loop: add ioctl for changing logical block size

This is a different approach from the first attempt in f2c6df7dbf9a
("loop: support 4k physical blocksize"). Rather than extending
LOOP_{GET,SET}_STATUS, add a separate ioctl just for setting the block
size.

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index c8125ec1f4f2..23158dbe2424 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -88,6 +88,7 @@ struct loop_info64 {
 #define LOOP_CHANGE_FD          0x4C06
 #define LOOP_SET_CAPACITY       0x4C07
 #define LOOP_SET_DIRECT_IO      0x4C08
+#define LOOP_SET_BLOCK_SIZE     0x4C09
 
 /* /dev/loop-control interface */
 #define LOOP_CTL_ADD            0x4C80