//
// Kernel >= 5.16 returns EOPNOTSUPP/ENOPROTOOPT in case of fallback.
// Older kernels will always return them even if MPTCP is used: not usable.
func hasFallenBack(fd *netFD) bool {
	_, err := fd.pfd.GetsockoptInt(_SOL_MPTCP, _MPTCP_INFO)

	// 2 expected errors in case of fallback depending on the address family
	//   - AF_INET:  EOPNOTSUPP
	//   - AF_INET6: ENOPROTOOPT

	return 0, 0, 0, nil, ENOSYS
}

func SendmsgN(fd int, p, oob []byte, to Sockaddr, flags int) (n int, err error) {
	return 0, ENOSYS
}

func GetsockoptInt(fd, level, opt int) (value int, err error) {
	return 0, ENOSYS
}

func SetsockoptInt(fd, level, opt int, value int) error {
	return ENOSYS
}

func SetReadDeadline(fd int, t int64) error {
	return ENOSYS
}

	}
	return s, nil
}

func newFileFD(f *os.File) (*netFD, error) {
	s, err := dupSocket(f)
	if err != nil {
		return nil, err
	}
	family := syscall.AF_UNSPEC
	sotype, err := syscall.GetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_TYPE)
	if err != nil {
		poll.CloseFunc(s)
		return nil, os.NewSyscallError("getsockopt", err)
	}
	lsa, _ := syscall.Getsockname(s)
	rsa, _ := syscall.Getpeername(s)

	FilterListen                          // for Listen
	FilterAccept                          // for Accept, Accept4 or AcceptEx
	FilterGetsockoptInt                   // for GetsockoptInt
	FilterClose                           // for Close or Closesocket
)

// A Filter represents a socket system call filter.
//
// It will only be executed before a system call for a socket that has

	msg.Namelen = uint32(SizeofSockaddrAny)
	var iov Iovec
	if len(p) > 0 {
		iov.Base = &p[0]
		iov.SetLen(len(p))
	}
	var dummy byte
	if len(oob) > 0 {
		var sockType int
		sockType, err = GetsockoptInt(fd, SOL_SOCKET, SO_TYPE)
		if err != nil {
			return
		}
		// receive at least one normal byte
		if sockType != SOCK_DGRAM && len(p) == 0 {
			iov.Base = &dummy
			iov.SetLen(1)
		}

	var rsa RawSockaddrAny
	var len _Socklen = SizeofSockaddrAny
	if err = getpeername(fd, &rsa, &len); err != nil {
		return
	}
	return anyToSockaddr(&rsa)
}

func GetsockoptInt(fd, level, opt int) (value int, err error) {
	var n int32
	vallen := _Socklen(4)
	err = getsockopt(fd, level, opt, unsafe.Pointer(&n), &vallen)
	return int(n), err
}

}

func GetsockoptByte(fd, level, opt int) (value byte, err error) {
	var n byte
	vallen := _Socklen(1)
	err = getsockopt(fd, level, opt, unsafe.Pointer(&n), &vallen)
	return n, err
}

func GetsockoptInt(fd, level, opt int) (value int, err error) {
	var n int32
	vallen := _Socklen(4)
	err = getsockopt(fd, level, opt, unsafe.Pointer(&n), &vallen)
	return int(n), err
}

	var iov Iovec
	if len(p) > 0 {
		iov.Base = &p[0]
		iov.SetLen(len(p))
	}
	var dummy byte
	if len(oob) > 0 {
		if len(p) == 0 {
			var sockType int
			sockType, err = GetsockoptInt(fd, SOL_SOCKET, SO_TYPE)
			if err != nil {
				return
			}
			// receive at least one normal byte
			if sockType != SOCK_DGRAM {
				iov.Base = &dummy
				iov.SetLen(1)
			}
		}

	copy(sa.raw.Service_name[:], sa.ServiceName)
	sa.raw.SetServiceNameLen(len(sa.ServiceName))
	return unsafe.Pointer(&sa.raw), SizeofSockaddrNFCLLCP, nil
}

var socketProtocol = func(fd int) (int, error) {
	return GetsockoptInt(fd, SOL_SOCKET, SO_PROTOCOL)
}

func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
	switch rsa.Addr.Family {
	case AF_NETLINK:
		pp := (*RawSockaddrNetlink)(unsafe.Pointer(rsa))

func Socket(domain, typ, proto int) (fd Handle, err error) {
	if domain == AF_INET6 && SocketDisableIPv6 {
		return InvalidHandle, EAFNOSUPPORT
	}
	return socket(int32(domain), int32(typ), int32(proto))
}

func SetsockoptInt(fd Handle, level, opt int, value int) (err error) {
	v := int32(value)
	return Setsockopt(fd, int32(level), int32(opt), (*byte)(unsafe.Pointer(&v)), int32(unsafe.Sizeof(v)))
}