Common storage of original MAC address

[Brooks Davis]

On Sun, Aug 17, 2014 at 11:31:19PM +0000, Pokala, Ravi wrote:
> Hi folks,
> 
> At attach-time, the NIC drivers call ether_ifattach(), which stores the
> MAC address in the sockaddr_dl. If the MAC is subsequently changed (like
> by adding the interface to a lagg), if_setlladdr() changes the value in
> the sockaddr_dl. At least, that's the way I'm reading things - is that
> correct?
> 
> If so, then we do not keep a copy of the original MAC address. For a
> couple of reasons (diagnostics, asset tracking and reporting), it would be
> very nice if the original MAC were kept somewhere, even after the working
> MAC was changed by if_setlladdr().
> 
> Up till now, Panasas has been saving the original MAC in the softc of
> specific network drivers that we use, and making it accessible via a
> sysctl. That's something we have to do on a per-driver basis, and
> something we have to keep track of on our own. We'd like to put that
> information in a structure all the NIC drivers already use, and get that
> code upstream. Storing it would require a simple change to
> ether_ifattach() to stash it in the new location in addition to in the
> sockaddr_dl, and adding some standard way (a new ioctl or sysctl?) to
> access it. Notably, it would not require changing all the individual
> drivers. 
> 
> Are there any objections to this idea? Any suggestions as to where we
> might stash the original MAC?

I think I'd store the original address in struct arpcom at attach time
and publish it in the dev.<driver>.<unit> sysctl namespace.

-- Brooks
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