ioctl在socket中的一些用法和示例

一、获取

以下例程通过ioctl获取设备"eth0"的IP/掩码/硬件址

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

#include "net/if.h"
#include "arpa/inet.h"
#include "linux/sockios.h"

int main(int argc,char *argv[])
{
    struct sockaddr_in *addr;
    struct ifreq ifr;
    char*address;
    int sockfd;

    char *name = "eth0";
    if( strlen(name) >= IFNAMSIZ)
        printf("device name is error.\n"), exit(0);
        
    strcpy( ifr.ifr_name, name);
        
    sockfd = socket(AF_INET,SOCK_DGRAM,0);

    //get inet addr
    if( ioctl( sockfd, SIOCGIFADDR, &ifr) == -1)
        printf("ioctl error.\n"), exit(0);

    addr = (struct sockaddr_in *)&(ifr.ifr_addr);
    address = inet_ntoa(addr->sin_addr);

    printf("inet addr: %s\n",address);

    //get Mask
    if( ioctl( sockfd, SIOCGIFNETMASK, &ifr) == -1)
        printf("ioctl error.\n"), exit(0);

    addr = (struct sockaddr_in *)&ifr.ifr_addr;
    address = inet_ntoa(addr->sin_addr);

    printf("Mask: %s\n",address);

    //get HWaddr 
    u_int8_t hd[6];
    if(ioctl(sockfd, SIOCGIFHWADDR, &ifr) == -1)
        printf("hwaddr error.\n"), exit(0);

    memcpy( hd, ifr.ifr_hwaddr.sa_data, sizeof(hd));
    printf("HWaddr: %02X:%02X:%02X:%02X:%02X:%02X\n", hd[0], hd[1], hd[2], hd[3], hd[4], hd[5]);
    
    exit(0);
}

 二、设置
以下例程设置eth0的IP地址.

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

#include "net/if.h"
#include "arpa/inet.h"
#include "linux/sockios.h"

int main(int argc,char *argv[])
{
    char *dev = "eth0";
    char *ip = "192.168.1.252";
    
    struct ifreq ifr;
    if( strlen(dev) >= IFNAMSIZ)
        printf("device name error.\n"), exit(0);
    else
        strcpy( ifr.ifr_name, dev);
    
    int sockfd = socket(AF_INET,SOCK_DGRAM,0);

    //get inet addr
    if( ioctl( sockfd, SIOCGIFADDR, &ifr) == -1)
        printf("ioctl error.\n"), exit(0);
    
    struct sockaddr_in *addr = (struct sockaddr_in *)&(ifr.ifr_addr);
    char * address = inet_ntoa(addr->sin_addr);

    printf("current inet addr: %s\n",address);

    //set inet addr
    struct sockaddr_in *p = (struct sockaddr_in *)&(ifr.ifr_addr);

    p->sin_family = AF_INET;
    inet_aton( ip, &(p->sin_addr));

    if( ioctl( sockfd, SIOCSIFADDR, &ifr) == -1)
     printf("ioctl error.\n"), exit(0);
    else    
        printf("change inet addr to: %s\n", ip);

    //any OS need active dev.
    /*ifr.ifr_flags |= IFF_UP;
    if( ioctl( sockfd, SIOCSIFFLAGS, &ifr) == -1)
        printf("active fault.\n"), exit(0);
    else
        printf("%s[%s] is working...\n", dev, ip);
    */
        
    close(sockfd);
    exit(1);
    //end
}

屏蔽的代码用于设置IP后, 激活新设置. 多数系统不需要这步操作. 
而且这步仅作演示. 真实使用的时候, 至少应该
1. 获取当前ifr.ifr_flags
2. ifr.ifr_flags |= IFF_UP;