Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Auger Eric <eric.auger@redhat.com>]

Hi Paolo,

On 6/24/20 6:16 PM, Paolo Bonzini wrote:
> On 24/06/20 18:02, Auger Eric wrote:
>> Hi Paolo,
>>
>> On 6/24/20 4:17 PM, Auger Eric wrote:
>>> Hi Paolo,
>>>
>>> On 6/24/20 4:12 PM, Paolo Bonzini wrote:
>>>> On 24/06/20 14:43, Eric Auger wrote:
>>>>> +    op = object_property_try_add(obj, name, type, object_get_child_property,
>>>>> +                                 NULL, object_finalize_child_property,
>>>>> +                                 child, errp);
>>>>> +    if (!op) {
>>>>> +        goto out;
>>>>> +    }
>>>>>      op->resolve = object_resolve_child_property;
>>>>> +out:
>>>>>      object_ref(child);
>>>>>      child->parent = obj;
>>>>>      return op;
>>>>
>>>> I think if there's an error you need to return NULL without ref-ing
>>>> child, shouldn't you?
>>> hum yes you're fully right, the out label is badly placed.
>> Looks the unref is done in user_creatable_add_type() in case of error.
> 
> There are two references involved:
> 
> - a reference returned from object_new.  user_creatable_add_type()
> passes it back to the caller.  The object_unref() you found is done
> before returning NULL, because in that case nothing is being passed to
> the caller
> 
> - a reference stored in child->parent.  In case of error that reference
> is dropped with object_property_del before returning NULL.

> object_property_try_add_child must not store anything in child->parent
> in case of error, and therefore it need not add that reference either.
> 
> I hope this is clearer.

Yes it helps. Thank you for the clarifications.

Eric
> 
> Thanks,
> 
> Paolo
> 
>> Isn't it the corresponding one? Anyway I think it is better to avoid
>> getting the ref here as you suggest (and also free type) and don't unref
>> in user_creatable_add_type.
>>
>> Thanks
>>
>> Eric
>>>>
>>>> You can then add another test that object_property_add_child succeeds
>>>> after object_property_try_add_child fails.
>>> OK
>>>
>>> Thanks
>>>
>>> Eric
>>>>
>>>> Paolo
>>>>
>>
> 
>