Function handle_rtable_change_cb

freebsd/net/route/fib_algo.c:537–612

* Rib subscription handler. Checks if the algorithm is ready to * receive updates, handles nexthop refcounting and passes change * data to the algorithm callback. */

 *  data to the algorithm callback.
 */
static void
handle_rtable_change_cb(struct rib_head *rnh, struct rib_cmd_info *rc,
    void *_data)
{
	struct fib_data *fd = (struct fib_data *)_data;
	enum flm_op_result result;

	RIB_WLOCK_ASSERT(rnh);

	/*
	 * There is a small gap between subscribing for route changes
	 *  and initiating rtable dump. Avoid receiving route changes
	 *  prior to finishing rtable dump by checking `init_done`.
	 */
	if (!fd->init_done)
		return;
	/*
	 * If algo requested rebuild, stop sending updates by default.
	 * This simplifies nexthop refcount handling logic.
	 */
	if (fd->fd_need_rebuild)
		return;

	/* Consider scheduling algorithm re-evaluation */
	schedule_algo_eval(fd);

	/*
	 * Maintain guarantee that every nexthop returned by the dataplane
	 *  lookup has > 0 refcount, so can be safely referenced within current
	 *  epoch.
	 */
	if (rc->rc_nh_new != NULL) {
		if (fib_ref_nhop(fd, rc->rc_nh_new) == 0) {
			/* ran out of indexes */
			schedule_fd_rebuild(fd, "ran out of nhop indexes");
			return;
		}
	}

	result = fd->fd_flm->flm_change_rib_item_cb(rnh, rc, fd->fd_algo_data);

	switch (result) {
	case FLM_SUCCESS:
		/* Unref old nexthop on success */
		if (rc->rc_nh_old != NULL)
			fib_unref_nhop(fd, rc->rc_nh_old);
		break;
	case FLM_REBUILD:

		/*
		 * Algo is not able to apply the update.
		 * Schedule algo rebuild.
		 */
		if (!need_immediate_rebuild(fd, rc)) {
			schedule_fd_rebuild(fd, "algo requested rebuild");
			break;
		}