Re: [virtio] [PATCH] ccw: split descriptor/available/used rings

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 8 Oct 2013 15:26:38 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Oct 08, 2013 at 02:16:06PM +0200, Cornelia Huck wrote:
> > On Tue, 8 Oct 2013 15:12:39 +0300
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > 
> > > This reminds me - our use of the SenseID format for device
> > > identification is not in the spec, is it?
> > > We should probably add it - want to do this?
> > 
> > I don't think there's a need to do so, as it is a standard channel
> > command. Every control unit/device since 1973 supports it :)
> 
> The format of the command is standard, yes.
> But I really meant which virtio field goes into which field
> and how does a driver match.
> 
> Linux guest does: CCW_DEVICE(0x3832, 0)
> so it ignores device type and model, and
> matches controller model against virtio device ID.
> 
> This really should be documented in spec - it's not good
> that people need to look at guest code to write hypervisors.

Ah, I see what you mean. It is already there in 2.3.3.1., but we could
it more explicit:

===

SenseID will return the following information for a virtio-ccw proxy
device:

----------------------------------------------
| control unit type     | 0x3832             |
|-----------------------|--------------------|
| control unit model    | <virtio device id> |
|-----------------------|--------------------|
| device type           | zeroes (unset)     |
|-----------------------|--------------------|
| device model          | zeroes (unset)     |
|-----------------------|--------------------|
| extended SenseId data | zeroes (unset)     |
----------------------------------------------

A driver for virtio-ccw devices should look for a control unit type of
0x3832 and ignore the device type.

===

I think ignoring the device type is obvious, though.