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Tsirkin" , Eric Blake Subject: Re: [PATCH v2 01/13] include: attempt to document device_class_set_props Message-ID: <20230523203050.GA140337@fedora> References: <20230418162140.373219-1-alex.bennee@linaro.org> <20230418162140.373219-2-alex.bennee@linaro.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PC9Bjrkp6WHWj9an" Content-Disposition: inline In-Reply-To: <20230418162140.373219-2-alex.bennee@linaro.org> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --PC9Bjrkp6WHWj9an Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Apr 18, 2023 at 05:21:28PM +0100, Alex Benn=E9e wrote: > I'm still not sure how I achieve by use case of the parent class > defining the following properties: >=20 > static Property vud_properties[] =3D { > 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(), > }; >=20 > But for the specialisation of the class I want the id to default to > the actual device id, e.g.: >=20 > static Property vu_rng_properties[] =3D { > DEFINE_PROP_UINT16("id", VHostUserDevice, id, VIRTIO_ID_RNG), > DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1), > DEFINE_PROP_END_OF_LIST(), > }; >=20 > 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? >=20 > Signed-off-by: Alex Benn=E9e > --- > include/hw/qdev-core.h | 9 +++++++++ > 1 file changed, 9 insertions(+) >=20 > 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); > =20 > +/** > + * 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 =3D=3D 0) { vud->id =3D 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. 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