code: func (f *FileStore) Free() error {
  	f.mu.RLock()
  	defer f.mu.RUnlock()
  	for _, f := range f.files {
  		if err := f.Free(); err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // Free releases any resources held by the FileStore.  The resources will be re-acquired
  // if necessary if they are needed after freeing them.