Re: [Qemu-devel] [PATCH 1/9] qom/user-creatable: add a few helper macros

[Eduardo Habkost]

On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:
> On Wed, 12 Sep 2018 16:55:23 +0400
> Marc-André Lureau <address@hidden> wrote:
> 
> > Improve a bit code readability.
> > 
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> >  include/qom/object_interfaces.h | 4 ++++
> >  qom/object.c                    | 4 ++--
> >  qom/object_interfaces.c         | 9 +++------
> >  3 files changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/qom/object_interfaces.h 
> > b/include/qom/object_interfaces.h
> > index 4d513fb329..46b0861457 100644
> > --- a/include/qom/object_interfaces.h
> > +++ b/include/qom/object_interfaces.h
> > @@ -9,9 +9,13 @@
> >  #define USER_CREATABLE_CLASS(klass) \
> >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> >                          TYPE_USER_CREATABLE)
> > +#define IS_USER_CREATABLE_CLASS(klass) \
> > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> >  #define USER_CREATABLE_GET_CLASS(obj) \
> >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> >                        TYPE_USER_CREATABLE)
> > +#define IS_USER_CREATABLE(obj) \
> > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> >  #define USER_CREATABLE(obj) \
> >       INTERFACE_CHECK(UserCreatable, (obj), \
> >                       TYPE_USER_CREATABLE)
> > diff --git a/qom/object.c b/qom/object.c
> > index 75d1d48944..0703e8e4ff 100644
> > --- a/qom/object.c
> > +++ b/qom/object.c
> > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const 
> > char *propname,
> >          goto out;
> >      }
> >  
> > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > +    if (IS_USER_CREATABLE(obj)) {
> >          user_creatable_complete(obj, &local_err);
> >          if (local_err) {
> >              object_unparent(obj);
> > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> >          goto error;
> >      }
> >  
> > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > +    if (IS_USER_CREATABLE(obj)) {
> >          user_creatable_complete(obj, &local_err);
> >          if (local_err) {
> >              object_unparent(obj);
> > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > index 72b97a8bed..e3084bc04a 100644
> > --- a/qom/object_interfaces.c
> > +++ b/qom/object_interfaces.c
> > @@ -10,18 +10,15 @@
> >  
> >  void user_creatable_complete(Object *obj, Error **errp)
> >  {
> > -
> >      UserCreatableClass *ucc;
> > -    UserCreatable *uc =
> > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> >  
> > -    if (!uc) {
> > +    if (!IS_USER_CREATABLE(obj)) {
> >          return;
> >      }
> >  
> > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> >      if (ucc->complete) {
> > -        ucc->complete(uc, errp);
> > +        ucc->complete(USER_CREATABLE(obj), errp);
>                          ^^^
> even though function becomes more concise,
> this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st 
> and discarded)
> so I'm not sure is a good idea to regress startup time for readability. 

(INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
enabled, so I don't understand how it would regress startup time.

-- 
Eduardo