[Devel] [PATCH hci-8.1 v8 3/6] dm-qcow2: extend the file for a new refblock in allocate_cluster()
Alexander Ivanov
alexander.ivanov at virtuozzo.com
Mon Oct 26 17:42:20 MSK 2026
place_r2() links a new refblock into R1, but moves neither file_size
nor file_preallocated_area_start. The refblock stays at or above the
watermark if truncate_prealloc_safe() in allocate_cluster() fails
after place_r2(), or if a parallel mark_cluster_unused() lowers
free_cluster_search_pos before the second pass of
find_unused_cluster(). Truncation of preallocations on suspend then
cuts the file under the refblock: R1 on disk points past EOF, and
the next session gets -EIO on allocations in the range it covers.
Make find_unused_cluster() report a position not covered by R2
instead of placing the refblock there itself. allocate_cluster()
prepares that cluster the same way as a data cluster, with the punch,
extend and watermark update moved into prepare_unused_cluster(), and
calls place_r2() before searching again.
https://virtuozzo.atlassian.net/browse/VSTOR-148171
Feature: dm-qcow2: block device over QCOW2 files driver
Signed-off-by: Alexander Ivanov <alexander.ivanov at virtuozzo.com>
---
drivers/md/dm-qcow2-map.c | 88 ++++++++++++++++++++++-----------------
1 file changed, 50 insertions(+), 38 deletions(-)
diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
index 78ee7cf5e881..5952b5feb8bf 100644
--- a/drivers/md/dm-qcow2-map.c
+++ b/drivers/md/dm-qcow2-map.c
@@ -2085,21 +2085,12 @@ static int parse_metadata(struct qcow2 *qcow2, struct qio **qio,
* and connects it to R1 table entry.
*/
static int place_r2(struct qcow2 *qcow2, struct qcow2_map_item *r1,
- struct qcow2_map_item *r2, loff_t r2_pos, struct qio **qio)
+ struct qcow2_map_item *r2, loff_t r2_pos)
{
struct dm_target *ti = qcow2->tgt->ti;
u64 page_id = r2_pos >> PAGE_SHIFT;
int ret;
- if (delay_if_writeback(qcow2, r1->md, r1->index_in_page, qio, true))
- return 0;
-
- ret = qcow2_punch_hole(qcow2->file, r2_pos, qcow2->clu_size);
- if (ret) {
- QC_ERR(ti, "punch hole: %d", ret);
- return ret;
- }
-
ret = qcow2_alloc_and_insert_md_page(qcow2, page_id, &r2->md);
if (ret < 0) {
QC_ERR(ti, "Can't alloc: ret=%d, page_id=%llu", ret, page_id);
@@ -2115,7 +2106,7 @@ static int place_r2(struct qcow2 *qcow2, struct qcow2_map_item *r1,
spin_unlock_irq(&qcow2->md_pages_lock);
mark_cluster_used(qcow2, r2->md, r2->index_in_page);
- return 1;
+ return 0;
}
static s32 find_unused_block_entry(struct qcow2 *qcow2, struct md_page *md,
@@ -2137,11 +2128,13 @@ static s32 find_unused_block_entry(struct qcow2 *qcow2, struct md_page *md,
static loff_t find_unused_cluster(struct qcow2 *qcow2, struct qio **qio,
struct qcow2_map_item *r1,
- struct qcow2_map_item *r2)
+ struct qcow2_map_item *r2, bool *needs_r2)
{
u32 clu_size = qcow2->clu_size;
s32 index, ret;
loff_t pos;
+
+ *needs_r2 = false;
again:
pos = READ_ONCE(qcow2->free_cluster_search_pos);
if (pos >= qcow2->reftable_max_file_size)
@@ -2153,15 +2146,15 @@ static loff_t find_unused_cluster(struct qcow2 *qcow2, struct qio **qio,
return ret;
/*
* Since pos is not covered by R2, the whole cluster
- * must be unused. Use it to store R2 cluster.
