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Fri, 30 Jun 2023 09:12:53 +0100 (BST) References: <20230627160943.2956928-1-alex.bennee@linaro.org> <20230627160943.2956928-26-alex.bennee@linaro.org> User-agent: mu4e 1.11.7; emacs 29.0.92 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: qemu-devel@nongnu.org, Wainer dos Santos Moschetta , Juan Quintela , Thomas Huth , Cleber Rosa , Leonardo Bras , Beraldo Leal , Peter Maydell , Bin Meng , Yanan Wang , Darren Kenny , Alexander Bulekov , Marcel Apfelbaum , Peter Xu , Radoslaw Biernacki , Laurent Vivier , Paolo Bonzini , Eduardo Habkost , qemu-arm@nongnu.org, Stefan Hajnoczi , Richard Henderson , Bandan Das , =?utf-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Alexandre Iooss , Marcin Juszkiewicz , Leif Lindholm , Laurent Vivier , Qiuhao Li , Mahmoud Mandour , Riku Voipio Subject: Re: [PATCH v3 25/36] docs/devel: introduce some key concepts for QOM development Date: Fri, 30 Jun 2023 09:03:56 +0100 In-reply-to: Message-ID: <87fs69xta2.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::42a; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x42a.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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 Philippe Mathieu-Daud=C3=A9 writes: > On 27/6/23 18:09, Alex Benn=C3=A9e wrote: >> Using QOM correctly is increasingly important to maintaining a modern >> code base. However the current documentation skips some important >> concepts before launching into a simple example. Lets: >> - at least mention properties >> - mention TYPE_OBJECT and TYPE_DEVICE >> - talk about why we have realize/unrealize >> - mention the QOM tree >> - lightly re-arrange the order we mention things >> Signed-off-by: Alex Benn=C3=A9e >> Message-Id: <20230619171437.357374-6-alex.bennee@linaro.org> >> --- >> v3 >> - moved around as per Paolo's review >> --- >> docs/devel/qom.rst | 58 +++++++++++++++++++++++++++++++++++++++++----- >> 1 file changed, 52 insertions(+), 6 deletions(-) > > >> +Creating a QOM class >> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >> + >> +A simple minimal device implementation may look something like bellow: >> .. code-block:: c >> :caption: Creating a minimal type >> @@ -48,6 +66,12 @@ In the above example, we create a simple type that is= described by #TypeInfo. >> #TypeInfo describes information about the type including what it inher= its >> from, the instance and class size, and constructor/destructor hooks. >> +The TYPE_DEVICE class is the parent class for all modern devices >> +implemented in QEMU and adds some specific methods to handle QEMU >> +device model. This includes managing the lifetime of devices from >> +creation through to when they become visible to the guest and >> +eventually unrealized. > > Good enough but we are mixing QOM vs QDev... Yeah, but one relies on the other. From the point of view of someone coming new to the code I think we do want to mention them both together. Most people implementing QOM classes will be for devices I think. Maybe we should enumerate all the types that have TYPE_OBJECT as their parent? > >> Alternatively several static types could be registered using helper ma= cro >> DEFINE_TYPES() > > >> +.. _device-life-cycle: >> + >> +Device Life-cycle >> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >> + >> +As class initialisation cannot fail devices have an two additional >> +methods to handle the creation of dynamic devices. The ``realize`` >> +function is called with ``Error **`` pointer which should be set if >> +the device cannot complete its setup. Otherwise on successful >> +completion of the ``realize`` method the device object is added to the >> +QOM tree and made visible to the guest. >> + >> +The reverse function is ``unrealize`` and should be were clean-up >> +code lives to tidy up after the system is done with the device. > > Worth mentioning hotplug devices must implement it? > >> +All devices can be instantiated by C code, however only some can >> +created dynamically via the command line or monitor. >> +Likewise only some can be unplugged after creation and need an >> +explicit ``unrealize`` implementation. > > Ah, here we go. > >> This is determined by the >> +``user_creatable`` variable in the root ``DeviceClass`` structure. >> +Devices can only be unplugged if their ``parent_bus`` has a registered >> +``HotplugHandler``. > > TODO on top, mentions the reset() handlers are called after realize(), > and can be called multiple times. Where is this TODO? I'm wary of talking about reset too much as the old reset handler is a deprecated API. > >> API Reference >> -------------- >> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >> See the :ref:`QOM API` and :ref:`QDEV API` >> documents for the complete API description. > > Reviewed-by: Philippe Mathieu-Daud=C3=A9 --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro