From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45105) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1evSJQ-0000cc-7M for qemu-devel@nongnu.org; Mon, 12 Mar 2018 14:36:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1evSJN-0005rq-3p for qemu-devel@nongnu.org; Mon, 12 Mar 2018 14:36:44 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49252 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1evSJM-0005rK-VH for qemu-devel@nongnu.org; Mon, 12 Mar 2018 14:36:41 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 26BD3406E897 for ; Mon, 12 Mar 2018 18:36:38 +0000 (UTC) From: Eric Blake Date: Mon, 12 Mar 2018 13:35:57 -0500 Message-Id: <20180312183628.394722-7-eblake@redhat.com> In-Reply-To: <20180312183628.394722-1-eblake@redhat.com> References: <20180312183628.394722-1-eblake@redhat.com> Subject: [Qemu-devel] [PULL 06/36] qapi: Add qobject_to() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Max Reitz , Markus Armbruster From: Max Reitz 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 Message-Id: <20180224154033.29559-3-mreitz@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Alberto Garcia [eblake: swap parameter order to list type first] Signed-off-by: Eric Blake --- 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