MT_CONTROL
m = m_getl(CMSG_SPACE(size), M_NOWAIT, MT_CONTROL, 0, NULL);
while (m && m->m_type == MT_CONTROL && error == 0) {
control = m_get(M_WAITOK, MT_CONTROL);
if (m->m_type == MT_CONTROL &&
{ MT_CONTROL, "ancillary data" },
{ MT_CONTROL, "control"},