linux-kernel - Re: [PATCH v3 03/10] block: introduce bio_required_sector

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Date:   Wed, 16 Jun 2021 17:37:20 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v3 03/10] block: introduce bio_required_sector_alignment()

On Fri, Jun 04, 2021 at 07:58:53PM +0000, Satya Tangirala wrote:
> This function returns the required alignment for the number of sectors in
> a bio. In particular, the number of sectors passed to bio_split() must be
> aligned to this value.
> 
> Signed-off-by: Satya Tangirala <satyat@...gle.com>
> ---
>  block/blk.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/block/blk.h b/block/blk.h
> index 8b3591aee0a5..c8dcad7dde81 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -262,6 +262,20 @@ static inline unsigned int bio_allowed_max_sectors(struct request_queue *q)
>  	return round_down(UINT_MAX, queue_logical_block_size(q)) >> 9;
>  }
>  
> +/*
> + * The required sector alignment for a bio. The number of sectors in any bio
> + * must be aligned to this value.
> + */
> +static inline unsigned int bio_required_sector_alignment(struct bio *bio)
> +{
> +	unsigned int alignmask =
> +		(bdev_logical_block_size(bio->bi_bdev) >> SECTOR_SHIFT) - 1;
> +
> +	alignmask |= blk_crypto_bio_sectors_alignment(bio) - 1;
> +
> +	return alignmask + 1;
> +}

Looks fine, but I think we could rework the comment to be a bit easier to
understand:

/*
 * Return the number of sectors to which the size of the given bio (and any bios
 * split from it) must be aligned.
 *
 * Normally this is just the disk's logical block size in sectors, but it may be
 * greater if the bio has an encryption context.
 */
static inline unsigned int bio_required_sector_alignment(struct bio *bio)
{
	unsigned int alignmask =
		(bdev_logical_block_size(bio->bi_bdev) >> SECTOR_SHIFT) - 1;

	alignmask |= blk_crypto_bio_sectors_alignment(bio) - 1;

	return alignmask + 1;
}