网络编程学习笔记（获取所有网络接口）

主要是用ioctl函数，同时需要头文件<net/if.h>

/* net/if.h -- declarations for inquiring about network interfaces
   Copyright (C) 1997-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifndef _NET_IF_H
#define _NET_IF_H	1

#include <features.h>

#ifdef __USE_MISC
# include <sys/types.h>
# include <sys/socket.h>
#endif


/* Length of interface name.  */
#define IF_NAMESIZE	16

struct if_nameindex
  {
    unsigned int if_index;	/* 1, 2, ... */
    char *if_name;		/* null terminated name: "eth0", ... */
  };


#ifdef __USE_MISC
/* Standard interface flags. */
enum
  {
    IFF_UP = 0x1,		/* Interface is up.  */
# define IFF_UP	IFF_UP
    IFF_BROADCAST = 0x2,	/* Broadcast address valid.  */
# define IFF_BROADCAST	IFF_BROADCAST
    IFF_DEBUG = 0x4,		/* Turn on debugging.  */
# define IFF_DEBUG	IFF_DEBUG
    IFF_LOOPBACK = 0x8,		/* Is a loopback net.  */
# define IFF_LOOPBACK	IFF_LOOPBACK
    IFF_POINTOPOINT = 0x10,	/* Interface is point-to-point link.  */
# define IFF_POINTOPOINT IFF_POINTOPOINT
    IFF_NOTRAILERS = 0x20,	/* Avoid use of trailers.  */
# define IFF_NOTRAILERS	IFF_NOTRAILERS
    IFF_RUNNING = 0x40,		/* Resources allocated.  */
# define IFF_RUNNING	IFF_RUNNING
    IFF_NOARP = 0x80,		/* No address resolution protocol.  */
# define IFF_NOARP	IFF_NOARP
    IFF_PROMISC = 0x100,	/* Receive all packets.  */
# define IFF_PROMISC	IFF_PROMISC

    /* Not supported */
    IFF_ALLMULTI = 0x200,	/* Receive all multicast packets.  */
# define IFF_ALLMULTI	IFF_ALLMULTI

    IFF_MASTER = 0x400,		/* Master of a load balancer.  */
# define IFF_MASTER	IFF_MASTER
    IFF_SLAVE = 0x800,		/* Slave of a load balancer.  */
# define IFF_SLAVE	IFF_SLAVE

    IFF_MULTICAST = 0x1000,	/* Supports multicast.  */
# define IFF_MULTICAST	IFF_MULTICAST

    IFF_PORTSEL = 0x2000,	/* Can set media type.  */
# define IFF_PORTSEL	IFF_PORTSEL
    IFF_AUTOMEDIA = 0x4000,	/* Auto media select active.  */
# define IFF_AUTOMEDIA	IFF_AUTOMEDIA
    IFF_DYNAMIC = 0x8000	/* Dialup device with changing addresses.  */
# define IFF_DYNAMIC	IFF_DYNAMIC
  };

/* The ifaddr structure contains information about one address of an
   interface.  They are maintained by the different address families,
   are allocated and attached when an address is set, and are linked
   together so all addresses for an interface can be located.  */

struct ifaddr
  {
    struct sockaddr ifa_addr;	/* Address of interface.  */
    union
      {
	struct sockaddr	ifu_broadaddr;
	struct sockaddr	ifu_dstaddr;
      } ifa_ifu;
    struct iface *ifa_ifp;	/* Back-pointer to interface.  */
    struct ifaddr *ifa_next;	/* Next address for interface.  */
  };

# define ifa_broadaddr	ifa_ifu.ifu_broadaddr	/* broadcast address	*/
# define ifa_dstaddr	ifa_ifu.ifu_dstaddr	/* other end of link	*/

/* Device mapping structure. I'd just gone off and designed a
   beautiful scheme using only loadable modules with arguments for
   driver options and along come the PCMCIA people 8)

   Ah well. The get() side of this is good for WDSETUP, and it'll be
   handy for debugging things. The set side is fine for now and being
   very small might be worth keeping for clean configuration.  */

struct ifmap
  {
    unsigned long int mem_start;
    unsigned long int mem_end;
    unsigned short int base_addr;
    unsigned char irq;
    unsigned char dma;
    unsigned char port;
    /* 3 bytes spare */
  };

