src/pkg/os/file.go - go - Git at Google

 // 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.

 // The os package provides a platform-independent interface to operating
 // system functionality.  The design is Unix-like.
 package os

 import (
 	"runtime"
 	"syscall"
 )

 // File represents an open file descriptor.
 type File struct {
 	fd      int
 	name    string
 	dirinfo *dirInfo // nil unless directory being read
 	nepipe  int      // number of consecutive EPIPE in Write
 }

 // Fd returns the integer Unix file descriptor referencing the open file.
 func (file *File) Fd() int { return file.fd }

 // Name returns the name of the file as presented to Open.
 func (file *File) Name() string { return file.name }

 // NewFile returns a new File with the given file descriptor and name.
 func NewFile(fd int, name string) *File {
 	if fd < 0 {
 		return nil
 	}
 	f := &File{fd, name, nil, 0}
 	runtime.SetFinalizer(f, (*File).Close)
 	return f
 }

 // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
 // standard output, and standard error file descriptors.
 var (
 	Stdin  = NewFile(syscall.Stdin, "/dev/stdin")
 	Stdout = NewFile(syscall.Stdout, "/dev/stdout")
 	Stderr = NewFile(syscall.Stderr, "/dev/stderr")
 )

 // Flags to Open wrapping those of the underlying system. Not all flags
 // may be implemented on a given system.
 const (
 	O_RDONLY   = syscall.O_RDONLY   // open the file read-only.
 	O_WRONLY   = syscall.O_WRONLY   // open the file write-only.
 	O_RDWR     = syscall.O_RDWR     // open the file read-write.
 	O_APPEND   = syscall.O_APPEND   // open the file append-only.
 	O_ASYNC    = syscall.O_ASYNC    // generate a signal when I/O is available.
 	O_CREAT    = syscall.O_CREAT    // create a new file if none exists.
 	O_EXCL     = syscall.O_EXCL     // used with O_CREAT, file must not exist
 	O_NOCTTY   = syscall.O_NOCTTY   // do not make file the controlling tty.
 	O_NONBLOCK = syscall.O_NONBLOCK // open in non-blocking mode.
 	O_NDELAY   = O_NONBLOCK         // synonym for O_NONBLOCK
 	O_SYNC     = syscall.O_SYNC     // open for synchronous I/O.
 	O_TRUNC    = syscall.O_TRUNC    // if possible, truncate file when opened.
 	O_CREATE   = O_CREAT            // create a new file if none exists.
 )

 type eofError int

 func (eofError) String() string { return "EOF" }

 // EOF is the Error returned by Read when no more input is available.
 // Functions should return EOF only to signal a graceful end of input.
 // If the EOF occurs unexpectedly in a structured data stream,
 // the appropriate error is either io.ErrUnexpectedEOF or some other error
 // giving more detail.
 var EOF Error = eofError(0)

 // Read reads up to len(b) bytes from the File.
 // It returns the number of bytes read and an Error, if any.
 // EOF is signaled by a zero count with err set to EOF.
 func (file *File) Read(b []byte) (n int, err Error) {
 	if file == nil {
 		return 0, EINVAL
 	}
 	n, e := syscall.Read(file.fd, b)
 	if n < 0 {
 		n = 0
 	}
 	if n == 0 && e == 0 {
 		return 0, EOF
 	}
 	if e != 0 {
 		err = &PathError{"read", file.name, Errno(e)}
 	}
 	return n, err
 }

 // ReadAt reads len(b) bytes from the File starting at byte offset off.
 // It returns the number of bytes read and the Error, if any.
 // EOF is signaled by a zero count with err set to EOF.
 // ReadAt always returns a non-nil Error when n != len(b).
 func (file *File) ReadAt(b []byte, off int64) (n int, err Error) {
 	if file == nil {
 		return 0, EINVAL
 	}
 	for len(b) > 0 {
 		m, e := syscall.Pread(file.fd, b, off)
 		if m == 0 && e == 0 {
 			return n, EOF
 		}
 		if e != 0 {
 			err = &PathError{"read", file.name, Errno(e)}
 			break
 		}
 		n += m
 		b = b[m:]
 		off += int64(m)
 	}
 	return
 }

