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使用ioctl的SIOCGIFCONF可以读取所有网卡信息。ioctl调用后返回指向ifconf的结构链表，其中包含了指向ifreq的结构指针。ifconf及ifreq定义在net/if.h中。

《UNIX网络编程》中提供了get_ifi_info函数的实现方法，使用这种方式来获取网络信息。在LINUX下，这种方式不能获得IPV6的网卡信息。《UNIX网络编程》中有如下描述：

在支持IPV6的系统中，没有关于对SIOCGIFCONF请求是否返回IPV6地址的标准。我们给支持IPV6的新系统增加了一个case语句， 这是为了预防万一。问题在于ifreq中的联合把返回的地址定义成一个通用的16字节套接口地址结构，适合16字节的IPV4 socket_in结构，但对于24字节的IPV6 socket_in6结构太小了。如果返回IPV6地址，将可能破环现有的在每个ifreq结构中采用固定大小的套接口地址结构的代码。

经测试，在fedor6-2.6.18kernel中无法返回ipv6地址，事实上，返回的地址簇总是AF_INET,而并非AF_INET6。


这种方法的实现代码如下：





net_if.h

#ifndef __NET_INF_H
#define __NET_INF_H

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define IFI_NAME 16
#define IFI_HADDR 8

typedef struct ifi_info
{
  char ifi_name[IFI_NAME];
  u_char ifi_haddr[IFI_HADDR];
  u_short ifi_hlen;
  short ifi_flags;
  short ifi_myflags;
  struct sockaddr *ifi_addr;
  struct sockaddr *ifi_brdaddr;
  struct sockaddr *ifi_dstaddr;
  struct ifi_info *ifi_next;
}ifi_info;

#define IFI_ALIAS 1

struct ifi_info *get_ifi_info(int, int);

void free_ifi_info(struct ifi_info *);

#endif

net_if.c

#include "net_if.h"

ifi_info *get_ifi_info(int family, int doaliases)
{
  ifi_info *ifi, *ifihead, **ifipnext;
  int sockfd, len, lastlen, flags, myflags;
  char *ptr, *buf, lastname[IFNAMSIZ], *cptr;
  struct ifconf ifc;
  struct ifreq *ifr, ifrcopy;
  struct sockaddr_in *sinptr;

  if ((sockfd=socket(family, SOCK_DGRAM, 0))<0)
  {
    printf("socket error.\n");
    exit(1);
  }

  lastlen = 0;

  len = 10*sizeof(struct ifreq);
  while (1)
  {
    buf = (char*)malloc(len);
    ifc.ifc_len = len;
    ifc.ifc_buf = buf;
    if (ioctl(sockfd, SIOCGIFCONF, &ifc)<0)
    {
      if (errno!=EINVAL||lastlen!=0)
      {
        printf("ioctl error.\n");
      }
    }
    else
    {
      if (ifc.ifc_len == lastlen)
        break;
      lastlen = ifc.ifc_len;
    }
    len += 10*sizeof(struct ifreq);
    free(buf);
  }

  ifihead = NULL;
  ifipnext = &ifihead;
  lastname[0] = 0;

  for (ptr = buf; ptrifr->ifr_addr.sa_len?sizeof(struct sockaddr):ifr->ifr_addr.sa_len;
#else
    switch (ifr->ifr_addr.sa_family)
    {
#ifdef IPV6
    case AF_INET6:
      len = sizeof(struct sockaddr_in6);
      break;
#endif
    case AF_INET:
    default:
      len = sizeof(struct sockaddr);
      break;
    }
#endif

    ptr += sizeof(ifr->ifr_name) + len;

    if (ifr->ifr_addr.sa_family != family)
      continue;

    myflags = 0;
    if ((cptr=strchr(ifr->ifr_name, ':'))!=NULL)
      *cptr = 0;
    if (strncmp(lastname, ifr->ifr_name, IFNAMSIZ)==0)
    {
      if (doaliases == 0)
        continue;
      myflags = IFI_ALIAS;
    }

    memcpy(lastname, ifr->ifr_name, IFNAMSIZ);

