如何在linux中从C设置IP地址

Question

通过使用strace和ifconfig，发现可以这样设置IP地址：

#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <string.h>

int main(int argc, const char *argv[]) {
    struct ifreq ifr;
    const char * name = "eth1";
    int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);

    strncpy(ifr.ifr_name, name, IFNAMSIZ);

    ifr.ifr_addr.sa_family = AF_INET;
    inet_pton(AF_INET, "10.12.0.1", ifr.ifr_addr.sa_data + 2);
    ioctl(fd, SIOCSIFADDR, &ifr);

    inet_pton(AF_INET, "255.255.0.0", ifr.ifr_addr.sa_data + 2);
    ioctl(fd, SIOCSIFNETMASK, &ifr);

    ioctl(fd, SIOCGIFFLAGS, &ifr);
    strncpy(ifr.ifr_name, name, IFNAMSIZ);
    ifr.ifr_flags |= (IFF_UP | IFF_RUNNING);

    ioctl(fd, SIOCSIFFLAGS, &ifr);

    return 0;
}

但我对这个解决方案不是很满意：

inet_pton(AF_INET, "10.12.0.1", ifr.ifr_addr.sa_data + 2);

这样做的“正确”方法是什么？

Answer 1

没有魔法 +2 的 IPv4 的“正确”方式：

struct sockaddr_in* addr = (struct sockaddr_in*)&ifr.ifr_addr;
inet_pton(AF_INET, "10.12.0.1", &addr->sin_addr);

要使用 IPv6，请将其转换为 sockaddr_in6

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>           // close()
#include <string.h>           // strcpy, memset(), and memcpy()

#include <netdb.h>            // struct addrinfo
#include <sys/types.h>        // needed for socket(), uint8_t, uint16_t
#include <sys/socket.h>       // needed for socket()
#include <netinet/in.h>       // IPPROTO_RAW, INET_ADDRSTRLEN
#include <netinet/ip.h>       // IP_MAXPACKET (which is 65535)
#include <arpa/inet.h>        // inet_pton() and inet_ntop()
#include <sys/ioctl.h>        // macro ioctl is defined
#include <bits/ioctls.h>      // defines values for argument "request" of ioctl.
#include <net/if.h>           // struct ifreq
#include <linux/if_ether.h>   // ETH_P_ARP = 0x0806
#include <linux/if_packet.h>  // struct sockaddr_ll (see man 7 packet)
#include <net/ethernet.h>

#include <errno.h>            // errno, perror()

#include <netinet/in.h>
#include <net/route.h>    


 /**
    * Create socket function
    */
    int create_socket() {

      int sockfd = 0;

      sockfd = socket(AF_INET, SOCK_DGRAM, 0);
      if(sockfd == -1){
        fprintf(stderr, "Could not get socket.\n");
        return -1;
      }

      return sockfd;

    }

    /**
    * Generic ioctrlcall to reduce code size
    */
    int generic_ioctrlcall(int sockfd, u_long *flags, struct ifreq *ifr) {

      if (ioctl(sockfd, (long unsigned int)flags, &ifr) < 0) {
        fprintf(stderr, "ioctl: %s\n", (char *)flags);
        return -1;
      }
      return 1;
    }

    /**
    * Set route with metric 100
    */
    int set_route(int sockfd, char *gateway_addr,  struct sockaddr_in *addr) {
      struct rtentry route;
      int err = 0;
      memset(&route, 0, sizeof(route));
      addr = (struct sockaddr_in*) &route.rt_gateway;
      addr->sin_family = AF_INET;
      addr->sin_addr.s_addr = inet_addr(gateway_addr);
      addr = (struct sockaddr_in*) &route.rt_dst;
      addr->sin_family = AF_INET;
      addr->sin_addr.s_addr = inet_addr("0.0.0.0");
      addr = (struct sockaddr_in*) &route.rt_genmask;
      addr->sin_family = AF_INET;
      addr->sin_addr.s_addr = inet_addr("0.0.0.0");
      route.rt_flags = RTF_UP | RTF_GATEWAY;
      route.rt_metric = 100;
      err = ioctl(sockfd, SIOCADDRT, &route);
      if ((err) < 0) {
        fprintf(stderr, "ioctl: %s\n",  "mahdi MOAHMMADI Error");
        return -1;
      }
      return 1;
    }

    /**
    * Set ip function
    */
    int set_ip(char *iface_name, char *ip_addr, char *gateway_addr)
    {
      if(!iface_name)
        return -1;
      struct ifreq ifr;
      struct sockaddr_in sin;
      int sockfd = create_socket();

      sin.sin_family = AF_INET;

      // Convert IP from numbers and dots to binary notation
      inet_aton(ip_addr,&sin.sin_addr.s_addr);

      /* get interface name */
      strncpy(ifr.ifr_name, iface_name, IFNAMSIZ);

      /* Read interface flags */
      generic_ioctrlcall(sockfd, (u_long *)"SIOCGIFFLAGS", &ifr);
      /*
      * Expected in <net/if.h> according to
      * "UNIX Network Programming".
      */
      #ifdef ifr_flags
      # define IRFFLAGS       ifr_flags
      #else   /* Present on kFreeBSD */
      # define IRFFLAGS       ifr_flagshigh
      #endif
      // If interface is down, bring it up
      if (ifr.IRFFLAGS | ~(IFF_UP)) {
        ifr.IRFFLAGS |= IFF_UP;
        generic_ioctrlcall(sockfd, (u_long *)"SIOCSIFFLAGS", &ifr);
      }
      // Set route
      set_route(sockfd, gateway_addr    ,  &sin);
      memcpy(&ifr.ifr_addr, &sin, sizeof(struct sockaddr)); 
      // Set interface address
      if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
        fprintf(stderr, "Cannot set IP address. ");
        perror(ifr.ifr_name);
        return -1;
      }             
      #undef IRFFLAGS 

      return 0;
    }

用法：

set_ip("eth0", "192.168.181.128", "192.168.181.1");

Answer 3

“正确”的做法是生成带有相关参数的 iproute2“ip”程序（在 /sbin/ip 中）的副本。

ioctl 接口通常已过时，不允许您配置所有参数（例如，未命名的 IP 别名）。

即使是像 dhcpcd 这样需要更改 IP 地址的守护进程，通常也是通过生成外部程序来完成的……你不会经常这样做。

Answer 4

您好：在 set_ip 函数中，它给了我一个错误。 我不得不改变：

inet_aton(ip_addr, &sin.sin_addr.s_addr);

到

inet_aton(ip_addr, &sin.sin_addr);

并且工作得很好。