OpenZFS 2605, 6980, 6902

2605 want to resume interrupted zfs send
Reviewed by: George Wilson <[email protected]>
Reviewed by: Paul Dagnelie <[email protected]>
Reviewed by: Richard Elling <[email protected]>
Reviewed by: Xin Li <[email protected]>
Reviewed by: Arne Jansen <[email protected]>
Approved by: Dan McDonald <[email protected]>
Ported-by: kernelOfTruth <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/2605
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/9c3fd12

6980 6902 causes zfs send to break due to 32-bit/64-bit struct mismatch
Reviewed by: Paul Dagnelie <[email protected]>
Reviewed by: George Wilson <[email protected]>
Approved by: Robert Mustacchi <[email protected]>
Ported by: Brian Behlendorf <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/6980
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/ea4a67f

Porting notes:
- All rsend and snapshop tests enabled and updated for Linux.
- Fix misuse of input argument in traverse_visitbp().
- Fix ISO C90 warnings and errors.
- Fix gcc 'missing braces around initializer' in
  'struct send_thread_arg to_arg =' warning.
- Replace 4 argument fletcher_4_native() with 3 argument version,
  this change was made in OpenZFS 4185 which has not been ported.
- Part of the sections for 'zfs receive' and 'zfs send' was
  rewritten and reordered to approximate upstream.
- Fix mktree xattr creation, 'user.' prefix required.
- Minor fixes to newly enabled test cases
- Long holds for volumes allowed during receive for minor registration.

8 files changed, 705 insertions, 115 deletions

diff --git a/module/zcommon/zfs_prop.c b/module/zcommon/zfs_prop.c
index 1dbeab084..1d68ca29e 100644
--- a/module/zcommon/zfs_prop.c
+++ b/module/zcommon/zfs_prop.c
@@ -375,6 +375,10 @@ zfs_prop_init(void)
 	zprop_register_string(ZFS_PROP_SELINUX_ROOTCONTEXT, "rootcontext",
 	    "none", PROP_DEFAULT, ZFS_TYPE_DATASET, "<selinux rootcontext>",
 	    "ROOTCONTEXT");
+	zprop_register_string(ZFS_PROP_RECEIVE_RESUME_TOKEN,
+	    "receive_resume_token",
+	    NULL, PROP_READONLY, ZFS_TYPE_FILESYSTEM | ZFS_TYPE_VOLUME,
+	    "<string token>", "RESUMETOK");
 
 	/* readonly number properties */
 	zprop_register_number(ZFS_PROP_USED, "used", 0, PROP_READONLY,
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c
index cdc897726..a9991aabb 100644
--- a/module/zfs/dmu_objset.c
+++ b/module/zfs/dmu_objset.c
@@ -405,6 +405,17 @@ dmu_objset_open_impl(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
 	 * checksum/compression/copies.
 	 */
 	if (ds != NULL) {
+		boolean_t needlock = B_FALSE;
+
+		/*
+		 * Note: it's valid to open the objset if the dataset is
+		 * long-held, in which case the pool_config lock will not
+		 * be held.
+		 */
+		if (!dsl_pool_config_held(dmu_objset_pool(os))) {
+			needlock = B_TRUE;
+			dsl_pool_config_enter(dmu_objset_pool(os), FTAG);
+		}
 		err = dsl_prop_register(ds,
 		    zfs_prop_to_name(ZFS_PROP_PRIMARYCACHE),
 		    primary_cache_changed_cb, os);
@@ -461,6 +472,8 @@ dmu_objset_open_impl(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
 				    dnodesize_changed_cb, os);
 			}
 		}
+		if (needlock)
+			dsl_pool_config_exit(dmu_objset_pool(os), FTAG);
 		if (err != 0) {
 			VERIFY(arc_buf_remove_ref(os->os_phys_buf,
 			    &os->os_phys_buf));
@@ -520,6 +533,13 @@ dmu_objset_from_ds(dsl_dataset_t *ds, objset_t **osp)
 {
 	int err = 0;
 
+	/*
+	 * We shouldn't be doing anything with dsl_dataset_t's unless the
+	 * pool_config lock is held, or the dataset is long-held.
+	 */
+	ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool) ||
+	    dsl_dataset_long_held(ds));
+
 	mutex_enter(&ds->ds_opening_lock);
 	if (ds->ds_objset == NULL) {
 		objset_t *os;
diff --git a/module/zfs/dmu_send.c b/module/zfs/dmu_send.c
index 901386a5a..1f903c7f3 100644
--- a/module/zfs/dmu_send.c
+++ b/module/zfs/dmu_send.c
@@ -23,6 +23,7 @@
  * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
+ * Copyright 2014 HybridCluster. All rights reserved.
  * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
  * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
@@ -64,12 +65,14 @@ int zfs_send_queue_length = 16 * 1024 * 1024;
 int zfs_recv_queue_length = 16 * 1024 * 1024;
 
 static char *dmu_recv_tag = "dmu_recv_tag";
-static const char *recv_clone_name = "%recv";
+const char *recv_clone_name = "%recv";
 
 #define	BP_SPAN(datablkszsec, indblkshift, level) \
 	(((uint64_t)datablkszsec) << (SPA_MINBLOCKSHIFT + \
 	(level) * (indblkshift - SPA_BLKPTRSHIFT)))
 
+static void byteswap_record(dmu_replay_record_t *drr);
+
 struct send_thread_arg {
 	bqueue_t	q;
 	dsl_dataset_t	*ds;		/* Dataset to traverse */
@@ -77,6 +80,7 @@ struct send_thread_arg {
 	int		flags;		/* flags to pass to traverse_dataset */
 	int		error_code;
 	boolean_t	cancel;
+	zbookmark_phys_t resume;
 };
 
 struct send_block_record {
@@ -99,7 +103,7 @@ dump_bytes_cb(void *arg)
 {
 	dump_bytes_io_t *dbi = (dump_bytes_io_t *)arg;
 	dmu_sendarg_t *dsp = dbi->dbi_dsp;
-	dsl_dataset_t *ds = dsp->dsa_os->os_dsl_dataset;
+	dsl_dataset_t *ds = dmu_objset_ds(dsp->dsa_os);
 	ssize_t resid; /* have to get resid to get detailed errno */
 	ASSERT0(dbi->dbi_len % 8);
 
@@ -180,7 +184,7 @@ dump_free(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
 	 * that the receiving system doesn't have any dbufs in the range
 	 * being freed.  This is always true because there is a one-record
 	 * constraint: we only send one WRITE record for any given
-	 * object+offset.  We know that the one-record constraint is
+	 * object,offset.  We know that the one-record constraint is
 	 * true because we always send data in increasing order by
 	 * object,offset.
 	 *
@@ -428,6 +432,19 @@ dump_dnode(dmu_sendarg_t *dsp, uint64_t object, dnode_phys_t *dnp)
 {
 	struct drr_object *drro = &(dsp->dsa_drr->drr_u.drr_object);
 
+	if (object < dsp->dsa_resume_object) {
+		/*
+		 * Note: when resuming, we will visit all the dnodes in
+		 * the block of dnodes that we are resuming from.  In
+		 * this case it's unnecessary to send the dnodes prior to
+		 * the one we are resuming from.  We should be at most one
+		 * block's worth of dnodes behind the resume point.
+		 */
+		ASSERT3U(dsp->dsa_resume_object - object, <,
+		    1 << (DNODE_BLOCK_SHIFT - DNODE_SHIFT));
+		return (0);
+	}
+
 	if (dnp == NULL || dnp->dn_type == DMU_OT_NONE)
 		return (dump_freeobjects(dsp, object, 1));
 
@@ -509,6 +526,9 @@ send_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	uint64_t record_size;
 	int err = 0;
 
+	ASSERT(zb->zb_object == DMU_META_DNODE_OBJECT ||
+	    zb->zb_object >= sta->resume.zb_object);
+
 	if (sta->cancel)
 		return (SET_ERROR(EINTR));
 
@@ -545,8 +565,10 @@ send_traverse_thread(void *arg)
 	struct send_block_record *data;
 
 	if (st_arg->ds != NULL) {
-		err = traverse_dataset(st_arg->ds, st_arg->fromtxg,
-		    st_arg->flags, send_cb, arg);
+		err = traverse_dataset_resume(st_arg->ds,
+		    st_arg->fromtxg, &st_arg->resume,
+		    st_arg->flags, send_cb, st_arg);
+
 		if (err != EINTR)
 			st_arg->error_code = err;
 	}
@@ -575,6 +597,9 @@ do_dump(dmu_sendarg_t *dsa, struct send_block_record *data)
 
