Philippe Mathieu-Daudé <phi...@linaro.org> writes:
> On 27/6/23 18:09, Alex Bennée 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 Bennée <alex.ben...@linaro.org> >> Message-Id: <20230619171437.357374-6-alex.ben...@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 >> +==================== >> + >> +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 inherits >> 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 macro >> DEFINE_TYPES() > > >> +.. _device-life-cycle: >> + >> +Device Life-cycle >> +================= >> + >> +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 >> -------------- >> +============= >> See the :ref:`QOM API<qom-api>` and :ref:`QDEV API<qdev-api>` >> documents for the complete API description. > > Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org> -- Alex Bennée Virtualisation Tech Lead @ Linaro