aboutsummaryrefslogtreecommitdiffstats
path: root/src/ap/acs.c
blob: 5e8380535854fd18fb837ac6b2f60f2555bf510a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
/*
 * ACS - Automatic Channel Selection module
 * Copyright (c) 2011, Atheros Communications
 * Copyright (c) 2013, Qualcomm Atheros, Inc.
 *
 * This software may be distributed under the terms of the BSD license.
 * See README for more details.
 */

#include "utils/includes.h"
#include <math.h>

#include "utils/common.h"
#include "utils/list.h"
#include "common/ieee802_11_defs.h"
#include "common/wpa_ctrl.h"
#include "drivers/driver.h"
#include "hostapd.h"
#include "ap_drv_ops.h"
#include "ap_config.h"
#include "hw_features.h"
#include "acs.h"

/*
 * Automatic Channel Selection
 * ===========================
 *
 * More info at
 * ------------
 * http://wireless.kernel.org/en/users/Documentation/acs
 *
 * How to use
 * ----------
 * - make sure you have CONFIG_ACS=y in hostapd's .config
 * - use channel=0 or channel=acs to enable ACS
 *
 * How does it work
 * ----------------
 * 1. passive scans are used to collect survey data
 *    (it is assumed that scan trigger collection of survey data in driver)
 * 2. interference factor is calculated for each channel
 * 3. ideal channel is picked depending on channel width by using adjacent
 *    channel interference factors
 *
 * Known limitations
 * -----------------
 * - Current implementation depends heavily on the amount of time willing to
 *   spend gathering survey data during hostapd startup. Short traffic bursts
 *   may be missed and a suboptimal channel may be picked.
 * - Ideal channel may end up overlapping a channel with 40 MHz intolerant BSS
 *
 * Todo / Ideas
 * ------------
 * - implement other interference computation methods
 *   - BSS/RSSI based
 *   - spectral scan based
 *   (should be possibly to hook this up with current ACS scans)
 * - add wpa_supplicant support (for P2P)
 * - collect a histogram of interference over time allowing more educated
 *   guess about an ideal channel (perhaps CSA could be used to migrate AP to a
 *   new "better" channel while running)
 * - include neighboring BSS scan to avoid conflicts with 40 MHz intolerant BSSs
 *   when choosing the ideal channel
 *
 * Survey interference factor implementation details
 * -------------------------------------------------
 * Generic interference_factor in struct hostapd_channel_data is used.
 *
 * The survey interference factor is defined as the ratio of the
 * observed busy time over the time we spent on the channel,
 * this value is then amplified by the observed noise floor on
 * the channel in comparison to the lowest noise floor observed
 * on the entire band.
 *
 * This corresponds to:
 * ---
 * (busy time - tx time) / (active time - tx time) * 2^(chan_nf + band_min_nf)
 * ---
 *
 * The coefficient of 2 reflects the way power in "far-field"
 * radiation decreases as the square of distance from the antenna [1].
 * What this does is it decreases the observed busy time ratio if the
 * noise observed was low but increases it if the noise was high,
 * proportionally to the way "far field" radiation changes over
 * distance.
 *
 * If channel busy time is not available the fallback is to use channel RX time.
 *
 * Since noise floor is in dBm it is necessary to convert it into Watts so that
 * combined channel interference (e.g., HT40, which uses two channels) can be
 * calculated easily.
 * ---
 * (busy time - tx time) / (active time - tx time) *
 *    2^(10^(chan_nf/10) + 10^(band_min_nf/10))
 * ---
 *
 * However to account for cases where busy/rx time is 0 (channel load is then
 * 0%) channel noise floor signal power is combined into the equation so a
 * channel with lower noise floor is preferred. The equation becomes:
 * ---
 * 10^(chan_nf/5) + (busy time - tx time) / (active time - tx time) *
 *    2^(10^(chan_nf/10) + 10^(band_min_nf/10))
 * ---
 *
 * All this "interference factor" is purely subjective and only time
 * will tell how usable this is. By using the minimum noise floor we
 * remove any possible issues due to card calibration. The computation
