libdm: support DM_NAME_LIST_FLAG

Kernel patch 8b638081bd4520f63db1defc660666ec5f65bc15
introduced support to return UUID in DM_LIST_DEVICES_CMD.

Useful when asking for UUID of each device where the list
could be now returned directly with NAME && UUID for each device.

Returning UUID is done in backward-compatible way. There's one unused
32-bit word value after the event number. This patch sets the bit
DM_NAME_LIST_FLAG_HAS_UUID if UUID is present and
DM_NAME_LIST_FLAG_DOESNT_HAVE_UUID if it isn't (if none of these bits is
set, then we have an old kernel that doesn't support returning UUIDs). The
UUID is stored after this word. The 'next' value is updated to point after
the UUID, so that old version of libdevmapper will skip the UUID without
attempting to interpret it.

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.181 - 
 ===================================
+  Add defines DM_NAME_LIST_FLAG_HAS_UUID, DM_NAME_LIST_FLAG_DOESNT_HAVE_UUID.
   Enhance tracking of activated devices when preloading dm tree.
   Fix bug in construction of cache table line (regression from 1.02.159).
 

libdm/misc/dm-ioctl.h

@@ -194,8 +194,22 @@ struct dm_name_list {
 	uint32_t next;		/* offset to the next record from
 				   the _start_ of this */
 	char name[0];
+
+	/*
+	 * The following members can be accessed by taking a pointer that
+	 * points immediately after the terminating zero character in "name"
+	 * and aligning this pointer to next 8-byte boundary.
+	 * Uuid is present if the flag DM_NAME_LIST_FLAG_HAS_UUID is set.
+	 *
+	 * uint32_t event_nr;
+	 * uint32_t flags;
+	 * char uuid[0];
+	 */
 };
 
+#define DM_NAME_LIST_FLAG_HAS_UUID		1
+#define DM_NAME_LIST_FLAG_DOESNT_HAVE_UUID	2
+
 /*
  * Used to retrieve the target versions
  */