Re: [Qemu-devel] [Xen-devel] [PATCH] Citrix PV Bus device

[Paul Durrant]

> -----Original Message-----
> From: Ian Campbell
> Sent: 02 July 2013 11:24
> To: Tim (Xen.org)
> Cc: Paul Durrant; address@hidden; address@hidden
> Subject: Re: [Xen-devel] [PATCH] Citrix PV Bus device
> 
> On Tue, 2013-07-02 at 11:15 +0100, Tim Deegan wrote:
> > At 10:56 +0100 on 02 Jul (1372762607), Ian Campbell wrote:
> > > On Tue, 2013-07-02 at 10:14 +0100, Paul Durrant wrote:
> > > > I had actually coded up a solution based on the existing Xen platform
> > > > device, by having it synthesize a device ID based on the Xen version
> > > > to which we could then host the xenbus driver, to allow us to deploy
> > > > multiple versions of xenbus should compatibility (with things such as
> > > > the shared info interface) become an issue. The co-installer for this
> > > > driver could also spot existing PV driver installations and make sure
> > > > they don't get trashed.
> > >
> > > I think only this last bit of functionality is critical here, and it
> > > allows us to avoid having to carry multiple platform devices in
> > > upstream, doesn't it?
> > >
> > > > This idea was rejected by Citrix product teams though, because we
> > > > would not be able to prevent any Windows guest without some known
> PV
> > > > drivers from downloading our new driver from Windows Update and
> this
> > > > was seen as undesirable.
> > >
> > > Well, if your product requirements are at odds with doing the right
> > > thing upstream then I think it would be best for you to just carry
> > > patches to make XS behave how you want.
> >
> > I think it's a reasonable aim to have the WU drivers not spontaneously
> > appear on VMs (on all Xen hosts, remember) where the admin has chosen
> > not to install PV drivers.
> >
> > Generally, the more I think about this the more I'm convinced that _not_
> > installing the drivers on any existing systems without explicit
> > permission is the most important thing.
> 
> Will WU install a completely fresh driver for a new (or indeed old) bit
> of hardware on native entirely without prompting?
> 
> I'd have expected the old "Windows has found a driver for your device"
> dance.
> 
> > > I hope we can find a suitable compromise though.
> >
> > Well, the WU drivers could refuse to install except as upgrade to
> > themselves (i.e. fail if there's any unknown driver bound to the xen
> > platform device, and also fail if there's _no_ driver bound).  Then the
> > guest admin can choose to install the drivers by hand and get automatic
> > updates after that.
> 
> That sounds reasonable. However I thought part of the point of getting
> things into WU was then that they could be "inbox" (either figuratively
> or literally) such that they would be installed by the Windows
> installer. Perhaps that's a separate thing though.
> 

No, that is the eventual aim so I don't think the 'upgrade only' options is 
really future-proof.

> > XS, XC and anyone else who chooses could carry a separate patch that
> > changes the default to 'install if there are no drivers', signalling
> > over xenstore, or ACPI, or a Windows domain policy, or whatever.
> 
> Right.
> 

Surely having a new device for the purposes of hosting Citrix PV drivers is a 
cleaner option for opting in? Note that I'm not proposing the new device 
displaces the existing platform device in any way.

  Paul