 * of the interference factor then is dependent on what the card itself
 * picks up as the minimum noise, not an actual real possible card
 * noise value.
 *
 * Total interference computation details
 * --------------------------------------
 * The above channel interference factor is calculated with no respect to
 * target operational bandwidth.
 *
 * To find an ideal channel the above data is combined by taking into account
 * the target operational bandwidth and selected band. E.g., on 2.4 GHz channels
 * overlap with 20 MHz bandwidth, but there is no overlap for 20 MHz bandwidth
 * on 5 GHz.
 *
 * Each valid and possible channel spec (i.e., channel + width) is taken and its
 * interference factor is computed by summing up interferences of each channel
 * it overlaps. The one with least total interference is picked up.
 *
 * Note: This implies base channel interference factor must be non-negative
 * allowing easy summing up.
 *
 * Example ACS analysis printout
 * -----------------------------
 *
 * ACS: Trying survey-based ACS
 * ACS: Survey analysis for channel 1 (2412 MHz)
 * ACS:  1: min_nf=-113 interference_factor=0.0802469 nf=-113 time=162 busy=0 rx=13
 * ACS:  2: min_nf=-113 interference_factor=0.0745342 nf=-113 time=161 busy=0 rx=12
 * ACS:  3: min_nf=-113 interference_factor=0.0679012 nf=-113 time=162 busy=0 rx=11
 * ACS:  4: min_nf=-113 interference_factor=0.0310559 nf=-113 time=161 busy=0 rx=5
 * ACS:  5: min_nf=-113 interference_factor=0.0248447 nf=-113 time=161 busy=0 rx=4
 * ACS:  * interference factor average: 0.0557166
 * ACS: Survey analysis for channel 2 (2417 MHz)
 * ACS:  1: min_nf=-113 interference_factor=0.0185185 nf=-113 time=162 busy=0 rx=3
 * ACS:  2: min_nf=-113 interference_factor=0.0246914 nf=-113 time=162 busy=0 rx=4
 * ACS:  3: min_nf=-113 interference_factor=0.037037 nf=-113 time=162 busy=0 rx=6
 * ACS:  4: min_nf=-113 interference_factor=0.149068 nf=-113 time=161 busy=0 rx=24
 * ACS:  5: min_nf=-113 interference_factor=0.0248447 nf=-113 time=161 busy=0 rx=4
 * ACS:  * interference factor average: 0.050832
 * ACS: Survey analysis for channel 3 (2422 MHz)
 * ACS:  1: min_nf=-113 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
 * ACS:  2: min_nf=-113 interference_factor=0.0185185 nf=-113 time=162 busy=0 rx=3
 * ACS:  3: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
 * ACS:  4: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
 * ACS:  5: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
 * ACS:  * interference factor average: 0.0148838
 * ACS: Survey analysis for channel 4 (2427 MHz)
 * ACS:  1: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  2: min_nf=-114 interference_factor=0.0555556 nf=-114 time=162 busy=0 rx=9
 * ACS:  3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
 * ACS:  4: min_nf=-114 interference_factor=0.0186335 nf=-114 time=161 busy=0 rx=3
 * ACS:  5: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
 * ACS:  * interference factor average: 0.0160801
 * ACS: Survey analysis for channel 5 (2432 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.409938 nf=-113 time=161 busy=0 rx=66
 * ACS:  2: min_nf=-114 interference_factor=0.0432099 nf=-113 time=162 busy=0 rx=7
 * ACS:  3: min_nf=-114 interference_factor=0.0124224 nf=-113 time=161 busy=0 rx=2
 * ACS:  4: min_nf=-114 interference_factor=0.677019 nf=-113 time=161 busy=0 rx=109
 * ACS:  5: min_nf=-114 interference_factor=0.0186335 nf=-114 time=161 busy=0 rx=3
 * ACS:  * interference factor average: 0.232244
 * ACS: Survey analysis for channel 6 (2437 MHz)
 * ACS:  1: min_nf=-113 interference_factor=0.552795 nf=-113 time=161 busy=0 rx=89
 * ACS:  2: min_nf=-113 interference_factor=0.0807453 nf=-112 time=161 busy=0 rx=13
 * ACS:  3: min_nf=-113 interference_factor=0.0310559 nf=-113 time=161 busy=0 rx=5
 * ACS:  4: min_nf=-113 interference_factor=0.434783 nf=-112 time=161 busy=0 rx=70
 * ACS:  5: min_nf=-113 interference_factor=0.0621118 nf=-113 time=161 busy=0 rx=10
 * ACS:  * interference factor average: 0.232298
 * ACS: Survey analysis for channel 7 (2442 MHz)
