policy: don't select better candidate with bad signal

Don't select a node as a better candidate where a STA has insufficient
signal to. This is the case when the roam_trigger_snr is greater than
the projected signal of the client.

This stops clients from being selected to roam to a node where the
signal is not sufficient to maintain the connection. A selection might
otherwise happen e.g. due to better channel load on the remote node.

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

policy.c

@@ -72,6 +72,18 @@ below_max_assoc(struct sta_info *si)
 	return !node->max_assoc || node->n_assoc < node->max_assoc;
 }
 
+static bool
+over_min_signal(struct sta_info *si)
+{
+	if (config.min_snr && si->signal < usteer_snr_to_signal(si->node, config.min_snr))
+		return false;
+
+	if (config.roam_trigger_snr && si->signal < usteer_snr_to_signal(si->node, config.roam_trigger_snr))
+		return false;
+	
+	return true;
+}
+
 static uint32_t
 is_better_candidate(struct sta_info *si_cur, struct sta_info *si_new)
 {
@@ -80,6 +92,9 @@ is_better_candidate(struct sta_info *si_cur, struct sta_info *si_new)
 	if (!below_max_assoc(si_new))
 		return 0;
 
+	if (!over_min_signal(si_new))
+		return 0;
+
 	if (below_assoc_threshold(si_cur, si_new) &&
 	    !below_assoc_threshold(si_new, si_cur))
 		reasons |= (1 << UEV_SELECT_REASON_NUM_ASSOC);