From 94cd049b8c81e2b58113db7cc289218f8925d27d Mon Sep 17 00:00:00 2001
From: Markus Armbruster <armbru@redhat.com>
Date: Mon, 18 Jun 2018 08:43:09 +0200
Subject: [PATCH 02/54] qobject: Ensure base is at offset 0
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RH-Author: Markus Armbruster <armbru@redhat.com>
Message-id: <20180618084330.30009-3-armbru@redhat.com>
Patchwork-id: 80724
O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 02/23] qobject: Ensure base is at offset 0
Bugzilla: 1557995
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

From: Marc-André Lureau <marcandre.lureau@redhat.com>

All QObject types have the base QObject as their first field. This
allows the simplification of qobject_to().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180419150145.24795-2-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message paragraph on type casts dropped, to avoid giving the
impression type casting would be okay]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
(cherry picked from commit 7ee9edfdb117da47c86c9764d90f0be11a648666)

Signed-off-by: Miroslav Rezanina <mrezanin@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 e022707..5206ff9 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 23600aa..87649c5 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 */
-- 
1.8.3.1