[PATCH] list.h: add list_for_each_entry_continue_rcu

[Johannes Berg <johannes@sipsolutions.net>]

To implement the multicast list callback in mac80211 we need to
do partial list iteration. Since I want to convert the interface
list to an RCU list, I need a new list walking primitive:
list_for_each_entry_continue_rcu().

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-kernel@vger.kernel.org
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>

---
How do we want to handle this? Is it ok to push this via net-2.6.24 so
we can merge it along with the fix that needs it?

 include/linux/list.h |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- wireless-dev.orig/include/linux/list.h	2007-09-07 00:16:07.374444290 +0200
+++ wireless-dev/include/linux/list.h	2007-08-29 21:08:14.802054000 +0200
@@ -665,6 +665,26 @@ static inline void list_splice_init_rcu(
 		prefetch(rcu_dereference((pos))->next), (pos) != (head); \
         	(pos) = (pos)->next)
 
+
+/**
+ * list_for_each_entry_continue_rcu - continue iteration over rcu list
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Continue to iterate over rcu list of given type, continuing after
+ * the current position.
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as list_add_rcu()
+ * as long as the traversal is guarded by rcu_read_lock().
+ */
+#define list_for_each_entry_continue_rcu(pos, head, member) \
+	for ((pos) = list_entry((pos)->member.next, typeof(*pos), member); \
+		prefetch(rcu_dereference((pos))->member.next), \
+			 &pos->member != (head); \
+        	(pos) = list_entry(pos->member.next, typeof(*pos), member))
+
 /*
  * Double linked lists with a single pointer list head.
  * Mostly useful for hash tables where the two pointer list head is