list.h: Add list_splice_tail() and list_splice_tail_init()

If you are using linked lists for queues list_splice() will not do what
you would expect even if you use the elements passed reversed. We need
to handle these differently. We add list_splice_tail() and
list_splice_tail_init().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 38 insertions, 9 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index 453916bc0412..a886f27a1181 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -215,21 +215,21 @@ static inline int list_is_singular(const struct list_head *head)
 }
 
 static inline void __list_splice(const struct list_head *list,
-                                 struct list_head *head)
+                                 struct list_head *prev,
+                                 struct list_head *next)
 {
         struct list_head *first = list->next;
         struct list_head *last = list->prev;
-        struct list_head *at = head->next;
 
-        first->prev = head;
-        head->next = first;
+        first->prev = prev;
+        prev->next = first;
 
-        last->next = at;
-        at->prev = last;
+        last->next = next;
+        next->prev = last;
 }
 
 /**
- * list_splice - join two lists
+ * list_splice - join two lists, this is designed for stacks
  * @list: the new list to add.
  * @head: the place to add it in the first list.
  */
@@ -237,7 +237,19 @@ static inline void list_splice(const struct list_head *list,
                                 struct list_head *head)
 {
         if (!list_empty(list))
-                __list_splice(list, head);
+                __list_splice(list, head, head->next);
+}
+
+/**
+ * list_splice_tail - join two lists, each list being a queue
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ */
+static inline void list_splice_tail(struct list_head *list,
+                                struct list_head *head)
+{
+        if (!list_empty(list))
+                __list_splice(list, head->prev, head);
 }
 
 /**
@@ -251,7 +263,24 @@ static inline void list_splice_init(struct list_head *list,
                                     struct list_head *head)
 {
         if (!list_empty(list)) {
-                __list_splice(list, head);
+                __list_splice(list, head, head->next);
+                INIT_LIST_HEAD(list);
+        }
+}
+
+/**
+ * list_splice_tail_init - join two lists, each list being a queue, and
+ *     reinitialise the emptied list.
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ *
+ * The list at @list is reinitialised
+ */
+static inline void list_splice_tail_init(struct list_head *list,
+                                         struct list_head *head)
+{
+        if (!list_empty(list)) {
+                __list_splice(list, head->prev, head);
                 INIT_LIST_HEAD(list);
         }
 }