 // Write writes len(b) bytes to the File.
 // It returns the number of bytes written and an Error, if any.
 // Write returns a non-nil Error when n != len(b).
 func (file *File) Write(b []byte) (n int, err Error) {
 	if file == nil {
 		return 0, EINVAL
 	}
 	n, e := syscall.Write(file.fd, b)
 	if n < 0 {
 		n = 0
 	}
 	if e == syscall.EPIPE {
 		file.nepipe++
 		if file.nepipe >= 10 {
 			Exit(syscall.EPIPE)
 		}
 	} else {
 		file.nepipe = 0
 	}
 	if e != 0 {
 		err = &PathError{"write", file.name, Errno(e)}
 	}
 	return n, err
 }

 // WriteAt writes len(b) bytes to the File starting at byte offset off.
 // It returns the number of bytes written and an Error, if any.
 // WriteAt returns a non-nil Error when n != len(b).
 func (file *File) WriteAt(b []byte, off int64) (n int, err Error) {
 	if file == nil {
 		return 0, EINVAL
 	}
 	for len(b) > 0 {
 		m, e := syscall.Pwrite(file.fd, b, off)
 		if e != 0 {
 			err = &PathError{"write", file.name, Errno(e)}
 			break
 		}
 		n += m
 		b = b[m:]
 		off += int64(m)
 	}
 	return
 }

 // Seek sets the offset for the next Read or Write on file to offset, interpreted
 // according to whence: 0 means relative to the origin of the file, 1 means
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an Error, if any.
 func (file *File) Seek(offset int64, whence int) (ret int64, err Error) {
 	r, e := syscall.Seek(file.fd, offset, whence)
 	if e == 0 && file.dirinfo != nil && r != 0 {
 		e = syscall.EISDIR
 	}
 	if e != 0 {
 		return 0, &PathError{"seek", file.name, Errno(e)}
 	}
 	return r, nil
 }

 // WriteString is like Write, but writes the contents of string s rather than
 // an array of bytes.
 func (file *File) WriteString(s string) (ret int, err Error) {
 	if file == nil {
 		return 0, EINVAL
 	}
 	b := syscall.StringByteSlice(s)
 	b = b[0 : len(b)-1]
 	return file.Write(b)
 }

 // Pipe returns a connected pair of Files; reads from r return bytes written to w.
 // It returns the files and an Error, if any.
 func Pipe() (r *File, w *File, err Error) {
 	var p [2]int

 	// See ../syscall/exec.go for description of lock.
 	syscall.ForkLock.RLock()
 	e := syscall.Pipe(&p)
 	if e != 0 {
 		syscall.ForkLock.RUnlock()
 		return nil, nil, NewSyscallError("pipe", e)
 	}
 	syscall.CloseOnExec(p[0])
 	syscall.CloseOnExec(p[1])
 	syscall.ForkLock.RUnlock()

 	return NewFile(p[0], "|0"), NewFile(p[1], "|1"), nil
 }

 // Mkdir creates a new directory with the specified name and permission bits.
 // It returns an error, if any.
 func Mkdir(name string, perm int) Error {
 	e := syscall.Mkdir(name, perm)
 	if e != 0 {
 		return &PathError{"mkdir", name, Errno(e)}
 	}
 	return nil
 }

 // Stat returns a FileInfo structure describing the named file and an error, if any.
 // If name names a valid symbolic link, the returned FileInfo describes
 // the file pointed at by the link and has fi.FollowedSymlink set to true.
 // If name names an invalid symbolic link, the returned FileInfo describes
 // the link itself and has fi.FollowedSymlink set to false.
 func Stat(name string) (fi *FileInfo, err Error) {
 	var lstat, stat syscall.Stat_t
 	e := syscall.Lstat(name, &lstat)
 	if e != 0 {
 		return nil, &PathError{"stat", name, Errno(e)}
 	}
 	statp := &lstat
 	if lstat.Mode&syscall.S_IFMT == syscall.S_IFLNK {
 		e := syscall.Stat(name, &stat)
 		if e == 0 {
 			statp = &stat
 		}
 	}
 	return fileInfoFromStat(name, new(FileInfo), &lstat, statp), nil
 }

