On Wed, 2013-07-31 at 11:29 +0100, Michael S. Tsirkin wrote:
> Em, which one of specs? What I'm talking about is reserving a "Subsystem
> > Device ID" (p.2.1 of the current spec) value 0 to a "device that does
> > nothing" (is not a network card, nor block device, nor console, nor etc.
> > nor anything else) and specifying how is the guest supposed to behave
> > with such device (do nothing). In the current speech it would be
> > "Appendix I: Doing Nothing Device", following "Appendix I: SCSI Host
> > Device". How does this break anything?
>
> It doesn't but then it will have to keep doing nothing :)
And that's the general plan. I had a vague idea of "dynamic
devices" (ie. changing their "identity" in runtime), but this is just
one step too far.
On Wed, 2013-07-31 at 11:34 +0100, Michael S. Tsirkin wrote:
> Reading through this, you want a way to say "there's no device there"
> for virtio-mmio?
And maybe virtio-ccw. And virtio-smoke-signals is anyone ever implements
it :-)
But seriously speaking, I'm just trying to formalize the current
behaviour of the core. Today it does nothing if there is no driver for a
particular VIRTIO_ID_*, and there is no (and will never be) driver with
0 in id_table.
>
> I think this is a bus-specific problem. PCI has a different, standard
> way to do this (report 0xfffffffff as both device and vendor ID).
>
And I want to provide a bus-agnostic solution. Of course the PCI
backends may never instantiate such device if they wish (and it probably
wouldn't make any sense whatsoever).
Paweł
