return 0, err
		}
	}
	if len(b.buf) < len(buf) {
		return 0, errLessData
	}
	n = copy(buf, b.buf)
	b.buf = b.buf[n:]
	return n, nil
}

// Returns whole-file bitrot reader.
func newWholeBitrotReader(disk StorageAPI, volume, filePath string, algo BitrotAlgorithm, tillOffset int64, sum []byte) *wholeBitrotReader {
	return &wholeBitrotReader{
		disk:       disk,
		volume:     volume,
		filePath:   filePath,