tcpKeepAlive, err := syscall.GetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_KEEPALIVE)
	if err != nil {
		return
	}
	tcpKeepAliveIdle, err := syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPIDLE)
	if err != nil {
		return
	}
	tcpKeepAliveInterval, err := syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPINTVL)
	if err != nil {
		return
	}

	tcpKeepAlive, err := syscall.GetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_KEEPALIVE)
	if err != nil {
		return
	}
	tcpKeepAliveIdle, err := syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPIDLE)
	if err != nil {
		return
	}
	tcpKeepAliveInterval, err := syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPINTVL)
	if err != nil {
		return
	}

		tcpKeepAliveCount        int
	)
	if unix.SupportTCPKeepAliveIdleIntvlCNT() {
		tcpKeepAliveIdle, err = syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPIDLE)
		if err != nil {
			return
		}
		tcpKeepAliveIdleTime = time.Duration(tcpKeepAliveIdle) * time.Second

		tcpKeepAliveInterval, err = syscall.GetsockoptInt(fd, syscall.IPPROTO_TCP, syscall_TCP_KEEPINTVL)
		if err != nil {
			return
		}

//go:build unix || windows

package poll

import "syscall"

// SetsockoptInt wraps the setsockopt network call with an int argument.
func (fd *FD) SetsockoptInt(level, name, arg int) error {
	if err := fd.incref(); err != nil {
		return err
	}
	defer fd.decref()
	return syscall.SetsockoptInt(fd.Sysfd, level, name, arg)
}

// SetsockoptInet4Addr wraps the setsockopt network call with an IPv4 address.

	connectFunc       func(int, syscall.Sockaddr) error = syscall.Connect
	listenFunc        func(int, int) error              = syscall.Listen
	getsockoptIntFunc func(int, int, int) (int, error)  = syscall.GetsockoptInt

	sw.stats.getLocked(nso.Cookie).Accepted++
	return ns, sa, nil
}

// GetsockoptInt wraps syscall.GetsockoptInt.
func (sw *Switch) GetsockoptInt(s, level, opt int) (soerr int, err error) {
	so := sw.sockso(s)
	if so == nil {
		return syscall.GetsockoptInt(s, level, opt)
	}
	sw.fmu.RLock()
	f := sw.fltab[FilterGetsockoptInt]
	sw.fmu.RUnlock()

	af, err := f.apply(so)

The [GetsockoptInt] function is now supported on Windows....

	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 nil
}

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

//
// 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
}