmem_free(newname, MAXPATHLEN);
+	kmem_free(oldname, MAXPATHLEN);
+#endif
 #endif
+	dsl_dataset_rele(ds, FTAG);
 
-	spa_history_log_internal_ds(ds, "rename", tx,
-	    "-> @%s", newsnapname);
-	dsl_dataset_rele(hds, FTAG);
+	return (0);
 }
 
-struct renamesnaparg {
-	dsl_sync_task_group_t *dstg;
-	char failed[MAXPATHLEN];
-	char *oldsnap;
-	char *newsnap;
-	int error;
-};
-
-static int
-dsl_snapshot_rename_one(const char *name, void *arg)
+static void
+dsl_dataset_rename_snapshot_sync(void *arg, dmu_tx_t *tx)
 {
-	struct renamesnaparg *ra = arg;
-	dsl_dataset_t *ds = NULL;
-	char *snapname;
-	int err;
-
-	snapname = kmem_asprintf("%s@%s", name, ra->oldsnap);
-	(void) strlcpy(ra->failed, snapname, sizeof (ra->failed));
+	dsl_dataset_rename_snapshot_arg_t *ddrsa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *hds;
 
-	/*
-	 * For recursive snapshot renames the parent won't be changing
-	 * so we just pass name for both the to/from argument.
-	 */
-	err = zfs_secpolicy_rename_perms(snapname, snapname, CRED());
-	if (err != 0) {
-		strfree(snapname);
-		return (err == ENOENT ? 0 : err);
+	VERIFY0(dsl_dataset_hold(dp, ddrsa->ddrsa_fsname, FTAG, &hds));
+	ddrsa->ddrsa_tx = tx;
+	if (ddrsa->ddrsa_recursive) {
+		VERIFY0(dmu_objset_find_dp(dp, hds->ds_dir->dd_object,
+		    dsl_dataset_rename_snapshot_sync_impl, ddrsa,
+		    DS_FIND_CHILDREN));
+	} else {
+		VERIFY0(dsl_dataset_rename_snapshot_sync_impl(dp, hds, ddrsa));
 	}
+	dsl_dataset_rele(hds, FTAG);
+}
 
-#ifdef _KERNEL
-	/*
-	 * For all filesystems undergoing rename, we'll need to unmount it.
-	 */
-	(void) zfs_unmount_snap(snapname, NULL);
-#endif
-	err = dsl_dataset_hold(snapname, ra->dstg, &ds);
-	strfree(snapname);
-	if (err != 0)
-		return (err == ENOENT ? 0 : err);
-
-	dsl_sync_task_create(ra->dstg, dsl_dataset_snapshot_rename_check,
-	    dsl_dataset_snapshot_rename_sync, ds, ra->newsnap, 0);
+int
+dsl_dataset_rename_snapshot(const char *fsname,
+    const char *oldsnapname, const char *newsnapname, boolean_t recursive)
+{
+	dsl_dataset_rename_snapshot_arg_t ddrsa;
 
-	/* First successful rename clears the error. */
-	ra->error = 0;
+	ddrsa.ddrsa_fsname = fsname;
+	ddrsa.ddrsa_oldsnapname = oldsnapname;
+	ddrsa.ddrsa_newsnapname = newsnapname;
+	ddrsa.ddrsa_recursive = recursive;
 
-	return (0);
+	return (dsl_sync_task(fsname, dsl_dataset_rename_snapshot_check,
+	    dsl_dataset_rename_snapshot_sync, &ddrsa, 1));
 }
 
 static int
-dsl_recursive_rename(char *oldname, const char *newname)
+dsl_dataset_rollback_check(void *arg, dmu_tx_t *tx)
 {
-	int err;
-	struct renamesnaparg *ra;
-	dsl_sync_task_t *dst;
-	spa_t *spa;
-	char *cp, *fsname = spa_strdup(oldname);
-	int len = strlen(oldname) + 1;
+	const char *fsname = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+	int64_t unused_refres_delta;
+	int error;
 
-	/* truncate the snapshot name to get the fsname */
-	cp = strchr(fsname, '@');
-	*cp = '\0';
+	error = dsl_dataset_hold(dp, fsname, FTAG, &ds);
+	if (error != 0)
+		return (error);
 
-	err = spa_open(fsname, &spa, FTAG);
-	if (err) {
-		kmem_free(fsname, len);
-		return (err);
+	/* must not be a snapshot */
+	if (dsl_dataset_is_snapshot(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EINVAL);
 	}
-	ra = kmem_alloc(sizeof (struct renamesnaparg), KM_SLEEP);
-	ra->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
 
-	ra->oldsnap = strchr(oldname, '@') + 1;
-	ra->newsnap = strchr(newname, '@') + 1;
-	*ra->failed = '\0';
-	ra->error = ENOENT;
-
-	err = dmu_objset_find(fsname, dsl_snapshot_rename_one, ra,
-	    DS_FIND_CHILDREN);
-	kmem_free(fsname, len);
-	if (err == 0)
-		err = ra->error;
-
-	if (err == 0)
-		err = dsl_sync_task_group_wait(ra->dstg);
-
-	for (dst = list_head(&ra->dstg->dstg_tasks); dst;
-	    dst = list_next(&ra->dstg->dstg_tasks, dst)) {
-		dsl_dataset_t *ds = dst->dst_arg1;
-		if (dst->dst_err) {
-			dsl_dir_name(ds->ds_dir, ra->failed);
-			(void) strlcat(ra->failed, "@", sizeof (ra->failed));
-			(void) strlcat(ra->failed, ra->newsnap,
-			    sizeof (ra->failed));
-		}
-		dsl_dataset_rele(ds, ra->dstg);
+	/* must have a most recent snapshot */
+	if (ds->ds_phys->ds_prev_snap_txg < TXG_INITIAL) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EINVAL);
 	}
 
-	if (err)
-		(void) strlcpy(oldname, ra->failed, sizeof (ra->failed));
+	if (dsl_dataset_long_held(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EBUSY);
+	}
 
-	dsl_sync_task_group_destroy(ra->dstg);
-	kmem_free(ra, sizeof (struct renamesnaparg));
-	spa_close(spa, FTAG);
-	return (err);
-}
+	/*
+	 * Check if the snap we are rolling back to uses more than
+	 * the refquota.
+	 */
+	if (ds->ds_quota != 0 &&
+	    ds->ds_prev->ds_phys->ds_referenced_bytes > ds->ds_quota) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EDQUOT);
+	}
 
-static int
-dsl_valid_rename(const char *oldname, void *arg)
-{
-	int delta = *(int *)arg;
+	/*
+	 * When we do the clone swap, we will temporarily use more space
+	 * due to the refreservation (the head will no longer have any
+	 * unique space, so the entire amount of the refreservation will need
+	 * to be free).  We will immediately destroy the clone, freeing
+	 * this space, but the freeing happens over many txg's.
+	 */
+	unused_refres_delta = (int64_t)MIN(ds->ds_reserved,
+	    ds->ds_phys->ds_unique_bytes);
 
-	if (strlen(oldname) + delta >= MAXNAMELEN)
-		return (ENAMETOOLONG);
+	if (unused_refres_delta > 0 &&
+	    unused_refres_delta >
+	    dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (ENOSPC);
+	}
 
+	dsl_dataset_rele(ds, FTAG);
 	return (0);
 }
 
-#pragma weak dmu_objset_rename = dsl_dataset_rename
-int
-dsl_dataset_rename(char *oldname, const char *newname, int flags)
+static void
+dsl_dataset_rollback_sync(void *arg, dmu_tx_t *tx)
 {
-	dsl_dir_t *dd;
-	dsl_dataset_t *ds;
-	const char *tail;
-	int err;
+	const char *fsname = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds, *clone;
+	uint64_t cloneobj;
 
-	err = dsl_dir_open(oldname, FTAG, &dd, &tail);
-	if (err)
-		return (err);
+	VERIFY0(dsl_dataset_hold(dp, fsname, FTAG, &ds));
 
-	if (tail == NULL) {
-		int delta = strlen(newname) - strlen(oldname);
+	cloneobj = dsl_dataset_create_sync(ds->ds_dir, "%rollback",
+	    ds->ds_prev, DS_CREATE_FLAG_NODIRTY, kcred, tx);
 
-		/* 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);
+	VERIFY0(dsl_dataset_hold_obj(dp, cloneobj, FTAG, &clone));
 
-		if (err == 0)
-			err = dsl_dir_rename(dd, newname, flags);
-		dsl_dir_close(dd, FTAG);
-		return (err);
-	}
-
-	if (tail[0] != '@') {
-		/* the name ended in a nonexistent component */
-		dsl_dir_close(dd, FTAG);
-		return (ENOENT);
-	}
-
-	dsl_dir_close(dd, FTAG);
-
-	/* new name must be snapshot in same filesystem */
-	tail = strchr(newname, '@');
-	if (tail == NULL)
-		return (EINVAL);
-	tail++;
-	if (strncmp(oldname, newname, tail - newname) != 0)
-		return (EXDEV);
-
-	if (flags & ZFS_RENAME_RECURSIVE) {
-		err = dsl_recursive_rename(oldname, newname);
-	} else {
-		err = dsl_dataset_hold(oldname, FTAG, &ds);
-		if (err)
-			return (err);
+	dsl_dataset_clone_swap_sync_impl(clone, ds, tx);
+	dsl_dataset_zero_zil(ds, tx);
 
-		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_destroy_head_sync_impl(clone, tx);
 
-		dsl_dataset_rele(ds, FTAG);
-	}
+	dsl_dataset_rele(clone, FTAG);
+	dsl_dataset_rele(ds, FTAG);
+}
 
-	return (err);
+int
+dsl_dataset_rollback(const char *fsname)
+{
+	return (dsl_sync_task(fsname, dsl_dataset_rollback_check,
+	    dsl_dataset_rollback_sync, (void *)fsname, 1));
 }
 
 struct promotenode {
@@ -2689,49 +1839,66 @@ struct promotenode {
 	dsl_dataset_t *ds;
 };
 
