1 files changed, 12 insertions, 1 deletions

diff --git a/include/linux/dm-log-userspace.h b/include/linux/dm-log-userspace.h
index 642e3017b51f..8a1f972c0fe9 100644
--- a/include/linux/dm-log-userspace.h
+++ b/include/linux/dm-log-userspace.h
@@ -371,7 +371,18 @@
         (DM_ULOG_REQUEST_MASK & (request_type))
 
 struct dm_ulog_request {
-        char uuid[DM_UUID_LEN]; /* Ties a request to a specific mirror log */
+        /*
+         * The local unique identifier (luid) and the universally unique
+         * identifier (uuid) are used to tie a request to a specific
+         * mirror log.  A single machine log could probably make due with
+         * just the 'luid', but a cluster-aware log must use the 'uuid' and
+         * the 'luid'.  The uuid is what is required for node to node
+         * communication concerning a particular log, but the 'luid' helps
+         * differentiate between logs that are being swapped and have the
+         * same 'uuid'.  (Think "live" and "inactive" device-mapper tables.)
+         */
+        uint64_t luid;
+        char uuid[DM_UUID_LEN];
         char padding[7];        /* Padding because DM_UUID_LEN = 129 */
 
         int32_t error;          /* Used to report back processing errors */