 * ACS:  1: min_nf=-113 interference_factor=0.440994 nf=-112 time=161 busy=0 rx=71
 * ACS:  2: min_nf=-113 interference_factor=0.385093 nf=-113 time=161 busy=0 rx=62
 * ACS:  3: min_nf=-113 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
 * ACS:  4: min_nf=-113 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
 * ACS:  5: min_nf=-113 interference_factor=0.0745342 nf=-113 time=161 busy=0 rx=12
 * ACS:  * interference factor average: 0.195031
 * ACS: Survey analysis for channel 8 (2447 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.0496894 nf=-112 time=161 busy=0 rx=8
 * ACS:  2: min_nf=-114 interference_factor=0.0496894 nf=-114 time=161 busy=0 rx=8
 * ACS:  3: min_nf=-114 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
 * ACS:  4: min_nf=-114 interference_factor=0.12963 nf=-113 time=162 busy=0 rx=21
 * ACS:  5: min_nf=-114 interference_factor=0.166667 nf=-114 time=162 busy=0 rx=27
 * ACS:  * interference factor average: 0.0865885
 * ACS: Survey analysis for channel 9 (2452 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.0124224 nf=-114 time=161 busy=0 rx=2
 * ACS:  2: min_nf=-114 interference_factor=0.0310559 nf=-114 time=161 busy=0 rx=5
 * ACS:  3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
 * ACS:  4: min_nf=-114 interference_factor=0.00617284 nf=-114 time=162 busy=0 rx=1
 * ACS:  5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  * interference factor average: 0.00993022
 * ACS: Survey analysis for channel 10 (2457 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
 * ACS:  2: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
 * ACS:  3: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
 * ACS:  4: min_nf=-114 interference_factor=0.0493827 nf=-114 time=162 busy=0 rx=8
 * ACS:  5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  * interference factor average: 0.0136033
 * ACS: Survey analysis for channel 11 (2462 MHz)
 * ACS:  1: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
 * ACS:  2: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=161 busy=0 rx=0
 * ACS:  3: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=161 busy=0 rx=0
 * ACS:  4: min_nf=-114 interference_factor=0.0432099 nf=-114 time=162 busy=0 rx=7
 * ACS:  5: min_nf=-114 interference_factor=0.0925926 nf=-114 time=162 busy=0 rx=15
 * ACS:  * interference factor average: 0.0271605
 * ACS: Survey analysis for channel 12 (2467 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.0621118 nf=-113 time=161 busy=0 rx=10
 * ACS:  2: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
 * ACS:  3: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
 * ACS:  4: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
 * ACS:  5: min_nf=-114 interference_factor=0.00617284 nf=-113 time=162 busy=0 rx=1
 * ACS:  * interference factor average: 0.0148992
 * ACS: Survey analysis for channel 13 (2472 MHz)
 * ACS:  1: min_nf=-114 interference_factor=0.0745342 nf=-114 time=161 busy=0 rx=12
 * ACS:  2: min_nf=-114 interference_factor=0.0555556 nf=-114 time=162 busy=0 rx=9
 * ACS:  3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  4: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
 * ACS:  * interference factor average: 0.0260179
 * ACS: Survey analysis for selected bandwidth 20MHz
 * ACS:  * channel 1: total interference = 0.121432
 * ACS:  * channel 2: total interference = 0.137512
 * ACS:  * channel 3: total interference = 0.369757
 * ACS:  * channel 4: total interference = 0.546338
 * ACS:  * channel 5: total interference = 0.690538
 * ACS:  * channel 6: total interference = 0.762242
 * ACS:  * channel 7: total interference = 0.756092
 * ACS:  * channel 8: total interference = 0.537451
 * ACS:  * channel 9: total interference = 0.332313
 * ACS:  * channel 10: total interference = 0.152182
 * ACS:  * channel 11: total interference = 0.0916111
 * ACS:  * channel 12: total interference = 0.0816809
 * ACS:  * channel 13: total interference = 0.0680776
 * ACS: Ideal channel is 13 (2472 MHz) with total interference factor of 0.0680776
 *
 * [1] http://en.wikipedia.org/wiki/Near_and_far_field
 */


