Re: [Xen-devel] 32-on-64: pvfb issue

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Thu, Jan 18, 2007 at 04:35:03PM +0100, Gerd Hoffmann wrote:
> Markus Armbruster wrote:
> > Gerd Hoffmann <kraxel@xxxxxxx> writes:
> > 
> >> and probably (hmm, does fc6 ship it?) not widely used yet that might be
> >> an option.
> > 
> > Breaking the API now is right out of the question, I fear :)
> 
> Yep, I've seen in the release notes fc6 ships pvfb, so it is used in the
> wild now and breaking the API is clearly out of question.  Damn.  Should
> have reviewed the patches earlier ...

Actually FC6 isn't a problem - the ABI already changed between the time we 
shipped it in FC6, and the time it got merged in xen-devel. For RHEL-5 though
we have synced to the ABI currently in xen-devel/xen-3.0.4. We plan to update
FC-6 to use this ABI too, to remove the incompatability. The downside is that
in FC-6 Xen userspace we now have to maintain some non-upstream back-compat
code to let both old &new kernels run on new userspace - that's the price
paid for shipping before upstream. Now it is upstream though we really don't
want to see incompatible changes again because it will screw over not just
Fedora, but RHEL too, and indeed any users of Xen 3.0.4 release.

BTW, the way we do the back-compat support is basically to ship two versions
of the xen-sdlfb & xen-vncfb  daemons - one speaking the old protocol, one
speaking the new. We try to launch the new versions & if they fail, we 
launch the old versions. A nasty hack, but it works.

Regards,
Dan.
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