public function getFilesInUse()
    {
        $list = ArrayList::create();

        // Check SiteTreeFileExtension
        if ($this->owner instanceof Folder) {
            // Join on tracking table
            $parents = static::nestedFolderIDs($this->owner->ID);
            $linkQuery = FileLink::get()->sql($linkParams);
            $list = File::get()->filter('ParentID', $parents)
                ->innerJoin(
                    "({$linkQuery})",
                    '"File"."ID" = "FileLinkTracking"."LinkedID"',
                    'FileLinkTracking',
                    20,
                    $linkParams
                );
        }

        // Allow extension
        $this->owner->extend('updateFilesInUse', $list);
        return $list;
    }