linux-kernel - Re: [PATCHv3 3/8] block: align the bio after building it

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Message-ID: <e2520739-e4c2-49e7-a5b1-3b205c79ef21@kernel.org>
Date: Wed, 20 Aug 2025 16:07:18 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Keith Busch <kbusch@...a.com>, linux-block@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: snitzer@...nel.org, axboe@...nel.dk, dw@...idwei.uk, brauner@...nel.org,
 hch@....de, martin.petersen@...cle.com, djwong@...nel.org,
 linux-xfs@...r.kernel.org, viro@...iv.linux.org.uk,
 Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCHv3 3/8] block: align the bio after building it

On 8/20/25 1:49 AM, Keith Busch wrote:
> From: Keith Busch <kbusch@...nel.org>
> 
> Instead of ensuring each vector is block size aligned while constructing
> the bio, just ensure the entire size is aligned after it's built. This
> makes getting bio pages more flexible to accepting device valid io
> vectors that would otherwise get rejected by alignment checks.
> 
> Signed-off-by: Keith Busch <kbusch@...nel.org>

[...]

> +/*
> + * Aligns the bio size to the len_align_mask, releasing any excessive bio vecs
> + * that  __bio_iov_iter_get_pages may have inserted and reverts that length for
> + * the next iteration.
> + */
> +static int bio_align(struct bio *bio, struct iov_iter *iter,
> +			    unsigned len_align_mask)
> +{
> +	size_t nbytes = bio->bi_iter.bi_size & len_align_mask;
> +
> +	if (!nbytes)
> +		return 0;
> +
> +	iov_iter_revert(iter, nbytes);
> +	bio->bi_iter.bi_size -= nbytes;
> +	while (nbytes) {
> +		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> +
> +		if (nbytes < bv->bv_len) {
> +			bv->bv_len -= nbytes;
> +			nbytes = 0;

Nit: remove the "nbytes = 0" and do a break here ?

> +		} else {
> +			bio_release_page(bio, bv->bv_page);
> +			bio->bi_vcnt--;
> +			nbytes -= bv->bv_len;
> +		}
> +	}
> +
> +	if (!bio->bi_iter.bi_size)
> +		return -EFAULT;
> +	return 0;
> +}
> +



-- 
Damien Le Moal
Western Digital Research