Re: [Qemu-devel] [PATCH] xen: make xen-platform a default device

[Paul Durrant]

> -----Original Message-----
> From: Stefano Stabellini [mailto:address@hidden
> Sent: 22 May 2014 14:57
> To: Gerd Hoffmann
> Cc: Paolo Bonzini; Stefano Stabellini; Paul Durrant; address@hidden;
> Anthony Liguori; address@hidden
> Subject: Re: [PATCH] xen: make xen-platform a default device
> 
> On Thu, 22 May 2014, Gerd Hoffmann wrote:
> > > > 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.
> > >
> > > In fact this code only runs for "-M xenfv".  If you use "-M pc", the
> > > xen-platform device has to be added manually.  Perhaps it would be
> > > worthwhile to do the opposite, i.e. add the xen-platform device to "-M
> > > pc" if not using -nodefaults.
> >
> > /me looks at the code.  Yes, all the differences between xenfv and pc
> > machine types are guarded by if (xen_enabled()) these days, except for
> > adding the platform device.
> >
> > So using the pc machine type should just work on xen, and give you a
> > machine without the platform device.  So it can be added via -device, at
> > any slot, if needed.  No need to patch qemu at all.  Adding or not
> > adding xen-platform can easily handled by libxl then, depending on the
> > xen_platform_pci switch in the config file.
> 
> I agree. Changing libxl to always use -M pc and using -device to add
> xen-platform when needed sounds like the best option.

Really? You opposed this before:

http://lists.xen.org/archives/html/xen-devel/2013-06/msg01946.html

stating that you wanted a mechanism to query the running version of QEMU before 
choosing the machine type.

  Paul