*/
#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))
+ ((char *)(member_ptr) \
+ - container_off((member_ptr), containing_type, member)))
+/**
+ * container_off - get offset 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
+ * typechecking and figures out the offset to the enclosing type.
+ *
+ * Note that @member_ptr is not evaluated.
+ *
+ * Example:
+ * struct foo {
+ * int fielda, fieldb;
+ * // ...
+ * };
+ * struct info {
+ * int some_other_field;
+ * struct foo my_foo;
+ * };
+ *
+ * static struct info *foo_to_info(struct foo *foo)
+ * {
+ * size_t off = container_off(foo, struct info, my_foo);
+ * return (void *)((char *)foo - off);
+ * }
+ */
+#define container_off(member_ptr, containing_type, member) \
+ (offsetof(containing_type, member) \
+ + check_types_match(*(member_ptr), ((containing_type *)0)->member))
/**
* container_of_var - get pointer to enclosing structure using a variable