 	ASSERT3U(zb->zb_level, >=, 0);
 
+	ASSERT(zb->zb_object == DMU_META_DNODE_OBJECT ||
+	    zb->zb_object >= dsa->dsa_resume_object);
+
 	if (zb->zb_object != DMU_META_DNODE_OBJECT &&
 	    DMU_OBJECT_IS_SPECIAL(zb->zb_object)) {
 		return (0);
@@ -637,6 +662,10 @@ do_dump(dmu_sendarg_t *dsa, struct send_block_record *data)
 		uint64_t offset;
 
 		ASSERT0(zb->zb_level);
+		ASSERT(zb->zb_object > dsa->dsa_resume_object ||
+		    (zb->zb_object == dsa->dsa_resume_object &&
+		    zb->zb_blkid * blksz >= dsa->dsa_resume_offset));
+
 		if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
 		    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
 		    &aflags, zb) != 0) {
@@ -697,8 +726,10 @@ get_next_record(bqueue_t *bq, struct send_block_record *data)
  */
 static int
 dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
-    zfs_bookmark_phys_t *ancestor_zb, boolean_t is_clone, boolean_t embedok,
-    boolean_t large_block_ok, int outfd, vnode_t *vp, offset_t *off)
+    zfs_bookmark_phys_t *ancestor_zb,
+    boolean_t is_clone, boolean_t embedok, boolean_t large_block_ok, int outfd,
+    uint64_t resumeobj, uint64_t resumeoff,
+    vnode_t *vp, offset_t *off)
 {
 	objset_t *os;
 	dmu_replay_record_t *drr;
@@ -707,6 +738,8 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 	uint64_t fromtxg = 0;
 	uint64_t featureflags = 0;
 	struct send_thread_arg to_arg;
+	void *payload = NULL;
+	size_t payload_len = 0;
 	struct send_block_record *to_data;
 
 	err = dmu_objset_from_ds(to_ds, &os);
@@ -721,6 +754,8 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 	DMU_SET_STREAM_HDRTYPE(drr->drr_u.drr_begin.drr_versioninfo,
 	    DMU_SUBSTREAM);
 
+	bzero(&to_arg, sizeof (to_arg));
+
 #ifdef _KERNEL
 	if (dmu_objset_type(os) == DMU_OST_ZFS) {
 		uint64_t version;
@@ -746,6 +781,10 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 			featureflags |= DMU_BACKUP_FEATURE_EMBED_DATA_LZ4;
 	}
 
+	if (resumeobj != 0 || resumeoff != 0) {
+		featureflags |= DMU_BACKUP_FEATURE_RESUMING;
+	}
+
 	DMU_SET_FEATUREFLAGS(drr->drr_u.drr_begin.drr_versioninfo,
 	    featureflags);
 
@@ -781,6 +820,8 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 	dsp->dsa_pending_op = PENDING_NONE;
 	dsp->dsa_incremental = (ancestor_zb != NULL);
 	dsp->dsa_featureflags = featureflags;
+	dsp->dsa_resume_object = resumeobj;
+	dsp->dsa_resume_offset = resumeoff;
 
 	mutex_enter(&to_ds->ds_sendstream_lock);
 	list_insert_head(&to_ds->ds_sendstreams, dsp);
@@ -789,7 +830,26 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 	dsl_dataset_long_hold(to_ds, FTAG);
 	dsl_pool_rele(dp, tag);
 
-	if (dump_record(dsp, NULL, 0) != 0) {
+	if (resumeobj != 0 || resumeoff != 0) {
+		dmu_object_info_t to_doi;
+		nvlist_t *nvl;
+		err = dmu_object_info(os, resumeobj, &to_doi);
+		if (err != 0)
+			goto out;
+		SET_BOOKMARK(&to_arg.resume, to_ds->ds_object, resumeobj, 0,
+		    resumeoff / to_doi.doi_data_block_size);
+
+		nvl = fnvlist_alloc();
+		fnvlist_add_uint64(nvl, "resume_object", resumeobj);
+		fnvlist_add_uint64(nvl, "resume_offset", resumeoff);
+		payload = fnvlist_pack(nvl, &payload_len);
+		drr->drr_payloadlen = payload_len;
+		fnvlist_free(nvl);
+	}
+
+	err = dump_record(dsp, payload, payload_len);
+	fnvlist_pack_free(payload, payload_len);
+	if (err != 0) {
 		err = dsp->dsa_err;
 		goto out;
 	}
@@ -899,19 +959,19 @@ dmu_send_obj(const char *pool, uint64_t tosnap, uint64_t fromsnap,
 		is_clone = (fromds->ds_dir != ds->ds_dir);
 		dsl_dataset_rele(fromds, FTAG);
 		err = dmu_send_impl(FTAG, dp, ds, &zb, is_clone,
-		    embedok, large_block_ok, outfd, vp, off);
+		    embedok, large_block_ok, outfd, 0, 0, vp, off);
 	} else {
 		err = dmu_send_impl(FTAG, dp, ds, NULL, B_FALSE,
-		    embedok, large_block_ok, outfd, vp, off);
+		    embedok, large_block_ok, outfd, 0, 0, vp, off);
 	}
 	dsl_dataset_rele(ds, FTAG);
 	return (err);
 }
 
 int
-dmu_send(const char *tosnap, const char *fromsnap,
-    boolean_t embedok, boolean_t large_block_ok,
-    int outfd, vnode_t *vp, offset_t *off)
+dmu_send(const char *tosnap, const char *fromsnap, boolean_t embedok,
+    boolean_t large_block_ok, int outfd, uint64_t resumeobj, uint64_t resumeoff,
+    vnode_t *vp, offset_t *off)
 {
 	dsl_pool_t *dp;
 	dsl_dataset_t *ds;
@@ -978,10 +1038,12 @@ dmu_send(const char *tosnap, const char *fromsnap,
 			return (err);
 		}
 		err = dmu_send_impl(FTAG, dp, ds, &zb, is_clone,
-		    embedok, large_block_ok, outfd, vp, off);
+		    embedok, large_block_ok,
+		    outfd, resumeobj, resumeoff, vp, off);
 	} else {
 		err = dmu_send_impl(FTAG, dp, ds, NULL, B_FALSE,
-		    embedok, large_block_ok, outfd, vp, off);
+		    embedok, large_block_ok,
+		    outfd, resumeobj, resumeoff, vp, off);
 	}
 	if (owned)
 		dsl_dataset_disown(ds, FTAG);
@@ -1221,6 +1283,7 @@ dmu_recv_begin_check(void *arg, dmu_tx_t *tx)
 
 	/* already checked */
 	ASSERT3U(drrb->drr_magic, ==, DMU_BACKUP_MAGIC);
+	ASSERT(!(featureflags & DMU_BACKUP_FEATURE_RESUMING));
 
 	if (DMU_GET_STREAM_HDRTYPE(drrb->drr_versioninfo) ==
 	    DMU_COMPOUNDSTREAM ||
@@ -1233,6 +1296,10 @@ dmu_recv_begin_check(void *arg, dmu_tx_t *tx)
 	    spa_version(dp->dp_spa) < SPA_VERSION_SA)
 		return (SET_ERROR(ENOTSUP));
 
+	if (drba->drba_cookie->drc_resumable &&
+	    !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_EXTENSIBLE_DATASET))
+		return (SET_ERROR(ENOTSUP));
+
 	/*
 	 * The receiving code doesn't know how to translate a WRITE_EMBEDDED
 	 * record to a plan WRITE record, so the pool must have the
@@ -1345,15 +1412,16 @@ dmu_recv_begin_sync(void *arg, dmu_tx_t *tx)
 {
 	dmu_recv_begin_arg_t *drba = arg;
 	dsl_pool_t *dp = dmu_tx_pool(tx);
+	objset_t *mos = dp->dp_meta_objset;
 	struct drr_begin *drrb = drba->drba_cookie->drc_drrb;
 	const char *tofs = drba->drba_cookie->drc_tofs;
 	dsl_dataset_t *ds, *newds;
 	uint64_t dsobj;
 	int error;
-	uint64_t crflags;
+	uint64_t crflags = 0;
 
-	crflags = (drrb->drr_flags & DRR_FLAG_CI_DATA) ?
-	    DS_FLAG_CI_DATASET : 0;
+	if (drrb->drr_flags & DRR_FLAG_CI_DATA)
+		crflags |= DS_FLAG_CI_DATASET;
 
 	error = dsl_dataset_hold(dp, tofs, FTAG, &ds);
 	if (error == 0) {
@@ -1391,6 +1459,32 @@ dmu_recv_begin_sync(void *arg, dmu_tx_t *tx)
 	}
 	VERIFY0(dsl_dataset_own_obj(dp, dsobj, dmu_recv_tag, &newds));
 
