usb-ks

syscall_linux.go (72891B)

---

 // 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"
 	"syscall"
 	"time"
 	"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)
 }
 
 func EpollCreate(size int) (fd int, err error) {
 	if size <= 0 {
 		return -1, EINVAL
 	}
 	return EpollCreate1(0)
 }
 
 //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)
 }
 
 func InotifyInit() (fd int, err error) {
 	return InotifyInit1(0)
 }
 
 //sys	ioctl(fd int, req uint, arg uintptr) (err error) = SYS_IOCTL
 //sys	ioctlPtr(fd int, req uint, arg unsafe.Pointer) (err error) = SYS_IOCTL
 
 // ioctl itself should not be exposed directly, but additional get/set functions
 // for specific types are permissible. These are defined in ioctl.go and
 // ioctl_linux.go.
 //
 // The third argument to ioctl is often a pointer but sometimes an integer.
 // Callers should use ioctlPtr when the third argument is a pointer and ioctl
 // when the third argument is an integer.
 //
 // TODO: some existing code incorrectly uses ioctl when it should use ioctlPtr.
 
 //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	openat2(dirfd int, path string, open_how *OpenHow, size int) (fd int, err error)
 
 func Openat2(dirfd int, path string, how *OpenHow) (fd int, err error) {
 	return openat2(dirfd, path, how, SizeofOpenHow)
 }
 
 func Pipe(p []int) error {
 	return Pipe2(p, 0)
 }
 
 //sysnb	pipe2(p *[2]_C_int, flags int) (err error)
 
 func Pipe2(p []int, flags int) error {
 	if len(p) != 2 {
 		return EINVAL
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
 	if err == nil {
 		p[0] = int(pp[0])
 		p[1] = int(pp[1])
 	}
 	return err
 }
 
 //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)
 }
 
 func Poll(fds []PollFd, timeout int) (n int, err error) {
 	var ts *Timespec
 	if timeout >= 0 {
 		ts = new(Timespec)
 		*ts = NsecToTimespec(int64(timeout) * 1e6)
 	}
 	return Ppoll(fds, ts, nil)
 }
 
 //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 {
 	return UtimesNanoAt(AT_FDCWD, path, ts, 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
 	}
 	// In some cases, Linux can return a path that starts with the
 	// "(unreachable)" prefix, which can potentially be a valid relative
 	// path. To work around that, return ENOENT if path is not absolute.
 	if buf[0] != '/' {
 		return "", ENOENT
 	}
 
 	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
 }
 
 //sys	Waitid(idType int, id int, info *Siginfo, options int, rusage *Rusage) (err error)
 
 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)
 	sa.raw.Addr = sa.Addr
 	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
 	sa.raw.Addr = sa.Addr
 	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
 	sa.raw.Addr = sa.Addr
 	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
 }
 
 // SockaddrCANJ1939 implements the Sockaddr interface for AF_CAN using J1939
 // protocol (https://en.wikipedia.org/wiki/SAE_J1939). For more information
 // on the purposes of the fields, check the official linux kernel documentation
 // available here: https://www.kernel.org/doc/Documentation/networking/j1939.rst
 type SockaddrCANJ1939 struct {
 	Ifindex int
 	Name    uint64
 	PGN     uint32
 	Addr    uint8
 	raw     RawSockaddrCAN
 }
 
 func (sa *SockaddrCANJ1939) 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)
 	n := (*[8]byte)(unsafe.Pointer(&sa.Name))
 	for i := 0; i < 8; i++ {
 		sa.raw.Addr[i] = n[i]
 	}
 	p := (*[4]byte)(unsafe.Pointer(&sa.PGN))
 	for i := 0; i < 4; i++ {
 		sa.raw.Addr[i+8] = p[i]
 	}
 	sa.raw.Addr[12] = sa.Addr
 	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_LOCAL: refers to local communication (loopback).
 	//  - VMADDR_CID_HOST: refers to other processes on the host.
 	CID   uint32
 	Port  uint32
 	Flags uint8
 	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
 	sa.raw.Flags = sa.Flags
 
 	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
 }
 
 // SockaddrL2TPIP implements the Sockaddr interface for IPPROTO_L2TP/AF_INET sockets.
 type SockaddrL2TPIP struct {
 	Addr   [4]byte
 	ConnId uint32
 	raw    RawSockaddrL2TPIP
 }
 
 func (sa *SockaddrL2TPIP) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Family = AF_INET
 	sa.raw.Conn_id = sa.ConnId
 	sa.raw.Addr = sa.Addr
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrL2TPIP, nil
 }
 
