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

[Vadim Rozenfeld]

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:
> > 05.02.2013 15:31, Vadim Rozenfeld wrote:
> > >On Mon, 2013-02-04 at 08:41 -0600, Anthony Liguori wrote:
> > >>Vadim Rozenfeld <address@hidden> writes:
> > 
> > >>>http://msdn.microsoft.com/en-us/library/windows/hardware/gg463287.aspx
> > >>
> > >>That's a useful link, thanks.
> > >>
> > >>I don't see anything in that link that would strictly require us to
> > >>change the revision ID.  It seems to focus on when the "software
> > >>interface changes".  I take that to mean, "change the revision ID if an
> > >>old driver wouldn't work anymore" which makes complete sense.
> > >Right, nobody can force you to change the revision id. It's just a good
> > >engineering practice to increase RevID every time the HW interface has
> > >changed, and you expect some compatibility issue between the new HW and
> > >old drivers. In this case, if Windows cannot locate the INF file which
> > >matches the new device identification strings, it just reports that it
> > >cannot find a suitable driver.
> > >>
> > >>But adding feature bits an altering the config size doesn't constitute a
> > >>change in the software interface IMHO.
> > >
> > >I agree, feature bits are good. The only one problem with them, is that
> > >driver usually doesn't have access to PCI space during the driver
> > >loading phase.
> > 
> > Vadim, can you please describe in a bit more details what the actual issue
> > here is, from the windows or windows driver point of view? 
If a driver receives descriptor with memory type resources it needs to
map physical address to logical. This process requires the number of
bytes to be mapped, and it is the best place for sanity check to verify
that the resources are valid and not corrupted. We usually do it by
comparing the resource size with some predefined value, that we expect
to see.
>  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.
> > Is this size specified in the inf file somehow?  Just for us to actually
> > understand the issue?
No, it is not specified in INF. We usually keep it hard-coded, but
technically it can be specified in INF and the Registry.  

Best regards,
Vadim.
> > 
> > Thanks!
> > 
> > /mjt
> 
> This should be educational:
> https://github.com/YanVugenfirer/kvm-guest-drivers-windows/commit/10413d2bbef295cc0e0e75131147793ccc382155
>