Linux--网络层IP

在Linux系统中，IP层的相关操作通常通过netlink套接字进行，这是一种允许进程向内核发送请求和接收内核消息的方式。以下是一个简单的示例，展示如何使用netlink套接字在用户空间中获取和设置IP地址。

#include <asm/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
 
#define BUFSIZE 8192
#define MAX_ADDRS 32
 
struct nlmsghdr *recv_nlmsg(int nl, struct nlmsghdr *h) {
    int len;
    while ((len = recv(nl, h, sizeof(struct nlmsghdr), 0)) > 0) {
        if (len == sizeof(struct nlmsghdr)) {
            if ((h->nlmsg_flags & NLM_F_MULTI) == 0) {
                return h;
            }
        } else {
            fprintf(stderr, "recv(): %s\n", strerror(errno));
            exit(1);
        }
    }
    return NULL;
}
 
int main() {
    struct {
        struct nlmsghdr nlmsg;
        struct rtgenmsg rtgen;
    } req;
 
    struct sockaddr_nl nls;
    struct iovec iov;
    struct msghdr msg;
    struct nlmsghdr *respptr;
    char buf[BUFSIZE];
    int len;
 
    memset(&req, 0, sizeof(req));
    memset(&nls, 0, sizeof(nls));
    memset(&iov, 0, sizeof(iov));
    memset(&msg, 0, sizeof(msg));
 
    // 创建netlink套接字
    int nl = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    if (nl < 0) {
        perror("socket()");
        exit(1);
    }
 
    // 准备请求
    req.nlmsg.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtgenmsg));
    req.nlmsg.nlmsg_type = RTM_GETADDR;
    req.nlmsg.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST;
    req.nlmsg.nlmsg_pid = getpid();
    req.nlmsg.nlmsg_seq = 123;
 
    // 发送请求
    iov.iov_base = (void *)&req;
    iov.iov_len = req.nlmsg.nlmsg_len;
    msg.msg_name = (void *)&nls;
    msg.msg_namelen = sizeof(nls);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
 
    sendmsg(nl, &msg, 0);
 
    // 接收响应
    respptr = (struct nlmsghdr *)buf;
    while ((respptr = recv_nlmsg(nl, respptr)) != NULL) {
        struct ifaddrmsg *ifaddr;
        struct rtattr *rta;
        int rtl;
 
        if (respptr->nlmsg_type == NLMSG_ERROR) {
            fprintf(stderr, "Received NLMSG_ERROR.\n");
            break;
        }
 
        if (respptr->nlmsg_type != RTM_NEWADDR) {
            continue;
        }
 
        ifaddr = (struct ifaddrmsg *)NLMSG_DATA(respptr);
        printf("Interface index: %d\n", ifaddr->ifindex);
 
        rta = (struct rtattr *)RTM_RTA(ifaddr);