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Date: Fri, 12 Jun 2009 11:12:55 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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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, "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>

Mark McLoughlin wrote:
> 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]. 
>   

I think the point is that you don't need version numbers if you have a 
proper device tree.  NB the device tree contains no host configuration 
information.

Regards,

Anthony Liguori

> 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)
>
>