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

[Paolo Bonzini]

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.

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
>>>
>