Mine

void
_oil_debug_init(void)
{
  const char *envvar;

  envvar = getenv ("OIL_DEBUG");
  if (envvar != NULL) {
    char *end = NULL;
    int level;
    level = strtol (envvar, &end, 0);
    if (end > envvar) {
      _oil_debug_level = level;
    }
  }

  OIL_INFO ("liboil-" VERSION " debug init");
}

static void
oil_debug_print_valist (int level, const char *file, const char *func,
        int line, const char *format, va_list args)
{
  static const char *level_names[] = { "NONE", "ERROR", "WARNING", "INFO",
    "DEBUG", "LOG" };
  const char *level_name = "unknown";

  if (level > _oil_debug_level) return;

  if(level>=OIL_DEBUG_NONE && level<=OIL_DEBUG_LOG){
    level_name = level_names[level];
  }
  
  fprintf (stderr, "OIL: %s %s %d: %s(): ", level_name, file, line, func);
  vfprintf (stderr, format, args);
  fprintf (stderr, "\n");
}

void
oil_debug_print (int level, const char *file, const char *func,
        int line, const char *format, ...)
{
  va_list var_args;

  va_start (var_args, format);
  _oil_debug_print_func (level, file, func, line, format, var_args);
  va_end (var_args);
}