md: allow an md array to appear with 0 drives if it has external metadata

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/md.c

@@ -4647,9 +4647,10 @@ static int md_ioctl(struct inode *inode, struct file *file,
 	 */
 	/* if we are not initialised yet, only ADD_NEW_DISK, STOP_ARRAY,
 	 * RUN_ARRAY, and GET_ and SET_BITMAP_FILE are allowed */
-	if (!mddev->raid_disks && cmd != ADD_NEW_DISK && cmd != STOP_ARRAY
-			&& cmd != RUN_ARRAY && cmd != SET_BITMAP_FILE
-	    		&& cmd != GET_BITMAP_FILE) {
+	if ((!mddev->raid_disks && !mddev->external)
+	    && cmd != ADD_NEW_DISK && cmd != STOP_ARRAY
+	    && cmd != RUN_ARRAY && cmd != SET_BITMAP_FILE
+	    && cmd != GET_BITMAP_FILE) {
 		err = -ENODEV;
 		goto abort_unlock;
 	}