tools lib: Add list_last_entry_or_null()

Add list_last_entry_or_null() to get the last element from a list,
returns NULL if the list is empty.

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220709015033.38326-6-yangjihong1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/include/linux/list.h b/tools/include/linux/list.h
index b2fc48d..a4dfb6a 100644 (file)
--- a/tools/include/linux/list.h
+++ b/tools/include/linux/list.h
@@ -385,6 +385,17 @@ static inline void list_splice_tail_init(struct list_head *list,
        (!list_empty(ptr) ? list_first_entry(ptr, 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) \
+       (!list_empty(ptr) ? list_last_entry(ptr, type, member) : NULL)
+
+/**
  * list_next_entry - get the next element in list
  * @pos:       the type * to cursor
  * @member:    the name of the list_head within the struct.