An empty begin/end pair is almost the same as a bare bdrv_drain except the aio_poll inside is wrapped by aio_disable_external/aio_enable_external.
This is safer, and is the only way to achieve quiescence in this aio_poll(), because bdrv_drained_begin/end pair cannot span across context detach/attach options, so it's not possible to do by the caller. Signed-off-by: Fam Zheng <f...@redhat.com> --- block.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/block.c b/block.c index 59a18a3..31f4a9f 100644 --- a/block.c +++ b/block.c @@ -3747,7 +3747,9 @@ void bdrv_attach_aio_context(BlockDriverState *bs, void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context) { - bdrv_drain(bs); /* ensure there are no in-flight requests */ + /* ensure there are no in-flight requests */ + bdrv_drained_begin(bs); + bdrv_drained_end(bs); bdrv_detach_aio_context(bs); -- 2.4.3