The switchdev driver can know a particular port's position in the topology by
monitoring NETDEV_CHANGEUPPER notifications. For example, a port moved into a
-bond will see it's upper master change. If that bond is moved into a bridge,
+bond will see its upper master change. If that bond is moved into a bridge,
the bond's upper master will change. And so on. The driver will track such
movements to know what position a port is in in the overall topology by
registering for netdevice events and acting on NETDEV_CHANGEUPPER.