hunk.code_window: type WebSocketRequest struct {
   	// Client-provided fields
   	Seq    int64                  `json:"seq"`
   	Action string                 `json:"action"`
   	Data   map[string]interface{} `json:"data"`
   	// Server-provided fields
   	Session Session              `json:"-"`
   	T       goi18n.TranslateFunc `json:"-"`
  
hunk.labels: keep keep replace replace replace keep keep keep keep
hunk.after_edit: 	Seq    int64                  `json:"seq"`    // A counter which is incremented for every request made.
   	Action string                 `json:"action"` // The action to perform for a request. For example: get_statuses, user_typing.
   	Data   map[string]interface{} `json:"data"`   // The metadata for an action.
  
hunk.file_path: model/websocket_request.go
hunk.type: replace
file: // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Linux system calls.
  // This file is compiled as ordinary Go code,
  // but it is also input to mksyscall,
  // which parses the //sys lines and generates system call stubs.
  // Note that sometimes we use a lowercase //sys name and
  // wrap it in our own nicer implementation.
  
  package unix
  
  import (
  	"encoding/binary"
  	"runtime"
  	"syscall"
  	"unsafe"
  )
  
  /*
   * Wrapped
   */
  
  func Access(path string, mode uint32) (err error) {
  	return Faccessat(AT_FDCWD, path, mode, 0)
  }
  
  func Chmod(path string, mode uint32) (err error) {
  	return Fchmodat(AT_FDCWD, path, mode, 0)
  }
  
  func Chown(path string, uid int, gid int) (err error) {
  	return Fchownat(AT_FDCWD, path, uid, gid, 0)
  }
  
  func Creat(path string, mode uint32) (fd int, err error) {
  	return Open(path, O_CREAT|O_WRONLY|O_TRUNC, mode)
  }
  
  //sys	FanotifyInit(flags uint, event_f_flags uint) (fd int, err error)
  //sys	fanotifyMark(fd int, flags uint, mask uint64, dirFd int, pathname *byte) (err error)
  
  func FanotifyMark(fd int, flags uint, mask uint64, dirFd int, pathname string) (err error) {
  	if pathname == "" {
  		return fanotifyMark(fd, flags, mask, dirFd, nil)
  	}
  	p, err := BytePtrFromString(pathname)
  	if err != nil {
  		return err
  	}
  	return fanotifyMark(fd, flags, mask, dirFd, p)
  }
  
  //sys	fchmodat(dirfd int, path string, mode uint32) (err error)
  
  func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
  	// Linux fchmodat doesn't support the flags parameter. Mimick glibc's behavior
  	// and check the flags. Otherwise the mode would be applied to the symlink
  	// destination which is not what the user expects.
  	if flags&^AT_SYMLINK_NOFOLLOW != 0 {
  		return EINVAL
  	} else if flags&AT_SYMLINK_NOFOLLOW != 0 {
  		return EOPNOTSUPP
  	}
  	return fchmodat(dirfd, path, mode)
  }
  
  //sys	ioctl(fd int, req uint, arg uintptr) (err error)
  
  // ioctl itself should not be exposed directly, but additional get/set
  // functions for specific types are permissible.
  
  // IoctlRetInt performs an ioctl operation specified by req on a device
  // associated with opened file descriptor fd, and returns a non-negative
  // integer that is returned by the ioctl syscall.
  func IoctlRetInt(fd int, req uint) (int, error) {
  	ret, _, err := Syscall(SYS_IOCTL, uintptr(fd), uintptr(req), 0)
  	if err != 0 {
  		return 0, err
  	}
  	return int(ret), nil
  }
  
  // IoctlSetPointerInt performs an ioctl operation which sets an
  // integer value on fd, using the specified request number. The ioctl
  // argument is called with a pointer to the integer value, rather than
  // passing the integer value directly.
  func IoctlSetPointerInt(fd int, req uint, value int) error {
  	v := int32(value)
  	return ioctl(fd, req, uintptr(unsafe.Pointer(&v)))
  }
  
  func IoctlSetRTCTime(fd int, value *RTCTime) error {
  	err := ioctl(fd, RTC_SET_TIME, uintptr(unsafe.Pointer(value)))
  	runtime.KeepAlive(value)
  	return err
  }
  
  func IoctlGetUint32(fd int, req uint) (uint32, error) {
  	var value uint32
  	err := ioctl(fd, req, uintptr(unsafe.Pointer(&value)))
  	return value, err
  }
  
  func IoctlGetRTCTime(fd int) (*RTCTime, error) {
  	var value RTCTime
  	err := ioctl(fd, RTC_RD_TIME, uintptr(unsafe.Pointer(&value)))
  	return &value, err
  }
  
  //sys	Linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error)
  
  func Link(oldpath string, newpath string) (err error) {
  	return Linkat(AT_FDCWD, oldpath, AT_FDCWD, newpath, 0)
  }
  
  func Mkdir(path string, mode uint32) (err error) {
  	return Mkdirat(AT_FDCWD, path, mode)
  }
  
  func Mknod(path string, mode uint32, dev int) (err error) {
  	return Mknodat(AT_FDCWD, path, mode, dev)
  }
  
  func Open(path string, mode int, perm uint32) (fd int, err error) {
  	return openat(AT_FDCWD, path, mode|O_LARGEFILE, perm)
  }
  
  //sys	openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
  
  func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
  	return openat(dirfd, path, flags|O_LARGEFILE, mode)
  }
  
  //sys	ppoll(fds *PollFd, nfds int, timeout *Timespec, sigmask *Sigset_t) (n int, err error)
  
  func Ppoll(fds []PollFd, timeout *Timespec, sigmask *Sigset_t) (n int, err error) {
  	if len(fds) == 0 {
  		return ppoll(nil, 0, timeout, sigmask)
  	}
  	return ppoll(&fds[0], len(fds), timeout, sigmask)
  }
  
  //sys	Readlinkat(dirfd int, path string, buf []byte) (n int, err error)
  
  func Readlink(path string, buf []byte) (n int, err error) {
  	return Readlinkat(AT_FDCWD, path, buf)
  }
  
  func Rename(oldpath string, newpath string) (err error) {
  	return Renameat(AT_FDCWD, oldpath, AT_FDCWD, newpath)
  }
  
  func Rmdir(path string) error {
  	return Unlinkat(AT_FDCWD, path, AT_REMOVEDIR)
  }
  
  //sys	Symlinkat(oldpath string, newdirfd int, newpath string) (err error)
  
  func Symlink(oldpath string, newpath string) (err error) {
  	return Symlinkat(oldpath, AT_FDCWD, newpath)
  }
  
  func Unlink(path string) error {
  	return Unlinkat(AT_FDCWD, path, 0)
  }
  
  //sys	Unlinkat(dirfd int, path string, flags int) (err error)
  
  func Utimes(path string, tv []Timeval) error {
  	if tv == nil {
  		err := utimensat(AT_FDCWD, path, nil, 0)
  		if err != ENOSYS {
  			return err
  		}
  		return utimes(path, nil)
  	}
  	if len(tv) != 2 {
  		return EINVAL
  	}
  	var ts [2]Timespec
  	ts[0] = NsecToTimespec(TimevalToNsec(tv[0]))
  	ts[1] = NsecToTimespec(TimevalToNsec(tv[1]))
  	err := utimensat(AT_FDCWD, path, (*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
  	if err != ENOSYS {
  		return err
  	}
  	return utimes(path, (*[2]Timeval)(unsafe.Pointer(&tv[0])))
  }
  
  //sys	utimensat(dirfd int, path string, times *[2]Timespec, flags int) (err error)
  
  func UtimesNano(path string, ts []Timespec) error {
  	if ts == nil {
  		err := utimensat(AT_FDCWD, path, nil, 0)
  		if err != ENOSYS {
  			return err
  		}
  		return utimes(path, nil)
  	}
  	if len(ts) != 2 {
  		return EINVAL
  	}
  	err := utimensat(AT_FDCWD, path, (*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
  	if err != ENOSYS {
  		return err
  	}
  	// If the utimensat syscall isn't available (utimensat was added to Linux
  	// in 2.6.22, Released, 8 July 2007) then fall back to utimes
  	var tv [2]Timeval
  	for i := 0; i < 2; i++ {
  		tv[i] = NsecToTimeval(TimespecToNsec(ts[i]))
  	}
  	return utimes(path, (*[2]Timeval)(unsafe.Pointer(&tv[0])))
  }
  
  func UtimesNanoAt(dirfd int, path string, ts []Timespec, flags int) error {
  	if ts == nil {
  		return utimensat(dirfd, path, nil, flags)
  	}
  	if len(ts) != 2 {
  		return EINVAL
  	}
  	return utimensat(dirfd, path, (*[2]Timespec)(unsafe.Pointer(&ts[0])), flags)
  }
  
  func Futimesat(dirfd int, path string, tv []Timeval) error {
  	if tv == nil {
  		return futimesat(dirfd, path, nil)
  	}
  	if len(tv) != 2 {
  		return EINVAL
  	}
  	return futimesat(dirfd, path, (*[2]Timeval)(unsafe.Pointer(&tv[0])))
  }
  
  func Futimes(fd int, tv []Timeval) (err error) {
  	// Believe it or not, this is the best we can do on Linux
  	// (and is what glibc does).
  	return Utimes("/proc/self/fd/"+itoa(fd), tv)
  }
  
  const ImplementsGetwd = true
  
  //sys	Getcwd(buf []byte) (n int, err error)
  
  func Getwd() (wd string, err error) {
  	var buf [PathMax]byte
  	n, err := Getcwd(buf[0:])
  	if err != nil {
  		return "", err
  	}
  	// Getcwd returns the number of bytes written to buf, including the NUL.
  	if n < 1 || n > len(buf) || buf[n-1] != 0 {
  		return "", EINVAL
  	}
  	return string(buf[0 : n-1]), nil
  }
  
  func Getgroups() (gids []int, err error) {
  	n, err := getgroups(0, nil)
  	if err != nil {
  		return nil, err
  	}
  	if n == 0 {
  		return nil, nil
  	}
  
