From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 3 Jul 2023 15:17:04 +0000 (-0400)
Subject: compiler.h: Introduce caa_container_of_check_null
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=4b3a7ebd5597b5e241c39110eb426f7832066308;p=userspace-rcu.git

compiler.h: Introduce caa_container_of_check_null

The approach taken by caa_unqual_scalar_typeof requires use of _Generic
which requires full C11 support. Currently liburcu supports C99.
Therefore, this approach is not appropriate for now.

Instead, introduce caa_container_of_check_null which returns NULL if the
ptr is NULL before offsetting by the member offset.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I0ac1cacc67d83bd3dad6fb6cd2e6595190735441
---

diff --git a/include/urcu/compiler.h b/include/urcu/compiler.h
index 827ec1f..09953f2 100644
--- a/include/urcu/compiler.h
+++ b/include/urcu/compiler.h
@@ -74,6 +74,23 @@
 		(type *)((char *)__ptr - offsetof(type, member));	\
 	})
 
+/*
+ * caa_container_of_check_null - Get the address of an object containing a field.
+ *
+ * @ptr: pointer to the field.
+ * @type: type of the object.
+ * @member: name of the field within the object.
+ *
+ * Return the address of the object containing the field. Return NULL if
+ * @ptr is NULL.
+ */
+#define caa_container_of_check_null(ptr, type, member)			\
+	__extension__							\
+	({								\
+		const __typeof__(((type *) NULL)->member) * __ptr = (ptr); \
+		(__ptr) ? (type *)((char *)__ptr - offsetof(type, member)) : NULL; \
+	})
+
 #define CAA_BUILD_BUG_ON_ZERO(cond) (sizeof(struct { int:-!!(cond); }))
 #define CAA_BUILD_BUG_ON(cond) ((void)CAA_BUILD_BUG_ON_ZERO(cond))