virt_net.c驱动：

// 参考 drivers\net\cs89x0.c

#include "linux/module.h"

#include "linux/errno.h"

#include "linux/netdevice.h"

#include "linux/etherdevice.h"

#include "linux/kernel.h"

#include "linux/types.h"

#include "linux/fcntl.h"

#include "linux/interrupt.h"

#include "linux/ioport.h"

#include "linux/in.h"

#include "linux/skbuff.h"

#include "linux/slab.h"

#include "linux/spinlock.h"

#include "linux/string.h"

#include "linux/init.h"

#include "linux/bitops.h"

#include "linux/delay.h"

#include "linux/ip.h"

#include "asm/system.h"

#include "asm/io.h"

#include "asm/irq.h"

static struct net_device *vnet_dev;

static void emulator_rx_packet(struct sk_buff *skb, struct net_device *dev)

{

    // 参考LDD3 

    unsigned char *type;

    struct iphdr *ih;

    __be32 *saddr, *daddr, tmp;

    unsigned char    tmp_dev_addr[ETH_ALEN];

    struct ethhdr *ethhdr;

    struct sk_buff *rx_skb;

    // 从硬件读出/保存数据

    // 对调"源/目的"的mac地址 

    ethhdr = (struct ethhdr *)skb->data;

    memcpy(tmp_dev_addr, ethhdr->h_dest, ETH_ALEN);

    memcpy(ethhdr->h_dest, ethhdr->h_source, ETH_ALEN);

    memcpy(ethhdr->h_source, tmp_dev_addr, ETH_ALEN);

    // 对调"源/目的"的ip地址     

    ih = (struct iphdr *)(skb->data + sizeof(struct ethhdr));

    saddr = &ih->saddr;

    daddr = &ih->daddr;

    tmp = *saddr;

    *saddr = *daddr;

    *daddr = tmp;

    //((u8 *)saddr)[2] ^= 1; // change the third octet (class C) 

    //((u8 *)daddr)[2] ^= 1;

    type = skb->data + sizeof(struct ethhdr) + sizeof(struct iphdr);

    //printk("tx package type = x\n", *type);

    // 修改类型, 原来0x8表示ping

    *type = 0;                  // 0表示reply 

    ih->check = 0;           // and rebuild the checksum (ip needs it) 

    ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);

    // 构造一个sk_buff

    rx_skb = dev_alloc_skb(skb->len + 2);

    skb_reserve(rx_skb, 2); // align IP on 16B boundary     

    memcpy(skb_put(rx_skb, skb->len), skb->data, skb->len);

    // Write metadata, and then pass to the receive level 

    rx_skb->dev = dev;

    rx_skb->protocol = eth_type_trans(rx_skb, dev);

    rx_skb->ip_summed = CHECKSUM_UNNECESSARY; // don't check it 

    dev->stats.rx_packets++;

    dev->stats.rx_bytes += skb->len;

    // 提交sk_buff

    netif_rx(rx_skb);

}

static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)

{

    static int cnt = 0;

    printk("virt_net_send_packet cnt = %d\n", ++cnt);

    // 对于真实的网卡, 把skb里的数据通过网卡发送出去 

    netif_stop_queue(dev); // 停止该网卡的队列 

    // ......                               // 把skb的数据写入网卡 

    // 构造一个假的sk_buff,上报 

    emulator_rx_packet(skb, dev);

    dev_kfree_skb (skb);       // 释放skb 

    netif_wake_queue(dev); // 数据全部发送出去后,唤醒网卡的队列 

    // 更新统计信息 

    dev->stats.tx_packets++;

    dev->stats.tx_bytes += skb->len;

    return 0;

}

static const struct net_device_ops virt_netdev_ops = {

    .ndo_start_xmit = virt_net_send_packet,

};

static int virt_net_init(void)

{

    // 1. 分配一个net_device结构体 

    vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);  // alloc_etherdev 

    // 2. 设置 

    vnet_dev->netdev_ops    = &virt_netdev_ops;

    // 设置MAC地址 

    vnet_dev->dev_addr[0] = 0x08;

    vnet_dev->dev_addr[1] = 0x89;

    vnet_dev->dev_addr[2] = 0x89;

    vnet_dev->dev_addr[3] = 0x89;

    vnet_dev->dev_addr[4] = 0x89;

    vnet_dev->dev_addr[5] = 0x11;

    // 设置下面两项才能ping通 

    vnet_dev->flags           |= IFF_NOARP;

    vnet_dev->features        |= NETIF_F_NO_CSUM;    

    // 3. 注册 

    //register_netdevice(vnet_dev);

    register_netdev(vnet_dev);

    return 0;

}

static void virt_net_exit(void)

{

    unregister_netdev(vnet_dev);

    free_netdev(vnet_dev);

}

module_init(virt_net_init);

module_exit(virt_net_exit);

MODULE_AUTHOR("thisway.diy@163.com,17653039@qq.com");

MODULE_LICENSE("GPL");