Re: [PATCH 1/3] block: add a bio_reuse helper

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jan 06, 2026 at 08:58:52AM +0100, Christoph Hellwig wrote:
> Add a helper to allow an existing bio to be resubmitted withtout
> having to re-add the payload.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>  block/bio.c         | 29 +++++++++++++++++++++++++++++
>  include/linux/bio.h |  1 +
>  2 files changed, 30 insertions(+)
> 
> diff --git a/block/bio.c b/block/bio.c
> index e726c0e280a8..ed99368c662f 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -311,6 +311,35 @@ void bio_reset(struct bio *bio, struct block_device *bdev, blk_opf_t opf)
>  }
>  EXPORT_SYMBOL(bio_reset);

General question about bio_reset -- it calls bio_uninit, which strips
off the integrity and crypt metadata.  I /think/ that will all get
re-added if necessary during the subsequent bio submission, right?

For your zonegc case, I wonder if it's actually a good idea to keep that
metadata attached as long as the bdev doesn't change across reuse?

--D

> +/**
> + * bio_reuse - reuse a bio with the payload left intact
> + * @bio bio to reuse
> + *
> + * Allow reusing an existing bio for another operation with all set up
> + * fields including the payload, device and end_io handler left intact.
> + *
> + * Typically used for bios first used to read data which is then written
> + * to another location without modification.  This must be used by the
> + * I/O submitter on an bio that is not in flight.  Can't be used for
> + * cloned bios.
> + */
> +void bio_reuse(struct bio *bio)
> +{
> +	unsigned short vcnt = bio->bi_vcnt, i;
> +	bio_end_io_t *end_io = bio->bi_end_io;
> +	void *private = bio->bi_private;
> +
> +	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
> +
> +	bio_reset(bio, bio->bi_bdev, bio->bi_opf);
> +	for (i = 0; i < vcnt; i++)
> +		bio->bi_iter.bi_size += bio->bi_io_vec[i].bv_len;
> +	bio->bi_vcnt = vcnt;
> +	bio->bi_private = private;
> +	bio->bi_end_io = end_io;
> +}
> +EXPORT_SYMBOL_GPL(bio_reuse);
> +
>  static struct bio *__bio_chain_endio(struct bio *bio)
>  {
>  	struct bio *parent = bio->bi_private;
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index ad2d57908c1c..c0190f8badde 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -414,6 +414,7 @@ static inline void bio_init_inline(struct bio *bio, struct block_device *bdev,
>  }
>  extern void bio_uninit(struct bio *);
>  void bio_reset(struct bio *bio, struct block_device *bdev, blk_opf_t opf);
> +void bio_reuse(struct bio *bio);
>  void bio_chain(struct bio *, struct bio *);
>  
>  int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,
> -- 
> 2.47.3
> 
>