前言

這篇文章寫了獲取本機(jī)的ip地址和子網(wǎng)掩碼：Linux c語言獲取本機(jī) ip、子網(wǎng)掩碼

一、獲取本機(jī)網(wǎng)關(guān) ip 地址

1.1 Netlink套接字簡介

關(guān)于Netlink套接字請(qǐng)參考：Linux 網(wǎng)絡(luò)之netlink 簡介

Linux Netlink套接字是一種用于在Linux內(nèi)核和用戶空間之間進(jìn)行通信的機(jī)制。它是Linux內(nèi)核中的一種通信協(xié)議，用于讓用戶空間程序與內(nèi)核進(jìn)行交互。使用Netlink套接字，用戶空間程序可以向內(nèi)核發(fā)送請(qǐng)求，以獲取系統(tǒng)信息、控制系統(tǒng)行為或獲取有關(guān)網(wǎng)絡(luò)接口、路由表、套接字等的信息。

Netlink套接字提供了一種可擴(kuò)展的、可靠的、異步的機(jī)制，用于在內(nèi)核和用戶空間之間傳輸大量的網(wǎng)絡(luò)相關(guān)信息。它還支持多播，可以同時(shí)向多個(gè)進(jìn)程發(fā)送消息。

Netlink套接字有多個(gè)協(xié)議族，每個(gè)協(xié)議族都有不同的目的和用途。其中最常見的是NETLINK_ROUTE協(xié)議族，它用于與網(wǎng)絡(luò)配置和路由相關(guān)的操作。

1.2 代碼示例

下面是使用Netlink套接字從Linux內(nèi)核的路由表中檢索默認(rèn)網(wǎng)關(guān)IP地址的代碼例程

代碼如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <unistd.h>

#define BUFSIZE 8192

struct nlreq {
    struct nlmsghdr hdr;
    struct rtmsg msg;
};

int main(void) 
{
    int sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    if (sockfd == -1) {
        perror("socket error");
        exit(1);
    }

    struct sockaddr_nl sa;
    memset(&sa, 0, sizeof(sa));
    sa.nl_family = AF_NETLINK;
    if (bind(sockfd, (struct sockaddr *) &sa, sizeof(sa)) == -1) {
        perror("bind error");
        exit(1);
    }
    
    struct nlreq req;
    memset(&req, 0, sizeof(req));
    req.hdr.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
    req.hdr.nlmsg_type = RTM_GETROUTE;
    req.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
    req.msg.rtm_family = AF_INET;
    req.msg.rtm_table = RT_TABLE_MAIN;
    req.msg.rtm_protocol = RTPROT_UNSPEC;
    req.msg.rtm_scope = RT_SCOPE_UNIVERSE;
    req.msg.rtm_type = RTN_UNICAST;

    struct iovec iov;
    memset(&iov, 0, sizeof(iov));
    iov.iov_base = &req;
    iov.iov_len = req.hdr.nlmsg_len;

    struct msghdr msg;
    memset(&msg, 0, sizeof(msg));
    msg.msg_name = &sa;
    msg.msg_namelen = sizeof(sa);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    
    char buf[BUFSIZE];
    memset(buf, 0, sizeof(buf));
    struct nlmsghdr *hdr;
    int len;
    if (sendmsg(sockfd, &msg, 0) == -1) {
        perror("sendmsg error");
        exit(1);
    }
    while ((len = recv(sockfd, buf, sizeof(buf), 0)) > 0) {
        for (hdr = (struct nlmsghdr *) buf; NLMSG_OK(hdr, len); hdr = NLMSG_NEXT(hdr, len)) {
            if (hdr->nlmsg_type == NLMSG_DONE) {
                goto finish;
            }
            if (hdr->nlmsg_type == NLMSG_ERROR) {
                perror("NLMSG_ERROR");
                exit(1);
            }
            struct rtmsg *rt = (struct rtmsg *) NLMSG_DATA(hdr);
            if (rt->rtm_family != AF_INET || rt->rtm_table != RT_TABLE_MAIN || rt->rtm_type != RTN_UNICAST) {
                continue;
            }
            struct rtattr *attr;
            int attrlen;
            for (attr = (struct rtattr *) RTM_RTA(rt), attrlen = RTM_PAYLOAD(hdr); RTA_OK(attr, attrlen); attr = RTA_NEXT(attr, attrlen)) {
                if (attr->rta_type == RTA_GATEWAY) {
                    char gw_addr[INET_ADDRSTRLEN];
                    struct in_addr addr;
                    memcpy(&addr, RTA_DATA(attr), sizeof(addr));
                    if (inet_ntop(AF_INET, &addr, gw_addr, sizeof(gw_addr)) == NULL) {
                        perror("inet_ntop error");
                        continue;
                    }
                    printf("Gateway address: %s\n", gw_addr);
                    goto finish;
                }
            }
        }
    }
finish:
    close(sockfd);
    return 0;
}