    ifrcopy = *ifr;
    ioctl(sockfd, SIOCGIFFLAGS, &ifrcopy);
    flags = ifrcopy.ifr_flags;
    if ((flags&IFF_UP)==0)
      continue;
    /*
    if ((flags&IFF_BROADCAST)==0)
      continue;
    */
    ifi = calloc(1, sizeof(struct ifi_info));
    *ifipnext = ifi;
    ifipnext = &ifi->ifi_next;
    ifi->ifi_flags = flags;
    ifi->ifi_myflags = myflags;
    memcpy(ifi->ifi_name, ifr->ifr_name, IFI_NAME);
    ifi->ifi_name[IFI_NAME-1] = '\0';

    switch (ifr->ifr_addr.sa_family)
    {
    case AF_INET:
      sinptr = (struct sockaddr_in *)&ifr->ifr_addr;
      if (ifi->ifi_addr == NULL)
      {
        ifi->ifi_addr = calloc(1, sizeof(struct sockaddr_in));
        memcpy(ifi->ifi_addr, sinptr, sizeof(struct sockaddr_in));
#ifdef SIOCGIFBRDADDR
        if (flags & IFF_BROADCAST)
        {
          ioctl(sockfd, SIOCGIFBRDADDR, &ifrcopy);
          sinptr = (struct sockaddr_in *)&ifrcopy.ifr_broadaddr;
          ifi->ifi_brdaddr = calloc(1, sizeof(struct sockaddr_in));
          memcpy(ifi->ifi_brdaddr, sinptr, sizeof(struct sockaddr_in));
        }
#endif
#ifdef SIOCGIFDSTADDR
        if (flags & IFF_POINTOPOINT)
        {
          ioctl(sockfd, SIOCGIFDSTADDR, &ifrcopy);
          sinptr = (struct sockaddr_in*)&ifrcopy.ifr_dstaddr;
          ifi->ifi_dstaddr = calloc(1, sizeof(struct sockaddr_in));
          memcpy(ifi->ifi_dstaddr, sinptr, sizeof(struct sockaddr_in));
        }
#endif
      }
      break;
    default:
      break;
    }
  }
  free(buf);
  return(ifihead);
}

void free_ifi_info(ifi_info *ifihead)
{
  ifi_info *ifi, *ifinext;
  for (ifi=ifihead; ifi!=NULL; ifi=ifinext)
  {
    if (ifi->ifi_addr!=NULL)
      free(ifi->ifi_addr);

    if (ifi->ifi_brdaddr!=NULL)
      free(ifi->ifi_brdaddr);
    if (ifi->ifi_dstaddr!=NULL)
      free(ifi->ifi_dstaddr);
    ifinext = ifi->ifi_next;

    free(ifi);
  }

}

char *sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
  char portstr[7];
  static char str[128];

  switch (sa->sa_family)
  {
  case AF_INET:
    {
      struct sockaddr_in *sin = (struct sockaddr_in *)sa;

      if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str))==NULL)
        return NULL;

      if (ntohs(sin->sin_port)!=0)
      {
        snprintf(portstr, sizeof(portstr), ".%d", ntohs(sin->sin_port));
        strcat(str, portstr);
      }
      return str;
    }
    break;
  case AF_INET6:
    {
      struct sockaddr_in6 *sin = (struct sockaddr_in6 *)sa;

      if (inet_ntop(AF_INET6, &sin->sin6_addr, str, sizeof(str))==NULL)
        return NULL;

      if (ntohs(sin->sin6_port)!=0)
      {
        snprintf(portstr, sizeof(portstr), ".%d", ntohs(sin->sin6_port));
        strcat(str, portstr);
      }
      return str;
    }
    break;
  default:
    return NULL;
    break;
  }