  	// Sanity check group count. Max is 1<<16 on Linux.
  	if n < 0 || n > 1<<20 {
  		return nil, EINVAL
  	}
  
  	a := make([]_Gid_t, n)
  	n, err = getgroups(n, &a[0])
  	if err != nil {
  		return nil, err
  	}
  	gids = make([]int, n)
  	for i, v := range a[0:n] {
  		gids[i] = int(v)
  	}
  	return
  }
  
  func Setgroups(gids []int) (err error) {
  	if len(gids) == 0 {
  		return setgroups(0, nil)
  	}
  
  	a := make([]_Gid_t, len(gids))
  	for i, v := range gids {
  		a[i] = _Gid_t(v)
  	}
  	return setgroups(len(a), &a[0])
  }
  
  type WaitStatus uint32
  
  // Wait status is 7 bits at bottom, either 0 (exited),
  // 0x7F (stopped), or a signal number that caused an exit.
  // The 0x80 bit is whether there was a core dump.
  // An extra number (exit code, signal causing a stop)
  // is in the high bits. At least that's the idea.
  // There are various irregularities. For example, the
  // "continued" status is 0xFFFF, distinguishing itself
  // from stopped via the core dump bit.
  
  const (
  	mask    = 0x7F
  	core    = 0x80
  	exited  = 0x00
  	stopped = 0x7F
  	shift   = 8
  )
  
  func (w WaitStatus) Exited() bool { return w&mask == exited }
  
  func (w WaitStatus) Signaled() bool { return w&mask != stopped && w&mask != exited }
  
  func (w WaitStatus) Stopped() bool { return w&0xFF == stopped }
  
  func (w WaitStatus) Continued() bool { return w == 0xFFFF }
  
  func (w WaitStatus) CoreDump() bool { return w.Signaled() && w&core != 0 }
  
  func (w WaitStatus) ExitStatus() int {
  	if !w.Exited() {
  		return -1
  	}
  	return int(w>>shift) & 0xFF
  }
  
  func (w WaitStatus) Signal() syscall.Signal {
  	if !w.Signaled() {
  		return -1
  	}
  	return syscall.Signal(w & mask)
  }
  
  func (w WaitStatus) StopSignal() syscall.Signal {
  	if !w.Stopped() {
  		return -1
  	}
  	return syscall.Signal(w>>shift) & 0xFF
  }
  
  func (w WaitStatus) TrapCause() int {
  	if w.StopSignal() != SIGTRAP {
  		return -1
  	}
  	return int(w>>shift) >> 8
  }
  
  //sys	wait4(pid int, wstatus *_C_int, options int, rusage *Rusage) (wpid int, err error)
  
  func Wait4(pid int, wstatus *WaitStatus, options int, rusage *Rusage) (wpid int, err error) {
  	var status _C_int
  	wpid, err = wait4(pid, &status, options, rusage)
  	if wstatus != nil {
  		*wstatus = WaitStatus(status)
  	}
  	return
  }
  
  func Mkfifo(path string, mode uint32) error {
  	return Mknod(path, mode|S_IFIFO, 0)
  }
  
  func Mkfifoat(dirfd int, path string, mode uint32) error {
  	return Mknodat(dirfd, path, mode|S_IFIFO, 0)
  }
  
  func (sa *SockaddrInet4) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if sa.Port < 0 || sa.Port > 0xFFFF {
  		return nil, 0, EINVAL
  	}
  	sa.raw.Family = AF_INET
  	p := (*[2]byte)(unsafe.Pointer(&sa.raw.Port))
  	p[0] = byte(sa.Port >> 8)
  	p[1] = byte(sa.Port)
  	for i := 0; i < len(sa.Addr); i++ {
  		sa.raw.Addr[i] = sa.Addr[i]
  	}
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrInet4, nil
  }
  
  func (sa *SockaddrInet6) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if sa.Port < 0 || sa.Port > 0xFFFF {
  		return nil, 0, EINVAL
  	}
  	sa.raw.Family = AF_INET6
  	p := (*[2]byte)(unsafe.Pointer(&sa.raw.Port))
  	p[0] = byte(sa.Port >> 8)
  	p[1] = byte(sa.Port)
  	sa.raw.Scope_id = sa.ZoneId
  	for i := 0; i < len(sa.Addr); i++ {
  		sa.raw.Addr[i] = sa.Addr[i]
  	}
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrInet6, nil
  }
  
  func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	name := sa.Name
  	n := len(name)
  	if n >= len(sa.raw.Path) {
  		return nil, 0, EINVAL
  	}
  	sa.raw.Family = AF_UNIX
  	for i := 0; i < n; i++ {
  		sa.raw.Path[i] = int8(name[i])
  	}
  	// length is family (uint16), name, NUL.
  	sl := _Socklen(2)
  	if n > 0 {
  		sl += _Socklen(n) + 1
  	}
  	if sa.raw.Path[0] == '@' {
  		sa.raw.Path[0] = 0
  		// Don't count trailing NUL for abstract address.
  		sl--
  	}
  
  	return unsafe.Pointer(&sa.raw), sl, nil
  }
  
  // SockaddrLinklayer implements the Sockaddr interface for AF_PACKET type sockets.
  type SockaddrLinklayer struct {
  	Protocol uint16
  	Ifindex  int
  	Hatype   uint16
  	Pkttype  uint8
  	Halen    uint8
  	Addr     [8]byte
  	raw      RawSockaddrLinklayer
  }
  
  func (sa *SockaddrLinklayer) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if sa.Ifindex < 0 || sa.Ifindex > 0x7fffffff {
  		return nil, 0, EINVAL
  	}
  	sa.raw.Family = AF_PACKET
  	sa.raw.Protocol = sa.Protocol
  	sa.raw.Ifindex = int32(sa.Ifindex)
  	sa.raw.Hatype = sa.Hatype
  	sa.raw.Pkttype = sa.Pkttype
  	sa.raw.Halen = sa.Halen
  	for i := 0; i < len(sa.Addr); i++ {
  		sa.raw.Addr[i] = sa.Addr[i]
  	}
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrLinklayer, nil
  }
  
  // SockaddrNetlink implements the Sockaddr interface for AF_NETLINK type sockets.
  type SockaddrNetlink struct {
  	Family uint16
  	Pad    uint16
  	Pid    uint32
  	Groups uint32
  	raw    RawSockaddrNetlink
  }
  
  func (sa *SockaddrNetlink) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_NETLINK
  	sa.raw.Pad = sa.Pad
  	sa.raw.Pid = sa.Pid
  	sa.raw.Groups = sa.Groups
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrNetlink, nil
  }
  
  // SockaddrHCI implements the Sockaddr interface for AF_BLUETOOTH type sockets
  // using the HCI protocol.
  type SockaddrHCI struct {
  	Dev     uint16
  	Channel uint16
  	raw     RawSockaddrHCI
  }
  
  func (sa *SockaddrHCI) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_BLUETOOTH
  	sa.raw.Dev = sa.Dev
  	sa.raw.Channel = sa.Channel
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrHCI, nil
  }
  
  // SockaddrL2 implements the Sockaddr interface for AF_BLUETOOTH type sockets
  // using the L2CAP protocol.
  type SockaddrL2 struct {
  	PSM      uint16
  	CID      uint16
  	Addr     [6]uint8
  	AddrType uint8
  	raw      RawSockaddrL2
  }
  
  func (sa *SockaddrL2) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_BLUETOOTH
  	psm := (*[2]byte)(unsafe.Pointer(&sa.raw.Psm))
  	psm[0] = byte(sa.PSM)
  	psm[1] = byte(sa.PSM >> 8)
  	for i := 0; i < len(sa.Addr); i++ {
  		sa.raw.Bdaddr[i] = sa.Addr[len(sa.Addr)-1-i]
  	}
  	cid := (*[2]byte)(unsafe.Pointer(&sa.raw.Cid))
  	cid[0] = byte(sa.CID)
  	cid[1] = byte(sa.CID >> 8)
  	sa.raw.Bdaddr_type = sa.AddrType
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrL2, nil
  }
  
