physical vs virtual mac address and mac address from NIC's firmware

Hi,

I am a newbie on linux and writing a small tool to get info of ethernet adapters

installed. Please find more details and discussions in this post:
http://www.linuxforums.org/forum/programming-scripting/177222-physical-vs-virtual-mac-address-mac-address-nics-firmware.html#post842296

As the tool plays an important role in licensing system thus I need to make sure

that solution should work
ideally on as many distros as possible. Considering the major and most commonly used distributions such as fedora, ubuntu, opensuse, debian etc. including their

latest versions and bit older ones (3-4 years), what are the cons I might face using ethtool
api to get perma address?

BTW, you are kernel guys and I hoping that you might give me an answer for differentiating between physical and virtual adapters.

The details of my distribution including requirements of app is posted on the above mentioned topic.

Best Regards

Prashant