getaddrinfo没有返回ipv6的详细信息

Question

我面临的问题是ipv6 using getaddrinfo():

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

int main()
{
        int soc = 00;
        struct addrinfo hints,*results,*res;
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_protocol = IPPROTO_TCP;
        hints.ai_flags = AI_PASSIVE;

        int m = getaddrinfo("myhost","2018",&hints,&results);
        if (m<0)
        {
                printf("getaddrinfo error :  %s\n", gai_strerror(m));
                return 1;
        }
        res=results;
        do
        {
                if(res->ai_family == AF_INET6)
                {
                        struct sockaddr_in6* a= (struct sockaddr_in6*)res->ai_addr;
                        char straddr[INET6_ADDRSTRLEN];
                        inet_ntop(AF_INET6, &a->sin6_addr, straddr, sizeof(straddr));
                        printf("IP v6 - %s\n",straddr);
                }
                if(res->ai_family == AF_INET)
                {
                        struct sockaddr_in* b= (struct sockaddr_in*)res->ai_addr;
                        const char* dotted_decimal1 = inet_ntoa(b->sin_addr);
                        printf("IP v4 - %s\n",dotted_decimal1);
                }
        }
        while((res=res->ai_next) !=NULL);

        return 0;
}

输出:

IP v4 - xx.xx.xx.xx

由于我已经设置hints.ai_family = AF_UNSPEC,它应该返回我的细节(ipv4和ipv6).但它只返回ipv4的细节.

注意:在命令中ifconfig我可以看到两者ipv4和ipv6地址.

> $ ifconfig
> eth3      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
> inet addr:x.x.x.x  Bcast:x.x.x.x  Mask:255.255.255.128
> inet6 addr: xx::xx:xx:xx:xx/64 Scope:Link

1. 可以onyone解释我为什么不选择ipv6？

2. 我是否需要在主机(Linux)上进行任何更改？

我删除了实际的ip详细信息并替换为xxxx.