code: func (s *Store) GetDriverList() []string {
  	var driverList []string
  	s.mu.Lock()
  	defer s.mu.Unlock()
  	for driverName := range s.extensions {
  		driverList = append(driverList, driverName)
  	}
  	sort.Strings(driverList)
  	return driverList
  }
docs: // GetDriverList returns list of volume drivers registered.
  // If no driver is registered, empty string list will be returned.