From: Max Reitz <mreitz@redhat.com>
Date: Wed, 3 May 2017 23:11:19 +0000 (+0200)
Subject: qcow2: Discard preallocated zero clusters
X-Git-Tag: v2.10.0-rc0~200^2~11
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=293073a56c6c921c9902da17711914a0042f29ba;p=thirdparty%2Fqemu.git

qcow2: Discard preallocated zero clusters

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>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index fb91fd8979e..31077d81021 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;