  // SockaddrRFCOMM implements the Sockaddr interface for AF_BLUETOOTH type sockets
  // using the RFCOMM protocol.
  //
  // Server example:
  //
  //      fd, _ := Socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM)
  //      _ = unix.Bind(fd, &unix.SockaddrRFCOMM{
  //      	Channel: 1,
  //      	Addr:    [6]uint8{0, 0, 0, 0, 0, 0}, // BDADDR_ANY or 00:00:00:00:00:00
  //      })
  //      _ = Listen(fd, 1)
  //      nfd, sa, _ := Accept(fd)
  //      fmt.Printf("conn addr=%v fd=%d", sa.(*unix.SockaddrRFCOMM).Addr, nfd)
  //      Read(nfd, buf)
  //
  // Client example:
  //
  //      fd, _ := Socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM)
  //      _ = Connect(fd, &SockaddrRFCOMM{
  //      	Channel: 1,
  //      	Addr:    [6]byte{0x11, 0x22, 0x33, 0xaa, 0xbb, 0xcc}, // CC:BB:AA:33:22:11
  //      })
  //      Write(fd, []byte(`hello`))
  type SockaddrRFCOMM struct {
  	// Addr represents a bluetooth address, byte ordering is little-endian.
  	Addr [6]uint8
  
  	// Channel is a designated bluetooth channel, only 1-30 are available for use.
  	// Since Linux 2.6.7 and further zero value is the first available channel.
  	Channel uint8
  
  	raw RawSockaddrRFCOMM
  }
  
  func (sa *SockaddrRFCOMM) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_BLUETOOTH
  	sa.raw.Channel = sa.Channel
  	sa.raw.Bdaddr = sa.Addr
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrRFCOMM, nil
  }
  
  // SockaddrCAN implements the Sockaddr interface for AF_CAN type sockets.
  // The RxID and TxID fields are used for transport protocol addressing in
  // (CAN_TP16, CAN_TP20, CAN_MCNET, and CAN_ISOTP), they can be left with
  // zero values for CAN_RAW and CAN_BCM sockets as they have no meaning.
  //
  // The SockaddrCAN struct must be bound to the socket file descriptor
  // using Bind before the CAN socket can be used.
  //
  //      // Read one raw CAN frame
  //      fd, _ := Socket(AF_CAN, SOCK_RAW, CAN_RAW)
  //      addr := &SockaddrCAN{Ifindex: index}
  //      Bind(fd, addr)
  //      frame := make([]byte, 16)
  //      Read(fd, frame)
  //
  // The full SocketCAN documentation can be found in the linux kernel
  // archives at: https://www.kernel.org/doc/Documentation/networking/can.txt
  type SockaddrCAN struct {
  	Ifindex int
  	RxID    uint32
  	TxID    uint32
  	raw     RawSockaddrCAN
  }
  
  func (sa *SockaddrCAN) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if sa.Ifindex < 0 || sa.Ifindex > 0x7fffffff {
  		return nil, 0, EINVAL
  	}
  	sa.raw.Family = AF_CAN
  	sa.raw.Ifindex = int32(sa.Ifindex)
  	rx := (*[4]byte)(unsafe.Pointer(&sa.RxID))
  	for i := 0; i < 4; i++ {
  		sa.raw.Addr[i] = rx[i]
  	}
  	tx := (*[4]byte)(unsafe.Pointer(&sa.TxID))
  	for i := 0; i < 4; i++ {
  		sa.raw.Addr[i+4] = tx[i]
  	}
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrCAN, nil
  }
  
  // SockaddrALG implements the Sockaddr interface for AF_ALG type sockets.
  // SockaddrALG enables userspace access to the Linux kernel's cryptography
  // subsystem. The Type and Name fields specify which type of hash or cipher
  // should be used with a given socket.
  //
  // To create a file descriptor that provides access to a hash or cipher, both
  // Bind and Accept must be used. Once the setup process is complete, input
  // data can be written to the socket, processed by the kernel, and then read
  // back as hash output or ciphertext.
  //
  // Here is an example of using an AF_ALG socket with SHA1 hashing.
  // The initial socket setup process is as follows:
  //
  //      // Open a socket to perform SHA1 hashing.
  //      fd, _ := unix.Socket(unix.AF_ALG, unix.SOCK_SEQPACKET, 0)
  //      addr := &unix.SockaddrALG{Type: "hash", Name: "sha1"}
  //      unix.Bind(fd, addr)
  //      // Note: unix.Accept does not work at this time; must invoke accept()
  //      // manually using unix.Syscall.
  //      hashfd, _, _ := unix.Syscall(unix.SYS_ACCEPT, uintptr(fd), 0, 0)
  //
  // Once a file descriptor has been returned from Accept, it may be used to
  // perform SHA1 hashing. The descriptor is not safe for concurrent use, but
  // may be re-used repeatedly with subsequent Write and Read operations.
  //
  // When hashing a small byte slice or string, a single Write and Read may
  // be used:
  //
  //      // Assume hashfd is already configured using the setup process.
  //      hash := os.NewFile(hashfd, "sha1")
  //      // Hash an input string and read the results. Each Write discards
  //      // previous hash state. Read always reads the current state.
  //      b := make([]byte, 20)
  //      for i := 0; i < 2; i++ {
  //          io.WriteString(hash, "Hello, world.")
  //          hash.Read(b)
  //          fmt.Println(hex.EncodeToString(b))
  //      }
  //      // Output:
  //      // 2ae01472317d1935a84797ec1983ae243fc6aa28
  //      // 2ae01472317d1935a84797ec1983ae243fc6aa28
  //
  // For hashing larger byte slices, or byte streams such as those read from
  // a file or socket, use Sendto with MSG_MORE to instruct the kernel to update
  // the hash digest instead of creating a new one for a given chunk and finalizing it.
  //
  //      // Assume hashfd and addr are already configured using the setup process.
  //      hash := os.NewFile(hashfd, "sha1")
  //      // Hash the contents of a file.
  //      f, _ := os.Open("/tmp/linux-4.10-rc7.tar.xz")
  //      b := make([]byte, 4096)
  //      for {
  //          n, err := f.Read(b)
  //          if err == io.EOF {
  //              break
  //          }
  //          unix.Sendto(hashfd, b[:n], unix.MSG_MORE, addr)
  //      }
  //      hash.Read(b)
  //      fmt.Println(hex.EncodeToString(b))
  //      // Output: 85cdcad0c06eef66f805ecce353bec9accbeecc5
  //
  // For more information, see: http://www.chronox.de/crypto-API/crypto/userspace-if.html.
  type SockaddrALG struct {
  	Type    string
  	Name    string
  	Feature uint32
  	Mask    uint32
  	raw     RawSockaddrALG
  }
  
  func (sa *SockaddrALG) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	// Leave room for NUL byte terminator.
  	if len(sa.Type) > 13 {
  		return nil, 0, EINVAL
  	}
  	if len(sa.Name) > 63 {
  		return nil, 0, EINVAL
  	}
  
  	sa.raw.Family = AF_ALG
  	sa.raw.Feat = sa.Feature
  	sa.raw.Mask = sa.Mask
  
  	typ, err := ByteSliceFromString(sa.Type)
  	if err != nil {
  		return nil, 0, err
  	}
  	name, err := ByteSliceFromString(sa.Name)
  	if err != nil {
  		return nil, 0, err
  	}
  
  	copy(sa.raw.Type[:], typ)
  	copy(sa.raw.Name[:], name)
  
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrALG, nil
  }
  
  // SockaddrVM implements the Sockaddr interface for AF_VSOCK type sockets.
  // SockaddrVM provides access to Linux VM sockets: a mechanism that enables
  // bidirectional communication between a hypervisor and its guest virtual
  // machines.
  type SockaddrVM struct {
  	// CID and Port specify a context ID and port address for a VM socket.
  	// Guests have a unique CID, and hosts may have a well-known CID of:
  	//  - VMADDR_CID_HYPERVISOR: refers to the hypervisor process.
  	//  - VMADDR_CID_HOST: refers to other processes on the host.
  	CID  uint32
  	Port uint32
  	raw  RawSockaddrVM
  }
  
  func (sa *SockaddrVM) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_VSOCK
  	sa.raw.Port = sa.Port
  	sa.raw.Cid = sa.CID
  
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrVM, nil
  }
  
  type SockaddrXDP struct {
  	Flags        uint16
  	Ifindex      uint32
  	QueueID      uint32
  	SharedUmemFD uint32
  	raw          RawSockaddrXDP
  }
  
  func (sa *SockaddrXDP) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	sa.raw.Family = AF_XDP
  	sa.raw.Flags = sa.Flags
  	sa.raw.Ifindex = sa.Ifindex
  	sa.raw.Queue_id = sa.QueueID
  	sa.raw.Shared_umem_fd = sa.SharedUmemFD
  
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrXDP, nil
  }
  
  // This constant mirrors the #define of PX_PROTO_OE in
  // linux/if_pppox.h. We're defining this by hand here instead of
  // autogenerating through mkerrors.sh because including
  // linux/if_pppox.h causes some declaration conflicts with other
  // includes (linux/if_pppox.h includes linux/in.h, which conflicts
  // with netinet/in.h). Given that we only need a single zero constant
  // out of that file, it's cleaner to just define it by hand here.
  const px_proto_oe = 0
  
  type SockaddrPPPoE struct {
  	SID    uint16
  	Remote []byte
  	Dev    string
  	raw    RawSockaddrPPPoX
  }
  
  func (sa *SockaddrPPPoE) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if len(sa.Remote) != 6 {
  		return nil, 0, EINVAL
  	}
  	if len(sa.Dev) > IFNAMSIZ-1 {
  		return nil, 0, EINVAL
  	}
  
