Re: [PATCH 64/78] dm: simplify flush_bio initialization in __send_empty_flush

[Hannes Reinecke <hare@xxxxxxx>]

On 11/16/20 3:57 PM, Christoph Hellwig wrote:
> We don't really need the struct block_device to initialize a bio.  So
> switch from using bio_set_dev to manually setting up bi_disk (bi_partno
> will always be zero and has been cleared by bio_init already).
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>   drivers/md/dm.c | 12 +++---------
>   1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 54739f1b579bc8..6d7eb72d41f9ea 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1422,18 +1422,12 @@ static int __send_empty_flush(struct clone_info *ci)
>          */
>         bio_init(&flush_bio, NULL, 0);
>         flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC;
> +       flush_bio.bi_disk = ci->io->md->disk;
> +       bio_associate_blkg(&flush_bio);
> +
>         ci->bio = &flush_bio;
>         ci->sector_count = 0;
>   
> -	/*
> -        * Empty flush uses a statically initialized bio, as the base for
> -        * cloning.  However, blkg association requires that a bdev is
> -        * associated with a gendisk, which doesn't happen until the bdev is
> -        * opened.  So, blkg association is done at issue time of the flush
> -        * rather than when the device is created in alloc_dev().
> -        */
> -       bio_set_dev(ci->bio, ci->io->md->bdev);
> -
>         BUG_ON(bio_has_data(ci->bio));
>         while ((ti = dm_table_get_target(ci->map, target_nr++)))
>                 __send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);
Ah, thought as much. I've stumbled across this while debugging 
blk-interposer.
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@xxxxxxx                              +49 911 74053 688
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