[Qemu-devel] [PATCH 11/21] VMDK: bugfix, align offset to cluster in get_whole_cluster

[Kevin Wolf <kwolf@redhat.com>]

From: Fam Zheng <famcool@gmail.com>

In get_whole_cluster, the offset is not aligned to cluster when reading
from backing_hd. When the first write to child is not at the cluster
boundary, wrong address data from parent is copied to child.

Signed-off-by: Fam Zheng <famcool@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/vmdk.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index 3b78583..03a4619 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -514,21 +514,23 @@ static int get_whole_cluster(BlockDriverState *bs,
     /* 128 sectors * 512 bytes each = grain size 64KB */
     uint8_t  whole_grain[extent->cluster_sectors * 512];
 
-    // we will be here if it's first write on non-exist grain(cluster).
-    // try to read from parent image, if exist
+    /* we will be here if it's first write on non-exist grain(cluster).
+     * try to read from parent image, if exist */
     if (bs->backing_hd) {
         int ret;
 
         if (!vmdk_is_cid_valid(bs))
             return -1;
 
+        /* floor offset to cluster */
+        offset -= offset % (extent->cluster_sectors * 512);
         ret = bdrv_read(bs->backing_hd, offset >> 9, whole_grain,
                 extent->cluster_sectors);
         if (ret < 0) {
             return -1;
         }
 
-        //Write grain only into the active image
+        /* Write grain only into the active image */
         ret = bdrv_write(extent->file, cluster_offset, whole_grain,
                 extent->cluster_sectors);
         if (ret < 0) {
-- 
1.7.6