Re: [Qemu-devel] [Xen-devel] [PATCH] Remove hardcoded xen-platform device initialization

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Ian Campbell
> Sent: 13 June 2013 18:44
> To: Stefano Stabellini
> Cc: Paul Durrant; qemu-devel@nongnu.org; xen-devel@lists.xen.org
> Subject: Re: [Xen-devel] [Qemu-devel] [PATCH] Remove hardcoded xen-
> platform device initialization
> 
> On Thu, 2013-06-13 at 18:33 +0100, Stefano Stabellini wrote:
> > On Thu, 13 Jun 2013, Paul Durrant wrote:
> > > The xen-platform device should be initialized by the Xen toolstack by
> > > passing the appropriate -device argument on the command line.
> > >
> > > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> >
> > This patch is problematic because we can't know for sure the version of
> > upstream QEMU that is going to be used with Xen.
> > If we apply this patch and QEMU 1.5 is going to be used with Xen 4.2,
> > guests won't be able to use PV drivers.
> 
> Is the right answer a lever to disable, rather than enable, it?
> 

I didn't want to add yes another xen specific command line argument to QEMU; it feels wrong when there's already a perfectly good way of specifying an arbitrary device on the command line, but I suppose I could add a xl version argument or somesuch and gate the device creation on xl version >= 4.3.0? Calling out the compatibility of different versions of xl with different versions of QEMU in some document seems like a better way to go though otherwise this sort of issue is probably going to come up again in future.

  Paul

> A workaround for the situation you envisage is to use the
> device_model_args config option, not ideal though.
> 
> >
> >
> >
> > >  hw/i386/pc_piix.c |    3 ---
> > >  1 file changed, 3 deletions(-)
> > >
> > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > index d618570..e25012d 100644
> > > --- a/hw/i386/pc_piix.c
> > > +++ b/hw/i386/pc_piix.c
> > > @@ -174,9 +174,6 @@ static void pc_init1(MemoryRegion
> *system_memory,
> > >      pc_register_ferr_irq(gsi[13]);
> > >
> > >      pc_vga_init(isa_bus, pci_enabled ? pci_bus : NULL);
> > > -    if (xen_enabled()) {
> > > -        pci_create_simple(pci_bus, -1, "xen-platform");
> > > -    }
> > >
> > >      /* init basic PC hardware */
> > >      pc_basic_device_init(isa_bus, gsi, &rtc_state, &floppy,
> xen_enabled());
> >
> >
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>