read_only_listener
struct read_only_listener *read_only_listener;
result = vdo_allocate(1, __func__, &read_only_listener);
*read_only_listener = (struct read_only_listener) {
thread->listeners = read_only_listener;
struct read_only_listener *listener = completion->parent;
struct read_only_listener *listener, *next;
struct read_only_listener *next;
struct read_only_listener *listeners;