 // SockaddrL2TPIP6 implements the Sockaddr interface for IPPROTO_L2TP/AF_INET6 sockets.
 type SockaddrL2TPIP6 struct {
 	Addr   [16]byte
 	ZoneId uint32
 	ConnId uint32
 	raw    RawSockaddrL2TPIP6
 }
 
 func (sa *SockaddrL2TPIP6) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Family = AF_INET6
 	sa.raw.Conn_id = sa.ConnId
 	sa.raw.Scope_id = sa.ZoneId
 	sa.raw.Addr = sa.Addr
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrL2TPIP6, nil
 }
 
 // SockaddrIUCV implements the Sockaddr interface for AF_IUCV sockets.
 type SockaddrIUCV struct {
 	UserID string
 	Name   string
 	raw    RawSockaddrIUCV
 }
 
 func (sa *SockaddrIUCV) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Family = AF_IUCV
 	// These are EBCDIC encoded by the kernel, but we still need to pad them
 	// with blanks. Initializing with blanks allows the caller to feed in either
 	// a padded or an unpadded string.
 	for i := 0; i < 8; i++ {
 		sa.raw.Nodeid[i] = ' '
 		sa.raw.User_id[i] = ' '
 		sa.raw.Name[i] = ' '
 	}
 	if len(sa.UserID) > 8 || len(sa.Name) > 8 {
 		return nil, 0, EINVAL
 	}
 	for i, b := range []byte(sa.UserID[:]) {
 		sa.raw.User_id[i] = int8(b)
 	}
 	for i, b := range []byte(sa.Name[:]) {
 		sa.raw.Name[i] = int8(b)
 	}
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrIUCV, nil
 }
 
 type SockaddrNFC struct {
 	DeviceIdx   uint32
 	TargetIdx   uint32
 	NFCProtocol uint32
 	raw         RawSockaddrNFC
 }
 
 func (sa *SockaddrNFC) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Sa_family = AF_NFC
 	sa.raw.Dev_idx = sa.DeviceIdx
 	sa.raw.Target_idx = sa.TargetIdx
 	sa.raw.Nfc_protocol = sa.NFCProtocol
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrNFC, nil
 }
 
 type SockaddrNFCLLCP struct {
 	DeviceIdx      uint32
 	TargetIdx      uint32
 	NFCProtocol    uint32
 	DestinationSAP uint8
 	SourceSAP      uint8
 	ServiceName    string
 	raw            RawSockaddrNFCLLCP
 }
 
 func (sa *SockaddrNFCLLCP) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Sa_family = AF_NFC
 	sa.raw.Dev_idx = sa.DeviceIdx
 	sa.raw.Target_idx = sa.TargetIdx
 	sa.raw.Nfc_protocol = sa.NFCProtocol
 	sa.raw.Dsap = sa.DestinationSAP
 	sa.raw.Ssap = sa.SourceSAP
 	if len(sa.ServiceName) > len(sa.raw.Service_name) {
 		return nil, 0, EINVAL
 	}
 	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))
 		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
 		sa.Addr = pp.Addr
 		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 := (*[len(pp.Path)]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
 		sa.Name = string(bytes)
 		return sa, nil
 
 	case AF_INET:
 		proto, err := socketProtocol(fd)
 		if err != nil {
 			return nil, err
 		}
 
 		switch proto {
 		case IPPROTO_L2TP:
 			pp := (*RawSockaddrL2TPIP)(unsafe.Pointer(rsa))
 			sa := new(SockaddrL2TPIP)
 			sa.ConnId = pp.Conn_id
 			sa.Addr = pp.Addr
 			return sa, nil
 		default:
 			pp := (*RawSockaddrInet4)(unsafe.Pointer(rsa))
 			sa := new(SockaddrInet4)
 			p := (*[2]byte)(unsafe.Pointer(&pp.Port))
 			sa.Port = int(p[0])<<8 + int(p[1])
 			sa.Addr = pp.Addr
 			return sa, nil
 		}
 
 	case AF_INET6:
 		proto, err := socketProtocol(fd)
 		if err != nil {
 			return nil, err
 		}
 
 		switch proto {
 		case IPPROTO_L2TP:
 			pp := (*RawSockaddrL2TPIP6)(unsafe.Pointer(rsa))
 			sa := new(SockaddrL2TPIP6)
 			sa.ConnId = pp.Conn_id
 			sa.ZoneId = pp.Scope_id
 			sa.Addr = pp.Addr
 			return sa, nil
 		default:
 			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
 			sa.Addr = pp.Addr
 			return sa, nil
 		}
 
