FWIW you can just use ethtool to determine the slot address quickly
in userspace. There's no real need to do this in the kernel.

# ethtool -i eth0
driver: e1000e
version: 0.2.0
firmware-version: 1.3-0
bus-info: 0000:00:19.0

And if it happens to be in a hotplug slot today with a suitable hotplug 
module (term?) loaded like acpiphp you can then map that to a more human 
friendly slot number/name.  In the future, once Alex Chiang's pci slots 
patches make it to mainline it will be possible even with non-hotplug slots.

netperf omni tests and a couple other tools try to find such mappings today.

rick jones