... We are now through discussing char and block drivers and are ready to move on to the fascinating world of networking. Network interfaces are the third standard class of Linux devices, and this chapter describes how they interact with the rest of the kernel. ... Device state. ... Included by netdevice.h , this file declares the interface flags ( IFF_ macros) and struct ifmap , which has a major role in the ioctl implementation for network drivers. void netif_carrier_off(struct net_device *dev); . ...