X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=include%2Flinux%2Frculist.h;h=3863352656e7d6e02431038e38e084febf3fe996;hb=75faafd41c3c6312b7df51ce8cda5ba84495a8f1;hp=d079290843a93f9b508f9d05cd9489ea263dc380;hpb=ed8f37370d83e695c0a4fa5d5fc7a83ecb947526;p=pandora-kernel.git

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index d079290843a9..3863352656e7 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -241,6 +241,24 @@ static inline void list_splice_init_rcu(struct list_head *list,
 #define list_first_entry_rcu(ptr, type, member) \
 	list_entry_rcu((ptr)->next, type, member)
 
+/**
+ * list_first_or_null_rcu - get the first element from a list
+ * @ptr:        the list head to take the element from.
+ * @type:       the type of the struct this is embedded in.
+ * @member:     the name of the list_struct within the struct.
+ *
+ * Note that if the list is empty, it returns NULL.
+ *
+ * This primitive may safely run concurrently with the _rcu list-mutation
+ * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
+ */
+#define list_first_or_null_rcu(ptr, type, member) \
+	({struct list_head *__ptr = (ptr); \
+	  struct list_head *__next = ACCESS_ONCE(__ptr->next); \
+	  likely(__ptr != __next) ? \
+		list_entry_rcu(__next, type, member) : NULL; \
+	})
+
 /**
  * list_for_each_entry_rcu	-	iterate over rcu list of given type
  * @pos:	the type * to use as a loop cursor.