  	*(*uint16)(unsafe.Pointer(&sa.raw[0])) = AF_PPPOX
  	// This next field is in host-endian byte order. We can't use the
  	// same unsafe pointer cast as above, because this value is not
  	// 32-bit aligned and some architectures don't allow unaligned
  	// access.
  	//
  	// However, the value of px_proto_oe is 0, so we can use
  	// encoding/binary helpers to write the bytes without worrying
  	// about the ordering.
  	binary.BigEndian.PutUint32(sa.raw[2:6], px_proto_oe)
  	// This field is deliberately big-endian, unlike the previous
  	// one. The kernel expects SID to be in network byte order.
  	binary.BigEndian.PutUint16(sa.raw[6:8], sa.SID)
  	copy(sa.raw[8:14], sa.Remote)
  	for i := 14; i < 14+IFNAMSIZ; i++ {
  		sa.raw[i] = 0
  	}
  	copy(sa.raw[14:], sa.Dev)
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrPPPoX, nil
  }
  
  // SockaddrTIPC implements the Sockaddr interface for AF_TIPC type sockets.
  // For more information on TIPC, see: http://tipc.sourceforge.net/.
  type SockaddrTIPC struct {
  	// Scope is the publication scopes when binding service/service range.
  	// Should be set to TIPC_CLUSTER_SCOPE or TIPC_NODE_SCOPE.
  	Scope int
  
  	// Addr is the type of address used to manipulate a socket. Addr must be
  	// one of:
  	//  - *TIPCSocketAddr: "id" variant in the C addr union
  	//  - *TIPCServiceRange: "nameseq" variant in the C addr union
  	//  - *TIPCServiceName: "name" variant in the C addr union
  	//
  	// If nil, EINVAL will be returned when the structure is used.
  	Addr TIPCAddr
  
  	raw RawSockaddrTIPC
  }
  
  // TIPCAddr is implemented by types that can be used as an address for
  // SockaddrTIPC. It is only implemented by *TIPCSocketAddr, *TIPCServiceRange,
  // and *TIPCServiceName.
  type TIPCAddr interface {
  	tipcAddrtype() uint8
  	tipcAddr() [12]byte
  }
  
  func (sa *TIPCSocketAddr) tipcAddr() [12]byte {
  	var out [12]byte
  	copy(out[:], (*(*[unsafe.Sizeof(TIPCSocketAddr{})]byte)(unsafe.Pointer(sa)))[:])
  	return out
  }
  
  func (sa *TIPCSocketAddr) tipcAddrtype() uint8 { return TIPC_SOCKET_ADDR }
  
  func (sa *TIPCServiceRange) tipcAddr() [12]byte {
  	var out [12]byte
  	copy(out[:], (*(*[unsafe.Sizeof(TIPCServiceRange{})]byte)(unsafe.Pointer(sa)))[:])
  	return out
  }
  
  func (sa *TIPCServiceRange) tipcAddrtype() uint8 { return TIPC_SERVICE_RANGE }
  
  func (sa *TIPCServiceName) tipcAddr() [12]byte {
  	var out [12]byte
  	copy(out[:], (*(*[unsafe.Sizeof(TIPCServiceName{})]byte)(unsafe.Pointer(sa)))[:])
  	return out
  }
  
  func (sa *TIPCServiceName) tipcAddrtype() uint8 { return TIPC_SERVICE_ADDR }
  
  func (sa *SockaddrTIPC) sockaddr() (unsafe.Pointer, _Socklen, error) {
  	if sa.Addr == nil {
  		return nil, 0, EINVAL
  	}
  
  	sa.raw.Family = AF_TIPC
  	sa.raw.Scope = int8(sa.Scope)
  	sa.raw.Addrtype = sa.Addr.tipcAddrtype()
  	sa.raw.Addr = sa.Addr.tipcAddr()
  
  	return unsafe.Pointer(&sa.raw), SizeofSockaddrTIPC, nil
  }
  
  func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
  	switch rsa.Addr.Family {
  	case AF_NETLINK:
  		pp := (*RawSockaddrNetlink)(unsafe.Pointer(rsa))
  		sa := new(SockaddrNetlink)
  		sa.Family = pp.Family
  		sa.Pad = pp.Pad
  		sa.Pid = pp.Pid
  		sa.Groups = pp.Groups
  		return sa, nil
  
  	case AF_PACKET:
  		pp := (*RawSockaddrLinklayer)(unsafe.Pointer(rsa))
  		sa := new(SockaddrLinklayer)
  		sa.Protocol = pp.Protocol
  		sa.Ifindex = int(pp.Ifindex)
  		sa.Hatype = pp.Hatype
  		sa.Pkttype = pp.Pkttype
  		sa.Halen = pp.Halen
  		for i := 0; i < len(sa.Addr); i++ {
  			sa.Addr[i] = pp.Addr[i]
  		}
  		return sa, nil
  
  	case AF_UNIX:
  		pp := (*RawSockaddrUnix)(unsafe.Pointer(rsa))
  		sa := new(SockaddrUnix)
  		if pp.Path[0] == 0 {
  			// "Abstract" Unix domain socket.
  			// Rewrite leading NUL as @ for textual display.
  			// (This is the standard convention.)
  			// Not friendly to overwrite in place,
  			// but the callers below don't care.
  			pp.Path[0] = '@'
  		}
  
  		// Assume path ends at NUL.
  		// This is not technically the Linux semantics for
  		// abstract Unix domain sockets--they are supposed
  		// to be uninterpreted fixed-size binary blobs--but
  		// everyone uses this convention.
  		n := 0
  		for n < len(pp.Path) && pp.Path[n] != 0 {
  			n++
  		}
  		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
  		sa.Name = string(bytes)
  		return sa, nil
  
  	case AF_INET:
  		pp := (*RawSockaddrInet4)(unsafe.Pointer(rsa))
  		sa := new(SockaddrInet4)
  		p := (*[2]byte)(unsafe.Pointer(&pp.Port))
  		sa.Port = int(p[0])<<8 + int(p[1])
  		for i := 0; i < len(sa.Addr); i++ {
  			sa.Addr[i] = pp.Addr[i]
  		}
  		return sa, nil
  
  	case AF_INET6:
  		pp := (*RawSockaddrInet6)(unsafe.Pointer(rsa))
  		sa := new(SockaddrInet6)
  		p := (*[2]byte)(unsafe.Pointer(&pp.Port))
  		sa.Port = int(p[0])<<8 + int(p[1])
  		sa.ZoneId = pp.Scope_id
  		for i := 0; i < len(sa.Addr); i++ {
  			sa.Addr[i] = pp.Addr[i]
  		}
  		return sa, nil
  
  	case AF_VSOCK:
  		pp := (*RawSockaddrVM)(unsafe.Pointer(rsa))
  		sa := &SockaddrVM{
  			CID:  pp.Cid,
  			Port: pp.Port,
  		}
  		return sa, nil
  	case AF_BLUETOOTH:
  		proto, err := GetsockoptInt(fd, SOL_SOCKET, SO_PROTOCOL)
  		if err != nil {
  			return nil, err
  		}
  		// only BTPROTO_L2CAP and BTPROTO_RFCOMM can accept connections
  		switch proto {
  		case BTPROTO_L2CAP:
  			pp := (*RawSockaddrL2)(unsafe.Pointer(rsa))
  			sa := &SockaddrL2{
  				PSM:      pp.Psm,
  				CID:      pp.Cid,
  				Addr:     pp.Bdaddr,
  				AddrType: pp.Bdaddr_type,
  			}
  			return sa, nil
  		case BTPROTO_RFCOMM:
  			pp := (*RawSockaddrRFCOMM)(unsafe.Pointer(rsa))
  			sa := &SockaddrRFCOMM{
  				Channel: pp.Channel,
  				Addr:    pp.Bdaddr,
  			}
  			return sa, nil
  		}
  	case AF_XDP:
  		pp := (*RawSockaddrXDP)(unsafe.Pointer(rsa))
  		sa := &SockaddrXDP{
  			Flags:        pp.Flags,
  			Ifindex:      pp.Ifindex,
  			QueueID:      pp.Queue_id,
  			SharedUmemFD: pp.Shared_umem_fd,
  		}
  		return sa, nil
  	case AF_PPPOX:
  		pp := (*RawSockaddrPPPoX)(unsafe.Pointer(rsa))
  		if binary.BigEndian.Uint32(pp[2:6]) != px_proto_oe {
  			return nil, EINVAL
  		}
  		sa := &SockaddrPPPoE{
  			SID:    binary.BigEndian.Uint16(pp[6:8]),
  			Remote: pp[8:14],
  		}
  		for i := 14; i < 14+IFNAMSIZ; i++ {
  			if pp[i] == 0 {
  				sa.Dev = string(pp[14:i])
  				break
  			}
  		}
  		return sa, nil
  	case AF_TIPC:
  		pp := (*RawSockaddrTIPC)(unsafe.Pointer(rsa))
  
  		sa := &SockaddrTIPC{
  			Scope: int(pp.Scope),
  		}
  
  		// Determine which union variant is present in pp.Addr by checking
  		// pp.Addrtype.
  		switch pp.Addrtype {
  		case TIPC_SERVICE_RANGE:
  			sa.Addr = (*TIPCServiceRange)(unsafe.Pointer(&pp.Addr))
  		case TIPC_SERVICE_ADDR:
  			sa.Addr = (*TIPCServiceName)(unsafe.Pointer(&pp.Addr))
  		case TIPC_SOCKET_ADDR:
  			sa.Addr = (*TIPCSocketAddr)(unsafe.Pointer(&pp.Addr))
  		default:
  			return nil, EINVAL
  		}
  
