[Qemu-block] [PATCH for-2.6 3/3] block: Update comment of bdrv_drained_begin

[Fam Zheng]

The limitation should be documented. Removing it is a post 2.6
material.

Signed-off-by: Fam Zheng <address@hidden>
---
 include/block/block.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/block/block.h b/include/block/block.h
index 3a73137..bb67652 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -530,6 +530,11 @@ void bdrv_flush_io_queue(BlockDriverState *bs);
  * this doesn't block timers or coroutines from submitting more requests, which
  * means block_job_pause is still necessary.
  *
+ * for now this only affacts the aio event loops (namely the data-plane
+ * iothreads and nested aio_poll() calls in block layer).  Specifically, the
+ * main loop can still dispatch external events, even after bdrv_drained_begin
+ * is called.
+ *
  * This function can be recursive.
  */
 void bdrv_drained_begin(BlockDriverState *bs);
-- 
2.8.0