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)
{
	struct freq_survey *survey, *tmp;

	if (dl_list_empty(&chan->survey_list))
		return;

	dl_list_for_each_safe(survey, tmp, &chan->survey_list,
			      struct freq_survey, list) {
		dl_list_del(&survey->list);
		os_free(survey);
	}
}


static void acs_cleanup(struct hostapd_iface *iface)
{
	int i;
	struct hostapd_channel_data *chan;

	for (i = 0; i < iface->current_mode->num_channels; i++) {
		chan = &iface->current_mode->channels[i];

		if (chan->flag & HOSTAPD_CHAN_SURVEY_LIST_INITIALIZED)
			acs_clean_chan_surveys(chan);

		dl_list_init(&chan->survey_list);
		chan->flag |= HOSTAPD_CHAN_SURVEY_LIST_INITIALIZED;
		chan->min_nf = 0;
	}

	iface->chans_surveyed = 0;
	iface->acs_num_completed_scans = 0;
}


static void acs_fail(struct hostapd_iface *iface)
{
	wpa_printf(MSG_ERROR, "ACS: Failed to start");
	acs_cleanup(iface);
	hostapd_disable_iface(iface);
}


static long double
acs_survey_interference_factor(struct freq_survey *survey, s8 min_nf)
{
	long double factor, busy, total;

	if (survey->filled & SURVEY_HAS_CHAN_TIME_BUSY)
		busy = survey->channel_time_busy;
	else if (survey->filled & SURVEY_HAS_CHAN_TIME_RX)
		busy = survey->channel_time_rx;
	else {
		/* This shouldn't really happen as survey data is checked in
		 * acs_sanity_check() */
		wpa_printf(MSG_ERROR, "ACS: Survey data missing");
		return 0;
	}

	total = survey->channel_time;

	if (survey->filled & SURVEY_HAS_CHAN_TIME_TX) {
		busy -= survey->channel_time_tx;
		total -= survey->channel_time_tx;
	}

	/* TODO: figure out the best multiplier for noise floor base */
	factor = pow(10, survey->nf / 5.0L) +
		(busy / total) *
		pow(2, pow(10, (long double) survey->nf / 10.0L) -
		    pow(10, (long double) min_nf / 10.0L));

	return factor;
}


static void
acs_survey_chan_interference_factor(struct hostapd_iface *iface,
				    struct hostapd_channel_data *chan)
{
	struct freq_survey *survey;
	unsigned int i = 0;
	long double int_factor = 0;
	unsigned count = 0;

	if (dl_list_empty(&chan->survey_list))
		return;

	if (chan->flag & HOSTAPD_CHAN_DISABLED)
		return;

	chan->interference_factor = 0;

