//sys	Chroot(path string) (err error)
//sys	Close(fd int) (err error)
//sys	Dup(fd int) (nfd int, err error)
//sys	Dup2(from int, to int) (err error)
//sys	Fchdir(fd int) (err error)
//sys	Fchflags(fd int, flags int) (err error)
//sys	Fchmod(fd int, mode uint32) (err error)
//sys	Fchown(fd int, uid int, gid int) (err error)
//sys	Flock(fd int, how int) (err error)
//sys	Fpathconf(fd int, name int) (val int, err error)

//sys	Fadvise(fd int, offset int64, length int64, advice int) (err error) = SYS_FADVISE64
//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) = SYS_NEWFSTATAT
//sys	Fstatfs(fd int, buf *Statfs_t) (err error)
//sys	Ftruncate(fd int, length int64) (err error)
//sysnb	Getegid() (egid int)

//sys	Fadvise(fd int, offset int64, length int64, advice int) (err error) = SYS_FADVISE64
//sys	Fchown(fd int, uid int, gid int) (err error)
//sys	Fstat(fd int, stat *Stat_t) (err error)
//sys	Fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
//sys	Fstatfs(fd int, buf *Statfs_t) (err error)
//sys	Ftruncate(fd int, length int64) (err error)
//sysnb	Getegid() (egid int)

// (386 default is 32-bit file system and 16-bit uid).
//sys	Dup2(oldfd int, newfd int) (err error)
//sys	Fchown(fd int, uid int, gid int) (err error) = SYS_FCHOWN32
//sys	Fstat(fd int, stat *Stat_t) (err error) = SYS_FSTAT64
//sys	fstatat(dirfd int, path string, stat *Stat_t, flags int) (err error) = SYS_FSTATAT64
//sys	Ftruncate(fd int, length int64) (err error) = SYS_FTRUNCATE64
//sysnb	Getegid() (egid int) = SYS_GETEGID32

	SYS_CAP_IOCTLS_GET           = 535 // { ssize_t cap_ioctls_get(int fd, u_long *cmds, size_t maxcmds); }
	SYS_CAP_FCNTLS_LIMIT         = 536 // { int cap_fcntls_limit(int fd, uint32_t fcntlrights); }
	SYS_CAP_FCNTLS_GET           = 537 // { int cap_fcntls_get(int fd, uint32_t *fcntlrightsp); }
	SYS_BINDAT                   = 538 // { int bindat(int fd, int s, caddr_t name, int namelen); }

	SYS_CAP_IOCTLS_GET           = 535 // { ssize_t cap_ioctls_get(int fd, u_long *cmds, size_t maxcmds); }
	SYS_CAP_FCNTLS_LIMIT         = 536 // { int cap_fcntls_limit(int fd, uint32_t fcntlrights); }
	SYS_CAP_FCNTLS_GET           = 537 // { int cap_fcntls_get(int fd, uint32_t *fcntlrightsp); }
	SYS_BINDAT                   = 538 // { int bindat(int fd, int s, caddr_t name, int namelen); }

	if d == 0 {
		d = defaultTCPKeepAliveInterval
	} else if d < 0 {
		return nil
	}

	// The kernel expects seconds so round to next highest second.
	secs := int(roundDurationUp(d, time.Second))
	err := fd.pfd.SetsockoptInt(syscall.IPPROTO_TCP, syscall.TCP_KEEPINTVL, secs)
	runtime.KeepAlive(fd)
	return wrapSyscallError("setsockopt", err)
}

	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)

//sys	Fdatasync(fd int) (err error)
//sys	Fgetxattr(fd int, attr string, dest []byte) (sz int, err error)
//sys	FinitModule(fd int, params string, flags int) (err error)
//sys	Flistxattr(fd int, dest []byte) (sz int, err error)
//sys	Flock(fd int, how int) (err error)
//sys	Fremovexattr(fd int, attr string) (err error)
//sys	Fsetxattr(fd int, attr string, dest []byte, flags int) (err error)