From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Tikhomirov Date: Fri, 14 Aug 2026 11:55:26 +0200 Subject: Re: [Devel] [PATCH VZ10 2/6] drivers/md/dm-qcow2: keep seek parse window within limit In-Reply-To: <20260810123000.19834-3-andrey.zhadchenko@virtuozzo.com> References: <20260810123000.19834-1-andrey.zhadchenko@virtuozzo.com> <20260810123000.19834-3-andrey.zhadchenko@virtuozzo.com> Message-ID: <23cafc93-d83e-4cf9-9c7b-4f6e0e317d02@virtuozzo.com> List-Id: On 8/10/26 14:29, Andrey Zhadchenko wrote: > seek_qio_next_clu() always sets the window size to the whole > cluster, so the window may cross the scan limit. The top level qio > then parses metadata past the virtual disk end if the disk size is > not cluster aligned, and SEEK_HOLE may report "sector + size" past > the limit. > This is especially painful for lower delta seeks, since at top > level this is luckily alleviated by blkdev_llseek_wrapper(). > > Add seek_qio_set_sector(), which sets bi_sector and also clamps > bi_size if needed. > > 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 | 29 +++++++++++++++++------------ > 1 file changed, 17 insertions(+), 12 deletions(-) > > diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c > index 542c7949321e5..342e4af688509 100644 > --- a/drivers/md/dm-qcow2-map.c > +++ b/drivers/md/dm-qcow2-map.c > @@ -4352,6 +4352,16 @@ struct qio_data_llseek_hole { > > #define SEEK_QIO_DATA(qio) ((struct qio_data_llseek_hole *)qio->data) > > +static void seek_qio_set_sector(struct qio *qio, sector_t bi_sector) > +{ > + loff_t pos = to_bytes(bi_sector); > + loff_t end = round_up(pos + 1, qio->qcow2->clu_size); > + > + qio->bi_iter.bi_sector = bi_sector; > + end = min_t(loff_t, end, SEEK_QIO_DATA(qio)->lim); > + qio->bi_iter.bi_size = end > pos ? end - pos : 0; > +} > + > static struct qio *alloc_seek_qio(struct qcow2 *qcow2, struct qio *parent, loff_t new_lim) > { > struct qio_data_llseek_hole *data; > @@ -4376,12 +4386,7 @@ static struct qio *alloc_seek_qio(struct qcow2 *qcow2, struct qio *parent, loff_ > > if (parent) { > data->higher = parent; > - qio->bi_iter.bi_sector = parent->bi_iter.bi_sector; > - > - if (to_bytes(qio->bi_iter.bi_sector) + parent->bi_iter.bi_size > new_lim) > - qio->bi_iter.bi_size = new_lim - to_bytes(qio->bi_iter.bi_sector); > - else > - qio->bi_iter.bi_size = parent->bi_iter.bi_size; > + seek_qio_set_sector(qio, parent->bi_iter.bi_sector); Can new_lim be smaller than the end derived from qio->qcow2->clu_size? It looks like now we ignore new_lim completely. > } > > return qio; > @@ -4422,16 +4427,18 @@ static inline sector_t get_next_clu(struct qio *qio) > > static inline void seek_qio_next_clu(struct qio *qio, struct qcow2_map *map) > { > + sector_t bi_sector; > + > /* > * Whole L2 table is unmapped - skip to next l2 table, > * but only if there is no backing image > */ > if (map && !(map->level & L2_LEVEL) && !qio->qcow2->lower) > - qio->bi_iter.bi_sector = get_next_l2(qio); > + bi_sector = get_next_l2(qio); > else > - qio->bi_iter.bi_sector = get_next_clu(qio); > + bi_sector = get_next_clu(qio); > > - qio->bi_iter.bi_size = qio->qcow2->clu_size; > + seek_qio_set_sector(qio, bi_sector); > } > > static struct qio *advance_and_spawn_lower_seek_qio(struct qio *old_qio, u32 size) > @@ -4567,9 +4574,7 @@ loff_t qcow2_llseek_hole(struct dm_target *ti, loff_t offset, int whence) > if (!qio) > return -ENOMEM; > > - qio->bi_iter.bi_sector = to_sector(offset); > - qio->bi_iter.bi_size = qcow2->clu_size - > - to_bytes(qio->bi_iter.bi_sector) % qcow2->clu_size; > + seek_qio_set_sector(qio, to_sector(offset)); > > ret = qcow2_llseek_hole_qio(qio, whence, &result); > /* In case of error remap ENXIO as it have special meaning for llseek */ -- Best regards, Pavel Tikhomirov Senior Software Developer, Virtuozzo.