ccan/list: Add list_empty_nocheck

This is the same as list_empty but without the debug checks. This is
useful when wanting to check for an empty list without locks held,
potentially racing with addition/removal, which can be a valid thing
to do under some circumstances.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/list/list.h

@@ -291,6 +291,21 @@ static inline bool list_empty_nodebug(const struct list_head *h)
 }
 #endif
 
+/**
+ * list_empty_nocheck - is a list empty?
+ * @h: the list_head
+ *
+ * If the list is empty, returns true. This doesn't perform any
+ * debug check for list consistency, so it can be called without
+ * locks, racing with the list being modified. This is ok for
+ * checks where an incorrect result is not an issue (optimized
+ * bail out path for example).
+ */
+static inline bool list_empty_nocheck(const struct list_head *h)
+{
+	return h->n.next == &h->n;
+}
+
 /**
  * list_del - delete an entry from an (unknown) linked list.
  * @n: the list_node to delete from the list.