[dm-devel] dm: don't save and restore bi_private

[Mike Snitzer]

On Wed, Nov 25 2015 at  4:03pm -0500,
Mikulas Patocka <mpatocka at redhat.com> wrote:

> Device mapper used the field bi_private to point to dm_target_io. However,
> since kernel 3.15, the bi_private field is unused, and so the targets do
> not need to save and restore this field.
> 
> This patch removes code that saves and restores bi_private from dm-cache,
> dm-snapshot and dm-verity.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> 
> ---
>  drivers/md/dm-cache-target.c |    3 ---
>  drivers/md/dm-snap.c         |    6 +-----
>  drivers/md/dm-verity.c       |    3 ---
>  3 files changed, 1 insertion(+), 11 deletions(-)
> 
> Index: linux-4.4-rc2/drivers/md/dm-cache-target.c
> ===================================================================
> --- linux-4.4-rc2.orig/drivers/md/dm-cache-target.c	2015-11-24 15:33:56.000000000 +0100
> +++ linux-4.4-rc2/drivers/md/dm-cache-target.c	2015-11-24 15:34:35.000000000 +0100
> @@ -118,14 +118,12 @@ static void iot_io_end(struct io_tracker
>   */
>  struct dm_hook_info {
>  	bio_end_io_t *bi_end_io;
> -	void *bi_private;
>  };
>  
>  static void dm_hook_bio(struct dm_hook_info *h, struct bio *bio,
>  			bio_end_io_t *bi_end_io, void *bi_private)
>  {
>  	h->bi_end_io = bio->bi_end_io;
> -	h->bi_private = bio->bi_private;
>  
>  	bio->bi_end_io = bi_end_io;
>  	bio->bi_private = bi_private;

As you can see dm_hook_bio() goes on to modify bi_private.
dm-cache uses it to get the migration object associated with a bio for
the overwrite_endio() case.

So NAK on the dm-cache change.

How closely have you reviewed your change for snapshot and verity?