Add a flag to BlockDriverState to advertise barriers support, and add a flags
argument to bdrv_aio_readv/writev to allow passing down the barrier flag.
Note that the flags argument to bdrv_aio_readv is for now actually superflous
because write barriers obviously only apply to writes. I kept the read side
argument so the API is symmetric and we can easily add more flags to both
of them.
@@ -1498,7 +1498,7 @@ static void qcow_aio_write_cb(void *opaq
acb->hd_aiocb = bdrv_aio_writev(s->hd,
(acb->cluster_offset >> 9) +
index_in_cluster,
&acb->hd_qiov, acb->n,
- qcow_aio_write_cb, acb);
+ qcow_aio_write_cb, acb, 2);