[Devel] [PATCH vz9] dm-qcow2: only use inline bvec if iteration is valid

[Pavel Tikhomirov]

Looks good. See small comment inline:

On 12/17/24 18:34, Alexander Atanasov wrote:
> In some cases qcow2 is passed requests without bvec set and
> zero bi_size - for such requests qcow2 resorts to inline bvecs
> which in that case are invalid.
> 
> To address this:
> - Check if bi_size is not zero, and only then use the inline bvecs.
> - Properly count number of segments in a NULL bvec.
> - Add warn on to catch if we have a requests without bvec and bi_size.
> 
> https://virtuozzo.atlassian.net/browse/PSBM-159903
> Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
> ---
>   drivers/md/dm-qcow2-map.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index 6585f3fac6e7..a28f6332dc08 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -308,6 +308,9 @@ static unsigned int qio_nr_segs(struct qio *qio)
>   	struct bvec_iter iter;
>   	struct bio_vec bv;
>   
> +	if (!qio->bi_io_vec)
> +		return nr_segs;

maybe just "return 0" (to improve readability) ?

> +
>   	qcow2_for_each_bvec(iter, bv, qio->bi_iter, qio->bi_io_vec)
>   		nr_segs++;
>   
> @@ -1248,6 +1251,7 @@ static void __submit_rw_mapped(struct qcow2 *qcow2, struct qio *qio, u32 nr_segs
>   	bvec = __bvec_iter_bvec(qio->bi_io_vec, qio->bi_iter);
>   	pos = to_bytes(qio->bi_iter.bi_sector);
>   
> +	WARN_ON(qio->bi_iter.bi_size && !bvec);
>   	iov_iter_bvec(&iter, rw, bvec, nr_segs, qio->bi_iter.bi_size);
>   	iter.iov_offset = qio->bi_iter.bi_bvec_done;
>   
> @@ -3538,7 +3542,7 @@ static void prepare_one_embedded_qio(struct qcow2 *qcow2, struct qio *qio,
>   	} else {
>   		/* Single bio already provides bvec array */
>   		bvec = rq->bio->bi_io_vec;
> -		if (!bvec) {
> +		if (!bvec && rq->bio->bi_iter.bi_size) {
>   			bvec = rq->bio->bi_inline_vecs;
>   			if (unlikely(!bvec)) {
>   				QC_ERR(qcow2->tgt->ti, "Expecting inline bvec");

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.