On Fri, Jul 13, 2018 at 11:07:15AM +0200, Thomas Huth wrote:
> On 12.07.2018 21:45, Eduardo Habkost wrote:
> > The documentation for QOM is not clear about who owns references
> > to objects (i.e. who is responsible for calling object_unref()
> > later).
> >
> > This is important considering there are a few inconsistencies in
> > the API (e.g. callers of object_new() need to call object_unref()
> > later, but callers of object_new_with_props() must not do it).
> >
> > Update the documentation so that every mention of object
> > references also mention who exactly owns the reference.
> >
> > Signed-off-by: Eduardo Habkost <ehabk...@redhat.com>
> > ---
> > include/qom/object.h | 73 +++++++++++++++++++++++++-------------------
> > 1 file changed, 42 insertions(+), 31 deletions(-)
> >
> > diff --git a/include/qom/object.h b/include/qom/object.h
> > index f3d2308d56..08a1bbba7d 100644
> > --- a/include/qom/object.h
> > +++ b/include/qom/object.h
> > @@ -376,7 +376,7 @@ typedef void (ObjectUnparent)(Object *obj);
> > * ObjectFree:
> > * @obj: the object being freed
> > *
> > - * Called when an object's last reference is removed.
> > + * Called when an object's last reference is dropped using object_unref().
> > */
> > typedef void (ObjectFree)(void *obj);
> >
> > @@ -601,8 +601,8 @@ struct InterfaceClass
> > * @typename: The name of the type of the object to instantiate.
> > *
> > * This function will initialize a new object using heap allocated memory.
> > - * The returned object has a reference count of 1, and will be freed when
> > - * the last reference is dropped.
> > + * The returned object has a reference count of 1, and the reference will
> > be
> > + * owned by the caller.
> > *
> > * Returns: The newly allocated and instantiated object.
> > */
> > @@ -617,8 +617,8 @@ Object *object_new(const char *typename);
> > * @...: list of property names and values
> > *
> > * This function will initialize a new object using heap allocated memory.
> > - * The returned object has a reference count of 1, and will be freed when
> > - * the last reference is dropped.
> > + * The returned object has a reference count of 1, and the reference will
> > + * be owned by the caller.
>
> That's the description of object_new_with_props here already, isn't it?
> So the reference will be owned by the parent object, not by the caller.
Oops, you're right. Thanks!
>
> > * The @id parameter will be used when registering the object as a
> > * child of @parent in the composition tree.
> > @@ -652,8 +652,8 @@ Object *object_new(const char *typename);
> > * </programlisting>
> > * </example>
> > *
> > - * The returned object will have one stable reference maintained
> > - * for as long as it is present in the object hierarchy.
> > + * The returned object will have one reference, <emphasis>owned by the
> > + * parent object</emphasis> (not by the caller).
>
> ... and then this information here is somewhat redundant. I suggest to
> remove one of the two spots.
Will change this to:
/**
* object_new_with_props:
* @typename: The name of the type of the object to instantiate.
* @parent: the parent object
* @id: The unique ID of the object
* @errp: pointer to error object
* @...: list of property names and values
*
* This function will initialize a new object using heap allocated memory.
- * The returned object has a reference count of 1, and will be freed when
- * the last reference is dropped.
+ * The returned object will have one reference, <emphasis>owned by the
+ * parent object</emphasis> (not by the caller).
*
* The @id parameter will be used when registering the object as a
* child of @parent in the composition tree.
*
* The variadic parameters are a list of pairs of (propname, propvalue)
* strings. The propname of %NULL indicates the end of the property
* list. If the object implements the user creatable interface, the
* object will be marked complete once all the properties have been
* processed.
*
* <example>
* <title>Creating an object with properties</title>
* <programlisting>
* Error *err = NULL;
* Object *obj;
*
* obj = object_new_with_props(TYPE_MEMORY_BACKEND_FILE,
* object_get_objects_root(),
* "hostmem0",
* &err,
* "share", "yes",
* "mem-path", "/dev/shm/somefile",
* "prealloc", "yes",
* "size", "1048576",
* NULL);
*
* if (!obj) {
* g_printerr("Cannot create memory backend: %s\n",
* error_get_pretty(err));
* }
* </programlisting>
* </example>
*
- * The returned object will have one stable reference maintained
- * for as long as it is present in the object hierarchy.
- *
* Returns: The newly allocated, instantiated & initialized object.
*/
Object *object_new_with_props(const char *typename,
Object *parent,
const char *id,
Error **errp,
...) QEMU_SENTINEL;
--
Eduardo
