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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: devel-bounces@openvz.org Errors-To: devel-bounces@openvz.org On 10/8/26 12:04, Alexander Ivanov wrote: > On postsuspend we truncate the image file only down to > file_preallocated_area_start, i.e. we drop preallocations only. > Clusters at the end of the file freed by discard (refcount dropped > to zero) are never given back, so the file size never shrinks. > > Add qcow2_calc_used_end(), which scans refcount blocks backward from > file_preallocated_area_start and returns the end of the last cluster > with non-zero refcount. Refcount ranges with no allocated refblock > are skipped at once. Metadata pages are taken from md cache or read > synchronously. This is called on suspended device after md writeback, > so R1 and R2 can't change under us. > > Truncate the file to the used end. Skip the scan if md writeback > failed, as refcounts on disk are stale then, and fall back to the old > behaviour on scan error. > > https://virtuozzo.atlassian.net/browse/VSTOR-148171 > Feature: dm-qcow2: block device over QCOW2 files driver > > Signed-off-by: Alexander Ivanov > --- > drivers/md/dm-qcow2-map.c | 56 ++++++++++++++++++++++++++++++++++++ > drivers/md/dm-qcow2-target.c | 12 +++++++- > drivers/md/dm-qcow2.h | 1 + > 3 files changed, 68 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c > index 78ee7cf5e881..65ee6ae144bf 100644 > --- a/drivers/md/dm-qcow2-map.c > +++ b/drivers/md/dm-qcow2-map.c > @@ -2208,6 +2208,62 @@ int qcow2_truncate_safe(struct file *file, loff_t new_len) > return do_ftruncate(file, new_len, 0); > } > > +/* > + * Returns the end of the last cluster, which is used according > + * to refcount table, clamped to file_preallocated_area_start since > + * the last cluster may be partial. Clusters freed by discard may > + * leave the tail of file unused. Everything at or above > + * file_preallocated_area_start is unused by construction, so the scan > + * starts below it. This must be called on suspended device after md > + * writeback, so nobody changes R1 and R2. > + */ > +loff_t qcow2_calc_used_end(struct qcow2 *qcow2) > +{ > + u32 clu_size = qcow2->clu_size; > + struct qcow2_map_item r1, r2; > + struct md_page *r1_md = NULL; > + loff_t pos; > + s32 i; > + int ret; > + > + pos = round_down(qcow2->file_preallocated_area_start - 1, clu_size); > + while (pos >= 0) { > + if (calc_refcounters_map(qcow2, pos, &r1, &r2) < 0) > + return -EIO; > + > + if (!r1_md || r1_md->id != r1.page_id) { > + ret = qcow2_md_page_read_sync(qcow2, r1.page_id, &r1_md); > + if (ret) > + return ret; > + } > + r1.md = r1_md; > + > + ret = calc_r2_page_id(qcow2, &r1, &r2); > + if (ret == -ENOENT) { > + /* No R2 cluster, so all clusters it covers are unused */ > + pos = (loff_t)r1.index * qcow2->refblock_entries * clu_size; > + pos -= clu_size; > + continue; > + } > + > + if (ret < 0) > + return ret; > + > + ret = qcow2_md_page_read_sync(qcow2, r2.page_id, &r2.md); > + if (ret) > + return ret; > + > + for (i = r2.index_in_page; i >= 0; i--, pos -= clu_size) { > + /* Last cluster is partial if size isn't cluster-aligned */ > + if (get_r2_entry(qcow2, r2.md, i)) > + return min_t(loff_t, pos + clu_size, > + qcow2->file_preallocated_area_start); > + } > + } > + > + return -EIO; > +} > + > static int truncate_prealloc_safe(struct qcow2 *qcow2, loff_t len, const char *func) > { > loff_t prealloc_len, max_prealloc_len = qcow2->reftable_max_file_size; > diff --git a/drivers/md/dm-qcow2-target.c b/drivers/md/dm-qcow2-target.c > index b3d5d5e8c7c2..5a72d0f2e9ef 100644 > --- a/drivers/md/dm-qcow2-target.c > +++ b/drivers/md/dm-qcow2-target.c > @@ -1042,11 +1042,21 @@ static void qcow2_truncate_preallocations(struct dm_target *ti) > { > struct qcow2_target *tgt = to_qcow2_target(ti); > struct qcow2 *qcow2 = top_qcow2_protected(ti); > - loff_t end = qcow2->file_preallocated_area_start; > + loff_t used_end, end = qcow2->file_preallocated_area_start; > int ret; > > if (!(dm_table_get_mode(ti->table) & FMODE_WRITE)) > return; > + > + /* Refcounts on disk are stale after failed md writeback */ > + if (!tgt->md_writeback_error) { > + used_end = qcow2_calc_used_end(qcow2); > + if (used_end < 0) > + QC_ERR(ti, "Can't find used end: %pe", ERR_PTR(used_end)); > + else > + end = used_end; > + } > + > if (end == qcow2->file_size) > return; > > diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h > index 69d3ae6fca8a..73d3cf175bbf 100644 > --- a/drivers/md/dm-qcow2.h > +++ b/drivers/md/dm-qcow2.h > @@ -411,6 +411,7 @@ void qcow2_ref_dec(struct qcow2_target *tgt, u8 ref_index); > int qcow2_inflight_ref_switch(struct qcow2_target *tgt); > void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2); > int qcow2_truncate_safe(struct file *file, loff_t new_len); > +loff_t qcow2_calc_used_end(struct qcow2 *qcow2); > > void qcow2_merge_backward_work(struct work_struct *work); > void qcow2_merge_backward_cancel(struct qcow2_target *tgt); Please say in the cover letter or the commit message that close and the RO reload also go through postsuspend, so readers don't have to work it out. _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel