hostapd: Add config option chanlist for DFS channels

Different channels allow different transmission power, at least in ETSI
countries. Also, ETSI requires a "channel plan" for DFS operation, and
channels should be randomly choosen from these channels.

Add a channel list configuration option for users to add channels
hostapd may pick from.

Signed-hostap: Simon Wunderlich <sw@simonwunderlich.de>

hostapd/config_file.c

@@ -2486,6 +2486,13 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 				conf->channel = 0;
 			} else
 				conf->channel = atoi(pos);
+		} else if (os_strcmp(buf, "chanlist") == 0) {
+			if (hostapd_parse_intlist(&conf->chanlist, pos)) {
+				wpa_printf(MSG_ERROR,
+					   "Line %d: invalid channel list",
+					   line);
+				errors++;
+			}
 		} else if (os_strcmp(buf, "beacon_int") == 0) {
 			int val = atoi(pos);
 			/* MIB defines range as 1..65535, but very small values

hostapd/hostapd.conf

@@ -154,6 +154,14 @@ channel=1
 # Defaults:
 #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.
+# Default: not set (allow any enabled channel to be selected)
+#chanlist=100 104 108 112 116
+
 # Beacon interval in kus (1.024 ms) (default: 100; range 15..65535)
 beacon_int=100
 

src/ap/ap_config.c

@@ -562,6 +562,7 @@ void hostapd_config_free(struct hostapd_config *conf)
 	os_free(conf->bss);
 	os_free(conf->supported_rates);
 	os_free(conf->basic_rates);
+	os_free(conf->chanlist);
 
 	os_free(conf);
 }

src/ap/ap_config.h

@@ -525,6 +525,7 @@ struct hostapd_config {
 	int fragm_threshold;
 	u8 send_probe_response;
 	u8 channel;
+	int *chanlist;
 	enum hostapd_hw_mode hw_mode; /* HOSTAPD_MODE_IEEE80211A, .. */
 	enum {
 		LONG_PREAMBLE = 0,

src/ap/dfs.c

@@ -139,6 +139,22 @@ static int dfs_chan_range_available(struct hostapd_hw_modes *mode,
 }
 
 
+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;
+}
+
+
 /*
  * The function assumes HT40+ operation.
  * Make sure to adjust the following variables after calling this:
@@ -171,6 +187,9 @@ static int dfs_find_channel(struct hostapd_iface *iface,
 		if (!dfs_chan_range_available(mode, i, n_chans, skip_radar))
 			continue;
 
+		if (!is_in_chanlist(iface, chan))
+			continue;
+
 		if (ret_chan && idx == channel_idx) {
 			wpa_printf(MSG_DEBUG, "Selected ch. #%d", chan->chan);
 			*ret_chan = chan;