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[PATCH v2] qcow2: keep reference on zeroize with discard-no-unref enable
From: |
Jean-Louis Dupond |
Subject: |
[PATCH v2] qcow2: keep reference on zeroize with discard-no-unref enabled |
Date: |
Tue, 5 Sep 2023 15:08:40 +0200 |
When the discard-no-unref flag is enabled, we keep the reference for
normal discard requests.
But when a discard is executed on a snapshot/qcow2 image with backing,
the discards are saved as zero clusters in the snapshot image.
When committing the snapshot to the backing file, not
discard_in_l2_slice is called but zero_in_l2_slice. Which did not had
any logic to keep the reference when discard-no-unref is enabled.
Therefor we add logic in the zero_in_l2_slice call to keep the reference
on commit.
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621
Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
---
block/qcow2-cluster.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index f4f6cd6ad0..fc764aea4d 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1984,7 +1984,7 @@ static int discard_in_l2_slice(BlockDriverState *bs,
uint64_t offset,
/* If we keep the reference, pass on the discard still */
bdrv_pdiscard(s->data_file, old_l2_entry & L2E_OFFSET_MASK,
s->cluster_size);
- }
+ }
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
@@ -2062,9 +2062,15 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
QCow2ClusterType type = qcow2_get_cluster_type(bs, old_l2_entry);
bool unmap = (type == QCOW2_CLUSTER_COMPRESSED) ||
((flags & BDRV_REQ_MAY_UNMAP) && qcow2_cluster_is_allocated(type));
- uint64_t new_l2_entry = unmap ? 0 : old_l2_entry;
+ bool keep_reference =
+ (s->discard_no_unref && type != QCOW2_CLUSTER_COMPRESSED);
+ uint64_t new_l2_entry = old_l2_entry;
uint64_t new_l2_bitmap = old_l2_bitmap;
+ if (unmap && !keep_reference) {
+ new_l2_entry = 0;
+ }
+
if (has_subclusters(s)) {
new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES;
} else {
@@ -2082,9 +2088,17 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap);
}
- /* Then decrease the refcount */
if (unmap) {
- qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST);
+ if (!keep_reference) {
+ /* Then decrease the refcount */
+ qcow2_free_any_cluster(bs, old_l2_entry,
QCOW2_DISCARD_REQUEST);
+ } else if (s->discard_passthrough[QCOW2_DISCARD_REQUEST] &&
+ (type == QCOW2_CLUSTER_NORMAL ||
+ type == QCOW2_CLUSTER_ZERO_ALLOC)) {
+ /* If we keep the reference, pass on the discard still */
+ bdrv_pdiscard(s->data_file, old_l2_entry & L2E_OFFSET_MASK,
+ s->cluster_size);
+ }
}
}
--
2.42.0
- [PATCH v2] qcow2: keep reference on zeroize with discard-no-unref enabled,
Jean-Louis Dupond <=