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Subject: Re: Configuration vs. compat hints [was Re: [Qemu-devel] [PATCHv3
	03/13] qemu: add routines to manage PCI capabilities]
From: Mark McLoughlin <markmc@redhat.com>
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Date: Fri, 12 Jun 2009 15:48:14 +0100
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Carsten Otte <cotte@de.ibm.com>, kvm@vger.kernel.org, Glauber Costa <glommer@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Blue Swirl <blauwirbel@gmail.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Paul Brook <paul@codesourcery.com>, Avi Kivity <avi@redhat.com>

On Fri, 2009-06-12 at 16:59 +0300, Michael S. Tsirkin wrote:
> On Fri, Jun 12, 2009 at 09:43:29AM +0100, Mark McLoughlin wrote:
> > = Solution - Separate configuration from compat hints =
> > 
> > As I suggested before:
> > 
> >   - Allow the VM manager to dump compat hints; this would be an opaque 
> >     file format, more like the savevm format than a config file
> 
> Why make it "like the savevm" format then?
> If they are opaque anyway, compat hints could be part of savevm format.

So a "savevm --only-compat-hints" command? It might make sense, since we
would want the compat hints with savevm too.

> >   - Use defaults where compat hints are not available; e.g. if the VM 
> >     manager specifies a device config, but no compat hints are 
> >     supplied for it, then just use default values
> > 
> >   - Make the config override compat hints; e.g. if there are compat 
> >     hints specified for a device not included in the machine config, 
> >     just ignore those hints
> > 
> > Cheers,
> > Mark.
> 
> If compat hints are opaque and only editable by qemu, we can get into a
> situation where one can't create a specific setup with a new qemu.

An example?

Cheers,
Mark.