+	if (drba->drba_cookie->drc_resumable) {
+		uint64_t one = 1;
+		uint64_t zero = 0;
+
+		dsl_dataset_zapify(newds, tx);
+		if (drrb->drr_fromguid != 0) {
+			VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_FROMGUID,
+			    8, 1, &drrb->drr_fromguid, tx));
+		}
+		VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_TOGUID,
+		    8, 1, &drrb->drr_toguid, tx));
+		VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_TONAME,
+		    1, strlen(drrb->drr_toname) + 1, drrb->drr_toname, tx));
+		VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_OBJECT,
+		    8, 1, &one, tx));
+		VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_OFFSET,
+		    8, 1, &zero, tx));
+		VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_BYTES,
+		    8, 1, &zero, tx));
+		if (DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo) &
+		    DMU_BACKUP_FEATURE_EMBED_DATA) {
+			VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_EMBEDOK,
+			    8, 1, &one, tx));
+		}
+	}
+
 	dmu_buf_will_dirty(newds->ds_dbuf, tx);
 	dsl_dataset_phys(newds)->ds_flags |= DS_FLAG_INCONSISTENT;
 
@@ -1408,56 +1502,191 @@ dmu_recv_begin_sync(void *arg, dmu_tx_t *tx)
 	spa_history_log_internal_ds(newds, "receive", tx, "");
 }
 
+static int
+dmu_recv_resume_begin_check(void *arg, dmu_tx_t *tx)
+{
+	dmu_recv_begin_arg_t *drba = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	struct drr_begin *drrb = drba->drba_cookie->drc_drrb;
+	int error;
+	uint64_t featureflags = DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo);
+	dsl_dataset_t *ds;
+	const char *tofs = drba->drba_cookie->drc_tofs;
+	char recvname[ZFS_MAXNAMELEN];
+	uint64_t val;
+
+	/* already checked */
+	ASSERT3U(drrb->drr_magic, ==, DMU_BACKUP_MAGIC);
+	ASSERT(featureflags & DMU_BACKUP_FEATURE_RESUMING);
+
+	if (DMU_GET_STREAM_HDRTYPE(drrb->drr_versioninfo) ==
+	    DMU_COMPOUNDSTREAM ||
+	    drrb->drr_type >= DMU_OST_NUMTYPES)
+		return (SET_ERROR(EINVAL));
+
+	/* Verify pool version supports SA if SA_SPILL feature set */
+	if ((featureflags & DMU_BACKUP_FEATURE_SA_SPILL) &&
+	    spa_version(dp->dp_spa) < SPA_VERSION_SA)
+		return (SET_ERROR(ENOTSUP));
+
+	/*
+	 * The receiving code doesn't know how to translate a WRITE_EMBEDDED
+	 * record to a plain WRITE record, so the pool must have the
+	 * EMBEDDED_DATA feature enabled if the stream has WRITE_EMBEDDED
+	 * records.  Same with WRITE_EMBEDDED records that use LZ4 compression.
+	 */
+	if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA) &&
+	    !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_EMBEDDED_DATA))
+		return (SET_ERROR(ENOTSUP));
+	if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA_LZ4) &&
+	    !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS))
+		return (SET_ERROR(ENOTSUP));
+
+	(void) snprintf(recvname, sizeof (recvname), "%s/%s",
+	    tofs, recv_clone_name);
+
+	if (dsl_dataset_hold(dp, recvname, FTAG, &ds) != 0) {
+		/* %recv does not exist; continue in tofs */
+		error = dsl_dataset_hold(dp, tofs, FTAG, &ds);
+		if (error != 0)
+			return (error);
+	}
+
+	/* check that ds is marked inconsistent */
+	if (!DS_IS_INCONSISTENT(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EINVAL));
+	}
+
+	/* check that there is resuming data, and that the toguid matches */
+	if (!dsl_dataset_is_zapified(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EINVAL));
+	}
+	error = zap_lookup(dp->dp_meta_objset, ds->ds_object,
+	    DS_FIELD_RESUME_TOGUID, sizeof (val), 1, &val);
+	if (error != 0 || drrb->drr_toguid != val) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EINVAL));
+	}
+
+	/*
+	 * Check if the receive is still running.  If so, it will be owned.
+	 * Note that nothing else can own the dataset (e.g. after the receive
+	 * fails) because it will be marked inconsistent.
+	 */
+	if (dsl_dataset_has_owner(ds)) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EBUSY));
+	}
+
+	/* There should not be any snapshots of this fs yet. */
+	if (ds->ds_prev != NULL && ds->ds_prev->ds_dir == ds->ds_dir) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EINVAL));
+	}
+
+	/*
+	 * Note: resume point will be checked when we process the first WRITE
+	 * record.
+	 */
+
+	/* check that the origin matches */
+	val = 0;
+	(void) zap_lookup(dp->dp_meta_objset, ds->ds_object,
+	    DS_FIELD_RESUME_FROMGUID, sizeof (val), 1, &val);
+	if (drrb->drr_fromguid != val) {
+		dsl_dataset_rele(ds, FTAG);
+		return (SET_ERROR(EINVAL));
+	}
+
+	dsl_dataset_rele(ds, FTAG);
+	return (0);
+}
+
+static void
+dmu_recv_resume_begin_sync(void *arg, dmu_tx_t *tx)
+{
+	dmu_recv_begin_arg_t *drba = arg;
+	dsl_pool_t *dp = dmu_tx_pool(tx);
+	const char *tofs = drba->drba_cookie->drc_tofs;
+	dsl_dataset_t *ds;
+	uint64_t dsobj;
+	char recvname[ZFS_MAXNAMELEN];
+
+	(void) snprintf(recvname, sizeof (recvname), "%s/%s",
+	    tofs, recv_clone_name);
+
+	if (dsl_dataset_hold(dp, recvname, FTAG, &ds) != 0) {
+		/* %recv does not exist; continue in tofs */
+		VERIFY0(dsl_dataset_hold(dp, tofs, FTAG, &ds));
+		drba->drba_cookie->drc_newfs = B_TRUE;
+	}
+
+	/* clear the inconsistent flag so that we can own it */
+	ASSERT(DS_IS_INCONSISTENT(ds));
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	dsl_dataset_phys(ds)->ds_flags &= ~DS_FLAG_INCONSISTENT;
+	dsobj = ds->ds_object;
+	dsl_dataset_rele(ds, FTAG);
+
+	VERIFY0(dsl_dataset_own_obj(dp, dsobj, dmu_recv_tag, &ds));
+
+	dmu_buf_will_dirty(ds->ds_dbuf, tx);
+	dsl_dataset_phys(ds)->ds_flags |= DS_FLAG_INCONSISTENT;
+
+	ASSERT(!BP_IS_HOLE(dsl_dataset_get_blkptr(ds)));
+
+	drba->drba_cookie->drc_ds = ds;
+
+	spa_history_log_internal_ds(ds, "resume receive", tx, "");
+}
+
 /*
  * NB: callers *MUST* call dmu_recv_stream() if dmu_recv_begin()
  * succeeds; otherwise we will leak the holds on the datasets.
  */
 int
-dmu_recv_begin(char *tofs, char *tosnap, struct drr_begin *drrb,
-    boolean_t force, char *origin, dmu_recv_cookie_t *drc)
+dmu_recv_begin(char *tofs, char *tosnap, dmu_replay_record_t *drr_begin,
+    boolean_t force, boolean_t resumable, char *origin, dmu_recv_cookie_t *drc)
 {
 	dmu_recv_begin_arg_t drba = { 0 };
-	dmu_replay_record_t *drr;
 
 	bzero(drc, sizeof (dmu_recv_cookie_t));
-	drc->drc_drrb = drrb;
+	drc->drc_drr_begin = drr_begin;
+	drc->drc_drrb = &drr_begin->drr_u.drr_begin;
 	drc->drc_tosnap = tosnap;
 	drc->drc_tofs = tofs;
 	drc->drc_force = force;
+	drc->drc_resumable = resumable;
 	drc->drc_cred = CRED();
 
