md: refuse to change shape of array if it is active but read-only

read-only arrays should not be changed.  This includes changing
the level, layout, size, or number of devices.

So reject those changes for readonly arrays.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -3448,6 +3448,8 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		mddev->level = LEVEL_NONE;
 		return rv;
 	}
+	if (mddev->ro)
+		return  -EROFS;
 
 	/* request to change the personality.  Need to ensure:
 	 *  - array is not engaged in resync/recovery/reshape
@@ -3634,6 +3636,8 @@ layout_store(struct mddev *mddev, const char *buf, size_t len)
 		int err;
 		if (mddev->pers->check_reshape == NULL)
 			return -EBUSY;
+		if (mddev->ro)
+			return -EROFS;
 		mddev->new_layout = n;
 		err = mddev->pers->check_reshape(mddev);
 		if (err) {
@@ -3723,6 +3727,8 @@ chunk_size_store(struct mddev *mddev, const char *buf, size_t len)
 		int err;
 		if (mddev->pers->check_reshape == NULL)
 			return -EBUSY;
+		if (mddev->ro)
+			return -EROFS;
 		mddev->new_chunk_sectors = n >> 9;
 		err = mddev->pers->check_reshape(mddev);
 		if (err) {
@@ -6135,6 +6141,8 @@ static int update_size(struct mddev *mddev, sector_t num_sectors)
 	 */
 	if (mddev->sync_thread)
 		return -EBUSY;
+	if (mddev->ro)
+		return -EROFS;
 
 	rdev_for_each(rdev, mddev) {
 		sector_t avail = rdev->sectors;
@@ -6157,6 +6165,8 @@ static int update_raid_disks(struct mddev *mddev, int raid_disks)
 	/* change the number of raid disks */
 	if (mddev->pers->check_reshape == NULL)
 		return -EINVAL;
+	if (mddev->ro)
+		return -EROFS;
 	if (raid_disks <= 0 ||
 	    (mddev->max_disks && raid_disks >= mddev->max_disks))
 		return -EINVAL;