Using biosdevname by default?

[Colin Watson]

Dell has asked for biosdevname to be enabled by default on new Ubuntu
installations on Dell PowerEdge servers:

  https://bugs.launchpad.net/ubuntu/+source/biosdevname/+bug/891258

I do not feel that this is a decision I can take on my own, and would
like to seek guidance from the good folks on these lists.

For those unfamiliar with biosdevname, it's a udev helper intended to
handle the problem of unstable network device enumeration ordering by
mapping them into different namespaces according to BIOS-provided naming
information.  More information can be found here:

  http://linux.dell.com/biosdevname/
  http://manpages.ubuntu.com/biosdevname

This is supported on an opt-in basis from Ubuntu 11.04 on (modulo a bug
in 11.04 to the effect that it didn't work with a separate /usr, fixed
in 11.10) by passing the "biosdevname=1" kernel parameter when starting
the installer.


There are certainly some advantages to enabling biosdevname by default.
On systems that support it, it makes it somewhat easier to write scripts
that predictably apply to a certain interface without having to mess
around with looking up interfaces by MAC address.

However, I have a few concerns about enabling this by default.  Firstly,
I think it is in general unwise to make this kind of change for a single
class of machine, at least for Ubuntu itself as opposed to
vendor-specific builds.  The effect of doing that is to divide our
testing efforts, so that tests of relevant functionality on one class of
machine can no longer be presumed to be valid for others.  This usually
ends up being to the detriment of everyone: Dell servers would no longer
be able to take advantage of the testing we do on other classes of
system.

Of course, not many other systems support biosdevname anyway; HP
ProLiants are explicitly handled in the biosdevname source, but for many
systems, including at least kvm but many real machines as well,
biosdevname will just leave the kernel-provided interface names in
place.  (Even if biosdevname supported no non-Dell systems right now,
I'd still be of the opinion that we should be as consistent about it as
we can on the basis that other BIOSes might add support at some point in
the next five years.)

Secondly, while as I said above I agree that enabling biosdevname solves
some problems, it seems likely that this change will cause problems of
its own.  For example, any software that needs to know about network
interfaces (let's say it listens on a particular interface) might well
default to eth0; this will break on many wireless-only systems and
require manual configuration, but if it's not the sort of thing that you
use on a laptop, many users might not previously have noticed.  Using
biosdevname by default would extend these problems to many server-class
machines out of the box.  While anything like this is certainly a bug
already, with the new scheme we'd *have* to fix everything like that and
it'd be easy to miss something.  The question of whether you see this as
an opportunity to expose existing bugs or as a risk rather depends on
your point of view. :-)

Still, I'm not typically working in environments where unstable network
device naming causes me any problems, so I tend to see the downsides
rather than the upsides.  I'd like to hear from people who do suffer
from this kind of problem, as well as from the server team who would
presumably be at the sharp end either way.

Thanks,

-- 
Colin Watson                                       [cjwatson at ubuntu.com]