13   list_node_t *tail;  member
71   return list->tail->data;  in list_back()
86   if (list->tail == prev_node)  in list_insert_after()
87     list->tail = node;  in list_insert_after()
106   if (list->tail == NULL)  in list_prepend()
107     list->tail = list->head;  in list_prepend()
125   if (list->tail == NULL) {  in list_append()
127     list->tail = node;  in list_append()
129     list->tail->next = node;  in list_append()
130     list->tail = node;  in list_append()
150     if (list->tail == list->head)  in list_remove()
151       list->tail = next;  in list_remove()
159       if (list->tail == node)  in list_remove()
160         list->tail = prev;  in list_remove()
174   list->tail = NULL;  in list_clear()