snapshot: fix merging

When the merging of snapshot is finished, we need to clean dm table
intries for snapshot and -cow device. So for merging snapshot
we have to activate_lv plain 'cow' LV and let the table
resolver to its work - shortly deactivation_lv() request
will follow - in cluster this needs LV lock to be held by clvmd.

Also update a test - add small wait - if lvremove is not 'fast enough'
and merging process has not been stopped and $lv1 removed in background.
Ortherwise the following lvcreate occasionally finds name $lv1 still in use.

(in release fix)

lib/metadata/snapshot_manip.c

@@ -296,6 +296,15 @@ int vg_remove_snapshot(struct logical_volume *cow)
 			log_error("Failed to resume %s.", origin->name);
 			return 0;
 		}
+
+		/*
+		 * For merged snapshot we activate cow so it can clean
+		 * left table entries and deactivate_lv() follows shortly.
+		 */
+		if (merging_snapshot && !activate_lv(cow->vg->cmd, cow)) {
+			log_error("Failed to activate %s.", cow->name);
+			return 0;
+		}
 	}
 
 	return 1;

test/shell/snapshot-merge.sh

@@ -78,6 +78,12 @@ dm_table $vg-$lv1 | grep " snapshot-merge " || dm_table $vg-$lv1 | grep " linear
 #    may test stopping an active merge
 lvremove -f $vg/$lv1
 
+# wait a while if the merge and remove is still not finished
+# since it may still keep  $lv1  in vg being present
+for i in 1 2 3 4 ; do
+	lvs $vg/$lv1 2>/dev/null || break;
+	sleep .2
+done
 
 # "onactivate merge" test
 # -- deactivate/remove after disallowed merge attempt, tests