[3/4] qcow2: Discard preallocated zero clusters
diff mbox

Message ID 20170503231120.23507-4-mreitz@redhat.com
State New
Headers show

Commit Message

Max Reitz May 3, 2017, 11:11 p.m. UTC
In discard_single_l2(), we completely discard normal clusters instead of
simply turning them into preallocated zero clusters. That means we
should probably do the same with such preallocated zero clusters:
Discard them instead of keeping them allocated.

Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-cluster.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Eric Blake May 4, 2017, 12:58 a.m. UTC | #1
On 05/03/2017 06:11 PM, Max Reitz wrote:
> In discard_single_l2(), we completely discard normal clusters instead of
> simply turning them into preallocated zero clusters. That means we
> should probably do the same with such preallocated zero clusters:
> Discard them instead of keeping them allocated.
> 
> Reported-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-cluster.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

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

> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index fb91fd8979..31077d8102 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1511,7 +1511,8 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset,
>                  break;
>  
>              case QCOW2_CLUSTER_ZERO:
> -                if (!full_discard) {
> +                /* Preallocated zero clusters should be discarded in any case */
> +                if (!full_discard && (old_l2_entry & L2E_OFFSET_MASK) == 0) {

Again, if we had a separate QCOW2_CLUSTER_* for plain vs. pre-allocated
zero, this might be easier to write.

Patch
diff mbox

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index fb91fd8979..31077d8102 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1511,7 +1511,8 @@  static int discard_single_l2(BlockDriverState *bs, uint64_t offset,
                 break;
 
             case QCOW2_CLUSTER_ZERO:
-                if (!full_discard) {
+                /* Preallocated zero clusters should be discarded in any case */
+                if (!full_discard && (old_l2_entry & L2E_OFFSET_MASK) == 0) {
                     continue;
                 }
                 break;