[PATCH 3/3] vfio/migration: Don't emit STOP_COPY state change event twice

[Avihai Horon]

When migrating a VFIO device that supports pre-copy, it is transitioned
to STOP_COPY twice: once in vfio_vmstate_change() and second time in
vfio_save_complete_precopy().

The second transition is harmless, as it's a STOP_COPY->STOP_COPY no-op
transition. However, with the newly added migration state change QAPI
event, the STOP_COPY state change event is undesirably emitted twice.

Prevent this by conditionally transitioning to STOP_COPY state in
vfio_save_complete_precopy().

Note that the STOP_COPY transition in vfio_save_complete_precopy() is
essential for VFIO devices that don't support pre-copy, for migrating an
already stopped guest and for snapshots.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 hw/vfio/migration.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 6bbccf6545..30a2b2ea74 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -591,14 +591,17 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque)
 static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
 {
     VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
     ssize_t data_size;
     int ret;
 
     /* We reach here with device state STOP or STOP_COPY only */
-    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
-                                   VFIO_DEVICE_STATE_STOP);
-    if (ret) {
-        return ret;
+    if (migration->device_state == VFIO_DEVICE_STATE_STOP) {
+        ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
+                                       VFIO_DEVICE_STATE_STOP);
+        if (ret) {
+            return ret;
+        }
     }
 
     do {
-- 
2.26.3