The failover module provides a generic interface for paravirtual
drivers to register a netdev and a set of ops with a failover
instance. The ops are used as event handlers that get called to
handle netdev register/unregister/link change/name change events
on slave pci ethernet devices with the same mac address as the
failover netdev. This enables paravirtual drivers to use a
VF as an accelerated low latency datapath. It also allows live
migration of VMs with direct attached VFs by failing over to the
paravirtual datapath when the VF is unplugged.

source code:

net/core/failover.c