-struct promotearg {
+typedef struct dsl_dataset_promote_arg {
+	const char *ddpa_clonename;
+	dsl_dataset_t *ddpa_clone;
 	list_t shared_snaps, origin_snaps, clone_snaps;
-	dsl_dataset_t *origin_origin;
+	dsl_dataset_t *origin_origin; /* origin of the origin */
 	uint64_t used, comp, uncomp, unique, cloneusedsnap, originusedsnap;
 	char *err_ds;
-};
+} dsl_dataset_promote_arg_t;
 
 static int snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep);
-static boolean_t snaplist_unstable(list_t *l);
+static int promote_hold(dsl_dataset_promote_arg_t *ddpa, dsl_pool_t *dp,
+    void *tag);
+static void promote_rele(dsl_dataset_promote_arg_t *ddpa, void *tag);
 
 static int
-dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
+dsl_dataset_promote_check(void *arg, 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_promote_arg_t *ddpa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *hds;
+	struct promotenode *snap;
+	dsl_dataset_t *origin_ds;
 	int err;
 	uint64_t unused;
 
-	/* Check that it is a real clone */
-	if (!dsl_dir_is_clone(hds->ds_dir))
-		return (EINVAL);
+	err = promote_hold(ddpa, dp, FTAG);
+	if (err != 0)
+		return (err);
 
-	/* Since this is so expensive, don't do the preliminary check */
-	if (!dmu_tx_is_syncing(tx))
-		return (0);
+	hds = ddpa->ddpa_clone;
 
-	if (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE)
+	if (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE) {
+		promote_rele(ddpa, FTAG);
 		return (EXDEV);
+	}
+
+	/*
+	 * Compute and check the amount of space to transfer.  Since this is
+	 * so expensive, don't do the preliminary check.
+	 */
+	if (!dmu_tx_is_syncing(tx)) {
+		promote_rele(ddpa, FTAG);
+		return (0);
+	}
+
+	snap = list_head(&ddpa->shared_snaps);
+	origin_ds = snap->ds;
 
 	/* compute origin's new unique space */
-	snap = list_tail(&pa->clone_snaps);
+	snap = list_tail(&ddpa->clone_snaps);
 	ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
 	dsl_deadlist_space_range(&snap->ds->ds_deadlist,
 	    origin_ds->ds_phys->ds_prev_snap_txg, UINT64_MAX,
-	    &pa->unique, &unused, &unused);
+	    &ddpa->unique, &unused, &unused);
 
 	/*
 	 * Walk the snapshots that we are moving
 	 *
 	 * Compute space to transfer.  Consider the incremental changes
-	 * to used for each snapshot:
+	 * to used by 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)
@@ -2742,18 +1909,28 @@ dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
 	 * Note however, if we stop before we reach the ORIGIN we get:
 	 * uN + kN + kN-1 + ... + kM - uM-1
 	 */
-	pa->used = origin_ds->ds_phys->ds_referenced_bytes;
-	pa->comp = origin_ds->ds_phys->ds_compressed_bytes;
-	pa->uncomp = origin_ds->ds_phys->ds_uncompressed_bytes;
-	for (snap = list_head(&pa->shared_snaps); snap;
-	    snap = list_next(&pa->shared_snaps, snap)) {
+	ddpa->used = origin_ds->ds_phys->ds_referenced_bytes;
+	ddpa->comp = origin_ds->ds_phys->ds_compressed_bytes;
+	ddpa->uncomp = origin_ds->ds_phys->ds_uncompressed_bytes;
+	for (snap = list_head(&ddpa->shared_snaps); snap;
+	    snap = list_next(&ddpa->shared_snaps, snap)) {
 		uint64_t val, dlused, dlcomp, dluncomp;
 		dsl_dataset_t *ds = snap->ds;
 
+		/*
+		 * If there are long holds, we won't be able to evict
+		 * the objset.
+		 */
+		if (dsl_dataset_long_held(ds)) {
+			err = EBUSY;
+			goto out;
+		}
+
 		/* Check that the snapshot name does not conflict */
-		VERIFY(0 == dsl_dataset_get_snapname(ds));
+		VERIFY0(dsl_dataset_get_snapname(ds));
 		err = dsl_dataset_snap_lookup(hds, ds->ds_snapname, &val);
 		if (err == 0) {
+			(void) strcpy(ddpa->err_ds, snap->ds->ds_snapname);
 			err = EEXIST;
 			goto out;
 		}
@@ -2766,26 +1943,27 @@ dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
 
 		dsl_deadlist_space(&ds->ds_deadlist,
 		    &dlused, &dlcomp, &dluncomp);
-		pa->used += dlused;
-		pa->comp += dlcomp;
-		pa->uncomp += dluncomp;
+		ddpa->used += dlused;
+		ddpa->comp += dlcomp;
+		ddpa->uncomp += dluncomp;
 	}
 
 	/*
 	 * If we are a clone of a clone then we never reached ORIGIN,
 	 * so we need to subtract out the clone origin's used space.
 	 */
-	if (pa->origin_origin) {
-		pa->used -= pa->origin_origin->ds_phys->ds_referenced_bytes;
-		pa->comp -= pa->origin_origin->ds_phys->ds_compressed_bytes;
-		pa->uncomp -= pa->origin_origin->ds_phys->ds_uncompressed_bytes;
+	if (ddpa->origin_origin) {
+		ddpa->used -= ddpa->origin_origin->ds_phys->ds_referenced_bytes;
+		ddpa->comp -= ddpa->origin_origin->ds_phys->ds_compressed_bytes;
+		ddpa->uncomp -=
+		    ddpa->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);
+	    ddpa->used);
+	if (err != 0)
+		goto out;
 
 	/*
 	 * Compute the amounts of space that will be used by snapshots
@@ -2803,68 +1981,75 @@ dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
 		 * calls will be fast because they do not have to
 		 * iterate over all bps.
 		 */
-		snap = list_head(&pa->origin_snaps);
-		err = snaplist_space(&pa->shared_snaps,
-		    snap->ds->ds_dir->dd_origin_txg, &pa->cloneusedsnap);
-		if (err)
-			return (err);
+		snap = list_head(&ddpa->origin_snaps);
+		err = snaplist_space(&ddpa->shared_snaps,
+		    snap->ds->ds_dir->dd_origin_txg, &ddpa->cloneusedsnap);
+		if (err != 0)
+			goto out;
 
-		err = snaplist_space(&pa->clone_snaps,
+		err = snaplist_space(&ddpa->clone_snaps,
 		    snap->ds->ds_dir->dd_origin_txg, &space);
-		if (err)
-			return (err);
-		pa->cloneusedsnap += space;
+		if (err != 0)
+			goto out;
+		ddpa->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);
+		err = snaplist_space(&ddpa->origin_snaps,
+		    origin_ds->ds_phys->ds_creation_txg, &ddpa->originusedsnap);
+		if (err != 0)
+			goto out;
 	}
 
-	return (0);
 out:
-	pa->err_ds =  snap->ds->ds_snapname;
+	promote_rele(ddpa, FTAG);
 	return (err);
 }
 
 static void
-dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *tx)
+dsl_dataset_promote_sync(void *arg, 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_promote_arg_t *ddpa = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *hds;
+	struct promotenode *snap;
+	dsl_dataset_t *origin_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 *dd;
 	dsl_dir_t *odd = NULL;
 	uint64_t oldnext_obj;
 	int64_t delta;
 
-	ASSERT(0 == (hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE));
+	VERIFY0(promote_hold(ddpa, dp, FTAG));
+	hds = ddpa->ddpa_clone;
 
-	snap = list_head(&pa->origin_snaps);
+	ASSERT0(hds->ds_phys->ds_flags & DS_FLAG_NOPROMOTE);
+
+	snap = list_head(&ddpa->shared_snaps);
+	origin_ds = snap->ds;
+	dd = hds->ds_dir;
+
+	snap = list_head(&ddpa->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,
+	VERIFY0(dsl_dir_hold_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);
+	snap = list_tail(&ddpa->clone_snaps);
 	ASSERT3U(snap->ds->ds_phys->ds_prev_snap_obj, ==, origin_ds->ds_object);
 	origin_ds->ds_phys->ds_next_snap_obj = snap->ds->ds_object;
 
 	/* change the origin's next clone */
 	if (origin_ds->ds_phys->ds_next_clones_obj) {
-		remove_from_next_clones(origin_ds, snap->ds->ds_object, tx);
-		VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
+		dsl_dataset_remove_from_next_clones(origin_ds,
+		    snap->ds->ds_object, tx);
+		VERIFY0(zap_add_int(dp->dp_meta_objset,
 		    origin_ds->ds_phys->ds_next_clones_obj,
 		    oldnext_obj, tx));
 	}
@@ -2881,39 +2066,43 @@ dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 
 	/* change dd_clone entries */
 	if (spa_version(dp->dp_spa) >= SPA_VERSION_DIR_CLONES) {
-		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
+		VERIFY0(zap_remove_int(dp->dp_meta_objset,
 		    odd->dd_phys->dd_clones, hds->ds_object, tx));
-		VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
-		    pa->origin_origin->ds_dir->dd_phys->dd_clones,
+		VERIFY0(zap_add_int(dp->dp_meta_objset,
+		    ddpa->origin_origin->ds_dir->dd_phys->dd_clones,
 		    hds->ds_object, tx));
 
-		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
-		    pa->origin_origin->ds_dir->dd_phys->dd_clones,
+		VERIFY0(zap_remove_int(dp->dp_meta_objset,
+		    ddpa->origin_origin->ds_dir->dd_phys->dd_clones,
 		    origin_head->ds_object, tx));
 		if (dd->dd_phys->dd_clones == 0) {
 			dd->dd_phys->dd_clones = zap_create(dp->dp_meta_objset,
 			    DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
 		}
-		VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
+		VERIFY0(zap_add_int(dp->dp_meta_objset,
 		    dd->dd_phys->dd_clones, origin_head->ds_object, tx));
-
 	}
 
 	/* move snapshots to this dir */
-	for (snap = list_head(&pa->shared_snaps); snap;
-	    snap = list_next(&pa->shared_snaps, snap)) {
+	for (snap = list_head(&ddpa->shared_snaps); snap;
+	    snap = list_next(&ddpa->shared_snaps, snap)) {
 		dsl_dataset_t *ds = snap->ds;
 
