Re: Configuration vs. compat hints [was Re: [Qemu-devel] [PATCHv3 03/13] qemu: add routines to manage PCI capabilities]

[Anthony Liguori]

Avi Kivity wrote:
> On 06/15/2009 12:09 PM, Mark McLoughlin wrote:
> > > > > I think the point is that you don't need version numbers if you 
> > > > > have a
> > > > > proper device tree.
> > > > >
> > > > >          
> > > > How do you add a new attribute to the device tree and, when a supplied
> > > > device tree lacking said attribute, distinguish between a device tree
> > > > from an old version of qemu (i.e. use the old default) and a partial
> > > > device tree from the VM manager (i.e. use the new default) ?
> > > >
> > > >        
> > > -baseline 0.10
> > >      
> >
> > That's a version number :-)
> >
> > (I was responding to Anthony's "you don't need a version number")
> >    
>
> If you want to prevent incompatibilities, you need to make everything 
> new (potentially including bugfixes) non-default.  Eventually the 
> default configuration becomes increasingly unusable and you need a new 
> baseline.  You must still be able to fall back to the old baseline for 
> older guests.  I don't think games with configuration files can hide 
> that.

-M pc1
-M pc2

etc.

This is pretty easy to maintain with config files.

Regards,

Anthony Liguori