//分配以太网设备描述符
1.1 struct net_device *alloc_etherdev(int sizeof_priv)
{
	//设备名默认为eth%d,其中%d随系统中以太网络设备数递增
	return alloc_netdev(sizeof_priv, "eth%d", ether_setup);
}

//网络设备描述符标准分配函数
//	alloc_etherdev->alloc_netdev
1.2 struct net_device *alloc_netdev(int sizeof_priv, const char *name,
		void (*setup)(struct net_device *))
{
	void *p;
	struct net_device *dev;
	int alloc_size;

	//对齐到32bit
	alloc_size = (sizeof(*dev) + NETDEV_ALIGN_CONST) & ~NETDEV_ALIGN_CONST;
	alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;

	//kmalloc物理内存上连续
	p = kmalloc(alloc_size, GFP_KERNEL);
	if (!p) {
		printk(KERN_ERR "alloc_dev: Unable to allocate device.\n");
		return NULL;
	}
	memset(p, 0, alloc_size);

	dev = (struct net_device *)
		(((long)p + NETDEV_ALIGN_CONST) & ~NETDEV_ALIGN_CONST);
	//在padded中保存为对齐dev到32bit浪费的字节数
	//dev-padded即可找到kmalloc分配的内存起始地址
	dev->padded = (char *)dev - (char *)p;

	if (sizeof_priv)
		dev->priv = netdev_priv(dev);
	//初始化设备的函数指针
	setup(dev);
	strcpy(dev->name, name);
	return dev;
}

//以太网设备通用的初始化函数
//	调用路径：alloc_netdev->ether_setup
1.3 void ether_setup(struct net_device *dev)
{
	dev->change_mtu		= eth_change_mtu;//保证ethdev的mtu > 68 && mtu < 1500
	dev->hard_header	= eth_header;//向skb填以太网报头
	dev->rebuild_header 	= eth_rebuild_header;//完成arp解析以后，重建以太网报头
	dev->set_mac_address 	= eth_mac_addr;//设置设备的mac地址
	dev->hard_header_cache	= eth_header_cache;//根据arp查询的结果，构造hh_cache，供邻居子系统使用
	dev->header_cache_update= eth_header_cache_update;//更新hh_cache中的以太网头
	dev->hard_header_parse	= eth_header_parse;//从skb中取出以太网头，填充到一个unsigned char*指针中

	dev->type		= ARPHRD_ETHER;//以太网类型
	dev->hard_header_len 	= ETH_HLEN;//以太网报头长度 14字节
	dev->mtu		= 1500; //最大支持的mtu
	dev->addr_len		= ETH_ALEN;//地址长度 6字节
	dev->tx_queue_len	= 1000;	//每个设备的传输队列长度	
	dev->flags		= IFF_BROADCAST|IFF_MULTICAST;//设备默认支持广播和多播

	memset(dev->broadcast,0xFF, ETH_ALEN);//以太网广播地址FF:FF:FF:FF:FF:FF

}