From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Tikhomirov Date: Fri, 14 Aug 2026 12:25:35 +0200 Subject: Re: [Devel] [PATCH VZ10 4/6] drivers/md/dm-qcow2: fix seek skip to the next L2 table In-Reply-To: <20260810123000.19834-5-andrey.zhadchenko@virtuozzo.com> References: <20260810123000.19834-1-andrey.zhadchenko@virtuozzo.com> <20260810123000.19834-5-andrey.zhadchenko@virtuozzo.com> Message-ID: <4b243dfd-3796-47aa-a384-221f1c065b25@virtuozzo.com> List-Id: On 8/10/26 14:29, Andrey Zhadchenko wrote: > get_next_l2() adds the number of remaining clusters to the current > sector, so for a position which is not cluster aligned (e.g. the > llseek offset itself) the result overshoots the L2 table boundary by > the in-cluster offset. > > Compute the boundary from the cluster index instead of adding to the > current position. > > https://virtuozzo.atlassian.net/browse/VSTOR-139407 > Feature: dm-qcow2: block device over QCOW2 files driver > Signed-off-by: Andrey Zhadchenko > --- > drivers/md/dm-qcow2-map.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c > index d6d15b04215c6..776e89fc4eb1b 100644 > --- a/drivers/md/dm-qcow2-map.c > +++ b/drivers/md/dm-qcow2-map.c > @@ -4405,12 +4405,12 @@ static struct qio *free_seek_qio_ret_higher(struct qio *qio) > static inline sector_t get_next_l2(struct qio *qio) > { > struct qcow2 *qcow2 = qio->qcow2; > - loff_t start, add; > + u64 base_l2, add; > > - start = to_bytes(qio->bi_iter.bi_sector); > - add = qcow2->l2_entries - (start / qcow2->clu_size) % qcow2->l2_entries; > + base_l2 = to_bytes(qio->bi_iter.bi_sector) / qcow2->clu_size; > + add = qcow2->l2_entries - base_l2 % qcow2->l2_entries; > > - return qio->bi_iter.bi_sector + (qcow2->clu_size / to_bytes(1)) * add; > + return to_sector((base_l2 + add) * qcow2->clu_size); The above code seems too complex to what it actually tries to accomplish, it's just an alignment, what about: static inline sector_t get_next_l2(struct qio *qio) { struct qcow2 *qcow2 = qio->qcow2; u64 l2_covered = (u64)qcow2->clu_size * qcow2->l2_entries; return to_sector(round_up(to_bytes(qio->bi_iter.bi_sector) + 1, l2_covered)); } > } > > static inline sector_t get_next_clu(struct qio *qio) -- Best regards, Pavel Tikhomirov Senior Software Developer, Virtuozzo.