linux下的ioctl函式原型如下：

#include <sys/ioctl.h>

int ioctl(int handle, int cmd, [int *argc, int argv])

函式成功返回0，失敗返回-1.

其相關命令介面如下：

在這裡我們需要用到的結構體

#include<netinet/in.h>

#include <net/if.h>

struct ifreq
{
#define IFHWADDRLEN 6
union
{
charifrn_name[IFNAMSIZ]; 
} ifr_ifrn;

union {
structsockaddr ifru_addr;
structsockaddr ifru_dstaddr;
structsockaddr ifru_broadaddr;
structsockaddr ifru_netmask;
struct sockaddr ifru_hwaddr;
shortifru_flags;
intifru_ivalue;
intifru_mtu;
struct ifmap ifru_map;
charifru_slave[IFNAMSIZ]; charifru_newname[IFNAMSIZ];
void __user * ifru_data;
structif_settings ifru_settings;
} ifr_ifru;
};

#define ifr_name ifr_ifrn.ifrn_name #define ifr_hwaddr ifr_ifru.ifru_hwaddr 
#defineifr_addr ifr_ifru.ifru_addr #defineifr_dstaddr ifr_ifru.ifru_dstaddr #defineifr_broadaddr ifr_ifru.ifru_broadaddr #defineifr_netmask ifr_ifru.ifru_netmask#defineifr_flags ifr_ifru.ifru_flags 
#defineifr_metric ifr_ifru.ifru_ivalue#defineifr_mtu ifr_ifru.ifru_mtu#define ifr_map ifr_ifru.ifru_map#define ifr_slave ifr_ifru.ifru_slave#defineifr_data ifr_ifru.ifru_data #define ifr_ifindex ifr_ifru.ifru_ivalue#define ifr_bandwidth ifr_ifru.ifru_ivalue #define ifr_qlen ifr_ifru.ifru_ivalue#define ifr_newname ifr_ifru.ifru_newname#define ifr_settings ifr_ifru.ifru_setting

ioctl函式能獲取到IP地址、子網掩碼、廣播地址、硬體MAC地址等資訊，至於閘道器及路由表比較複雜，在此不討論。

具體程式碼如下：（測試通過）

#include <stdio.h>

#include <stdlib.h>

#include <net/if.h>

#include <unistd.h>

#include <sys/ioctl.h>

#include <arpa/inet.h>

#include <sys/stat.h>

#include <sys/types.h>

#include <errno.h>

#include <fcntl.h>

#include <netinet/in.h>

#include <net/route.h>

#include <string.h>

#include <net/if_arp.h>

int main()

{

   struct sockaddr_in *sin;

   struct ifreq ifr;

   FILE *dns;

   FILE *gw;

   char *ip = new char(16);

   char *netmask = new char(16);

   char *broadcast = new char(16);

   //char *ip = (char *)malloc(16);

   char *mac = new  char(32);

   //char *mac = (char *)malloc(32);

   int socket_fd;

       if((socket_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){

               perror("socket");

               exit(1);

       }

       memset(&ifr, 0, sizeof(ifr));

       strcpy(ifr.ifr_name, "eth0");

       memset(&sin, 0, sizeof(sin));

//獲取IP地址

       if(ioctl(socket_fd, SIOCGIFADDR, &ifr) != -1){

               sin = (struct sockaddr_in *)&ifr.ifr_addr;

               strcpy(ip, inet_ntoa(sin->sin_addr));

               printf("IP address is %s\n", ip);

       }

//獲取廣播地址

       if(ioctl(socket_fd, SIOCGIFBRDADDR, &ifr) != -1){

               sin = (struct sockaddr_in *)&ifr.ifr_broadaddr;

               strcpy(broadcast, inet_ntoa(sin->sin_addr));

               printf("Broadcast is %s\n", broadcast);

       }

//獲取子網掩碼

       if(ioctl(socket_fd, SIOCGIFNETMASK, &ifr) != -1){

               sin = (struct sockaddr_in *)&ifr.ifr_broadaddr;

               strcpy(netmask, inet_ntoa(sin->sin_addr));

               printf("Net-mask is %s\n", netmask);

       }

//獲取硬體MAC地址

       if(ioctl(socket_fd, SIOCGIFHWADDR, &ifr) != -1){

               sin = (struct sockaddr_in *)&ifr.ifr_netmask;

               sprintf(mac, "%02x:%02x:%02x:%02x:%02x:%02x",

               (unsigned char)ifr.ifr_netmask.sa_data[0],

               (unsigned char)ifr.ifr_netmask.sa_data[1],

               (unsigned char)ifr.ifr_netmask.sa_data[2],

               (unsigned char)ifr.ifr_netmask.sa_data[3],

               (unsigned char)ifr.ifr_netmask.sa_data[4],

               (unsigned char)ifr.ifr_netmask.sa_data[5]);

               printf("Mac address is %s\n", mac);

       }

   return 0;

}

至於獲取閘道器以及DNS，我是通過相關命令獲得的。

主要程式碼如下：

//獲取閘道器，利用route -n 命令可以看到相關的閘道器。連線標誌是‘UG’

if(gw_fd = popen("route -n | grep 'UG'", "r")){

   fread(temp,1,128, gw_fd);

   sscanf(temp, "%*s%s", szNetGate);

   printf("Gateway is %s\n", szNetGate);

