[PULL 17/47] vfio/migration: Don't emit STOP_COPY VFIO migration QAPI event twice

[Cédric Le Goater]

From: Avihai Horon <avihaih@nvidia.com>

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 VFIO migration QAPI event, the
STOP_COPY event is undesirably emitted twice.

Prevent this by returning early in vfio_migration_set_state() if
new_state is the same as current device state.

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>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 hw/vfio/migration.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 
af579b868d7caa726fde1eeb73c832ebc3136a7a..56edffaf6251e28e39ef32991394697abb1b9e55
 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -150,6 +150,10 @@ static int vfio_migration_set_state(VFIODevice *vbasedev,
         g_strdup_printf("%s: Failed setting device state to %s.",
                         vbasedev->name, mig_state_to_str(new_state));
 
+    if (new_state == migration->device_state) {
+        return 0;
+    }
+
     feature->argsz = sizeof(buf);
     feature->flags =
         VFIO_DEVICE_FEATURE_SET | VFIO_DEVICE_FEATURE_MIG_DEVICE_STATE;
-- 
2.45.1