 // Stat returns the FileInfo structure describing file.
 // It returns the FileInfo and an error, if any.
 func (file *File) Stat() (fi *FileInfo, err Error) {
 	var stat syscall.Stat_t
 	e := syscall.Fstat(file.fd, &stat)
 	if e != 0 {
 		return nil, &PathError{"stat", file.name, Errno(e)}
 	}
 	return fileInfoFromStat(file.name, new(FileInfo), &stat, &stat), nil
 }

 // Lstat returns the FileInfo structure describing the named file and an
 // error, if any.  If the file is a symbolic link, the returned FileInfo
 // describes the symbolic link.  Lstat makes no attempt to follow the link.
 func Lstat(name string) (fi *FileInfo, err Error) {
 	var stat syscall.Stat_t
 	e := syscall.Lstat(name, &stat)
 	if e != 0 {
 		return nil, &PathError{"lstat", name, Errno(e)}
 	}
 	return fileInfoFromStat(name, new(FileInfo), &stat, &stat), nil
 }

 // Chdir changes the current working directory to the named directory.
 func Chdir(dir string) Error {
 	if e := syscall.Chdir(dir); e != 0 {
 		return &PathError{"chdir", dir, Errno(e)}
 	}
 	return nil
 }

 // Chdir changes the current working directory to the file,
 // which must be a directory.
 func (f *File) Chdir() Error {
 	if e := syscall.Fchdir(f.fd); e != 0 {
 		return &PathError{"chdir", f.name, Errno(e)}
 	}
 	return nil
 }

 // Remove removes the named file or directory.
 func Remove(name string) Error {
 	// System call interface forces us to know
 	// whether name is a file or directory.
 	// Try both: it is cheaper on average than
 	// doing a Stat plus the right one.
 	e := syscall.Unlink(name)
 	if e == 0 {
 		return nil
 	}
 	e1 := syscall.Rmdir(name)
 	if e1 == 0 {
 		return nil
 	}

 	// Both failed: figure out which error to return.
 	// OS X and Linux differ on whether unlink(dir)
 	// returns EISDIR, so can't use that.  However,
 	// both agree that rmdir(file) returns ENOTDIR,
 	// so we can use that to decide which error is real.
 	// Rmdir might also return ENOTDIR if given a bad
 	// file path, like /etc/passwd/foo, but in that case,
 	// both errors will be ENOTDIR, so it's okay to
 	// use the error from unlink.
 	if e1 != syscall.ENOTDIR {
 		e = e1
 	}
 	return &PathError{"remove", name, Errno(e)}
 }

 // LinkError records an error during a link or symlink or rename
 // system call and the paths that caused it.
 type LinkError struct {
 	Op    string
 	Old   string
 	New   string
 	Error Error
 }

 func (e *LinkError) String() string {
 	return e.Op + " " + e.Old + " " + e.New + ": " + e.Error.String()
 }

 // Link creates a hard link.
 func Link(oldname, newname string) Error {
 	e := syscall.Link(oldname, newname)
 	if e != 0 {
 		return &LinkError{"link", oldname, newname, Errno(e)}
 	}
 	return nil
 }

 // Symlink creates a symbolic link.
 func Symlink(oldname, newname string) Error {
 	e := syscall.Symlink(oldname, newname)
 	if e != 0 {
 		return &LinkError{"symlink", oldname, newname, Errno(e)}
 	}
 	return nil
 }

 // Readlink reads the contents of a symbolic link: the destination of
 // the link.  It returns the contents and an Error, if any.
 func Readlink(name string) (string, Error) {
 	for len := 128; ; len *= 2 {
 		b := make([]byte, len)
 		n, e := syscall.Readlink(name, b)
 		if e != 0 {
 			return "", &PathError{"readlink", name, Errno(e)}
 		}
 		if n < len {
 			return string(b[0:n]), nil
 		}
 	}
 	// Silence 6g.
 	return "", nil
 }

