code: func MakeDataDir(ctx *cli.Context) string {
  	if path := ctx.GlobalString(DataDirFlag.Name); path != "" {
  		if ctx.GlobalBool(TestnetFlag.Name) {
  			return filepath.Join(path, "testnet")
  		}
  		if ctx.GlobalBool(RinkebyFlag.Name) {
  			return filepath.Join(path, "rinkeby")
  		}
  		if ctx.GlobalBool(GoerliFlag.Name) {
  			return filepath.Join(path, "goerli")
  		}
  		return path
  	}
  	Fatalf("Cannot determine default data directory, please set manually (--datadir)")
  	return ""
  }
docs: // MakeDataDir retrieves the currently requested data directory, terminating
  // if none (or the empty string) is specified. If the node is starting a testnet,
  // the a subdirectory of the specified datadir will be used.