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

From: Ian Campbell
Subject: Re: [Qemu-devel] [Xen-devel] [PATCH] Add Xen platform PCI device version 2.
Date: Wed, 19 Jun 2013 11:07:32 +0100

On Wed, 2013-06-19 at 10:43 +0100, Paul Durrant wrote:
> > -----Original Message-----
> > From: Ian Campbell
> > Sent: 19 June 2013 10:42
> > To: Paul Durrant
> > Cc: address@hidden; address@hidden
> > Subject: Re: [Xen-devel] [PATCH] Add Xen platform PCI device version 2.
> > 
> > On Wed, 2013-06-19 at 10:32 +0100, Paul Durrant wrote:
> > > The XenServer 6.1+ Citrix Windows PV bus driver binds to a new version
> > > of the Xen platform device (since the newer driver set cannot co-exist
> > > with previous drivers which bind to the existing "xen-platform" type of
> > > device). This patch introduces a new "xen-platform-2" device type with
> > > the appropriate device_id and revision.
> > 
> > What is the difference between these two devices?
> > 
> As the comment implies, the device_id (2 rather than 1) and the revision (2 
> rather than 1).

So what is the point of it?

Changing these IDs won't work for any other existing PV drivers, it will
break the Linux PVHVM ones and the BSD ones etc.

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".

It sounds to me as if this is a hack to workaround some shortcoming of
the Windows driver model. If this is the case then I'm afraid you are
going to have to find a way to deal with this from within Windows and/or
your drivers. Failing that then I think you'll just have to document an
upgrade path for the users of your older drivers. Pushing the pain onto
the entire world is just not the right way to go about this.


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