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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Ian Campbell
> Sent: 02 July 2013 11:57
> To: Tim (Xen.org)
> Cc: Paul Durrant; qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH] Citrix PV Bus device
> 
> On Tue, 2013-07-02 at 11:49 +0100, Tim Deegan wrote:
> > At 10:31 +0000 on 02 Jul (1372761105), Paul Durrant wrote:
> > > > > 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.
> >
> > Well, you can have them install by default on platforms that want it, or
> > on new enough Xen versions.  Or, even better, on new enough _windows_
> > versions.
> >
> > > > > 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?
> >
> > Only if it's OK that the _host_ admin has to be involved (which was the
> > original objection).  Upgrade-only but hooked to the existing ID lets a
> > guest admin install the drivers manually without plumbing it through
> > $CLOUDPROVIDER's toolstack, and without having it appear suddenly on
> > existing VMs in the dead of night.
> 
> I think part of the problem here is that it is unclear who the target
> audience for these drivers are.
> 
> Paul, are you intending that these drivers be only for XenServer users
> or are you intending for them to be used by the broader community on a
> variety of different Xen platforms?
> 

My intention is that the drivers are widely available to all who want them, but 
the key word there is 'want'. No-one should get a surprise when we publish to 
Windows Update so having the drivers bind to a new device which can then be 
added to the VM config seems like the cleanest solution.
I realise that this involves the VM provider having to do something to enable a 
VM to get drivers from Windows Update rather that the guest admin, but I think 
that's actually the right way to do it. Adding this device into a VM is 
essentially enabling new functionality in the same way that adding a new 
network device or storage device would be.

  Paul

  
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