Re: [PATCH 2/2] qcow2: put discards in discard queue when discard-no-unref is enabled

[Jean-Louis Dupond]

On 5/12/25 14:28, Hanna Czenczek wrote:

On 29.04.25 12:31, Jean-Louis Dupond wrote:

When discard-no-unref is enabled, discards are not queued like it
should.
This was broken since discard-no-unref was added.

Add some helper function qcow2_discard_cluster which handles some common
checks and calls the queue_discards function if needed to add the
discard request to the queue.

Signed-off-by: Jean-Louis Dupond <jean-lo...@dupond.be>
---
  block/qcow2-cluster.c  | 16 ++++++----------
  block/qcow2-refcount.c | 19 ++++++++++++++++++-
  block/qcow2.h          |  4 ++++
  3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index ce8c0076b3..c655bf6df4 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c

@@ -1978,12 +1978,10 @@ discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, uint64_t nb_clusters,

          if (!keep_reference) {
              /* Then decrease the refcount */
              qcow2_free_any_cluster(bs, old_l2_entry, type);
-        } else if (s->discard_passthrough[type] &&
-                   (cluster_type == QCOW2_CLUSTER_NORMAL ||
-                    cluster_type == QCOW2_CLUSTER_ZERO_ALLOC)) {
+        } else {
              /* 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_discard_cluster(bs, old_l2_entry & L2E_OFFSET_MASK,
+                                  s->cluster_size, cluster_type, type);
          }
      }

  @@ -2092,12 +2090,10 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,

              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)) {
+            } else {

                  /* 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_discard_cluster(bs, old_l2_entry & L2E_OFFSET_MASK, +                            s->cluster_size, type, QCOW2_DISCARD_REQUEST);

              }
          }
      }
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index d796018970..e1f830504d 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c

@@ -1205,6 +1205,23 @@ void qcow2_free_any_cluster(BlockDriverState *bs, uint64_t l2_entry,

      }
  }
  +void qcow2_discard_cluster(BlockDriverState *bs, uint64_t offset,
+                           uint64_t length, QCow2ClusterType ctype,
+                           enum qcow2_discard_type dtype) {
+

QEMU coding style requires putting the { on a separate line.

Fixed

+    BDRVQcow2State *s = bs->opaque;
+
+    if (s->discard_passthrough[dtype] &&
+        (ctype == QCOW2_CLUSTER_NORMAL ||
+         ctype == QCOW2_CLUSTER_ZERO_ALLOC)) {
+        if (has_data_file(bs)) {
+            bdrv_pdiscard(s->data_file, offset, length);
+        } else {
+            queue_discard(bs, offset, length);
+        }
+    }
+}
+
  int qcow2_write_caches(BlockDriverState *bs)
  {
      BDRVQcow2State *s = bs->opaque;

@@ -3619,7 +3636,7 @@ qcow2_discard_refcount_block(BlockDriverState *bs, uint64_t discard_block_offs)

          /* discard refblock from the cache if refblock is cached */
          qcow2_cache_discard(s->refcount_block_cache, refblock);
      }
-    update_refcount_discard(bs, discard_block_offs, s->cluster_size);
+    queue_discard(bs, discard_block_offs, s->cluster_size);
        return 0;
  }

This hunk should go into the previous patch.

Fixed

diff --git a/block/qcow2.h b/block/qcow2.h
index a9e3481c6e..547bb2b814 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h

@@ -880,6 +880,10 @@ void GRAPH_RDLOCK qcow2_free_clusters(BlockDriverState *bs,

  void GRAPH_RDLOCK
  qcow2_free_any_cluster(BlockDriverState *bs, uint64_t l2_entry,
                         enum qcow2_discard_type type);
+void GRAPH_RDLOCK
+qcow2_discard_cluster(BlockDriverState *bs, uint64_t offset,
+                      uint64_t length, QCow2ClusterType ctype,
+                      enum qcow2_discard_type dtype);
    int GRAPH_RDLOCK

  qcow2_update_snapshot_refcount(BlockDriverState *bs, int64_t l1_table_offset,

With the above done, for both patch 1 and 2:

Reviewed-by: Hanna Czenczek <hre...@redhat.com>

Send v2 patch with comments addressed.

Thanks
Jean-Louis