-		/* unregister props as dsl_dir is changing */
+		/*
+		 * Property callbacks are registered to a particular
+		 * dsl_dir.  Since ours is changing, evict the objset
+		 * so that they will be unregistered from the old dsl_dir.
+		 */
 		if (ds->ds_objset) {
 			dmu_objset_evict(ds->ds_objset);
 			ds->ds_objset = NULL;
 		}
+
 		/* move snap name entry */
-		VERIFY(0 == dsl_dataset_get_snapname(ds));
-		VERIFY(0 == dsl_dataset_snap_remove(origin_head,
+		VERIFY0(dsl_dataset_get_snapname(ds));
+		VERIFY0(dsl_dataset_snap_remove(origin_head,
 		    ds->ds_snapname, tx));
-		VERIFY(0 == zap_add(dp->dp_meta_objset,
+		VERIFY0(zap_add(dp->dp_meta_objset,
 		    hds->ds_phys->ds_snapnames_zapobj, ds->ds_snapname,
 		    8, 1, &ds->ds_object, tx));
 
@@ -2922,8 +2111,8 @@ dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *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,
+		dsl_dir_rele(ds->ds_dir, ds);
+		VERIFY0(dsl_dir_hold_obj(dp, dd->dd_object,
 		    NULL, ds, &ds->ds_dir));
 
 		/* move any clone references */
@@ -2947,20 +2136,20 @@ dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 					continue;
 				}
 
-				VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
+				VERIFY0(dsl_dataset_hold_obj(dp,
 				    za.za_first_integer, FTAG, &cnds));
 				o = cnds->ds_dir->dd_phys->dd_head_dataset_obj;
 
-				VERIFY3U(zap_remove_int(dp->dp_meta_objset,
-				    odd->dd_phys->dd_clones, o, tx), ==, 0);
-				VERIFY3U(zap_add_int(dp->dp_meta_objset,
-				    dd->dd_phys->dd_clones, o, tx), ==, 0);
+				VERIFY0(zap_remove_int(dp->dp_meta_objset,
+				    odd->dd_phys->dd_clones, o, tx));
+				VERIFY0(zap_add_int(dp->dp_meta_objset,
+				    dd->dd_phys->dd_clones, o, tx));
 				dsl_dataset_rele(cnds, FTAG);
 			}
 			zap_cursor_fini(&zc);
 		}
 
-		ASSERT0(dsl_prop_numcb(ds));
+		ASSERT(!dsl_prop_hascb(ds));
 	}
 
 	/*
@@ -2970,31 +2159,31 @@ dsl_dataset_promote_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 	 * is true for each of {clone,origin} independently.
 	 */
 
-	delta = pa->cloneusedsnap -
+	delta = ddpa->cloneusedsnap -
 	    dd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
 	ASSERT3S(delta, >=, 0);
-	ASSERT3U(pa->used, >=, delta);
+	ASSERT3U(ddpa->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);
+	    ddpa->used - delta, ddpa->comp, ddpa->uncomp, tx);
 
-	delta = pa->originusedsnap -
+	delta = ddpa->originusedsnap -
 	    odd->dd_phys->dd_used_breakdown[DD_USED_SNAP];
 	ASSERT3S(delta, <=, 0);
-	ASSERT3U(pa->used, >=, -delta);
+	ASSERT3U(ddpa->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);
+	    -ddpa->used - delta, -ddpa->comp, -ddpa->uncomp, tx);
 
-	origin_ds->ds_phys->ds_unique_bytes = pa->unique;
+	origin_ds->ds_phys->ds_unique_bytes = ddpa->unique;
 
 	/* log history record */
 	spa_history_log_internal_ds(hds, "promote", tx, "");
 
-	dsl_dir_close(odd, FTAG);
+	dsl_dir_rele(odd, FTAG);
+	promote_rele(ddpa, 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
@@ -3002,13 +2191,11 @@ static char *snaplist_tag = "snaplist";
  * 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)
+snaplist_make(dsl_pool_t *dp,
+    uint64_t first_obj, uint64_t last_obj, list_t *l, void *tag)
 {
 	uint64_t obj = last_obj;
 
-	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock));
-
 	list_create(l, sizeof (struct promotenode),
 	    offsetof(struct promotenode, link));
 
@@ -3017,28 +2204,15 @@ snaplist_make(dsl_pool_t *dp, boolean_t own,
 		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) {
+		err = dsl_dataset_hold_obj(dp, obj, tag, &ds);
+		ASSERT(err != ENOENT);
+		if (err != 0)
 			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 = kmem_alloc(sizeof (*snap), KM_SLEEP);
 		snap->ds = ds;
 		list_insert_tail(l, snap);
 		obj = ds->ds_phys->ds_prev_snap_obj;
@@ -3063,208 +2237,209 @@ snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep)
 }
 
 static void
-snaplist_destroy(list_t *l, boolean_t own)
+snaplist_destroy(list_t *l, void *tag)
 {
 	struct promotenode *snap;
 
-	if (!l || !list_link_active(&l->list_head))
+	if (l == NULL || !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));
+		dsl_dataset_rele(snap->ds, tag);
+		kmem_free(snap, sizeof (*snap));
 	}
 	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, char *conflsnap)
+static int
+promote_hold(dsl_dataset_promote_arg_t *ddpa, dsl_pool_t *dp, void *tag)
 {
-	dsl_dataset_t *ds;
+	int error;
 	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);
-	}
+	error = dsl_dataset_hold(dp, ddpa->ddpa_clonename, tag,
+	    &ddpa->ddpa_clone);
+	if (error != 0)
+		return (error);
+	dd = ddpa->ddpa_clone->ds_dir;
 
-	if (dsl_dataset_is_snapshot(ds) || dd->dd_phys->dd_origin_obj == 0) {
-		dsl_dataset_rele(ds, FTAG);
+	if (dsl_dataset_is_snapshot(ddpa->ddpa_clone) ||
+	    !dsl_dir_is_clone(dd)) {
+		dsl_dataset_rele(ddpa->ddpa_clone, tag);
 		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)
+	error = snaplist_make(dp, 0, dd->dd_phys->dd_origin_obj,
+	    &ddpa->shared_snaps, tag);
+	if (error != 0)
 		goto out;
 
-	err = snaplist_make(dp, B_FALSE, 0, ds->ds_object, &pa.clone_snaps);
-	if (err != 0)
+	error = snaplist_make(dp, 0, ddpa->ddpa_clone->ds_object,
+	    &ddpa->clone_snaps, tag);
+	if (error != 0)
 		goto out;
 
-	snap = list_head(&pa.shared_snaps);
+	snap = list_head(&ddpa->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)
+	error = snaplist_make(dp, dd->dd_phys->dd_origin_obj,
+	    snap->ds->ds_dir->dd_phys->dd_head_dataset_obj,
+	    &ddpa->origin_snaps, tag);
+	if (error != 0)
 		goto out;
 
 	if (snap->ds->ds_dir->dd_phys->dd_origin_obj != 0) {
-		err = dsl_dataset_hold_obj(dp,
+		error = dsl_dataset_hold_obj(dp,
 		    snap->ds->ds_dir->dd_phys->dd_origin_obj,
-		    FTAG, &pa.origin_origin);
-		if (err != 0)
+		    tag, &ddpa->origin_origin);
+		if (error != 0)
 			goto out;
 	}
-
 out:
-	rw_exit(&dp->dp_config_rwlock);
+	if (error != 0)
+		promote_rele(ddpa, tag);
+	return (error);
+}
+
+static void
+promote_rele(dsl_dataset_promote_arg_t *ddpa, void *tag)
+{
+	snaplist_destroy(&ddpa->shared_snaps, tag);
+	snaplist_destroy(&ddpa->clone_snaps, tag);
+	snaplist_destroy(&ddpa->origin_snaps, tag);
+	if (ddpa->origin_origin != NULL)
+		dsl_dataset_rele(ddpa->origin_origin, tag);
+	dsl_dataset_rele(ddpa->ddpa_clone, tag);
+}
+
+/*
+ * Promote a clone.
+ *
+ * If it fails due to a conflicting snapshot name, "conflsnap" will be filled
+ * in with the name.  (It must be at least MAXNAMELEN bytes long.)
+ */
+int
+dsl_dataset_promote(const char *name, char *conflsnap)
+{
+	dsl_dataset_promote_arg_t ddpa = { 0 };
+	uint64_t numsnaps;
+	int error;
+	objset_t *os;
 
 	/*
-	 * 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.
+	 * We will modify space proportional to the number of
+	 * snapshots.  Compute numsnaps.
 	 */
-	if (err == 0) {
-		err = dsl_sync_task_do(dp, dsl_dataset_promote_check,
-		    dsl_dataset_promote_sync, ds, &pa,
-		    2 + 2 * doi.doi_physical_blocks_512);
-		if (err && pa.err_ds && conflsnap)
-			(void) strncpy(conflsnap, pa.err_ds, MAXNAMELEN);
-	}
+	error = dmu_objset_hold(name, FTAG, &os);
+	if (error != 0)
+		return (error);
+	error = zap_count(dmu_objset_pool(os)->dp_meta_objset,
+	    dmu_objset_ds(os)->ds_phys->ds_snapnames_zapobj, &numsnaps);
+	dmu_objset_rele(os, FTAG);
+	if (error != 0)
+		return (error);
 
-	snaplist_destroy(&pa.shared_snaps, B_TRUE);
-	snaplist_destroy(&pa.clone_snaps, B_FALSE);
-	snaplist_destroy(&pa.origin_snaps, B_FALSE);
-	if (pa.origin_origin)
-		dsl_dataset_rele(pa.origin_origin, FTAG);
-	dsl_dataset_rele(ds, FTAG);
-	return (err);
-}
+	ddpa.ddpa_clonename = name;
+	ddpa.err_ds = conflsnap;
 
-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 */
-};
+	return (dsl_sync_task(name, dsl_dataset_promote_check,
+	    dsl_dataset_promote_sync, &ddpa, 2 + numsnaps));
+}
 
