1 /*
2  * WPA Supplicant - background scan and roaming module: simple
3  * Copyright (c) 2009-2010, Jouni Malinen <j@w1.fi>
4  *
5  * This software may be distributed under the terms of the BSD license.
6  * See README for more details.
7  */
8 
9 #include "includes.h"
10 
11 #include "common.h"
12 #include "eloop.h"
13 #include "drivers/driver.h"
14 #include "config_ssid.h"
15 #include "wpa_supplicant_i.h"
16 #include "driver_i.h"
17 #include "scan.h"
18 #include "bgscan.h"
19 
20 struct bgscan_simple_data {
21 	struct wpa_supplicant *wpa_s;
22 	const struct wpa_ssid *ssid;
23 	int scan_interval;
24 	int signal_threshold;
25 	int short_scan_count; /* counter for scans using short scan interval */
26 	int max_short_scans; /* maximum times we short-scan before back-off */
27 	int short_interval; /* use if signal < threshold */
28 	int long_interval; /* use if signal > threshold */
29 	struct os_reltime last_bgscan;
30 };
31 
32 
33 static void bgscan_simple_timeout(void *eloop_ctx, void *timeout_ctx)
34 {
35 	struct bgscan_simple_data *data = eloop_ctx;
36 	struct wpa_supplicant *wpa_s = data->wpa_s;
37 	struct wpa_driver_scan_params params;
38 
39 	os_memset(&params, 0, sizeof(params));
40 	params.num_ssids = 1;
41 	params.ssids[0].ssid = data->ssid->ssid;
42 	params.ssids[0].ssid_len = data->ssid->ssid_len;
43 	params.freqs = data->ssid->scan_freq;
44 
45 	/*
46 	 * A more advanced bgscan module would learn about most like channels
47 	 * over time and request scans only for some channels (probing others
48 	 * every now and then) to reduce effect on the data connection.
49 	 */
50 
51 	wpa_printf(MSG_DEBUG, "bgscan simple: Request a background scan");
52 	if (wpa_supplicant_trigger_scan(wpa_s, &params)) {
53 		wpa_printf(MSG_DEBUG, "bgscan simple: Failed to trigger scan");
54 		eloop_register_timeout(data->scan_interval, 0,
55 				       bgscan_simple_timeout, data, NULL);
56 	} else {
57 		if (data->scan_interval == data->short_interval) {
58 			data->short_scan_count++;
59 			/*
60 			 * Spend at most the duration of a long scan interval
61 			 * scanning at the short scan interval. After that,
62 			 * revert to the long scan interval.
63 			 */
64 			if (data->short_scan_count > data->max_short_scans) {
65 				data->scan_interval = data->long_interval;
66 				wpa_printf(MSG_DEBUG, "bgscan simple: Backing "
67 					   "off to long scan interval");
68 			}
69 		} else if (data->short_scan_count > 0) {
70 			/*
71 			 * If we lasted a long scan interval without any
72 			 * CQM triggers, decrease the short-scan count,
73 			 * which allows 1 more short-scan interval to
74 			 * occur in the future when CQM triggers.
75 			 */
76 			data->short_scan_count--;
77 		}
78 		os_get_reltime(&data->last_bgscan);
79 	}
80 }
81 
82 
83 static int bgscan_simple_get_params(struct bgscan_simple_data *data,
84 				    const char *params)
85 {
86 	const char *pos;
87 
88 	if (params == NULL)
89 		return 0;
90 
91 	data->short_interval = atoi(params);
92 
93 	pos = os_strchr(params, ':');
94 	if (pos == NULL)
95 		return 0;
96 	pos++;
97 	data->signal_threshold = atoi(pos);
98 	pos = os_strchr(pos, ':');
99 	if (pos == NULL) {
100 		wpa_printf(MSG_ERROR, "bgscan simple: Missing scan interval "
101 			   "for high signal");
102 		return -1;
103 	}
104 	pos++;
105 	data->long_interval = atoi(pos);
106 
107 	return 0;
108 }
109 
110 
111 static void * bgscan_simple_init(struct wpa_supplicant *wpa_s,
112 				 const char *params,
113 				 const struct wpa_ssid *ssid)
114 {
115 	struct bgscan_simple_data *data;
116 
117 	data = os_zalloc(sizeof(*data));
118 	if (data == NULL)
119 		return NULL;
120 	data->wpa_s = wpa_s;
121 	data->ssid = ssid;
122 	if (bgscan_simple_get_params(data, params) < 0) {
123 		os_free(data);
124 		return NULL;
125 	}
126 	if (data->short_interval <= 0)
127 		data->short_interval = 30;
128 	if (data->long_interval <= 0)
129 		data->long_interval = 30;
130 
131 	wpa_printf(MSG_DEBUG, "bgscan simple: Signal strength threshold %d  "
132 		   "Short bgscan interval %d  Long bgscan interval %d",
133 		   data->signal_threshold, data->short_interval,
134 		   data->long_interval);
135 
136 	if (data->signal_threshold &&
137 	    wpa_drv_signal_monitor(wpa_s, data->signal_threshold, 4) < 0) {
138 		wpa_printf(MSG_ERROR, "bgscan simple: Failed to enable "
139 			   "signal strength monitoring");
140 	}
141 
142 	data->scan_interval = data->short_interval;
143 	data->max_short_scans = data->long_interval / data->short_interval + 1;
144 	if (data->signal_threshold) {
145 		/* Poll for signal info to set initial scan interval */
146 		struct wpa_signal_info siginfo;
147 		if (wpa_drv_signal_poll(wpa_s, &siginfo) == 0 &&
148 		    siginfo.current_signal >= data->signal_threshold)
149 			data->scan_interval = data->long_interval;
150 	}
151 	wpa_printf(MSG_DEBUG, "bgscan simple: Init scan interval: %d",
152 		   data->scan_interval);
153 	eloop_register_timeout(data->scan_interval, 0, bgscan_simple_timeout,
154 			       data, NULL);
155 
156 	/*
157 	 * This function is called immediately after an association, so it is
158 	 * reasonable to assume that a scan was completed recently. This makes
159 	 * us skip an immediate new scan in cases where the current signal
160 	 * level is below the bgscan threshold.