  		return sa, nil
  	}
  	return nil, EAFNOSUPPORT
  }
  
  func Accept(fd int) (nfd int, sa Sockaddr, err error) {
  	var rsa RawSockaddrAny
  	var len _Socklen = SizeofSockaddrAny
  	nfd, err = accept(fd, &rsa, &len)
  	if err != nil {
  		return
  	}
  	sa, err = anyToSockaddr(fd, &rsa)
  	if err != nil {
  		Close(nfd)
  		nfd = 0
  	}
  	return
  }
  
  func Accept4(fd int, flags int) (nfd int, sa Sockaddr, err error) {
  	var rsa RawSockaddrAny
  	var len _Socklen = SizeofSockaddrAny
  	nfd, err = accept4(fd, &rsa, &len, flags)
  	if err != nil {
  		return
  	}
  	if len > SizeofSockaddrAny {
  		panic("RawSockaddrAny too small")
  	}
  	sa, err = anyToSockaddr(fd, &rsa)
  	if err != nil {
  		Close(nfd)
  		nfd = 0
  	}
  	return
  }
  
  func Getsockname(fd int) (sa Sockaddr, err error) {
  	var rsa RawSockaddrAny
  	var len _Socklen = SizeofSockaddrAny
  	if err = getsockname(fd, &rsa, &len); err != nil {
  		return
  	}
  	return anyToSockaddr(fd, &rsa)
  }
  
  func GetsockoptIPMreqn(fd, level, opt int) (*IPMreqn, error) {
  	var value IPMreqn
  	vallen := _Socklen(SizeofIPMreqn)
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&value), &vallen)
  	return &value, err
  }
  
  func GetsockoptUcred(fd, level, opt int) (*Ucred, error) {
  	var value Ucred
  	vallen := _Socklen(SizeofUcred)
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&value), &vallen)
  	return &value, err
  }
  
  func GetsockoptTCPInfo(fd, level, opt int) (*TCPInfo, error) {
  	var value TCPInfo
  	vallen := _Socklen(SizeofTCPInfo)
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&value), &vallen)
  	return &value, err
  }
  
  // GetsockoptString returns the string value of the socket option opt for the
  // socket associated with fd at the given socket level.
  func GetsockoptString(fd, level, opt int) (string, error) {
  	buf := make([]byte, 256)
  	vallen := _Socklen(len(buf))
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&buf[0]), &vallen)
  	if err != nil {
  		if err == ERANGE {
  			buf = make([]byte, vallen)
  			err = getsockopt(fd, level, opt, unsafe.Pointer(&buf[0]), &vallen)
  		}
  		if err != nil {
  			return "", err
  		}
  	}
  	return string(buf[:vallen-1]), nil
  }
  
  func GetsockoptTpacketStats(fd, level, opt int) (*TpacketStats, error) {
  	var value TpacketStats
  	vallen := _Socklen(SizeofTpacketStats)
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&value), &vallen)
  	return &value, err
  }
  
  func GetsockoptTpacketStatsV3(fd, level, opt int) (*TpacketStatsV3, error) {
  	var value TpacketStatsV3
  	vallen := _Socklen(SizeofTpacketStatsV3)
  	err := getsockopt(fd, level, opt, unsafe.Pointer(&value), &vallen)
  	return &value, err
  }
  
  func SetsockoptIPMreqn(fd, level, opt int, mreq *IPMreqn) (err error) {
  	return setsockopt(fd, level, opt, unsafe.Pointer(mreq), unsafe.Sizeof(*mreq))
  }
  
  func SetsockoptPacketMreq(fd, level, opt int, mreq *PacketMreq) error {
  	return setsockopt(fd, level, opt, unsafe.Pointer(mreq), unsafe.Sizeof(*mreq))
  }
  
  // SetsockoptSockFprog attaches a classic BPF or an extended BPF program to a
  // socket to filter incoming packets.  See 'man 7 socket' for usage information.
  func SetsockoptSockFprog(fd, level, opt int, fprog *SockFprog) error {
  	return setsockopt(fd, level, opt, unsafe.Pointer(fprog), unsafe.Sizeof(*fprog))
  }
  
  func SetsockoptCanRawFilter(fd, level, opt int, filter []CanFilter) error {
  	var p unsafe.Pointer
  	if len(filter) > 0 {
  		p = unsafe.Pointer(&filter[0])
  	}
  	return setsockopt(fd, level, opt, p, uintptr(len(filter)*SizeofCanFilter))
  }
  
  func SetsockoptTpacketReq(fd, level, opt int, tp *TpacketReq) error {
  	return setsockopt(fd, level, opt, unsafe.Pointer(tp), unsafe.Sizeof(*tp))
  }
  
  func SetsockoptTpacketReq3(fd, level, opt int, tp *TpacketReq3) error {
  	return setsockopt(fd, level, opt, unsafe.Pointer(tp), unsafe.Sizeof(*tp))
  }
  
  // Keyctl Commands (http://man7.org/linux/man-pages/man2/keyctl.2.html)
  
  // KeyctlInt calls keyctl commands in which each argument is an int.
  // These commands are KEYCTL_REVOKE, KEYCTL_CHOWN, KEYCTL_CLEAR, KEYCTL_LINK,
  // KEYCTL_UNLINK, KEYCTL_NEGATE, KEYCTL_SET_REQKEY_KEYRING, KEYCTL_SET_TIMEOUT,
  // KEYCTL_ASSUME_AUTHORITY, KEYCTL_SESSION_TO_PARENT, KEYCTL_REJECT,
  // KEYCTL_INVALIDATE, and KEYCTL_GET_PERSISTENT.
  //sys	KeyctlInt(cmd int, arg2 int, arg3 int, arg4 int, arg5 int) (ret int, err error) = SYS_KEYCTL
  
  // KeyctlBuffer calls keyctl commands in which the third and fourth
  // arguments are a buffer and its length, respectively.
  // These commands are KEYCTL_UPDATE, KEYCTL_READ, and KEYCTL_INSTANTIATE.
  //sys	KeyctlBuffer(cmd int, arg2 int, buf []byte, arg5 int) (ret int, err error) = SYS_KEYCTL
  
  // KeyctlString calls keyctl commands which return a string.
  // These commands are KEYCTL_DESCRIBE and KEYCTL_GET_SECURITY.
  func KeyctlString(cmd int, id int) (string, error) {
  	// We must loop as the string data may change in between the syscalls.
  	// We could allocate a large buffer here to reduce the chance that the
  	// syscall needs to be called twice; however, this is unnecessary as
  	// the performance loss is negligible.
  	var buffer []byte
  	for {
  		// Try to fill the buffer with data
  		length, err := KeyctlBuffer(cmd, id, buffer, 0)
  		if err != nil {
  			return "", err
  		}
  
  		// Check if the data was written
  		if length <= len(buffer) {
  			// Exclude the null terminator
  			return string(buffer[:length-1]), nil
  		}
  
  		// Make a bigger buffer if needed
  		buffer = make([]byte, length)
  	}
  }
  
  // Keyctl commands with special signatures.
  
  // KeyctlGetKeyringID implements the KEYCTL_GET_KEYRING_ID command.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_get_keyring_ID.3.html
  func KeyctlGetKeyringID(id int, create bool) (ringid int, err error) {
  	createInt := 0
  	if create {
  		createInt = 1
  	}
  	return KeyctlInt(KEYCTL_GET_KEYRING_ID, id, createInt, 0, 0)
  }
  
  // KeyctlSetperm implements the KEYCTL_SETPERM command. The perm value is the
  // key handle permission mask as described in the "keyctl setperm" section of
  // http://man7.org/linux/man-pages/man1/keyctl.1.html.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_setperm.3.html
  func KeyctlSetperm(id int, perm uint32) error {
  	_, err := KeyctlInt(KEYCTL_SETPERM, id, int(perm), 0, 0)
  	return err
  }
  
  //sys	keyctlJoin(cmd int, arg2 string) (ret int, err error) = SYS_KEYCTL
  
  // KeyctlJoinSessionKeyring implements the KEYCTL_JOIN_SESSION_KEYRING command.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_join_session_keyring.3.html
  func KeyctlJoinSessionKeyring(name string) (ringid int, err error) {
  	return keyctlJoin(KEYCTL_JOIN_SESSION_KEYRING, name)
  }
  
  //sys	keyctlSearch(cmd int, arg2 int, arg3 string, arg4 string, arg5 int) (ret int, err error) = SYS_KEYCTL
  
  // KeyctlSearch implements the KEYCTL_SEARCH command.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_search.3.html
  func KeyctlSearch(ringid int, keyType, description string, destRingid int) (id int, err error) {
  	return keyctlSearch(KEYCTL_SEARCH, ringid, keyType, description, destRingid)
  }
  
  //sys	keyctlIOV(cmd int, arg2 int, payload []Iovec, arg5 int) (err error) = SYS_KEYCTL
  