-/* ARGSUSED */
-static int
-dsl_dataset_clone_swap_check(void *arg1, void *arg2, dmu_tx_t *tx)
+int
+dsl_dataset_clone_swap_check_impl(dsl_dataset_t *clone,
+    dsl_dataset_t *origin_head, boolean_t force)
 {
-	struct cloneswaparg *csa = arg1;
+	int64_t unused_refres_delta;
 
 	/* they should both be heads */
-	if (dsl_dataset_is_snapshot(csa->cds) ||
-	    dsl_dataset_is_snapshot(csa->ohds))
+	if (dsl_dataset_is_snapshot(clone) ||
+	    dsl_dataset_is_snapshot(origin_head))
 		return (EINVAL);
 
 	/* the branch point should be just before them */
-	if (csa->cds->ds_prev != csa->ohds->ds_prev)
+	if (clone->ds_prev != origin_head->ds_prev)
 		return (EINVAL);
 
-	/* cds should be the clone (unless they are unrelated) */
-	if (csa->cds->ds_prev != NULL &&
-	    csa->cds->ds_prev != csa->cds->ds_dir->dd_pool->dp_origin_snap &&
-	    csa->ohds->ds_object !=
-	    csa->cds->ds_prev->ds_phys->ds_next_snap_obj)
+	/* clone should be the clone (unless they are unrelated) */
+	if (clone->ds_prev != NULL &&
+	    clone->ds_prev != clone->ds_dir->dd_pool->dp_origin_snap &&
+	    origin_head->ds_object !=
+	    clone->ds_prev->ds_phys->ds_next_snap_obj)
 		return (EINVAL);
 
 	/* the clone should be a child of the origin */
-	if (csa->cds->ds_dir->dd_parent != csa->ohds->ds_dir)
+	if (clone->ds_dir->dd_parent != origin_head->ds_dir)
 		return (EINVAL);
 
-	/* ohds shouldn't be modified unless 'force' */
-	if (!csa->force && dsl_dataset_modified_since_lastsnap(csa->ohds))
+	/* origin_head shouldn't be modified unless 'force' */
+	if (!force && dsl_dataset_modified_since_lastsnap(origin_head))
 		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);
+	/* origin_head should have no long holds (e.g. is not mounted) */
+	if (dsl_dataset_long_held(origin_head))
+		return (EBUSY);
+
+	/* check amount of any unconsumed refreservation */
+	unused_refres_delta =
+	    (int64_t)MIN(origin_head->ds_reserved,
+	    origin_head->ds_phys->ds_unique_bytes) -
+	    (int64_t)MIN(origin_head->ds_reserved,
+	    clone->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))
+	if (unused_refres_delta > 0 &&
+	    unused_refres_delta >
+	    dsl_dir_space_available(origin_head->ds_dir, NULL, 0, TRUE))
 		return (ENOSPC);
 
-	if (csa->ohds->ds_quota != 0 &&
-	    csa->cds->ds_phys->ds_unique_bytes > csa->ohds->ds_quota)
+	/* clone can't be over the head's refquota */
+	if (origin_head->ds_quota != 0 &&
+	    clone->ds_phys->ds_referenced_bytes > origin_head->ds_quota)
 		return (EDQUOT);
 
 	return (0);
 }
 
-/* ARGSUSED */
-static void
-dsl_dataset_clone_swap_sync(void *arg1, void *arg2, dmu_tx_t *tx)
+void
+dsl_dataset_clone_swap_sync_impl(dsl_dataset_t *clone,
+    dsl_dataset_t *origin_head, dmu_tx_t *tx)
 {
-	struct cloneswaparg *csa = arg1;
-	dsl_pool_t *dp = csa->cds->ds_dir->dd_pool;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	int64_t unused_refres_delta;
 
-	ASSERT(csa->cds->ds_reserved == 0);
-	ASSERT(csa->ohds->ds_quota == 0 ||
-	    csa->cds->ds_phys->ds_unique_bytes <= csa->ohds->ds_quota);
+	ASSERT(clone->ds_reserved == 0);
+	ASSERT(origin_head->ds_quota == 0 ||
+	    clone->ds_phys->ds_unique_bytes <= origin_head->ds_quota);
 
-	dmu_buf_will_dirty(csa->cds->ds_dbuf, tx);
-	dmu_buf_will_dirty(csa->ohds->ds_dbuf, tx);
+	dmu_buf_will_dirty(clone->ds_dbuf, tx);
+	dmu_buf_will_dirty(origin_head->ds_dbuf, tx);
 
-	if (csa->cds->ds_objset != NULL) {
-		dmu_objset_evict(csa->cds->ds_objset);
-		csa->cds->ds_objset = NULL;
+	if (clone->ds_objset != NULL) {
+		dmu_objset_evict(clone->ds_objset);
+		clone->ds_objset = NULL;
 	}
 
-	if (csa->ohds->ds_objset != NULL) {
-		dmu_objset_evict(csa->ohds->ds_objset);
-		csa->ohds->ds_objset = NULL;
+	if (origin_head->ds_objset != NULL) {
+		dmu_objset_evict(origin_head->ds_objset);
+		origin_head->ds_objset = NULL;
 	}
 
+	unused_refres_delta =
+	    (int64_t)MIN(origin_head->ds_reserved,
+	    origin_head->ds_phys->ds_unique_bytes) -
+	    (int64_t)MIN(origin_head->ds_reserved,
+	    clone->ds_phys->ds_unique_bytes);
+
 	/*
 	 * Reset origin's unique bytes, if it exists.
 	 */
-	if (csa->cds->ds_prev) {
-		dsl_dataset_t *origin = csa->cds->ds_prev;
+	if (clone->ds_prev) {
+		dsl_dataset_t *origin = clone->ds_prev;
 		uint64_t comp, uncomp;
 
 		dmu_buf_will_dirty(origin->ds_dbuf, tx);
-		dsl_deadlist_space_range(&csa->cds->ds_deadlist,
+		dsl_deadlist_space_range(&clone->ds_deadlist,
 		    origin->ds_phys->ds_prev_snap_txg, UINT64_MAX,
 		    &origin->ds_phys->ds_unique_bytes, &comp, &uncomp);
 	}
@@ -3272,9 +2447,9 @@ dsl_dataset_clone_swap_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 	/* 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;
+		tmp = origin_head->ds_phys->ds_bp;
+		origin_head->ds_phys->ds_bp = clone->ds_phys->ds_bp;
+		clone->ds_phys->ds_bp = tmp;
 	}
 
 	/* set dd_*_bytes */
@@ -3283,25 +2458,25 @@ dsl_dataset_clone_swap_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 		uint64_t cdl_used, cdl_comp, cdl_uncomp;
 		uint64_t odl_used, odl_comp, odl_uncomp;
 
-		ASSERT3U(csa->cds->ds_dir->dd_phys->
+		ASSERT3U(clone->ds_dir->dd_phys->
 		    dd_used_breakdown[DD_USED_SNAP], ==, 0);
 
-		dsl_deadlist_space(&csa->cds->ds_deadlist,
+		dsl_deadlist_space(&clone->ds_deadlist,
 		    &cdl_used, &cdl_comp, &cdl_uncomp);
-		dsl_deadlist_space(&csa->ohds->ds_deadlist,
+		dsl_deadlist_space(&origin_head->ds_deadlist,
 		    &odl_used, &odl_comp, &odl_uncomp);
 
-		dused = csa->cds->ds_phys->ds_referenced_bytes + cdl_used -
-		    (csa->ohds->ds_phys->ds_referenced_bytes + odl_used);
-		dcomp = csa->cds->ds_phys->ds_compressed_bytes + cdl_comp -
-		    (csa->ohds->ds_phys->ds_compressed_bytes + odl_comp);
-		duncomp = csa->cds->ds_phys->ds_uncompressed_bytes +
+		dused = clone->ds_phys->ds_referenced_bytes + cdl_used -
+		    (origin_head->ds_phys->ds_referenced_bytes + odl_used);
+		dcomp = clone->ds_phys->ds_compressed_bytes + cdl_comp -
+		    (origin_head->ds_phys->ds_compressed_bytes + odl_comp);
+		duncomp = clone->ds_phys->ds_uncompressed_bytes +
 		    cdl_uncomp -
-		    (csa->ohds->ds_phys->ds_uncompressed_bytes + odl_uncomp);
+		    (origin_head->ds_phys->ds_uncompressed_bytes + odl_uncomp);
 
-		dsl_dir_diduse_space(csa->ohds->ds_dir, DD_USED_HEAD,
+		dsl_dir_diduse_space(origin_head->ds_dir, DD_USED_HEAD,
 		    dused, dcomp, duncomp, tx);
-		dsl_dir_diduse_space(csa->cds->ds_dir, DD_USED_HEAD,
+		dsl_dir_diduse_space(clone->ds_dir, DD_USED_HEAD,
 		    -dused, -dcomp, -duncomp, tx);
 
 		/*
@@ -3310,86 +2485,46 @@ dsl_dataset_clone_swap_sync(void *arg1, void *arg2, dmu_tx_t *tx)
 		 * deadlist (since that's the only thing that's
 		 * changing that affects the snapused).
 		 */
-		dsl_deadlist_space_range(&csa->cds->ds_deadlist,
-		    csa->ohds->ds_dir->dd_origin_txg, UINT64_MAX,
+		dsl_deadlist_space_range(&clone->ds_deadlist,
+		    origin_head->ds_dir->dd_origin_txg, UINT64_MAX,
 		    &cdl_used, &cdl_comp, &cdl_uncomp);
-		dsl_deadlist_space_range(&csa->ohds->ds_deadlist,
-		    csa->ohds->ds_dir->dd_origin_txg, UINT64_MAX,
+		dsl_deadlist_space_range(&origin_head->ds_deadlist,
+		    origin_head->ds_dir->dd_origin_txg, UINT64_MAX,
 		    &odl_used, &odl_comp, &odl_uncomp);
-		dsl_dir_transfer_space(csa->ohds->ds_dir, cdl_used - odl_used,
+		dsl_dir_transfer_space(origin_head->ds_dir, cdl_used - odl_used,
 		    DD_USED_HEAD, DD_USED_SNAP, tx);
 	}
 
