ACS: Accept channel if any (rather than all) survey results are valid

Previously, a channel with even a single scan/survey result missing
information was skipped in ACS. This may not be desirable in cases when
multiple scan iterations are used (which is the case by default in
hostapd). Instead, use all channels that provided at least one complete
set of results. Calculate the average interference factor as an average
of the iterations that did provide complete values.

This seems to help with some cases, e.g., when ath9k may not be able to
report the noise floor for all channels from the first scan iteration
immediately after the driver has been loaded, but then returns it for
all other scan iterations.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/ap/acs.c

@@ -242,6 +242,7 @@
 
 
 static int acs_request_scan(struct hostapd_iface *iface);
+static int acs_survey_is_sufficient(struct freq_survey *survey);
 
 
 static void acs_clean_chan_surveys(struct hostapd_channel_data *chan)
@@ -328,6 +329,7 @@ acs_survey_chan_interference_factor(struct hostapd_iface *iface,
 	struct freq_survey *survey;
 	unsigned int i = 0;
 	long double int_factor = 0;
+	unsigned count = 0;
 
 	if (dl_list_empty(&chan->survey_list))
 		return;
@@ -339,18 +341,27 @@ acs_survey_chan_interference_factor(struct hostapd_iface *iface,
 
 	dl_list_for_each(survey, &chan->survey_list, struct freq_survey, list)
 	{
+		i++;
+
+		if (!acs_survey_is_sufficient(survey)) {
+			wpa_printf(MSG_DEBUG, "ACS: %d: insufficient data", i);
+			continue;
+		}
+
+		count++;
 		int_factor = acs_survey_interference_factor(survey,
 							    iface->lowest_nf);
 		chan->interference_factor += int_factor;
 		wpa_printf(MSG_DEBUG, "ACS: %d: min_nf=%d interference_factor=%Lg nf=%d time=%lu busy=%lu rx=%lu",
-			   ++i, chan->min_nf, int_factor,
+			   i, chan->min_nf, int_factor,
 			   survey->nf, (unsigned long) survey->channel_time,
 			   (unsigned long) survey->channel_time_busy,
 			   (unsigned long) survey->channel_time_rx);
 	}
 
-	chan->interference_factor = chan->interference_factor /
-		dl_list_len(&chan->survey_list);
+	if (!count)
+		return;
+	chan->interference_factor /= count;
 }
 
 
@@ -384,18 +395,19 @@ static int acs_usable_vht80_chan(struct hostapd_channel_data *chan)
 static int acs_survey_is_sufficient(struct freq_survey *survey)
 {
 	if (!(survey->filled & SURVEY_HAS_NF)) {
-		wpa_printf(MSG_ERROR, "ACS: Survey is missing noise floor");
+		wpa_printf(MSG_INFO, "ACS: Survey is missing noise floor");
 		return 0;
 	}
 
 	if (!(survey->filled & SURVEY_HAS_CHAN_TIME)) {
-		wpa_printf(MSG_ERROR, "ACS: Survey is missing channel time");
+		wpa_printf(MSG_INFO, "ACS: Survey is missing channel time");
 		return 0;
 	}
 
 	if (!(survey->filled & SURVEY_HAS_CHAN_TIME_BUSY) &&
 	    !(survey->filled & SURVEY_HAS_CHAN_TIME_RX)) {
-		wpa_printf(MSG_ERROR, "ACS: Survey is missing RX and busy time (at least one is required)");
+		wpa_printf(MSG_INFO,
+			   "ACS: Survey is missing RX and busy time (at least one is required)");
 		return 0;
 	}
 
@@ -406,18 +418,27 @@ static int acs_survey_is_sufficient(struct freq_survey *survey)
 static int acs_survey_list_is_sufficient(struct hostapd_channel_data *chan)
 {
 	struct freq_survey *survey;
+	int ret = -1;
 
 	dl_list_for_each(survey, &chan->survey_list, struct freq_survey, list)
 	{
-		if (!acs_survey_is_sufficient(survey)) {
-			wpa_printf(MSG_ERROR, "ACS: Channel %d has insufficient survey data",
-				   chan->chan);
-			return 0;
+		if (acs_survey_is_sufficient(survey)) {
+			ret = 1;
+			break;
 		}
+		ret = 0;
 	}
 
-	return 1;
+	if (ret == -1)
+		ret = 1; /* no survey list entries */
+
+	if (!ret) {
+		wpa_printf(MSG_INFO,
+			   "ACS: Channel %d has insufficient survey data",
+			   chan->chan);
+	}
 
+	return ret;
 }