Re: [Qemu-devel] [PATCH 1/2] object: Add can_be_deleted callback to TypeInfo and TypeImpl

[Andreas Färber]

Am 26.03.2015 um 11:05 schrieb Igor Mammedov:
> On Wed, 25 Mar 2015 23:47:46 +0800
> Lin Ma <address@hidden> wrote:
>> 在 2015年03月23日 21:30, Igor Mammedov 写道:
>>> On Mon, 23 Mar 2015 14:13:07 +0100
>>> Andreas Färber <address@hidden> wrote:
>>>> Am 23.03.2015 um 13:06 schrieb Paolo Bonzini:
>>>>> On 23/03/2015 11:36, Peter Crosthwaite wrote:
>>>>>> I don't think TypeInfo is the right place for this. You can however
>>>>>> define function hooks for Object in ObjectClass. See the unparent
>>>>>> field of ObjectClass for a precedent.
>>>> Agree.
>>>>
>>>>> In this case, the right place could be UserCreatable.
>>>> Maybe, not so familiar with that interface myself. Does object_del allow
>>>> to delete non-UserCreatable objects? Then it wouldn't help much.
>>> object_del() works only with /objects children, and so far the only way
>>> that child placed there is via object_add() which requires a new object
>>> to have TYPE_USER_CREATABLE interface.
>>> I'd go this way rather than overhaul object_unparent() in this case.
>> What about these changes?
>> 1. Add a callback function named 'ObjectCanBeDeleted *can_be_deleted' to 
>> struct ObjectClass in object.h
>> 2. Call the function in qmp_object_del of qmp.c, says:
>>      ObjectClass *obj_class = object_get_class(obj);
>>          if (obj_class->can_be_deleted)
>>              if (!obj_class->can_be_deleted(obj))
>>                  error out
>>
>> 3. Then implement can_be_deleted callback in backends, says:
>>      static bool host_memory_backend_can_be_deleted(Object *obj) {......}
>>
>>      static void host_memory_backend_class_init(ObjectClass *oc, void 
>> *data) {
>>          ......
>>          oc->can_be_deleted = host_memory_backend_can_be_deleted;
>>      }
> 
> all backends currently implement TYPE_USER_CREATABLE interface,
> so I'd rather extend UserCreatableClass with:
> 
>      bool can_be_deleted(UserCreatable *uc)
> 
> callback, which backends could implement if needed.

As for the implementation, could we simply look at Object::ref field?

Regards,
Andreas

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