text: // 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.
  
  // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
  
  package os
  
  import (
  	"syscall"
  	"time"
  )
  
  func sigpipe() // implemented in package runtime
  
  // Readlink returns the destination of the named symbolic link.
  // If there is an error, it will be of type *PathError.
  func Readlink(name string) (string, error) {
  	for len := 128; ; len *= 2 {
  		b := make([]byte, len)
  		n, e := fixCount(syscall.Readlink(name, b))
  		if e != nil {
  			return "", &PathError{"readlink", name, e}
  		}
  		if n < len {
  			return string(b[0:n]), nil
  		}
  	}
  }
  
  // syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
  func syscallMode(i FileMode) (o uint32) {
  	o |= uint32(i.Perm())
  	if i&ModeSetuid != 0 {
  		o |= syscall.S_ISUID
  	}
  	if i&ModeSetgid != 0 {
  		o |= syscall.S_ISGID
  	}
  	if i&ModeSticky != 0 {
  		o |= syscall.S_ISVTX
  	}
  	// No mapping for Go's ModeTemporary (plan9 only).
  	return
  }
  
  // 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.
  // If there is an error, it will be of type *PathError.
  func Chmod(name string, mode FileMode) error {
  	if e := syscall.Chmod(name, syscallMode(mode)); e != nil {
  		return &PathError{"chmod", name, e}
  	}
  	return nil
  }
  
  // Chmod changes the mode of the file to mode.
  // If there is an error, it will be of type *PathError.
  func (f *File) Chmod(mode FileMode) error {
  	if f == nil {
  		return ErrInvalid
  	}
  	if e := syscall.Fchmod(f.fd, syscallMode(mode)); e != nil {
  		return &PathError{"chmod", f.name, 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.
  // If there is an error, it will be of type *PathError.
  func Chown(name string, uid, gid int) error {
  	if e := syscall.Chown(name, uid, gid); e != nil {
  		return &PathError{"chown", name, 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.
  // If there is an error, it will be of type *PathError.
  func Lchown(name string, uid, gid int) error {
  	if e := syscall.Lchown(name, uid, gid); e != nil {
  		return &PathError{"lchown", name, e}
  	}
  	return nil
  }
  
  // Chown changes the numeric uid and gid of the named file.
  // If there is an error, it will be of type *PathError.
  func (f *File) Chown(uid, gid int) error {
  	if f == nil {
  		return ErrInvalid
  	}
  	if e := syscall.Fchown(f.fd, uid, gid); e != nil {
  		return &PathError{"chown", f.name, e}
  	}
  	return nil
  }
  
  // Truncate changes the size of the file.
  // It does not change the I/O offset.
  // If there is an error, it will be of type *PathError.
  func (f *File) Truncate(size int64) error {
  	if f == nil {
  		return ErrInvalid
  	}
  	if e := syscall.Ftruncate(f.fd, size); e != nil {
  		return &PathError{"truncate", f.name, e}
  	}
  	return nil
  }
  
  // Sync commits the current contents of the file to stable storage.
  // Typically, this means flushing the file system's in-memory copy
  // of recently written data to disk.
  func (f *File) Sync() error {
  	if f == nil {
  		return ErrInvalid
  	}
  	if e := syscall.Fsync(f.fd); e != nil {
  		return NewSyscallError("fsync", e)
  	}
  	return nil
  }
  
  // Chtimes changes the access and modification times of the named
  // file, similar to the Unix utime() or utimes() functions.
  //
  // The underlying filesystem may truncate or round the values to a
  // less precise time unit.
  // If there is an error, it will be of type *PathError.
  func Chtimes(name string, atime time.Time, mtime time.Time) error {
  	var utimes [2]syscall.Timespec
  	utimes[0] = syscall.NsecToTimespec(atime.UnixNano())
  	utimes[1] = syscall.NsecToTimespec(mtime.UnixNano())
  	if e := syscall.UtimesNano(name, utimes[0:]); e != nil {
  		return &PathError{"chtimes", name, e}
  	}
  	return nil
  }
  