 // Rename renames a file.
 func Rename(oldname, newname string) Error {
 	e := syscall.Rename(oldname, newname)
 	if e != 0 {
 		return &LinkError{"rename", oldname, newname, Errno(e)}
 	}
 	return nil
 }

 // Chmod changes the mode of the named file to mode.
 // If the file is a symbolic link, it changes the mode of the link's target.
 func Chmod(name string, mode int) Error {
 	if e := syscall.Chmod(name, mode); e != 0 {
 		return &PathError{"chmod", name, Errno(e)}
 	}
 	return nil
 }

 // Chmod changes the mode of the file to mode.
 func (f *File) Chmod(mode int) Error {
 	if e := syscall.Fchmod(f.fd, mode); e != 0 {
 		return &PathError{"chmod", f.name, Errno(e)}
 	}
 	return nil
 }

 // Chown changes the numeric uid and gid of the named file.
 // If the file is a symbolic link, it changes the uid and gid of the link's target.
 func Chown(name string, uid, gid int) Error {
 	if e := syscall.Chown(name, uid, gid); e != 0 {
 		return &PathError{"chown", name, Errno(e)}
 	}
 	return nil
 }

 // Lchown changes the numeric uid and gid of the named file.
 // If the file is a symbolic link, it changes the uid and gid of the link itself.
 func Lchown(name string, uid, gid int) Error {
 	if e := syscall.Lchown(name, uid, gid); e != 0 {
 		return &PathError{"lchown", name, Errno(e)}
 	}
 	return nil
 }

 // Chown changes the numeric uid and gid of the named file.
 func (f *File) Chown(uid, gid int) Error {
 	if e := syscall.Fchown(f.fd, uid, gid); e != 0 {
 		return &PathError{"chown", f.name, Errno(e)}
 	}
 	return nil
 }

 // Truncate changes the size of the named file.
 // If the file is a symbolic link, it changes the size of the link's target.
 func Truncate(name string, size int64) Error {
 	if e := syscall.Truncate(name, size); e != 0 {
 		return &PathError{"truncate", name, Errno(e)}
 	}
 	return nil
 }

 // Truncate changes the size of the file.
 // It does not change the I/O offset.
 func (f *File) Truncate(size int64) Error {
 	if e := syscall.Ftruncate(f.fd, size); e != 0 {
 		return &PathError{"truncate", f.name, Errno(e)}
 	}
 	return nil
 }
	// 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.

	// The os package provides a platform-independent interface to operating
	// system functionality. The design is Unix-like.
	package os

	import (
	"runtime"
	"syscall"
	)

	// File represents an open file descriptor.
	type File struct {
	fd int
	name string
	dirinfo *dirInfo // nil unless directory being read
	nepipe int // number of consecutive EPIPE in Write
	}

	// Fd returns the integer Unix file descriptor referencing the open file.
	func (file *File) Fd() int { return file.fd }

	// Name returns the name of the file as presented to Open.
	func (file *File) Name() string { return file.name }

	// NewFile returns a new File with the given file descriptor and name.
	func NewFile(fd int, name string) *File {
	if fd < 0 {
	return nil
	}
	f := &File{fd, name, nil, 0}
	runtime.SetFinalizer(f, (*File).Close)
	return f
	}

	// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
	// standard output, and standard error file descriptors.
	var (
	Stdin = NewFile(syscall.Stdin, "/dev/stdin")
	Stdout = NewFile(syscall.Stdout, "/dev/stdout")
	Stderr = NewFile(syscall.Stderr, "/dev/stderr")
	)

