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Subject[PATCH v2 01/26] rculist: introduce list_next_or_null_rr_rcu()
Date
Function is going to be used in transport over RDMA module
in subsequent patches.

Function returns next element in round-robin fashion,
i.e. head will be skipped. NULL will be returned if list
is observed as empty.

Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org
---
include/linux/rculist.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 127f534fec94..b0840d5ab25a 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -339,6 +339,25 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
})

/**
+ * list_next_or_null_rr_rcu - get next list element in round-robin fashion.
+ * @head: the head for the list.
+ * @ptr: the list head to take the next element from.
+ * @type: the type of the struct this is embedded in.
+ * @memb: the name of the list_head within the struct.
+ *
+ * Next element returned in round-robin fashion, i.e. head will be skipped,
+ * but if list is observed as empty, NULL will be returned.
+ *
+ * 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_next_or_null_rr_rcu(head, ptr, type, memb) \
+({ \
+ list_next_or_null_rcu(head, ptr, type, memb) ?: \
+ list_next_or_null_rcu(head, READ_ONCE((ptr)->next), type, memb); \
+})
+
+/**
* 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.
--
2.13.1
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