Linux下C语言获取IPv6地址和前缀

在Linux系统中需要编程获取某个接口的IPv4地址比较常见, 可以使用ioctl函数等方法, 但是要获取IPv6地址, 以前的一些方法就不一定适合, 
从网上查找了很多方法, 有两种我试过都可以得到相应的IPv6地址, 
此处直接以一段代码做示例展示如何获取指定接口的(IPv6)本地链路地址(注意, 前提是你的Linux支持IPv6, 目前流行的大多数Linux系统早已支持IPv6).
#include <stdio.h>
#include <string.h>
#include <error.h>
#include <stdlib.h>

#define DEBUG
//#define UNSUPPORT_IFADDRS

/* struct in6_addr */
#include <netinet/in.h>
/* getifaddrs, freeifaddrs */
#include <sys/types.h>
#ifndef UNSUPPORT_IFADDRS
#include <ifaddrs.h>
#endif
/* inet_ntop, inet_pton */
#include <arpa/inet.h>

#if defined(DEBUG)
#define DG(a, b...) printf("[%s][%s][%d]"a, __FILE__, __func__, __LINE__, ##b)
#else
#define DG(a, b...)
#endif

#define ER(a, b...) printf("[%s][%s][%d]"a, __FILE__, __func__, __LINE__, ##b)

#ifndef UNSUPPORT_IFADDRS
/**
 * Whlie head file  is not existed in you include directory, just define
 * macro UNSUPPORT_IFADDRS to disable this function.
 * Because of function getifaddrs() and freeifaddrs() are declared in this head file,
 * the function can't pass compiling process if lack  in your system.
 */
int get_linklocal_ipv6addr(struct in6_addr *addr6, char *iface)
{
    struct ifaddrs *ifa, *p;
    int family;
    char address[200];
    
    if (!addr6 || !iface) {
        ER("addr6 and iface can't be NULL!\n");
        return -1;
    }
    
    if (getifaddrs(&ifa)) {
        ER("");
        perror("getifaddrs error");
        return -1;
    }
    
    for (p = ifa; p != NULL; p = p->ifa_next) {
        DG("ifa_name = %s, family = 0x%X(%s)\n", p->ifa_name, family,
           (family == AF_PACKET) ? "AF_PACKET" :
                                   (family == AF_INET) ?   "AF_INET" :
                                                           (family == AF_INET6) ?  "AF_INET6" : "");
        
        family = p->ifa_addr->sa_family;
        /* Just check IPv6 address */
        if (family != AF_INET6)
            continue;
        
        *addr6 = ((struct sockaddr_in6 *)(p->ifa_addr))->sin6_addr;
        /* Just get IPv6 linklocal address of the interface */
        if (!strcmp(iface, p->ifa_name) && IN6_IS_ADDR_LINKLOCAL(addr6)) {
            if (inet_ntop(AF_INET6, addr6, address, sizeof(address))) {
                DG("find out %s's linklocal IPv6 address: %s\n", iface, address);
            }
            break;
        }
    }
    
    freeifaddrs(ifa);
    return 0;
}
#else
/**
 * If head file  is not existed in your system, you could get information of IPv6 address
 * in file /proc/net/if_inet6.
 *
 * Contents of file "/proc/net/if_inet6" like as below:
 * 00000000000000000000000000000001 01 80 10 80       lo
 * fe8000000000000032469afffe08aa0f 08 40 20 80     ath0
 * fe8000000000000032469afffe08aa0f 07 40 20 80    wifi0
 * fe8000000000000032469afffe08aa0f 05 40 20 80     eth1
 * fe8000000000000032469afffe08aa0f 03 40 20 80      br0
 * fe8000000000000032469afffe08aa10 04 40 20 80     eth0
 *
 * +------------------------------+ ++ ++ ++ ++    +---+
 * |                                |  |  |  |     |
 * 1                                2  3  4  5     6
 *
 * There are 6 row items parameters:
 * 1 => IPv6 address without ':'
 * 2 => Interface index
 * 3 => Length of prefix
 * 4 => Scope value (see kernel source "include/net/ipv6.h" and "net/ipv6/addrconf.c")
 * 5 => Interface flags (see kernel source "include/linux/rtnetlink.h" and "net/ipv6/addrconf.c" "linux/include/if_addr.h")
 * 6 => Device name
 *
 * Note that all values of row 1~5 are hexadecimal string
 */


int get_linklocal_ipv6addr(struct in6_addr *addr6, char *iface)
{
#define IF_INET6 "/proc/net/if_inet6"
    char str[128], address[64];
    char *addr, *index, *prefix, *scope, *flags, *name;
    char *delim = " \t\n", *p, *q;
    FILE *fp;
    int count;
    
    if (!addr6 || !iface) {
        ER("addr6 and iface can't be NULL!\n");
        return -1;
    }
    
    if (NULL == (fp = fopen(IF_INET6, "r"))) {
        ER("");
        perror("fopen error");
        return -1;
    }
    
#define IPV6_ADDR_LINKLOCAL 0x0020U
    while (fgets(str, sizeof(str), fp)) {
        DG("str:%s", str);
        addr = strtok(str, delim);
        index = strtok(NULL, delim);
        prefix = strtok(NULL, delim);
        scope = strtok(NULL, delim);
        flags = strtok(NULL, delim);
        name = strtok(NULL, delim);
        DG("addr:%s, index:0x%s, prefix:0x%s, scope:0x%s, flags:0x%s, name:%s\n",
           addr, index, prefix, scope, flags, name);
        
        if (strcmp(name, iface))
            continue;
        
        /* Just get IPv6 linklocal address */
        if (IPV6_ADDR_LINKLOCAL != (unsigned int)strtoul(scope, NULL, 16))
            continue;
        
        memset(address, 0x00, sizeof(address));
        p = addr;
        q = address;
        count = 0;
        while (*p != '') {
            if (count == 4) {
                *q++ = ':';
                count = 0;
            }
            *q++ = *p++;
            count++;
        }
        DG("find out %s's linklocal IPv6 address: %s\n", iface, address);
        
        inet_pton(AF_INET6, address, addr6);
        break;
    }
#undef IPV6_ADDR_LINKLOCAL
    
    fclose(fp);
    return 0;
}
#endif

int main (int argc, char *argv[])
{
    struct in6_addr addr6;
    char *ifname = "eth0";
    char address[64];
    
    if (get_linklocal_ipv6addr(&addr6, ifname)) {
        printf("\nGet IPv6 linklocal address of %s failed :(\n", ifname);
        return -1;
    }
    if (inet_ntop(AF_INET6, &addr6, address, sizeof(address)))
        printf("\nIPv6 linklocal address of %s is %s :)\n", ifname, address);
    
    return 0;
}

 

注意：

关于Interface flags

/* ifa_flags */
#define IFA_F_SECONDARY  0x01
#define IFA_F_TEMPORARY  IFA_F_SECONDARY

#define IFA_F_NODAD  0x02
#define IFA_F_OPTIMISTIC 0x04
#define IFA_F_HOMEADDRESS 0x10
#define IFA_F_DEPRECATED 0x20
#define IFA_F_TENTATIVE  0x40
#define IFA_F_PERMANENT  0x80

一般请情况下flag的值应为0x80,如果为其他值应该怀疑interface在init的时候是否有起来

bug record:

flag=0xc0, init 不对，导致这个interface sendmsg 出错（22）

 

转自：http://yangxy84.blog.163.com/blog/static/708443020119171265179/