Add createtxg sort support for simple snapshot iterator

- When iterating snapshots with name only, e.g., "-o name -s name",
libzfs uses simple snapshot iterator and results are displayed
in alphabetic order. This PR adds support for faster version of
createtxg sort by avoiding nvlist parsing for properties. Flags
"-o name -s createtxg" will enable createtxg sort while using
simple snapshot iterator.
- Added support to read createtxg property directly from zfs handle
for filesystem, volume and snapshot types instead of parsing nvlist.

Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Signed-off-by: Ameer Hamza <[email protected]>
Closes #13577 

1 files changed, 2 insertions, 0 deletions

diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 0c4334550..571e55573 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -2322,6 +2322,8 @@ zfs_ioc_snapshot_list_next(zfs_cmd_t *zc)
 		}
 
 		if (zc->zc_simple) {
+			zc->zc_objset_stats.dds_creation_txg =
+			    dsl_get_creationtxg(ds);
 			dsl_dataset_rele(ds, FTAG);
 			break;
 		}