code: func (writer *NsenterWriter) WriteFile(filename string, data []byte, perm os.FileMode) error {
  	cmd := "nsenter"
  	base_args := []string{
  		"--mount=/rootfs/proc/1/ns/mnt",
  		"--",
  	}
  
  	echo_args := append(base_args, "sh", "-c", fmt.Sprintf("cat > %s", filename))
  	glog.V(5).Infof("Command to write data to file: %v %v", cmd, echo_args)
  	command := exec.Command(cmd, echo_args...)
  	command.Stdin = bytes.NewBuffer(data)
  	outputBytes, err := command.CombinedOutput()
  	if err != nil {
  		glog.Errorf("Output from writing to %q: %v", filename, string(outputBytes))
  		return err
  	}
  
  	chmod_args := append(base_args, "chmod", fmt.Sprintf("%o", perm), filename)
  	glog.V(5).Infof("Command to change permissions to file: %v %v", cmd, chmod_args)
  	outputBytes, err = exec.Command(cmd, chmod_args...).CombinedOutput()
  	if err != nil {
  		glog.Errorf("Output from chmod command: %v", string(outputBytes))
  		return err
  	}
  
  	return nil
  }
docs: // TODO: should take a writer, not []byte