net_failover(kernel)                            |    network.service (user)    |          systemd-udevd (user)
--------------------------------------------------+------------------------------+--------------------------------------------
(standby virtio-net and net_failover              |                              |
devices created and initialized,                  |                              |
i.e. virtnet_probe()->                            |                              |
       net_failover_create()                      |                              |
was done.)                                        |                              |
                                                  |                              |
                                                  |  runs `ifup ens3' ->         |
                                                  |    ip link set dev ens3 up   |
net_failover_open()                               |                              |
  dev_open(virtnet_dev)                           |                              |
    virtnet_open(virtnet_dev)                     |                              |
  netif_carrier_on(failover_dev)                  |                              |
  ...                                             |                              |
                                                  |                              |
(VF hot plugged in)                               |                              |
ixgbevf_probe()                                   |                              |
 register_netdev(ixgbevf_netdev)                  |                              |
  netdev_register_kobject(ixgbevf_netdev)         |                              |
   kobject_add(ixgbevf_dev)                       |                              |
    device_add(ixgbevf_dev)                       |                              |
     kobject_uevent(&ixgbevf_dev->kobj, KOBJ_ADD) |                              |
      netlink_broadcast()                         |                              |
  ...                                             |                              |
  call_netdevice_notifiers(NETDEV_REGISTER)       |                              |
   failover_event(..., NETDEV_REGISTER, ...)      |                              |
    failover_slave_register(ixgbevf_netdev)       |                              |
     net_failover_slave_register(ixgbevf_netdev)  |                              |
      dev_open(ixgbevf_netdev)                    |                              |
                                                  |                              |
                                                  |                              |
                                                  |                              |   received ADD uevent from netlink fd
                                                  |                              |   ...
                                                  |                              |   udev-builtin-net_id.c:dev_pci_slot()
                                                  |                              |   (decided to renamed 'eth0' )
                                                  |                              |     ip link set dev eth0 name ens4
(dev_change_name() returns -EBUSY as              |                              |
ixgbevf_netdev->flags has IFF_UP)                 |                              |
                                                  |                              |