linux tun/tap编程

blog 归档 网络编程 tun/tap Linux

功能: 创建tun接口, 处理ping数据报

#include <linux/if_tun.h>
#include <net/if.h>     /* for struct ifreq */
#include <sys/types.h>      /* for open() */
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>     /* for bzero() */
#include <sys/ioctl.h>
#include <unistd.h>
#define BUF_SIZE 4096
#define SWAP(a, b, size)        \
    do {                \
        char t[size];       \
        memcpy(t, &a, size);    \
        memcpy(&a, &b, size);   \
        memcpy(&b, t, size);    \
    }while (0)
int main()
{
    struct ifreq ifr;
    int fd, n;
    char buf[BUF_SIZE];
    if ((fd = open("/dev/net/tun", O_RDWR)) == -1)
    {
        perror("open");
        exit(errno);
    }
    bzero(&ifr, sizeof(ifr));
    ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
    strncpy(ifr.ifr_name, "", IFNAMSIZ);
    if (ioctl(fd, TUNSETIFF, &ifr) == -1)
    {
        perror("ioctl");
        exit(errno);
    }
    printf("ifname is %s\n", ifr.ifr_name);
    while (1)
    {
        if ((n = read(fd, buf, BUF_SIZE)) == -1)
        {
            perror("read");
            exit(errno);
        }
        else if (n == 0)
        {
            exit(0);
        }
        printf("%d bytes read\n", n);
        SWAP(buf[12], buf[16], 4);  /* swap ip */
        buf[20] = 0;
        (*((unsigned short*)&buf[22])) += 8;
        if ((n = write(fd, buf, n)) <= 0)
        {
            perror("write");
            exit(errno);
        }
        printf("%d bytes written\n", n);
    }
    return 0;
}

sudo ifconfig tun0 192.168.0.1/24 pointopoint 192.168.0.2 up
ping 192.168.0.2