int main(int argc, char* argv[])
{
 if(argc != 2)
 {
              fprintf(stderr, "usage: %s <ethname>", argv[0]);
     return -1;
    }
    if(getuid() != 0)
    {
        fprintf(stderr, "Netlink Status Check Need Root Power.\n");
        return 1;
    }
   
    printf("Net link status: %s\n", get_netlink_status(argv[1])==1?"up":"down");
    return 0;
}
// if_name like "ath0", "eth0". Notice: call this function
// need root privilege.
// return value:
// -1 -- error , details can check errno
// 1 -- interface link up
// 0 -- interface link down.
int get_netlink_status(const char *if_name)
{
    int skfd;
    struct ifreq ifr;
    struct ethtool_value edata;
    edata.cmd = ETHTOOL_GLINK;
    edata.data = 0;
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, if_name, sizeof(ifr.ifr_name) - 1);
    ifr.ifr_data = (char *) &edata;
    if (( skfd = socket( AF_INET, SOCK_DGRAM, 0 )) == 0)
        return -1;
    if(ioctl( skfd, SIOCETHTOOL, &ifr ) == -1)
    {
        close(skfd);
        return -1;
    }
    close(skfd);
    return edata.data;
}