Socket::Ifaddr#ifindex

static VALUE
ifaddr_ifindex(VALUE self)
{
    struct ifaddrs *ifa = get_ifaddrs(self);
    unsigned int ifindex = if_nametoindex(ifa->ifa_name);
    if (ifindex == 0) {
        rb_raise(rb_eArgError, "invalid interface name: %s", ifa->ifa_name);
    }
    return UINT2NUM(ifindex);
}