called with a directory entry as the arg
function _prepopulate_metadata(_arg, _cb) {
        var entry;
        try {
            entry = JSON.parse(_arg);
        } catch (e) {
            _cb();
            return;
        }

        var nm = path.join(entry.parent, entry.name);

        var k = sprintf(FILES_KEY_FMT, nm);

        // if already in LRU cache, return
        var stats = self.cache.get(k);
        if (stats) {
            _cb();
            return;
        }

        self.db.get(k, function (err, val) {
            // if already in db, return
            if (!err) {
                _cb();
                return;
            }

            var fh = uuid.v4();
            var info;
            var cfile = path.join(self.location, 'fscache', fh);
            if (entry.type !== 'directory') {
                info = {
                    name: entry.name,
                    extension: 'bin',
                    type: 'application/octet-stream',
                    size: entry.size,
                    headers: {
                        'last-modified': entry.mtime
                    },
                    _fhandle: fh,
                    _cacheFile: cfile,
                    last_stat: now
                };

            } else {
                info = {
                    name: entry.name,
                    extension: 'directory',
                    type: 'application/x-json-stream; type=directory',
                    headers: {
                        'last-modified': entry.mtime,
                        'result-set-size': 3
                    },
                    last_modified: entry.mtime,
                    _fhandle: fh,
                    _cacheFile: cfile,
                    last_stat: now
                };
            }

            var k1 = sprintf(FHANDLE_KEY_FMT, nm);
            var k2 = sprintf(FNAME_KEY_FMT, fh);

            self.db.batch()
                .put(k, info)
                .put(k1, fh)
                .put(k2, nm)
                .write(function (err2) {
                    if (!err2)
                        self.cache.set(k, info);
                    _cb();
                });
        });
    }