Re: [Qemu-devel] Headsup: windows virtio networking does not work on current git

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Feb 07, 2013 at 09:53:39PM +1100, Vadim Rozenfeld wrote:
> On Thu, 2013-02-07 at 12:18 +0200, Michael S. Tsirkin wrote:
> > On Thu, Feb 07, 2013 at 08:24:10PM +1100, Vadim Rozenfeld wrote:
> > > On Thu, 2013-02-07 at 11:33 +1030, Rusty Russell wrote:
> > > > Vadim Rozenfeld <vrozenfe@redhat.com> writes:
> > > > > On Tue, 2013-02-05 at 13:58 +0200, Michael S. Tsirkin wrote:
> > > > >> On Tue, Feb 05, 2013 at 03:45:38PM +0400, Michael Tokarev wrote:
> > > > >>  Is it really
> > > > >> > that bad that the config space size changed?  Why it has this effect?
> > > > > Because in this case it's hard to distinguish between resource's
> > > > > corruption and HW update.
> > > > 
> > > > But it's also true that if we'd incremented revid you'd have the same
> > > > failure in this case, right?
> > > 
> > > It depends. If we have explicitly specified revision id in inf file and
> > > this id doesn't mach the new revision id, Windows will not try to load
> > > the "incompatible" driver, and finish up with "device driver not found"
> > > dialog.
> > > 
> > > Best regards,
> > > Vadim.
> > >   
> > > > 
> > > > Cheers,
> > > > Rusty.
> > 
> > Well that's all in theory, in practice it does not look like revision ID
> > is specified in the NetKVM inf so this won't work?
> > 
> > From what I see this inf specifies:
> > 
> > NetKVM/wlh/netkvm.inf:%kvmnet6.DeviceDesc%    = kvmnet6.ndi, PCI\VEN_1AF4&DEV_1000&SUBSYS_00011AF4
> > NetKVM/wxp/netkvm.inf:%kvmnet5.DeviceDesc%    = kvmnet5.ndi, PCI\VEN_1AF4&DEV_1000&SUBSYS_00011AF4
> > NetKVM/wxp/netkvm2k.inf:%kvmnet5.DeviceDesc%    = kvmnet5.ndi, PCI\VEN_1AF4&DEV_1000&SUBSYS_00011AF4
> > 
> > So we can tweak any of vendor device and subsystem id.
> > 
> Unfortunately, it won't. Only balloon has revision id, specified as a
> part of device HW descriptor. But it's only because virtio doesn't use 
> revision ids. Otherwise it differential will be there. 

So your driver will load and attempt to work on rev=2 devices?
If yes it's a bug.  virtio spec specifies revision id as an ABI version.
Linux driver does:

        if (pci_dev->revision != VIRTIO_PCI_ABI_VERSION) {
                printk(KERN_ERR "virtio_pci: expected ABI version %d, got %d\n",
                       VIRTIO_PCI_ABI_VERSION, pci_dev->revision);
                return -ENODEV;
        }


> > 
> > Changing subsystem vendor ID actually will be completely
> > transparent to linux which for some reason looks at the
> > subsystem device ID (why? no idea) but not the subsystem vendor ID.
> > Of course this requires a valid vendor ID, getting this
> > costs $3000 I think.
> > We could tweak device ID too but that might break some other guests
> > which don't copy the crazy 'replace device id with subsystem device id'
> > logic from Linux.
> > 
> 

Apropos, would you guys like to start to copy your patches to
virtualization@lists.linux-foundation.org?
If you do, you might get some review and feedback, allowing
us to catch such forward compatibility issues earlier.

Of course it's your project so entirely up to you.


-- 
MST