sub tie_session {
  my ($hash) = @_; 

  eval {
    tie %$hash, 'Apache::Session::File', undef, {
      Directory     => $r->dir_config('Blah'),
      LockDirectory => $r->dir_config('Blah'),
    };
  };
  return $@ if $@;
  return $hash;  # not actually necessary, but it returns true
}