Detecting if the link is up on eth0 device

From: vss (vsrivastav_at_gmail.com)
Date: 03/30/05 

Date: 30 Mar 2005 12:50:54 -0800

I need to find out if the eth0 device is connected or not. Is there a
way to probe the device? The driver for ethernet interface is compiled
in the kernel.

What is it that I can do to find that out?