[PATCH 1/2] list: introduce list_replace() helper

[Oleg Nesterov <oleg@tv-sign.ru>]

list_replace() is similar to list_replace_rcu(), but
unlike list_replace_rcu() it

	could be used when list_empty(old) == 1

	doesn't use barriers

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.17-rc4/include/linux/list.h~1_REPLACE	2006-05-18 03:29:13.000000000 +0400
+++ 2.6.17-rc4/include/linux/list.h	2006-05-18 03:38:13.000000000 +0400
@@ -197,12 +197,35 @@ static inline void list_del_rcu(struct l
 	entry->prev = LIST_POISON2;
 }
 
+/**
+ * list_replace - replace old entry by new one
+ * @old : the element to be replaced
+ * @new : the new element to insert
+ * Note: if 'old' was empty, it will be overwritten.
+ */
+static inline void list_replace(struct list_head *old,
+				struct list_head *new)
+{
+	new->next = old->next;
+	new->next->prev = new;
+	new->prev = old->prev;
+	new->prev->next = new;
+}
+
+static inline void list_replace_init(struct list_head *old,
+					struct list_head *new)
+{
+	list_replace(old, new);
+	INIT_LIST_HEAD(old);
+}
+
 /*
  * list_replace_rcu - replace old entry by new one
  * @old : the element to be replaced
  * @new : the new element to insert
  *
  * The old entry will be replaced with the new entry atomically.
+ * Note: 'old' should not be empty.
  */
 static inline void list_replace_rcu(struct list_head *old,
 				struct list_head *new)