ACS: Allow subset of channels to be configured

Add the possibility to define a subset of channels used by the ACS
engine when not operating on DFS channels.

Signed-off-by: Adrien Decostre <ad.decostre@gmail.com>

hostapd/hostapd.conf

@@ -158,10 +158,7 @@ channel=1
 #acs_num_scans=5
 
 # Channel list restriction. This option allows hostapd to select one of the
-# provided channels when a channel should be automatically selected. This
-# is currently only used for DFS when the current channels becomes unavailable
-# due to radar interference, and is currently only useful when ieee80211h=1 is
-# set.
+# provided channels when a channel should be automatically selected.
 # Default: not set (allow any enabled channel to be selected)
 #chanlist=100 104 108 112 116
 

src/ap/acs.c

@@ -455,6 +455,22 @@ static int acs_usable_chan(struct hostapd_channel_data *chan)
 }
 
 
+static int is_in_chanlist(struct hostapd_iface *iface,
+			  struct hostapd_channel_data *chan)
+{
+	int *entry;
+
+	if (!iface->conf->chanlist)
+		return 1;
+
+	for (entry = iface->conf->chanlist; *entry != -1; entry++) {
+		if (*entry == chan->chan)
+			return 1;
+	}
+	return 0;
+}
+
+
 static void acs_survey_all_chans_intereference_factor(
 	struct hostapd_iface *iface)
 {
@@ -467,6 +483,9 @@ static void acs_survey_all_chans_intereference_factor(
 		if (!acs_usable_chan(chan))
 			continue;
 
+		if (!is_in_chanlist(iface, chan))
+			continue;
+
 		wpa_printf(MSG_DEBUG, "ACS: Survey analysis for channel %d (%d MHz)",
 			   chan->chan, chan->freq);
 
@@ -543,6 +562,8 @@ acs_find_ideal_chan(struct hostapd_iface *iface)
 		if (chan->flag & HOSTAPD_CHAN_DISABLED)
 			continue;
 
+		if (!is_in_chanlist(iface, chan))
+			continue;
 
 		/* HT40 on 5 GHz has a limited set of primary channels as per
 		 * 11n Annex J */