code: function openFromSnapshot (path_, cb) {
      var cb2 = cb || rethrow;
      var path = normalizePath(path_);
      // console.log("openFromSnapshot", path);
      var entity = VIRTUAL_FILESYSTEM[path];
      if (!entity) return cb2(error_ENOENT('File or directory', path));
      var dock = { path: path, entity: entity, position: 0 };
      var nullDevice = windows ? '\\\\.\\NUL' : '/dev/null';
      if (cb) {
        ancestor.open.call(fs, nullDevice, 'r', function (error, fd) {
          if (error) return cb(error);
          docks[fd] = dock;
          cb(null, fd);
        });
      } else {
        var fd = ancestor.openSync.call(fs, nullDevice, 'r');
        docks[fd] = dock;
        return fd;
      }
    }
docs: /////////////////////////////////////////////////////////////// open ////////////////////////////////////////////////////////// ///////////////////////////////////////////////////////////////