On Tue, Apr 18, 2023 at 05:21:28PM +0100, Alex Bennée wrote:
> I'm still not sure how I achieve by use case of the parent class
> defining the following properties:
>
> static Property vud_properties[] = {
> DEFINE_PROP_CHR("chardev", VHostUserDevice, chardev),
> DEFINE_PROP_UINT16("id", VHostUserDevice, id, 0),
> DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> But for the specialisation of the class I want the id to default to
> the actual device id, e.g.:
>
> static Property vu_rng_properties[] = {
> DEFINE_PROP_UINT16("id", VHostUserDevice, id, VIRTIO_ID_RNG),
> DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> And so far the API for doing that isn't super clear.Does this mean this patch is an RFC and this patch is not intended to be merged? > > Signed-off-by: Alex Bennée <[email protected]> > --- > include/hw/qdev-core.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h > index bd50ad5ee1..d4bbc30c92 100644 > --- a/include/hw/qdev-core.h > +++ b/include/hw/qdev-core.h > @@ -776,6 +776,15 @@ BusState *sysbus_get_default(void); > char *qdev_get_fw_dev_path(DeviceState *dev); > char *qdev_get_own_fw_dev_path_from_handler(BusState *bus, DeviceState *dev); > > +/** > + * device_class_set_props(): add a set of properties to an device > + * @dc: the parent DeviceClass all devices inherit > + * @props: an array of properties, terminate by DEFINE_PROP_END_OF_LIST() > + * > + * This will add a set of properties to the object. It will fault if > + * you attempt to add an existing property defined by a parent class. > + * To modify an inherited property you need to use???? > + */ > void device_class_set_props(DeviceClass *dc, Property *props); I don't know the answer. There doesn't seem to be a way for child classes to override parent DeviceClass properties. The assumption is the sets of properties are disjoint (no property name collisions). Here is a workaround in the vhost-user-rng code: /* Set our default if the user didn't specify the id */ if (vud->id == 0) { vud->id = VIRTIO_ID_RNG; } This could be a problem because the value 0 may be valid and there is no way to distinguish between a user setting 0 and the default 0 value. Stefan
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