On 01/20/2018 09:44 AM, Max Reitz wrote: > This is a dynamic casting macro that, given a QObject type, returns an > object as that type or NULL if the object is of a different type (or > NULL itself). > > The macro uses lower-case letters because: > 1. There does not seem to be a hard rule on whether qemu macros have to > be upper-cased, > 2. The current situation in qapi/qmp is inconsistent (compare e.g. > QINCREF() vs. qdict_put()), > 3. qobject_to() will evaluate its @obj parameter only once, thus it is > generally not important to the caller whether it is a macro or not, > 4. I prefer it aesthetically. > > Signed-off-by: Max Reitz <mre...@redhat.com> > --- > You're more than welcome to convince me to call it QOBJECT_TO()!
I can live with the lower-case version; especially with your good list
of reasons for it ;)
> ---
> include/qapi/qmp/qobject.h | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> diff --git a/include/qapi/qmp/qobject.h b/include/qapi/qmp/qobject.h
> index 38ac68845c..1211989ca0 100644
> --- a/include/qapi/qmp/qobject.h
> +++ b/include/qapi/qmp/qobject.h
> @@ -50,6 +50,24 @@ struct QObject {
> #define QDECREF(obj) \
> qobject_decref(obj ? QOBJECT(obj) : NULL)
>
> +/* Required for qobject_to() */
> +#define QTYPE_CAST_TO_QNull QTYPE_QNULL
> +#define QTYPE_CAST_TO_QNum QTYPE_QNUM
> +#define QTYPE_CAST_TO_QString QTYPE_QSTRING
> +#define QTYPE_CAST_TO_QDict QTYPE_QDICT
> +#define QTYPE_CAST_TO_QList QTYPE_QLIST
> +#define QTYPE_CAST_TO_QBool QTYPE_QBOOL
> +
> +#ifdef CONFIG_STATIC_ASSERT
> +_Static_assert(QTYPE__MAX == 7,
> + "The QTYPE_CAST_TO_* list needs to be extended");
> +#endif
Why not use QEMU_BUILD_BUG_ON() instead of _Static_assert? That way,
this check will break the build even on older compilers that lack
_Static_assert but where we still know how to trigger a build failure.
> +
> +#define qobject_to(obj, type) \
> + container_of(qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)) ?: \
> + QOBJECT((type *)NULL), \
> + type, base)
Slick!
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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