首先，它使用socket（）函數(shù)創(chuàng)建一個(gè)Netlink套接字，并使用bind（）將其綁定到本地地址。然后，它使用nlreq結(jié)構(gòu)體變量初始化Netlink消息的參數(shù)。消息請(qǐng)求使用RTM_GETROUTE類型檢索路由表，并指定要檢索的路由的地址族、表、協(xié)議、范圍和類型。消息還指定了NLM_F_DUMP標(biāo)志以檢索所有可用路由。

消息使用sendmsg（）發(fā)送到內(nèi)核，并使用recv（）接收。接收到的數(shù)據(jù)通過一個(gè)循環(huán)解析緩沖區(qū)中的Netlink消息。該循環(huán)跳過與IPv4單播路由和主表無關(guān)的消息。對(duì)于每個(gè)相關(guān)消息，它使用另一個(gè)循環(huán)迭代路由屬性，并檢索網(wǎng)關(guān)地址（如果存在）。網(wǎng)關(guān)地址使用printf（）打印到控制臺(tái)，并使用goto語句退出循環(huán)。

1.3 代碼詳解介紹

（1）使用socket函數(shù)創(chuàng)建一個(gè)Netlink套接字

int sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
if (sockfd == -1) {
    perror("socket error");
    exit(1);
}

/* Protocol families.  */
#define	PF_NETLINK	16

/* Address families.  */
#define	AF_NETLINK	PF_NETLINK

/* Types of sockets.  */
enum __socket_type
{
  SOCK_RAW = 3,			/* Raw protocol interface.  */
#define SOCK_RAW SOCK_RAW
};

#define NETLINK_ROUTE		0	/* Routing/device hook				*/

NETLINK_ROUTE：用于與網(wǎng)絡(luò)配置和路由相關(guān)的操作，如獲取和修改網(wǎng)絡(luò)接口、路由表和ARP緩存等。

（2）綁定套接字到本地地址

struct sockaddr_nl sa;
memset(&sa, 0, sizeof(sa));
sa.nl_family = AF_NETLINK;
if (bind(sockfd, (struct sockaddr *) &sa, sizeof(sa)) == -1) {
    perror("bind error");
    exit(1);
}

綁定套接字到本地地址。這是為了確保接收到內(nèi)核發(fā)送的Netlink消息。

（3）創(chuàng)建一個(gè)Netlink消息

struct nlreq req;
memset(&req, 0, sizeof(req));
req.hdr.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
req.hdr.nlmsg_type = RTM_GETROUTE;
req.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
req.msg.rtm_family = AF_INET;
req.msg.rtm_table = RT_TABLE_MAIN;
req.msg.rtm_protocol = RTPROT_UNSPEC;
req.msg.rtm_scope = RT_SCOPE_UNIVERSE;
req.msg.rtm_type = RTN_UNICAST;

創(chuàng)建一個(gè)Netlink消息，用于向內(nèi)核請(qǐng)求路由表。我們?cè)O(shè)置消息頭部的長度、類型和標(biāo)志，以及rtmsg結(jié)構(gòu)體的成員。這里我們只請(qǐng)求主路由表中的單播路由表項(xiàng)，以獲取默認(rèn)網(wǎng)關(guān)的地址。

