[Qemu-devel] [PATCH] qcow2: Fix offset in qcow2_read_extensions

[Qemu-devel] [PATCH] qcow2: Fix offset in qcow2_read_extensions

[Kevin Wolf]

The spec says that the length of extensions is padded to 8 bytes, not
the offset. Currently this is the same because the header size is a
multiple of 8, so this is only about compatibility with future changes
to the header size.

While touching it, move the calculation to a common place instead of
duplicating it for each header extension type.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index dea12c1..f68f0e1 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -126,7 +126,6 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
 #ifdef DEBUG_EXT
             printf("Qcow2: Got format extension %s\n", bs->backing_format);
 #endif
-            offset = ((offset + ext.len + 7) & ~7);
             break;
 
         default:
@@ -143,11 +142,11 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
                 if (ret < 0) {
                     return ret;
                 }
-
-                offset = ((offset + ext.len + 7) & ~7);
             }
             break;
         }
+
+        offset += ((ext.len + 7) & ~7);
     }
 
     return 0;
-- 
1.7.6.5

Re: [Qemu-devel] [PATCH] qcow2: Fix offset in qcow2_read_extensions

[Stefan Hajnoczi]

On Mon, Feb 27, 2012 at 4:27 PM, Kevin Wolf <kwolf@redhat.com> wrote:
> The spec says that the length of extensions is padded to 8 bytes, not
> the offset. Currently this is the same because the header size is a
> multiple of 8, so this is only about compatibility with future changes
> to the header size.
>
> While touching it, move the calculation to a common place instead of
> duplicating it for each header extension type.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>