Re: [Qemu-trivial] [Qemu-devel] [PATCH] Remove PCI class code from virtio balloon device

[Michael S. Tsirkin]

On Wed, Mar 21, 2012 at 09:42:41AM -0500, Anthony Liguori wrote:
> On 03/21/2012 08:08 AM, Michael S. Tsirkin wrote:
> >On Wed, Mar 21, 2012 at 11:26:15AM +0000, Stefan Hajnoczi wrote:
> >>On Tue, Mar 20, 2012 at 09:19:47PM +1100, David Gibson wrote:
> >>Looking at hw/pc_piix.c there are QEMUMachine types for each QEMU
> >>release.  Legacy machine types (e.g. pc_machine_v0_14) have a
> >>.compat_props array that can override qdev properties.
> >>
> >>Perhaps Michael Tsirkin or someone else can comment on how to wire up
> >>hw/virtio-pci.c so that the class code can be overridden.
> >>
> >>Stefan
> >
> >afaik we already let users over-write it for some other pci devices,
> >look there for examples.
> 
> From hw/pc_piix.c:
> 
>     .name = "pc-0.10",
>     .desc = "Standard PC, qemu 0.10",
>     .init = pc_init_pci_no_kvmclock,
>     .max_cpus = 255,
>     .compat_props = (GlobalProperty[]) {
>         {
>             .driver   = "virtio-blk-pci",
>             .property = "class",
>             .value    = stringify(PCI_CLASS_STORAGE_OTHER),
>         },{
> 
> And from the earlier part of the thread, yes, it's imperative that
> we do not change anything in the PCI configuration space for older
> pc versions regardless of whether it may or may not work.
> 
> Certain guests (like Windows) use a complex fingerprinting algorithm
> to determine when hardware changes.  It can be hard to detect in
> simple testing because it's based on a threshold.
> 
> Regards,
> 
> Anthony Liguori

Which reminds me - qemu sticks the release version in
guest visible places like CPU version.
This is wrong and causes windows guests to print messages
about driver updates when you switch.
We should find all these places and stop doing this.

> >
> >