func (fs *Datastore) Query(q query.Query) (query.Results, error) {
	if (q.Prefix != "" && q.Prefix != "/") ||
		len(q.Filters) > 0 ||
		len(q.Orders) > 0 ||
		q.Limit > 0 ||
		q.Offset > 0 ||
		!q.KeysOnly {
		// TODO this is overly simplistic, but the only caller is
		// `ipfs refs local` for now, and this gets us moving.
		return nil, errors.New("flatfs only supports listing all keys in random order")
	}

	// TODO this dumb implementation gathers all keys into a single slice.
	root, err := os.Open(fs.path)
	if err != nil {
		return nil, err
	}
	defer root.Close()

	var res []query.Entry
	prefixes, err := root.Readdir(0)
	if err != nil {
		return nil, err
	}
	for _, fi := range prefixes {
		var err error
		res, err = fs.enumerateKeys(fi, res)
		if err != nil {
			return nil, err
		}
	}
	return query.ResultsWithEntries(q, res), nil
}
// Query implements Datastore.Query
func (d *MapDatastore) Query(q dsq.Query) (dsq.Results, error) {
	re := make([]dsq.Entry, 0, len(d.values))
	for k, v := range d.values {
		re = append(re, dsq.Entry{Key: k.String(), Value: v})
	}
	r := dsq.ResultsWithEntries(q, re)
	r = dsq.NaiveQueryApply(q, r)
	return r, nil
}
// Query implements Datastore.Query
func (d *NullDatastore) Query(q dsq.Query) (dsq.Results, error) {
	return dsq.ResultsWithEntries(q, nil), nil
}