Re: [Qemu-devel] [RFC v2 06/20] qdev: Add 'accepted-device-types' property to BusClass

[Eduardo Habkost]

On Tue, Nov 29, 2016 at 02:57:07PM +0100, Cornelia Huck wrote:
> On Fri, 25 Nov 2016 20:05:42 -0200
> Eduardo Habkost <address@hidden> wrote:
> 
> > Each bus class will now be aware of the specific device types
> > that can be plugged on it. That will be useful for:
> > 
> > * Runtime check for which devices types can be plugged to the
> >   machine;
> > * Validation of query-machines output by automated tests.
> > 
> > By default, a single type name is used on all bus instances (set
> > at BusClass::device_type), but bus instances can override it and
> > return a different type list.
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
> 
> I've read (well, more skimmed through) the whole patchset and I think
> we have different cases of "multiple device types for one bus":
> 
> - the q35 root bus case later in this patchset, where just a certain
> instance of the bus can accept multiple types
> - the case where every instance of a bus may accept multiple types
> (none currently; but this will be the case for e.g. virtual-css once we
> have other derivates of CCW_DEVICE than virtio-ccw)

Are all going to be subclasses of TYPE_CCW_DEVICE, and are all
TYPE_CCW_DEVICE subclasses going to be accepted by virtual-css?
In this case, you could just set BusClass::device_type to
TYPE_CCW_DEVICE on virtual-css-bus.

> 
> For the second case, a static initializer for multiple types in the
> class makes sense;

If necessary, we can change BusClass::device_type to a
BusClass::device_types list. I didn't do that because it didn't
seem necessary (and I would like to encourage buses to encode
compatiblity using a single type/interface name whenever
possible).


>                    but the first case is a bit hackish. Should there be
> a generic way to pass a list of types to the individual bus instance's
> initializers (that could fall back to a static list in the class)?

Sound good, but I don't know how that generic mechanism could
look like. Would a:
  void bus_add_accepted_device_type(BusState *bus, const char *devtype)
function be enough?

-- 
Eduardo