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: 26 June 2013 21:00
> To: Paul Durrant; Tim (Xen.org)
> Cc: Ian Campbell; Matt Wilson; xen-devel@xxxxxxxxxxxxx; qemu-
> devel@xxxxxxxxxx; Alex Bligh
> Subject: RE: [Xen-devel] [Qemu-devel] [PATCH] Add Xen platform PCI device
> version 2.
> 
> 
> 
> --On 26 June 2013 12:06:31 +0000 Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> wrote:
> 
> > The issue is the old s/w not the new s/w. The old drivers make
> > assumptions about each other's presence as we can't change that because
> > they are already out there.
> 
> Then (without knowing the details) what's to prevent the new drivers not
> making such assumptions, and carrying some versioning information, such
> that we need one new PCI device now, but no more in the future?
> 

The new drivers are architected very differently such that they are suitable 
for Windows Update. That means each driver is separately installable and 
upgradeable and can make no assumptions about presence or version of any other 
driver. Thus all discovery is done at runtime and each individual interface 
carries a version number.
I still think we need the option to control some aspect of the PCI device that 
the top level bus driver binds to so that we have the possibility of using 
different PV drivers sets on different VMs. I'm not saying that this is 
necessarily a good idea but the idea of a virtual hardware platform version 
(which is essentially what I believe this top level device represents, since we 
have no other way of indicating that to Windows Update) has precedent; VMWare 
have had such a concept for a very long time 
(http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003746)
 and so it seems quite reasonable for a product such as XenServer to have a 
similar concept. I'll submit code for a new Citrix PV Bus device shortly.

  Paul

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