Xen/OpenVZ out-of-tree module builds and ABI

[Ian Campbell]

On Sun, 2010-10-10 at 19:34 +0100, Ben Hutchings wrote:
> On Sun, 2010-10-10 at 09:51 -0700, Russ Allbery wrote:
> > Hello, kernel folks.
> > 
> > We (the NVIDIA packaging team) noticed a commit from the latest Debian
> > kernel packaging that said:
> > 
> >      Refresh ABI reference files
> > 
> >      Remove files for OpenVZ and Xen featuresets, where we are not
> >      trying to keep the module ABI stable.
> > 
> > (r16351) and weren't entirely sure what that meant.
> > 
> > We maintain module builds for the NVIDIA kernel drivers (which are
> > non-free) using a build package that builds versions for the current
> > kernel, primarily for stable releases.  Currently, we're building modules
> > for Xen and OpenVZ kernels as well as the regular kernels.
> > 
> > Does this change mean that the module builds for Xen and OpenVZ kernels
> > may not continue working with later versions of those kernels because the
> > ABI might not be stable?
> 
> Correct.  We try hard to avoid ABI breakage after a freeze and in stable
> updates and we have so far succeeded with the 'standard' images, but we
> have given up on a stable ABI for the OpenVZ and Xen featuresets.

I can't speak for OpenVZ but I think we are unlikely to pull in a
complete new drop of the Xen pvops patch now that we are frozen (Bastian
-- what do you think?) so in theory we can maintain the ABI we have
today for future uploads. That would still mean that there had been
multiple different things calling themselves ABI 5 in Squeeze during
development but at least it would have one meaning in the actually
released version of Squeeze.

> Unfortunately we currently use a single ABI number across all image
> packages so there is no indication of when the ABI changes for them.
> 
> > Or is this a more limited change that means
> > something more restrictive than that and isn't something we need to worry
> > about?
> > 
> > I ask primarily because we want to be sure it makes sense to release
> > pre-built modules for Xen and OpenVZ kernels with squeeze.
> 
> I don't think it does.

In my experience the closed source Nvidia drivers don't work with pvops
Xen anyway. I believe Nouveau does but I had already switched to ATI
when that went mainstream.

Ian.
-- 
Ian Campbell
Current Noise: Sabbat - Hosanna In Excelsis

Wow, I'm being shot at from both sides.  That means I *must* be right.  :-)
		-- Larry Wall in <199710211959.MAA18990 at wall.org>