[PATCH 2/8] io-wq: add helper to merge two wq_lists

[Hao Xu <haoxu@linux.alibaba.com>]

add a helper to merge two wq_lists, it will be useful in the next
patches.

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---
 fs/io-wq.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/fs/io-wq.h b/fs/io-wq.h
index 8369a51b65c0..f1d92cf4ee31 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -39,6 +39,27 @@ static inline void wq_list_add_after(struct io_wq_work_node *node,
 		list->last = node;
 }
 
+/**
+ * wq_list_merge - merge the second list to the first one.
+ * @list0: the first list
+ * @list1: the second list
+ * Return list0 if list1 is NULL, and vice versa.
+ * Otherwise after merge, list0 contains the merged list.
+ */
+static inline struct io_wq_work_list *wq_list_merge(struct io_wq_work_list *list0,
+						    struct io_wq_work_list *list1)
+{
+	if (!list1 || !list1->first)
+		return list0;
+
+	if (!list0 || !list0->first)
+		return list1;
+
+	list0->last->next = list1->first;
+	list0->last = list1->last;
+	return list0;
+}
+
 static inline void wq_list_add_tail(struct io_wq_work_node *node,
 				    struct io_wq_work_list *list)
 {
-- 
2.24.4