[PATCH v2 0/2] qcow2: queue discards when discard-no-unref enabled

[PATCH v2 0/2] qcow2: queue discards when discard-no-unref enabled

[Jean-Louis Dupond]

Partially based on the proposal of Andrey in
https://patchew.org/QEMU/20240913163942.423050-1-andrey.drobyshev@virtuozzo.com/
Split up this from the rest might get it merged a bit quicker hopefully :)

Since the implementation of discard-no-unref, we did not queue the discards correctly
when discard-no-unref was enabled.

Jean-Louis Dupond (2):
  qcow2: rename update_refcount_discard to queue_discard
  qcow2: put discards in discard queue when discard-no-unref is enabled

 block/qcow2-cluster.c  | 16 ++++++----------
 block/qcow2-refcount.c | 25 +++++++++++++++++++++----
 block/qcow2.h          |  4 ++++
 3 files changed, 31 insertions(+), 14 deletions(-)

-- 
2.49.0

[PATCH v2 1/2] qcow2: rename update_refcount_discard to queue_discard

[Jean-Louis Dupond]

The function just queues discards, and doesn't do any refcount change.
So let's change the function name to align with its function.

Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
---
 block/qcow2-refcount.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 0266542cee..8fb210501c 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -754,8 +754,8 @@ void qcow2_process_discards(BlockDriverState *bs, int ret)
     }
 }
 
-static void update_refcount_discard(BlockDriverState *bs,
-                                    uint64_t offset, uint64_t length)
+static void queue_discard(BlockDriverState *bs,
+                          uint64_t offset, uint64_t length)
 {
     BDRVQcow2State *s = bs->opaque;
     Qcow2DiscardRegion *d, *p, *next;
@@ -902,7 +902,7 @@ update_refcount(BlockDriverState *bs, int64_t offset, int64_t length,
             }
 
             if (s->discard_passthrough[type]) {
-                update_refcount_discard(bs, cluster_offset, s->cluster_size);
+                queue_discard(bs, cluster_offset, s->cluster_size);
             }
         }
     }
@@ -3619,7 +3619,7 @@ 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;
 }
-- 
2.49.0

[PATCH v2 2/2] qcow2: put discards in discard queue when discard-no-unref is enabled

[Jean-Louis Dupond]

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-louis@dupond.be>
---
 block/qcow2-cluster.c  | 16 ++++++----------
 block/qcow2-refcount.c | 17 +++++++++++++++++
 block/qcow2.h          |  4 ++++
 3 files changed, 27 insertions(+), 10 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 8fb210501c..6512cda407 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)
+{
+    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;
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,
-- 
2.49.0

Re: [PATCH v2 1/2] qcow2: rename update_refcount_discard to queue_discard

[Eric Blake]

On Tue, May 13, 2025 at 03:26:27PM +0200, Jean-Louis Dupond wrote:
> The function just queues discards, and doesn't do any refcount change.
> So let's change the function name to align with its function.
> 
> Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
> ---

Reviewed-by: Eric Blake <eblake@redhat.com>

>  block/qcow2-refcount.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 0266542cee..8fb210501c 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -754,8 +754,8 @@ void qcow2_process_discards(BlockDriverState *bs, int ret)
>      }
>  }
>  
> -static void update_refcount_discard(BlockDriverState *bs,
> -                                    uint64_t offset, uint64_t length)
> +static void queue_discard(BlockDriverState *bs,
> +                          uint64_t offset, uint64_t length)
>  {
>      BDRVQcow2State *s = bs->opaque;
>      Qcow2DiscardRegion *d, *p, *next;
> @@ -902,7 +902,7 @@ update_refcount(BlockDriverState *bs, int64_t offset, int64_t length,
>              }
>  
>              if (s->discard_passthrough[type]) {
> -                update_refcount_discard(bs, cluster_offset, s->cluster_size);
> +                queue_discard(bs, cluster_offset, s->cluster_size);
>              }
>          }
>      }
> @@ -3619,7 +3619,7 @@ 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;
>  }
> -- 
> 2.49.0
> 
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org

Re: [PATCH v2 2/2] qcow2: put discards in discard queue when discard-no-unref is enabled

[Eric Blake]

On Tue, May 13, 2025 at 03:26:28PM +0200, 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

s/Add some/Add a/

(presumably the maintainer will fix the typo when queueing the patch,
no need to respin if the only change is a trivial commit message typo)

> checks and calls the queue_discards function if needed to add the
> discard request to the queue.
> 
> Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
> ---
>  block/qcow2-cluster.c  | 16 ++++++----------
>  block/qcow2-refcount.c | 17 +++++++++++++++++
>  block/qcow2.h          |  4 ++++
>  3 files changed, 27 insertions(+), 10 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org

Re: [PATCH v2 0/2] qcow2: queue discards when discard-no-unref enabled

[Jean-Louis Dupond]

On 13/05/2025 15:26, Jean-Louis Dupond wrote:
> Partially based on the proposal of Andrey in
> https://patchew.org/QEMU/20240913163942.423050-1-andrey.drobyshev@virtuozzo.com/
> Split up this from the rest might get it merged a bit quicker hopefully :)
>
> Since the implementation of discard-no-unref, we did not queue the discards correctly
> when discard-no-unref was enabled.
>
> Jean-Louis Dupond (2):
>    qcow2: rename update_refcount_discard to queue_discard
>    qcow2: put discards in discard queue when discard-no-unref is enabled
>
>   block/qcow2-cluster.c  | 16 ++++++----------
>   block/qcow2-refcount.c | 25 +++++++++++++++++++++----
>   block/qcow2.h          |  4 ++++
>   3 files changed, 31 insertions(+), 14 deletions(-)
>
This was already reviewed.
Reviewed-by: Eric Blake <eblake@redhat.com>

Any chance on getting this merged?

Thanks
Jean-Louis