Re: [PATCH 01/15] block: add a BIO_MAX_SIZE constant and use it

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

On Mon, Jan 26, 2026 at 06:53:32AM +0100, Christoph Hellwig wrote:
> Currently the only constant for the maximum bio size is BIO_MAX_SECTORS,
> which is in units of 512-byte sectors, but a lot of user need a byte
> limit.
> 
> Add a BIO_MAX_SIZE constant, redefine BIO_MAX_SECTORS in terms of it, and
> switch all bio-related uses of UINT_MAX for the maximum size to use the
> symbolic names instead.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Yay, thanks!
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  block/bio.c               | 10 +++++-----
>  block/blk-lib.c           |  9 ++++-----
>  block/blk-merge.c         |  8 ++++----
>  include/linux/blk_types.h |  3 ++-
>  4 files changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 2359c0723b88..ac7703e149c6 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -924,7 +924,7 @@ static inline bool bio_full(struct bio *bio, unsigned len)
>  {
>  	if (bio->bi_vcnt >= bio->bi_max_vecs)
>  		return true;
> -	if (bio->bi_iter.bi_size > UINT_MAX - len)
> +	if (bio->bi_iter.bi_size > BIO_MAX_SIZE - len)
>  		return true;
>  	return false;
>  }
> @@ -1030,7 +1030,7 @@ int bio_add_page(struct bio *bio, struct page *page,
>  {
>  	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>  		return 0;
> -	if (bio->bi_iter.bi_size > UINT_MAX - len)
> +	if (bio->bi_iter.bi_size > BIO_MAX_SIZE - len)
>  		return 0;
>  
>  	if (bio->bi_vcnt > 0) {
> @@ -1057,7 +1057,7 @@ void bio_add_folio_nofail(struct bio *bio, struct folio *folio, size_t len,
>  {
>  	unsigned long nr = off / PAGE_SIZE;
>  
> -	WARN_ON_ONCE(len > UINT_MAX);
> +	WARN_ON_ONCE(len > BIO_MAX_SIZE);
>  	__bio_add_page(bio, folio_page(folio, nr), len, off % PAGE_SIZE);
>  }
>  EXPORT_SYMBOL_GPL(bio_add_folio_nofail);
> @@ -1081,7 +1081,7 @@ bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
>  {
>  	unsigned long nr = off / PAGE_SIZE;
>  
> -	if (len > UINT_MAX)
> +	if (len > BIO_MAX_SIZE)
>  		return false;
>  	return bio_add_page(bio, folio_page(folio, nr), len, off % PAGE_SIZE) > 0;
>  }
> @@ -1238,7 +1238,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  		extraction_flags |= ITER_ALLOW_P2PDMA;
>  
>  	size = iov_iter_extract_pages(iter, &pages,
> -				      UINT_MAX - bio->bi_iter.bi_size,
> +				      BIO_MAX_SIZE - bio->bi_iter.bi_size,
>  				      nr_pages, extraction_flags, &offset);
>  	if (unlikely(size <= 0))
>  		return size ? size : -EFAULT;
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 9e2cc58f881f..0be3acdc3eb5 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -32,7 +32,7 @@ static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
>  	 * Align the bio size to the discard granularity to make splitting the bio
>  	 * at discard granularity boundaries easier in the driver if needed.
>  	 */
> -	return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
> +	return round_down(BIO_MAX_SIZE, discard_granularity) >> SECTOR_SHIFT;
>  }
>  
>  struct bio *blk_alloc_discard_bio(struct block_device *bdev,
> @@ -107,8 +107,7 @@ static sector_t bio_write_zeroes_limit(struct block_device *bdev)
>  {
>  	sector_t bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
>  
> -	return min(bdev_write_zeroes_sectors(bdev),
> -		(UINT_MAX >> SECTOR_SHIFT) & ~bs_mask);
> +	return min(bdev_write_zeroes_sectors(bdev), BIO_MAX_SECTORS & ~bs_mask);
>  }
>  
>  /*
> @@ -337,8 +336,8 @@ int blkdev_issue_secure_erase(struct block_device *bdev, sector_t sector,
>  	int ret = 0;
>  
>  	/* make sure that "len << SECTOR_SHIFT" doesn't overflow */
> -	if (max_sectors > UINT_MAX >> SECTOR_SHIFT)
> -		max_sectors = UINT_MAX >> SECTOR_SHIFT;
> +	if (max_sectors > BIO_MAX_SECTORS)
> +		max_sectors = BIO_MAX_SECTORS;
>  	max_sectors &= ~bs_mask;
>  
>  	if (max_sectors == 0)
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index b82c6d304658..0eb0aef97197 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -95,13 +95,13 @@ static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
>  }
>  
>  /*
> - * The max size one bio can handle is UINT_MAX becasue bvec_iter.bi_size
> - * is defined as 'unsigned int', meantime it has to be aligned to with the
> + * The maximum size that a bio can fit has to be aligned down to the
>   * logical block size, which is the minimum accepted unit by hardware.
>   */
>  static unsigned int bio_allowed_max_sectors(const struct queue_limits *lim)
>  {
> -	return round_down(UINT_MAX, lim->logical_block_size) >> SECTOR_SHIFT;
> +	return round_down(BIO_MAX_SIZE, lim->logical_block_size) >>
> +			SECTOR_SHIFT;
>  }
>  
>  /*
> @@ -502,7 +502,7 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
>  
>  	rq_for_each_bvec(bv, rq, iter)
>  		bvec_split_segs(&rq->q->limits, &bv, &nr_phys_segs, &bytes,
> -				UINT_MAX, UINT_MAX);
> +				UINT_MAX, BIO_MAX_SIZE);
>  	return nr_phys_segs;
>  }
>  
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 19a888a2f104..d59553324a84 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -281,7 +281,8 @@ struct bio {
>  };
>  
>  #define BIO_RESET_BYTES		offsetof(struct bio, bi_max_vecs)
> -#define BIO_MAX_SECTORS		(UINT_MAX >> SECTOR_SHIFT)
> +#define BIO_MAX_SIZE		UINT_MAX /* max value of bi_iter.bi_size */
> +#define BIO_MAX_SECTORS		(BIO_MAX_SIZE >> SECTOR_SHIFT)
>  
>  static inline struct bio_vec *bio_inline_vecs(struct bio *bio)
>  {
> -- 
> 2.47.3
> 
>