New variant of container_of: container_of_var, for list.h

[ccan] / container_of / container_of.h

diff --git a/container_of/container_of.h b/container_of/container_of.h
index 49f20b5670c99ddf5e6d98903c49e62912abf6ed..1f4b18e4426a1c3c0bfc5c47e2a4e807ae7e2a52 100644 (file)
--- 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 */