Re: [Xen-devel] [PATCH] Add a device_model_machine option for HVM domains to libxl.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:stefano.stabellini@xxxxxxxxxxxxx]
> Sent: 19 June 2013 18:26
> To: Paul Durrant
> Cc: Stefano Stabellini; xen-devel@xxxxxxxxxxxxx
> Subject: RE: [Xen-devel] [PATCH] Add a device_model_machine option for
> HVM domains to libxl.
> 
> On Wed, 19 Jun 2013, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Stefano Stabellini [mailto:stefano.stabellini@xxxxxxxxxxxxx]
> > > Sent: 18 June 2013 20:06
> > > To: Paul Durrant
> > > Cc: xen-devel@xxxxxxxxxxxxx
> > > Subject: Re: [Xen-devel] [PATCH] Add a device_model_machine option
> for
> > > HVM domains to libxl.
> > >
> > > On Mon, 17 Jun 2013, Paul Durrant wrote:
> > > > The device-model machine type used for HVM domains is currently
> > > hardcoded to
> > > > 'xenfv'. This patch adds a device_model_machine option, which
> defaults to
> > > > 'xenfv' for comatibility, but allows the specification of an alternative
> > > > machine type 'pc'.
> > > > Note that use of the 'pc' machine type relies on patches that I have
> > > > submitted to qemu-devel.
> > > >
> > > > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > >
> > > NACK
> > >
> > > I don't think that this kind of option should exposed to the user except
> > > maybe for debugging purposed.
> > > We need a way to automatically select the right one.
> > >
> >
> > Ok, but what is the *right* one? Would you accept this patch without the
> manpage tweak? Xenfv's hardcoded platform device creation is completely
> stalling my attempts to get Citrix Windows PV drivers running on upstream.
> Having this option and defaulting it to xenfv seems like a fairly pragmatic
> approach to me.
> 
> Sorry, I realize that my messages have been a bit confusing.
> 
> I am not opposed to having this option as a companion of
> device_model_override, I am just opposed to using this option to solve
> the compatibility problem with QEMU.
> 
> I would like to see an additional patch that queries the running QEMU
> for its version and uses it to determine the default QEMU machine
> version.  Then we can also allow users to override it with something
> like this patch.

Yes, that's quite reasonable and such an additional patch series is my 
intention, but like so many things I don't have time to work on that now. So, 
if you think the new option has implications beyond my intention as an override 
then I'd be happy to modify it.
Here's a plan:

- I make it freeform, rather than an enumeration (meaning folks have to add the 
,accel=xen option themselves, but giving flexibility)
- I make it more clear in the manpage (and possibly in the option name itself) 
that it is an override

Does that sound ok?

  Paul

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