block/vhdx.c: Don't blindly update the header

The VHDX specification requires that before user data modification of
the vhdx image, the VHDX header file and data GUIDs need to be updated.
In vhdx_open(), if the image is set to RDWR, we go ahead and update the
header.

However, just because the image is set to RDWR does not mean we can go
ahead and write at this point - specifically, if the QEMU run state is
INMIGRATE, the underlying file BS may be set to inactive via the BDS
open flag of BDRV_O_INACTIVE.  Attempting to write under this condition
will cause an assert in bdrv_co_pwritev().

We can alternatively latch the first time the image is written.  And lo
and behold, we do just that, via vhdx_user_visible_write() in
vhdx_co_writev().  This means the call to vhdx_update_headers() in
vhdx_open() is likely just vestigial, and can be removed.

Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: 659e4cdba6ef4c651737852777c8c93d27b38040.1510059970.git.jcody@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Max Reitz <mreitz@redhat.com>

diff --git a/block/vhdx.c b/block/vhdx.c
index 7ae4589879bc7d621e44ddefa206e64004de2f6c..9956933da60c6e0c1c2ba5ebd1e09d0bc6096c0a 100644 (file)
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -1008,13 +1008,6 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    if (flags & BDRV_O_RDWR) {
-        ret = vhdx_update_headers(bs, s, false, NULL);
-        if (ret < 0) {
-            goto fail;
-        }
-    }
-
     /* TODO: differencing files */
 
     return 0;