	// Flags to Open wrapping those of the underlying system. Not all flags
	// may be implemented on a given system.
	const (
	O_RDONLY = syscall.O_RDONLY // open the file read-only.
	O_WRONLY = syscall.O_WRONLY // open the file write-only.
	O_RDWR = syscall.O_RDWR // open the file read-write.
	O_APPEND = syscall.O_APPEND // open the file append-only.
	O_ASYNC = syscall.O_ASYNC // generate a signal when I/O is available.
	O_CREAT = syscall.O_CREAT // create a new file if none exists.
	O_EXCL = syscall.O_EXCL // used with O_CREAT, file must not exist
	O_NOCTTY = syscall.O_NOCTTY // do not make file the controlling tty.
	O_NONBLOCK = syscall.O_NONBLOCK // open in non-blocking mode.
	O_NDELAY = O_NONBLOCK // synonym for O_NONBLOCK
	O_SYNC = syscall.O_SYNC // open for synchronous I/O.
	O_TRUNC = syscall.O_TRUNC // if possible, truncate file when opened.
	O_CREATE = O_CREAT // create a new file if none exists.
	)

	type eofError int

	func (eofError) String() string { return "EOF" }

	// EOF is the Error returned by Read when no more input is available.
	// Functions should return EOF only to signal a graceful end of input.
	// If the EOF occurs unexpectedly in a structured data stream,
	// the appropriate error is either io.ErrUnexpectedEOF or some other error
	// giving more detail.
	var EOF Error = eofError(0)

	// Read reads up to len(b) bytes from the File.
	// It returns the number of bytes read and an Error, if any.
	// EOF is signaled by a zero count with err set to EOF.
	func (file *File) Read(b []byte) (n int, err Error) {
	if file == nil {
	return 0, EINVAL
	}
	n, e := syscall.Read(file.fd, b)
	if n < 0 {
	n = 0
	}
	if n == 0 && e == 0 {
	return 0, EOF
	}
	if e != 0 {
	err = &PathError{"read", file.name, Errno(e)}
	}
	return n, err
	}

	// ReadAt reads len(b) bytes from the File starting at byte offset off.
	// It returns the number of bytes read and the Error, if any.
	// EOF is signaled by a zero count with err set to EOF.
	// ReadAt always returns a non-nil Error when n != len(b).
	func (file *File) ReadAt(b []byte, off int64) (n int, err Error) {
	if file == nil {
	return 0, EINVAL
	}
	for len(b) > 0 {
	m, e := syscall.Pread(file.fd, b, off)
	if m == 0 && e == 0 {
	return n, EOF
	}
	if e != 0 {
	err = &PathError{"read", file.name, Errno(e)}
	break
	}
	n += m
	b = b[m:]
	off += int64(m)
	}
	return
	}

	// Write writes len(b) bytes to the File.
	// It returns the number of bytes written and an Error, if any.
	// Write returns a non-nil Error when n != len(b).
	func (file *File) Write(b []byte) (n int, err Error) {
	if file == nil {
	return 0, EINVAL
	}
	n, e := syscall.Write(file.fd, b)
	if n < 0 {
	n = 0
	}
	if e == syscall.EPIPE {
	file.nepipe++
	if file.nepipe >= 10 {
	Exit(syscall.EPIPE)
	}
	} else {
	file.nepipe = 0
	}
	if e != 0 {
	err = &PathError{"write", file.name, Errno(e)}
	}
	return n, err
	}

	// WriteAt writes len(b) bytes to the File starting at byte offset off.
	// It returns the number of bytes written and an Error, if any.
	// WriteAt returns a non-nil Error when n != len(b).
	func (file *File) WriteAt(b []byte, off int64) (n int, err Error) {
	if file == nil {
	return 0, EINVAL
	}
	for len(b) > 0 {
	m, e := syscall.Pwrite(file.fd, b, off)
	if e != 0 {
	err = &PathError{"write", file.name, Errno(e)}
	break
	}
	n += m
	b = b[m:]
	off += int64(m)
	}
	return
	}

	// Seek sets the offset for the next Read or Write on file to offset, interpreted
	// according to whence: 0 means relative to the origin of the file, 1 means
	// relative to the current offset, and 2 means relative to the end.
	// It returns the new offset and an Error, if any.
	func (file *File) Seek(offset int64, whence int) (ret int64, err Error) {
	r, e := syscall.Seek(file.fd, offset, whence)
	if e == 0 && file.dirinfo != nil && r != 0 {
	e = syscall.EISDIR
	}
	if e != 0 {
	return 0, &PathError{"seek", file.name, Errno(e)}
	}
	return r, nil
	}

