list: introduce list_last_entry(), use list_{first,last}_entry()

We already have list_first_entry(), it makes sense to also add
list_last_entry() for consistency.  And we use both helpers in
list_for_each_*().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eilon Greenstein <eilong@broadcom.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/list.h b/include/linux/list.h
index c88a591..ef95941 100644 (file)
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -362,6 +362,17 @@ static inline void list_splice_tail_init(struct list_head *list,
        list_entry((ptr)->next, type, member)
 
 /**
+ * list_last_entry - 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_struct within the struct.
+ *
+ * Note, that list is expected to be not empty.
+ */
+#define list_last_entry(ptr, type, member) \
+       list_entry((ptr)->prev, type, member)
+
+/**
  * list_first_entry_or_null - get the first element from a list
  * @ptr:       the list head to take the element from.
  * @type:      the type of the struct this is embedded in.
@@ -432,7 +443,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * @member:    the name of the list_struct within the struct.
  */
 #define list_for_each_entry(pos, head, member)                         \
-       for (pos = list_entry((head)->next, typeof(*pos), member);      \
+       for (pos = list_first_entry(head, typeof(*pos), member);        \
             &pos->member != (head);                                    \
             pos = list_next_entry(pos, member))
 
@@ -443,7 +454,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * @member:    the name of the list_struct within the struct.
  */
 #define list_for_each_entry_reverse(pos, head, member)                 \
-       for (pos = list_entry((head)->prev, typeof(*pos), member);      \
+       for (pos = list_last_entry(head, typeof(*pos), member);         \
             &pos->member != (head);                                    \
             pos = list_prev_entry(pos, member))
 
@@ -506,7 +517,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * @member:    the name of the list_struct within the struct.
  */
 #define list_for_each_entry_safe(pos, n, head, member)                 \
-       for (pos = list_entry((head)->next, typeof(*pos), member),      \
+       for (pos = list_first_entry(head, typeof(*pos), member),        \
                n = list_next_entry(pos, member);                       \
             &pos->member != (head);                                    \
             pos = n, n = list_next_entry(n, member))
@@ -553,7 +564,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * of list entry.
  */
 #define list_for_each_entry_safe_reverse(pos, n, head, member)         \
-       for (pos = list_entry((head)->prev, typeof(*pos), member),      \
+       for (pos = list_last_entry(head, typeof(*pos), member),         \
                n = list_prev_entry(pos, member);                       \
             &pos->member != (head);                                    \
             pos = n, n = list_prev_entry(n, member))