Linux Device Drivers, Second Edition

Quick Reference

This section provides a reference for the concepts introduced in this chapter. It also explains the role of each header file that a driver needs to include. The lists of fields in the net_device and sk_buff structures, however, are not repeated here.

#include <linux/netdevice.h>

This header hosts the definitions of struct net_device and struct net_device_stats, and includes a few other headers that are needed by network drivers.

int register_netdev(struct net_device *dev); , void unregister_netdev(struct net_device *dev);

Register and unregister a network device.

SET_MODULE_OWNER(struct net_device *dev);

This macro will store a pointer to the current module in the device structure (or in any structure with an owner field, actually); it is used to enable the networking subsystem to manage the module’s use count.

netif_start_queue(struct net_device *dev); , netif_stop_queue(struct net_device *dev); , netif_wake_queue(struct net_device *dev);

These functions control the passing of packets to the driver for transmission. No packets will be transmitted until netif_start_queue has been called. netif_stop_queue suspends transmission, and netif_wake_queue restarts the queue and pokes the network layer to restart transmitting packets.

void netif_rx(struct sk_buff *skb);

This function can be called (including at interrupt time) to notify the kernel that a packet has been received and encapsulated into a socket buffer.

#include <linux/if.h>

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); , void netif_carrier_on(struct net_device *dev); , int netif_carrier_ok(struct net_device *dev);

The first two functions may be used to tell the kernel whether a carrier signal is currently present on the given interface. netif_carrier_ok will test the carrier state as reflected in the device structure.

#include <linux/if_ether.h> , ETH_ALEN , ETH_P_IP , struct ethhdr;

Included by netdevice.h, if_ether.h defines all the ETH_ macros used to represent octet lengths (such as the address length) and network protocols (such as IP). It also defines the ethhdr structure.

#include <linux/skbuff.h>

The definition of struct sk_buff and related structures, as well as several inline functions to act on the buffers. This header is included by netdevice.h.

struct sk_buff *alloc_skb(unsigned int len, int priority); , struct sk_buff *dev_alloc_skb(unsigned int len); , void kfree_skb(struct sk_buff *skb); , void dev_kfree_skb(struct sk_buff *skb);

These functions handle the allocation and freeing of socket buffers. Drivers should normally use the dev_ variants, which are intended for that purpose.

unsigned char *skb_put(struct sk_buff *skb, int len); , unsigned char *__skb_put(struct sk_buff *skb, int len); , unsigned char *skb_push(struct sk_buff *skb, int len); , unsigned char *__skb_push(struct sk_buff *skb, int len);

These functions add data to an skb; skb_put puts the data at the end of the skb, while skb_push puts it at the beginning. The regular versions perform checking to ensure that adequate space is available; double-underscore versions leave those tests out.

int skb_headroom(struct sk_buff *skb); , int skb_tailroom(struct sk_buff *skb); , void skb_reserve(struct sk_buff *skb, int len);

These functions perform management of space within an skb. skb_headroom and skb_tailroom tell how much space is available at the beginning and end, respectively, of an skb. skb_reserve may be used to reserve space at the beginning of an skb, which must be empty.

unsigned char *skb_pull(struct sk_buff *skb, int len);

skb_pull will “remove” data from an skb by adjusting the internal pointers.

#include <linux/etherdevice.h> , void ether_setup(struct net_device *dev);

This function sets most device methods to the general-purpose implementation for Ethernet drivers. It also sets dev->flags and assigns the next available ethx name to dev->name if the first character in the name is a blank space or the null character.

unsigned short eth_type_trans(struct sk_buff *skb, struct net_device *dev);

When an Ethernet interface receives a packet, this function can be called to set skb->pkt_type. The return value is a protocol number that is usually stored in skb->protocol.

#include <linux/sockios.h> , SIOCDEVPRIVATE

This is the first of 16 ioctl commands that can be implemented by each driver for its own private use. All the network ioctl commands are defined in sockios.h.