[Qemu-devel] [PATCH v4 07/12] block: Add "drained begin/end" for transactional backup

[Fam Zheng <famz@redhat.com>]

This ensures the atomicity of the transaction by avoiding processing of
external requests such as those from ioeventfd.

Move the assignment to state->bs up right after bdrv_drained_begin, so
that we can use it in the clean callback. The abort callback will still
check bs->job and state->job, so it's OK.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index fc63c3d..e3e68e6 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1597,6 +1597,8 @@ static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
     /* AioContext is released in .clean() */
     state->aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(state->aio_context);
+    bdrv_drained_begin(bs);
+    state->bs = bs;
 
     qmp_drive_backup(backup->device, backup->target,
                      backup->has_format, backup->format,
@@ -1612,7 +1614,6 @@ static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
         return;
     }
 
-    state->bs = bs;
     state->job = state->bs->job;
 }
 
@@ -1632,6 +1633,7 @@ static void drive_backup_clean(BlkTransactionState *common)
     DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
 
     if (state->aio_context) {
+        bdrv_drained_end(state->bs);
         aio_context_release(state->aio_context);
     }
 }
-- 
2.4.3