-	if (drrb->drr_magic == BSWAP_64(DMU_BACKUP_MAGIC))
+	if (drc->drc_drrb->drr_magic == BSWAP_64(DMU_BACKUP_MAGIC)) {
 		drc->drc_byteswap = B_TRUE;
-	else if (drrb->drr_magic != DMU_BACKUP_MAGIC)
-		return (SET_ERROR(EINVAL));
-
-	drr = kmem_zalloc(sizeof (dmu_replay_record_t), KM_SLEEP);
-	drr->drr_type = DRR_BEGIN;
-	drr->drr_u.drr_begin = *drc->drc_drrb;
-	if (drc->drc_byteswap) {
-		fletcher_4_incremental_byteswap(drr,
+		fletcher_4_incremental_byteswap(drr_begin,
 		    sizeof (dmu_replay_record_t), &drc->drc_cksum);
-	} else {
-		fletcher_4_incremental_native(drr,
+		byteswap_record(drr_begin);
+	} else if (drc->drc_drrb->drr_magic == DMU_BACKUP_MAGIC) {
+		fletcher_4_incremental_native(drr_begin,
 		    sizeof (dmu_replay_record_t), &drc->drc_cksum);
-	}
-	kmem_free(drr, sizeof (dmu_replay_record_t));
-
-	if (drc->drc_byteswap) {
-		drrb->drr_magic = BSWAP_64(drrb->drr_magic);
-		drrb->drr_versioninfo = BSWAP_64(drrb->drr_versioninfo);
-		drrb->drr_creation_time = BSWAP_64(drrb->drr_creation_time);
-		drrb->drr_type = BSWAP_32(drrb->drr_type);
-		drrb->drr_toguid = BSWAP_64(drrb->drr_toguid);
-		drrb->drr_fromguid = BSWAP_64(drrb->drr_fromguid);
+	} else {
+		return (SET_ERROR(EINVAL));
 	}
 
 	drba.drba_origin = origin;
 	drba.drba_cookie = drc;
 	drba.drba_cred = CRED();
 
-	return (dsl_sync_task(tofs, dmu_recv_begin_check, dmu_recv_begin_sync,
-	    &drba, 5, ZFS_SPACE_CHECK_NORMAL));
+	if (DMU_GET_FEATUREFLAGS(drc->drc_drrb->drr_versioninfo) &
+	    DMU_BACKUP_FEATURE_RESUMING) {
+		return (dsl_sync_task(tofs,
+		    dmu_recv_resume_begin_check, dmu_recv_resume_begin_sync,
+		    &drba, 5, ZFS_SPACE_CHECK_NORMAL));
+	} else  {
+		return (dsl_sync_task(tofs,
+		    dmu_recv_begin_check, dmu_recv_begin_sync,
+		    &drba, 5, ZFS_SPACE_CHECK_NORMAL));
+	}
 }
 
 struct receive_record_arg {
@@ -1469,6 +1698,7 @@ struct receive_record_arg {
 	 */
 	arc_buf_t *write_buf;
 	int payload_size;
+	uint64_t bytes_read; /* bytes read from stream when record created */
 	boolean_t eos_marker; /* Marks the end of the stream */
 	bqueue_node_t node;
 };
@@ -1477,6 +1707,7 @@ struct receive_writer_arg {
 	objset_t *os;
 	boolean_t byteswap;
 	bqueue_t q;
+
 	/*
 	 * These three args are used to signal to the main thread that we're
 	 * done.
@@ -1484,15 +1715,20 @@ struct receive_writer_arg {
 	kmutex_t mutex;
 	kcondvar_t cv;
 	boolean_t done;
+
 	int err;
 	/* A map from guid to dataset to help handle dedup'd streams. */
 	avl_tree_t *guid_to_ds_map;
+	boolean_t resumable;
+	uint64_t last_object, last_offset;
+	uint64_t bytes_read; /* bytes read when current record created */
 };
 
 struct receive_arg  {
 	objset_t *os;
 	vnode_t *vp; /* The vnode to read the stream from */
 	uint64_t voff; /* The current offset in the stream */
+	uint64_t bytes_read;
 	/*
 	 * A record that has had its payload read in, but hasn't yet been handed
 	 * off to the worker thread.
@@ -1564,14 +1800,21 @@ receive_read(struct receive_arg *ra, int len, void *buf)
 		    ra->voff, UIO_SYSSPACE, FAPPEND,
 		    RLIM64_INFINITY, CRED(), &resid);
 
-		if (resid == len - done)
-			ra->err = SET_ERROR(EINVAL);
+		if (resid == len - done) {
+			/*
+			 * Note: ECKSUM indicates that the receive
+			 * was interrupted and can potentially be resumed.
+			 */
+			ra->err = SET_ERROR(ECKSUM);
+		}
 		ra->voff += len - done - resid;
 		done = len - resid;
 		if (ra->err != 0)
 			return (ra->err);
 	}
 
+	ra->bytes_read += len;
+
 	ASSERT3U(done, ==, len);
 	return (0);
 }
@@ -1675,6 +1918,43 @@ deduce_nblkptr(dmu_object_type_t bonus_type, uint64_t bonus_size)
 	}
 }
 
+static void
+save_resume_state(struct receive_writer_arg *rwa,
+    uint64_t object, uint64_t offset, dmu_tx_t *tx)
+{
+	int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;
+
+	if (!rwa->resumable)
+		return;
+
+	/*
+	 * We use ds_resume_bytes[] != 0 to indicate that we need to
+	 * update this on disk, so it must not be 0.
+	 */
+	ASSERT(rwa->bytes_read != 0);
+
+	/*
+	 * We only resume from write records, which have a valid
+	 * (non-meta-dnode) object number.
+	 */
+	ASSERT(object != 0);
+
+	/*
+	 * For resuming to work correctly, we must receive records in order,
+	 * sorted by object,offset.  This is checked by the callers, but
+	 * assert it here for good measure.
+	 */
+	ASSERT3U(object, >=, rwa->os->os_dsl_dataset->ds_resume_object[txgoff]);
+	ASSERT(object != rwa->os->os_dsl_dataset->ds_resume_object[txgoff] ||
+	    offset >= rwa->os->os_dsl_dataset->ds_resume_offset[txgoff]);
+	ASSERT3U(rwa->bytes_read, >=,
+	    rwa->os->os_dsl_dataset->ds_resume_bytes[txgoff]);
+
+	rwa->os->os_dsl_dataset->ds_resume_object[txgoff] = object;
+	rwa->os->os_dsl_dataset->ds_resume_offset[txgoff] = offset;
+	rwa->os->os_dsl_dataset->ds_resume_bytes[txgoff] = rwa->bytes_read;
+}
+
 noinline static int
 receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 	void *data)
@@ -1773,6 +2053,7 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 		dmu_buf_rele(db, FTAG);
 	}
 	dmu_tx_commit(tx);
+
 	return (0);
 }
 
@@ -1820,6 +2101,18 @@ receive_write(struct receive_writer_arg *rwa, struct drr_write *drrw,
 	    !DMU_OT_IS_VALID(drrw->drr_type))
 		return (SET_ERROR(EINVAL));
 
+	/*
+	 * For resuming to work, records must be in increasing order
+	 * by (object, offset).
+	 */
+	if (drrw->drr_object < rwa->last_object ||
+	    (drrw->drr_object == rwa->last_object &&
+	    drrw->drr_offset < rwa->last_offset)) {
+		return (SET_ERROR(EINVAL));
+	}
+	rwa->last_object = drrw->drr_object;
+	rwa->last_offset = drrw->drr_offset;
+
 	if (dmu_object_info(rwa->os, drrw->drr_object, NULL) != 0)
 		return (SET_ERROR(EINVAL));
 
@@ -1842,8 +2135,17 @@ receive_write(struct receive_writer_arg *rwa, struct drr_write *drrw,
 	if (dmu_bonus_hold(rwa->os, drrw->drr_object, FTAG, &bonus) != 0)
 		return (SET_ERROR(EINVAL));
 	dmu_assign_arcbuf(bonus, drrw->drr_offset, abuf, tx);
+
+	/*
+	 * Note: If the receive fails, we want the resume stream to start
+	 * with the same record that we last successfully received (as opposed
+	 * to the next record), so that we can verify that we are
+	 * resuming from the correct location.
+	 */
+	save_resume_state(rwa, drrw->drr_object, drrw->drr_offset, tx);
 	dmu_tx_commit(tx);
 	dmu_buf_rele(bonus, FTAG);
+
 	return (0);
 }
 
@@ -1902,43 +2204,48 @@ receive_write_byref(struct receive_writer_arg *rwa,
 	dmu_write(rwa->os, drrwbr->drr_object,
 	    drrwbr->drr_offset, drrwbr->drr_length, dbp->db_data, tx);
 	dmu_buf_rele(dbp, FTAG);
+
+	/* See comment in restore_write. */
+	save_resume_state(rwa, drrwbr->drr_object, drrwbr->drr_offset, tx);
 	dmu_tx_commit(tx);
 	return (0);
 }
 
 static int
 receive_write_embedded(struct receive_writer_arg *rwa,
-    struct drr_write_embedded *drrwnp, void *data)
+    struct drr_write_embedded *drrwe, void *data)
 {
 	dmu_tx_t *tx;
 	int err;
 
