try {
  list($xml, $stderr) = $repository->execxRemoteCommand(
    'log --xml --quiet --limit %d %s',
    $limit,
    $repository->getSubversionBaseURI($at_rev));
} catch (CommandException $ex) {
  $stderr = $ex->getStdErr();
  if (preg_match('/(path|File) not found/', $stderr)) {
    // We've gone all the way back through history and this path was not
    // affected by earlier commits.
    break;
  }
  throw $ex;
}