X-Git-Url: https://git.ozlabs.org/?p=ccan;a=blobdiff_plain;f=container_of%2Fcontainer_of.h;h=1f4b18e4426a1c3c0bfc5c47e2a4e807ae7e2a52;hp=bdb23d07a163e2e0933568db35f0892c1dce7b5c;hb=53edefb8b2de84c873f8ecc35b61003d559b18dd;hpb=7bbd49fdb03503688dd34ab860e0e02e852ed267

diff --git a/container_of/container_of.h b/container_of/container_of.h
index bdb23d07..1f4b18e4 100644
--- a/container_of/container_of.h
+++ b/container_of/container_of.h
@@ -32,4 +32,34 @@
 	  - 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 */