cache: support cached origin for snapshot

Enable  'lvcreate/lvconvert -s' for cached LV.
and supported operations:

Create a snapshot of cached LV

Split/Join snapshot LV to cached origin LV.

4 files changed, 18 insertions, 3 deletions

diff --git a/WHATS_NEW b/WHATS_NEW
index ab113aea7..fa8f5c3cf 100644
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.169 - 
 =====================================
+  Enable usage of cached volumes as snapshot origin LV.
   Fix displayed lv name when splitting snapshot (2.02.146).
   Warn about command not making metadata backup just once per command.
   Enable usage of cached volume as thin volume's external origin.
diff --git a/lib/metadata/cache_manip.c b/lib/metadata/cache_manip.c
index 12b10547c..404b1af79 100644
--- a/lib/metadata/cache_manip.c
+++ b/lib/metadata/cache_manip.c
@@ -322,7 +322,7 @@ int validate_lv_cache_create_origin(const struct logical_volume *origin_lv)
 	if (lv_is_cache_type(origin_lv) ||
 	    lv_is_mirror_type(origin_lv) ||
 	    lv_is_thin_volume(origin_lv) || lv_is_thin_pool_metadata(origin_lv) ||
-	    lv_is_origin(origin_lv) || lv_is_merging_origin(origin_lv) ||
+	    lv_is_merging_origin(origin_lv) ||
 	    lv_is_cow(origin_lv) || lv_is_merging_cow(origin_lv) ||
 	    lv_is_virtual(origin_lv)) {
 		log_error("Cache is not supported with %s segment type of the original logical volume %s.",
diff --git a/lib/metadata/lv_manip.c b/lib/metadata/lv_manip.c
index 92a6d449f..3862f110c 100644
--- a/lib/metadata/lv_manip.c
+++ b/lib/metadata/lv_manip.c
@@ -7428,7 +7428,7 @@ static struct logical_volume *_lv_create_an_lv(struct volume_group *vg,
 				return NULL;
 			}
 
-			if (lv_is_cache_type(origin_lv)) {
+			if (lv_is_cache_type(origin_lv) && !lv_is_cache(origin_lv)) {
 				log_error("Snapshots of cache type volume %s "
 					  "is not supported.", display_lvname(origin_lv));
 				return NULL;
diff --git a/tools/lvconvert.c b/tools/lvconvert.c
index 41039954b..0f0f0addb 100644
--- a/tools/lvconvert.c
+++ b/tools/lvconvert.c
@@ -2336,7 +2336,7 @@ static int _lvconvert_snapshot(struct cmd_context *cmd,
 		return_0;
 
 	if (lv_is_locked(org) ||
-	    lv_is_cache_type(org) ||
+	    (lv_is_cache_type(org) && !lv_is_cache(org)) ||
 	    lv_is_thin_type(org) ||
 	    lv_is_pvmove(org) ||
 	    lv_is_mirrored(org) ||
@@ -3771,6 +3771,16 @@ static int _convert_cache_volume_thin_pool(struct cmd_context *cmd, struct logic
 }
 
 /*
+ * Convert/Recombine  cacheLV to be an origin for snapshot
+ * lvconvert --type snapshot cacheLV snapshotLV
+ */
+static int _convert_cache_volume_snapshot(struct cmd_context *cmd, struct logical_volume *lv,
+					  struct lvconvert_params *lp)
+{
+	return _lvconvert_snapshot(cmd, lv, lp);
+}
+
+/*
  * Split a cache volume from a cache pool LV.
  * lvconvert --splitcache LV
  */
@@ -4311,6 +4321,10 @@ static int _convert_cache_volume(struct cmd_context *cmd, struct logical_volume
 	    arg_is_set(cmd, thinpool_ARG))
 		return _convert_cache_volume_thin_pool(cmd, lv, lp);
 
+	if (!strcmp(lp->type_str, SEG_TYPE_NAME_SNAPSHOT) ||
+	    arg_is_set(cmd, snapshot_ARG))
+		return _convert_cache_volume_snapshot(cmd, lv, lp);
+
 	/* The --thinpool alternative for --type thin-pool is not preferred, so not shown. */
 
 	log_error("Operation not permitted on cache LV %s.", display_lvname(lv));