[PATCH] list: introduce list_bulk_move_tail helper

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Move all entries between @first and including @last before @head.

This is useful for LRU lists where a whole block of entries should be
moved to the end of the list.

Used as a band aid in TTM, but better placed in the common list headers.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c | 25 +++++--------------------
 include/linux/list.h         | 23 +++++++++++++++++++++++
 2 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index b2a33bf1ef10..26b889f86670 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -247,20 +247,6 @@ void ttm_bo_move_to_lru_tail(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(ttm_bo_move_to_lru_tail);
 
-static void ttm_list_move_bulk_tail(struct list_head *list,
-				    struct list_head *first,
-				    struct list_head *last)
-{
-	first->prev->next = last->next;
-	last->next->prev = first->prev;
-
-	list->prev->next = first;
-	first->prev = list->prev;
-
-	last->next = list;
-	list->prev = last;
-}
-
 void ttm_bo_bulk_move_lru_tail(struct ttm_lru_bulk_move *bulk)
 {
 	unsigned i;
@@ -276,8 +262,8 @@ void ttm_bo_bulk_move_lru_tail(struct ttm_lru_bulk_move *bulk)
 		reservation_object_assert_held(pos->last->resv);
 
 		man = &pos->first->bdev->man[TTM_PL_TT];
-		ttm_list_move_bulk_tail(&man->lru[i], &pos->first->lru,
-					&pos->last->lru);
+		list_bulk_move_tail(&man->lru[i], &pos->first->lru,
+				    &pos->last->lru);
 	}
 
 	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
@@ -291,8 +277,8 @@ void ttm_bo_bulk_move_lru_tail(struct ttm_lru_bulk_move *bulk)
 		reservation_object_assert_held(pos->last->resv);
 
 		man = &pos->first->bdev->man[TTM_PL_VRAM];
-		ttm_list_move_bulk_tail(&man->lru[i], &pos->first->lru,
-					&pos->last->lru);
+		list_bulk_move_tail(&man->lru[i], &pos->first->lru,
+				    &pos->last->lru);
 	}
 
 	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
@@ -306,8 +292,7 @@ void ttm_bo_bulk_move_lru_tail(struct ttm_lru_bulk_move *bulk)
 		reservation_object_assert_held(pos->last->resv);
 
 		lru = &pos->first->bdev->glob->swap_lru[i];
-		ttm_list_move_bulk_tail(lru, &pos->first->swap,
-					&pos->last->swap);
+		list_bulk_move_tail(lru, &pos->first->swap, &pos->last->swap);
 	}
 }
 EXPORT_SYMBOL(ttm_bo_bulk_move_lru_tail);
diff --git a/include/linux/list.h b/include/linux/list.h
index de04cc5ed536..edb7628e46ed 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -183,6 +183,29 @@ static inline void list_move_tail(struct list_head *list,
 	list_add_tail(list, head);
 }
 
+/**
+ * list_bulk_move_tail - move a subsection of a list to its tail
+ * @head: the head that will follow our entry
+ * @first: first entry to move
+ * @last: last entry to move, can be the same as first
+ *
+ * Move all entries between @first and including @last before @head.
+ * All three entries must belong to the same linked list.
+ */
+static inline void list_bulk_move_tail(struct list_head *head,
+				       struct list_head *first,
+				       struct list_head *last)
+{
+	first->prev->next = last->next;
+	last->next->prev = first->prev;
+
+	head->prev->next = first;
+	first->prev = head->prev;
+
+	last->next = head;
+	head->prev = last;
+}
+
 /**
  * list_is_last - tests whether @list is the last entry in list @head
  * @list: the entry to test
-- 
2.14.1