[Qemu-devel] [PATCH v5 13/13] block/mirror: Block "device IO" during mirror exit

[Fam Zheng <famz@redhat.com>]

When mirror should complete, the source and target are in sync.  But we
call bdrv_swap() only a while later in the main loop bh. If the guest
writes something before that, target will not get the new data.

Block "device IO" before bdrv_drain and unblock it after bdrw_swap().

Reported-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/mirror.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/mirror.c b/block/mirror.c
index 58f391a..f400456 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -320,6 +320,8 @@ static void mirror_drain(MirrorBlockJob *s)
 
 typedef struct {
     int ret;
+    /* Use to pause device IO during mirror exit */
+    Error *blocker;
 } MirrorExitData;
 
 static void mirror_exit(BlockJob *job, void *opaque)
@@ -328,6 +330,8 @@ static void mirror_exit(BlockJob *job, void *opaque)
     MirrorExitData *data = opaque;
     AioContext *replace_aio_context = NULL;
 
+    bdrv_op_unblock(s->common.bs, BLOCK_OP_TYPE_DEVICE_IO, data->blocker);
+    error_free(data->blocker);
     if (s->to_replace) {
         replace_aio_context = bdrv_get_aio_context(s->to_replace);
         aio_context_acquire(replace_aio_context);
@@ -376,6 +380,8 @@ static void coroutine_fn mirror_run(void *opaque)
                                  checking for a NULL string */
     int ret = 0;
     int n;
+    data = g_malloc0(sizeof(*data));
+    error_setg(&data->blocker, "mirror job exiting");
 
     if (block_job_is_cancelled(&s->common)) {
         goto immediate_exit;
@@ -521,6 +527,7 @@ static void coroutine_fn mirror_run(void *opaque)
              * mirror_populate runs.
              */
             trace_mirror_before_drain(s, cnt);
+            bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, data->blocker);
             bdrv_drain(bs);
             cnt = bdrv_get_dirty_count(s->dirty_bitmap);
         }
@@ -543,6 +550,7 @@ static void coroutine_fn mirror_run(void *opaque)
             s->common.cancelled = false;
             break;
         }
+        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, data->blocker);
         last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
     }
 
@@ -563,7 +571,6 @@ immediate_exit:
     bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
     bdrv_iostatus_disable(s->target);
 
-    data = g_malloc(sizeof(*data));
     data->ret = ret;
     block_job_defer_to_main_loop(&s->common, mirror_exit, data);
 }
-- 
2.4.1