container_of: don't put member_ptr in container_off.

[ccan] / ccan / container_of / container_of.h

diff --git a/ccan/container_of/container_of.h b/ccan/container_of/container_of.h
index 1f4b18e4426a1c3c0bfc5c47e2a4e807ae7e2a52..ea8f1dd36cc191d6d3d3f690d342c0845d61d32e 100644 (file)
--- a/ccan/container_of/container_of.h
+++ b/ccan/container_of/container_of.h
@@ -3,7 +3,7 @@
 #include <stddef.h>
 
 #include "config.h"
-#include "check_type/check_type.h"
+#include <ccan/check_type/check_type.h>
 
 /**
  * container_of - get pointer to enclosing structure
@@ -15,51 +15,77 @@
  * subtraction to return the pointer to the enclosing type.
  *
  * Example:
- *     struct info
- *     {
+ *     struct foo {
+ *             int fielda, fieldb;
+ *             // ...
+ *     };
+ *     struct info {
  *             int some_other_field;
  *             struct foo my_foo;
  *     };
  *
- *     struct info *foo_to_info(struct foo *foop)
+ *     static struct info *foo_to_info(struct foo *foo)
  *     {
  *             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))
+         ((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
  * 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)
+ *     static struct info *foo_to_i(struct foo *foo)
  *     {
  *             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)
+#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, var, member) \
-       ((void *)((char *)(member_ptr) - offsetof(containing_type, member)))
+#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 */