code: func AtomicWriteFile(filename string, data []byte, perm os.FileMode) error {
  	f, err := ioutil.TempFile(filepath.Dir(filename), ".tmp-"+filepath.Base(filename))
  	if err != nil {
  		return err
  	}
  	err = os.Chmod(f.Name(), perm)
  	if err != nil {
  		f.Close()
  		return err
  	}
  	n, err := f.Write(data)
  	if err == nil && n < len(data) {
  		f.Close()
  		return io.ErrShortWrite
  	}
  	if err != nil {
  		f.Close()
  		return err
  	}
  	if err := f.Sync(); err != nil {
  		f.Close()
  		return err
  	}
  	if err := f.Close(); err != nil {
  		return err
  	}
  	return os.Rename(f.Name(), filename)
  }
docs: // todo: split docker/pkg/ioutils into a separate repo
  // AtomicWriteFile atomically writes data to a file specified by filename.