diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
index 5eecc23f891e..aad00863f814 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
@@ -1489,10 +1489,18 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
 	 * objects may be dirtied in syncing context, but only if they
 	 * were already pre-dirtied in open context.
 	 */
+#ifdef DEBUG
+	if (dn->dn_objset->os_dsl_dataset != NULL) {
+		rrw_enter(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock,
+		    RW_READER, FTAG);
+	}
 	ASSERT(!dmu_tx_is_syncing(tx) ||
 	    BP_IS_HOLE(dn->dn_objset->os_rootbp) ||
 	    DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
 	    dn->dn_objset->os_dsl_dataset == NULL);
+	if (dn->dn_objset->os_dsl_dataset != NULL)
+		rrw_exit(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock, FTAG);
+#endif
 	/*
 	 * We make this assert for private objects as well, but after we
 	 * check if we're already dirty.  They are allowed to re-dirty
@@ -1517,12 +1525,21 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
 	 * Don't set dirtyctx to SYNC if we're just modifying this as we
 	 * initialize the objset.
 	 */
-	if (dn->dn_dirtyctx == DN_UNDIRTIED &&
-	    !BP_IS_HOLE(dn->dn_objset->os_rootbp)) {
-		dn->dn_dirtyctx =
-		    (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN);
-		ASSERT(dn->dn_dirtyctx_firstset == NULL);
-		dn->dn_dirtyctx_firstset = kmem_alloc(1, KM_SLEEP);
+	if (dn->dn_dirtyctx == DN_UNDIRTIED) {
+		if (dn->dn_objset->os_dsl_dataset != NULL) {
+			rrw_enter(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock,
+			    RW_READER, FTAG);
+		}
+		if (!BP_IS_HOLE(dn->dn_objset->os_rootbp)) {
+			dn->dn_dirtyctx = (dmu_tx_is_syncing(tx) ?
+			    DN_DIRTY_SYNC : DN_DIRTY_OPEN);
+			ASSERT(dn->dn_dirtyctx_firstset == NULL);
+			dn->dn_dirtyctx_firstset = kmem_alloc(1, KM_SLEEP);
+		}
+		if (dn->dn_objset->os_dsl_dataset != NULL) {
+			rrw_exit(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock,
+			    FTAG);
+		}
 	}
 	mutex_exit(&dn->dn_mtx);
 
@@ -1567,8 +1584,14 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
 	 * this assertion only if we're not already dirty.
 	 */
 	os = dn->dn_objset;
+#ifdef DEBUG
+	if (dn->dn_objset->os_dsl_dataset != NULL)
+		rrw_enter(&os->os_dsl_dataset->ds_bp_rwlock, RW_READER, FTAG);
 	ASSERT(!dmu_tx_is_syncing(tx) || DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
 	    os->os_dsl_dataset == NULL || BP_IS_HOLE(os->os_rootbp));
+	if (dn->dn_objset->os_dsl_dataset != NULL)
+		rrw_exit(&os->os_dsl_dataset->ds_bp_rwlock, FTAG);
+#endif
 	ASSERT(db->db.db_size != 0);
 
 	dprintf_dbuf(db, "size=%llx\n", (u_longlong_t)db->db.db_size);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
index b6ae9680ca6e..f31ad2fe8f70 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
@@ -489,8 +489,10 @@ dmu_objset_from_ds(dsl_dataset_t *ds, objset_t **osp)
 	mutex_enter(&ds->ds_opening_lock);
 	if (ds->ds_objset == NULL) {
 		objset_t *os;
+		rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 		err = dmu_objset_open_impl(dsl_dataset_get_spa(ds),
 		    ds, dsl_dataset_get_blkptr(ds), &os);
+		rrw_exit(&ds->ds_bp_rwlock, FTAG);
 
 		if (err == 0) {
 			mutex_enter(&ds->ds_lock);
@@ -876,9 +878,11 @@ dmu_objset_create_sync(void *arg, dmu_tx_t *tx)
 	    doca->doca_cred, tx);
 
 	VERIFY0(dsl_dataset_hold_obj(pdd->dd_pool, obj, FTAG, &ds));
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	bp = dsl_dataset_get_blkptr(ds);
 	os = dmu_objset_create_impl(pdd->dd_pool->dp_spa,
 	    ds, bp, doca->doca_type, tx);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 
 	if (doca->doca_userfunc != NULL) {
 		doca->doca_userfunc(os, doca->doca_userarg,
@@ -1051,7 +1055,6 @@ dmu_objset_write_ready(zio_t *zio, arc_buf_t *abuf, void *arg)
 	dnode_phys_t *dnp = &os->os_phys->os_meta_dnode;
 
