advance_last_with_data(struct evbuffer *buf)
{
	int n = 0;
	ASSERT_EVBUFFER_LOCKED(buf);

	if (!*buf->last_with_datap)
		return 0;

	while ((*buf->last_with_datap)->next && (*buf->last_with_datap)->next->off) {
		buf->last_with_datap = &(*buf->last_with_datap)->next;
		++n;
	}
	return n;
}