	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,
			   survey->nf, (unsigned long) survey->channel_time,
			   (unsigned long) survey->channel_time_busy,
			   (unsigned long) survey->channel_time_rx);
	}

	if (!count)
		return;
	chan->interference_factor /= count;
}


static int acs_usable_ht40_chan(struct hostapd_channel_data *chan)
{
	const int allowed[] = { 36, 44, 52, 60, 100, 108, 116, 124, 132, 149,
				157, 184, 192 };
	unsigned int i;

	for (i = 0; i < ARRAY_SIZE(allowed); i++)
		if (chan->chan == allowed[i])
			return 1;

	return 0;
}


static int acs_usable_vht80_chan(struct hostapd_channel_data *chan)
{
	const int allowed[] = { 36, 52, 100, 116, 132, 149 };
	unsigned int i;

	for (i = 0; i < ARRAY_SIZE(allowed); i++)
		if (chan->chan == allowed[i])
			return 1;

	return 0;
}


static int acs_survey_is_sufficient(struct freq_survey *survey)
{
	if (!(survey->filled & SURVEY_HAS_NF)) {
		wpa_printf(MSG_INFO, "ACS: Survey is missing noise floor");
		return 0;
	}

	if (!(survey->filled & SURVEY_HAS_CHAN_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_INFO,
			   "ACS: Survey is missing RX and busy time (at least one is required)");
		return 0;
	}

	return 1;
}


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)) {
			ret = 1;
			break;
		}
		ret = 0;
	}

	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;
}


static int acs_surveys_are_sufficient(struct hostapd_iface *iface)
{
	int i;
	struct hostapd_channel_data *chan;
	int valid = 0;

	for (i = 0; i < iface->current_mode->num_channels; i++) {
		chan = &iface->current_mode->channels[i];
		if (chan->flag & HOSTAPD_CHAN_DISABLED)
			continue;

		if (!acs_survey_list_is_sufficient(chan))
			continue;

		valid++;
	}

	/* We need at least survey data for one channel */
	return !!valid;
}


static int acs_usable_chan(struct hostapd_channel_data *chan)
{
	if (dl_list_empty(&chan->survey_list))
		return 0;
	if (chan->flag & HOSTAPD_CHAN_DISABLED)
		return 0;
	if (!acs_survey_list_is_sufficient(chan))
		return 0;
	return 1;
}


static int is_in_chanlist(struct hostapd_iface *iface,
			  struct hostapd_channel_data *chan)
{
	if (!iface->conf->acs_ch_list.num)
		return 1;

	return freq_range_list_includes(&iface->conf->acs_ch_list, chan->chan);
}


static void acs_survey_all_chans_intereference_factor(
	struct hostapd_iface *iface)
{
	int i;
	struct hostapd_channel_data *chan;

	for (i = 0; i < iface->current_mode->num_channels; i++) {
		chan = &iface->current_mode->channels[i];

		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);

		acs_survey_chan_interference_factor(iface, chan);

		wpa_printf(MSG_DEBUG, "ACS:  * interference factor average: %Lg",
			   chan->interference_factor);
	}
}


static struct hostapd_channel_data *acs_find_chan(struct hostapd_iface *iface,
						  int freq)
{
	struct hostapd_channel_data *chan;
	int i;

	for (i = 0; i < iface->current_mode->num_channels; i++) {
		chan = &iface->current_mode->channels[i];

		if (chan->flag & HOSTAPD_CHAN_DISABLED)
			continue;

		if (chan->freq == freq)
			return chan;
	}

	return NULL;
}


static int is_24ghz_mode(enum hostapd_hw_mode mode)
{
	return mode == HOSTAPD_MODE_IEEE80211B ||
		mode == HOSTAPD_MODE_IEEE80211G;
}


static int is_common_24ghz_chan(int chan)
{
	return chan == 1 || chan == 6 || chan == 11;
}


#ifndef ACS_ADJ_WEIGHT
#define ACS_ADJ_WEIGHT 0.85
#endif /* ACS_ADJ_WEIGHT */

#ifndef ACS_NEXT_ADJ_WEIGHT
#define ACS_NEXT_ADJ_WEIGHT 0.55
#endif /* ACS_NEXT_ADJ_WEIGHT */

#ifndef ACS_24GHZ_PREFER_1_6_11
/*
 * Select commonly used channels 1, 6, 11 by default even if a neighboring
 * channel has a smaller interference factor as long as it is not better by more
 * than this multiplier.
 */
#define ACS_24GHZ_PREFER_1_6_11 0.8
#endif /* ACS_24GHZ_PREFER_1_6_11 */

