bgscan_simple.c revision c5ec7f57ead87efa365800228aa0b09a12d9e6c4 
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
20struct 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_time last_bgscan;
30};
31
32
33static 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_time(&data->last_bgscan);
79	}
80}
81
82
83static 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
111static 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_time(&data->last_bgscan);
163
164	return data;
165}
166
167
168static 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
178static 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
200static 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
207static 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_time 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_time(&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_time(&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
276const 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