fs: Block writes to mounted block devices

Ask block layer to block writes to block devices mounted by filesystems.
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231101174325.10596-5-jack@suse.czReviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

include/linux/blkdev.h

@@ -1494,7 +1494,8 @@ extern const struct blk_holder_ops fs_holder_ops;
  * as stored in sb->s_flags.
  */
 #define sb_open_mode(flags) \
-	(BLK_OPEN_READ | (((flags) & SB_RDONLY) ? 0 : BLK_OPEN_WRITE))
+	(BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES | \
+	 (((flags) & SB_RDONLY) ? 0 : BLK_OPEN_WRITE))
 
 struct bdev_handle {
 	struct block_device *bdev;