From b3dfd2aca0730c466fc64d07b8aa01ef3d44dbc8 Mon Sep 17 00:00:00 2001
From: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Date: Thu, 26 Apr 2012 13:36:01 -0300
Subject: [PATCH] util: introduce container_of() macro

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.
(cherry picked from commit c4326aa4af424ada8ab9e6fe77035db1cf222ffa)
---
 src/shared/util.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/shared/util.h b/src/shared/util.h
index a69807d..0d82b13 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"