[PATCH 1/9] list: add list_last_entry_or_null()

[Luca Ceresoli]

Add an equivalent of list_first_entry_or_null() to obtain the last element
of a list.

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>

---

Cc: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Zijun Hu <quic_zijuhu at quicinc.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 include/linux/list.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index e7e28afd28f8eef94ab6baec77e69ea104ba0391..7f7657e416209a2941b3f292b1334e9e0f2a3ca5 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -636,6 +636,20 @@ static inline void list_splice_tail_init(struct list_head *list,
 	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
 })
 
+/**
+ * list_last_entry_or_null - 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.
+ */
+#define list_last_entry_or_null(ptr, type, member) ({ \
+	struct list_head *head__ = (ptr); \
+	struct list_head *pos__ = READ_ONCE(head__->prev); \
+	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
+
 /**
  * list_next_entry - get the next element in list
  * @pos:	the type * to cursor

-- 
2.50.0