if c.fd.isConnected && addr != nil {
		return 0, 0, ErrWriteToConnected
	}
	if !c.fd.isConnected && addr == nil {
		return 0, 0, errMissingAddress
	}
	sa, err := addr.sockaddr(c.fd.family)
	if err != nil {
		return 0, 0, err
	}
	return c.fd.writeMsg(b, oob, sa)
}

func (c *UDPConn) writeMsgAddrPort(b, oob []byte, addr netip.AddrPort) (n, oobn int, err error) {
	if c.fd.isConnected && addr.IsValid() {

// Implemented in assembly to avoid allocation.
func seek(fd int, offset int64, whence int) (newoffset int64, err Errno)

func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
	newoffset, errno := seek(fd, offset, whence)
	if errno != 0 {
		return 0, errno
	}
	return newoffset, nil
}

//sys	accept4(s int, rsa *RawSockaddrAny, addrlen *_Socklen, flags int) (fd int, err error)

}

func (fd *netFD) netFD() (*netFD, error) {
	return newFD(fd.net, fd.n, fd.listen, fd.ctl, fd.data, fd.laddr, fd.raddr)
}

func (fd *netFD) acceptPlan9() (nfd *netFD, err error) {
	defer func() { fixErr(err) }()
	if err := fd.pfd.ReadLock(); err != nil {
		return nil, err
	}
	defer fd.pfd.ReadUnlock()
	listen, err := os.Open(fd.dir + "/listen")
	if err != nil {
		return nil, err

var fcntl64Syscall uintptr = SYS_FCNTL

func fcntl(fd int, cmd, arg int) (int, error) {
	valptr, _, errno := Syscall(fcntl64Syscall, uintptr(fd), uintptr(cmd), uintptr(arg))
	var err error
	if errno != 0 {
		err = errno
	}
	return int(valptr), err
}

// FcntlInt performs a fcntl syscall on fd with the provided command and argument.
func FcntlInt(fd uintptr, cmd, arg int) (int, error) {
	return fcntl(int(fd), cmd, arg)

import (
	"os"
	"runtime"
	"syscall"
)

func setIPv4MulticastInterface(fd *netFD, ifi *Interface) error {
	ip, err := interfaceToIPv4Addr(ifi)
	if err != nil {
		return os.NewSyscallError("setsockopt", err)
	}
	var a [4]byte
	copy(a[:], ip.To4())
	err = fd.pfd.SetsockoptInet4Addr(syscall.IPPROTO_IP, syscall.IP_MULTICAST_IF, a)
	runtime.KeepAlive(fd)
	return wrapSyscallError("setsockopt", err)
}

type fakeNs struct {
	closed *atomic.Bool
	fd     uintptr
	inode  uint64
}

func newFakeNs(fd uintptr) *fakeNs {
	// the fake inode is the fd! magic.
	return &fakeNs{closed: &atomic.Bool{}, fd: fd, inode: uint64(fd)}
}

func newFakeNsInode(fd uintptr, inode uint64) *fakeNs {
	return &fakeNs{closed: &atomic.Bool{}, fd: fd, inode: inode}
}

// Fd returns the file descriptor
func (f *fakeNs) Fd() uintptr {

//sys	Fchown(fd int, uid int, gid int) (err error)
//sys	Fstat(fd int, stat *Stat_t) (err error)
//sys	fstatat(dirfd int, path string, stat *Stat_t, flags int) (err error)

func Fstatat(fd int, path string, stat *Stat_t, flags int) error {
	return fstatat(fd, path, stat, flags)
}

//sys	Fstatfs(fd int, buf *Statfs_t) (err error)
//sys	Ftruncate(fd int, length int64) (err error)

// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT

func Dup(oldfd int, newfd int) (fd int, err error) {
	r0, _, e1 := Syscall(SYS_DUP, uintptr(oldfd), uintptr(newfd), 0)
	fd = int(r0)
	if int32(r0) == -1 {
		err = e1
	}
	return
}

// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT

func Pread(fd int, p []byte, offset int64) (n int, err error) {
	var _p0 unsafe.Pointer
	if len(p) > 0 {

	return nil
}

func setReadBuffer(fd *netFD, bytes int) error {
	if fd.fakeNetFD != nil {
		return fd.fakeNetFD.setReadBuffer(bytes)
	}
	return syscall.ENOPROTOOPT
}

func setWriteBuffer(fd *netFD, bytes int) error {
	if fd.fakeNetFD != nil {
		return fd.fakeNetFD.setWriteBuffer(bytes)
	}
	return syscall.ENOPROTOOPT
}

func setKeepAlive(fd *netFD, keepalive bool) error {
	return syscall.ENOPROTOOPT

		// reissued the fd in a later call to open(2), leading
		// to crashes being written to the wrong file.
		//
		// So, we duplicate the fd to obtain a private one
		// that cannot be closed by the user.
		// This also alleviates us from concerns about the
		// lifetime and finalization of f.
		// (DupCloseOnExec returns an fd, not a *File, so
		// there is no finalizer, and we are responsible for