how to make a patch file

[Stefano Curtarolo <auro@nietzsche.mit.edu>]

Hi guys,

I did a supersmall modification in a driver of version 2.4.0. 
I would like to submit the patch to other users so they can test
if it works. I have 2 big directories: 
kernel-source-2.4.0-test4
and
kernel-source-2.4.0-test4-patched
How can I do the patch file ???

Thanks

Stefano (not yet patched !)