linux-kernel - Re: [PATCH v2 06/28] block: Add bio_for_each_folio

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Message-ID: <20211117044837.GQ24307@magnolia>
Date:   Tue, 16 Nov 2021 20:48:37 -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 06/28] block: Add bio_for_each_folio_all()

On Mon, Nov 08, 2021 at 04:05:29AM +0000, Matthew Wilcox (Oracle) wrote:
> Allow callers to iterate over each folio instead of each page.  The
> bio need not have been constructed using folios originally.
> 
> 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

> ---
>  Documentation/core-api/kernel-api.rst |  1 +
>  include/linux/bio.h                   | 53 ++++++++++++++++++++++++++-
>  2 files changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
> index 2e7186805148..7f0cb604b6ab 100644
> --- a/Documentation/core-api/kernel-api.rst
> +++ b/Documentation/core-api/kernel-api.rst
> @@ -279,6 +279,7 @@ Accounting Framework
>  Block Devices
>  =============
>  
> +.. kernel-doc:: include/linux/bio.h
>  .. kernel-doc:: block/blk-core.c
>     :export:
>  
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index a783cac49978..e3c9e8207f12 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -166,7 +166,7 @@ static inline void bio_advance(struct bio *bio, unsigned int nbytes)
>   */
>  #define bio_for_each_bvec_all(bvl, bio, i)		\
>  	for (i = 0, bvl = bio_first_bvec_all(bio);	\
> -	     i < (bio)->bi_vcnt; i++, bvl++)		\
> +	     i < (bio)->bi_vcnt; i++, bvl++)
>  
>  #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
>  
> @@ -260,6 +260,57 @@ static inline struct bio_vec *bio_last_bvec_all(struct bio *bio)
>  	return &bio->bi_io_vec[bio->bi_vcnt - 1];
>  }
>  
> +/**
> + * struct folio_iter - State for iterating all folios in a bio.
> + * @folio: The current folio we're iterating.  NULL after the last folio.
> + * @offset: The byte offset within the current folio.
> + * @length: The number of bytes in this iteration (will not cross folio
> + *	boundary).
> + */
> +struct folio_iter {
> +	struct folio *folio;
> +	size_t offset;
> +	size_t length;
> +	/* private: for use by the iterator */
> +	size_t _seg_count;
> +	int _i;
> +};
> +
> +static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
> +				   int i)
> +{
> +	struct bio_vec *bvec = bio_first_bvec_all(bio) + i;
> +
> +	fi->folio = page_folio(bvec->bv_page);
> +	fi->offset = bvec->bv_offset +
> +			PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
> +	fi->_seg_count = bvec->bv_len;
> +	fi->length = min(folio_size(fi->folio) - fi->offset, fi->_seg_count);
> +	fi->_i = i;
> +}
> +
> +static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
> +{
> +	fi->_seg_count -= fi->length;
> +	if (fi->_seg_count) {
> +		fi->folio = folio_next(fi->folio);
> +		fi->offset = 0;
> +		fi->length = min(folio_size(fi->folio), fi->_seg_count);
> +	} else if (fi->_i + 1 < bio->bi_vcnt) {
> +		bio_first_folio(fi, bio, fi->_i + 1);
> +	} else {
> +		fi->folio = NULL;
> +	}
> +}
> +
> +/**
> + * bio_for_each_folio_all - Iterate over each folio in a bio.
> + * @fi: struct folio_iter which is updated for each folio.
> + * @bio: struct bio to iterate over.
> + */
> +#define bio_for_each_folio_all(fi, bio)				\
> +	for (bio_first_folio(&fi, bio, 0); fi.folio; bio_next_folio(&fi, bio))
> +
>  enum bip_flags {
>  	BIP_BLOCK_INTEGRITY	= 1 << 0, /* block layer owns integrity data */
>  	BIP_MAPPED_INTEGRITY	= 1 << 1, /* ref tag has been remapped */
> -- 
> 2.33.0
>