}

//獲取DNS；一般DNS儲存在/etc/reslov.conf檔案中。具體獲得方法要根據實際情況而定。

我的配置檔案中是這樣的

[email protected]:/home/arm-none-linux# cat /etc/resolv.conf

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)

#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 202.96.134.133  

上面的202.96.134.133就是我需要獲取的主DNS，沒有備用DNS

if(dns_fd = popen("cat /etc/reslov.conf | grep 'nameserver'", "r")){

   fread(temp,1,128, gw_fd);

   sscanf(temp, "%*s%s%*s%s", szDNS1,szDNS2);

   printf("DNS1 is %s",szDNS1);

   printf("DNS2is %s", szDNS2);

}

寫在前面

獲取與設定網絡卡資訊的方法有很多種，本文就傳統的通過ioctl介面獲取的方法做個記錄。

此外，通過ioctl還可以獲取網絡卡裝置的對映屬性。更進一步，可以讓我們檢視，修改，刪除系統的ARP快取記憶體和路由表資訊。

相關結構體

這裡主要相關的兩個結構體定義在glibc標頭檔案/usr/include/net/if.h中，分別為struct ifconf和struct ifreq。

/* Structure used in SIOCGIFCONF request.  Used to retrieve interface
   configuration for machine (useful for programs which must know all
   networks accessible).  */

struct ifconf
  {
    int ifc_len;                        /* Size of buffer.  */
    union
      {
        __caddr_t ifcu_buf;
        struct ifreq *ifcu_req;
      } ifc_ifcu;
  };
# define ifc_buf        ifc_ifcu.ifcu_buf       /* Buffer address.  */
# define ifc_req        ifc_ifcu.ifcu_req       /* Array of structures.  */
# define _IOT_ifconf _IOT(_IOTS(struct ifconf),1,0,0,0,0) /* not right */
#endif  /* Misc.  */

從註釋資訊中可以看出struct ifconf主要是用來利用ioctl函式的SIOCGIFCONF request來獲取系統中所有網路介面的資訊。關於它的具體用法，後文會有示例。

既然是關於系統中所有的網路介面資訊，那麼一個網路介面資訊用什麼結構來表示呢？ 這就是struct ifreq的用處了。

/* Interface request structure used for socket ioctl's.  All interface
   ioctl's must have parameter definitions which begin with ifr_name.
   The remainder may be interface specific.  */

struct ifreq
  {
# define IFHWADDRLEN	6
# define IFNAMSIZ	IF_NAMESIZE
    union
      {
	char ifrn_name[IFNAMSIZ];	/* Interface name, e.g. "en0".  */
      } ifr_ifrn;

    union
      {
	struct sockaddr ifru_addr;
	struct sockaddr ifru_dstaddr;
	struct sockaddr ifru_broadaddr;
	struct sockaddr ifru_netmask;
	struct sockaddr ifru_hwaddr;
	short int ifru_flags;
	int ifru_ivalue;
	int ifru_mtu;
	struct ifmap ifru_map;
	char ifru_slave[IFNAMSIZ];	/* Just fits the size */
	char ifru_newname[IFNAMSIZ];
	__caddr_t ifru_data;
      } ifr_ifru;
  };
# define ifr_name	ifr_ifrn.ifrn_name	/* interface name 	*/
# define ifr_hwaddr	ifr_ifru.ifru_hwaddr	/* MAC address 		*/
# define ifr_addr	ifr_ifru.ifru_addr	/* address		*/
# define ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-p lnk	*/
# define ifr_broadaddr	ifr_ifru.ifru_broadaddr	/* broadcast address	*/
# define ifr_netmask	ifr_ifru.ifru_netmask	/* interface net mask	*/
# define ifr_flags	ifr_ifru.ifru_flags	/* flags		*/
# define ifr_metric	ifr_ifru.ifru_ivalue	/* metric		*/
# define ifr_mtu	ifr_ifru.ifru_mtu	/* mtu			*/
# define ifr_map	ifr_ifru.ifru_map	/* device map		*/
# define ifr_slave	ifr_ifru.ifru_slave	/* slave device		*/
# define ifr_data	ifr_ifru.ifru_data	/* for use by interface	*/
# define ifr_ifindex	ifr_ifru.ifru_ivalue    /* interface index      */
# define ifr_bandwidth	ifr_ifru.ifru_ivalue	/* link bandwidth	*/
# define ifr_qlen	ifr_ifru.ifru_ivalue	/* queue length		*/
# define ifr_newname	ifr_ifru.ifru_newname	/* New name		*/
# define _IOT_ifreq	_IOT(_IOTS(char),IFNAMSIZ,_IOTS(char),16,0,0)
# define _IOT_ifreq_short _IOT(_IOTS(char),IFNAMSIZ,_IOTS(short),1,0,0)
# define _IOT_ifreq_int	_IOT(_IOTS(char),IFNAMSIZ,_IOTS(int),1,0,0)