Bug#812575: udev: predictable network device names fails for USB devices without a permanent hw address

[Martin Pitt]

Control: tag -1 pending

Hello Bjørn,

Bjørn Mork [2016-01-25  9:27 +0100]:
> 1) the name is derived from a random mac address, which is regenerated
>    on each boot.  Note that the address does have the 'local' bit set:
>     2a:c5:66:37:bc:cb
> 
> The old persistent network device logic used to avoid mapping against
> locally administered mac addresses.  This logic needs to be kept for
> the new  "predictable" names too.  Anything else is a regression.

Argh, thanks for pointing this out! I fixed this in

 https://anonscm.debian.org/cgit/pkg-systemd/systemd.git/commit/?id=ec7e332

Now only devices with universally administered MACs will get a MAC
based name, for the locally administered ones we'll use the default
naming schema of all other types, i. e. location based.

For the record, I actually don't like the MAC based names very much;
these were a compromise from the discussion a year ago, and by and
large emulate what the old 75-persistent-net stuff used to do with
such USB devices. But I don't want to completely drop this without a
followup discussion (I started one for Ubuntu in
https://lists.ubuntu.com/archives/ubuntu-devel/2016-April/039302.html,
but we might need to have this on Debian again too).

Bjørn Mork [2016-02-02 14:08 +0100]:
> And I recall even being part of that discussion.  Obviously without
> getting the message trough.  So let me try again:
> 
>    You CANNOT create a stable name for USB devices.
> 
> The reason is pretty simple and should be bloody obvious: You have no
> stable and unique input parameteres.  Every single attribute you have
> access to is either shared with multiple devices or subject to change.

This isn't true for universally administered MAC addresses, like
commonly for USB ethernet adapters. We've used the MAC for identifying
those for many many years.

The locally administered ones indeed don't have any intrinsic property
to build a name from. As the kernel name for them is also
random/unstable, I believe having path based names is the best policy
for them: At least you get reliable names if you plug them into the
same port (which is rather intuitive for things like RasPi boards);
and if you change ports, then we don't have any stable property and
the name doesn't matter at all (you can't use it in /e/n/interfaces or
firewall scripts anyway).

Thanks,

Martin

-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)
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