On Wed, Jun 20, 2018 at 11:53:59AM +0200, Cornelia Huck wrote:

On Tue, 19 Jun 2018 23:32:06 +0300
"Michael S. Tsirkin" [off-list ref] wrote:

quoted

On Tue, Jun 19, 2018 at 12:54:53PM +0200, Cornelia Huck wrote:

quoted

Sorry about dragging mainframes into this, but this will only work for
homogenous device coupling, not for heterogenous. Consider my vfio-pci
+ virtio-net-ccw example again: The guest cannot find out that the two
belong together by checking some group ID, it has to either use the MAC
or some needs-to-be-architectured property.

Alternatively, we could propose that mechanism as pci-only, which means
we can rely on mechanisms that won't necessarily work on non-pci
transports. (FWIW, I don't see a use case for using vfio-ccw to pass
through a network card anytime in the near future, due to the nature of
network cards currently in use on s390.)  

That's what it boils down to, yes.  If there's need to have this for
non-pci devices, then we should put it in config space.
Cornelia, what do you think?

I think the only really useful config on s390 is the vfio-pci network
card coupled with a virtio-net-ccw device: Using an s390 network card
via vfio-ccw is out due to the nature of the s390 network cards, and
virtio-ccw is the default transport (virtio-pci is not supported on any
enterprise distro AFAIK).

For this, having a uuid in the config space could work (vfio-pci
devices have a config space by virtue of being pci devices, and
virtio-net-ccw devices have a config space by virtue of being virtio
devices -- ccw devices usually don't have that concept).

OK so this calls for adding such a field generally (it's
device agnostic right now).

How would you suggest doing that?


-- 
MST