How to add a menu that belongs to parent blog to all child-blogs?

Well, thanks to @toscho … For your help I found a way to achieve show the primary nav that belongs to parent blog to all child blogs:

/**
 * Plugin Name: Network Primary Nav
 * Network: true
 */

add_filter( 'wp_nav_menu_objects', 'network_primary_nav', 100, 2 );

function network_primary_nav( $menu_items, $args )
{
  global $blog_id;
  $menu_name="primary";

  if ( ( $blog_id > 1 ) && $menu_name == $args->theme_location )
  {

    // to parent blog
    switch_to_blog(1);

    $locations = get_nav_menu_locations();

    // get primary nav of parent blog
    if ( isset( $locations[ $menu_name ] ) )
    {
      $menu       = wp_get_nav_menu_object( $locations[ $menu_name ] );
      $menu_items = wp_get_nav_menu_items( $menu->term_id);
    }

    // to child blog
    restore_current_blog();

  }

  return $menu_items;

}