Re: [Xen-devel] [PATCH v2 3/3] libxl: add domain config parameter to force start of qemu

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Mar 29, 2016 at 06:44:32AM +0200, Juergen Gross wrote:
> On 28/03/16 16:50, Konrad Rzeszutek Wilk wrote:
> > On Tue, Mar 22, 2016 at 08:29:23AM +0100, Juergen Gross wrote:
> >> Today the device model (qemu) is started for a pv domain only in case
> >> a device requiring qemu is specified in the domain configuration
> >> (qdisk, vfb, channel). If there is no such device the device model
> >> isn't started and hence it is possible to add such a device to the
> >> domain later.
> >>
> >> Add a domain configuration parameter to specify the device model is
> >> to be started in any case. This will enable adding devices with a
> >> qemu based backend later.
> > 
> > .. s/devices/PV devices/
> > 
> > As surely PV guests can't use emulated devices. Or could they? That
> > would be quite interesting in a not kind of fun way.
> 
> Would require some work.
> 
> > 
> >>
> >> While the optimal solution would be to start the device model
> >> automatically when needed this would require some major rework of
> >> libxl at multiple places.
> > 
> > But you are not using this now (late start of QEMU), so why this patch?
> 
> This was the reason for the patch: start the device model early in order
> to have it running in case it would be needed later.


OK. However I am missing something here. My understanding is that the
QEMU Xen PV USB backend is not in the code-base. So why do this if QEMU
won't even support this?

Would it make more sense to wait until QEMU has this support, then
have this patch, or work on making libxl be able to start QEMU later
(during the time QEMU gains the XEn PV USB backend)?

> 
> Juergen

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