/*
 * At this point it's assumed chan->interface_factor has been computed.
 * This function should be reusable regardless of interference computation
 * option (survey, BSS, spectral, ...). chan->interference factor must be
 * summable (i.e., must be always greater than zero).
 */
static struct hostapd_channel_data *
acs_find_ideal_chan(struct hostapd_iface *iface)
{
	struct hostapd_channel_data *chan, *adj_chan, *ideal_chan = NULL,
		*rand_chan = NULL;
	long double factor, ideal_factor = 0;
	int i, j;
	int n_chans = 1;
	unsigned int k;

	/* TODO: HT40- support */

	if (iface->conf->ieee80211n &&
	    iface->conf->secondary_channel == -1) {
		wpa_printf(MSG_ERROR, "ACS: HT40- is not supported yet. Please try HT40+");
		return NULL;
	}

	if (iface->conf->ieee80211n &&
	    iface->conf->secondary_channel)
		n_chans = 2;

	if (iface->conf->ieee80211ac &&
	    iface->conf->vht_oper_chwidth == 1)
		n_chans = 4;

	/* TODO: VHT80+80, VHT160. Update acs_adjust_vht_center_freq() too. */

	wpa_printf(MSG_DEBUG, "ACS: Survey analysis for selected bandwidth %d MHz",
		   n_chans == 1 ? 20 :
		   n_chans == 2 ? 40 :
		   80);

	for (i = 0; i < iface->current_mode->num_channels; i++) {
		double total_weight;
		struct acs_bias *bias, tmp_bias;

		chan = &iface->current_mode->channels[i];

		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 */
		if (iface->current_mode->mode == HOSTAPD_MODE_IEEE80211A &&
		    iface->conf->ieee80211n &&
		    iface->conf->secondary_channel &&
		    !acs_usable_ht40_chan(chan)) {
			wpa_printf(MSG_DEBUG, "ACS: Channel %d: not allowed as primary channel for HT40",
				   chan->chan);
			continue;
		}

		if (iface->current_mode->mode == HOSTAPD_MODE_IEEE80211A &&
		    iface->conf->ieee80211ac &&
		    iface->conf->vht_oper_chwidth == 1 &&
		    !acs_usable_vht80_chan(chan)) {
			wpa_printf(MSG_DEBUG, "ACS: Channel %d: not allowed as primary channel for VHT80",
				   chan->chan);
			continue;
		}

		factor = 0;
		if (acs_usable_chan(chan))
			factor = chan->interference_factor;
		total_weight = 1;

		for (j = 1; j < n_chans; j++) {
			adj_chan = acs_find_chan(iface, chan->freq + (j * 20));
			if (!adj_chan)
				break;

			if (acs_usable_chan(adj_chan)) {
				factor += adj_chan->interference_factor;
				total_weight += 1;
			}
		}

		if (j != n_chans) {
			wpa_printf(MSG_DEBUG, "ACS: Channel %d: not enough bandwidth",
				   chan->chan);
			continue;
		}

		/* 2.4 GHz has overlapping 20 MHz channels. Include adjacent
		 * channel interference factor. */
		if (is_24ghz_mode(iface->current_mode->mode)) {
			for (j = 0; j < n_chans; j++) {
				adj_chan = acs_find_chan(iface, chan->freq +
							 (j * 20) - 5);
				if (adj_chan && acs_usable_chan(adj_chan)) {
					factor += ACS_ADJ_WEIGHT *
						adj_chan->interference_factor;
					total_weight += ACS_ADJ_WEIGHT;
				}

				adj_chan = acs_find_chan(iface, chan->freq +
							 (j * 20) - 10);
				if (adj_chan && acs_usable_chan(adj_chan)) {
					factor += ACS_NEXT_ADJ_WEIGHT *
						adj_chan->interference_factor;
					total_weight += ACS_NEXT_ADJ_WEIGHT;
				}

				adj_chan = acs_find_chan(iface, chan->freq +
							 (j * 20) + 5);
				if (adj_chan && acs_usable_chan(adj_chan)) {
					factor += ACS_ADJ_WEIGHT *
						adj_chan->interference_factor;
					total_weight += ACS_ADJ_WEIGHT;
				}

