/// `FileSystem` is never called (see
  /// https://github.com/tensorflow/tensorflow/issues/27535). In turn, this
  /// function will never be called. There are plans to refactor registration
  /// and fix this.
  ///
  /// TODO(b/139060984): After all filesystems are converted, revisit note.
  ///
  /// This operation must be provided. See "REQUIRED OPERATIONS" above.
  void (*cleanup)(TF_Filesystem* filesystem);