struct ifreq学习和实例

一、struct ifreq结构体

这个结构定义在/usr/include/net/if.h，用来配置和获取ip地址，掩码，MTU等接口信息的。

/* 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)

二、用法：

通过ioctl()函数调用
下表列出了网络相关ioctl请求的request 参数以及arg 地址必须指向的数据类型：

　　

类别	Request	说明	数据类型
套 接 口	SIOCATMARK  SIOCSPGRP  SIOCGPGRP	是否位于带外标记  设置套接口的进程ID 或进程组ID  获取套接口的进程ID 或进程组ID	int  int  int
文 件	FIONBIN  FIOASYNC  FIONREAD  FIOSETOWN  FIOGETOWN	设置/ 清除非阻塞I/O 标志  设置/ 清除信号驱动异步I/O 标志  获取接收缓存区中的字节数  设置文件的进程ID 或进程组ID  获取文件的进程ID 或进程组ID	int  int  int  int  int
接 口	SIOCGIFCONF  SIOCSIFADDR  SIOCGIFADDR  SIOCSIFFLAGS  SIOCGIFFLAGS  SIOCSIFDSTADDR  SIOCGIFDSTADDR  SIOCGIFBRDADDR  SIOCSIFBRDADDR  SIOCGIFNETMASK  SIOCSIFNETMASK  SIOCGIFMETRIC  SIOCSIFMETRIC  SIOCGIFMTU  SIOCxxx	获取所有接口的清单  设置接口地址  获取接口地址  设置接口标志  获取接口标志  设置点到点地址  获取点到点地址  获取广播地址  设置广播地址  获取子网掩码  设置子网掩码  获取接口的测度  设置接口的测度  获取接口MTU  （还有很多取决于系统的实现）	struct ifconf  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq  struct ifreq
ARP	SIOCSARP  SIOCGARP  SIOCDARP	创建/ 修改ARP 表项  获取ARP 表项  删除ARP 表项	struct arpreq  struct arpreq  struct arpreq
路 由	SIOCADDRT  SIOCDELRT	增加路径  删除路径	struct rtentry  struct rtentry
流	I_xxx

实例一，获取网卡的IP地址：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
int main()
{
        int inet_sock;
        struct ifreq ifr;
        inet_sock = socket(AF_INET, SOCK_DGRAM, 0);

        strcpy(ifr.ifr_name, "eth0");
        //SIOCGIFADDR标志代表获取接口地址
        if (ioctl(inet_sock, SIOCGIFADDR, &ifr) <  0)
                perror("ioctl");
        printf("%s\n", inet_ntoa(((struct sockaddr_in*)&(ifr.ifr_addr))->sin_addr));
        return 0;
}

实例二，实现简单ifconfig功能：

/**
 * \file getifstat.c
 * \author  wzj
 * \brief 访问这个struct ifconf 修改，查询状态
 * \version 
 * \note  
 * \date: 2012年08月11日星期六22:55:25
 */ 
#include 		/* for ifconf */
#include 	/* for net status mask */
#include 		/* for sockaddr_in */
#include 
#include 
#include 
#include 

#define MAX_INTERFACE	(16)

void port_status(unsigned int flags);

/* set == 0: do clean , set == 1: do set! */
int set_if_flags(char *pif_name, int sock, int status, int set)
{
	struct ifreq ifr;
	int ret = 0;
	
	strncpy(ifr.ifr_name, pif_name, strlen(pif_name) + 1);
	ret = ioctl(sock, SIOCGIFFLAGS, &ifr);
	if(ret)
		return -1;
	/* set or clean */	
	if(set)
		ifr.ifr_flags |= status;
	else 
		ifr.ifr_flags &= ~status;
	/* set flags */
	ret = ioctl(sock, SIOCSIFFLAGS, &ifr);
	if(ret)
		return -1;
	
	return 0;
}

int get_if_info(int fd)
{
	struct ifreq buf[MAX_INTERFACE];	
	struct ifconf ifc;
	int ret = 0;
	int if_num = 0;

	ifc.ifc_len = sizeof(buf);
	ifc.ifc_buf = (caddr_t) buf;
	
	ret = ioctl(fd, SIOCGIFCONF, (char*)&ifc);
	if(ret)
	{
		printf("get if config info failed");
		return -1;
	}
	/* 网口总数 ifc.ifc_len 应该是一个出入参数 */	
	if_num = ifc.ifc_len/sizeof(struct ifreq);
	printf("interface num is interface = %d\n", if_num);
	while(if_num-- > 0)
	{
		printf("net device: %s\n", buf[if_num].ifr_name);	
		/* 获取第n个网口信息 */
		ret = ioctl(fd, SIOCGIFFLAGS, (char*)&buf[if_num]);
		if(ret)
			continue;

		/* 获取网口状态 */
		port_status(buf[if_num].ifr_flags);
		
		/* 获取当前网卡的ip地址 */
		ret = ioctl(fd, SIOCGIFADDR, (char*)&buf[if_num]);
		if(ret)
			continue;
		printf("IP address is: \n%s\n", inet_ntoa(((struct sockaddr_in *)(&buf[if_num].ifr_addr))->sin_addr));

		/* 获取当前网卡的mac */
		ret = ioctl(fd, SIOCGIFHWADDR, (char*)&buf[if_num]);
		if(ret)
			continue;

		printf("%02x:%02x:%02x:%02x:%02x:%02x\n\n",
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[0],
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[1],
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[2],
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[3],
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[4],
			(unsigned char)buf[if_num].ifr_hwaddr.sa_data[5]
			);
	}
}

void port_status(unsigned int flags)
{
	if(flags & IFF_UP)	
	{
		printf("is up\n");		
	}
	if(flags & IFF_BROADCAST)	
	{
		printf("is broadcast\n");	
	}
	if(flags & IFF_LOOPBACK)	
	{
		printf("is loop back\n");	
	}
	if(flags & IFF_POINTOPOINT)	
	{
		printf("is point to point\n");	
	}
	if(flags & IFF_RUNNING)	
	{
		printf("is running\n");	
	}
	if(flags & IFF_PROMISC)	
	{
		printf("is promisc\n");	
	}
}

int main()
{
	int fd;

	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if(fd > 0)
	{
		get_if_info(fd);
		close(fd);
	}

	return 0;
}

运行结果：

interface num is interface = 2
net device: eth0
is up
is broadcast
is running
IP address is: 
192.168.100.200
54:be:f7:33:57:26


net device: lo
is up
is loop back
is running
IP address is: 
127.0.0.1
00:00:00:00:00:00

参考转载博客地址：

http://blog.csdn.net/dsg333/article/details/7525634

http://blog.csdn.net/kulung/article/details/6442597

http://blog.csdn.net/joker0910/article/details/7855998