code: func createFilesManager(rootDir string, openedFilesLimit int64) *filesManager {
  	fm := &filesManager{
  		rootDir: rootDir,
  		limit:   openedFilesLimit,
  		files:   make(map[fileID]*file),
  	}
  	return fm
  }
docs: ////////////////////////////////////////////////////////////////////////////
  // filesManager methods
  ////////////////////////////////////////////////////////////////////////////
  // createFilesManager returns an instance of the files manager.