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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 16:53:27 +0100
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Carsten Otte <cotte@de.ibm.com>, kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, 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 09:55 -0500, Anthony Liguori wrote:
> Mark McLoughlin wrote:
> > On Wed, 2009-06-10 at 20:27 +0100, Jamie Lokier 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
> >   
> 
> How is compat hints different from a device tree?
> 
> In my mind, that's what compat hints is.  I don't see another sane way 
> to implement it.

A device tree with a different purpose than a config file.

In its simplest form it could be a device tree with a version number for
each device[1]. 

The other obvious piece to add to it would be PCI addresses, so that
even if you remove a device, the addresses assigned to existing devices
don't change.

Cheers,
Mark.

[1] - Adding such a per-device version number to the config file would
solve problem (2)