Re: [PATCH 1/6] block: add a bio_reuse helper

Kent Overstreet
2018-06-12T06:16:30Z

On Mon, Jun 11, 2018 at 09:48:01PM +0200, Christoph Hellwig wrote:
> This abstracts out a way to reuse a bio without destroying the
> data pointers.

What is the point of this? What "data pointers" does it not destroy?

>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> block/bio.c | 20 ++++++++++++++++++++
> include/linux/bio.h | 1 +
> 2 files changed, 21 insertions(+)
>
> diff --git a/block/bio.c b/block/bio.c
> index 70c4e1b6dd45..fa1b7ab50784 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -308,6 +308,26 @@ void bio_reset(struct bio *bio)
> }
> EXPORT_SYMBOL(bio_reset);
>
> +/**
> + * bio_reuse - prepare a bio for reuse
> + * @bio: bio to reuse
> + *
> + * Prepares an already setup and possible used bio for reusing it another
> + * time. Compared to bio_reset() this preserves the bio size and the
> + * layout and contents of the bio vectors.
> + */
> +void bio_reuse(struct bio *bio)
> +{
> + unsigned int size = bio->bi_iter.bi_size;
> + unsigned short vcnt = bio->bi_vcnt;
> +
> + bio_reset(bio);
> +
> + bio->bi_iter.bi_size = size;
> + bio->bi_vcnt = vcnt;
> +}
> +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 f08f5fe7bd08..15c871ab50db 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -475,6 +475,7 @@ extern void bio_init(struct bio *bio, struct bio_vec *table,
> unsigned short max_vecs);
> extern void bio_uninit(struct bio *);
> extern void bio_reset(struct bio *);
> +void bio_reuse(struct bio *);
> void bio_chain(struct bio *, struct bio *);
>
> extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
> --
> 2.17.1
>
> --
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