 	case AF_VSOCK:
 		pp := (*RawSockaddrVM)(unsafe.Pointer(rsa))
 		sa := &SockaddrVM{
 			CID:   pp.Cid,
 			Port:  pp.Port,
 			Flags: pp.Flags,
 		}
 		return sa, nil
 	case AF_BLUETOOTH:
 		proto, err := socketProtocol(fd)
 		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
 	case AF_IUCV:
 		pp := (*RawSockaddrIUCV)(unsafe.Pointer(rsa))
 
 		var user [8]byte
 		var name [8]byte
 
 		for i := 0; i < 8; i++ {
 			user[i] = byte(pp.User_id[i])
 			name[i] = byte(pp.Name[i])
 		}
 
 		sa := &SockaddrIUCV{
 			UserID: string(user[:]),
 			Name:   string(name[:]),
 		}
 		return sa, nil
 
 	case AF_CAN:
 		proto, err := socketProtocol(fd)
 		if err != nil {
 			return nil, err
 		}
 
 		pp := (*RawSockaddrCAN)(unsafe.Pointer(rsa))
 
 		switch proto {
 		case CAN_J1939:
 			sa := &SockaddrCANJ1939{
 				Ifindex: int(pp.Ifindex),
 			}
 			name := (*[8]byte)(unsafe.Pointer(&sa.Name))
 			for i := 0; i < 8; i++ {
 				name[i] = pp.Addr[i]
 			}
 			pgn := (*[4]byte)(unsafe.Pointer(&sa.PGN))
 			for i := 0; i < 4; i++ {
 				pgn[i] = pp.Addr[i+8]
 			}
 			addr := (*[1]byte)(unsafe.Pointer(&sa.Addr))
 			addr[0] = pp.Addr[12]
 			return sa, nil
 		default:
 			sa := &SockaddrCAN{
 				Ifindex: int(pp.Ifindex),
 			}
 			rx := (*[4]byte)(unsafe.Pointer(&sa.RxID))
 			for i := 0; i < 4; i++ {
 				rx[i] = pp.Addr[i]
 			}
 			tx := (*[4]byte)(unsafe.Pointer(&sa.TxID))
 			for i := 0; i < 4; i++ {
 				tx[i] = pp.Addr[i+4]
 			}
 			return sa, nil
 		}
 	case AF_NFC:
 		proto, err := socketProtocol(fd)
 		if err != nil {
 			return nil, err
 		}
 		switch proto {
 		case NFC_SOCKPROTO_RAW:
 			pp := (*RawSockaddrNFC)(unsafe.Pointer(rsa))
 			sa := &SockaddrNFC{
 				DeviceIdx:   pp.Dev_idx,
 				TargetIdx:   pp.Target_idx,
 				NFCProtocol: pp.Nfc_protocol,
 			}
 			return sa, nil
 		case NFC_SOCKPROTO_LLCP:
 			pp := (*RawSockaddrNFCLLCP)(unsafe.Pointer(rsa))
 			if uint64(pp.Service_name_len) > uint64(len(pp.Service_name)) {
 				return nil, EINVAL
 			}
 			sa := &SockaddrNFCLLCP{
 				DeviceIdx:      pp.Dev_idx,
 				TargetIdx:      pp.Target_idx,
 				NFCProtocol:    pp.Nfc_protocol,
 				DestinationSAP: pp.Dsap,
 				SourceSAP:      pp.Ssap,
 				ServiceName:    string(pp.Service_name[:pp.Service_name_len]),
 			}
 			return sa, nil
 		default:
 			return nil, EINVAL
 		}
 	}
 	return nil, EAFNOSUPPORT
 }
 
 func Accept(fd int) (nfd int, sa Sockaddr, err error) {
 	var rsa RawSockaddrAny
 	var len _Socklen = SizeofSockaddrAny
 	nfd, err = accept4(fd, &rsa, &len, 0)
 	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))
 }
 
 func SetsockoptTCPRepairOpt(fd, level, opt int, o []TCPRepairOpt) (err error) {
 	if len(o) == 0 {
 		return EINVAL
 	}
 	return setsockopt(fd, level, opt, unsafe.Pointer(&o[0]), uintptr(SizeofTCPRepairOpt*len(o)))
 }
 
