[Qemu-devel] [PATCH untested] mirror: start drained section earlier

[Paolo Bonzini <pbonzini@redhat.com>]

Ensure that the guest does not write anything to disk after cnt is
read for the final time.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
        Untested.

 block/mirror.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 0e8f556..e57c246 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -562,8 +562,18 @@ static void coroutine_fn mirror_run(void *opaque)
              * mirror_populate runs.
              */
             trace_mirror_before_drain(s, cnt);
-            bdrv_drain(bs);
+            bdrv_drained_begin(s->common.bs);
             cnt = bdrv_get_dirty_count(s->dirty_bitmap);
+
+            if (cnt == 0) {
+                /* The two disks are in sync.  Exit and report successful
+                 * completion.
+                 */
+                assert(QLIST_EMPTY(&bs->tracked_requests));
+                s->common.cancelled = false;
+                break;
+            }
+            bdrv_drained_end(s->common.bs);
         }
 
         ret = 0;
@@ -576,13 +586,6 @@ static void coroutine_fn mirror_run(void *opaque)
         } else if (!should_complete) {
             delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
             block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
-        } else if (cnt == 0) {
-            /* The two disks are in sync.  Exit and report successful
-             * completion.
-             */
-            assert(QLIST_EMPTY(&bs->tracked_requests));
-            s->common.cancelled = false;
-            break;
         }
         last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
     }
@@ -608,9 +611,6 @@ immediate_exit:
 
     data = g_malloc(sizeof(*data));
     data->ret = ret;
-    /* Before we switch to target in mirror_exit, make sure data doesn't
-     * change. */
-    bdrv_drained_begin(s->common.bs);
     block_job_defer_to_main_loop(&s->common, mirror_exit, data);
 }
 
-- 
2.5.0