（4）將req結(jié)構(gòu)體打包成一個(gè)iovec結(jié)構(gòu)體

struct iovec iov;
memset(&iov, 0, sizeof(iov));
iov.iov_base = &req;
iov.iov_len = req.hdr.nlmsg_len;

struct msghdr msg;
memset(&msg, 0, sizeof(msg));
msg.msg_name = &sa;
msg.msg_namelen = sizeof(sa);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;

將req結(jié)構(gòu)體打包成一個(gè)iovec結(jié)構(gòu)體，用于在消息中發(fā)送。我們還創(chuàng)建了一個(gè)msghdr結(jié)構(gòu)體，指定發(fā)送和接收消息的參數(shù)。

（5）使用sendmsg函數(shù)將消息發(fā)送到內(nèi)核

if (sendmsg(sockfd, &msg, 0) == -1) {
    perror("sendmsg error");
    exit(1);
}

（6）使用recv函數(shù)從內(nèi)核接收消息

char buf[BUFSIZE];
memset(buf, 0, sizeof(buf));
struct nlmsghdr *hdr;
int len;
if (sendmsg(sockfd, &msg, 0) == -1) {
    perror("sendmsg error");
    exit(1);
}
while ((len = recv(sockfd, buf, sizeof(buf), 0)) > 0) {
    for (hdr = (struct nlmsghdr *) buf; NLMSG_OK(hdr, len); hdr = NLMSG_NEXT(hdr, len)) {
        if (hdr->nlmsg_type == NLMSG_DONE) {
            goto finish;
        }
        if (hdr->nlmsg_type == NLMSG_ERROR) {
            perror("NLMSG_ERROR");
            exit(1);
        }
        // 解析路由表項(xiàng)
    }
}

使用recv函數(shù)從內(nèi)核接收消息，并使用NLMSG_OK、NLMSG_NEXT和NLMSG_DATA宏來循環(huán)遍歷消息中的所有路由表項(xiàng)。

（7）獲取默認(rèn)網(wǎng)關(guān)的地址

struct rtmsg *rt = (struct rtmsg *) NLMSG_DATA(hdr);
if (rt->rtm_family != AF_INET || rt->rtm_table != RT_TABLE_MAIN || rt->rtm_type != RTN_UNICAST) {
    continue;
}
struct rtattr *attr;
int attrlen;
for (attr = (struct rtattr *) RTM_RTA(rt), attrlen = RTM_PAYLOAD(hdr); RTA_OK(attr, attrlen); attr = RTA_NEXT(attr, attrlen)) {
    if (attr->rta_type == RTA_GATEWAY) {
        char gw_addr[INET_ADDRSTRLEN];
        struct in_addr addr;
        memcpy(&addr, RTA_DATA(attr), sizeof(addr));
        if (inet_ntop(AF_INET, &addr, gw_addr, sizeof(gw_addr)) == NULL) {
            perror("inet_ntop error");
            continue;
        }
        printf("Gateway address: %s\n", gw_addr);
        goto finish;
    }
}
finish:
    close(sockfd);
    return 0;
}

/* Routing message attributes */

enum rtattr_type_t {
	RTA_GATEWAY,
};

檢查每個(gè)路由表項(xiàng)的類型和成員，以確定是否找到了默認(rèn)網(wǎng)關(guān)的地址。如果找到了，使用inet_ntop函數(shù)將地址轉(zhuǎn)換為可讀形式，并打印它。

二、使用Netlink套接字實(shí)時(shí)監(jiān)控網(wǎng)絡(luò)事件

2.1 簡介

可以使用Netlink套接字實(shí)時(shí)監(jiān)控網(wǎng)絡(luò)事件。Netlink是一種基于套接字的接口，用于與Linux內(nèi)核通信。內(nèi)核中的各個(gè)子系統(tǒng)都使用Netlink與用戶空間應(yīng)用程序通信，包括網(wǎng)絡(luò)子系統(tǒng)。

網(wǎng)絡(luò)子系統(tǒng)使用Netlink在某些網(wǎng)絡(luò)事件發(fā)生時(shí)向用戶空間應(yīng)用程序發(fā)送消息，例如添加或刪除網(wǎng)絡(luò)接口、更改網(wǎng)絡(luò)路由和更改網(wǎng)絡(luò)地址。這些消息可以被用戶空間應(yīng)用程序用于實(shí)時(shí)監(jiān)控網(wǎng)絡(luò)事件。

