From: Zhi Yong Wu <wu...@linux.vnet.ibm.com>
Signed-off-by: Zhi Yong Wu <wu...@linux.vnet.ibm.com>
[ Iterate until all block devices have processed all requests,
add comments. - Paolo ]
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
block.c | 24 ++++++++++++++++++++++--
1 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/block.c b/block.c
index 52ffe14..52dabd0 100644
--- a/block.c
+++ b/block.c
@@ -858,12 +858,32 @@ void bdrv_close_all(void)
*
* This function does not flush data to disk, use bdrv_flush_all() for that
* after calling this function.
- */
+ *
+ * Note that completion of an asynchronous I/O operation can trigger any
+ * number of other I/O operations on other devices---for example a coroutine
+ * can be arbitrarily complex and a constant flow of I/O to multiple devices
+ * can come until the coroutine is complete. Because of this, it is not
+ * possible to drain a single device's I/O queue.
+*/
void bdrv_drain_all(void)
{
BlockDriverState *bs;
+ bool busy;
- qemu_aio_flush();
+ do {
+ busy = false;
+ qemu_aio_flush();
+
+ /* FIXME: We do not have timer support here, so this is effectively
+ * a busy wait.
+ */
+ QTAILQ_FOREACH(bs, &bdrv_states, list) {
+ if (!qemu_co_queue_empty(&bs->throttled_reqs)) {
+ qemu_co_queue_restart_all(&bs->throttled_reqs);
+ busy = true;
+ }
+ }
+ } while (busy);
/* If requests are still pending there is a bug somewhere */
QTAILQ_FOREACH(bs, &bdrv_states, list) {
--
1.7.6
