Illumos 5765 - add support for estimating send stream size with lzc_send_space when source is a bookmark

5765 add support for estimating send stream size with lzc_send_space when source is a bookmark
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Christopher Siden <[email protected]>
Reviewed by: Steven Hartland <[email protected]>
Reviewed by: Bayard Bell <[email protected]>
Approved by: Albert Lee <[email protected]>

References:
  https://www.illumos.org/issues/5765
  https://github.com/illumos/illumos-gate/commit/643da460

Porting notes:
* Unused variable 'recordsize' in dmu_send_estimate() dropped

Ported-by: DHE <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #3397

1 files changed, 17 insertions, 5 deletions

diff --git a/lib/libzfs_core/libzfs_core.c b/lib/libzfs_core/libzfs_core.c
index 69df5579b..b706e6f6b 100644
--- a/lib/libzfs_core/libzfs_core.c
+++ b/lib/libzfs_core/libzfs_core.c
@@ -20,7 +20,7 @@
  */
 
 /*
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
@@ -485,18 +485,30 @@ lzc_send(const char *snapname, const char *from, int fd,
 }
 
 /*
- * If fromsnap is NULL, a full (non-incremental) stream will be estimated.
+ * "from" can be NULL, a snapshot, or a bookmark.
+ *
+ * If from is NULL, a full (non-incremental) stream will be estimated.  This
+ * is calculated very efficiently.
+ *
+ * If from is a snapshot, lzc_send_space uses the deadlists attached to
+ * each snapshot to efficiently estimate the stream size.
+ *
+ * If from is a bookmark, the indirect blocks in the destination snapshot
+ * are traversed, looking for blocks with a birth time since the creation TXG of
+ * the snapshot this bookmark was created from.  This will result in
+ * significantly more I/O and be less efficient than a send space estimation on
+ * an equivalent snapshot.
  */
 int
-lzc_send_space(const char *snapname, const char *fromsnap, uint64_t *spacep)
+lzc_send_space(const char *snapname, const char *from, uint64_t *spacep)
 {
 	nvlist_t *args;
 	nvlist_t *result;
 	int err;
 
 	args = fnvlist_alloc();
-	if (fromsnap != NULL)
-		fnvlist_add_string(args, "fromsnap", fromsnap);
+	if (from != NULL)
+		fnvlist_add_string(args, "from", from);
 	err = lzc_ioctl(ZFS_IOC_SEND_SPACE, snapname, args, &result);
 	nvlist_free(args);
 	if (err == 0)