 // 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 recvmsgRaw(fd int, p, oob []byte, flags int, rsa *RawSockaddrAny) (n, oobn int, recvflags int, err error) {
 	var msg Msghdr
 	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)
 	return
 }
 
 func sendmsgN(fd int, p, oob []byte, ptr unsafe.Pointer, salen _Socklen, flags int) (n int, err error) {
 	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 PtraceInterrupt(pid int) (err error) { return ptrace(PTRACE_INTERRUPT, pid, 0, 0) }
 
 func PtraceAttach(pid int) (err error) { return ptrace(PTRACE_ATTACH, pid, 0, 0) }
 
 func PtraceSeize(pid int) (err error) { return ptrace(PTRACE_SEIZE, 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)
 }
 
 //sys	mountSetattr(dirfd int, pathname string, flags uint, attr *MountAttr, size uintptr) (err error) = SYS_MOUNT_SETATTR
 
 // MountSetattr is a wrapper for mount_setattr(2).
 // https://man7.org/linux/man-pages/man2/mount_setattr.2.html
 //
 // Requires kernel >= 5.12.
 func MountSetattr(dirfd int, pathname string, flags uint, attr *MountAttr) error {
 	return mountSetattr(dirfd, pathname, flags, attr, unsafe.Sizeof(*attr))
 }
 
 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)
 //sysnb	Capget(hdr *CapUserHeader, data *CapUserData) (err error)
 //sysnb	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	CloseRange(first uint, last uint, flags uint) (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)
 
 func Dup2(oldfd, newfd int) error {
 	return Dup3(oldfd, newfd, 0)
 }
 
 //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	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	Fsmount(fd int, flags int, mountAttrs int) (fsfd int, err error)
 //sys	Fsopen(fsName string, flags int) (fd int, err error)
 //sys	Fspick(dirfd int, pathName string, flags int) (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	MoveMount(fromDirfd int, fromPathName string, toDirfd int, toPathName string, flags int) (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
 //sys	OpenTree(dfd int, fileName string, flags uint) (r int, 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)
 
 // PrctlRetInt performs a prctl operation specified by option and further
 // optional arguments arg2 through arg5 depending on option. It returns a
 // non-negative integer that is returned by the prctl syscall.
 func PrctlRetInt(option int, arg2 uintptr, arg3 uintptr, arg4 uintptr, arg5 uintptr) (int, error) {
 	ret, _, err := Syscall6(SYS_PRCTL, uintptr(option), uintptr(arg2), uintptr(arg3), uintptr(arg4), uintptr(arg5), 0)
 	if err != 0 {
 		return 0, err
 	}
 	return int(ret), nil
 }
 
 // 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
 }
 
 // SetfsgidRetGid sets fsgid for current thread and returns previous fsgid set.
 // setfsgid(2) will return a non-nil error only if its caller lacks CAP_SETUID capability.
 // If the call fails due to other reasons, current fsgid will be returned.
 func SetfsgidRetGid(gid int) (int, error) {
 	return setfsgid(gid)
 }
 
 // SetfsuidRetUid sets fsuid for current thread and returns previous fsuid set.
 // setfsgid(2) will return a non-nil error only if its caller lacks CAP_SETUID capability
 // If the call fails due to other reasons, current fsuid will be returned.
 func SetfsuidRetUid(uid int) (int, error) {
 	return setfsuid(uid)
 }
 
 func Setfsgid(gid int) error {
 	_, err := setfsgid(gid)
 	return err
 }
 
 func Setfsuid(uid int) error {
 	_, err := setfsuid(uid)
 	return err
 }
 
 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	TimerfdCreate(clockid int, flags int) (fd int, err error)
 //sysnb	TimerfdGettime(fd int, currValue *ItimerSpec) (err error)
 //sysnb	TimerfdSettime(fd int, flags int, newValue *ItimerSpec, oldValue *ItimerSpec) (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
 //sys	readv(fd int, iovs []Iovec) (n int, err error) = SYS_READV
 //sys	writev(fd int, iovs []Iovec) (n int, err error) = SYS_WRITEV
 //sys	preadv(fd int, iovs []Iovec, offs_l uintptr, offs_h uintptr) (n int, err error) = SYS_PREADV
 //sys	pwritev(fd int, iovs []Iovec, offs_l uintptr, offs_h uintptr) (n int, err error) = SYS_PWRITEV
 //sys	preadv2(fd int, iovs []Iovec, offs_l uintptr, offs_h uintptr, flags int) (n int, err error) = SYS_PREADV2
 //sys	pwritev2(fd int, iovs []Iovec, offs_l uintptr, offs_h uintptr, flags int) (n int, err error) = SYS_PWRITEV2
 
 func bytes2iovec(bs [][]byte) []Iovec {
 	iovecs := make([]Iovec, len(bs))
 	for i, b := range bs {
 		iovecs[i].SetLen(len(b))
 		if len(b) > 0 {
 			iovecs[i].Base = &b[0]
 		} else {
 			iovecs[i].Base = (*byte)(unsafe.Pointer(&_zero))
 		}
 	}
 	return iovecs
 }
 
