+/* CC0 (Public domain) - see LICENSE file for details */
#ifndef CCAN_CONTAINER_OF_H
#define CCAN_CONTAINER_OF_H
#include <stddef.h>
*/
#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(containing_type, member)) \
+ + check_types_match(*(member_ptr), ((containing_type *)0)->member))
+/**
+ * container_off - get offset to enclosing structure
+ * @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.
+ *
+ * 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(struct info, my_foo);
+ * return (void *)((char *)foo - off);
+ * }
+ */
+#define container_off(containing_type, member) \
+ offsetof(containing_type, 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
+ * @container_var: a pointer of same type as this member's container
* @member: the name of this member within the structure.
*
* Given a pointer to a member of a structure, this macro does pointer
* return i;
* }
*/
-#ifdef HAVE_TYPEOF
-#define container_of_var(member_ptr, var, member) \
- container_of(member_ptr, typeof(*var), member)
+#if HAVE_TYPEOF
+#define container_of_var(member_ptr, container_var, member) \
+ container_of(member_ptr, typeof(*container_var), member)
+#else
+#define container_of_var(member_ptr, container_var, member) \
+ ((void *)((char *)(member_ptr) - \
+ container_off_var(container_var, member)))
+#endif
+
+/**
+ * container_off_var - get offset of a field in enclosing structure
+ * @container_var: a pointer to a container structure
+ * @member: the name of a member within the structure.
+ *
+ * Given (any) pointer to a structure and a its member name, this
+ * macro does pointer subtraction to return offset of member in a
+ * structure memory layout.
+ *
+ */
+#if HAVE_TYPEOF
+#define container_off_var(var, member) \
+ container_off(typeof(*var), member)
#else
-#define container_of_var(member_ptr, var, member) \
- ((void *)((char *)(member_ptr) - offsetof(containing_type, member)))
+#define container_off_var(var, member) \
+ ((const char *)&(var)->member - (const char *)(var))
#endif
#endif /* CCAN_CONTAINER_OF_H */