				adj_chan = acs_find_chan(iface, chan->freq +
							 (j * 20) + 10);
				if (adj_chan && acs_usable_chan(adj_chan)) {
					factor += ACS_NEXT_ADJ_WEIGHT *
						adj_chan->interference_factor;
					total_weight += ACS_NEXT_ADJ_WEIGHT;
				}
			}
		}

		factor /= total_weight;

		bias = NULL;
		if (iface->conf->acs_chan_bias) {
			for (k = 0; k < iface->conf->num_acs_chan_bias; k++) {
				bias = &iface->conf->acs_chan_bias[k];
				if (bias->channel == chan->chan)
					break;
				bias = NULL;
			}
		} else if (is_24ghz_mode(iface->current_mode->mode) &&
			   is_common_24ghz_chan(chan->chan)) {
			tmp_bias.channel = chan->chan;
			tmp_bias.bias = ACS_24GHZ_PREFER_1_6_11;
			bias = &tmp_bias;
		}

		if (bias) {
			factor *= bias->bias;
			wpa_printf(MSG_DEBUG,
				   "ACS:  * channel %d: total interference = %Lg (%f bias)",
				   chan->chan, factor, bias->bias);
		} else {
			wpa_printf(MSG_DEBUG,
				   "ACS:  * channel %d: total interference = %Lg",
				   chan->chan, factor);
		}

		if (acs_usable_chan(chan) &&
		    (!ideal_chan || factor < ideal_factor)) {
			ideal_factor = factor;
			ideal_chan = chan;
		}

		/* This channel would at least be usable */
		if (!rand_chan)
			rand_chan = chan;
	}

	if (ideal_chan) {
		wpa_printf(MSG_DEBUG, "ACS: Ideal channel is %d (%d MHz) with total interference factor of %Lg",
			   ideal_chan->chan, ideal_chan->freq, ideal_factor);
		return ideal_chan;
	}

	return rand_chan;
}


static void acs_adjust_vht_center_freq(struct hostapd_iface *iface)
{
	int offset;

	wpa_printf(MSG_DEBUG, "ACS: Adjusting VHT center frequency");

	switch (iface->conf->vht_oper_chwidth) {
	case VHT_CHANWIDTH_USE_HT:
		offset = 2 * iface->conf->secondary_channel;
		break;
	case VHT_CHANWIDTH_80MHZ:
		offset = 6;
		break;
	default:
		/* TODO: How can this be calculated? Adjust
		 * acs_find_ideal_chan() */
		wpa_printf(MSG_INFO, "ACS: Only VHT20/40/80 is supported now");
		return;
	}

	iface->conf->vht_oper_centr_freq_seg0_idx =
		iface->conf->channel + offset;
}


static int acs_study_survey_based(struct hostapd_iface *iface)
{
	wpa_printf(MSG_DEBUG, "ACS: Trying survey-based ACS");

	if (!iface->chans_surveyed) {
		wpa_printf(MSG_ERROR, "ACS: Unable to collect survey data");
		return -1;
	}

	if (!acs_surveys_are_sufficient(iface)) {
		wpa_printf(MSG_ERROR, "ACS: Surveys have insufficient data");
		return -1;
	}

	acs_survey_all_chans_intereference_factor(iface);
	return 0;
}


static int acs_study_options(struct hostapd_iface *iface)
{
	int err;

	err = acs_study_survey_based(iface);
	if (err == 0)
		return 0;

