Linux下获取所有可用网卡信息

在Linux下开发网络程序时，经常会遇到需要取本地网络接口名、IP、广播地址、子网掩码或者MAC地址等信息的需求，最常见的办法是配合SIOCGIFHWADDR、SIOCGIFADDR、SIOCGIFBRDADDR与SIOCGIFNETMASK作为参数调用函数ioctl分别获得MAC地址、IP地址、广播地址与子网掩码来实现。

struct ifreq

这个结构定义在include/net/if.h，用来配置ip地址，激活接口，配置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)

struct ifconf

通常是用来保存所有接口信息的

/* 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 */

完整代码如下：

/*============================================================================
Name        : Exercise.cbp
Author      : Haier
Version     : 1.01
Copyright   : Copyright (c) 2014
Description : File Encryption in C, Ansi-style, Compile by Code::Block
============================================================================*/
#include <stdio.h>
#include <string.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <errno.h>

int getLocalInfo(void)
{
int fd;
int interfaceNum = 0;
struct ifreq buf[16];
struct ifconf ifc;
struct ifreq ifrcopy;
char mac[16] = {0};
char ip[32] = {0};
char broadAddr[32] = {0};
char subnetMask[32] = {0};

if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket");
close(fd);
return -1;
}

ifc.ifc_len = sizeof(buf);
ifc.ifc_buf = (caddr_t)buf;
if (!ioctl(fd, SIOCGIFCONF, (char *)&ifc))
{
interfaceNum = ifc.ifc_len / sizeof(struct ifreq);
printf("interface num = %d\n", interfaceNum);
while (interfaceNum-- > 0)
{
printf("\ndevice name: %s\n", buf[interfaceNum].ifr_name);

//ignore the interface that not up or not runing
ifrcopy = buf[interfaceNum];
if (ioctl(fd, SIOCGIFFLAGS, &ifrcopy))
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}

//get the mac of this interface
if (!ioctl(fd, SIOCGIFHWADDR, (char *)(&buf[interfaceNum])))
{
memset(mac, 0, sizeof(mac));
snprintf(mac, sizeof(mac), "%02x%02x%02x%02x%02x%02x",
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[0],
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[1],
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[2],
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[3],
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[4],
(unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[5]);
printf("device mac: %s\n", mac);
}
else
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}

//get the IP of this interface
if (!ioctl(fd, SIOCGIFADDR, (char *)&buf[interfaceNum]))
{
snprintf(ip, sizeof(ip), "%s",
(char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_addr))->sin_addr));
printf("device ip: %s\n", ip);
}
else
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}

//get the broad address of this interface
if (!ioctl(fd, SIOCGIFBRDADDR, &buf[interfaceNum]))
{
snprintf(broadAddr, sizeof(broadAddr), "%s",
(char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_broadaddr))->sin_addr));
printf("device broadAddr: %s\n", broadAddr);
}
else
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}

//get the subnet mask of this interface
if (!ioctl(fd, SIOCGIFNETMASK, &buf[interfaceNum]))
{
snprintf(subnetMask, sizeof(subnetMask), "%s",
(char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_netmask))->sin_addr));
printf("device subnetMask: %s\n", subnetMask);
}
else
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}
}
}
else
{
printf("ioctl: %s [%s:%d]\n", strerror(errno), __FILE__, __LINE__);
close(fd);
return -1;
}

close(fd);

return 0;
}

int main(void)
{
getLocalInfo();

return 0;
}

使用ioctl函数虽然可以获取所有的信息，但是使用起来比较麻烦，如果不需要获取MAC地址，那么使用getifaddrs函数来获取更加方便与简洁。值得一提的是，在MacOS或iOS系统上（如iPhone程序开发），上述iotcl函数没法获得mac地址跟子网掩码，这个使用，使用getifaddrs函数便更有优势了。下面是使用getiaddrs函数获取网卡信息的C语言代码实现。

/*============================================================================
Name        : Exercise.cbp
Author      : Haier
Version     : 1.01
Copyright   : Copyright (c) 2014
Description : File Encryption in C, Ansi-style, Compile by Code::Block
============================================================================*/
#include <stdio.h>
#include <ifaddrs.h>
#include <arpa/inet.h>

int getSubnetMask()
{
struct sockaddr_in *sin = NULL;
struct ifaddrs *ifa = NULL, *ifList;

if (getifaddrs(&ifList) < 0) return -1;

for (ifa = ifList; ifa != NULL; ifa = ifa->ifa_next)
{
if(ifa->ifa_addr->sa_family == AF_INET)
{
printf("\n>>> interfaceName: %s\n", ifa->ifa_name);

sin = (struct sockaddr_in *)ifa->ifa_addr;
printf(">>> ipAddress: %s\n", inet_ntoa(sin->sin_addr));

sin = (struct sockaddr_in *)ifa->ifa_dstaddr;
printf(">>> broadcast: %s\n", inet_ntoa(sin->sin_addr));

sin = (struct sockaddr_in *)ifa->ifa_netmask;
printf(">>> subnetMask: %s\n", inet_ntoa(sin->sin_addr));
}
}

freeifaddrs(ifList);

return 0;
}

int main(void)
{
getSubnetMask();

return 0;
}