[Qemu-devel] [PATCH v3 1/4] qobject: ensure base is at offset 0

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

All QObject types have the base QObject as first field. This allows to
simplify qobject_to() and will allow further simplification in
following patch.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qapi/qmp/qobject.h | 5 ++---
 qobject/qobject.c          | 9 +++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/qapi/qmp/qobject.h b/include/qapi/qmp/qobject.h
index e022707578..5206ff9ee1 100644
--- a/include/qapi/qmp/qobject.h
+++ b/include/qapi/qmp/qobject.h
@@ -61,9 +61,8 @@ struct QObject {
 QEMU_BUILD_BUG_MSG(QTYPE__MAX != 7,
                    "The QTYPE_CAST_TO_* list needs to be extended");
 
-#define qobject_to(type, obj) ({ \
-    QObject *_tmp = qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)); \
-    _tmp ? container_of(_tmp, type, base) : (type *)NULL; })
+#define qobject_to(type, obj)                                       \
+    ((type *)qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)))
 
 /* Initialize an object to default values */
 static inline void qobject_init(QObject *obj, QType type)
diff --git a/qobject/qobject.c b/qobject/qobject.c
index 23600aa1c1..87649c5be5 100644
--- a/qobject/qobject.c
+++ b/qobject/qobject.c
@@ -16,6 +16,15 @@
 #include "qapi/qmp/qlist.h"
 #include "qapi/qmp/qstring.h"
 
+QEMU_BUILD_BUG_MSG(
+    offsetof(QNull, base) != 0 ||
+    offsetof(QNum, base) != 0 ||
+    offsetof(QString, base) != 0 ||
+    offsetof(QDict, base) != 0 ||
+    offsetof(QList, base) != 0 ||
+    offsetof(QBool, base) != 0,
+    "base qobject must be at offset 0");
+
 static void (*qdestroy[QTYPE__MAX])(QObject *) = {
     [QTYPE_NONE] = NULL,               /* No such object exists */
     [QTYPE_QNULL] = NULL,              /* qnull_ is indestructible */
-- 
2.17.0.rc1.36.gcedb63ea2f