dm thin: emit ignore_discard in status when discards disabled

If "ignore_discard" is specified when creating the thin pool device then
discard support is disabled for that device.  The pool device's status
should reflect this fact rather than stating "no_discard_passdown"
(which implies discards are enabled but passdown is disabled).
Reported-by: NZdenek Kabelac <zkabelac@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin.c

@@ -2391,7 +2391,9 @@ static int pool_status(struct dm_target *ti, status_type_t type,
 		else
 			DMEMIT("rw ");
 
-		if (pool->pf.discard_enabled && pool->pf.discard_passdown)
+		if (!pool->pf.discard_enabled)
+			DMEMIT("ignore_discard");
+		else if (pool->pf.discard_passdown)
 			DMEMIT("discard_passdown");
 		else
 			DMEMIT("no_discard_passdown");
@@ -2487,7 +2489,7 @@ static struct target_type pool_target = {
 	.name = "thin-pool",
 	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
 		    DM_TARGET_IMMUTABLE,
-	.version = {1, 5, 0},
+	.version = {1, 6, 0},
 	.module = THIS_MODULE,
 	.ctr = pool_ctr,
 	.dtr = pool_dtr,