  // KeyctlInstantiateIOV implements the KEYCTL_INSTANTIATE_IOV command. This
  // command is similar to KEYCTL_INSTANTIATE, except that the payload is a slice
  // of Iovec (each of which represents a buffer) instead of a single buffer.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_instantiate_iov.3.html
  func KeyctlInstantiateIOV(id int, payload []Iovec, ringid int) error {
  	return keyctlIOV(KEYCTL_INSTANTIATE_IOV, id, payload, ringid)
  }
  
  //sys	keyctlDH(cmd int, arg2 *KeyctlDHParams, buf []byte) (ret int, err error) = SYS_KEYCTL
  
  // KeyctlDHCompute implements the KEYCTL_DH_COMPUTE command. This command
  // computes a Diffie-Hellman shared secret based on the provide params. The
  // secret is written to the provided buffer and the returned size is the number
  // of bytes written (returning an error if there is insufficient space in the
  // buffer). If a nil buffer is passed in, this function returns the minimum
  // buffer length needed to store the appropriate data. Note that this differs
  // from KEYCTL_READ's behavior which always returns the requested payload size.
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_dh_compute.3.html
  func KeyctlDHCompute(params *KeyctlDHParams, buffer []byte) (size int, err error) {
  	return keyctlDH(KEYCTL_DH_COMPUTE, params, buffer)
  }
  
  // KeyctlRestrictKeyring implements the KEYCTL_RESTRICT_KEYRING command. This
  // command limits the set of keys that can be linked to the keyring, regardless
  // of keyring permissions. The command requires the "setattr" permission.
  //
  // When called with an empty keyType the command locks the keyring, preventing
  // any further keys from being linked to the keyring.
  //
  // The "asymmetric" keyType defines restrictions requiring key payloads to be
  // DER encoded X.509 certificates signed by keys in another keyring. Restrictions
  // for "asymmetric" include "builtin_trusted", "builtin_and_secondary_trusted",
  // "key_or_keyring:<key>", and "key_or_keyring:<key>:chain".
  //
  // As of Linux 4.12, only the "asymmetric" keyType defines type-specific
  // restrictions.
  //
  // See the full documentation at:
  // http://man7.org/linux/man-pages/man3/keyctl_restrict_keyring.3.html
  // http://man7.org/linux/man-pages/man2/keyctl.2.html
  func KeyctlRestrictKeyring(ringid int, keyType string, restriction string) error {
  	if keyType == "" {
  		return keyctlRestrictKeyring(KEYCTL_RESTRICT_KEYRING, ringid)
  	}
  	return keyctlRestrictKeyringByType(KEYCTL_RESTRICT_KEYRING, ringid, keyType, restriction)
  }
  
  //sys keyctlRestrictKeyringByType(cmd int, arg2 int, keyType string, restriction string) (err error) = SYS_KEYCTL
  //sys keyctlRestrictKeyring(cmd int, arg2 int) (err error) = SYS_KEYCTL
  
  func Recvmsg(fd int, p, oob []byte, flags int) (n, oobn int, recvflags int, from Sockaddr, err error) {
  	var msg Msghdr
  	var rsa RawSockaddrAny
  	msg.Name = (*byte)(unsafe.Pointer(&rsa))
  	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 {
  		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)
  			}
  		}
  		msg.Control = &oob[0]
  		msg.SetControllen(len(oob))
  	}
  	msg.Iov = &iov
  	msg.Iovlen = 1
  	if n, err = recvmsg(fd, &msg, flags); err != nil {
  		return
  	}
  	oobn = int(msg.Controllen)
  	recvflags = int(msg.Flags)
  	// source address is only specified if the socket is unconnected
  	if rsa.Addr.Family != AF_UNSPEC {
  		from, err = anyToSockaddr(fd, &rsa)
  	}
  	return
  }
  
  func Sendmsg(fd int, p, oob []byte, to Sockaddr, flags int) (err error) {
  	_, err = SendmsgN(fd, p, oob, to, flags)
  	return
  }
  
  func SendmsgN(fd int, p, oob []byte, to Sockaddr, flags int) (n int, err error) {
  	var ptr unsafe.Pointer
  	var salen _Socklen
  	if to != nil {
  		var err error
  		ptr, salen, err = to.sockaddr()
  		if err != nil {
  			return 0, err
  		}
  	}
  	var msg Msghdr
  	msg.Name = (*byte)(ptr)
  	msg.Namelen = uint32(salen)
  	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 0, err
  			}
  			// send at least one normal byte
  			if sockType != SOCK_DGRAM {
  				iov.Base = &dummy
  				iov.SetLen(1)
  			}
  		}
  		msg.Control = &oob[0]
  		msg.SetControllen(len(oob))
  	}
  	msg.Iov = &iov
  	msg.Iovlen = 1
  	if n, err = sendmsg(fd, &msg, flags); err != nil {
  		return 0, err
  	}
  	if len(oob) > 0 && len(p) == 0 {
  		n = 0
  	}
  	return n, nil
  }
  
  // BindToDevice binds the socket associated with fd to device.
  func BindToDevice(fd int, device string) (err error) {
  	return SetsockoptString(fd, SOL_SOCKET, SO_BINDTODEVICE, device)
  }
  
  //sys	ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
  
  func ptracePeek(req int, pid int, addr uintptr, out []byte) (count int, err error) {
  	// The peek requests are machine-size oriented, so we wrap it
  	// to retrieve arbitrary-length data.
  
  	// The ptrace syscall differs from glibc's ptrace.
  	// Peeks returns the word in *data, not as the return value.
  
  	var buf [SizeofPtr]byte
  
  	// Leading edge. PEEKTEXT/PEEKDATA don't require aligned
  	// access (PEEKUSER warns that it might), but if we don't
  	// align our reads, we might straddle an unmapped page
  	// boundary and not get the bytes leading up to the page
  	// boundary.
  	n := 0
  	if addr%SizeofPtr != 0 {
  		err = ptrace(req, pid, addr-addr%SizeofPtr, uintptr(unsafe.Pointer(&buf[0])))
  		if err != nil {
  			return 0, err
  		}
  		n += copy(out, buf[addr%SizeofPtr:])
  		out = out[n:]
  	}
  
  	// Remainder.
  	for len(out) > 0 {
  		// We use an internal buffer to guarantee alignment.
  		// It's not documented if this is necessary, but we're paranoid.
  		err = ptrace(req, pid, addr+uintptr(n), uintptr(unsafe.Pointer(&buf[0])))
  		if err != nil {
  			return n, err
  		}
  		copied := copy(out, buf[0:])
  		n += copied
  		out = out[copied:]
  	}
  
  	return n, nil
  }
  
  func PtracePeekText(pid int, addr uintptr, out []byte) (count int, err error) {
  	return ptracePeek(PTRACE_PEEKTEXT, pid, addr, out)
  }
  
  func PtracePeekData(pid int, addr uintptr, out []byte) (count int, err error) {
  	return ptracePeek(PTRACE_PEEKDATA, pid, addr, out)
  }
  
  func PtracePeekUser(pid int, addr uintptr, out []byte) (count int, err error) {
  	return ptracePeek(PTRACE_PEEKUSR, pid, addr, out)
  }
  
  func ptracePoke(pokeReq int, peekReq int, pid int, addr uintptr, data []byte) (count int, err error) {
  	// As for ptracePeek, we need to align our accesses to deal
  	// with the possibility of straddling an invalid page.
  
  	// Leading edge.
  	n := 0
  	if addr%SizeofPtr != 0 {
  		var buf [SizeofPtr]byte
  		err = ptrace(peekReq, pid, addr-addr%SizeofPtr, uintptr(unsafe.Pointer(&buf[0])))
  		if err != nil {
  			return 0, err
  		}
  		n += copy(buf[addr%SizeofPtr:], data)
  		word := *((*uintptr)(unsafe.Pointer(&buf[0])))
  		err = ptrace(pokeReq, pid, addr-addr%SizeofPtr, word)
  		if err != nil {
  			return 0, err
  		}
  		data = data[n:]
  	}
  
  	// Interior.
  	for len(data) > SizeofPtr {
  		word := *((*uintptr)(unsafe.Pointer(&data[0])))
  		err = ptrace(pokeReq, pid, addr+uintptr(n), word)
  		if err != nil {
  			return n, err
  		}
  		n += SizeofPtr
  		data = data[SizeofPtr:]
  	}
  
