TF_Buffer* output_op_def, TF_Status* status) {
  const OpDef* op_def;
  {
    mutex_lock l(graph->mu);
    status->status = graph->graph.op_registry()->LookUpOpDef(op_name, &op_def);
    if (!status->status.ok()) return;
  }
  status->status = MessageToBuffer(*op_def, output_op_def);
}

void TF_GraphVersions(TF_Graph* graph, TF_Buffer* output_version_def,