h, dbuf, err := socketControlMessageHeaderAndData(b)
	if err != nil {
		return Cmsghdr{}, nil, nil, err
	}
	if i := cmsgAlignOf(int(h.Len)); i < len(b) {
		remainder = b[i:]
	}
	return *h, dbuf, remainder, nil
}

func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))

	var msgs []SocketControlMessage
	i := 0
	for i+CmsgLen(0) <= len(b) {
		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
		if err != nil {
			return nil, err
		}
		m := SocketControlMessage{Header: *h, Data: dbuf}
		msgs = append(msgs, m)
		i += cmsgAlignOf(int(h.Len))
	}
	return msgs, nil
}

func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))