  	// Trailing edge.
  	if len(data) > 0 {
  		var buf [SizeofPtr]byte
  		err = ptrace(peekReq, pid, addr+uintptr(n), uintptr(unsafe.Pointer(&buf[0])))
  		if err != nil {
  			return n, err
  		}
  		copy(buf[0:], data)
  		word := *((*uintptr)(unsafe.Pointer(&buf[0])))
  		err = ptrace(pokeReq, pid, addr+uintptr(n), word)
  		if err != nil {
  			return n, err
  		}
  		n += len(data)
  	}
  
  	return n, nil
  }
  
  func PtracePokeText(pid int, addr uintptr, data []byte) (count int, err error) {
  	return ptracePoke(PTRACE_POKETEXT, PTRACE_PEEKTEXT, pid, addr, data)
  }
  
  func PtracePokeData(pid int, addr uintptr, data []byte) (count int, err error) {
  	return ptracePoke(PTRACE_POKEDATA, PTRACE_PEEKDATA, pid, addr, data)
  }
  
  func PtracePokeUser(pid int, addr uintptr, data []byte) (count int, err error) {
  	return ptracePoke(PTRACE_POKEUSR, PTRACE_PEEKUSR, pid, addr, data)
  }
  
  func PtraceGetRegs(pid int, regsout *PtraceRegs) (err error) {
  	return ptrace(PTRACE_GETREGS, pid, 0, uintptr(unsafe.Pointer(regsout)))
  }
  
  func PtraceSetRegs(pid int, regs *PtraceRegs) (err error) {
  	return ptrace(PTRACE_SETREGS, pid, 0, uintptr(unsafe.Pointer(regs)))
  }
  
  func PtraceSetOptions(pid int, options int) (err error) {
  	return ptrace(PTRACE_SETOPTIONS, pid, 0, uintptr(options))
  }
  
  func PtraceGetEventMsg(pid int) (msg uint, err error) {
  	var data _C_long
  	err = ptrace(PTRACE_GETEVENTMSG, pid, 0, uintptr(unsafe.Pointer(&data)))
  	msg = uint(data)
  	return
  }
  
  func PtraceCont(pid int, signal int) (err error) {
  	return ptrace(PTRACE_CONT, pid, 0, uintptr(signal))
  }
  
  func PtraceSyscall(pid int, signal int) (err error) {
  	return ptrace(PTRACE_SYSCALL, pid, 0, uintptr(signal))
  }
  
  func PtraceSingleStep(pid int) (err error) { return ptrace(PTRACE_SINGLESTEP, pid, 0, 0) }
  
  func PtraceAttach(pid int) (err error) { return ptrace(PTRACE_ATTACH, pid, 0, 0) }
  
  func PtraceDetach(pid int) (err error) { return ptrace(PTRACE_DETACH, pid, 0, 0) }
  
  //sys	reboot(magic1 uint, magic2 uint, cmd int, arg string) (err error)
  
  func Reboot(cmd int) (err error) {
  	return reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd, "")
  }
  
  func direntIno(buf []byte) (uint64, bool) {
  	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
  }
  
  func direntReclen(buf []byte) (uint64, bool) {
  	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
  }
  
  func direntNamlen(buf []byte) (uint64, bool) {
  	reclen, ok := direntReclen(buf)
  	if !ok {
  		return 0, false
  	}
  	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
  }
  
  //sys	mount(source string, target string, fstype string, flags uintptr, data *byte) (err error)
  
  func Mount(source string, target string, fstype string, flags uintptr, data string) (err error) {
  	// Certain file systems get rather angry and EINVAL if you give
  	// them an empty string of data, rather than NULL.
  	if data == "" {
  		return mount(source, target, fstype, flags, nil)
  	}
  	datap, err := BytePtrFromString(data)
  	if err != nil {
  		return err
  	}
  	return mount(source, target, fstype, flags, datap)
  }
  
  func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) {
  	if raceenabled {
  		raceReleaseMerge(unsafe.Pointer(&ioSync))
  	}
  	return sendfile(outfd, infd, offset, count)
  }
  
  // Sendto
  // Recvfrom
  // Socketpair
  
  /*
   * Direct access
   */
  //sys	Acct(path string) (err error)
  //sys	AddKey(keyType string, description string, payload []byte, ringid int) (id int, err error)
  //sys	Adjtimex(buf *Timex) (state int, err error)
  //sys	Capget(hdr *CapUserHeader, data *CapUserData) (err error)
  //sys	Capset(hdr *CapUserHeader, data *CapUserData) (err error)
  //sys	Chdir(path string) (err error)
  //sys	Chroot(path string) (err error)
  //sys	ClockGetres(clockid int32, res *Timespec) (err error)
  //sys	ClockGettime(clockid int32, time *Timespec) (err error)
  //sys	ClockNanosleep(clockid int32, flags int, request *Timespec, remain *Timespec) (err error)
  //sys	Close(fd int) (err error)
  //sys	CopyFileRange(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error)
  //sys	DeleteModule(name string, flags int) (err error)
  //sys	Dup(oldfd int) (fd int, err error)
  //sys	Dup3(oldfd int, newfd int, flags int) (err error)
  //sysnb	EpollCreate1(flag int) (fd int, err error)
  //sysnb	EpollCtl(epfd int, op int, fd int, event *EpollEvent) (err error)
  //sys	Eventfd(initval uint, flags int) (fd int, err error) = SYS_EVENTFD2
  //sys	Exit(code int) = SYS_EXIT_GROUP
  //sys	Fallocate(fd int, mode uint32, off int64, len int64) (err error)
  //sys	Fchdir(fd int) (err error)
  //sys	Fchmod(fd int, mode uint32) (err error)
  //sys	Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error)
  //sys	fcntl(fd int, cmd int, arg int) (val 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)
  //sys	Fsync(fd int) (err error)
  //sys	Getdents(fd int, buf []byte) (n int, err error) = SYS_GETDENTS64
  //sysnb	Getpgid(pid int) (pgid int, err error)
  
  func Getpgrp() (pid int) {
  	pid, _ = Getpgid(0)
  	return
  }
  
  //sysnb	Getpid() (pid int)
  //sysnb	Getppid() (ppid int)
  //sys	Getpriority(which int, who int) (prio int, err error)
  //sys	Getrandom(buf []byte, flags int) (n int, err error)
  //sysnb	Getrusage(who int, rusage *Rusage) (err error)
  //sysnb	Getsid(pid int) (sid int, err error)
  //sysnb	Gettid() (tid int)
  //sys	Getxattr(path string, attr string, dest []byte) (sz int, err error)
  //sys	InitModule(moduleImage []byte, params string) (err error)
  //sys	InotifyAddWatch(fd int, pathname string, mask uint32) (watchdesc int, err error)
  //sysnb	InotifyInit1(flags int) (fd int, err error)
  //sysnb	InotifyRmWatch(fd int, watchdesc uint32) (success int, err error)
  //sysnb	Kill(pid int, sig syscall.Signal) (err error)
  //sys	Klogctl(typ int, buf []byte) (n int, err error) = SYS_SYSLOG
  //sys	Lgetxattr(path string, attr string, dest []byte) (sz int, err error)
  //sys	Listxattr(path string, dest []byte) (sz int, err error)
  //sys	Llistxattr(path string, dest []byte) (sz int, err error)
  //sys	Lremovexattr(path string, attr string) (err error)
  //sys	Lsetxattr(path string, attr string, data []byte, flags int) (err error)
  //sys	MemfdCreate(name string, flags int) (fd int, err error)
  //sys	Mkdirat(dirfd int, path string, mode uint32) (err error)
  //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (err error)
  //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
  //sys	PerfEventOpen(attr *PerfEventAttr, pid int, cpu int, groupFd int, flags int) (fd int, err error)
  //sys	PivotRoot(newroot string, putold string) (err error) = SYS_PIVOT_ROOT
  //sysnb prlimit(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) = SYS_PRLIMIT64
  //sys   Prctl(option int, arg2 uintptr, arg3 uintptr, arg4 uintptr, arg5 uintptr) (err error)
  //sys	Pselect(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *Timespec, sigmask *Sigset_t) (n int, err error) = SYS_PSELECT6
  //sys	read(fd int, p []byte) (n int, err error)
  //sys	Removexattr(path string, attr string) (err error)
  //sys	Renameat2(olddirfd int, oldpath string, newdirfd int, newpath string, flags uint) (err error)
  //sys	RequestKey(keyType string, description string, callback string, destRingid int) (id int, err error)
  //sys	Setdomainname(p []byte) (err error)
  //sys	Sethostname(p []byte) (err error)
  //sysnb	Setpgid(pid int, pgid int) (err error)
  //sysnb	Setsid() (pid int, err error)
  //sysnb	Settimeofday(tv *Timeval) (err error)
  //sys	Setns(fd int, nstype int) (err error)
  
  // issue 1435.
  // On linux Setuid and Setgid only affects the current thread, not the process.
  // This does not match what most callers expect so we must return an error
  // here rather than letting the caller think that the call succeeded.
  
  func Setuid(uid int) (err error) {
  	return EOPNOTSUPP
  }
  
  func Setgid(uid int) (err error) {
  	return EOPNOTSUPP
  }
  
  func Signalfd(fd int, sigmask *Sigset_t, flags int) (newfd int, err error) {
  	return signalfd(fd, sigmask, _C__NSIG/8, flags)
  }
  
  //sys	Setpriority(which int, who int, prio int) (err error)
  //sys	Setxattr(path string, attr string, data []byte, flags int) (err error)
  //sys	signalfd(fd int, sigmask *Sigset_t, maskSize uintptr, flags int) (newfd int, err error) = SYS_SIGNALFD4
  //sys	Statx(dirfd int, path string, flags int, mask int, stat *Statx_t) (err error)
  //sys	Sync()
  //sys	Syncfs(fd int) (err error)
  //sysnb	Sysinfo(info *Sysinfo_t) (err error)
  //sys	Tee(rfd int, wfd int, len int, flags int) (n int64, err error)
  //sysnb	Tgkill(tgid int, tid int, sig syscall.Signal) (err error)
  //sysnb	Times(tms *Tms) (ticks uintptr, err error)
  //sysnb	Umask(mask int) (oldmask int)
  //sysnb	Uname(buf *Utsname) (err error)
  //sys	Unmount(target string, flags int) (err error) = SYS_UMOUNT2
  //sys	Unshare(flags int) (err error)
  //sys	write(fd int, p []byte) (n int, err error)
  //sys	exitThread(code int) (err error) = SYS_EXIT
  //sys	readlen(fd int, p *byte, np int) (n int, err error) = SYS_READ
  //sys	writelen(fd int, p *byte, np int) (n int, err error) = SYS_WRITE
  
