h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
	h.Level = SOL_IP
	h.Type = IP_PKTINFO
	h.SetLen(CmsgLen(SizeofInet4Pktinfo))
	*(*Inet4Pktinfo)(h.data(0)) = *info
	return b
}

// PktInfo6 encodes Inet6Pktinfo into a socket control message of type IPV6_PKTINFO.
func PktInfo6(info *Inet6Pktinfo) []byte {
	b := make([]byte, CmsgSpace(SizeofInet6Pktinfo))
	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
	h.Level = SOL_IPV6

}

type IPv6Mreq struct {
	Multiaddr [16]byte /* in6_addr */
	Interface uint32
}

type Msghdr struct {
	Name       *byte
	Iov        *Iovec
	Control    *byte
	Flags      int32
	Namelen    int32
	Iovlen     int32
	Controllen int32
}

type Cmsghdr struct {
	Len   int32
	Level int32
	Type  int32
}

type Inet4Pktinfo struct {
	Addr    [4]byte /* in_addr */

	req := &nl.NetlinkRequest{
		// netlink message header
		// (definition: https://github.com/torvalds/linux/blob/v6.7/include/uapi/linux/netlink.h#L44-L58)
		NlMsghdr: unix.NlMsghdr{
			Len:   uint32(unix.SizeofNlMsghdr),
			Type:  uint16(cmd | (unix.NFNL_SUBSYS_ACCT << 8)),
			Flags: flags,
		},
		Sockets: map[int]*nl.SocketHandle{
			unix.NETLINK_NETFILTER: {Socket: n.socket},
		},