}

int main(int argc, char *argv[])
{
  ifi_info *ifi, *ifihead;
  struct sockaddr *sa;
  u_char *ptr;
  int i, family, doaliases;
  if (argc!=3)
  {
    printf("usage: ./prifinfo  ");
    exit(1);
  }

  if (strcmp(argv[1], "inet4") == 0)
    family = AF_INET;
#ifdef IPV6
  else if (strcmp(argv[1], "inet6") == 0)
    family =AF_INET6;
#endif
  else
  {
    printf("invalid
");
    exit(1);
  }

  doaliases = atoi(argv[2]);

  for(ifihead = ifi = get_ifi_info(family, doaliases);
      ifi!=NULL;ifi=ifi->ifi_next)
  {
    printf("%s:<", ifi->ifi_name);
    if (ifi->ifi_flags&IFF_UP) printf("UP");
    if (ifi->ifi_flags&IFF_BROADCAST) printf("BCAST");
    if (ifi->ifi_flags&IFF_MULTICAST) printf("MCAST");
    if (ifi->ifi_flags&IFF_LOOPBACK) printf("LOOP");
    if (ifi->ifi_flags&IFF_POINTOPOINT) printf("P2P");
    printf(">\n");

    if ((i=ifi->ifi_hlen)>0)
    {
      ptr = ifi->ifi_haddr;
      do
      {
        printf("%s%x", (i==ifi->ifi_hlen)?" ":":", *ptr++);
      }while(--i>0);

      printf("\n");
    }

    if ((sa=ifi->ifi_addr)!=NULL)
      printf(" IP addr: %s\n",
             sock_ntop(sa, sizeof(*sa)));
    if ((sa=ifi->ifi_brdaddr)!=NULL)
      printf(" broadcast addr: %s\n",
             sock_ntop(sa, sizeof(*sa)));
    if ((sa=ifi->ifi_dstaddr)!=NULL)
      printf(" destnation addr: %s\n",
             sock_ntop(sa, sizeof(*sa)));
  }

  free_ifi_info(ifihead);

  exit(0);
}

使用gcc net_if.c -o net_if -DIPV6编译，在IPV4模式下运行输出为：

[root@localhost net_if]./net_if inet4 1


lo:


IP addr: 127.0.0.1


eth1:


IP addr: 192.168.1.2


broadcast addr: 192.168.1.255


eth0:


IP addr: 192.168.125.99


broadcast addr: 192.168.125.255

执行./net_if inet6 1在输出为空。

第二种方式是使用getifaddrs函数获取，需要包含ifaddrs.h头文件，这种方式可以获得IPV6地址，改写的《UNIX网络编程》中的get_ifi_info函数如下所示：

znet.h

#ifndef __ZNET_H__
#define __ZNET_H__

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define	IFI_NAME	16			/* same as IFNAMSIZ in  */
#define	IFI_HADDR	 8			/* allow for 64-bit EUI-64 in future */

struct ifi_info {
  char    ifi_name[IFI_NAME];	/* interface name, null-terminated */
  short   ifi_index;			/* interface index */
  short   ifi_flags;			/* IFF_xxx constants from  */
  struct sockaddr  *ifi_addr;	/* primary address */
  struct sockaddr  *ifi_brdaddr;/* broadcast address */
  struct ifi_info  *ifi_next;	/* next of these structures */
};

struct ifi_info* get_ifi_info(int, int);
void free_ifi_info(struct ifi_info *);

#endif

znet.c

#include "znet.h"

struct ifi_info* get_ifi_info(int family, int doaliases) {
	struct ifi_info		*ifi, *ifihead, **ifipnext,*p;
	struct sockaddr_in	*sinptr;
	struct sockaddr_in6	*sin6ptr;
	struct ifaddrs *ifas;
//	char addr[128];
	int sockfd;

	ifihead = NULL;
	ifipnext = &ifihead;

	if(getifaddrs(&ifas)!=0)
		return ;

	for(;ifas!=NULL;ifas=(*ifas).ifa_next) {
		if (((*ifas).ifa_addr)->sa_family != family)
			continue;	// ignore if not desired address family
/*
		printf("%s %d\n",(*ifas).ifa_name,((*ifas).ifa_addr)->sa_family);
		if(((*ifas).ifa_addr)->sa_family!=AF_INET6)
			inet_ntop(AF_INET,&(((struct sockaddr_in *)((*ifas).ifa_addr))->sin_addr),addr,sizeof(addr));
		else
			inet_ntop(AF_INET6,&(((struct sockaddr_in6 *)((*ifas).ifa_addr))->sin6_addr),addr,sizeof(addr));
		printf("%s\t",addr);
		printf("\n");
*/
		ifi = (struct ifi_info*)calloc(1,sizeof(struct ifi_info));
		*ifipnext = ifi;
		ifipnext = &ifi->ifi_next;	

