list: Add list_next_entry_circular() and list_prev_entry_circular()

Add macros to get the next or previous entries and wraparound if
needed. For example, calling list_next_entry_circular() on the last
element should return the first element in the list.

Signed-off-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/list.h b/include/linux/list.h
index dd6c2041d09c1d67e0b2be843143b08c137acc9f..c147eeb2d39d7c07017dbdaf827ac5cac643ea3f 100644 (file)
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -563,6 +563,19 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_next_entry(pos, member) \
        list_entry((pos)->member.next, typeof(*(pos)), member)
 
+/**
+ * list_next_entry_circular - get the next element in list
+ * @pos:       the type * to cursor.
+ * @head:      the list head to take the element from.
+ * @member:    the name of the list_head within the struct.
+ *
+ * Wraparound if pos is the last element (return the first element).
+ * Note, that list is expected to be not empty.
+ */
+#define list_next_entry_circular(pos, head, member) \
+       (list_is_last(&(pos)->member, head) ? \
+       list_first_entry(head, typeof(*(pos)), member) : list_next_entry(pos, member))
+
 /**
  * list_prev_entry - get the prev element in list
  * @pos:       the type * to cursor
@@ -571,6 +584,19 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_prev_entry(pos, member) \
        list_entry((pos)->member.prev, typeof(*(pos)), member)
 
+/**
+ * list_prev_entry_circular - get the prev element in list
+ * @pos:       the type * to cursor.
+ * @head:      the list head to take the element from.
+ * @member:    the name of the list_head within the struct.
+ *
+ * Wraparound if pos is the first element (return the last element).
+ * Note, that list is expected to be not empty.
+ */
+#define list_prev_entry_circular(pos, head, member) \
+       (list_is_first(&(pos)->member, head) ? \
+       list_last_entry(head, typeof(*(pos)), member) : list_prev_entry(pos, member))
+
 /**
  * list_for_each       -       iterate over a list
  * @pos:       the &struct list_head to use as a loop cursor.