hmm, on second thought, I think I would prefer the attached patch
(compiled but not tested).

Hardware usually returns all 1's when it's not present, or not working,
so think checking for addresses filled with 1's is a good idea too.

I also took the patch from alan's tree and made the memcmp against
six-byte 'zaddr' rather than a seven-byte string :)

-- 
Jeff Garzik       | May you have warm words on a cold evening,
Building 1024     | a full mooon on a dark night,
MandrakeSoft      | and a smooth road all the way to your door.