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Date: Fri, 12 Jun 2009 16:59:36 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: Configuration vs. compat hints [was Re: [Qemu-devel] [PATCHv3
	03/13] qemu: add routines to manage PCI capabilities]
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To: Mark McLoughlin <markmc@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, 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.

>   - 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.

-- 
MST