[Qemu-devel] [PATCH 1/4] block: Use drained section in bdrv_set_aio_context

[Fam Zheng <famz@redhat.com>]

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 <famz@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