Re: [PULL 25/41] rust: qom: put class_init together from multiple ClassInitImpl<>

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 7/1/25 17:29, Paolo Bonzini wrote:
> On Tue, Jan 7, 2025 at 5:24 PM Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>>> but I don't really like the two parameters and also I don't like that
>>> class_init is called differently for classes and interfaces. It's
>>> probably possible to design a better API, but I didn't spend too much
>>> time on it because it may require rethinking how classes are declared
>>> (not a huge deal, as we have only four of them).
>>
>> Are you saying this is not a problem related to QDev Reset, but
>> a limitation with any QOM interface, and we can not instantiate
>> any type implementing TYPE_INTERFACE? As in:
>>
>>     .interfaces = (InterfaceInfo[]) {
>>       ...
>>     },
> 
> So far there was no need for that, so it is not implemented. There are
> three parts:
> 
> 1) adding interfaces to the TypeInfo
> 
> 2) filling in vtables for the interfaces
> 
> 3) filling in the ResettableClass vtable based on a trait
> 
> None of these is supported by Rust code right now, but only (2) and
> (3) are needed for qdev reset. That's because the Resettable interface
> is declared in DeviceState rather than in the individual devices.
> 
> (2) boils down to wrapping object_class_dynamic_cast into a
> nice-enough API. The commit that I added to rust-next covers that and
> it should work, but the API is a bit unorthogonal.

OK, thanks for explaining.

So currently we can not implement any device requiring one of
these interfaces:

$ git grep -hwA1 INTERFACE_CHECK
31:    INTERFACE_CHECK(void, obj, TYPE_RESETTABLE_INTERFACE);
--
12:     INTERFACE_CHECK(AcpiDevAmlIf, (obj), TYPE_ACPI_DEV_AML_IF)
--
24:     INTERFACE_CHECK(AcpiDeviceIf, (obj), \
25-                     TYPE_ACPI_DEVICE_IF)
--
16:    INTERFACE_CHECK(ARMLinuxBootIf, (obj), TYPE_ARM_LINUX_BOOT_IF)
--
29:     INTERFACE_CHECK(FWPathProvider, (obj), TYPE_FW_PATH_PROVIDER)
--
23:     INTERFACE_CHECK(HotplugHandler, (obj), TYPE_HOTPLUG_HANDLER)
--
12:    INTERFACE_CHECK(InterruptStatsProvider, (obj), \
13-                    TYPE_INTERRUPT_STATS_PROVIDER)
--
113:     INTERFACE_CHECK(IPMIInterface, (obj), TYPE_IPMI_INTERFACE)
--
25:    INTERFACE_CHECK(IsaDma, (obj), TYPE_ISADMA)
--
26:     INTERFACE_CHECK(MemoryDeviceState, (obj), TYPE_MEMORY_DEVICE)
--
21:     INTERFACE_CHECK(XlnxCfiIf, (obj), TYPE_XLNX_CFI_IF)
--
33:     INTERFACE_CHECK(NMIState, (obj), TYPE_NMI)
--
30:    INTERFACE_CHECK(PnvXScomInterface, (obj), TYPE_PNV_XSCOM_INTERFACE)
--
50:    INTERFACE_CHECK(SpaprInterruptController, (obj), TYPE_SPAPR_INTC)
--
141:    INTERFACE_CHECK(XICSFabric, (obj), TYPE_XICS_FABRIC)
--
156:    INTERFACE_CHECK(XiveNotifier, (obj), TYPE_XIVE_NOTIFIER)
--
431:    INTERFACE_CHECK(XivePresenter, (obj), TYPE_XIVE_PRESENTER)
--
463:    INTERFACE_CHECK(XiveFabric, (obj), TYPE_XIVE_FABRIC)
--
38:    INTERFACE_CHECK(Nvram, (obj), TYPE_NVRAM)
--
12:     INTERFACE_CHECK(StreamSink, (obj), TYPE_STREAM_SINK)
--
20:    INTERFACE_CHECK(VMStateIf, (obj), TYPE_VMSTATE_IF)
--
14:     INTERFACE_CHECK(UserCreatable, (obj), \
15-                     TYPE_USER_CREATABLE)
--
35:    INTERFACE_CHECK(TPMIf, (obj), TYPE_TPM_IF)
--
35:    INTERFACE_CHECK(IDAUInterface, (obj), TYPE_IDAU_INTERFACE)
--
23:     INTERFACE_CHECK(TestIf, (obj), TYPE_TEST_IF)

Not a big deal at this point, but just to keep it in mind.

Regards,

Phil.