Add list_last_or_null_rcu(), to simplify getting the last entry from a
rcu-protected list. The standard list_last_entry() can't be used as it
is not rcu-protected; the list may be modified concurrently. And the
->prev pointer can't be used, as only the ->next pointers are protected
by rcu.
This simply iterates forward through the entire list, to get to the last
entry. If the list is empty, it returns NULL.
Signed-off-by: Dan Streetman <ddstr...@ieee.org>
---
include/linux/rculist.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index a18b16f..954fde5 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -293,6 +293,27 @@ static inline void list_splice_init_rcu(struct list_head
*list,
})
/**
+ * list_last_or_null_rcu - get the last 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_head 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_last_or_null_rcu(ptr, type, member) \
+({ \
+ struct list_head *__ptr = (ptr); \
+ struct list_head *__last = __ptr; \
+ struct list_head *__entry = list_next_rcu(__ptr); \
+ for (; __entry != __ptr; __entry = list_next_rcu(__entry)) \
+ __last = __entry; \
+ likely(__ptr != __last) ? list_entry_rcu(__last, type, member) : NULL; \
+})
+
+/**
* list_for_each_entry_rcu - iterate over rcu list of given type
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
--
2.1.0
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