container_of: don't put member_ptr in container_off.

It's convenient to check that the member is the given type, but we can leave
that to the callers.

ccan/container_of/container_of.h

@@ -32,19 +32,17 @@
 #define container_of(member_ptr, containing_type, member)		\
 	 ((containing_type *)						\
 	  ((char *)(member_ptr)						\
-	   - container_off((member_ptr), containing_type, member)))
+	   - container_off(containing_type, member))			\
+	  + check_types_match(*(member_ptr), ((containing_type *)0)->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;
@@ -57,18 +55,17 @@
  *
  *	static struct info *foo_to_info(struct foo *foo)
  *	{
- *		size_t off = container_off(foo, struct info, my_foo);
+ *		size_t off = container_off(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))
+#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
@@ -82,12 +79,13 @@
  *	}
  */
 #if HAVE_TYPEOF
-#define container_of_var(member_ptr, var, member) \
-	container_of(member_ptr, typeof(*var), member)
+#define container_of_var(member_ptr, container_var, member) \
+	container_of(member_ptr, typeof(*container_var), member)
 #else
-#define container_of_var(member_ptr, var, member)		\
-	((void *)((char *)(member_ptr)				\
-		  - ((char *)&(var)->member - (char *)(var))))
+#define container_of_var(member_ptr, container_var, member)		\
+	((void *)((char *)(member_ptr)					\
+		  - ((char *)&(container_var)->member			\
+		     - (char *)(container_var))))
 #endif
 
 #endif /* CCAN_CONTAINER_OF_H */

ccan/container_of/test/run.c

@@ -18,7 +18,7 @@ int main(int argc, char *argv[])
 	ok1(container_of_var(intp, &foo, a) == &foo);
 	ok1(container_of_var(charp, &foo, b) == &foo);
 
-	ok1(container_off(intp, struct foo, a) == 0);
-	ok1(container_off(charp, struct foo, b) == offsetof(struct foo, b));
+	ok1(container_off(struct foo, a) == 0);
+	ok1(container_off(struct foo, b) == offsetof(struct foo, b));
 	return exit_status();
 }

ccan/list/list.h

@@ -4,6 +4,7 @@
 #include <stdbool.h>
 #include <assert.h>
 #include <ccan/container_of/container_of.h>
+#include <ccan/check_type/check_type.h>
 
 /**
  * struct list_node - an entry in a doubly-linked list
@@ -280,7 +281,7 @@ static inline void list_del_from(struct list_head *h, struct list_node *n)
  *	first = list_top(&parent->children, struct child, list);
  */
 #define list_top(h, type, member)					\
-	((type *)list_top_((h), container_off((h)->n.next, type, member)))
+	((type *)list_top_((h), list_off_(type, member)))
 
 static inline const void *list_top_(const struct list_head *h, size_t off)
 {
@@ -302,7 +303,7 @@ static inline const void *list_top_(const struct list_head *h, size_t off)
  *	last = list_tail(&parent->children, struct child, list);
  */
 #define list_tail(h, type, member) \
-	((type *)list_tail_((h), container_off((h)->n.next, type, member)))
+	((type *)list_tail_((h), list_off_(type, member)))
 
 static inline const void *list_tail_(const struct list_head *h, size_t off)
 {
@@ -370,4 +371,10 @@ static inline const void *list_tail_(const struct list_head *h, size_t off)
 		nxt = container_of_var(i->member.next, i, member);	\
 	     &i->member != &(h)->n;					\
 	     i = nxt, nxt = container_of_var(i->member.next, i, member))
+
+/* Get the offset of the member, but make sure it's a list_node. */
+#define list_off_(type, member)					\
+	(container_off(type, member) +				\
+	 check_type(((type *)0)->member, struct list_node))
+
 #endif /* CCAN_LIST_H */