-	if (drrwnp->drr_offset + drrwnp->drr_length < drrwnp->drr_offset)
+	if (drrwe->drr_offset + drrwe->drr_length < drrwe->drr_offset)
 		return (EINVAL);
 
-	if (drrwnp->drr_psize > BPE_PAYLOAD_SIZE)
+	if (drrwe->drr_psize > BPE_PAYLOAD_SIZE)
 		return (EINVAL);
 
-	if (drrwnp->drr_etype >= NUM_BP_EMBEDDED_TYPES)
+	if (drrwe->drr_etype >= NUM_BP_EMBEDDED_TYPES)
 		return (EINVAL);
-	if (drrwnp->drr_compression >= ZIO_COMPRESS_FUNCTIONS)
+	if (drrwe->drr_compression >= ZIO_COMPRESS_FUNCTIONS)
 		return (EINVAL);
 
 	tx = dmu_tx_create(rwa->os);
 
-	dmu_tx_hold_write(tx, drrwnp->drr_object,
-	    drrwnp->drr_offset, drrwnp->drr_length);
+	dmu_tx_hold_write(tx, drrwe->drr_object,
+	    drrwe->drr_offset, drrwe->drr_length);
 	err = dmu_tx_assign(tx, TXG_WAIT);
 	if (err != 0) {
 		dmu_tx_abort(tx);
 		return (err);
 	}
 
-	dmu_write_embedded(rwa->os, drrwnp->drr_object,
-	    drrwnp->drr_offset, data, drrwnp->drr_etype,
-	    drrwnp->drr_compression, drrwnp->drr_lsize, drrwnp->drr_psize,
+	dmu_write_embedded(rwa->os, drrwe->drr_object,
+	    drrwe->drr_offset, data, drrwe->drr_etype,
+	    drrwe->drr_compression, drrwe->drr_lsize, drrwe->drr_psize,
 	    rwa->byteswap ^ ZFS_HOST_BYTEORDER, tx);
 
+	/* See comment in restore_write. */
+	save_resume_state(rwa, drrwe->drr_object, drrwe->drr_offset, tx);
 	dmu_tx_commit(tx);
 	return (0);
 }
@@ -2012,10 +2319,16 @@ receive_free(struct receive_writer_arg *rwa, struct drr_free *drrf)
 static void
 dmu_recv_cleanup_ds(dmu_recv_cookie_t *drc)
 {
-	char name[MAXNAMELEN];
-	dsl_dataset_name(drc->drc_ds, name);
-	dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
-	(void) dsl_destroy_head(name);
+	if (drc->drc_resumable) {
+		/* wait for our resume state to be written to disk */
+		txg_wait_synced(drc->drc_ds->ds_dir->dd_pool, 0);
+		dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
+	} else {
+		char name[MAXNAMELEN];
+		dsl_dataset_name(drc->drc_ds, name);
+		dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
+		(void) dsl_destroy_head(name);
+	}
 }
 
 static void
@@ -2044,12 +2357,17 @@ receive_read_payload_and_next_header(struct receive_arg *ra, int len, void *buf)
 
 	if (len != 0) {
 		ASSERT3U(len, <=, SPA_MAXBLOCKSIZE);
-		ra->rrd->payload = buf;
-		ra->rrd->payload_size = len;
-		err = receive_read(ra, len, ra->rrd->payload);
+		err = receive_read(ra, len, buf);
 		if (err != 0)
 			return (err);
-		receive_cksum(ra, len, ra->rrd->payload);
+		receive_cksum(ra, len, buf);
+
+		/* note: rrd is NULL when reading the begin record's payload */
+		if (ra->rrd != NULL) {
+			ra->rrd->payload = buf;
+			ra->rrd->payload_size = len;
+			ra->rrd->bytes_read = ra->bytes_read;
+		}
 	}
 
 	ra->prev_cksum = ra->cksum;
@@ -2057,6 +2375,7 @@ receive_read_payload_and_next_header(struct receive_arg *ra, int len, void *buf)
 	ra->next_rrd = kmem_zalloc(sizeof (*ra->next_rrd), KM_SLEEP);
 	err = receive_read(ra, sizeof (ra->next_rrd->header),
 	    &ra->next_rrd->header);
+	ra->next_rrd->bytes_read = ra->bytes_read;
 	if (err != 0) {
 		kmem_free(ra->next_rrd, sizeof (*ra->next_rrd));
 		ra->next_rrd = NULL;
@@ -2236,7 +2555,7 @@ receive_read_record(struct receive_arg *ra)
 	{
 		struct drr_end *drre = &ra->rrd->header.drr_u.drr_end;
 		if (!ZIO_CHECKSUM_EQUAL(ra->prev_cksum, drre->drr_checksum))
-			return (SET_ERROR(EINVAL));
+			return (SET_ERROR(ECKSUM));
 		return (0);
 	}
 	case DRR_SPILL:
@@ -2263,6 +2582,10 @@ receive_process_record(struct receive_writer_arg *rwa,
 {
 	int err;
 
+	/* Processing in order, therefore bytes_read should be increasing. */
+	ASSERT3U(rrd->bytes_read, >=, rwa->bytes_read);
+	rwa->bytes_read = rrd->bytes_read;
+
 	switch (rrd->header.drr_type) {
 	case DRR_OBJECT:
 	{
@@ -2357,6 +2680,33 @@ receive_writer_thread(void *arg)
 	mutex_exit(&rwa->mutex);
 }
 
+static int
+resume_check(struct receive_arg *ra, nvlist_t *begin_nvl)
+{
+	uint64_t val;
+	objset_t *mos = dmu_objset_pool(ra->os)->dp_meta_objset;
+	uint64_t dsobj = dmu_objset_id(ra->os);
+	uint64_t resume_obj, resume_off;
+
+	if (nvlist_lookup_uint64(begin_nvl,
+	    "resume_object", &resume_obj) != 0 ||
+	    nvlist_lookup_uint64(begin_nvl,
+	    "resume_offset", &resume_off) != 0) {
+		return (SET_ERROR(EINVAL));
+	}
+	VERIFY0(zap_lookup(mos, dsobj,
+	    DS_FIELD_RESUME_OBJECT, sizeof (val), 1, &val));
+	if (resume_obj != val)
+		return (SET_ERROR(EINVAL));
+	VERIFY0(zap_lookup(mos, dsobj,
+	    DS_FIELD_RESUME_OFFSET, sizeof (val), 1, &val));
+	if (resume_off != val)
+		return (SET_ERROR(EINVAL));
+
+	return (0);
+}
+
+
 /*
  * Read in the stream's records, one by one, and apply them to the pool.  There
  * are two threads involved; the thread that calls this function will spin up a
@@ -2378,6 +2728,9 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 	struct receive_writer_arg *rwa;
 	int featureflags;
 	struct receive_ign_obj_node *n;
+	uint32_t payloadlen;
+	void *payload;
+	nvlist_t *begin_nvl = NULL;
 
 	ra = kmem_zalloc(sizeof (*ra), KM_SLEEP);
 	rwa = kmem_zalloc(sizeof (*rwa), KM_SLEEP);
@@ -2386,6 +2739,13 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 	ra->cksum = drc->drc_cksum;
 	ra->vp = vp;
 	ra->voff = *voffp;
+
+	if (dsl_dataset_is_zapified(drc->drc_ds)) {
+		(void) zap_lookup(drc->drc_ds->ds_dir->dd_pool->dp_meta_objset,
+		    drc->drc_ds->ds_object, DS_FIELD_RESUME_BYTES,
+		    sizeof (ra->bytes_read), 1, &ra->bytes_read);
+	}
+
 	list_create(&ra->ignore_obj_list, sizeof (struct receive_ign_obj_node),
 		offsetof(struct receive_ign_obj_node, node));
 
@@ -2438,9 +2798,29 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 		drc->drc_guid_to_ds_map = rwa->guid_to_ds_map;
 	}
 
