diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h
index fca2d76..7d16b5e 100644
--- a/include/common/mini-clist.h
+++ b/include/common/mini-clist.h
@@ -19,6 +19,20 @@
     struct list *p;	/* prev */
 };
 
+/* a back-ref is a pointer to a target list entry. It is used to detect when an
+ * element being deleted is currently being tracked by another user. The best
+ * example is a user dumping the session table. The table does not fit in the
+ * output buffer so we have to set a mark on a session and go on later. But if
+ * that marked session gets deleted, we don't want the user's pointer to go in
+ * the wild. So we can simply link this user's request to the list of this
+ * session's users, and put a pointer to the list element in ref, that will be
+ * used as the mark for next iteration.
+ */
+struct bref {
+	struct list users;
+	struct list *ref; /* pointer to the target's list entry */
+};
+
 /* First undefine some macros which happen to also be defined on OpenBSD,
  * in sys/queue.h, used by sys/event.h
  */