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

[Paolo Bonzini <pbonzini@redhat.com>]

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: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/qcow2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 56fccf9..bb04432 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);
Stage this hunk [y,n,q,a,d,/,e,?]? y

diff --git a/block/qcow2.c b/block/qcow2.c
index 7610e56..b4c7c54 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -584,7 +584,7 @@ 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 */
@@ -665,10 +665,6 @@ 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;
 
-- 
1.8.1.2