要使用Netlink實(shí)時(shí)監(jiān)控網(wǎng)絡(luò)事件，您需要?jiǎng)?chuàng)建一個(gè)Netlink套接字，將其綁定到特定的Netlink協(xié)議，然后使用recv函數(shù)從內(nèi)核接收Netlink消息。然后，您可以解析消息以提取有關(guān)已發(fā)生的網(wǎng)絡(luò)事件的信息。

2.2 示例代碼

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

#define BUFFER_SIZE 4096

int main(int argc, char *argv[]) {
    int netlinkSocket = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    if (netlinkSocket < 0) {
        perror("創(chuàng)建Netlink套接字失敗");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_nl addr;
    memset(&addr, 0, sizeof(addr));
    addr.nl_family = AF_NETLINK;
    addr.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR;

    if (bind(netlinkSocket, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("將Netlink套接字綁定到地址失敗");
        close(netlinkSocket);
        exit(EXIT_FAILURE);
    }

    char buffer[BUFFER_SIZE];
    struct iovec iov = { buffer, sizeof(buffer) };
    struct msghdr msg = { (void *)&addr, sizeof(addr), &iov, 1, NULL, 0, 0 };

    while (1) {
        ssize_t len = recvmsg(netlinkSocket, &msg, 0);
        if (len < 0) {
            perror("接收Netlink消息失敗");
            close(netlinkSocket);
            exit(EXIT_FAILURE);
        }

        struct nlmsghdr *nlh;
        for (nlh = (struct nlmsghdr *)buffer; NLMSG_OK(nlh, len); nlh = NLMSG_NEXT(nlh, len)) {
            switch(nlh->nlmsg_type) {
                case RTM_NEWLINK:
                    printf("檢測(cè)到新鏈接\n");
                    break;
                case RTM_DELLINK:
                    printf("鏈接已刪除\n");
                    break;
                case RTM_NEWADDR:
                    printf("檢測(cè)到新地址\n");
                    break;
                case RTM_DELADDR:
                    printf("地址已刪除\n");
                    break;
                default:
                    printf("未知的消息類型 (%d)\n", nlh->nlmsg_type);
                    break;
            }
        }
    }

    close(netlinkSocket);
    return 0;
}

在一個(gè)終端上編譯程序并運(yùn)行。

在另一個(gè)終端上輸入以下命令來更改網(wǎng)絡(luò)接口的狀態(tài)：

sudo ifconfig eth0 down

sudo ifconfig eth0 up

這只是一個(gè)簡單的示例，可以使用Netlink監(jiān)控許多其他類型的網(wǎng)絡(luò)事件。

rtnetlink.h頭文件提供了所有可能的Netlink消息類型的列表，可以用于監(jiān)控其他類型的網(wǎng)絡(luò)事件。
如下所示：文章來源地址http://www.zghlxwxcb.cn/news/detail-733408.html

/****
 *		Routing/neighbour discovery messages.
 ****/

/* Types of messages */

enum {
	RTM_BASE	= 16,
#define RTM_BASE	RTM_BASE

	RTM_NEWLINK	= 16,
#define RTM_NEWLINK	RTM_NEWLINK
	RTM_DELLINK,
#define RTM_DELLINK	RTM_DELLINK
	RTM_GETLINK,
#define RTM_GETLINK	RTM_GETLINK
	RTM_SETLINK,
#define RTM_SETLINK	RTM_SETLINK

	RTM_NEWADDR	= 20,
#define RTM_NEWADDR	RTM_NEWADDR
	RTM_DELADDR,
#define RTM_DELADDR	RTM_DELADDR
	RTM_GETADDR,
#define RTM_GETADDR	RTM_GETADDR

	RTM_NEWROUTE	= 24,
#define RTM_NEWROUTE	RTM_NEWROUTE
	RTM_DELROUTE,
#define RTM_DELROUTE	RTM_DELROUTE
	RTM_GETROUTE,
#define RTM_GETROUTE	RTM_GETROUTE