 	ASSERT(!BP_IS_EMBEDDED(bp));
-	ASSERT3P(bp, ==, os->os_rootbp);
 	ASSERT3U(BP_GET_TYPE(bp), ==, DMU_OT_OBJSET);
 	ASSERT0(BP_GET_LEVEL(bp));
 
@@ -1064,6 +1067,11 @@ dmu_objset_write_ready(zio_t *zio, arc_buf_t *abuf, void *arg)
 	bp->blk_fill = 0;
 	for (int i = 0; i < dnp->dn_nblkptr; i++)
 		bp->blk_fill += BP_GET_FILL(&dnp->dn_blkptr[i]);
+	if (os->os_dsl_dataset != NULL)
+		rrw_enter(&os->os_dsl_dataset->ds_bp_rwlock, RW_WRITER, FTAG);
+	*os->os_rootbp = *bp;
+	if (os->os_dsl_dataset != NULL)
+		rrw_exit(&os->os_dsl_dataset->ds_bp_rwlock, FTAG);
 }
 
 /* ARGSUSED */
@@ -1083,6 +1091,7 @@ dmu_objset_write_done(zio_t *zio, arc_buf_t *abuf, void *arg)
 		(void) dsl_dataset_block_kill(ds, bp_orig, tx, B_TRUE);
 		dsl_dataset_block_born(ds, bp, tx);
 	}
+	kmem_free(bp, sizeof (*bp));
 }
 
 /* called from dsl */
@@ -1096,6 +1105,8 @@ dmu_objset_sync(objset_t *os, zio_t *pio, dmu_tx_t *tx)
 	list_t *list;
 	list_t *newlist = NULL;
 	dbuf_dirty_record_t *dr;
+	blkptr_t *blkptr_copy = kmem_alloc(sizeof (*os->os_rootbp), KM_SLEEP);
+	*blkptr_copy = *os->os_rootbp;
 
 	dprintf_ds(os->os_dsl_dataset, "txg=%llu\n", tx->tx_txg);
 
@@ -1123,7 +1134,7 @@ dmu_objset_sync(objset_t *os, zio_t *pio, dmu_tx_t *tx)
 	dmu_write_policy(os, NULL, 0, 0, &zp);
 
 	zio = arc_write(pio, os->os_spa, tx->tx_txg,
-	    os->os_rootbp, os->os_phys_buf, DMU_OS_IS_L2CACHEABLE(os),
+	    blkptr_copy, os->os_phys_buf, DMU_OS_IS_L2CACHEABLE(os),
 	    &zp, dmu_objset_write_ready, NULL, NULL, dmu_objset_write_done,
 	    os, ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
index 21ea6efec65d..28c6c4859c05 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
@@ -1510,10 +1510,12 @@ dmu_recv_begin_sync(void *arg, dmu_tx_t *tx)
 	 * If we actually created a non-clone, we need to create the
 	 * objset in our new dataset.
 	 */
+	rrw_enter(&newds->ds_bp_rwlock, RW_READER, FTAG);
 	if (BP_IS_HOLE(dsl_dataset_get_blkptr(newds))) {
 		(void) dmu_objset_create_impl(dp->dp_spa,
 		    newds, dsl_dataset_get_blkptr(newds), drrb->drr_type, tx);
 	}
+	rrw_exit(&newds->ds_bp_rwlock, FTAG);
 
 	drba->drba_cookie->drc_ds = newds;
 
@@ -1656,7 +1658,9 @@ dmu_recv_resume_begin_sync(void *arg, dmu_tx_t *tx)
 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
 	dsl_dataset_phys(ds)->ds_flags |= DS_FLAG_INCONSISTENT;
 
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	ASSERT(!BP_IS_HOLE(dsl_dataset_get_blkptr(ds)));
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 
 	drba->drba_cookie->drc_ds = ds;
 
