net/core/dev.c

7939 				   struct net_device *new_dev,
7949 	if (!new_dev)
7952 	if (old_dev && new_dev != old_dev)
7954 	err = __netdev_upper_dev_link(new_dev, dev, false, NULL, NULL, &priv,
7957 		if (old_dev && new_dev != old_dev)
7967 				   struct net_device *new_dev,
7975 	if (!new_dev || !old_dev)
7978 	if (new_dev == old_dev)
7987 				  struct net_device *new_dev,
7995 	if (!new_dev)
7998 	if (old_dev && new_dev != old_dev)
8001 	__netdev_upper_dev_unlink(new_dev, dev, &priv);