 	/* swap ds_*_bytes */
-	SWITCH64(csa->ohds->ds_phys->ds_referenced_bytes,
-	    csa->cds->ds_phys->ds_referenced_bytes);
-	SWITCH64(csa->ohds->ds_phys->ds_compressed_bytes,
-	    csa->cds->ds_phys->ds_compressed_bytes);
-	SWITCH64(csa->ohds->ds_phys->ds_uncompressed_bytes,
-	    csa->cds->ds_phys->ds_uncompressed_bytes);
-	SWITCH64(csa->ohds->ds_phys->ds_unique_bytes,
-	    csa->cds->ds_phys->ds_unique_bytes);
+	SWITCH64(origin_head->ds_phys->ds_referenced_bytes,
+	    clone->ds_phys->ds_referenced_bytes);
+	SWITCH64(origin_head->ds_phys->ds_compressed_bytes,
+	    clone->ds_phys->ds_compressed_bytes);
+	SWITCH64(origin_head->ds_phys->ds_uncompressed_bytes,
+	    clone->ds_phys->ds_uncompressed_bytes);
+	SWITCH64(origin_head->ds_phys->ds_unique_bytes,
+	    clone->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);
+	dsl_dir_diduse_space(origin_head->ds_dir, DD_USED_REFRSRV,
+	    unused_refres_delta, 0, 0, tx);
 
 	/*
 	 * Swap deadlists.
 	 */
-	dsl_deadlist_close(&csa->cds->ds_deadlist);
-	dsl_deadlist_close(&csa->ohds->ds_deadlist);
-	SWITCH64(csa->ohds->ds_phys->ds_deadlist_obj,
-	    csa->cds->ds_phys->ds_deadlist_obj);
-	dsl_deadlist_open(&csa->cds->ds_deadlist, dp->dp_meta_objset,
-	    csa->cds->ds_phys->ds_deadlist_obj);
-	dsl_deadlist_open(&csa->ohds->ds_deadlist, dp->dp_meta_objset,
-	    csa->ohds->ds_phys->ds_deadlist_obj);
-
-	dsl_scan_ds_clone_swapped(csa->ohds, csa->cds, tx);
-
-	spa_history_log_internal_ds(csa->cds, "clone swap", tx,
-	    "parent=%s", csa->ohds->ds_dir->dd_myname);
-}
+	dsl_deadlist_close(&clone->ds_deadlist);
+	dsl_deadlist_close(&origin_head->ds_deadlist);
+	SWITCH64(origin_head->ds_phys->ds_deadlist_obj,
+	    clone->ds_phys->ds_deadlist_obj);
+	dsl_deadlist_open(&clone->ds_deadlist, dp->dp_meta_objset,
+	    clone->ds_phys->ds_deadlist_obj);
+	dsl_deadlist_open(&origin_head->ds_deadlist, dp->dp_meta_objset,
+	    origin_head->ds_phys->ds_deadlist_obj);
 
-/*
- * Swap 'clone' with its origin head datasets.  Used at the end of "zfs
- * recv" into an existing fs to swizzle the file system to the new
- * version, and by "zfs rollback".  Can also be used to swap two
- * independent head datasets if neither has any snapshots.
- */
-int
-dsl_dataset_clone_swap(dsl_dataset_t *clone, dsl_dataset_t *origin_head,
-    boolean_t force)
-{
-	struct cloneswaparg csa;
-	int error;
+	dsl_scan_ds_clone_swapped(origin_head, clone, tx);
 
-	ASSERT(clone->ds_owner);
-	ASSERT(origin_head->ds_owner);
-retry:
-	/*
-	 * Need exclusive access for the swap. If we're swapping these
-	 * datasets back after an error, we already hold the locks.
-	 */
-	if (!RW_WRITE_HELD(&clone->ds_rwlock))
-		rw_enter(&clone->ds_rwlock, RW_WRITER);
-	if (!RW_WRITE_HELD(&origin_head->ds_rwlock) &&
-	    !rw_tryenter(&origin_head->ds_rwlock, RW_WRITER)) {
-		rw_exit(&clone->ds_rwlock);
-		rw_enter(&origin_head->ds_rwlock, RW_WRITER);
-		if (!rw_tryenter(&clone->ds_rwlock, RW_WRITER)) {
-			rw_exit(&origin_head->ds_rwlock);
-			goto retry;
-		}
-	}
-	csa.cds = clone;
-	csa.ohds = origin_head;
-	csa.force = force;
-	error = dsl_sync_task_do(clone->ds_dir->dd_pool,
-	    dsl_dataset_clone_swap_check,
-	    dsl_dataset_clone_swap_sync, &csa, NULL, 9);
-	return (error);
+	spa_history_log_internal_ds(clone, "clone swap", tx,
+	    "parent=%s", origin_head->ds_dir->dd_myname);
 }
 
 /*
@@ -3399,21 +2534,20 @@ retry:
 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)
+	error = dsl_pool_hold(pname, FTAG, &dp);
+	if (error != 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) {
+
+	error = dsl_dataset_hold_obj(dp, obj, FTAG, &ds);
+	if (error == 0) {
 		dsl_dataset_name(ds, buf);
 		dsl_dataset_rele(ds, FTAG);
 	}
-	rw_exit(&dp->dp_config_rwlock);
-	spa_close(spa, FTAG);
+	dsl_pool_rele(dp, FTAG);
 
 	return (error);
 }
@@ -3466,102 +2600,134 @@ dsl_dataset_check_quota(dsl_dataset_t *ds, boolean_t check_quota,
 	return (error);
 }
 
+typedef struct dsl_dataset_set_qr_arg {
+	const char *ddsqra_name;
+	zprop_source_t ddsqra_source;
+	uint64_t ddsqra_value;
+} dsl_dataset_set_qr_arg_t;
+
+
 /* ARGSUSED */
 static int
-dsl_dataset_set_quota_check(void *arg1, void *arg2, dmu_tx_t *tx)
+dsl_dataset_set_refquota_check(void *arg, dmu_tx_t *tx)
 {
-	dsl_dataset_t *ds = arg1;
-	dsl_prop_setarg_t *psa = arg2;
-	int err;
+	dsl_dataset_set_qr_arg_t *ddsqra = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+	int error;
+	uint64_t newval;
 
-	if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_REFQUOTA)
+	if (spa_version(dp->dp_spa) < SPA_VERSION_REFQUOTA)
 		return (ENOTSUP);
 
-	if ((err = dsl_prop_predict_sync(ds->ds_dir, psa)) != 0)
-		return (err);
+	error = dsl_dataset_hold(dp, ddsqra->ddsqra_name, FTAG, &ds);
+	if (error != 0)
+		return (error);
+
+	if (dsl_dataset_is_snapshot(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EINVAL);
+	}
 
-	if (psa->psa_effective_value == 0)
+	error = dsl_prop_predict(ds->ds_dir,
+	    zfs_prop_to_name(ZFS_PROP_REFQUOTA),
+	    ddsqra->ddsqra_source, ddsqra->ddsqra_value, &newval);
+	if (error != 0) {
+		dsl_dataset_rele(ds, FTAG);
+		return (error);
+	}
+
+	if (newval == 0) {
+		dsl_dataset_rele(ds, FTAG);
 		return (0);
+	}
 
-	if (psa->psa_effective_value < ds->ds_phys->ds_referenced_bytes ||
-	    psa->psa_effective_value < ds->ds_reserved)
+	if (newval < ds->ds_phys->ds_referenced_bytes ||
+	    newval < ds->ds_reserved) {
+		dsl_dataset_rele(ds, FTAG);
 		return (ENOSPC);
+	}
 
+	dsl_dataset_rele(ds, FTAG);
 	return (0);
 }
 
-extern void dsl_prop_set_sync(void *, void *, dmu_tx_t *);
-
-void
-dsl_dataset_set_quota_sync(void *arg1, void *arg2, dmu_tx_t *tx)
+static void
+dsl_dataset_set_refquota_sync(void *arg, dmu_tx_t *tx)
 {
-	dsl_dataset_t *ds = arg1;
-	dsl_prop_setarg_t *psa = arg2;
-	uint64_t effective_value = psa->psa_effective_value;
+	dsl_dataset_set_qr_arg_t *ddsqra = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+	uint64_t newval;
+
+	VERIFY0(dsl_dataset_hold(dp, ddsqra->ddsqra_name, FTAG, &ds));
+
+	dsl_prop_set_sync_impl(ds,
+	    zfs_prop_to_name(ZFS_PROP_REFQUOTA),
+	    ddsqra->ddsqra_source, sizeof (ddsqra->ddsqra_value), 1,
+	    &ddsqra->ddsqra_value, tx);
 
-	dsl_prop_set_sync(ds, psa, tx);
-	DSL_PROP_CHECK_PREDICTION(ds->ds_dir, psa);
+	VERIFY0(dsl_prop_get_int_ds(ds,
+	    zfs_prop_to_name(ZFS_PROP_REFQUOTA), &newval));
 
-	if (ds->ds_quota != effective_value) {
+	if (ds->ds_quota != newval) {
 		dmu_buf_will_dirty(ds->ds_dbuf, tx);
-		ds->ds_quota = effective_value;
+		ds->ds_quota = newval;
 	}
+	dsl_dataset_rele(ds, FTAG);
 }
 
 int
-dsl_dataset_set_quota(const char *dsname, zprop_source_t source, uint64_t quota)
+dsl_dataset_set_refquota(const char *dsname, zprop_source_t source,
+    uint64_t refquota)
 {
-	dsl_dataset_t *ds;
-	dsl_prop_setarg_t psa;
-	int err;
-
-	dsl_prop_setarg_init_uint64(&psa, "refquota", source, &quota);
-
-	err = dsl_dataset_hold(dsname, FTAG, &ds);
-	if (err)
-		return (err);
+	dsl_dataset_set_qr_arg_t ddsqra;
 
-	/*
-	 * 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);
+	ddsqra.ddsqra_name = dsname;
+	ddsqra.ddsqra_source = source;
+	ddsqra.ddsqra_value = refquota;
 