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 eb203feaffe3..3b7131e3cf2d 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
@@ -312,6 +312,7 @@ dsl_dataset_evict(void *dbu)
 	mutex_destroy(&ds->ds_opening_lock);
 	mutex_destroy(&ds->ds_sendstream_lock);
 	refcount_destroy(&ds->ds_longholds);
+	rrw_destroy(&ds->ds_bp_rwlock);
 
 	kmem_free(ds, sizeof (dsl_dataset_t));
 }
@@ -441,6 +442,7 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		mutex_init(&ds->ds_lock, NULL, MUTEX_DEFAULT, NULL);
 		mutex_init(&ds->ds_opening_lock, NULL, MUTEX_DEFAULT, NULL);
 		mutex_init(&ds->ds_sendstream_lock, NULL, MUTEX_DEFAULT, NULL);
+		rrw_init(&ds->ds_bp_rwlock, B_FALSE);
 		refcount_create(&ds->ds_longholds);
 
 		bplist_create(&ds->ds_pending_deadlist);
@@ -831,7 +833,9 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
 		    dsl_dataset_phys(origin)->ds_compressed_bytes;
 		dsphys->ds_uncompressed_bytes =
 		    dsl_dataset_phys(origin)->ds_uncompressed_bytes;
+		rrw_enter(&origin->ds_bp_rwlock, RW_READER, FTAG);
 		dsphys->ds_bp = dsl_dataset_phys(origin)->ds_bp;
+		rrw_exit(&origin->ds_bp_rwlock, FTAG);
 
 		/*
 		 * Inherit flags that describe the dataset's contents
@@ -1389,7 +1393,9 @@ dsl_dataset_snapshot_sync_impl(dsl_dataset_t *ds, const char *snapname,
 	dsphys->ds_uncompressed_bytes =
 	    dsl_dataset_phys(ds)->ds_uncompressed_bytes;
 	dsphys->ds_flags = dsl_dataset_phys(ds)->ds_flags;
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	dsphys->ds_bp = dsl_dataset_phys(ds)->ds_bp;
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 	dmu_buf_rele(dbuf, FTAG);
 
 	for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
@@ -1981,7 +1987,9 @@ dsl_dataset_space(dsl_dataset_t *ds,
 		else
 			*availbytesp = 0;
 	}
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	*usedobjsp = BP_GET_FILL(&dsl_dataset_phys(ds)->ds_bp);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 	*availobjsp = DN_MAX_OBJECT - *usedobjsp;
 }
 
@@ -1989,12 +1997,15 @@ boolean_t
 dsl_dataset_modified_since_snap(dsl_dataset_t *ds, dsl_dataset_t *snap)
 {
 	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	uint64_t birth;
 
 	ASSERT(dsl_pool_config_held(dp));
 	if (snap == NULL)
 		return (B_FALSE);
-	if (dsl_dataset_phys(ds)->ds_bp.blk_birth >
-	    dsl_dataset_phys(snap)->ds_creation_txg) {
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
+	birth = dsl_dataset_get_blkptr(ds)->blk_birth;
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
+	if (birth > dsl_dataset_phys(snap)->ds_creation_txg) {
 		objset_t *os, *os_snap;
 		/*
 		 * It may be that only the ZIL differs, because it was
@@ -3058,11 +3069,15 @@ dsl_dataset_clone_swap_sync_impl(dsl_dataset_t *clone,
 
 	/* swap blkptrs */
 	{
+		rrw_enter(&clone->ds_bp_rwlock, RW_WRITER, FTAG);
+		rrw_enter(&origin_head->ds_bp_rwlock, RW_WRITER, FTAG);
 		blkptr_t tmp;
 		tmp = dsl_dataset_phys(origin_head)->ds_bp;
 		dsl_dataset_phys(origin_head)->ds_bp =
 		    dsl_dataset_phys(clone)->ds_bp;
 		dsl_dataset_phys(clone)->ds_bp = tmp;
+		rrw_exit(&origin_head->ds_bp_rwlock, FTAG);
+		rrw_exit(&clone->ds_bp_rwlock, FTAG);
 	}
 
 	/* set dd_*_bytes */
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c
index b8971761d7a9..09fa5406ec60 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_destroy.c
@@ -246,7 +246,9 @@ dsl_destroy_snapshot_sync_impl(dsl_dataset_t *ds, boolean_t defer, dmu_tx_t *tx)
 	uint64_t obj;
 