	// WriteString is like Write, but writes the contents of string s rather than
	// an array of bytes.
	func (file *File) WriteString(s string) (ret int, err Error) {
	if file == nil {
	return 0, EINVAL
	}
	b := syscall.StringByteSlice(s)
	b = b[0 : len(b)-1]
	return file.Write(b)
	}

	// Pipe returns a connected pair of Files; reads from r return bytes written to w.
	// It returns the files and an Error, if any.
	func Pipe() (r File, w File, err Error) {
	var p [2]int

	// See ../syscall/exec.go for description of lock.
	syscall.ForkLock.RLock()
	e := syscall.Pipe(&p)
	if e != 0 {
	syscall.ForkLock.RUnlock()
	return nil, nil, NewSyscallError("pipe", e)
	}
	syscall.CloseOnExec(p[0])
	syscall.CloseOnExec(p[1])
	syscall.ForkLock.RUnlock()

	return NewFile(p[0], "\|0"), NewFile(p[1], "\|1"), nil
	}

	// Mkdir creates a new directory with the specified name and permission bits.
	// It returns an error, if any.
	func Mkdir(name string, perm int) Error {
	e := syscall.Mkdir(name, perm)
	if e != 0 {
	return &PathError{"mkdir", name, Errno(e)}
	}
	return nil
	}

	// Stat returns a FileInfo structure describing the named file and an error, if any.
	// If name names a valid symbolic link, the returned FileInfo describes
	// the file pointed at by the link and has fi.FollowedSymlink set to true.
	// If name names an invalid symbolic link, the returned FileInfo describes
	// the link itself and has fi.FollowedSymlink set to false.
	func Stat(name string) (fi *FileInfo, err Error) {
	var lstat, stat syscall.Stat_t
	e := syscall.Lstat(name, &lstat)
	if e != 0 {
	return nil, &PathError{"stat", name, Errno(e)}
	}
	statp := &lstat
	if lstat.Mode&syscall.S_IFMT == syscall.S_IFLNK {
	e := syscall.Stat(name, &stat)
	if e == 0 {
	statp = &stat
	}
	}
	return fileInfoFromStat(name, new(FileInfo), &lstat, statp), nil
	}

	// Stat returns the FileInfo structure describing file.
	// It returns the FileInfo and an error, if any.
	func (file File) Stat() (fi FileInfo, err Error) {
	var stat syscall.Stat_t
	e := syscall.Fstat(file.fd, &stat)
	if e != 0 {
	return nil, &PathError{"stat", file.name, Errno(e)}
	}
	return fileInfoFromStat(file.name, new(FileInfo), &stat, &stat), nil
	}

	// Lstat returns the FileInfo structure describing the named file and an
	// error, if any. If the file is a symbolic link, the returned FileInfo
	// describes the symbolic link. Lstat makes no attempt to follow the link.
	func Lstat(name string) (fi *FileInfo, err Error) {
	var stat syscall.Stat_t
	e := syscall.Lstat(name, &stat)
	if e != 0 {
	return nil, &PathError{"lstat", name, Errno(e)}
	}
	return fileInfoFromStat(name, new(FileInfo), &stat, &stat), nil
	}

	// Chdir changes the current working directory to the named directory.
	func Chdir(dir string) Error {
	if e := syscall.Chdir(dir); e != 0 {
	return &PathError{"chdir", dir, Errno(e)}
	}
	return nil
	}

	// Chdir changes the current working directory to the file,
	// which must be a directory.
	func (f *File) Chdir() Error {
	if e := syscall.Fchdir(f.fd); e != 0 {
	return &PathError{"chdir", f.name, Errno(e)}
	}
	return nil
	}

	// Remove removes the named file or directory.
	func Remove(name string) Error {
	// System call interface forces us to know
	// whether name is a file or directory.
	// Try both: it is cheaper on average than
	// doing a Stat plus the right one.
	e := syscall.Unlink(name)
	if e == 0 {
	return nil
	}
	e1 := syscall.Rmdir(name)
	if e1 == 0 {
	return nil
	}

