Re: [Qemu-devel] [RFC PATCH v1 0/7] QOM Super class access

[Andreas Färber]

Am 18.06.2013 12:23, schrieb Michael S. Tsirkin:
> On Tue, Jun 18, 2013 at 07:43:11PM +1000, address@hidden wrote:
>> From: Peter Crosthwaite <address@hidden>
>>
>>
>> This series enables QOM super class access and demostrates some usages.
>> Replaces the save->override->call via FooClass technique, to reduce
>> some of the boiler plate in recently fully QOMified devices.
>>
>> Applied the change to ARM CPU, MB CPU and some of Andreas's recently
>> QOMified i386 devices, all which have the save->override->call issue.
>> ARMCPU I've done a brief test on and seems to work.
>>
>> ARM CPU was particularly difficult, as it has 3 layers of heirachy,
>> where a non-concrete class (TYPE_ARM_CPU) need to super class itself
>> (to TYPE_CPU). This sees the need for super-classers to specify their
>> expected base class level. See patches for illustration.
>>
>> The main future work to the series is to apply the change pattern to
>> the reset of the tree
> 
> Looks good to me overall.
> Some nits:
> - Super is an immediate parent in java and python.
> - One of the design points of QOM is that it let
>   you ignore which class is a parent and which is a child.
>   All casts look the same.
> 
> So, why do we need the new APIs with _SUPER?
> What's wrong with simple
>       object_class_by_name()
> and casting to that?

I guess the idea was to avoid open-coding that multiple times, but I
think I would then prefer something more local like

#define ARM_CPU_SUPER_CLASS() \
  object_class_get_parent(object_class_by_name(TYPE_ARM_CPU))

and then use

DEVICE_CLASS(ARM_CPU_SUPER_CLASS())
or
CPU_CLASS(ARM_CPU_SUPER_CLASS())

as needed. What do you think?

Andreas

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