code: func (store *FSMetadataStore) Set(namespace, key string, value []byte) error {
  	store.Lock()
  	defer store.Unlock()
  
  	path := store.path(namespace, key)
  	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
  		return err
  	}
  	return ioutils.AtomicWriteFile(path, value, 0644)
  }
docs: // Set writes data indexed by namespace and key. The data is written to a file
  // named after the key, stored in the namespace's directory.