	// Both failed: figure out which error to return.
	// OS X and Linux differ on whether unlink(dir)
	// returns EISDIR, so can't use that. However,
	// both agree that rmdir(file) returns ENOTDIR,
	// so we can use that to decide which error is real.
	// Rmdir might also return ENOTDIR if given a bad
	// file path, like /etc/passwd/foo, but in that case,
	// both errors will be ENOTDIR, so it's okay to
	// use the error from unlink.
	if e1 != syscall.ENOTDIR {
	e = e1
	}
	return &PathError{"remove", name, Errno(e)}
	}

	// LinkError records an error during a link or symlink or rename
	// system call and the paths that caused it.
	type LinkError struct {
	Op string
	Old string
	New string
	Error Error
	}

	func (e *LinkError) String() string {
	return e.Op + " " + e.Old + " " + e.New + ": " + e.Error.String()
	}

	// Link creates a hard link.
	func Link(oldname, newname string) Error {
	e := syscall.Link(oldname, newname)
	if e != 0 {
	return &LinkError{"link", oldname, newname, Errno(e)}
	}
	return nil
	}

	// Symlink creates a symbolic link.
	func Symlink(oldname, newname string) Error {
	e := syscall.Symlink(oldname, newname)
	if e != 0 {
	return &LinkError{"symlink", oldname, newname, Errno(e)}
	}
	return nil
	}

	// Readlink reads the contents of a symbolic link: the destination of
	// the link. It returns the contents and an Error, if any.
	func Readlink(name string) (string, Error) {
	for len := 128; ; len *= 2 {
	b := make([]byte, len)
	n, e := syscall.Readlink(name, b)
	if e != 0 {
	return "", &PathError{"readlink", name, Errno(e)}
	}
	if n < len {
	return string(b[0:n]), nil
	}
	}
	// Silence 6g.
	return "", nil
	}

	// Rename renames a file.
	func Rename(oldname, newname string) Error {
	e := syscall.Rename(oldname, newname)
	if e != 0 {
	return &LinkError{"rename", oldname, newname, Errno(e)}
	}
	return nil
	}

	// Chmod changes the mode of the named file to mode.
	// If the file is a symbolic link, it changes the mode of the link's target.
	func Chmod(name string, mode int) Error {
	if e := syscall.Chmod(name, mode); e != 0 {
	return &PathError{"chmod", name, Errno(e)}
	}
	return nil
	}

	// Chmod changes the mode of the file to mode.
	func (f *File) Chmod(mode int) Error {
	if e := syscall.Fchmod(f.fd, mode); e != 0 {
	return &PathError{"chmod", f.name, Errno(e)}
	}
	return nil
	}

	// Chown changes the numeric uid and gid of the named file.
	// If the file is a symbolic link, it changes the uid and gid of the link's target.
	func Chown(name string, uid, gid int) Error {
	if e := syscall.Chown(name, uid, gid); e != 0 {
	return &PathError{"chown", name, Errno(e)}
	}
	return nil
	}

	// Lchown changes the numeric uid and gid of the named file.
	// If the file is a symbolic link, it changes the uid and gid of the link itself.
	func Lchown(name string, uid, gid int) Error {
	if e := syscall.Lchown(name, uid, gid); e != 0 {
	return &PathError{"lchown", name, Errno(e)}
	}
	return nil
	}

	// Chown changes the numeric uid and gid of the named file.
	func (f *File) Chown(uid, gid int) Error {
	if e := syscall.Fchown(f.fd, uid, gid); e != 0 {
	return &PathError{"chown", f.name, Errno(e)}
	}
	return nil
	}

	// Truncate changes the size of the named file.
	// If the file is a symbolic link, it changes the size of the link's target.
	func Truncate(name string, size int64) Error {
	if e := syscall.Truncate(name, size); e != 0 {
	return &PathError{"truncate", name, Errno(e)}
	}
	return nil
	}

	// Truncate changes the size of the file.
	// It does not change the I/O offset.
	func (f *File) Truncate(size int64) Error {
	if e := syscall.Ftruncate(f.fd, size); e != 0 {
	return &PathError{"truncate", f.name, Errno(e)}
	}
	return nil
	}