inuse, unused := filterUnusedLogs(logs)
	for _, l := range unused {
		if err := c.osInterface.Remove(l); err != nil {
			return nil, fmt.Errorf("failed to remove unused log %q: %v", l, err)
		}
	}
	return inuse, nil
}

// filterUnusedLogs splits logs into 2 groups, the 1st group is in used logs,
// the second group is unused logs.
func filterUnusedLogs(logs []string) (inuse []string, unused []string) {