Re: [Qemu-devel] [PATCH 1/5] qom/object: Add a new function object_initialize_as_child()

[Thomas Huth]

On 12.07.2018 18:52, Eduardo Habkost wrote:
> On Thu, Jul 12, 2018 at 05:30:59PM +0200, Thomas Huth wrote:
>> A lot of code is using the object_initialize() function followed by a call to
>> object_property_add_child() to add the newly initialized object as a child of
>> the current object. Both functions increase the reference counter of the new
>> object, but many spots that call these two functions then forget to drop one
>> of the superfluous references. So the newly created object is often not 
>> cleaned
>> up correctly when the parent is destroyed. In the worst case, this can cause
>> crashes, e.g. because device objects are not correctly removed from their
>> parent_bus.
>> Since this is a common pattern between many code spots, let's introdcue a
>> new function that takes care of calling all three required initialization
>> functions, first object_initialize(), then object_property_add_child() and
>> finally object_unref().
>>
>> Signed-off-by: Thomas Huth <address@hidden>
>> ---
>>  include/qom/object.h | 19 +++++++++++++++++++
>>  qom/object.c         | 14 ++++++++++++++
>>  2 files changed, 33 insertions(+)
>>
>> diff --git a/include/qom/object.h b/include/qom/object.h
>> index f3d2308..c1b254c 100644
>> --- a/include/qom/object.h
>> +++ b/include/qom/object.h
>> @@ -749,6 +749,25 @@ int object_set_propv(Object *obj,
>>  void object_initialize(void *obj, size_t size, const char *typename);
>>  
>>  /**
>> + * object_initialize_as_child:
>> + * @parentobj: The parent object to add a property to
>> + * @propname: The name of the property
>> + * @childobj: A pointer to the memory to be used for the object.
>> + * @size: The maximum size available at @obj for the object.
>> + * @type: The name of the type of the object to instantiate.
>> + * @errp: If an error occurs, a pointer to an area to store the area
>> + *
>> + * This function will initialize an object. The memory for the object should
>> + * have already been allocated. The object will then be added as child 
>> property
>> + * to a parent with object_property_add_child() function. The returned 
>> object
>> + * has a reference count of 1, and will be finalized when the last 
>> reference is
>> + * dropped.
>> + */
>> +void object_initialize_as_child(Object *parentobj, const char *propname,
>> +                                void *childobj, size_t size, const char 
>> *type,
>> +                                Error **errp);
> 
> Why did you use void* instead of Object*?

That's the same what object_initialize() is doing (see above). Otherwise
all the callers have to cast their pointers with OBJECT() first.

 Thomas