band-steering: add band-steering component

This adds a new band-steering component to usteer.

With band-steering enabled, usteer will attempt to move clients with a
consistently good SNR / signal from 2.4 GHz to the 5 GHz band.

In contrast to existing policies usteer tracks, band-steering is
non-invasive and will not lead to forceful connection termination.

Signed-off-by: David Bauer <mail@david-bauer.net>

band_steering.c

@@ -0,0 +1,98 @@
+/*
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
+ *
+ *   Copyright (C) 2022 David Bauer <mail@david-bauer.net>
+ */
+
+#include "usteer.h"
+#include "node.h"
+
+void usteer_band_steering_sta_update(struct sta_info *si)
+{
+	if (si->signal < usteer_snr_to_signal(si->node, config.band_steering_min_snr))
+		si->band_steering.below_snr = true;
+}
+
+bool usteer_band_steering_is_target(struct usteer_local_node *ln, struct usteer_node *node)
+{
+	if (&ln->node == node)
+		return false;
+
+	if (strcmp(ln->node.ssid, node->ssid))
+		return false;
+
+	if (node->freq < 4000)
+		return false;
+
+	if (!usteer_policy_node_below_max_assoc(node))
+		return false;
+	
+	/* ToDo: Skip nodes with active load-kick */
+	
+	return true;
+ }
+
+
+static bool usteer_band_steering_has_target_iface(struct usteer_local_node *ln)
+{
+	struct usteer_node *node;
+
+	for_each_local_node(node) {
+		if (usteer_band_steering_is_target(ln, node))
+			return true;
+	}
+
+	return false;
+}
+
+void usteer_band_steering_perform_steer(struct usteer_local_node *ln)
+{
+	unsigned int min_count = DIV_ROUND_UP(config.band_steering_interval, config.local_sta_update);
+	struct sta_info *si;
+
+	if (!config.band_steering_interval)
+		return;
+
+	/* Band-Steering is only available on 2.4 GHz interfaces */
+	if (ln->node.freq > 4000)
+		return;
+
+	/* Check if we have an interface we can steer to */
+	if (!usteer_band_steering_has_target_iface(ln))
+		return;
+
+	/* Only steer every interval */
+	if (ln->band_steering_interval < min_count) {
+		ln->band_steering_interval++;
+		return;
+	}
+
+	ln->band_steering_interval = 0;
+
+	list_for_each_entry(si, &ln->node.sta_info, node_list) {
+		if (si->connected != STA_CONNECTED)
+			continue;
+
+		/* Skip clients with insufficient SNR-state */
+		if (si->band_steering.below_snr) {
+			si->band_steering.below_snr = false;
+			continue;
+		}
+
+		if (si->bss_transition)
+			usteer_ubus_band_steering_request(si);
+
+		si->band_steering.below_snr = false;
+	}
+}