网卡是是网络中最基本的硬件之一。

在内核中，每个网络设备都一个一个net_device 结构体实例，在进行初始化完成之后，会将该结构注册到内核中。然能内核知道该结构的存在。

这会创建一个sysfs项，这，关联到该设备的对应目录中。该目录为

[root@localhost ~]# ls -l /sys/class/net
总计 0
drwxr-xr-x 3 root root 0 10-08 00:17 eth0
drwxr-xr-x 3 root root 0 10-08 00:17 lo
drwxr-xr-x 4 root root 0 10-08 00:17 peth0
drwxr-xr-x 3 root root 0 10-08 00:17 sit0
drwxr-xr-x 3 root root 0 10-08 00:17 veth1
drwxr-xr-x 3 root root 0 10-08 00:17 veth2
drwxr-xr-x 3 root root 0 10-08 00:17 veth3
drwxr-xr-x 4 root root 0 10-08 00:17 vif0.0
drwxr-xr-x 3 root root 0 10-08 00:17 vif0.1
drwxr-xr-x 3 root root 0 10-08 00:17 vif0.2
drwxr-xr-x 3 root root 0 10-08 00:17 vif0.3
drwxr-xr-x 5 root root 0 10-08 00:17 xenbr0

可以看到 我虚拟机上的网络设备有以上的设备。eth0 是第一个网卡。其他的我也不知道干嘛的。

该设备不是全局的。因此也是在一个命名空间的。

所有网络设备都保存在一个单链表中。表头为dev_base.

按设备名散列。

按接口索引散列

下面我就不得不晓得linux中 最大的一个结构体数据结构。几百行代码

如下代码

/*
 *	The DEVICE structure.
 *	Actually, this whole structure is a big mistake.  It mixes I/O
 *	data with strictly "high-level" data, and it has to know about
 *	almost every data structure used in the INET module.
 *
 *	FIXME: cleanup struct net_device such that network protocol info
 *	moves out.
 */

struct net_device
{

	/*
	 * This is the first field of the "visible" part of this structure
	 * (i.e. as seen by users in the "Space.c" file).  It is the name
	 * the interface.
	 */
	char			name[IFNAMSIZ];

	/*
	 *	I/O specific fields
	 *	FIXME: Merge these and struct ifmap into one
	 */
	unsigned long		mem_end;	/* shared mem end	*/
	unsigned long		mem_start;	/* shared mem start	*/
	unsigned long		base_addr;	/* device I/O address	*/
	unsigned int		irq;		/* device IRQ number	*/

	/*
	 *	Some hardware also needs these fields, but they are not
	 *	part of the usual set specified in Space.c.
	 */

	unsigned char		if_port;	/* Selectable AUI, TP,..*/
	unsigned char		dma;		/* DMA channel		*/

	unsigned long		state;

	struct net_device	*next;
	
	/* The device initialization function. Called only once. */
	int			(*init)(struct net_device *dev);

	/* ------- Fields preinitialized in Space.c finish here ------- */

	struct net_device	*next_sched;

	/* Interface index. Unique device identifier	*/
	int			ifindex;
	int			iflink;


	struct net_device_stats* (*get_stats)(struct net_device *dev);
	struct iw_statistics*	(*get_wireless_stats)(struct net_device *dev);

	/* List of functions to handle Wireless Extensions (instead of ioctl).
	 * See <net/iw_handler.h> for details. Jean II */
	struct iw_handler_def *	wireless_handlers;

	struct ethtool_ops *ethtool_ops;

	/*
	 * This marks the end of the "visible" part of the structure. All
	 * fields hereafter are internal to the system, and may change at
	 * will (read: may be cleaned up at will).
	 */

	/* These may be needed for future network-power-down code. */
	unsigned long		trans_start;	/* Time (in jiffies) of last Tx	*/
	unsigned long		last_rx;	/* Time of last Rx	*/

	unsigned short		flags;	/* interface flags (a la BSD)	*/
	unsigned short		gflags;
        unsigned short          priv_flags; /* Like 'flags' but invisible to userspace. */
        unsigned short          unused_alignment_fixer; /* Because we need priv_flags,
                                                         * and we want to be 32-bit aligned.
                                                         */

	unsigned		mtu;	/* interface MTU value		*/
	unsigned short		type;	/* interface hardware type	*/
	unsigned short		hard_header_len;	/* hardware hdr length	*/
	void			*priv;	/* pointer to private data	*/

	struct net_device	*master; /* Pointer to master device of a group,
					  * which this device is member of.
					  */

	/* Interface address info. */
	unsigned char		broadcast[MAX_ADDR_LEN];	/* hw bcast add	*/
	unsigned char		dev_addr[MAX_ADDR_LEN];	/* hw address	*/
	un