	RTM_NEWNEIGH	= 28,
#define RTM_NEWNEIGH	RTM_NEWNEIGH
	RTM_DELNEIGH,
#define RTM_DELNEIGH	RTM_DELNEIGH
	RTM_GETNEIGH,
#define RTM_GETNEIGH	RTM_GETNEIGH

	RTM_NEWRULE	= 32,
#define RTM_NEWRULE	RTM_NEWRULE
	RTM_DELRULE,
#define RTM_DELRULE	RTM_DELRULE
	RTM_GETRULE,
#define RTM_GETRULE	RTM_GETRULE

	RTM_NEWQDISC	= 36,
#define RTM_NEWQDISC	RTM_NEWQDISC
	RTM_DELQDISC,
#define RTM_DELQDISC	RTM_DELQDISC
	RTM_GETQDISC,
#define RTM_GETQDISC	RTM_GETQDISC

	RTM_NEWTCLASS	= 40,
#define RTM_NEWTCLASS	RTM_NEWTCLASS
	RTM_DELTCLASS,
#define RTM_DELTCLASS	RTM_DELTCLASS
	RTM_GETTCLASS,
#define RTM_GETTCLASS	RTM_GETTCLASS

	RTM_NEWTFILTER	= 44,
#define RTM_NEWTFILTER	RTM_NEWTFILTER
	RTM_DELTFILTER,
#define RTM_DELTFILTER	RTM_DELTFILTER
	RTM_GETTFILTER,
#define RTM_GETTFILTER	RTM_GETTFILTER

	RTM_NEWACTION	= 48,
#define RTM_NEWACTION   RTM_NEWACTION
	RTM_DELACTION,
#define RTM_DELACTION   RTM_DELACTION
	RTM_GETACTION,
#define RTM_GETACTION   RTM_GETACTION

	RTM_NEWPREFIX	= 52,
#define RTM_NEWPREFIX	RTM_NEWPREFIX

	RTM_GETMULTICAST = 58,
#define RTM_GETMULTICAST RTM_GETMULTICAST

	RTM_GETANYCAST	= 62,
#define RTM_GETANYCAST	RTM_GETANYCAST

	RTM_NEWNEIGHTBL	= 64,
#define RTM_NEWNEIGHTBL	RTM_NEWNEIGHTBL
	RTM_GETNEIGHTBL	= 66,
#define RTM_GETNEIGHTBL	RTM_GETNEIGHTBL
	RTM_SETNEIGHTBL,
#define RTM_SETNEIGHTBL	RTM_SETNEIGHTBL

	RTM_NEWNDUSEROPT = 68,
#define RTM_NEWNDUSEROPT RTM_NEWNDUSEROPT

	RTM_NEWADDRLABEL = 72,
#define RTM_NEWADDRLABEL RTM_NEWADDRLABEL
	RTM_DELADDRLABEL,
#define RTM_DELADDRLABEL RTM_DELADDRLABEL
	RTM_GETADDRLABEL,
#define RTM_GETADDRLABEL RTM_GETADDRLABEL

	RTM_GETDCB = 78,
#define RTM_GETDCB RTM_GETDCB
	RTM_SETDCB,
#define RTM_SETDCB RTM_SETDCB

	RTM_NEWNETCONF = 80,
#define RTM_NEWNETCONF RTM_NEWNETCONF
	RTM_GETNETCONF = 82,
#define RTM_GETNETCONF RTM_GETNETCONF

	RTM_NEWMDB = 84,
#define RTM_NEWMDB RTM_NEWMDB
	RTM_DELMDB = 85,
#define RTM_DELMDB RTM_DELMDB
	RTM_GETMDB = 86,
#define RTM_GETMDB RTM_GETMDB

	RTM_NEWNSID = 88,
#define RTM_NEWNSID RTM_NEWNSID
	RTM_DELNSID = 89,
#define RTM_DELNSID RTM_DELNSID
	RTM_GETNSID = 90,
#define RTM_GETNSID RTM_GETNSID

	RTM_NEWSTATS = 92,
#define RTM_NEWSTATS RTM_NEWSTATS
	RTM_GETSTATS = 94,
#define RTM_GETSTATS RTM_GETSTATS

	__RTM_MAX,
#define RTM_MAX		(((__RTM_MAX + 3) & ~3) - 1)
};

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