		ifi->ifi_flags = (*ifas).ifa_flags;
		memcpy(ifi->ifi_name, (*ifas).ifa_name, IFI_NAME);
		ifi->ifi_name[IFI_NAME-1] = '\0';

		switch (((*ifas).ifa_addr)->sa_family) {
			case AF_INET:
				sinptr = (struct sockaddr_in *) (*ifas).ifa_addr;
				ifi->ifi_addr = (struct sockaddr*)calloc(1, sizeof(struct sockaddr_in));
				memcpy(ifi->ifi_addr, sinptr, sizeof(struct sockaddr_in));
#ifdef	SIOCGIFBRDADDR
				if (ifi->ifi_flags & IFF_BROADCAST) {
					sinptr = (struct sockaddr_in *) (*ifas).ifa_broadaddr;
					ifi->ifi_brdaddr = (struct sockaddr*)calloc(1, sizeof(struct sockaddr_in));
					memcpy(ifi->ifi_brdaddr, sinptr, sizeof(struct sockaddr_in));
				}
#endif
				break; 

			case AF_INET6:
				sin6ptr = (struct sockaddr_in6 *) (*ifas).ifa_addr;
				ifi->ifi_addr = (struct sockaddr*)calloc(1, sizeof(struct sockaddr_in6));
				memcpy(ifi->ifi_addr, sin6ptr, sizeof(struct sockaddr_in6));
				break; 

			default:
				break;
		}
	}
	freeifaddrs(ifas);	

	return(ifihead);
}

int main(int argc, char *argv[]) {
	int family;
	if (argc!=2) {
	    printf("usage: ./znet \n");
	    exit(1);
	}
	if (strcmp(argv[1], "inet4") == 0)
		family = AF_INET;
	else if (strcmp(argv[1], "inet6") == 0)
		family =AF_INET6;
	else {
    printf("invalid
\n");
    exit(1);
    	}

	char addr[128];
	struct ifi_info	*ifi, *ifihead;
	printf("name\tflag\tIP\t\tbroadcastaddr\n");
	for (ifihead = ifi = get_ifi_info(family,1); ifi != NULL; ifi = ifi->ifi_next) {

		printf("%s\t",ifi->ifi_name);
		printf("%d\t",ifi->ifi_flags);
		if((ifi->ifi_addr)->sa_family!=AF_INET6)
			inet_ntop(AF_INET,&(((struct sockaddr_in *)(ifi->ifi_addr))->sin_addr),addr,sizeof(addr));
		else
			inet_ntop(AF_INET6,&(((struct sockaddr_in6 *)(ifi->ifi_addr))->sin6_addr),addr,sizeof(addr));
		printf("%s\t",addr);
#ifdef	SIOCGIFBRDADDR
		if ((ifi->ifi_flags & IFF_BROADCAST) && (ifi->ifi_addr)->sa_family!=AF_INET6) {
			inet_ntop(AF_INET,&(((struct sockaddr_in *) (ifi->ifi_brdaddr))->sin_addr),addr,sizeof(addr));
			printf("%s\t",addr);
		}
#endif
		printf("\n+++++++++++++++++++++++++++++++++++++++++++\n");
	}
	return 0;
}

这段代码输出如下：

[root@localhost net_if]./znet inet4


name flag IP broadcastaddr


lo 73 127.0.0.1


++++++++++++++++++++++++++++++


eth1 4099 192.168.1.2 192.168.1.255


++++++++++++++++++++++++++++++


eth0 4163 192.168.125.99 192.168.125.255


++++++++++++++++++++++++++++++


[root@localhost net_if]./znet inet6


name flag IP broadcastaddr


lo 73 ::1


++++++++++++++++++++++++++++++


eth1 4163 2001:250:1800:1::1


++++++++++++++++++++++++++++++


eth0 4163 2001:250:1888:1::1