[systemd-devel] [PATCH 1/2] util: introduce container_of() macro

[Lucas De Marchi]

This macro comes from kernel and it's useful for unwrapping structs
inside another one. The generated code is actually the same to the one
where this logic is used in udev, but using this macro is much cleaner
and less error prone.
---
 src/shared/util.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/shared/util.h b/src/shared/util.h
index 17ffd19..0246dfd 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -59,6 +59,17 @@ typedef struct dual_timestamp {
 #define USEC_PER_MONTH (2629800ULL*USEC_PER_SEC)
 #define USEC_PER_YEAR (31557600ULL*USEC_PER_SEC)
 
+/*
+ * container_of - cast a member of a structure out to the containing structure
+ * @ptr: the pointer to the member.
+ * @type: the type of the container struct this is embedded in.
+ * @member: the name of the member within the struct.
+ *
+ */
+#define container_of(ptr, type, member) ({ \
+        const typeof( ((type *)0)->member ) *__mptr = (ptr); \
+        (type *)( (char *)__mptr - offsetof(type,member) );})
+
 /* What is interpreted as whitespace? */
 #define WHITESPACE " \t\n\r"
 #define NEWLINE "\n\r"
-- 
1.7.10