/* 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)


/* 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.  */

__BEGIN_DECLS

/* Convert an interface name to an index, and vice versa.  */
extern unsigned int if_nametoindex (const char *__ifname) __THROW;
extern char *if_indextoname (unsigned int __ifindex, char *__ifname) __THROW;

/* Return a list of all interfaces and their indices.  */
extern struct if_nameindex *if_nameindex (void) __THROW;

/* Free the data returned from if_nameindex.  */
extern void if_freenameindex (struct if_nameindex *__ptr) __THROW;

__END_DECLS

#endif /* net/if.h */

首先创建SOCK_DGRAM套接口，然后用ioctl的命令参数SIOCGIFCONF获取网络接口，因为设备上的网络接口上可能有多个，缓冲区可能不够，用到累加的方法 ，如果当前次获取的ifreq的长度与上一次的长度不一样，就添加10个ifreq的长度，直到与前次的长度一样，说明所有的网络接口已经获取到了。在获取到网络接口后，需要判断接口是什么 类型的，是否是回环，广播地址，多播地址，这个涉及到ioctl的命令参数SIOCGIFFLAGS。将多个网络接口用链表形式连接起来，当中用到二级指针来连接，ifihead和二级指针ifipnext，刚开始ifihead=NULL,ifipnext = &ifinext，当找到一个网络接口后，将找到的网络接口赋值给*ifipnext,而将ifipnext重新赋值给这个找到的网络接口的成员ifi_next

#include <sys/socket.h>
#include <sys/types.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>

#define IFI_NAME 16
#define IFI_HADDR 8
#define IFI_ALIAS 1


struct ifi_info
{
	char ifi_name[IFI_NAME];	
	char ifi_haddr[IFI_HADDR];
	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;
};

struct ifi_info *get_ifi_info(int,int);
struct ifi_info *Get_ifi_info(int, int);
void free_ifi_info(struct ifi_info *);
char *sock_ntop(struct sockaddr*, int);

int main(int argc, char **argv)
{
	struct ifi_info *ifi, *ifihead;
	struct sockaddr *sa;
	char *ptr;
	int i, family, doaliases;

	if (argc != 3) {
		fprintf(stderr, "usage:prifinfo <inet4|inet6> <doaliases>\n");
		return -1;
	}

	if (strcmp(argv[1], "inet4") == 0) {
		family = AF_INET;
	} else if (strcmp(argv[1], "inet6") == 0) {
		family = AF_INET6;
	}

	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(" destination addr: %s\n", sock_ntop(sa, sizeof(*sa)));	
		}

		
	}
	
	free_ifi_info(ifihead);
	return 0;
}

struct ifi_info *get_ifi_info(int family, int doaliases)
{
	struct ifi_info *ifi, *ifihead, **ifipnext;
	int sockfd, len, lastlen, flags, myflags;
	char *ptr, *buf, lastname[128], *cptr;
	struct ifconf ifc;
	struct ifreq *ifr, ifrcopy;
	struct sockaddr_in *sinptr;
	
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	if (sockfd < 0) {
		fprintf(stderr, "socket error:%s\n", strerror(errno));
		return NULL;
	}

	lastlen = 0;
	len = 100 * sizeof(struct ifreq);
	for (;;) {
		buf = malloc(len);
		ifc.ifc_len = len;
		ifc.ifc_buf = buf;
		if (ioctl(sockfd, SIOCGIFCONF, &ifc) < 0) {
			if (errno != EINVAL || lastlen != 0) {
				fprintf(stderr, "ioctl error:%s\n", strerror(errno));
				return NULL;
			}
		} 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; ptr < buf + ifc.ifc_len;) {
		ifr = (struct ifreq*)ptr;
		switch(ifr->ifr_addr.sa_family) {
		case AF_INET6:
			len = sizeof(struct sockaddr_in6);
			break;	
		case AF_INET:
		default:
			len = sizeof(struct sockaddr_in);
			break;
		}

		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;

		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));
			}
			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));	
			}
			
			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));
			}

			break;
		default:
			break;
		}
	} 

	free(buf);
	return(ifihead);
}

void free_ifi_info(struct ifi_info *ifihead)
{
	struct 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(struct sockaddr* sa, int len)
{
	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;
	}
	}

	return NULL;
}

	

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