[Qemu-devel] [PATCH 15/28] qcow2: make is_allocated return true for zero clusters

[Stefan Hajnoczi]

From: Paolo Bonzini <address@hidden>

Otherwise, live migration of the top layer will miss zero clusters and
let the backing file show through.  This also matches what is done in qed.

QCOW2_CLUSTER_ZERO clusters are invalid in v2 image files.  Check this
directly in qcow2_get_cluster_offset instead of replicating the test
everywhere.

Cc: address@hidden
Signed-off-by: Paolo Bonzini <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 block/qcow2-cluster.c | 3 +++
 block/qcow2.c         | 6 +-----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index ff9ae18..d72d063 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -454,6 +454,9 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t 
offset,
         *cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;
         break;
     case QCOW2_CLUSTER_ZERO:
+        if (s->qcow_version < 3) {
+            return -EIO;
+        }
         c = count_contiguous_clusters(nb_clusters, s->cluster_size,
                 &l2_table[l2_index], 0,
                 QCOW_OFLAG_COMPRESSED | QCOW_OFLAG_ZERO);
diff --git a/block/qcow2.c b/block/qcow2.c
index ad43a13..1f99866 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -621,7 +621,7 @@ static int coroutine_fn 
qcow2_co_is_allocated(BlockDriverState *bs,
         *pnum = 0;
     }
 
-    return (cluster_offset != 0);
+    return (cluster_offset != 0) || (ret == QCOW2_CLUSTER_ZERO);
 }
 
 /* handle reading after the end of the backing file */
@@ -702,10 +702,6 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState 
*bs, int64_t sector_num,
             break;
 
         case QCOW2_CLUSTER_ZERO:
-            if (s->qcow_version < 3) {
-                ret = -EIO;
-                goto fail;
-            }
             qemu_iovec_memset(&hd_qiov, 0, 0, 512 * cur_nr_sectors);
             break;
 
-- 
1.8.1.4