	/* TODO: If no surveys are available/sufficient this is a good
	 * place to fallback to BSS-based ACS */

	return -1;
}


static void acs_study(struct hostapd_iface *iface)
{
	struct hostapd_channel_data *ideal_chan;
	int err;

	err = acs_study_options(iface);
	if (err < 0) {
		wpa_printf(MSG_ERROR, "ACS: All study options have failed");
		goto fail;
	}

	ideal_chan = acs_find_ideal_chan(iface);
	if (!ideal_chan) {
		wpa_printf(MSG_ERROR, "ACS: Failed to compute ideal channel");
		err = -1;
		goto fail;
	}

	iface->conf->channel = ideal_chan->chan;

	if (iface->conf->ieee80211ac)
		acs_adjust_vht_center_freq(iface);

	err = 0;
fail:
	/*
	 * hostapd_setup_interface_complete() will return -1 on failure,
	 * 0 on success and 0 is HOSTAPD_CHAN_VALID :)
	 */
	if (hostapd_acs_completed(iface, err) == HOSTAPD_CHAN_VALID) {
		acs_cleanup(iface);
		return;
	}

	/* This can possibly happen if channel parameters (secondary
	 * channel, center frequencies) are misconfigured */
	wpa_printf(MSG_ERROR, "ACS: Possibly channel configuration is invalid, please report this along with your config file.");
	acs_fail(iface);
}


static void acs_scan_complete(struct hostapd_iface *iface)
{
	int err;

	iface->scan_cb = NULL;

	wpa_printf(MSG_DEBUG, "ACS: Using survey based algorithm (acs_num_scans=%d)",
		   iface->conf->acs_num_scans);

	err = hostapd_drv_get_survey(iface->bss[0], 0);
	if (err) {
		wpa_printf(MSG_ERROR, "ACS: Failed to get survey data");
		goto fail;
	}

	if (++iface->acs_num_completed_scans < iface->conf->acs_num_scans) {
		err = acs_request_scan(iface);
		if (err) {
			wpa_printf(MSG_ERROR, "ACS: Failed to request scan");
			goto fail;
		}

		return;
	}

	acs_study(iface);
	return;
fail:
	hostapd_acs_completed(iface, 1);
	acs_fail(iface);
}


static int acs_request_scan(struct hostapd_iface *iface)
{
	struct wpa_driver_scan_params params;
	struct hostapd_channel_data *chan;
	int i, *freq;

	os_memset(&params, 0, sizeof(params));
	params.freqs = os_calloc(iface->current_mode->num_channels + 1,
				 sizeof(params.freqs[0]));
	if (params.freqs == NULL)
		return -1;

	freq = params.freqs;
	for (i = 0; i < iface->current_mode->num_channels; i++) {
		chan = &iface->current_mode->channels[i];
		if (chan->flag & HOSTAPD_CHAN_DISABLED)
			continue;

		if (!is_in_chanlist(iface, chan))
			continue;

		*freq++ = chan->freq;
	}
	*freq = 0;

	iface->scan_cb = acs_scan_complete;

	wpa_printf(MSG_DEBUG, "ACS: Scanning %d / %d",
		   iface->acs_num_completed_scans + 1,
		   iface->conf->acs_num_scans);

	if (hostapd_driver_scan(iface->bss[0], &params) < 0) {
		wpa_printf(MSG_ERROR, "ACS: Failed to request initial scan");
		acs_cleanup(iface);
		os_free(params.freqs);
		return -1;
	}

	os_free(params.freqs);
	return 0;
}


enum hostapd_chan_status acs_init(struct hostapd_iface *iface)
{
	int err;

	wpa_printf(MSG_INFO, "ACS: Automatic channel selection started, this may take a bit");

	if (iface->drv_flags & WPA_DRIVER_FLAGS_ACS_OFFLOAD) {
		wpa_printf(MSG_INFO, "ACS: Offloading to driver");
		err = hostapd_drv_do_acs(iface->bss[0]);
		if (err)
			return HOSTAPD_CHAN_INVALID;
		return HOSTAPD_CHAN_ACS;
	}

	if (!iface->current_mode)
		return HOSTAPD_CHAN_INVALID;

	acs_cleanup(iface);

	err = acs_request_scan(iface);
	if (err < 0)
		return HOSTAPD_CHAN_INVALID;

	hostapd_set_state(iface, HAPD_IFACE_ACS);
	wpa_msg(iface->bss[0]->msg_ctx, MSG_INFO, ACS_EVENT_STARTED);

	return HOSTAPD_CHAN_ACS;
}