code: func (r *Store) checkMounts() error {
  	paths := make(map[string]string, len(r.mounts))
  	for k, v := range r.mounts {
  		if _, found := paths[v.Path()]; found {
  			return errors.Errorf("Doubly mounted path at %s: %s", v.Path(), k)
  		}
  		paths[v.Path()] = k
  	}
  	return nil
  }
docs: // checkMounts performs some sanity checks on our mounts. At the moment it
  // only checks if some path is mounted twice.