CodeIgniter - Log controller/method where error occurred

MY_Exceptions.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class MY_Exceptions extends CI_Exceptions {

// this file goes in application/core

	public function __construct()
	{
		$this->ob_level = ob_get_level();
		// Note:  Do not log messages from this constructor.
	}

	function log_exception($severity, $message, $filepath, $line)
	{
		$severity = ( ! isset($this->levels[$severity])) ? $severity : $this->levels[$severity];

		$router =& load_class('Router', 'core');

		log_message('error', 'Severity: '.$severity.'  --> '.$message. ' '.$filepath.' '.$line, TRUE);
		log_message('error', 'Above error occurred in '.$router->fetch_class().' controller, inside '. $router->fetch_method() . ' method.');
	}
}