net/virtio: fix dev_unplug_pending

.dev_unplug_pending is set up by virtio-net code indepent of failover
support was set for the device or not. This gives a wrong result when
we check for existing primary devices in migration code.

Fix this by actually calling dev_unplug_pending() instead of just
checking if the function pointer was set. When the feature was not
negotiated dev_unplug_pending() will always return false. This prevents
us from going into the wait-unplug state when there's no primary device
present.

Fixes: 9711cd0d ("net/virtio: add failover support")
Signed-off-by: NJens Freimann <jfreimann@redhat.com>
Reported-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>

hw/net/virtio-net.c

@@ -3124,6 +3124,9 @@ static bool primary_unplug_pending(void *opaque)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIONet *n = VIRTIO_NET(vdev);
 
+    if (!virtio_vdev_has_feature(vdev, VIRTIO_NET_F_STANDBY)) {
+        return false;
+    }
     return n->primary_dev ? n->primary_dev->pending_deleted_event : false;
 }
 

migration/savevm.c

@@ -1119,7 +1119,8 @@ int qemu_savevm_nr_failover_devices(void)
     int n = 0;
 
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
-        if (se->vmsd && se->vmsd->dev_unplug_pending) {
+        if (se->vmsd && se->vmsd->dev_unplug_pending &&
+            se->vmsd->dev_unplug_pending(se->opaque)) {
             n++;
         }
     }