  // mmap varies by architecture; see syscall_linux_*.go.
  //sys	munmap(addr uintptr, length uintptr) (err error)
  
  var mapper = &mmapper{
  	active: make(map[*byte][]byte),
  	mmap:   mmap,
  	munmap: munmap,
  }
  
  func Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
  	return mapper.Mmap(fd, offset, length, prot, flags)
  }
  
  func Munmap(b []byte) (err error) {
  	return mapper.Munmap(b)
  }
  
  //sys	Madvise(b []byte, advice int) (err error)
  //sys	Mprotect(b []byte, prot int) (err error)
  //sys	Mlock(b []byte) (err error)
  //sys	Mlockall(flags int) (err error)
  //sys	Msync(b []byte, flags int) (err error)
  //sys	Munlock(b []byte) (err error)
  //sys	Munlockall() (err error)
  
  // Vmsplice splices user pages from a slice of Iovecs into a pipe specified by fd,
  // using the specified flags.
  func Vmsplice(fd int, iovs []Iovec, flags int) (int, error) {
  	var p unsafe.Pointer
  	if len(iovs) > 0 {
  		p = unsafe.Pointer(&iovs[0])
  	}
  
  	n, _, errno := Syscall6(SYS_VMSPLICE, uintptr(fd), uintptr(p), uintptr(len(iovs)), uintptr(flags), 0, 0)
  	if errno != 0 {
  		return 0, syscall.Errno(errno)
  	}
  
  	return int(n), nil
  }
  
  //sys	faccessat(dirfd int, path string, mode uint32) (err error)
  
  func Faccessat(dirfd int, path string, mode uint32, flags int) (err error) {
  	if flags & ^(AT_SYMLINK_NOFOLLOW|AT_EACCESS) != 0 {
  		return EINVAL
  	}
  
  	// The Linux kernel faccessat system call does not take any flags.
  	// The glibc faccessat implements the flags itself; see
  	// https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/faccessat.c;hb=HEAD
  	// Because people naturally expect syscall.Faccessat to act
  	// like C faccessat, we do the same.
  
  	if flags == 0 {
  		return faccessat(dirfd, path, mode)
  	}
  
  	var st Stat_t
  	if err := Fstatat(dirfd, path, &st, flags&AT_SYMLINK_NOFOLLOW); err != nil {
  		return err
  	}
  
  	mode &= 7
  	if mode == 0 {
  		return nil
  	}
  
  	var uid int
  	if flags&AT_EACCESS != 0 {
  		uid = Geteuid()
  	} else {
  		uid = Getuid()
  	}
  
  	if uid == 0 {
  		if mode&1 == 0 {
  			// Root can read and write any file.
  			return nil
  		}
  		if st.Mode&0111 != 0 {
  			// Root can execute any file that anybody can execute.
  			return nil
  		}
  		return EACCES
  	}
  
  	var fmode uint32
  	if uint32(uid) == st.Uid {
  		fmode = (st.Mode >> 6) & 7
  	} else {
  		var gid int
  		if flags&AT_EACCESS != 0 {
  			gid = Getegid()
  		} else {
  			gid = Getgid()
  		}
  
  		if uint32(gid) == st.Gid {
  			fmode = (st.Mode >> 3) & 7
  		} else {
  			fmode = st.Mode & 7
  		}
  	}
  
  	if fmode&mode == mode {
  		return nil
  	}
  
  	return EACCES
  }
  
  //sys nameToHandleAt(dirFD int, pathname string, fh *fileHandle, mountID *_C_int, flags int) (err error) = SYS_NAME_TO_HANDLE_AT
  //sys openByHandleAt(mountFD int, fh *fileHandle, flags int) (fd int, err error) = SYS_OPEN_BY_HANDLE_AT
  
  // fileHandle is the argument to nameToHandleAt and openByHandleAt. We
  // originally tried to generate it via unix/linux/types.go with "type
  // fileHandle C.struct_file_handle" but that generated empty structs
  // for mips64 and mips64le. Instead, hard code it for now (it's the
  // same everywhere else) until the mips64 generator issue is fixed.
  type fileHandle struct {
  	Bytes uint32
  	Type  int32
  }
  
  // FileHandle represents the C struct file_handle used by
  // name_to_handle_at (see NameToHandleAt) and open_by_handle_at (see
  // OpenByHandleAt).
  type FileHandle struct {
  	*fileHandle
  }
  
  // NewFileHandle constructs a FileHandle.
  func NewFileHandle(handleType int32, handle []byte) FileHandle {
  	const hdrSize = unsafe.Sizeof(fileHandle{})
  	buf := make([]byte, hdrSize+uintptr(len(handle)))
  	copy(buf[hdrSize:], handle)
  	fh := (*fileHandle)(unsafe.Pointer(&buf[0]))
  	fh.Type = handleType
  	fh.Bytes = uint32(len(handle))
  	return FileHandle{fh}
  }
  
  func (fh *FileHandle) Size() int   { return int(fh.fileHandle.Bytes) }
  func (fh *FileHandle) Type() int32 { return fh.fileHandle.Type }
  func (fh *FileHandle) Bytes() []byte {
  	n := fh.Size()
  	if n == 0 {
  		return nil
  	}
  	return (*[1 << 30]byte)(unsafe.Pointer(uintptr(unsafe.Pointer(&fh.fileHandle.Type)) + 4))[:n:n]
  }
  
  // NameToHandleAt wraps the name_to_handle_at system call; it obtains
  // a handle for a path name.
  func NameToHandleAt(dirfd int, path string, flags int) (handle FileHandle, mountID int, err error) {
  	var mid _C_int
  	// Try first with a small buffer, assuming the handle will
  	// only be 32 bytes.
  	size := uint32(32 + unsafe.Sizeof(fileHandle{}))
  	didResize := false
  	for {
  		buf := make([]byte, size)
  		fh := (*fileHandle)(unsafe.Pointer(&buf[0]))
  		fh.Bytes = size - uint32(unsafe.Sizeof(fileHandle{}))
  		err = nameToHandleAt(dirfd, path, fh, &mid, flags)
  		if err == EOVERFLOW {
  			if didResize {
  				// We shouldn't need to resize more than once
  				return
  			}
  			didResize = true
  			size = fh.Bytes + uint32(unsafe.Sizeof(fileHandle{}))
  			continue
  		}
  		if err != nil {
  			return
  		}
  		return FileHandle{fh}, int(mid), nil
  	}
  }
  
  // OpenByHandleAt wraps the open_by_handle_at system call; it opens a
  // file via a handle as previously returned by NameToHandleAt.
  func OpenByHandleAt(mountFD int, handle FileHandle, flags int) (fd int, err error) {
  	return openByHandleAt(mountFD, handle.fileHandle, flags)
  }
  
  /*
   * Unimplemented
   */
  // AfsSyscall
  // Alarm
  // ArchPrctl
  // Brk
  // ClockNanosleep
  // ClockSettime
  // Clone
  // EpollCtlOld
  // EpollPwait
  // EpollWaitOld
  // Execve
  // Fork
  // Futex
  // GetKernelSyms
  // GetMempolicy
  // GetRobustList
  // GetThreadArea
  // Getitimer
  // Getpmsg
  // IoCancel
  // IoDestroy
  // IoGetevents
  // IoSetup
  // IoSubmit
  // IoprioGet
  // IoprioSet
  // KexecLoad
  // LookupDcookie
  // Mbind
  // MigratePages
  // Mincore
  // ModifyLdt
  // Mount
  // MovePages
  // MqGetsetattr
  // MqNotify
  // MqOpen
  // MqTimedreceive
  // MqTimedsend
  // MqUnlink
  // Mremap
  // Msgctl
  // Msgget
  // Msgrcv
  // Msgsnd
  // Nfsservctl
  // Personality
  // Pselect6
  // Ptrace
  // Putpmsg
  // Quotactl
  // Readahead
  // Readv
  // RemapFilePages
  // RestartSyscall
  // RtSigaction
  // RtSigpending
  // RtSigprocmask
  // RtSigqueueinfo
  // RtSigreturn
  // RtSigsuspend
  // RtSigtimedwait
  // SchedGetPriorityMax
  // SchedGetPriorityMin
  // SchedGetparam
  // SchedGetscheduler
  // SchedRrGetInterval
  // SchedSetparam
  // SchedYield
  // Security
  // Semctl
  // Semget
  // Semop
  // Semtimedop
  // SetMempolicy
  // SetRobustList
  // SetThreadArea
  // SetTidAddress
  // Shmat
  // Shmctl
  // Shmdt
  // Shmget
  // Sigaltstack
  // Swapoff
  // Swapon
  // Sysfs
  // TimerCreate
  // TimerDelete
  // TimerGetoverrun
  // TimerGettime
  // TimerSettime
  // Timerfd
  // Tkill (obsolete)
  // Tuxcall
  // Umount2
  // Uselib
  // Utimensat
  // Vfork
  // Vhangup
  // Vserver
  // Waitid
  // _Sysctl
  