Re: [Qemu-devel] [libvirt] [Qemu-ppc] [RFC PATCH qemu] spapr_pci: Create PCI-express root bus by default

[Eric Blake]

On 11/21/2016 07:08 AM, Andrea Bolognani wrote:

>> If libvirt is using a specific version of pseries, then it already knows
>> that <=2.7 has pci.0 as a root, pcie.0 otherwise. libvirt has a knowledge
>> what QEMU version has what, right?
> 
> It doesn't yet, that's the point :)
> 
> We *could* add such knowledge to libvirt[1], but *existing*
> libvirt versions would still not know about it, which means
> that upgrading QEMU withough upgrading libvirt will result
> in failure to create new guests.

But that's okay.  In general, we try to promise that:

old qemu + old libvirt works
new qemu + new libvirt works
old qemu + new libvirt works
new qemu + old libvirt is untested, and may require a libvirt upgrade

In other words, as long as you update your stack from top down (libvirt
before qemu), you should be fine.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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