code: func (s *VolumeStore) hasRef(name string) bool {
  	s.globalLock.RLock()
  	l := len(s.refs[name])
  	s.globalLock.RUnlock()
  	return l > 0
  }
docs: // hasRef returns true if the given name has at least one ref.
  // Callers of this function are expected to hold the name lock.