-	err = dsl_sync_task_do(ds->ds_dir->dd_pool,
-	    dsl_dataset_set_quota_check, dsl_dataset_set_quota_sync,
-	    ds, &psa, 0);
-
-	dsl_dataset_rele(ds, FTAG);
-	return (err);
+	return (dsl_sync_task(dsname, dsl_dataset_set_refquota_check,
+	    dsl_dataset_set_refquota_sync, &ddsqra, 0));
 }
 
 static int
-dsl_dataset_set_reservation_check(void *arg1, void *arg2, dmu_tx_t *tx)
+dsl_dataset_set_refreservation_check(void *arg, dmu_tx_t *tx)
 {
-	dsl_dataset_t *ds = arg1;
-	dsl_prop_setarg_t *psa = arg2;
-	uint64_t effective_value;
-	uint64_t unique;
-	int err;
+	dsl_dataset_set_qr_arg_t *ddsqra = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	dsl_dataset_t *ds;
+	int error;
+	uint64_t newval, unique;
 
-	if (spa_version(ds->ds_dir->dd_pool->dp_spa) <
-	    SPA_VERSION_REFRESERVATION)
+	if (spa_version(dp->dp_spa) < SPA_VERSION_REFRESERVATION)
 		return (ENOTSUP);
 
-	if (dsl_dataset_is_snapshot(ds))
-		return (EINVAL);
+	error = dsl_dataset_hold(dp, ddsqra->ddsqra_name, FTAG, &ds);
+	if (error != 0)
+		return (error);
 
-	if ((err = dsl_prop_predict_sync(ds->ds_dir, psa)) != 0)
-		return (err);
+	if (dsl_dataset_is_snapshot(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (EINVAL);
+	}
 
-	effective_value = psa->psa_effective_value;
+	error = dsl_prop_predict(ds->ds_dir,
+	    zfs_prop_to_name(ZFS_PROP_REFRESERVATION),
+	    ddsqra->ddsqra_source, ddsqra->ddsqra_value, &newval);
+	if (error != 0) {
+		dsl_dataset_rele(ds, FTAG);
+		return (error);
+	}
 
 	/*
 	 * If we are doing the preliminary check in open context, the
 	 * space estimates may be inaccurate.
 	 */
-	if (!dmu_tx_is_syncing(tx))
+	if (!dmu_tx_is_syncing(tx)) {
+		dsl_dataset_rele(ds, FTAG);
 		return (0);
+	}
 
 	mutex_enter(&ds->ds_lock);
 	if (!DS_UNIQUE_IS_ACCURATE(ds))
@@ -3569,637 +2735,75 @@ dsl_dataset_set_reservation_check(void *arg1, void *arg2, dmu_tx_t *tx)
 	unique = ds->ds_phys->ds_unique_bytes;
 	mutex_exit(&ds->ds_lock);
 
-	if (MAX(unique, effective_value) > MAX(unique, ds->ds_reserved)) {
-		uint64_t delta = MAX(unique, effective_value) -
+	if (MAX(unique, newval) > MAX(unique, ds->ds_reserved)) {
+		uint64_t delta = MAX(unique, newval) -
 		    MAX(unique, ds->ds_reserved);
 
-		if (delta > dsl_dir_space_available(ds->ds_dir, NULL, 0, TRUE))
-			return (ENOSPC);
-		if (ds->ds_quota > 0 &&
-		    effective_value > ds->ds_quota)
+		if (delta >
+		    dsl_dir_space_available(ds->ds_dir, NULL, 0, B_TRUE) ||
+		    (ds->ds_quota > 0 && newval > ds->ds_quota)) {
+			dsl_dataset_rele(ds, FTAG);
 			return (ENOSPC);
+		}
 	}
 
+	dsl_dataset_rele(ds, FTAG);
 	return (0);
 }
 
-static void
-dsl_dataset_set_reservation_sync(void *arg1, void *arg2, dmu_tx_t *tx)
+void
+dsl_dataset_set_refreservation_sync_impl(dsl_dataset_t *ds,
+    zprop_source_t source, uint64_t value, dmu_tx_t *tx)
 {
-	dsl_dataset_t *ds = arg1;
-	dsl_prop_setarg_t *psa = arg2;
-	uint64_t effective_value = psa->psa_effective_value;
+	uint64_t newval;
 	uint64_t unique;
 	int64_t delta;
 
-	dsl_prop_set_sync(ds, psa, tx);
-	DSL_PROP_CHECK_PREDICTION(ds->ds_dir, psa);
+	dsl_prop_set_sync_impl(ds, zfs_prop_to_name(ZFS_PROP_REFRESERVATION),
+	    source, sizeof (value), 1, &value, tx);
 
-	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	VERIFY0(dsl_prop_get_int_ds(ds,
+	    zfs_prop_to_name(ZFS_PROP_REFRESERVATION), &newval));
 
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
 	mutex_enter(&ds->ds_dir->dd_lock);
 	mutex_enter(&ds->ds_lock);
 	ASSERT(DS_UNIQUE_IS_ACCURATE(ds));
 	unique = ds->ds_phys->ds_unique_bytes;
-	delta = MAX(0, (int64_t)(effective_value - unique)) -
+	delta = MAX(0, (int64_t)(newval - unique)) -
 	    MAX(0, (int64_t)(ds->ds_reserved - unique));
-	ds->ds_reserved = effective_value;
+	ds->ds_reserved = newval;
 	mutex_exit(&ds->ds_lock);
 
 	dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV, delta, 0, 0, tx);
 	mutex_exit(&ds->ds_dir->dd_lock);
 }
 
-int
-dsl_dataset_set_reservation(const char *dsname, zprop_source_t source,
-    uint64_t reservation)
-{
-	dsl_dataset_t *ds;
-	dsl_prop_setarg_t psa;
-	int err;
-
-	dsl_prop_setarg_init_uint64(&psa, "refreservation", source,
-	    &reservation);
-
-	err = dsl_dataset_hold(dsname, FTAG, &ds);
-	if (err)
-		return (err);
-
-	err = dsl_sync_task_do(ds->ds_dir->dd_pool,
-	    dsl_dataset_set_reservation_check,
-	    dsl_dataset_set_reservation_sync, ds, &psa, 0);
-
-	dsl_dataset_rele(ds, FTAG);
-	return (err);
-}
-
-typedef struct zfs_hold_cleanup_arg {
-	dsl_pool_t *dp;
-	uint64_t dsobj;
-	char htag[MAXNAMELEN];
-} zfs_hold_cleanup_arg_t;
-
 static void
-dsl_dataset_user_release_onexit(void *arg)
-{
-	zfs_hold_cleanup_arg_t *ca = arg;
-
-	(void) dsl_dataset_user_release_tmp(ca->dp, ca->dsobj, ca->htag,
-	    B_TRUE);
-	kmem_free(ca, sizeof (zfs_hold_cleanup_arg_t));
-}
-
-void
-dsl_register_onexit_hold_cleanup(dsl_dataset_t *ds, const char *htag,
-    minor_t minor)
+dsl_dataset_set_refreservation_sync(void *arg, dmu_tx_t *tx)
 {
-	zfs_hold_cleanup_arg_t *ca;
-
-	ca = kmem_alloc(sizeof (zfs_hold_cleanup_arg_t), KM_SLEEP);
-	ca->dp = ds->ds_dir->dd_pool;
-	ca->dsobj = ds->ds_object;
-	(void) strlcpy(ca->htag, htag, sizeof (ca->htag));
-	VERIFY3U(0, ==, zfs_onexit_add_cb(minor,
-	    dsl_dataset_user_release_onexit, ca, NULL));
-}
-
-/*
- * If you add new checks here, you may need to add
- * additional checks to the "temporary" case in
- * snapshot_check() in dmu_objset.c.
- */
-static int
-dsl_dataset_user_hold_check(void *arg1, void *arg2, dmu_tx_t *tx)
-{
-	dsl_dataset_t *ds = arg1;
-	struct dsl_ds_holdarg *ha = arg2;
-	const char *htag = ha->htag;
-	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
-	int error = 0;
-
-	if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_USERREFS)
-		return (ENOTSUP);
-
-	if (!dsl_dataset_is_snapshot(ds))
-		return (EINVAL);
-
-	/* tags must be unique */
-	mutex_enter(&ds->ds_lock);
-	if (ds->ds_phys->ds_userrefs_obj) {
-		error = zap_lookup(mos, ds->ds_phys->ds_userrefs_obj, htag,
-		    8, 1, tx);
-		if (error == 0)
-			error = EEXIST;
-		else if (error == ENOENT)
-			error = 0;
-	}
-	mutex_exit(&ds->ds_lock);
-
-	if (error == 0 && ha->temphold &&
-	    strlen(htag) + MAX_TAG_PREFIX_LEN >= MAXNAMELEN)
-		error = E2BIG;
-
-	return (error);
-}
-
-void
-dsl_dataset_user_hold_sync(void *arg1, void *arg2, dmu_tx_t *tx)
-{
-	dsl_dataset_t *ds = arg1;
-	struct dsl_ds_holdarg *ha = arg2;
-	const char *htag = ha->htag;
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
-	objset_t *mos = dp->dp_meta_objset;
-	uint64_t now = gethrestime_sec();
-	uint64_t zapobj;
-
-	mutex_enter(&ds->ds_lock);
-	if (ds->ds_phys->ds_userrefs_obj == 0) {
-		/*
-		 * This is the first user hold for this dataset.  Create
-		 * the userrefs zap object.
-		 */
-		dmu_buf_will_dirty(ds->ds_dbuf, tx);
-		zapobj = ds->ds_phys->ds_userrefs_obj =
-		    zap_create(mos, DMU_OT_USERREFS, DMU_OT_NONE, 0, tx);
-	} else {
-		zapobj = ds->ds_phys->ds_userrefs_obj;
-	}
-	ds->ds_userrefs++;
-	mutex_exit(&ds->ds_lock);
-
-	VERIFY(0 == zap_add(mos, zapobj, htag, 8, 1, &now, tx));
-
-	if (ha->temphold) {
-		VERIFY(0 == dsl_pool_user_hold(dp, ds->ds_object,
-		    htag, &now, tx));
-	}
-
-	spa_history_log_internal_ds(ds, "hold", tx,
-	    "tag = %s temp = %d holds now = %llu",
-	    htag, (int)ha->temphold, ds->ds_userrefs);
-}
-
-static int
-dsl_dataset_user_hold_one(const char *dsname, void *arg)
-{
-	struct dsl_ds_holdarg *ha = arg;
+	dsl_dataset_set_qr_arg_t *ddsqra = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
 	dsl_dataset_t *ds;
-	int error;
-	char *name;
-
-	/* alloc a buffer to hold dsname@snapname plus terminating NULL */
-	name = kmem_asprintf("%s@%s", dsname, ha->snapname);
-	error = dsl_dataset_hold(name, ha->dstg, &ds);
-	strfree(name);
-	if (error == 0) {
-		ha->gotone = B_TRUE;
-		dsl_sync_task_create(ha->dstg, dsl_dataset_user_hold_check,
-		    dsl_dataset_user_hold_sync, ds, ha, 0);
-	} else if (error == ENOENT && ha->recursive) {
-		error = 0;
-	} else {
-		(void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
-	}
-	return (error);
-}
-
-int
-dsl_dataset_user_hold_for_send(dsl_dataset_t *ds, char *htag,
-    boolean_t temphold)
-{
-	struct dsl_ds_holdarg *ha;
-	int error;
-
-	ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);
-	ha->htag = htag;
-	ha->temphold = temphold;
-	error = dsl_sync_task_do(ds->ds_dir->dd_pool,
-	    dsl_dataset_user_hold_check, dsl_dataset_user_hold_sync,
-	    ds, ha, 0);
-	kmem_free(ha, sizeof (struct dsl_ds_holdarg));
-
-	return (error);
-}
-
-int
-dsl_dataset_user_hold(char *dsname, char *snapname, char *htag,
-    boolean_t recursive, boolean_t temphold, int cleanup_fd)
-{
-	struct dsl_ds_holdarg *ha;
-	dsl_sync_task_t *dst;
-	spa_t *spa;
-	int error;
-	minor_t minor = 0;
-
-	if (cleanup_fd != -1) {
-		/* Currently we only support cleanup-on-exit of tempholds. */
-		if (!temphold)
-			return (EINVAL);
-		error = zfs_onexit_fd_hold(cleanup_fd, &minor);
-		if (error)
-			return (error);
-	}
-
-	ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);
-
-	(void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
-
-	error = spa_open(dsname, &spa, FTAG);
-	if (error) {
-		kmem_free(ha, sizeof (struct dsl_ds_holdarg));
-		if (cleanup_fd != -1)
-			zfs_onexit_fd_rele(cleanup_fd);
-		return (error);
-	}
-
-	ha->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
-	ha->htag = htag;
-	ha->snapname = snapname;
-	ha->recursive = recursive;
-	ha->temphold = temphold;
-
-	if (recursive) {
-		error = dmu_objset_find(dsname, dsl_dataset_user_hold_one,
-		    ha, DS_FIND_CHILDREN);
-	} else {
-		error = dsl_dataset_user_hold_one(dsname, ha);
-	}
-	if (error == 0)
-		error = dsl_sync_task_group_wait(ha->dstg);
-
-	for (dst = list_head(&ha->dstg->dstg_tasks); dst;
-	    dst = list_next(&ha->dstg->dstg_tasks, dst)) {
-		dsl_dataset_t *ds = dst->dst_arg1;
-
-		if (dst->dst_err) {
-			dsl_dataset_name(ds, ha->failed);
-			*strchr(ha->failed, '@') = '\0';
-		} else if (error == 0 && minor != 0 && temphold) {
-			/*
-			 * If this hold is to be released upon process exit,
-			 * register that action now.
-			 */
-			dsl_register_onexit_hold_cleanup(ds, htag, minor);
-		}
-		dsl_dataset_rele(ds, ha->dstg);
-	}
 