-	err = receive_read_payload_and_next_header(ra, 0, NULL);
-	if (err)
+	payloadlen = drc->drc_drr_begin->drr_payloadlen;
+	payload = NULL;
+	if (payloadlen != 0)
+		payload = kmem_alloc(payloadlen, KM_SLEEP);
+
+	err = receive_read_payload_and_next_header(ra, payloadlen, payload);
+	if (err != 0) {
+		if (payloadlen != 0)
+			kmem_free(payload, payloadlen);
 		goto out;
+	}
+	if (payloadlen != 0) {
+		err = nvlist_unpack(payload, payloadlen, &begin_nvl, KM_SLEEP);
+		kmem_free(payload, payloadlen);
+		if (err != 0)
+			goto out;
+	}
+
+	if (featureflags & DMU_BACKUP_FEATURE_RESUMING) {
+		err = resume_check(ra, begin_nvl);
+		if (err != 0)
+			goto out;
+	}
 
 	(void) bqueue_init(&rwa->q, zfs_recv_queue_length,
 	    offsetof(struct receive_record_arg, node));
@@ -2448,6 +2828,7 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 	mutex_init(&rwa->mutex, NULL, MUTEX_DEFAULT, NULL);
 	rwa->os = ra->os;
 	rwa->byteswap = drc->drc_byteswap;
+	rwa->resumable = drc->drc_resumable;
 
 	(void) thread_create(NULL, 0, receive_writer_thread, rwa, 0, curproc,
 	    TS_RUN, minclsyspri);
@@ -2461,7 +2842,7 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 	 * We can leave this loop in 3 ways:  First, if rwa->err is
 	 * non-zero.  In that case, the writer thread will free the rrd we just
 	 * pushed.  Second, if  we're interrupted; in that case, either it's the
-	 * first loop and ra->rrd was never allocated, or it's later, and ra.rrd
+	 * first loop and ra->rrd was never allocated, or it's later and ra->rrd
 	 * has been handed off to the writer thread who will free it.  Finally,
 	 * if receive_read_record fails or we're at the end of the stream, then
 	 * we free ra->rrd and exit.
@@ -2506,13 +2887,15 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 		err = rwa->err;
 
 out:
+	nvlist_free(begin_nvl);
 	if ((featureflags & DMU_BACKUP_FEATURE_DEDUP) && (cleanup_fd != -1))
 		zfs_onexit_fd_rele(cleanup_fd);
 
 	if (err != 0) {
 		/*
-		 * destroy what we created, so we don't leave it in the
-		 * inconsistent restoring state.
+		 * Clean up references. If receive is not resumable,
+		 * destroy what we created, so we don't leave it in
+		 * the inconsistent state.
 		 */
 		dmu_recv_cleanup_ds(drc);
 	}
@@ -2674,6 +3057,20 @@ dmu_recv_end_sync(void *arg, dmu_tx_t *tx)
 
 		dmu_buf_will_dirty(ds->ds_dbuf, tx);
 		dsl_dataset_phys(ds)->ds_flags &= ~DS_FLAG_INCONSISTENT;
+		if (dsl_dataset_has_resume_receive_state(ds)) {
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_FROMGUID, tx);
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_OBJECT, tx);
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_OFFSET, tx);
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_BYTES, tx);
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_TOGUID, tx);
+			(void) zap_remove(dp->dp_meta_objset, ds->ds_object,
+			    DS_FIELD_RESUME_TONAME, tx);
+		}
 	}
 	drc->drc_newsnapobj = dsl_dataset_phys(drc->drc_ds)->ds_prev_snap_obj;
 	zvol_create_minors(dp->dp_spa, drc->drc_tofs, B_TRUE);
diff --git a/module/zfs/dmu_traverse.c b/module/zfs/dmu_traverse.c
index 44ba74181..0df12fac8 100644
--- a/module/zfs/dmu_traverse.c
+++ b/module/zfs/dmu_traverse.c
@@ -47,6 +47,7 @@ typedef struct prefetch_data {
 	int pd_flags;
 	boolean_t pd_cancel;
 	boolean_t pd_exited;
+	zbookmark_phys_t pd_resume;
 } prefetch_data_t;
 
 typedef struct traverse_data {
@@ -323,30 +324,29 @@ traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp,
 		uint32_t flags = ARC_FLAG_WAIT;
 		int32_t i;
 		int32_t epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;
-		dnode_phys_t *cdnp;
+		dnode_phys_t *child_dnp;
 
 		err = arc_read(NULL, td->td_spa, bp, arc_getbuf_func, &buf,
 		    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
 		if (err != 0)
 			goto post;
-		cdnp = buf->b_data;
+		child_dnp = buf->b_data;
 
-		for (i = 0; i < epb; i += cdnp[i].dn_extra_slots + 1) {
-			prefetch_dnode_metadata(td, &cdnp[i], zb->zb_objset,
-			    zb->zb_blkid * epb + i);
+		for (i = 0; i < epb; i += child_dnp[i].dn_extra_slots + 1) {
+			prefetch_dnode_metadata(td, &child_dnp[i],
+			    zb->zb_objset, zb->zb_blkid * epb + i);
 		}
 
 		/* recursively visitbp() blocks below this */
-		for (i = 0; i < epb; i += cdnp[i].dn_extra_slots + 1) {
-			err = traverse_dnode(td, &cdnp[i], zb->zb_objset,
-			    zb->zb_blkid * epb + i);
+		for (i = 0; i < epb; i += child_dnp[i].dn_extra_slots + 1) {
+			err = traverse_dnode(td, &child_dnp[i],
+			    zb->zb_objset, zb->zb_blkid * epb + i);
 			if (err != 0)
 				break;
 		}
 	} else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) {
 		arc_flags_t flags = ARC_FLAG_WAIT;
 		objset_phys_t *osp;
-		dnode_phys_t *mdnp, *gdnp, *udnp;
 
 		err = arc_read(NULL, td->td_spa, bp, arc_getbuf_func, &buf,
 		    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
@@ -354,11 +354,7 @@ traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp,
 			goto post;
 
 		osp = buf->b_data;
-		mdnp = &osp->os_meta_dnode;
-		gdnp = &osp->os_groupused_dnode;
-		udnp = &osp->os_userused_dnode;
-
-		prefetch_dnode_metadata(td, mdnp, zb->zb_objset,
+		prefetch_dnode_metadata(td, &osp->os_meta_dnode, zb->zb_objset,
 		    DMU_META_DNODE_OBJECT);
 		/*
 		 * See the block comment above for the goal of this variable.
@@ -370,21 +366,21 @@ traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp,
 			td->td_realloc_possible = B_FALSE;
 
 		if (arc_buf_size(buf) >= sizeof (objset_phys_t)) {
-			prefetch_dnode_metadata(td, gdnp, zb->zb_objset,
-			    DMU_GROUPUSED_OBJECT);
-			prefetch_dnode_metadata(td, udnp, zb->zb_objset,
-			    DMU_USERUSED_OBJECT);
+			prefetch_dnode_metadata(td, &osp->os_groupused_dnode,
+			    zb->zb_objset, DMU_GROUPUSED_OBJECT);
+			prefetch_dnode_metadata(td, &osp->os_userused_dnode,
+			    zb->zb_objset, DMU_USERUSED_OBJECT);
 		}
 
-		err = traverse_dnode(td, mdnp, zb->zb_objset,
+		err = traverse_dnode(td, &osp->os_meta_dnode, zb->zb_objset,
 		    DMU_META_DNODE_OBJECT);
 		if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) {
-			err = traverse_dnode(td, gdnp, zb->zb_objset,
-			    DMU_GROUPUSED_OBJECT);
+			err = traverse_dnode(td, &osp->os_groupused_dnode,
+			    zb->zb_objset, DMU_GROUPUSED_OBJECT);
 		}
 		if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) {
-			err = traverse_dnode(td, udnp, zb->zb_objset,
-			    DMU_USERUSED_OBJECT);
+			err = traverse_dnode(td, &osp->os_userused_dnode,
+			    zb->zb_objset, DMU_USERUSED_OBJECT);
 		}
 	}
 
@@ -416,9 +412,15 @@ post:
 		 * Set the bookmark to the first level-0 block that we need
 		 * to visit.  This way, the resuming code does not need to
 		 * deal with resuming from indirect blocks.
+		 *
+		 * Note, if zb_level <= 0, dnp may be NULL, so we don't want
+		 * to dereference it.
 		 */
-		td->td_resume->zb_blkid = zb->zb_blkid <<
-		    (zb->zb_level * (dnp->dn_indblkshift - SPA_BLKPTRSHIFT));
+		td->td_resume->zb_blkid = zb->zb_blkid;
+		if (zb->zb_level > 0) {
+			td->td_resume->zb_blkid <<= zb->zb_level *
+			    (dnp->dn_indblkshift - SPA_BLKPTRSHIFT);
+		}
 		td->td_paused = B_TRUE;
 	}
 
