Do not iterate through filesystems unnecessarily

Currently, when attempting to list snapshots ZFS may do a lot of
extra work checking child datasets. This is because the code does
not realize that it will not be able to reach any snapshots
contained within snapshots that are at the depth limit since the
snapshots of those datasets are counted as an additional layer
deeper. This patch corrects this issue.

In addition, this patch adds the ability to do perform the commands:

$ zfs list -t snapshot <dataset>
$ zfs get -t snapshot <prop> <dataset>

as a convenient way to list out properties of all snapshots of a
given dataset without having to use the depth limit.

Reviewed-by: Alek Pinchuk <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Richard Laager <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes #8539 

2 files changed, 40 insertions, 5 deletions

diff --git a/cmd/zfs/zfs_iter.c b/cmd/zfs/zfs_iter.c
index 9ad691938..d10bbed7d 100644
--- a/cmd/zfs/zfs_iter.c
+++ b/cmd/zfs/zfs_iter.c
@@ -134,16 +134,31 @@ zfs_callback(zfs_handle_t *zhp, void *data)
 	    ((cb->cb_flags & ZFS_ITER_DEPTH_LIMIT) == 0 ||
 	    cb->cb_depth < cb->cb_depth_limit)) {
 		cb->cb_depth++;
-		if (zfs_get_type(zhp) == ZFS_TYPE_FILESYSTEM)
+
+		/*
+		 * If we are not looking for filesystems, we don't need to
+		 * recurse into filesystems when we are at our depth limit.
+		 */
+		if ((cb->cb_depth < cb->cb_depth_limit ||
+		    (cb->cb_flags & ZFS_ITER_DEPTH_LIMIT) == 0 ||
+		    (cb->cb_types &
+		    (ZFS_TYPE_FILESYSTEM | ZFS_TYPE_VOLUME))) &&
+		    zfs_get_type(zhp) == ZFS_TYPE_FILESYSTEM) {
 			(void) zfs_iter_filesystems(zhp, zfs_callback, data);
+		}
+
 		if (((zfs_get_type(zhp) & (ZFS_TYPE_SNAPSHOT |
-		    ZFS_TYPE_BOOKMARK)) == 0) && include_snaps)
+		    ZFS_TYPE_BOOKMARK)) == 0) && include_snaps) {
 			(void) zfs_iter_snapshots(zhp,
-			    (cb->cb_flags & ZFS_ITER_SIMPLE) != 0, zfs_callback,
-			    data, 0, 0);
+			    (cb->cb_flags & ZFS_ITER_SIMPLE) != 0,
+			    zfs_callback, data, 0, 0);
+		}
+
 		if (((zfs_get_type(zhp) & (ZFS_TYPE_SNAPSHOT |
-		    ZFS_TYPE_BOOKMARK)) == 0) && include_bmarks)
+		    ZFS_TYPE_BOOKMARK)) == 0) && include_bmarks) {
 			(void) zfs_iter_bookmarks(zhp, zfs_callback, data);
+		}
+
 		cb->cb_depth--;
 	}
 
diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c
index 21c4d4334..57eb30528 100644
--- a/cmd/zfs/zfs_main.c
+++ b/cmd/zfs/zfs_main.c
@@ -1922,6 +1922,16 @@ zfs_do_get(int argc, char **argv)
 
 	fields = argv[0];
 
+	/*
+	 * Handle users who want to get all snapshots of the current
+	 * dataset (ex. 'zfs get -t snapshot refer <dataset>').
+	 */
+	if (types == ZFS_TYPE_SNAPSHOT &&
+	    (flags & ZFS_ITER_RECURSE) == 0 && limit == 0) {
+		flags |= (ZFS_ITER_DEPTH_LIMIT | ZFS_ITER_RECURSE);
+		limit = 1;
+	}
+
 	if (zprop_get_list(g_zfs, fields, &cb.cb_proplist, ZFS_TYPE_DATASET)
 	    != 0)
 		usage(B_FALSE);
@@ -3417,6 +3427,16 @@ zfs_do_list(int argc, char **argv)
 		types &= ~ZFS_TYPE_SNAPSHOT;
 
 	/*
+	 * Handle users who want to list all snapshots of the current
+	 * dataset (ex. 'zfs list -t snapshot <dataset>').
+	 */
+	if (types == ZFS_TYPE_SNAPSHOT &&
+	    (flags & ZFS_ITER_RECURSE) == 0 && limit == 0) {
+		flags |= (ZFS_ITER_DEPTH_LIMIT | ZFS_ITER_RECURSE);
+		limit = 1;
+	}
+
+	/*
 	 * If the user specifies '-o all', the zprop_get_list() doesn't
 	 * normally include the name of the dataset.  For 'zfs list', we always
 	 * want this property to be first.