MFC r289362, r289445: 2605 want to resume interrupted zfs send

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Xin Li <delphij@freebsd.org>
Reviewed by: Arne Jansen <sensille@gmx.net>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Matthew Ahrens <mahrens@delphix.com>

illumos/illumos-gate@9c3fd1216fa7fb02cfbc78a2518a686d54b48ab8

For more info, see:
 - slides http://www.slideshare.net/MatthewAhrens/openzfs-send-and-receive
 - video https://www.youtube.com/watch?v=iY44jPMvxog
 - manpage changes (for zfs resume -s and zfs send -t)
 - upcoming talk at the OpenZFS Developer Summit

The TL;DR is:
Use "zfs receive -s" to save the partially received state on failure.
On failure, get the receive token with "zfs get receive_resume_token <fs>"
Resume the send with "zfs send -t <token_value>"

Relnotes:       yes

1 files changed, 20 insertions, 0 deletions

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 6846572..79de1d1 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
@@ -362,6 +362,17 @@ 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);
@@ -413,6 +424,8 @@ dmu_objset_open_impl(spa_t *spa, dsl_dataset_t *ds, blkptr_t *bp,
 				    recordsize_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));
@@ -469,6 +482,13 @@ 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;