+ * must be unused. The caller stores R2 cluster there.
* Both indexes must be 0 here, because of we allocate
* clusters from small to big.
*/
WARN_ON_ONCE(r2->index_in_page != 0 || r2->index != 0);
- ret = place_r2(qcow2, r1, r2, pos, qio);
- if (ret <= 0)
- return ret;
- goto again;
+ if (delay_if_writeback(qcow2, r1->md, r1->index_in_page, qio, true))
+ return 0;
+ *needs_r2 = true;
+ return pos;
}
spin_lock_irq(&qcow2->md_pages_lock);
@@ -2432,6 +2425,37 @@ static int relocate_refcount_table(struct qcow2 *qcow2, struct qio **qio)
return -EIO;
}
+/*
+ * Zero the unused cluster at @pos and make the file size and
+ * file_preallocated_area_start cover it.
+ */
+static int prepare_unused_cluster(struct qcow2 *qcow2, loff_t pos)
+{
+ loff_t off, end = pos + qcow2->clu_size;
+ loff_t old_size = qcow2->file_size;
+ int ret;
+
+ if (pos < qcow2->file_preallocated_area_start) {
+ /* Clu at @pos may contain dirty data */
+ off = min_t(loff_t, old_size, end);
+ ret = qcow2_punch_hole(qcow2->file, pos, off - pos);
+ if (ret) {
+ QC_ERR(qcow2->tgt->ti, "punch hole: %d", ret);
+ return ret;
+ }
+ }
+
+ if (end > old_size) {
+ ret = truncate_prealloc_safe(qcow2, end, __func__);
+ if (ret)
+ return ret;
+ }
+
+ if (end > qcow2->file_preallocated_area_start)
+ qcow2->file_preallocated_area_start = end;
+ return 0;
+}
+
/*
* This function is aimed to be called only from main work.
* In case of wish to use it from more places, it's needed
@@ -2441,13 +2465,12 @@ static int relocate_refcount_table(struct qcow2 *qcow2, struct qio **qio)
static loff_t allocate_cluster(struct qcow2 *qcow2, struct qio *qio,
struct md_page **r2_md, u32 *r2_index_in_page)
{
- u32 clu_size = qcow2->clu_size;
- struct file *file = qcow2->file;
- loff_t pos, off, end, old_size;
struct qcow2_map_item r1, r2;
+ bool needs_r2;
+ loff_t pos;
int ret;
again:
- pos = find_unused_cluster(qcow2, &qio, &r1, &r2);
+ pos = find_unused_cluster(qcow2, &qio, &r1, &r2, &needs_r2);
if (unlikely(pos == -ENOENT)) {
ret = relocate_refcount_table(qcow2, &qio);
if (ret <= 0)
@@ -2457,28 +2480,17 @@ static loff_t allocate_cluster(struct qcow2 *qcow2, struct qio *qio,
if (pos <= 0)
return pos;
- end = pos + clu_size;
- old_size = qcow2->file_size;
-
- if (pos < qcow2->file_preallocated_area_start) {
- /* Clu at @pos may contain dirty data */
- off = min_t(loff_t, old_size, end);
- ret = qcow2_punch_hole(file, pos, off - pos);
- if (ret) {
- QC_ERR(qcow2->tgt->ti, "punch hole: %d", ret);
- return ret;
- }
- }
+ ret = prepare_unused_cluster(qcow2, pos);
+ if (ret)
+ return ret;
- if (end > old_size) {
- ret = truncate_prealloc_safe(qcow2, end, __func__);
+ if (needs_r2) {
+ ret = place_r2(qcow2, &r1, &r2, pos);
if (ret)
return ret;
+ goto again;
}
- if (end > qcow2->file_preallocated_area_start)
- qcow2->file_preallocated_area_start = end;
-
mark_cluster_used(qcow2, r2.md, r2.index_in_page);
if (r2_md)
*r2_md = r2.md;
--
2.53.0
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