 	ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	ASSERT3U(dsl_dataset_phys(ds)->ds_bp.blk_birth, <=, tx->tx_txg);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 	ASSERT(refcount_is_zero(&ds->ds_longholds));
 
 	if (defer &&
@@ -720,7 +722,9 @@ dsl_destroy_head_sync_impl(dsl_dataset_t *ds, dmu_tx_t *tx)
 	ASSERT3U(dsl_dataset_phys(ds)->ds_num_children, <=, 1);
 	ASSERT(ds->ds_prev == NULL ||
 	    dsl_dataset_phys(ds->ds_prev)->ds_next_snap_obj != ds->ds_object);
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	ASSERT3U(dsl_dataset_phys(ds)->ds_bp.blk_birth, <=, tx->tx_txg);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 	ASSERT(RRW_WRITE_HELD(&dp->dp_config_rwlock));
 
 	/* We need to log before removing it from the namespace. */
@@ -812,10 +816,12 @@ dsl_destroy_head_sync_impl(dsl_dataset_t *ds, dmu_tx_t *tx)
 		ASSERT(!DS_UNIQUE_IS_ACCURATE(ds) ||
 		    dsl_dataset_phys(ds)->ds_unique_bytes == used);
 
+		rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 		bptree_add(mos, dp->dp_bptree_obj,
 		    &dsl_dataset_phys(ds)->ds_bp,
 		    dsl_dataset_phys(ds)->ds_prev_snap_txg,
 		    used, comp, uncomp, tx);
+		rrw_exit(&ds->ds_bp_rwlock, FTAG);
 		dsl_dir_diduse_space(ds->ds_dir, DD_USED_HEAD,
 		    -used, -comp, -uncomp, tx);
 		dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c
index 95cf9b75b5e1..9de2d802a00e 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
@@ -493,8 +493,10 @@ dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
 
 	/* create the root objset */
 	VERIFY0(dsl_dataset_hold_obj(dp, obj, FTAG, &ds));
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	os = dmu_objset_create_impl(dp->dp_spa, ds,
 	    dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 #ifdef _KERNEL
 	zfs_create_fs(os, kcred, zplprops, tx);
 #endif
@@ -807,7 +809,9 @@ upgrade_clones_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
 		 * The $ORIGIN can't have any data, or the accounting
 		 * will be wrong.
 		 */
+		rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 		ASSERT0(dsl_dataset_phys(prev)->ds_bp.blk_birth);
+		rrw_exit(&ds->ds_bp_rwlock, FTAG);
 
 		/* The origin doesn't get attached to itself */
 		if (ds->ds_object == prev->ds_object) {
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
index f68a6ba62b3a..4ebbc1a42050 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
@@ -1113,7 +1113,9 @@ dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
 	 * Iterate over the bps in this ds.
 	 */
 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
 	dsl_scan_visit_rootbp(scn, ds, &dsl_dataset_phys(ds)->ds_bp, tx);
+	rrw_exit(&ds->ds_bp_rwlock, FTAG);
 
 	char *dsname = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);
 	dsl_dataset_name(ds, dsname);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu_objset.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu_objset.h
index f05b2cf453f5..977232de453b 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu_objset.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu_objset.h
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
@@ -101,9 +101,14 @@ struct objset {
 	zfs_redundant_metadata_type_t os_redundant_metadata;
 	int os_recordsize;
 
+	/*
+	 * Pointer is constant; the blkptr it points to is protected by
+	 * os_dsl_dataset->ds_bp_rwlock
+	 */
+	blkptr_t *os_rootbp;
+
 	/* no lock needed: */
 	struct dmu_tx *os_synctx; /* XXX sketchy */
-	blkptr_t *os_rootbp;
 	zil_header_t os_zil_header;
 	list_t os_synced_dnodes;
 	uint64_t os_flags;
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
index 54c63b92368e..18466bb405e7 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
@@ -39,6 +39,7 @@
 #include <sys/zfs_context.h>
 #include <sys/dsl_deadlist.h>
 #include <sys/refcount.h>
+#include <sys/rrwlock.h>
 #include <zfeature_common.h>
 
 #ifdef	__cplusplus
@@ -141,6 +142,7 @@ typedef struct dsl_dataset_phys {
 
 typedef struct dsl_dataset {
 	dmu_buf_user_t ds_dbu;
+	rrwlock_t ds_bp_rwlock; /* Protects ds_phys->ds_bp */
 
 	/* Immutable: */
 	struct dsl_dir *ds_dir;