 // offs2lohi splits offs into its lower and upper unsigned long. On 64-bit
 // systems, hi will always be 0. On 32-bit systems, offs will be split in half.
 // preadv/pwritev chose this calling convention so they don't need to add a
 // padding-register for alignment on ARM.
 func offs2lohi(offs int64) (lo, hi uintptr) {
 	return uintptr(offs), uintptr(uint64(offs) >> SizeofLong)
 }
 
 func Readv(fd int, iovs [][]byte) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	n, err = readv(fd, iovecs)
 	readvRacedetect(iovecs, n, err)
 	return n, err
 }
 
 func Preadv(fd int, iovs [][]byte, offset int64) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	lo, hi := offs2lohi(offset)
 	n, err = preadv(fd, iovecs, lo, hi)
 	readvRacedetect(iovecs, n, err)
 	return n, err
 }
 
 func Preadv2(fd int, iovs [][]byte, offset int64, flags int) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	lo, hi := offs2lohi(offset)
 	n, err = preadv2(fd, iovecs, lo, hi, flags)
 	readvRacedetect(iovecs, n, err)
 	return n, err
 }
 
 func readvRacedetect(iovecs []Iovec, n int, err error) {
 	if !raceenabled {
 		return
 	}
 	for i := 0; n > 0 && i < len(iovecs); i++ {
 		m := int(iovecs[i].Len)
 		if m > n {
 			m = n
 		}
 		n -= m
 		if m > 0 {
 			raceWriteRange(unsafe.Pointer(iovecs[i].Base), m)
 		}
 	}
 	if err == nil {
 		raceAcquire(unsafe.Pointer(&ioSync))
 	}
 }
 
 func Writev(fd int, iovs [][]byte) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	if raceenabled {
 		raceReleaseMerge(unsafe.Pointer(&ioSync))
 	}
 	n, err = writev(fd, iovecs)
 	writevRacedetect(iovecs, n)
 	return n, err
 }
 
 func Pwritev(fd int, iovs [][]byte, offset int64) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	if raceenabled {
 		raceReleaseMerge(unsafe.Pointer(&ioSync))
 	}
 	lo, hi := offs2lohi(offset)
 	n, err = pwritev(fd, iovecs, lo, hi)
 	writevRacedetect(iovecs, n)
 	return n, err
 }
 
 func Pwritev2(fd int, iovs [][]byte, offset int64, flags int) (n int, err error) {
 	iovecs := bytes2iovec(iovs)
 	if raceenabled {
 		raceReleaseMerge(unsafe.Pointer(&ioSync))
 	}
 	lo, hi := offs2lohi(offset)
 	n, err = pwritev2(fd, iovecs, lo, hi, flags)
 	writevRacedetect(iovecs, n)
 	return n, err
 }
 
 func writevRacedetect(iovecs []Iovec, n int) {
 	if !raceenabled {
 		return
 	}
 	for i := 0; n > 0 && i < len(iovecs); i++ {
 		m := int(iovecs[i].Len)
 		if m > n {
 			m = n
 		}
 		n -= m
 		if m > 0 {
 			raceReadRange(unsafe.Pointer(iovecs[i].Base), m)
 		}
 	}
 }
 
 // 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
 }
 
 func isGroupMember(gid int) bool {
 	groups, err := Getgroups()
 	if err != nil {
 		return false
 	}
 
 	for _, g := range groups {
 		if g == gid {
 			return true
 		}
 	}
 	return false
 }
 
 //sys	faccessat(dirfd int, path string, mode uint32) (err error)
 //sys	Faccessat2(dirfd int, path string, mode uint32, flags int) (err error)
 
 func Faccessat(dirfd int, path string, mode uint32, flags int) (err error) {
 	if flags == 0 {
 		return faccessat(dirfd, path, mode)
 	}
 
 	if err := Faccessat2(dirfd, path, mode, flags); err != ENOSYS && err != EPERM {
 		return err
 	}
 
