func: void trace_init_file(const char *file)
  
  {
  
  #ifdef CONFIG_TRACE_SIMPLE
  
      st_set_trace_file(file);
  
  #elif defined CONFIG_TRACE_LOG
  
      /* If both the simple and the log backends are enabled, "-trace file"
  
       * only applies to the simple backend; use "-D" for the log backend.
  
       */
  
      if (file) {
  
          qemu_set_log_filename(file);
  
      }
  
  #else
  
      if (file) {
  
          fprintf(stderr, "error: -trace file=...: "
  
                  "option not supported by the selected tracing backends\n");
  
          exit(1);
  
      }
  
  #endif
  
  }
  