code: func (p *Pod) GetStage1TreeStoreID() (string, error) {
  	s1IDb, err := p.readFile(common.Stage1TreeStoreIDFilename)
  	if err != nil {
  		return "", err
  	}
  	return string(s1IDb), nil
  }
docs: // GetStage1TreeStoreID returns the treeStoreID of the stage1 image used in
  // this pod
  // TODO(yifan): Maybe make this unexported.