ifconfig命令

一个简单的C程序，模拟了ifconfig命令的功能，包括设置指定网络接口的IP地址、MAC地址和MTU

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// 显示网络接口信息
void show_interface_info(char *ifname)
{
    int sockfd;
    struct ifreq ifr;
    struct sockaddr_in *sin;
    char ipaddr[INET_ADDRSTRLEN];

    // 创建socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        return;
    }

    // 获取网络接口信息
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);
    if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }
    printf("%s: HWaddr %02x:%02x:%02x:%02x:%02x:%02x\n", ifname,
           (unsigned char)ifr.ifr_hwaddr.sa_data[0], (unsigned char)ifr.ifr_hwaddr.sa_data[1],
           (unsigned char)ifr.ifr_hwaddr.sa_data[2], (unsigned char)ifr.ifr_hwaddr.sa_data[3],
           (unsigned char)ifr.ifr_hwaddr.sa_data[4], (unsigned char)ifr.ifr_hwaddr.sa_data[5]);

    if (ioctl(sockfd, SIOCGIFMTU, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }
    printf("      MTU:%d\n", ifr.ifr_mtu);

    if (ioctl(sockfd, SIOCGIFADDR, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }
    sin = (struct sockaddr_in *)&ifr.ifr_addr;
    inet_ntop(AF_INET, &sin->sin_addr, ipaddr, sizeof(ipaddr));
    printf("      inet addr:%s\n", ipaddr);

    // 关闭socket
    close(sockfd);
}

// 设置网络接口IP地址
void set_interface_ip(char *ifname, char *ipaddr)
{
    int sockfd;
    struct ifreq ifr;
    struct sockaddr_in sin;

    // 创建socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        return;
    }

    // 设置网络接口IP地址
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);
    sin.sin_family = AF_INET;
    inet_pton(AF_INET, ipaddr, &sin.sin_addr);
    memcpy(&ifr.ifr_addr, &sin, sizeof(sin));
    if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }

    // 关闭socket
    close(sockfd);
}

// 设置网络接口MAC地址
void set_interface_mac(char *ifname, char *macaddr)
{
    int sockfd;
    struct ifreq ifr;

    // 创建socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        return;
    }

    // 设置网络接口MAC地址
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);
    ifr.ifr_hwaddr.sa_family = 1;
    sscanf(macaddr, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
           &ifr.ifr_hwaddr.sa_data[0], &ifr.ifr_hwaddr.sa_data[1],
           &ifr.ifr_hwaddr.sa_data[2], &ifr.ifr_hwaddr.sa_data[3],
           &ifr.ifr_hwaddr.sa_data[4], &ifr.ifr_hwaddr.sa_data[5]);
    if (ioctl(sockfd, SIOCSIFHWADDR, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }

    // 关闭socket
    close(sockfd);
}

// 设置网络接口MTU
void set_interface_mtu(char *ifname, int mtu)
{
    int sockfd;
    struct ifreq ifr;

    // 创建socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        return;
    }

    // 设置网络接口MTU
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);
    ifr.ifr_mtu = mtu;
    if (ioctl(sockfd, SIOCSIFMTU, &ifr) < 0) {
        perror("ioctl");
        close(sockfd);
        return;
    }

    // 关闭socket
    close(sockfd);
}

int main(int argc, char **argv)
{
    // 显示指定网络接口的信息
    if (argc > 1) {
        show_interface_info(argv[1]);
    }
    // 设置指定网络接口的IP地址、MAC地址和MTU
    if (argc > 2) {
        if (strcmp(argv[2], "ip") == 0 && argc > 3) {
            set_interface_ip(argv[1], argv[3]);
        }
        else if (strcmp(argv[2], "mac") == 0 && argc > 3) {
            set_interface_mac(argv[1], argv[3]);
        }
        else if (strcmp(argv[2], "mtu") == 0 && argc > 3) {
            set_interface_mtu(argv[1], atoi(argv[3]));
        }
        else {
            printf("Usage: %s <interface> [ip <ipaddr>|mac <macaddr>|mtu <mtu>]\n", argv[0]);
        }
    }
    // 显示所有网络接口的信息
    else {
        printf("Usage: %s <interface> [ip <ipaddr>|mac <macaddr>|mtu <mtu>]\n", argv[0]);
        printf("Available interfaces:\n");

        struct if_nameindex *if_nidxs, *p;
        if_nidxs = if_nameindex();
        if (if_nidxs == NULL) {
            perror("if_nameindex");
            return 1;
        }

        for (p = if_nidxs; p->if_index != 0 || p->if_name != NULL; p++) {
            printf("%s\n", p->if_name);
        }

        if_freenameindex(if_nidxs);
    }

    return 0;
}