X-Git-Url: http://git.ozlabs.org/?a=blobdiff_plain;f=container_of%2Fcontainer_of.h;h=1f4b18e4426a1c3c0bfc5c47e2a4e807ae7e2a52;hb=4cdcc6486e0f406c2ef98e37935f529250d1dbb3;hp=49f20b5670c99ddf5e6d98903c49e62912abf6ed;hpb=fdfcdafbfa7957b6ca393bb4000fbaad3813a61a;p=ccan

diff --git a/container_of/container_of.h b/container_of/container_of.h
index 49f20b56..1f4b18e4 100644
--- a/container_of/container_of.h
+++ b/container_of/container_of.h
@@ -5,10 +5,61 @@
 #include "config.h"
 #include "check_type/check_type.h"
 
+/**
+ * container_of - get pointer to enclosing structure
+ * @member_ptr: pointer to the structure member
+ * @containing_type: the type this member is within
+ * @member: the name of this member within the structure.
+ *
+ * Given a pointer to a member of a structure, this macro does pointer
+ * subtraction to return the pointer to the enclosing type.
+ *
+ * Example:
+ *	struct info
+ *	{
+ *		int some_other_field;
+ *		struct foo my_foo;
+ *	};
+ *
+ *	struct info *foo_to_info(struct foo *foop)
+ *	{
+ *		return container_of(foo, struct info, my_foo);
+ *	}
+ */
 #define container_of(member_ptr, containing_type, member)		\
 	 ((containing_type *)						\
 	  ((char *)(member_ptr) - offsetof(containing_type, member))	\
 	  - check_types_match(*(member_ptr), ((containing_type *)0)->member))
 
 
+/**
+ * container_of_var - get pointer to enclosing structure using a variable
+ * @member_ptr: pointer to the structure member
+ * @var: a pointer to a structure of same type as this member is within
+ * @member: the name of this member within the structure.
+ *
+ * Given a pointer to a member of a structure, this macro does pointer
+ * subtraction to return the pointer to the enclosing type.
+ *
+ * Example:
+ *	struct info
+ *	{
+ *		int some_other_field;
+ *		struct foo my_foo;
+ *	};
+ *
+ *	struct info *foo_to_info(struct foo *foop)
+ *	{
+ *		struct info *i = container_of_var(foo, i, my_foo);
+ *		return i;
+ *	}
+ */
+#ifdef HAVE_TYPEOF
+#define container_of_var(member_ptr, var, member) \
+	container_of(member_ptr, typeof(*var), member)
+#else
+#define container_of_var(member_ptr, var, member) \
+	((void *)((char *)(member_ptr) - offsetof(containing_type, member)))
+#endif
+
 #endif /* CCAN_CONTAINER_OF_H */