-	if (error == 0 && recursive && !ha->gotone)
-		error = ENOENT;
-
-	if (error)
-		(void) strlcpy(dsname, ha->failed, sizeof (ha->failed));
-
-	dsl_sync_task_group_destroy(ha->dstg);
-
-	kmem_free(ha, sizeof (struct dsl_ds_holdarg));
-	spa_close(spa, FTAG);
-	if (cleanup_fd != -1)
-		zfs_onexit_fd_rele(cleanup_fd);
-	return (error);
-}
-
-struct dsl_ds_releasearg {
-	dsl_dataset_t *ds;
-	const char *htag;
-	boolean_t own;		/* do we own or just hold ds? */
-};
-
-static int
-dsl_dataset_release_might_destroy(dsl_dataset_t *ds, const char *htag,
-    boolean_t *might_destroy)
-{
-	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
-	uint64_t zapobj;
-	uint64_t tmp;
-	int error;
-
-	*might_destroy = B_FALSE;
-
-	mutex_enter(&ds->ds_lock);
-	zapobj = ds->ds_phys->ds_userrefs_obj;
-	if (zapobj == 0) {
-		/* The tag can't possibly exist */
-		mutex_exit(&ds->ds_lock);
-		return (ESRCH);
-	}
-
-	/* Make sure the tag exists */
-	error = zap_lookup(mos, zapobj, htag, 8, 1, &tmp);
-	if (error) {
-		mutex_exit(&ds->ds_lock);
-		if (error == ENOENT)
-			error = ESRCH;
-		return (error);
-	}
-
-	if (ds->ds_userrefs == 1 && ds->ds_phys->ds_num_children == 1 &&
-	    DS_IS_DEFER_DESTROY(ds))
-		*might_destroy = B_TRUE;
-
-	mutex_exit(&ds->ds_lock);
-	return (0);
-}
-
-static int
-dsl_dataset_user_release_check(void *arg1, void *tag, dmu_tx_t *tx)
-{
-	struct dsl_ds_releasearg *ra = arg1;
-	dsl_dataset_t *ds = ra->ds;
-	boolean_t might_destroy;
-	int error;
-
-	if (spa_version(ds->ds_dir->dd_pool->dp_spa) < SPA_VERSION_USERREFS)
-		return (ENOTSUP);
-
-	error = dsl_dataset_release_might_destroy(ds, ra->htag, &might_destroy);
-	if (error)
-		return (error);
-
-	if (might_destroy) {
-		struct dsl_ds_destroyarg dsda = {0};
-
-		if (dmu_tx_is_syncing(tx)) {
-			/*
-			 * If we're not prepared to remove the snapshot,
-			 * we can't allow the release to happen right now.
-			 */
-			if (!ra->own)
-				return (EBUSY);
-		}
-		dsda.ds = ds;
-		dsda.releasing = B_TRUE;
-		return (dsl_dataset_destroy_check(&dsda, tag, tx));
-	}
-
-	return (0);
-}
-
-static void
-dsl_dataset_user_release_sync(void *arg1, void *tag, dmu_tx_t *tx)
-{
-	struct dsl_ds_releasearg *ra = arg1;
-	dsl_dataset_t *ds = ra->ds;
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
-	objset_t *mos = dp->dp_meta_objset;
-	uint64_t zapobj;
-	uint64_t refs;
-	int error;
-
-	mutex_enter(&ds->ds_lock);
-	ds->ds_userrefs--;
-	refs = ds->ds_userrefs;
-	mutex_exit(&ds->ds_lock);
-	error = dsl_pool_user_release(dp, ds->ds_object, ra->htag, tx);
-	VERIFY(error == 0 || error == ENOENT);
-	zapobj = ds->ds_phys->ds_userrefs_obj;
-	VERIFY(0 == zap_remove(mos, zapobj, ra->htag, tx));
-
-	spa_history_log_internal_ds(ds, "release", tx,
-	    "tag = %s refs now = %lld", ra->htag, (longlong_t)refs);
-
-	if (ds->ds_userrefs == 0 && ds->ds_phys->ds_num_children == 1 &&
-	    DS_IS_DEFER_DESTROY(ds)) {
-		struct dsl_ds_destroyarg dsda = {0};
-
-		ASSERT(ra->own);
-		dsda.ds = ds;
-		dsda.releasing = B_TRUE;
-		/* We already did the destroy_check */
-		dsl_dataset_destroy_sync(&dsda, tag, tx);
-	}
-}
-
-static int
-dsl_dataset_user_release_one(const char *dsname, void *arg)
-{
-	struct dsl_ds_holdarg *ha = arg;
-	struct dsl_ds_releasearg *ra;
-	dsl_dataset_t *ds;
-	int error;
-	void *dtag = ha->dstg;
-	char *name;
-	boolean_t own = B_FALSE;
-	boolean_t might_destroy;
-
-	/* alloc a buffer to hold dsname@snapname, plus the terminating NULL */
-	name = kmem_asprintf("%s@%s", dsname, ha->snapname);
-	error = dsl_dataset_hold(name, dtag, &ds);
-	strfree(name);
-	if (error == ENOENT && ha->recursive)
-		return (0);
-	(void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
-	if (error)
-		return (error);
-
-	ha->gotone = B_TRUE;
-
-	ASSERT(dsl_dataset_is_snapshot(ds));
-
-	error = dsl_dataset_release_might_destroy(ds, ha->htag, &might_destroy);
-	if (error) {
-		dsl_dataset_rele(ds, dtag);
-		return (error);
-	}
-
-	if (might_destroy) {
-#ifdef _KERNEL
-		name = kmem_asprintf("%s@%s", dsname, ha->snapname);
-		error = zfs_unmount_snap(name, NULL);
-		strfree(name);
-		if (error) {
-			dsl_dataset_rele(ds, dtag);
-			return (error);
-		}
-#endif
-		if (!dsl_dataset_tryown(ds, B_TRUE, dtag)) {
-			dsl_dataset_rele(ds, dtag);
-			return (EBUSY);
-		} else {
-			own = B_TRUE;
-			dsl_dataset_make_exclusive(ds, dtag);
-		}
-	}
-
-	ra = kmem_alloc(sizeof (struct dsl_ds_releasearg), KM_SLEEP);
-	ra->ds = ds;
-	ra->htag = ha->htag;
-	ra->own = own;
-	dsl_sync_task_create(ha->dstg, dsl_dataset_user_release_check,
-	    dsl_dataset_user_release_sync, ra, dtag, 0);
-
-	return (0);
-}
-
-int
-dsl_dataset_user_release(char *dsname, char *snapname, char *htag,
-    boolean_t recursive)
-{
-	struct dsl_ds_holdarg *ha;
-	dsl_sync_task_t *dst;
-	spa_t *spa;
-	int error;
-
-top:
-	ha = kmem_zalloc(sizeof (struct dsl_ds_holdarg), KM_SLEEP);
-
-	(void) strlcpy(ha->failed, dsname, sizeof (ha->failed));
-
-	error = spa_open(dsname, &spa, FTAG);
-	if (error) {
-		kmem_free(ha, sizeof (struct dsl_ds_holdarg));
-		return (error);
-	}
-
-	ha->dstg = dsl_sync_task_group_create(spa_get_dsl(spa));
-	ha->htag = htag;
-	ha->snapname = snapname;
-	ha->recursive = recursive;
-	if (recursive) {
-		error = dmu_objset_find(dsname, dsl_dataset_user_release_one,
-		    ha, DS_FIND_CHILDREN);
-	} else {
-		error = dsl_dataset_user_release_one(dsname, ha);
-	}
-	if (error == 0)
-		error = dsl_sync_task_group_wait(ha->dstg);
-
-	for (dst = list_head(&ha->dstg->dstg_tasks); dst;
-	    dst = list_next(&ha->dstg->dstg_tasks, dst)) {
-		struct dsl_ds_releasearg *ra = dst->dst_arg1;
-		dsl_dataset_t *ds = ra->ds;
-
-		if (dst->dst_err)
-			dsl_dataset_name(ds, ha->failed);
-
-		if (ra->own)
-			dsl_dataset_disown(ds, ha->dstg);
-		else
-			dsl_dataset_rele(ds, ha->dstg);
-
-		kmem_free(ra, sizeof (struct dsl_ds_releasearg));
-	}
-
-	if (error == 0 && recursive && !ha->gotone)
-		error = ENOENT;
-
-	if (error && error != EBUSY)
-		(void) strlcpy(dsname, ha->failed, sizeof (ha->failed));
-
-	dsl_sync_task_group_destroy(ha->dstg);
-	kmem_free(ha, sizeof (struct dsl_ds_holdarg));
-	spa_close(spa, FTAG);
-
-	/*
-	 * We can get EBUSY if we were racing with deferred destroy and
-	 * dsl_dataset_user_release_check() hadn't done the necessary
-	 * open context setup.  We can also get EBUSY if we're racing
-	 * with destroy and that thread is the ds_owner.  Either way
-	 * the busy condition should be transient, and we should retry
-	 * the release operation.
-	 */
-	if (error == EBUSY)
-		goto top;
-
-	return (error);
-}
-
-/*
- * Called at spa_load time (with retry == B_FALSE) to release a stale
- * temporary user hold. Also called by the onexit code (with retry == B_TRUE).
- */
-int
-dsl_dataset_user_release_tmp(dsl_pool_t *dp, uint64_t dsobj, char *htag,
-    boolean_t retry)
-{
-	dsl_dataset_t *ds;
-	char *snap;
-	char *name;
-	int namelen;
-	int error;
-
-	do {
-		rw_enter(&dp->dp_config_rwlock, RW_READER);
-		error = dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds);
-		rw_exit(&dp->dp_config_rwlock);
-		if (error)
-			return (error);
-		namelen = dsl_dataset_namelen(ds)+1;
-		name = kmem_alloc(namelen, KM_SLEEP);
-		dsl_dataset_name(ds, name);
-		dsl_dataset_rele(ds, FTAG);
-
-		snap = strchr(name, '@');
-		*snap = '\0';
-		++snap;
-		error = dsl_dataset_user_release(name, snap, htag, B_FALSE);
-		kmem_free(name, namelen);
-
-		/*
-		 * The object can't have been destroyed because we have a hold,
-		 * but it might have been renamed, resulting in ENOENT.  Retry
-		 * if we've been requested to do so.
-		 *
-		 * It would be nice if we could use the dsobj all the way
-		 * through and avoid ENOENT entirely.  But we might need to
-		 * unmount the snapshot, and there's currently no way to lookup
-		 * a vfsp using a ZFS object id.
-		 */
-	} while ((error == ENOENT) && retry);
-
-	return (error);
-}
-
-int
-dsl_dataset_get_holds(const char *dsname, nvlist_t **nvp)
-{
-	dsl_dataset_t *ds;
-	int err;
-
-	err = dsl_dataset_hold(dsname, FTAG, &ds);
-	if (err)
-		return (err);
-
-	VERIFY(0 == nvlist_alloc(nvp, NV_UNIQUE_NAME, KM_SLEEP));
-	if (ds->ds_phys->ds_userrefs_obj != 0) {
-		zap_attribute_t *za;
-		zap_cursor_t zc;
-
-		za = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
-		for (zap_cursor_init(&zc, ds->ds_dir->dd_pool->dp_meta_objset,
-		    ds->ds_phys->ds_userrefs_obj);
-		    zap_cursor_retrieve(&zc, za) == 0;
-		    zap_cursor_advance(&zc)) {
-			VERIFY(0 == nvlist_add_uint64(*nvp, za->za_name,
-			    za->za_first_integer));
-		}
-		zap_cursor_fini(&zc);
-		kmem_free(za, sizeof (zap_attribute_t));
-	}
+	VERIFY0(dsl_dataset_hold(dp, ddsqra->ddsqra_name, FTAG, &ds));
+	dsl_dataset_set_refreservation_sync_impl(ds,
+	    ddsqra->ddsqra_source, ddsqra->ddsqra_value, tx);
 	dsl_dataset_rele(ds, FTAG);
-	return (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)
+dsl_dataset_set_refreservation(const char *dsname, zprop_source_t source,
+    uint64_t refreservation)
 {
-	dsl_dataset_t *ds;
+	dsl_dataset_set_qr_arg_t ddsqra;
 
