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Date: Thu, 22 May 2014 17:00:51 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] xen: make xen-platform a default device
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Paul Durrant <paul.durrant@citrix.com>, qemu-devel@nongnu.org, Anthony Liguori <aliguori@amazon.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>

On Thu, May 22, 2014 at 02:53:19PM +0200, Gerd Hoffmann wrote:
> On Do, 2014-05-22 at 15:35 +0300, Michael S. Tsirkin wrote:
> > On Thu, May 22, 2014 at 01:11:28PM +0100, Stefano Stabellini wrote:
> > > On Thu, 22 May 2014, Gerd Hoffmann wrote:
> > > > Patch hooks up the xen platform device to the default device code we
> > > > have in qemu.  Two effects:
> > > > 
> > > >   (1) The device will not be created in case -nodefaults is specified
> > > >       on the command line.
> > > >   (2) Autocreating the device is also turned off in case xen-platform
> > > >       is added manually via -device.
> > > > 
> > > > With the patch applied you can move the xen-platform device to some
> > > > other place with a simple 'qemu -device xen-platform,addr=$slot'.
> > > > 
> > > > Tested-by: Tiejun Chen <tiejun.chen@intel.com>
> > > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > > 
> > > Given that libxl always passes -nodefaults to QEMU, this patch is going
> > > to effectively disable xen_platform_pci for all Xen users. It is not a
> > > good idea. With the patch applied a Xen user would have no way to enable
> > > xen_platform_pci except for passing some magic command line runes via
> > > device_model_args_hvm.
> > > 
> > 
> > Yes, it's an unfortunate use of the interface.
> > How about a new machine type for xenfv - that's the only one
> > that's affected, right?
> > It's time xen started versioning qemu hardware anyway.
> 
> That would do the trick for sure.  Question is what versioning scheme.
> Might be useful for xen machine types to version after xen releases,
> i.e. xenfv-4.4 would would be supposed to be compatible with the xen-4.4
> toolstack etc.
> 
> cheers,
>   Gerd
> 

It's much easier for us to version it with qemu machine version,
like we do for pc, if that can work at all.