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[Qemu-devel] [PULL 06/36] qapi: Add qobject_to()
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PULL 06/36] qapi: Add qobject_to() |
Date: |
Mon, 12 Mar 2018 13:35:57 -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]
Signed-off-by: Eric Blake <address@hidden>
---
include/qapi/qmp/qobject.h | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/include/qapi/qmp/qobject.h b/include/qapi/qmp/qobject.h
index 012439a2e3b..ea9702270e7 100644
--- a/include/qapi/qmp/qobject.h
+++ b/include/qapi/qmp/qobject.h
@@ -50,6 +50,22 @@ 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) \
+ container_of(qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)) ?: \
+ QOBJECT((type *)NULL), \
+ type, base)
+
/* Initialize an object to default values */
static inline void qobject_init(QObject *obj, QType type)
{
@@ -102,4 +118,18 @@ 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
- [Qemu-devel] [PULL 00/36] QAPI patches for 2018-03-12, 2.12 softfreeze, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 02/36] qlit: use QType instead of int, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 05/36] compiler: Add QEMU_BUILD_BUG_MSG() macro, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 08/36] qapi: Remove qobject_to_X() functions, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 06/36] qapi: Add qobject_to(),
Eric Blake <=
- [Qemu-devel] [PULL 03/36] qlit: add qobject_from_qlit(), Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 09/36] qapi: Make more of qobject_to(), Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 04/36] qapi: generate a literal qobject for introspection, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 16/36] monitor: move skip_flush into monitor_data_init, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 18/36] monitor: unify global init, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 11/36] block: Deprecate "backing": "", Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 17/36] monitor: move the cur_mon hack deeper for QMP, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 10/36] block: Handle null backing link, Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 13/36] qobject: introduce qstring_get_try_str(), Eric Blake, 2018/03/12
- [Qemu-devel] [PULL 26/36] qmp: add new event "command-dropped", Eric Blake, 2018/03/12