dm thin: display 'needs_check' in status if it is set

There is currently no way to see that the needs_check flag has been set
in the metadata.  Display 'needs_check' in the thin-pool status if it is
set in the thinp metadata.

Also, update thinp documentation.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Documentation/device-mapper/thin-provisioning.txt

@@ -296,7 +296,7 @@ ii) Status
 	underlying device.  When this is enabled when loading the table,
 	it can get disabled if the underlying device doesn't support it.
 
-    ro|rw
+    ro|rw|out_of_data_space
 	If the pool encounters certain types of device failures it will
 	drop into a read-only metadata mode in which no changes to
 	the pool metadata (like allocating new blocks) are permitted.
@@ -314,6 +314,13 @@ ii) Status
 	module parameter can be used to change this timeout -- it
 	defaults to 60 seconds but may be disabled using a value of 0.
 
+    needs_check
+	A metadata operation has failed, resulting in the needs_check
+	flag being set in the metadata's superblock.  The metadata
+	device must be deactivated and checked/repaired before the
+	thin-pool can be made fully operational again.  '-' indicates
+	needs_check is not set.
+
 iii) Messages
 
     create_thin <dev id>

drivers/md/dm-thin.c

@@ -3738,6 +3738,7 @@ static void emit_flags(struct pool_features *pf, char *result,
  * Status line is:
  *    <transaction id> <used metadata sectors>/<total metadata sectors>
  *    <used data sectors>/<total data sectors> <held metadata root>
+ *    <pool mode> <discard config> <no space config> <needs_check>
  */
 static void pool_status(struct dm_target *ti, status_type_t type,
 			unsigned status_flags, char *result, unsigned maxlen)
@@ -3839,6 +3840,11 @@ static void pool_status(struct dm_target *ti, status_type_t type,
 		else
 			DMEMIT("queue_if_no_space ");
 
+		if (dm_pool_metadata_needs_check(pool->pmd))
+			DMEMIT("needs_check ");
+		else
+			DMEMIT("- ");
+
 		break;
 
 	case STATUSTYPE_TABLE:
@@ -3942,7 +3948,7 @@ static struct target_type pool_target = {
 	.name = "thin-pool",
 	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
 		    DM_TARGET_IMMUTABLE,
-	.version = {1, 15, 0},
+	.version = {1, 16, 0},
 	.module = THIS_MODULE,
 	.ctr = pool_ctr,
 	.dtr = pool_dtr,
@@ -4329,7 +4335,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type thin_target = {
 	.name = "thin",
-	.version = {1, 15, 0},
+	.version = {1, 16, 0},
 	.module	= THIS_MODULE,
 	.ctr = thin_ctr,
 	.dtr = thin_dtr,