获取网络接口信息——ioctl()函数与结构体struct ifreq、 struct ifconf

转载请注明出处：windeal专栏

Linux 下 可以使用ioctl()函数 以及 结构体 struct ifreq  结构体struct ifconf来获取网络接口的各种信息。

ioctl

首先看ioctl()用法

ioctl()原型如下：

       #include <sys/ioctl.h>
       int ioctl(int fd, int request, ...);

参数：

    fd     ： 文件描述符

request：  表示要请求的信息。如IP地址、网络掩码等

     ...     ：  后面的可变参数根据request而定

比如我们请求所有网络接口的清单：

struct ifconf IoCtlReq;
...
ioctl( Sock, SIOCGIFCONF, &IoCtlReq )

其中IoCtlReq 是一个

与接口相关的request如下表所示（来源： <http://baike.baidu.com/view/1081282.htm?fr=aladdin>）：

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

关于ioctl的详细解释清查阅本博其它博文

struct ifreq

结构体 struct ifreq用来保存某个接口的信息。

// if.h
/*
 * 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
	union
	{
		char	ifrn_name[IFNAMSIZ];		/* if 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	ifru_flags;
		int	ifru_ivalue;
		int	ifru_mtu;
		struct  ifmap ifru_map;
		char	ifru_slave[IFNAMSIZ];	/* Just fits the size */
		char	ifru_newname[IFNAMSIZ];
		void __user *	ifru_data;
		struct	if_settings ifru_settings;
	} 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 ifr_settings	ifr_ifru.ifru_settings	/* Device/proto settings*/

ifr_name 标识了某一接口。

可以通过ioctl获取该接口的信息。如：

ioctl(Sock, SIOCGIFNETMASK, &IfReq);//获取网络接口地址掩码

该代码需要先对IfReq->ifr_name赋值，然后获取与IfReq->ifr_name向匹配的网络接口 的地址掩码

struct ifconf

结构体struct ifconf通常用来保存所有接口信息

// if.h
/*
 * 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 {
		char __user *ifcu_buf;
		struct ifreq __user *ifcu_req;
	} ifc_ifcu;
};
#define	ifc_buf	ifc_ifcu.ifcu_buf		/* buffer address	*/
#define	ifc_req	ifc_ifcu.ifcu_req		/* array of structures	*/

该结构体可以用来获取所哟网络接口的名字和信息（不是全部信息，是ip地址）

（图片来自：http://tech.sunplusedu.com/space/post-4064.aspx）

Example：

#include <sys/types.h>  
#include <sys/ioctl.h>  
#include <sys/socket.h>  
#include <net/if.h>  
#include <stdio.h>  
#include <stdlib.h>  
#include <unistd.h>  
#include <netdb.h>  
#include <string.h>  
#include <fcntl.h>  
#include <string.h>  
#include <errno.h>
typedef uint32_t uint32; 
#define MAX_IF 10
int 
main()
{
	struct ifreq ifVec[MAX_IF];//用来保存所有接口
	
	int sock = -1;
	if ( (sock = socket( AF_INET, SOCK_DGRAM, 0 )) < 0 )
		fprintf(stderr, "Error:%d, cannot open RAM;
");
	
	// get if vector
 	struct ifconf ioIfConf;
    	ioIfConf.ifc_buf = (void *)ifVec;
       	ioIfConf.ifc_len = sizeof(ifVec);
	 printf("Len:%d
", ioIfConf.ifc_len);     
		
	if (ioctl(sock, SIOCGIFCONF, &ioIfConf) < 0 )//获取所有网络接口信息
		fprintf(stderr, "Error:%d   ioctl IFCONF
");
	
	 printf("Len:%d
", ioIfConf.ifc_len);// 和前面到len对比，发现ioctl修改里len到大小     
	//循环打印每个网络接口到信息
	{
		struct ifreq *ifPt;
		struct ifreq *ifEndPt;
		ifPt = ifVec;
		ifEndPt = (void *)((char *)ifVec + ioIfConf.ifc_len);
		for (ifPt = ifVec; ifPt < ifEndPt; ifPt++)
		{
			struct ifreq ifReq;
			if ( ifPt->ifr_addr.sa_family != AF_INET ) {
                		continue;
            		}
			
			// Temp keepers of interface params...
			uint32 u32_addr, u32_mask;
			
			/*	打印ip地址	*/
			char ipDotBuf[16], subnetDotBuf[16], maskDotBuf[16]; // 保存点分十进制到ip地址
			u32_addr = ((struct sockaddr_in *)&ifPt->ifr_addr)->sin_addr.s_addr;
			inet_ntop(AF_INET, &u32_addr, ipDotBuf, (socklen_t )sizeof(ipDotBuf)); 
			printf("IP Address: %s
", ipDotBuf);
			
			/*    打印地址掩码    */
			bzero(&ifReq,sizeof(struct ifreq));  
			memcpy(ifReq.ifr_name, ifPt->ifr_name, sizeof(ifReq.ifr_name));  
			if (ioctl(sock, SIOCGIFNETMASK, &ifReq ) < 0){
				fprintf(stderr, "Error: %d, cannot get mask
", errno);
			}
			else{
				u32_mask = ((struct sockaddr_in *)&ifReq.ifr_addr)->sin_addr.s_addr;
				inet_ntop(AF_INET, &u32_mask, maskDotBuf, (socklen_t )sizeof(maskDotBuf));
				printf("Mask: %s
", maskDotBuf);
			}	
			/*    打印MTU    */
			bzero(&ifReq,sizeof(struct ifreq));  
			memcpy(ifReq.ifr_name, ifPt->ifr_name, sizeof(ifReq.ifr_name));  
			if (ioctl(sock, SIOCGIFMTU, &ifReq ) < 0){
				fprintf(stderr, "Error: %d, cannot get MTU
", errno);
			}
			else{
				printf("SIOCGIFMTU:%d
", ifReq.ifr_mtu); 
			}
	           /*    其他信息的打印方式与掩码和MTU相同    */
		}
	}
	
	
	
}

运行结果：

windeal@ubuntu:~/Windeal/apue$ ./exe 
Len:320
Len:64
IP Address: 127.0.0.1
Mask: 255.0.0.0
SIOCGIFMTU:16436
IP Address: 172.17.92.198
Mask: 255.255.254.0
SIOCGIFMTU:1500
windeal@ubuntu:~/Windeal/apue$