161 	 */
162 	os_get_reltime(&data->last_bgscan);
163 
164 	return data;
165 }
166 
167 
168 static void bgscan_simple_deinit(void *priv)
169 {
170 	struct bgscan_simple_data *data = priv;
171 	eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
172 	if (data->signal_threshold)
173 		wpa_drv_signal_monitor(data->wpa_s, 0, 0);
174 	os_free(data);
175 }
176 
177 
178 static int bgscan_simple_notify_scan(void *priv,
179 				     struct wpa_scan_results *scan_res)
180 {
181 	struct bgscan_simple_data *data = priv;
182 
183 	wpa_printf(MSG_DEBUG, "bgscan simple: scan result notification");
184 
185 	eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
186 	eloop_register_timeout(data->scan_interval, 0, bgscan_simple_timeout,
187 			       data, NULL);
188 
189 	/*
190 	 * A more advanced bgscan could process scan results internally, select
191 	 * the BSS and request roam if needed. This sample uses the existing
192 	 * BSS/ESS selection routine. Change this to return 1 if selection is
193 	 * done inside the bgscan module.
194 	 */
195 
196 	return 0;
197 }
198 
199 
200 static void bgscan_simple_notify_beacon_loss(void *priv)
201 {
202 	wpa_printf(MSG_DEBUG, "bgscan simple: beacon loss");
203 	/* TODO: speed up background scanning */
204 }
205 
206 
207 static void bgscan_simple_notify_signal_change(void *priv, int above,
208 					       int current_signal,
209 					       int current_noise,
210 					       int current_txrate)
211 {
212 	struct bgscan_simple_data *data = priv;
213 	int scan = 0;
214 	struct os_reltime now;
215 
216 	if (data->short_interval == data->long_interval ||
217 	    data->signal_threshold == 0)
218 		return;
219 
220 	wpa_printf(MSG_DEBUG, "bgscan simple: signal level changed "
221 		   "(above=%d current_signal=%d current_noise=%d "
222 		   "current_txrate=%d))", above, current_signal,
223 		   current_noise, current_txrate);
224 	if (data->scan_interval == data->long_interval && !above) {
225 		wpa_printf(MSG_DEBUG, "bgscan simple: Start using short "
226 			   "bgscan interval");
227 		data->scan_interval = data->short_interval;
228 		os_get_reltime(&now);
229 		if (now.sec > data->last_bgscan.sec + 1 &&
230 		    data->short_scan_count <= data->max_short_scans)
231 			/*
232 			 * If we haven't just previously (<1 second ago)
233 			 * performed a scan, and we haven't depleted our
234 			 * budget for short-scans, perform a scan
235 			 * immediately.
236 			 */
237 			scan = 1;
238 		else if (data->last_bgscan.sec + data->long_interval >
239 			 now.sec + data->scan_interval) {
240 			/*
241 			 * Restart scan interval timer if currently scheduled
242 			 * scan is too far in the future.
243 			 */
244 			eloop_cancel_timeout(bgscan_simple_timeout, data,
245 					     NULL);
246 			eloop_register_timeout(data->scan_interval, 0,
247 					       bgscan_simple_timeout, data,
248 					       NULL);
249 		}
250 	} else if (data->scan_interval == data->short_interval && above) {
251 		wpa_printf(MSG_DEBUG, "bgscan simple: Start using long bgscan "
252 			   "interval");
253 		data->scan_interval = data->long_interval;
254 		eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
255 		eloop_register_timeout(data->scan_interval, 0,
256 				       bgscan_simple_timeout, data, NULL);
257 	} else if (!above) {
258 		/*
259 		 * Signal dropped further 4 dB. Request a new scan if we have
260 		 * not yet scanned in a while.
261 		 */
262 		os_get_reltime(&now);
263 		if (now.sec > data->last_bgscan.sec + 10)
264 			scan = 1;
265 	}
266 
267 	if (scan) {
268 		wpa_printf(MSG_DEBUG, "bgscan simple: Trigger immediate scan");
269 		eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
270 		eloop_register_timeout(0, 0, bgscan_simple_timeout, data,
271 				       NULL);
272 	}
273 }
274 
275 
276 const struct bgscan_ops bgscan_simple_ops = {
277 	.name = "simple",
278 	.init = bgscan_simple_init,
279 	.deinit = bgscan_simple_deinit,
280 	.notify_scan = bgscan_simple_notify_scan,
281 	.notify_beacon_loss = bgscan_simple_notify_beacon_loss,
282 	.notify_signal_change = bgscan_simple_notify_signal_change,
283 };
284