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

[Tim Deegan <tim@xxxxxxx>]

At 11:23 +0000 on 26 Jun (1372245783), Paul Durrant wrote:
>  We could blacklist all existing Citrix PV drivers in upstream QEMU,
> to avoid the clash, but that seems like a very unfriendly
> approach. Also, it's not going to stop someone with an existing VM,
> who happens to be using legacy Citrix PV drivers (an AWS VM for
> instance) receiving a driver from Windows Update that will blue-screen
> their VM on next reboot. Hence the only way forward is to bind the new
> drivers to something new, that we can control, so we know what driver
> a VM is going to get from Windows Update.

I don't think you ever got an answer about whether this could be
finagled using version numbers in the drivers.

Also: would it not be possible to have a blkfront driver (even a trivial
one) in your new bus driver so it can detect and avoid this problem?

Or: have your bus driver detect when the blkfront driver is missing and
not unplug the emulated disk?  In fact wouldn't having the emulated disk
driver do the unplug solve it for free?

> And we may indeed need to
> modify its revision in future so that we can retire old sets of PV
> drivers and replace them with new ones, but only for newer XenServer
> releases. Thus, I also propose to make the PCI revision of the new
> device a command line parameter.

I'd rather not.  This gets straight back to having host-admin controls
that have to manually be matched to in-guest software. 

Tim.

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