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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tim Deegan [mailto:tim@xxxxxxx]
> Sent: 19 June 2013 21:15
> To: Matt Wilson
> Cc: Alex Bligh; Paul Durrant; xen-devel@xxxxxxxxxxxxx; Ian Campbell; qemu-
> devel@xxxxxxxxxx
> Subject: Re: [Xen-devel] [Qemu-devel] [PATCH] Add Xen platform PCI device
> version 2.
> 
> At 11:21 -0700 on 19 Jun (1371640904), Matt Wilson wrote:
> > On Wed, Jun 19, 2013 at 11:42:06AM +0100, Alex Bligh wrote:
> > >
> > > --On 19 June 2013 10:13:17 +0000 Paul Durrant
> > > <Paul.Durrant@xxxxxxxxxx> wrote:
> > >
> > > >>We obviously can't say to users "Are you running Windows and are you
> > > >>running PV drivers >= X.Y, if so set lever A to position B, otherwise if
> > > >>you are running some other OS or an earlier version of the Windows
> PV
> > > >>driver set it to position A".
> > > >
> > > >Why not? The device can be chosen on a per-VM basis.
> > >
> > > Not everyone knows what guest some random user will be running
> > > (consider cloud platforms).
> >
> > I agree. If this is really the only solution, we would need to have
> > both versions presented to the guest so that old drivers continue to
> > work without any intervention.
> 
> I suspect that if we expose both, both sets of drivers try to run the
> same PV connections, and hilarity ensues.
> 

Actually I think I can make that work, and it is the conclusion I came to after 
Alex's comment. I'll create a new patch which introduces a new device, let's 
call it citrix-pv-bus or somesuch, which will have the necessary device id and 
revision and will be a dedicate device purely for the Citrix PV drivers. Then, 
if someone wants to create a VM which will be able use Citrix PV drivers they 
add this device to their config but leave all other aspects of the config 
unchanged, thus not precluding using that VM with any drivers that bind to the 
xen platform device.
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.

  Paul

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