@@ -450,6 +452,10 @@ traverse_dnode(traverse_data_t *td, const dnode_phys_t *dnp,
 	int j, err = 0;
 	zbookmark_phys_t czb;
 
+	if (object != DMU_META_DNODE_OBJECT && td->td_resume != NULL &&
+	    object < td->td_resume->zb_object)
+		return (0);
+
 	if (td->td_flags & TRAVERSE_PRE) {
 		SET_BOOKMARK(&czb, objset, object, ZB_DNODE_LEVEL,
 		    ZB_DNODE_BLKID);
@@ -527,6 +533,7 @@ traverse_prefetch_thread(void *arg)
 	td.td_func = traverse_prefetcher;
 	td.td_arg = td_main->td_pfd;
 	td.td_pfd = NULL;
+	td.td_resume = &td_main->td_pfd->pd_resume;
 
 	SET_BOOKMARK(&czb, td.td_objset,
 	    ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
@@ -556,12 +563,6 @@ traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp,
 	ASSERT(ds == NULL || objset == ds->ds_object);
 	ASSERT(!(flags & TRAVERSE_PRE) || !(flags & TRAVERSE_POST));
 
-	/*
-	 * The data prefetching mechanism (the prefetch thread) is incompatible
-	 * with resuming from a bookmark.
-	 */
-	ASSERT(resume == NULL || !(flags & TRAVERSE_PREFETCH_DATA));
-
 	td = kmem_alloc(sizeof (traverse_data_t), KM_SLEEP);
 	pd = kmem_zalloc(sizeof (prefetch_data_t), KM_SLEEP);
 	czb = kmem_alloc(sizeof (zbookmark_phys_t), KM_SLEEP);
@@ -586,6 +587,8 @@ traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp,
 	}
 
 	pd->pd_flags = flags;
+	if (resume != NULL)
+		pd->pd_resume = *resume;
 	mutex_init(&pd->pd_mtx, NULL, MUTEX_DEFAULT, NULL);
 	cv_init(&pd->pd_cv, NULL, CV_DEFAULT, NULL);
 
@@ -638,11 +641,19 @@ traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp,
  * in syncing context).
  */
 int
-traverse_dataset(dsl_dataset_t *ds, uint64_t txg_start, int flags,
-    blkptr_cb_t func, void *arg)
+traverse_dataset_resume(dsl_dataset_t *ds, uint64_t txg_start,
+    zbookmark_phys_t *resume,
+    int flags, blkptr_cb_t func, void *arg)
 {
 	return (traverse_impl(ds->ds_dir->dd_pool->dp_spa, ds, ds->ds_object,
-	    &dsl_dataset_phys(ds)->ds_bp, txg_start, NULL, flags, func, arg));
+	    &dsl_dataset_phys(ds)->ds_bp, txg_start, resume, flags, func, arg));
+}
+
+int
+traverse_dataset(dsl_dataset_t *ds, uint64_t txg_start,
+    int flags, blkptr_cb_t func, void *arg)
+{
+	return (traverse_dataset_resume(ds, txg_start, NULL, flags, func, arg));
 }
 
 int
@@ -675,7 +686,7 @@ traverse_pool(spa_t *spa, uint64_t txg_start, int flags,
 
 	/* visit each dataset */
 	for (obj = 1; err == 0;
-	    err = dmu_object_next(mos, &obj, FALSE, txg_start)) {
+	    err = dmu_object_next(mos, &obj, B_FALSE, txg_start)) {
 		dmu_object_info_t doi;
 
 		err = dmu_object_info(mos, obj, &doi);
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 9c275b234..e86e6cc73 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -52,6 +52,9 @@
 #include <sys/dsl_userhold.h>
 #include <sys/dsl_bookmark.h>
 #include <sys/policy.h>
+#include <sys/dmu_send.h>
+#include <sys/zio_compress.h>
+#include <zfs_fletcher.h>
 
 /*
  * The SPA supports block sizes up to 16MB.  However, very large blocks
@@ -704,6 +707,7 @@ dsl_dataset_tryown(dsl_dataset_t *ds, void *tag)
 {
 	boolean_t gotit = FALSE;
 
+	ASSERT(dsl_pool_config_held(ds->ds_dir->dd_pool));
 	mutex_enter(&ds->ds_lock);
 	if (ds->ds_owner == NULL && !DS_IS_INCONSISTENT(ds)) {
 		ds->ds_owner = tag;
@@ -714,6 +718,16 @@ dsl_dataset_tryown(dsl_dataset_t *ds, void *tag)
 	return (gotit);
 }
 
+boolean_t
+dsl_dataset_has_owner(dsl_dataset_t *ds)
+{
+	boolean_t rv;
+	mutex_enter(&ds->ds_lock);
+	rv = (ds->ds_owner != NULL);
+	mutex_exit(&ds->ds_lock);
+	return (rv);
+}
+
 static void
 dsl_dataset_activate_feature(uint64_t dsobj, spa_feature_t f, dmu_tx_t *tx)
 {
@@ -1615,6 +1629,21 @@ dsl_dataset_sync(dsl_dataset_t *ds, zio_t *zio, dmu_tx_t *tx)
 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
 	dsl_dataset_phys(ds)->ds_fsid_guid = ds->ds_fsid_guid;
 
+	if (ds->ds_resume_bytes[tx->tx_txg & TXG_MASK] != 0) {
+		VERIFY0(zap_update(tx->tx_pool->dp_meta_objset,
+		    ds->ds_object, DS_FIELD_RESUME_OBJECT, 8, 1,
+		    &ds->ds_resume_object[tx->tx_txg & TXG_MASK], tx));
+		VERIFY0(zap_update(tx->tx_pool->dp_meta_objset,
+		    ds->ds_object, DS_FIELD_RESUME_OFFSET, 8, 1,
+		    &ds->ds_resume_offset[tx->tx_txg & TXG_MASK], tx));
+		VERIFY0(zap_update(tx->tx_pool->dp_meta_objset,
+		    ds->ds_object, DS_FIELD_RESUME_BYTES, 8, 1,
+		    &ds->ds_resume_bytes[tx->tx_txg & TXG_MASK], tx));
+		ds->ds_resume_object[tx->tx_txg & TXG_MASK] = 0;
+		ds->ds_resume_offset[tx->tx_txg & TXG_MASK] = 0;
+		ds->ds_resume_bytes[tx->tx_txg & TXG_MASK] = 0;
+	}
+
 	dmu_objset_sync(ds->ds_objset, zio, tx);
 
 	for (f = 0; f < SPA_FEATURES; f++) {
@@ -1670,6 +1699,78 @@ fail:
 	nvlist_free(propval);
 }
 
+static void
+get_receive_resume_stats(dsl_dataset_t *ds, nvlist_t *nv)
+{
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+
+	if (dsl_dataset_has_resume_receive_state(ds)) {
+		char *str;
+		void *packed;
+		uint8_t *compressed;
+		uint64_t val;
+		nvlist_t *token_nv = fnvlist_alloc();
+		size_t packed_size, compressed_size;
+		zio_cksum_t cksum;
+		char *propval;
+		char buf[MAXNAMELEN];
+		int i;
+
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_FROMGUID, sizeof (val), 1, &val) == 0) {
+			fnvlist_add_uint64(token_nv, "fromguid", val);
+		}
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_OBJECT, sizeof (val), 1, &val) == 0) {
+			fnvlist_add_uint64(token_nv, "object", val);
+		}
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_OFFSET, sizeof (val), 1, &val) == 0) {
+			fnvlist_add_uint64(token_nv, "offset", val);
+		}
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_BYTES, sizeof (val), 1, &val) == 0) {
+			fnvlist_add_uint64(token_nv, "bytes", val);
+		}
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_TOGUID, sizeof (val), 1, &val) == 0) {
+			fnvlist_add_uint64(token_nv, "toguid", val);
+		}
+		if (zap_lookup(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_TONAME, 1, sizeof (buf), buf) == 0) {
+			fnvlist_add_string(token_nv, "toname", buf);
+		}
+		if (zap_contains(dp->dp_meta_objset, ds->ds_object,
+		    DS_FIELD_RESUME_EMBEDOK) == 0) {
+			fnvlist_add_boolean(token_nv, "embedok");
+		}
+		packed = fnvlist_pack(token_nv, &packed_size);
+		fnvlist_free(token_nv);
+		compressed = kmem_alloc(packed_size, KM_SLEEP);
+
+		compressed_size = gzip_compress(packed, compressed,
+		    packed_size, packed_size, 6);
+
+		fletcher_4_native(compressed, compressed_size, &cksum);
+
+		str = kmem_alloc(compressed_size * 2 + 1, KM_SLEEP);
+		for (i = 0; i < compressed_size; i++) {
+			(void) sprintf(str + i * 2, "%02x", compressed[i]);
+		}
+		str[compressed_size * 2] = '\0';
+		propval = kmem_asprintf("%u-%llx-%llx-%s",
+		    ZFS_SEND_RESUME_TOKEN_VERSION,
+		    (longlong_t)cksum.zc_word[0],
+		    (longlong_t)packed_size, str);
+		dsl_prop_nvlist_add_string(nv,
+		    ZFS_PROP_RECEIVE_RESUME_TOKEN, propval);
+		kmem_free(packed, packed_size);
+		kmem_free(str, compressed_size * 2 + 1);
+		kmem_free(compressed, packed_size);
+		strfree(propval);
+	}
+}
+
 void
 dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 {
@@ -1743,6 +1844,29 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 		}
 	}
 
