Re: [Socratic RFC PATCH] include: attempt to document device_class_set_props

[Mark Cave-Ayland]

On 27/03/2023 14:15, 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.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   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);
>   
>   /**

Hmmm that's an interesting one. Looking at the source in hw/core/qdev-properties.c 
you could possibly get away with something like this in vu_rng_class_init():

    ObjectProperty *op = object_class_property_find(klass, "id");
    object_property_set_default_uint(op, VIRTIO_ID_RNG);

Of course this is all completely untested :)


ATB,

Mark.