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

On Fri, Jun 12, 2009 at 04:53:27PM +0100, Mark McLoughlin wrote:

On Fri, 2009-06-12 at 09:55 -0500, Anthony Liguori wrote:

quoted

Mark McLoughlin wrote:

quoted

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.

Could you clarify this requirement please?

If we want to remove a device from under a running guest, you need
hotplug. So we can't just remove several lines from the config and hope
that it'll work simply because the PCI address is stable.

OTOH, if you reboot the guest, it's ok for addresses to change.

Cheers,
Mark.

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

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