[PATCH -mm] [2/3] add list_merge to list.h

["Nate Diller" <nate.diller@gmail.com>]

list_merge behaves like list_splice, except it can be used with
headless lists.  that is, the resulting list will have @head
immediately preceeding @list.

This is used by the contig list feature in the Elevator I/O scheduler

Signed-off-by: Nate Diller <nate.diller@gmail.com>

---
 list.h |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
---

diff -urpN -X dontdiff linux-2.6.18-rc1-mm2/include/linux/list.h
linux-dput/include/linux/list.h
--- linux-2.6.18-rc1-mm2/include/linux/list.h	2006-07-18
15:00:53.000000000 -0700
+++ linux-dput/include/linux/list.h	2006-08-03 18:42:00.000000000 -0700
@@ -357,6 +357,27 @@ static inline void list_splice_init(stru
 	}
 }

+/**
+ * list_merge - merge two headless lists
+ * @list: the new list to merge.
+ * @head: the place to add it in the first list.
+ *
+ * This is similar to list_splice(), except it merges every item onto @list,
+ * not excluding @head itself.  It is a noop if @head already immediately
+ * preceeds @list.
+ */
+static inline void list_merge(struct list_head *list, struct list_head *head)
+{
+	struct list_head *last = list->prev;
+	struct list_head *at = head->next;
+
+	list->prev = head;
+	head->next = list;
+
+	last->next = at;
+	at->prev = last;
+}
+
 /**
  * list_entry - get the struct for this entry
  * @ptr:	the &struct list_head pointer.