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[Qemu-devel] [PATCH 3/3] block: fix bdrv_flush() ordering in bdrv_close(

From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH 3/3] block: fix bdrv_flush() ordering in bdrv_close()
Date: Fri, 5 Jul 2013 13:32:52 +0200

Since 80ccf93b we flush the block device during close.  The
bdrv_drain_all() call should come before bdrv_flush() to ensure guest
write requests have completed.  Otherwise we may miss pending writes
when flushing.

Call bdrv_drain_all() again for safety as the final step after
bdrv_flush().  This should not be necessary but we can be paranoid here
in case bdrv_flush() left I/O pending.

Cc: address@hidden
Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
 block.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 6c493ad..183fec8 100644
--- a/block.c
+++ b/block.c
@@ -1358,11 +1358,12 @@ void bdrv_reopen_abort(BDRVReopenState *reopen_state)
 void bdrv_close(BlockDriverState *bs)
-    bdrv_flush(bs);
     if (bs->job) {
-    bdrv_drain_all();
+    bdrv_drain_all(); /* complete I/O */
+    bdrv_flush(bs);
+    bdrv_drain_all(); /* in case flush left pending I/O */
     notifier_list_notify(&bs->close_notifiers, bs);
     if (bs->drv) {

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