block: always open drivers in writeback mode

Formats are entirely in charge of flushes for metadata writes.  For
guest-initiated writes, a writethrough cache is faked in the block layer.
So we can always open in writeback mode.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/block.c b/block.c
index e4396a6c46..48528fd431 100644
--- a/block.c
+++ b/block.c
@@ -649,12 +649,13 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
     bs->opaque = g_malloc0(drv->instance_size);
 
     bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB);
+    open_flags = flags | BDRV_O_CACHE_WB;
 
     /*
      * Clear flags that are internal to the block layer before opening the
      * image.
      */
-    open_flags = flags & ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
+    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
 
     /*
      * Snapshots should be writable.