+	if (!dsl_dataset_is_snapshot(ds)) {
+		dsl_dataset_t *recv_ds;
+		char recvname[ZFS_MAXNAMELEN];
+
+		/*
+		 * A failed "newfs" (e.g. full) resumable receive leaves
+		 * the stats set on this dataset.  Check here for the prop.
+		 */
+		get_receive_resume_stats(ds, nv);
+
+		/*
+		 * A failed incremental resumable receive leaves the
+		 * stats set on our child named "%recv".  Check the child
+		 * for the prop.
+		 */
+		dsl_dataset_name(ds, recvname);
+		(void) strcat(recvname, "/");
+		(void) strcat(recvname, recv_clone_name);
+		if (dsl_dataset_hold(dp, recvname, FTAG, &recv_ds) == 0) {
+			get_receive_resume_stats(recv_ds, nv);
+			dsl_dataset_rele(recv_ds, FTAG);
+		}
+	}
 }
 
 void
@@ -1970,7 +2094,8 @@ dsl_dataset_rename_snapshot(const char *fsname,
  * only one long hold on the dataset.  We're not allowed to change anything here
  * so we don't permanently release the long hold or regular hold here.  We want
  * to do this only when syncing to avoid the dataset unexpectedly going away
- * when we release the long hold.
+ * when we release the long hold.  Allow a long hold to exist for volumes, this
+ * may occur when asynchronously registering the minor with the kernel.
  */
 static int
 dsl_dataset_handoff_check(dsl_dataset_t *ds, void *owner, dmu_tx_t *tx)
@@ -1985,7 +2110,7 @@ dsl_dataset_handoff_check(dsl_dataset_t *ds, void *owner, dmu_tx_t *tx)
 		dsl_dataset_long_rele(ds, owner);
 	}
 
-	held = dsl_dataset_long_held(ds);
+	held = (dsl_dataset_long_held(ds) && (ds->ds_owner != zvol_tag));
 
 	if (owner != NULL)
 		dsl_dataset_long_hold(ds, owner);
@@ -3391,6 +3516,23 @@ dsl_dataset_zapify(dsl_dataset_t *ds, dmu_tx_t *tx)
 	dmu_object_zapify(mos, ds->ds_object, DMU_OT_DSL_DATASET, tx);
 }
 
+boolean_t
+dsl_dataset_is_zapified(dsl_dataset_t *ds)
+{
+	dmu_object_info_t doi;
+
+	dmu_object_info_from_db(ds->ds_dbuf, &doi);
+	return (doi.doi_type == DMU_OTN_ZAP_METADATA);
+}
+
+boolean_t
+dsl_dataset_has_resume_receive_state(dsl_dataset_t *ds)
+{
+	return (dsl_dataset_is_zapified(ds) &&
+	    zap_contains(ds->ds_dir->dd_pool->dp_meta_objset,
+	    ds->ds_object, DS_FIELD_RESUME_TOGUID) == 0);
+}
+
 #if defined(_KERNEL) && defined(HAVE_SPL)
 #if defined(_LP64)
 module_param(zfs_max_recordsize, int, 0644);
diff --git a/module/zfs/dsl_destroy.c b/module/zfs/dsl_destroy.c
index d7c34c9a4..716081ba3 100644
--- a/module/zfs/dsl_destroy.c
+++ b/module/zfs/dsl_destroy.c
@@ -978,9 +978,17 @@ dsl_destroy_inconsistent(const char *dsname, void *arg)
 	objset_t *os;
 
 	if (dmu_objset_hold(dsname, FTAG, &os) == 0) {
-		boolean_t inconsistent = DS_IS_INCONSISTENT(dmu_objset_ds(os));
+		boolean_t need_destroy = DS_IS_INCONSISTENT(dmu_objset_ds(os));
+
+		/*
+		 * If the dataset is inconsistent because a resumable receive
+		 * has failed, then do not destroy it.
+		 */
+		if (dsl_dataset_has_resume_receive_state(dmu_objset_ds(os)))
+			need_destroy = B_FALSE;
+
 		dmu_objset_rele(os, FTAG);
-		if (inconsistent)
+		if (need_destroy)
 			(void) dsl_destroy_head(dsname);
 	}
 	return (0);
diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 30338ac14..825e83847 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -4005,6 +4005,7 @@ static boolean_t zfs_ioc_recv_inject_err;
  * zc_guid		force flag
  * zc_cleanup_fd	cleanup-on-exit file descriptor
  * zc_action_handle	handle for this guid/ds mapping (or zero on first call)
+ * zc_resumable		if data is incomplete assume sender will resume
  *
  * outputs:
  * zc_cookie		number of bytes read
@@ -4051,13 +4052,13 @@ zfs_ioc_recv(zfs_cmd_t *zc)
 		return (SET_ERROR(EBADF));
 	}
 
-	VERIFY(nvlist_alloc(&errors, NV_UNIQUE_NAME, KM_SLEEP) == 0);
+	errors = fnvlist_alloc();
 
 	if (zc->zc_string[0])
 		origin = zc->zc_string;
 
 	error = dmu_recv_begin(tofs, tosnap,
-	    &zc->zc_begin_record, force, origin, &drc);
+	    &zc->zc_begin_record, force, zc->zc_resumable, origin, &drc);
 	if (error != 0)
 		goto out;
 
@@ -5182,6 +5183,8 @@ zfs_ioc_space_snaps(const char *lastsnap, nvlist_t *innvl, nvlist_t *outnvl)
  *         indicates that blocks > 128KB are permitted
  *     (optional) "embedok" -> (value ignored)
  *         presence indicates DRR_WRITE_EMBEDDED records are permitted
+ *     (optional) "resume_object" and "resume_offset" -> (uint64)
+ *         if present, resume send stream from specified object and offset.
  * }
  *
  * outnvl is unused
@@ -5197,6 +5200,8 @@ zfs_ioc_send_new(const char *snapname, nvlist_t *innvl, nvlist_t *outnvl)
 	file_t *fp;
 	boolean_t largeblockok;
 	boolean_t embedok;
+	uint64_t resumeobj = 0;
+	uint64_t resumeoff = 0;
 
 	error = nvlist_lookup_int32(innvl, "fd", &fd);
 	if (error != 0)
@@ -5207,12 +5212,15 @@ zfs_ioc_send_new(const char *snapname, nvlist_t *innvl, nvlist_t *outnvl)
 	largeblockok = nvlist_exists(innvl, "largeblockok");
 	embedok = nvlist_exists(innvl, "embedok");
 
+	(void) nvlist_lookup_uint64(innvl, "resume_object", &resumeobj);
+	(void) nvlist_lookup_uint64(innvl, "resume_offset", &resumeoff);
+
 	if ((fp = getf(fd)) == NULL)
 		return (SET_ERROR(EBADF));
 
 	off = fp->f_offset;
-	error = dmu_send(snapname, fromname, embedok, largeblockok,
-	    fd, fp->f_vnode, &off);
+	error = dmu_send(snapname, fromname, embedok, largeblockok, fd,
+	    resumeobj, resumeoff, fp->f_vnode, &off);
 
 	if (VOP_SEEK(fp->f_vnode, fp->f_offset, &off, NULL) == 0)
 		fp->f_offset = off;
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 9c89493ed..73277901f 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -61,7 +61,7 @@ unsigned long zvol_max_discard_blocks = 16384;
 
 static kmutex_t zvol_state_lock;
 static list_t zvol_state_list;
-static char *zvol_tag = "zvol_tag";
+void *zvol_tag = "zvol_tag";
 
 /*
  * The in-core state of each volume.