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 03:02:45PM +0200, Yan Vugenfirer wrote:
> 
> On Feb 7, 2013, at 1:46 PM, Vadim Rozenfeld wrote:
> 
> > On Thu, 2013-02-07 at 13:33 +0200, Michael S. Tsirkin wrote:
> >> 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?
> > 
> > All virtio-win drivers (net, serial, block, and scsi), except for
> > balloon will.
> > 
> >> 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;
> >>        }
> >> 
> 
> We can add it from next release. Provided that everyone understand the consequences especially for boot devices (virtio-block and virtio-scsi).
> 

Same as Linux - guest won't boot.

> >> 
> >>>> 
> >>>> 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.
> >> 
> >> 
> > 
> >