How can i detect presence of USB keyboard from user space program ?

From: pweichel (runtime_at_mail.dk)
Date: 11/08/05 

Date: 8 Nov 2005 02:37:37 -0800

Hi all,

I have written a user space program which traps keyboard input from
several input sources using select() function on the /dev/input/eventX
files.

It works nicely, but how can i detect from that same program if user
decides to pull-out a USB connected keyboard or insert another in the
USB port of the embedded Linux system ?

B.Rgds.
Peter
Denmark