linux-kernel - Re: [PATCH v2 05/28] block: Add bio_add

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Date:   Tue, 16 Nov 2021 20:48:10 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 05/28] block: Add bio_add_folio()

On Mon, Nov 08, 2021 at 04:05:28AM +0000, Matthew Wilcox (Oracle) wrote:
> This is a thin wrapper around bio_add_page().  The main advantage here
> is the documentation that folios larger than 2GiB are not supported.
> It's not currently possible to allocate folios that large, but if it
> ever becomes possible, this function will fail gracefully instead of
> doing I/O to the wrong bytes.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Reviewed-by: Jens Axboe <axboe@...nel.dk>
> Reviewed-by: Christoph Hellwig <hch@....de>

Looks ok,
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> ---
>  block/bio.c         | 22 ++++++++++++++++++++++
>  include/linux/bio.h |  3 ++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 15ab0d6d1c06..4b3087e20d51 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1033,6 +1033,28 @@ int bio_add_page(struct bio *bio, struct page *page,
>  }
>  EXPORT_SYMBOL(bio_add_page);
>  
> +/**
> + * bio_add_folio - Attempt to add part of a folio to a bio.
> + * @bio: BIO to add to.
> + * @folio: Folio to add.
> + * @len: How many bytes from the folio to add.
> + * @off: First byte in this folio to add.
> + *
> + * Filesystems that use folios can call this function instead of calling
> + * bio_add_page() for each page in the folio.  If @off is bigger than
> + * PAGE_SIZE, this function can create a bio_vec that starts in a page
> + * after the bv_page.  BIOs do not support folios that are 4GiB or larger.
> + *
> + * Return: Whether the addition was successful.
> + */
> +bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
> +		   size_t off)
> +{
> +	if (len > UINT_MAX || off > UINT_MAX)
> +		return 0;
> +	return bio_add_page(bio, &folio->page, len, off) > 0;
> +}
> +
>  void __bio_release_pages(struct bio *bio, bool mark_dirty)
>  {
>  	struct bvec_iter_all iter_all;
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index fe6bdfbbef66..a783cac49978 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -409,7 +409,8 @@ extern void bio_uninit(struct bio *);
>  extern void bio_reset(struct bio *);
>  void bio_chain(struct bio *, struct bio *);
>  
> -extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
> +int bio_add_page(struct bio *, struct page *, unsigned len, unsigned off);
> +bool bio_add_folio(struct bio *, struct folio *, size_t len, size_t off);
>  extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
>  			   unsigned int, unsigned int);
>  int bio_add_zone_append_page(struct bio *bio, struct page *page,
> -- 
> 2.33.0
>