DbUpdateController::handle

public DbUpdateController::handle($op, Request $request)

public function handle($op, Request $request) {
  require_once $this->root . '/core/includes/install.inc';
  require_once $this->root . '/core/includes/update.inc';

  drupal_load_updates();
  update_fix_compatibility();

  if ($request->query->get('continue')) {
    $_SESSION['update_ignore_warnings'] = TRUE;
  }

  $regions = array();
  $requirements = update_check_requirements();
  $severity = drupal_requirements_severity($requirements);
  if ($severity == REQUIREMENT_ERROR || ($severity == REQUIREMENT_WARNING && empty($_SESSION['update_ignore_warnings']))) {
    $regions['sidebar_first'] = $this->updateTasksList('requirements');
    $output = $this->requirements($severity, $requirements, $request);
  }
  else {
    switch ($op) {
      case 'selection':
        $regions['sidebar_first'] = $this->updateTasksList('selection');
        $output = $this->selection($request);
        break;

      case 'run':
        $regions['sidebar_first'] = $this->updateTasksList('run');
        $output = $this->triggerBatch($request);
        break;

      case 'info':
        $regions['sidebar_first'] = $this->updateTasksList('info');
        $output = $this->info($request);
        break;

      case 'results':
        $regions['sidebar_first'] = $this->updateTasksList('results');
        $output = $this->results($request);
        break;

        // Regular batch ops : defer to batch processing API.
      default:
        require_once $this->root . '/core/includes/batch.inc';
        $regions['sidebar_first'] = $this->updateTasksList('run');
        $output = _batch_page($request);
        break;
    }
  }

  if ($output instanceof Response) {
    return $output;
  }
  $title = isset($output['#title']) ? $output['#title'] : $this->t('Drupal database update');

  return $this->bareHtmlPageRenderer->renderBarePage($output, $title, 'maintenance_page', $regions);
}