[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: [libvirt] [PATCH for-4.0 v2] virtio: Provide version-specific variants of virtio PCI devices



On Tue, Nov 20, 2018 at 11:52:27AM +0100, Cornelia Huck wrote:
> On Mon, 19 Nov 2018 22:44:54 -0200
> Eduardo Habkost <ehabkost redhat com> wrote:
> 
> > On Thu, Nov 15, 2018 at 11:50:56AM +0100, Cornelia Huck wrote:
> > > On Thu, 15 Nov 2018 10:05:59 +0000
> > > Daniel P. Berrangé <berrange redhat com> wrote:
> 
> > > > If libvirt did this compatibility approach, can you
> > > > confirm this would be live migration state compatible.
> > > > 
> > > > ie can live migrate virtio-*-pci -> virtio-*-pci-transitional,
> > > > provided only PCI bus was used.  
> > > 
> > > It also needs to make sure that neither disable-legacy nor
> > > disable-modern is set. Then this would have a compatible state AFAICS.
> > >   
> > > >   
> > > > > - virtio-*-pci-non-transitional: modern-only
> > > > >   - Supports both Conventional PCI and PCI Express buses    
> > > > 
> > > > IIUC, libvirt can again provide compatibility with old
> > > > QEMU by simply using the existing device type and setting
> > > > disable-legacy ?  Can you confirm this would be live
> > > > migration compatible
> > > > 
> > > >   virtio-*-pci + disable-legacy -> virtio-*pci-non-transitional  
> > > 
> > > I think yes.  
> > 
> > This is exactly how it is implemented internally, but I'm not
> > promising that this will be kept compatible forever.  And I
> > wouldn't like to make that promise unless there's an important
> > use case for that.
> 
> Shouldn't we be able to ensure compatibility by normal virtio feature
> bit handling, as we have already done in the past?

Ensuring compatibility is possible, and even likely.  I just want
to avoid spending effort keeping such a promise unless it's
really necessary.

> 
> > 
> > We could easily ensure it will be compatible in pc-4.0 and older,
> > though.  Would that be enough for the use case we have in mind?
> > 
> 

-- 
Eduardo


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]