}

static int GetChildren(const TF_Filesystem* filesystem, const char* path,
                       char*** entries, TF_Status* status) {
  struct dirent** dir_entries = nullptr;
  /* we don't promise entries would be sorted */
  int num_entries =
      scandir(path, &dir_entries, RemoveSpecialDirectoryEntries, nullptr);
  if (num_entries < 0) {
    TF_SetStatusFromIOError(status, errno, path);
  } else {

  // a tensor with the result.
  virtual Gradient* AggregateGradients(
      gtl::ArraySlice<Gradient*> gradient_tensors) const = 0;

  // Calls the passed-in backward function.
  //
  // `unneeded_gradients` contains sorted list of input indices for which a
  // gradient is not required.
  virtual Status CallBackwardFunction(
      const string& op_type, BackwardFunction* backward_function,
      const std::vector<int64_t>& unneeded_gradients,