Re: [Xen-devel] [Qemu-devel] [PATCH] Add Xen platform PCI device version 2.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Alex Bligh [mailto:alex@xxxxxxxxxxx]
> Sent: 20 June 2013 09:09
> To: Paul Durrant; Tim (Xen.org); Matt Wilson
> Cc: xen-devel@xxxxxxxxxxxxx; Ian Campbell; qemu-devel@xxxxxxxxxx; Alex
> Bligh
> Subject: RE: [Xen-devel] [Qemu-devel] [PATCH] Add Xen platform PCI device
> version 2.
> 
> 
> 
> --On 20 June 2013 07:47:12 +0000 Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> wrote:
> 
> > If someone has a VM that has the old Citrix drivers installed, or GPLPV,
> > I think I should be able to spot this and make sure that the new bus
> > driver quiesces itself to prevent strangeness ensuing. If and when said
> > previous drivers are un-installed then the new bus driver can wake up and
> > enumerate the device nodes for the other pv drivers and Windows Update
> > can carry on doing its stuff.
> 
> I have no clue about Windows device drivers, so this may be a silly
> suggestion. If your suggestion above already requires a Xen code change,
> one possibility might be copy the idea behind the PCI unplug logic. Either
> if the new PCI device is used, it could unplug the old one, or vice versa.
> Drivers magically unplugging themselves may not be ideal, but it beats
> having 2 drivers fighting over the same device.
> 

Unfortunately, whilst it sounds good on the face of it, it's not as 
straightforward as that. The old Citrix PV drivers did not just bind to the Xen 
platform device, and make that device go away automagically would actually 
cause the system disk to disappear without any clean fallback to emulation.
As long as nothing actually breaks if and when Windows fetches the new PV bus 
driver from Windows Update then we can document the need to manually uninstall 
any other PV drivers.

  Paul

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