+/**
+ * Return pointer to the wrapping struct instance.
+ *
+ * Example:
+ *
+ * struct wrapper {
+ * ...
+ * struct child c;
+ * ...
+ * };
+ *
+ * struct child *x = obtain(...);
+ * struct wrapper *w = container_of(x, struct wrapper, c);
+ */
+#ifndef container_of
+#define container_of(ptr, type, member) __extension__ ({ \
+ const typeof(((type *)0)->member) *_ptr = (ptr); \
+ __attribute__((unused)) type *_target_ptr = \
+ (type *)(ptr); \
+ (type *)(((uintptr_t)_ptr) - offsetof(type, member)); \
+ })
+#endif
+