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[Qemu-devel] [PULL v4 06/38] qapi: Add qobject_to()
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PULL v4 06/38] qapi: Add qobject_to() |
Date: |
Mon, 19 Mar 2018 15:24:00 -0500 |
From: Max Reitz <address@hidden>
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.
The macro parameter order is chosen with typename first for
consistency with other QAPI macros like QAPI_CLONE(), as well as
for legibility (read it as "qobject to" type "applied to" obj).
Signed-off-by: Max Reitz <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Alberto Garcia <address@hidden>
[eblake: swap parameter order to list type first, avoid clang ubsan
warning on QOBJECT(NULL) and container_of(NULL,type,base)]
Signed-off-by: Eric Blake <address@hidden>
---
include/qapi/qmp/qobject.h | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/include/qapi/qmp/qobject.h b/include/qapi/qmp/qobject.h
index 012439a2e3b..e0227075789 100644
--- a/include/qapi/qmp/qobject.h
+++ b/include/qapi/qmp/qobject.h
@@ -50,6 +50,21 @@ 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
+
+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; })
+
/* Initialize an object to default values */
static inline void qobject_init(QObject *obj, QType type)
{
@@ -102,4 +117,18 @@ static inline QType qobject_type(const QObject *obj)
return obj->type;
}
+/**
+ * qobject_check_type(): Helper function for the qobject_to() macro.
+ * Return @obj, but only if @obj is not NULL and @type is equal to
+ * @obj's type. Return NULL otherwise.
+ */
+static inline QObject *qobject_check_type(const QObject *obj, QType type)
+{
+ if (obj && qobject_type(obj) == type) {
+ return (QObject *)obj;
+ } else {
+ return NULL;
+ }
+}
+
#endif /* QOBJECT_H */
--
2.14.3