从netlink消息中提取当前路由,附加代码

#include<linux/netlink.h>
#include<linux/rtnetlink.h>
#include <net/if.h>
#include <netinet/in.h>
#include<stdio.h>
#include <stdlib.h>
#include<string.h>
#include <sys/socket.h>
#include <unistd.h>

#define BUFFER_SIZE 4096

int main() {
    int sockfd;
    struct sockaddr_nl sa;
    char buffer[BUFFER_SIZE];
    struct nlmsghdr *nlh;
    struct rtmsg *rtm;
    struct rtattr *rta;
    int len;

    sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    if (sockfd < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    memset(&sa, 0, sizeof(sa));
    sa.nl_family = AF_NETLINK;
    sa.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_ROUTE | RTMGRP_IPV6_ROUTE;

    if (bind(sockfd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    nlh = (struct nlmsghdr *)buffer;
    rtm = (struct rtmsg *)NLMSG_DATA(nlh);
    rta = (struct rtattr *)RTM_RTA(rtm);

    nlh->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
    nlh->nlmsg_type = RTM_GETROUTE;
    nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
    nlh->nlmsg_seq = 1;
    nlh->nlmsg_pid = getpid();

    rtm->rtm_family = AF_UNSPEC;
    rtm->rtm_table = RT_TABLE_MAIN;

    len = send(sockfd, nlh, nlh->nlmsg_len, 0);
    if (len < 0) {
        perror("send");
        exit(EXIT_FAILURE);
    }

    len = recv(sockfd, buffer, BUFFER_SIZE, 0);
    if (len < 0) {
        perror("recv");
        exit(EXIT_FAILURE);
    }

    close(sockfd);

    return 0;
}