-	if (dsl_dataset_own(dsname, B_TRUE, FTAG, &ds) == 0) {
-		if (DS_IS_INCONSISTENT(ds))
-			(void) dsl_dataset_destroy(ds, FTAG, B_FALSE);
-		else
-			dsl_dataset_disown(ds, FTAG);
-	}
-	return (0);
+	ddsqra.ddsqra_name = dsname;
+	ddsqra.ddsqra_source = source;
+	ddsqra.ddsqra_value = refreservation;
+
+	return (dsl_sync_task(dsname, dsl_dataset_set_refreservation_check,
+	    dsl_dataset_set_refreservation_sync, &ddsqra, 0));
 }
 
 /*
@@ -4227,6 +2831,8 @@ dsl_dataset_space_written(dsl_dataset_t *oldsnap, dsl_dataset_t *new,
 	uint64_t snapobj;
 	dsl_pool_t *dp = new->ds_dir->dd_pool;
 
+	ASSERT(dsl_pool_config_held(dp));
+
 	*usedp = 0;
 	*usedp += new->ds_phys->ds_referenced_bytes;
 	*usedp -= oldsnap->ds_phys->ds_referenced_bytes;
@@ -4239,7 +2845,6 @@ dsl_dataset_space_written(dsl_dataset_t *oldsnap, dsl_dataset_t *new,
 	*uncompp += new->ds_phys->ds_uncompressed_bytes;
 	*uncompp -= oldsnap->ds_phys->ds_uncompressed_bytes;
 
-	rw_enter(&dp->dp_config_rwlock, RW_READER);
 	snapobj = new->ds_object;
 	while (snapobj != oldsnap->ds_object) {
 		dsl_dataset_t *snap;
@@ -4288,7 +2893,6 @@ dsl_dataset_space_written(dsl_dataset_t *oldsnap, dsl_dataset_t *new,
 		}
 
 	}
-	rw_exit(&dp->dp_config_rwlock);
 	return (err);
 }
 
@@ -4330,7 +2934,6 @@ dsl_dataset_space_wouldfree(dsl_dataset_t *firstsnap,
 
 	*usedp = *compp = *uncompp = 0;
 
-	rw_enter(&dp->dp_config_rwlock, RW_READER);
 	snapobj = lastsnap->ds_phys->ds_next_snap_obj;
 	while (snapobj != firstsnap->ds_object) {
 		dsl_dataset_t *ds;
@@ -4351,6 +2954,42 @@ dsl_dataset_space_wouldfree(dsl_dataset_t *firstsnap,
 		ASSERT3U(snapobj, !=, 0);
 		dsl_dataset_rele(ds, FTAG);
 	}
-	rw_exit(&dp->dp_config_rwlock);
 	return (err);
 }
+
+/*
+ * Return TRUE if 'earlier' is an earlier snapshot in 'later's timeline.
+ * For example, they could both be snapshots of the same filesystem, and
+ * 'earlier' is before 'later'.  Or 'earlier' could be the origin of
+ * 'later's filesystem.  Or 'earlier' could be an older snapshot in the origin's
+ * filesystem.  Or 'earlier' could be the origin's origin.
+ */
+boolean_t
+dsl_dataset_is_before(dsl_dataset_t *later, dsl_dataset_t *earlier)
+{
+	dsl_pool_t *dp = later->ds_dir->dd_pool;
+	int error;
+	boolean_t ret;
+
+	ASSERT(dsl_pool_config_held(dp));
+
+	if (earlier->ds_phys->ds_creation_txg >=
+	    later->ds_phys->ds_creation_txg)
+		return (B_FALSE);
+
+	if (later->ds_dir == earlier->ds_dir)
+		return (B_TRUE);
+	if (!dsl_dir_is_clone(later->ds_dir))
+		return (B_FALSE);
+
+	if (later->ds_dir->dd_phys->dd_origin_obj == earlier->ds_object)
+		return (B_TRUE);
+	dsl_dataset_t *origin;
+	error = dsl_dataset_hold_obj(dp,
+	    later->ds_dir->dd_phys->dd_origin_obj, FTAG, &origin);
+	if (error != 0)
+		return (B_FALSE);
+	ret = dsl_dataset_is_before(origin, earlier);
+	dsl_dataset_rele(origin, FTAG);
+	return (ret);
+}