WiFi and changed MAC addrs

[Ben Woodard <woodard@redhat.com>]

I just spent basically a day of my weekend grappling with this problem 
http://wiki.xensource.com/xenwiki/XenWifi
before I understood it well enough to realize that the fact that Xen 
changed the MAC addr for my WiFi card was the root cause of the problem. 
This got me thinking:

If a particular piece of hardware will refuse to send frames after the 
MAC address has been changed, then shouldn't the card's driver refuse to 
allow a change of the MAC address and return an error in response to the 
IOCTL that tries to change it? I can't think of a situation where this 
wouldn't be the right thing to do. However, before I submit a patch to 
fix this, does anyone else know of any special cases that I might need 
to deal with?

Also is behavior of refusing to send frames with a non-hardware 
specified MAC address part of the WiFi spec or is it particular to 
certain WiFi cards? IOW at what level do I need to fix it? Should I just 
fix it for the Intel cards that I've tested or do I need to fix it for 
all WiFi cards?

-ben