block: change flush to co_flush

Since coroutine operation is now mandatory, convert all bdrv_flush
implementations to coroutines.  For qcow2, this means taking the lock.
Other implementations are simpler and just forward bdrv_flush to the
underlying protocol, so they can avoid the lock.

The bdrv_flush callback is then unused and can be eliminated.

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

1 files changed, 0 insertions, 2 deletions

diff --git a/block.c b/block.c
index 28508f21d1..81fb709011 100644
--- a/block.c
+++ b/block.c
@@ -2892,8 +2892,6 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
             qemu_coroutine_yield();
             return co.ret;
         }
-    } else if (bs->drv->bdrv_flush) {
-        return bs->drv->bdrv_flush(bs);
     } else {
         /*
          * Some block drivers always operate in either writethrough or unsafe