Re: [Xen-devel] Re: [Qemu-devel] [PATCH 1/7] xen: groundwork for xen support

[Gerd Hoffmann <kraxel@redhat.com>]

Anthony Liguori wrote:
> Daniel P. Berrange wrote:
>> That would work for certain setup tasks, but not all. In Xen's branch
>> of QEMU, the machine init function has to set various hypervisor
>> parameters which aren't directly associated with QEMU command line
>> args, and initialize things like the map-cache for > 4GB guest support.
> 
> map-cache is one of those things I don't expect to ever get merged.

And the need for that will go away over time IMHO.  If your Dom0 is
64bit you have no address space pressure and thus no need for mapcache.
 Given we have 32-on-64 and non-PAE Xen is depricated anyway there is
almost no reason to not run 64bit Xen and Dom0.

> Ideally, I'd like to see Xen/KVM integration look like this:
> 
> 1) Xen support is detected in configure (libxc et al) and conditionally
> enabled.
> 2) When running on bare metal, detect whether KVM acceleration is
> available, also detect if kqemu acceleration is available
> 3) When running under Xen, detect that Xen is available, and create a
> full virt domain
> 4) If a user specifies a type=xen device, it should Just Work provided
> you are in a Xen environment (erroring appropriately)
> 5) A user can explicitly specify -M xenpv.  If running under Xen, this
> would create a Xen PV guest.  If running on bare metal, Xenner would be
> used to present a Xen shim layer.  This should work with KVM
> acceleration or without KVM acceleration.  Bonus points if it works with
> kqemu too.

I'm surprised how well you can read my mind.
Yes, I wanna have the bonus points ;)

There are two additional points you didn't see though:

For (3) and (5) qemu should support two modes:  First, attach to an
existing domain.  This is how Xen works today.  And we want get rid of
the qemu-dm fork, right?  Second, optionally also create the domain,
like Xenite.

(4) should also just work when you are *not* in a Xen environment[1]

cheers,
  Gerd

[1]  It actually does, btw.  Code isn't ready yet for merging.
     Stay tuned ;)

-- 
http://kraxel.fedorapeople.org/xenner/