 	// 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 & ^(AT_SYMLINK_NOFOLLOW|AT_EACCESS) != 0 {
 		return EINVAL
 	}
 
 	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 || isGroupMember(int(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)
 }
 
 // Klogset wraps the sys_syslog system call; it sets console_loglevel to
 // the value specified by arg and passes a dummy pointer to bufp.
 func Klogset(typ int, arg int) (err error) {
 	var p unsafe.Pointer
 	_, _, errno := Syscall(SYS_SYSLOG, uintptr(typ), uintptr(p), uintptr(arg))
 	if errno != 0 {
 		return errnoErr(errno)
 	}
 	return nil
 }
 
 // RemoteIovec is Iovec with the pointer replaced with an integer.
 // It is used for ProcessVMReadv and ProcessVMWritev, where the pointer
 // refers to a location in a different process' address space, which
 // would confuse the Go garbage collector.
 type RemoteIovec struct {
 	Base uintptr
 	Len  int
 }
 
 //sys	ProcessVMReadv(pid int, localIov []Iovec, remoteIov []RemoteIovec, flags uint) (n int, err error) = SYS_PROCESS_VM_READV
 //sys	ProcessVMWritev(pid int, localIov []Iovec, remoteIov []RemoteIovec, flags uint) (n int, err error) = SYS_PROCESS_VM_WRITEV
 
 //sys	PidfdOpen(pid int, flags int) (fd int, err error) = SYS_PIDFD_OPEN
 //sys	PidfdGetfd(pidfd int, targetfd int, flags int) (fd int, err error) = SYS_PIDFD_GETFD
 //sys	PidfdSendSignal(pidfd int, sig Signal, info *Siginfo, flags int) (err error) = SYS_PIDFD_SEND_SIGNAL
 
 //sys	shmat(id int, addr uintptr, flag int) (ret uintptr, err error)
 //sys	shmctl(id int, cmd int, buf *SysvShmDesc) (result int, err error)
 //sys	shmdt(addr uintptr) (err error)
 //sys	shmget(key int, size int, flag int) (id int, err error)
 
 //sys	getitimer(which int, currValue *Itimerval) (err error)
 //sys	setitimer(which int, newValue *Itimerval, oldValue *Itimerval) (err error)
 
 // MakeItimerval creates an Itimerval from interval and value durations.
 func MakeItimerval(interval, value time.Duration) Itimerval {
 	return Itimerval{
 		Interval: NsecToTimeval(interval.Nanoseconds()),
 		Value:    NsecToTimeval(value.Nanoseconds()),
 	}
 }
 
 // A value which may be passed to the which parameter for Getitimer and
 // Setitimer.
 type ItimerWhich int
 
 // Possible which values for Getitimer and Setitimer.
 const (
 	ItimerReal    ItimerWhich = ITIMER_REAL
 	ItimerVirtual ItimerWhich = ITIMER_VIRTUAL
 	ItimerProf    ItimerWhich = ITIMER_PROF
 )
 
 // Getitimer wraps getitimer(2) to return the current value of the timer
 // specified by which.
 func Getitimer(which ItimerWhich) (Itimerval, error) {
 	var it Itimerval
 	if err := getitimer(int(which), &it); err != nil {
 		return Itimerval{}, err
 	}
 
 	return it, nil
 }
 
 // Setitimer wraps setitimer(2) to arm or disarm the timer specified by which.
 // It returns the previous value of the timer.
 //
 // If the Itimerval argument is the zero value, the timer will be disarmed.
 func Setitimer(which ItimerWhich, it Itimerval) (Itimerval, error) {
 	var prev Itimerval
 	if err := setitimer(int(which), &it, &prev); err != nil {
 		return Itimerval{}, err
 	}
 
 	return prev, nil
 }
 
 /*
  * Unimplemented
  */
 // AfsSyscall
 // ArchPrctl
 // Brk
 // ClockNanosleep
 // ClockSettime
 // Clone
 // EpollCtlOld
 // EpollPwait
 // EpollWaitOld
 // Execve
 // Fork
 // Futex
 // GetKernelSyms
 // GetMempolicy
 // GetRobustList
 // GetThreadArea
 // 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
 // Sigaltstack
 // Swapoff
 // Swapon
 // Sysfs
 // TimerCreate
 // TimerDelete
 // TimerGetoverrun
 // TimerGettime
 // TimerSettime
 // Tkill (obsolete)
 // Tuxcall
 // Umount2
 // Uselib
 // Utimensat
 // Vfork
 // Vhangup
 // Vserver
 // _Sysctl