ifr_index
if (ioctl(sock, SIOCGIFPAIR, &ifrdesc) == 0 && ifrdesc.ifr_index != 0 &&
if_indextoname(ifrdesc.ifr_index, pifname) != NULL)
if ((ifr.ifr_index = if_nametoindex(val)) == 0) {
ifr.ifr_index = 0;
if (sc->sc_pairedif == ifr->ifr_index)
if (ifr->ifr_index == ifp->if_index) {
newifp = if_get(ifr->ifr_index);
sc->sc_pairedif = ifr->ifr_index;
ifr->ifr_index = sc->sc_pairedif;