Re: [Xen-users] Xen domU version compatibility questions

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> What is the expected compatibility of domU image versions on various
> dom0 systems.

Hmmm.  Slightly tricky question...

> dom0 3.0.4
>       Can it run a HVM domU that was created on a 3.2 dom0

I'd guess the safe answer here is probably "maybe"...  The potential problem I 
see is where the virtual hardware features differ between different Xen 
versions.

I don't know of any showstoppers for doing this with either Windows or Linux 
guests (whereas if you used an older Xen, say 3.0.3, then HVM ACPI wasn't 
available and that's likely to cause more problems).  But I'm not comfortable 
to assert it will work, because I don't know enough about the HVM support.

>       Can it run a PV domU that was created on a 3.2 dom0

In general compatibility is only guaranteed with *older* guests.  In practice, 
XenSource's XenLinux contains some compatibility options enabling it to 
fallback to old APIs to run on older Xens, so these may run on quite old Xen 
releases.  So for one of these kernels, the guest will definitely run on the 
old dom0.

I don't even know if any compatibility code is required for a 3.2 domU to run 
on 3.0.4 - there may not have been any significant API changes...

> dom0 3.2
>       Can it run a HVM domU that was created on a 3.0.4 dom0

Again, I would guess this would probably work and I don't know of any 
showstoppers.  The potential problems again revolve around any changes in the 
virtual hardware that might upset the guest.  I suspect this might work OK, 
but I'm not going to assert it definitely will.

>       Can it run a PV domU that was created on a 3.0.4 dom0

Yes, definitely, this compatibility direction (older guest on newer Xen) is 
always intended to work.

> Is there a compatibility chart somewhere?

Maybe on the wiki?  I've certainly posted related information on the list 
before but I've never actually gone and published it somewhere central.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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