codeigniter multiple file upload

public function save_multiple_images()
{
         for($i=0; $i<$total_items; $i++)
        {
           if(!empty($_POST['item_name'][$i]) && !empty($_POST['item_name'][$i]))
           {
               if(isset($_FILES['item_image']['name'][$i]))
               {
                  $this->load->library('upload');
                  $files = $_FILES;
                  $_FILES['userfile']['name'] = $files['item_image']['name'][$i];
                  $_FILES['userfile']['type']= $files['item_image']['type'][$i];
                  $_FILES['userfile']['tmp_name']= $files['item_image']['tmp_name'][$i];            
                  $_FILES['userfile']['error']= $files['item_image']['error'][$i];
                  $_FILES['userfile']['size']= $files['item_image']['size'][$i];
                  $fileName = $_FILES['userfile']['name'];
                 //Calls set upload funtions
                   $this->upload->initialize($this->set_upload_options($i));
                    if($fileName!='')
                   {
                      $this->upload->do_upload();
                      $upload_data = $this->upload->data();
                      $fileSize = $upload_data['file_size'];
                      if($this->upload->display_errors())
                      {
                        echo json_encode($this->upload->display_errors()); exit;
                      }
                      $fileName = base_url('files/reward_images/'.$upload_data['file_name']);
                  }
                 else{
                      $fileName = base_url('files/reward_images/no_image.png');
                  }
               }
               $reward_image = $fileName;
               $item_id =0;
               $res = $this->rewards_model->save_reward_item($reward_image);
           }
        }
    }
}
private function set_upload_options($i)
 {
      //upload an image options
      $config = array();
      $config['upload_path'] = './files/reward_images/';
      $config['file_name'] = 'File'.time().$i;
     $config['allowed_types'] = '*'; \
     $config['max_size'] = '52528800';
     $config['overwrite'] = FALSE;
     return $config;
}