Linux Audio

Check our new training course

Embedded Linux Audio

Check our new training course
with Creative Commons CC-BY-SA
lecture materials

Bootlin logo

Elixir Cross Referencer

Loading...
   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
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
/*
 *  net/dccp/feat.c
 *
 *  Feature negotiation for the DCCP protocol (RFC 4340, section 6)
 *
 *  Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
 *  Rewrote from scratch, some bits from earlier code by
 *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 *
 *
 *  ASSUMPTIONS
 *  -----------
 *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
 *    changes of parameters of an established connection are not supported.
 *  o Changing non-negotiable (NN) values is supported in state OPEN/PARTOPEN.
 *  o All currently known SP features have 1-byte quantities. If in the future
 *    extensions of RFCs 4340..42 define features with item lengths larger than
 *    one byte, a feature-specific extension of the code will be required.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */
#include <linux/module.h>
#include <linux/slab.h>
#include "ccid.h"
#include "feat.h"

/* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
unsigned long	sysctl_dccp_sequence_window __read_mostly = 100;
int		sysctl_dccp_rx_ccid	    __read_mostly = 2,
		sysctl_dccp_tx_ccid	    __read_mostly = 2;

/*
 * Feature activation handlers.
 *
 * These all use an u64 argument, to provide enough room for NN/SP features. At
 * this stage the negotiated values have been checked to be within their range.
 */
static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct ccid *new_ccid = ccid_new(ccid, sk, rx);

	if (new_ccid == NULL)
		return -ENOMEM;

	if (rx) {
		ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
		dp->dccps_hc_rx_ccid = new_ccid;
	} else {
		ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
		dp->dccps_hc_tx_ccid = new_ccid;
	}
	return 0;
}

static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);

	if (rx) {
		dp->dccps_r_seq_win = seq_win;
		/* propagate changes to update SWL/SWH */
		dccp_update_gsr(sk, dp->dccps_gsr);
	} else {
		dp->dccps_l_seq_win = seq_win;
		/* propagate changes to update AWL */
		dccp_update_gss(sk, dp->dccps_gss);
	}
	return 0;
}

static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
{
	if (rx)
		dccp_sk(sk)->dccps_r_ack_ratio = ratio;
	else
		dccp_sk(sk)->dccps_l_ack_ratio = ratio;
	return 0;
}

static int dccp_hdlr_ackvec(struct sock *sk, u64 enable, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);

	if (rx) {
		if (enable && dp->dccps_hc_rx_ackvec == NULL) {
			dp->dccps_hc_rx_ackvec = dccp_ackvec_alloc(gfp_any());
			if (dp->dccps_hc_rx_ackvec == NULL)
				return -ENOMEM;
		} else if (!enable) {
			dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
			dp->dccps_hc_rx_ackvec = NULL;
		}
	}
	return 0;
}

static int dccp_hdlr_ndp(struct sock *sk, u64 enable, bool rx)
{
	if (!rx)
		dccp_sk(sk)->dccps_send_ndp_count = (enable > 0);
	return 0;
}

/*
 * Minimum Checksum Coverage is located at the RX side (9.2.1). This means that
 * `rx' holds when the sending peer informs about his partial coverage via a
 * ChangeR() option. In the other case, we are the sender and the receiver
 * announces its coverage via ChangeL() options. The policy here is to honour
 * such communication by enabling the corresponding partial coverage - but only
 * if it has not been set manually before; the warning here means that all
 * packets will be dropped.
 */
static int dccp_hdlr_min_cscov(struct sock *sk, u64 cscov, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);

	if (rx)
		dp->dccps_pcrlen = cscov;
	else {
		if (dp->dccps_pcslen == 0)
			dp->dccps_pcslen = cscov;
		else if (cscov > dp->dccps_pcslen)
			DCCP_WARN("CsCov %u too small, peer requires >= %u\n",
				  dp->dccps_pcslen, (u8)cscov);
	}
	return 0;
}

static const struct {
	u8			feat_num;		/* DCCPF_xxx */
	enum dccp_feat_type	rxtx;			/* RX or TX  */
	enum dccp_feat_type	reconciliation;		/* SP or NN  */
	u8			default_value;		/* as in 6.4 */
	int (*activation_hdlr)(struct sock *sk, u64 val, bool rx);
/*
 *    Lookup table for location and type of features (from RFC 4340/4342)
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | Feature                  | Location | Reconc. | Initial |  Section  |
 *  |                          | RX | TX  | SP | NN |  Value  | Reference |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
 *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
 *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
 *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
 *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
 *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
 *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
 *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
 *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
 *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 */
} dccp_feat_table[] = {
	{ DCCPF_CCID,		 FEAT_AT_TX, FEAT_SP, 2,   dccp_hdlr_ccid     },
	{ DCCPF_SHORT_SEQNOS,	 FEAT_AT_TX, FEAT_SP, 0,   NULL },
	{ DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100, dccp_hdlr_seq_win  },
	{ DCCPF_ECN_INCAPABLE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
	{ DCCPF_ACK_RATIO,	 FEAT_AT_TX, FEAT_NN, 2,   dccp_hdlr_ack_ratio},
	{ DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_ackvec   },
	{ DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0,   dccp_hdlr_ndp      },
	{ DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_min_cscov},
	{ DCCPF_DATA_CHECKSUM,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
	{ DCCPF_SEND_LEV_RATE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
};
#define DCCP_FEAT_SUPPORTED_MAX		ARRAY_SIZE(dccp_feat_table)

/**
 * dccp_feat_index  -  Hash function to map feature number into array position
 * Returns consecutive array index or -1 if the feature is not understood.
 */
static int dccp_feat_index(u8 feat_num)
{
	/* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
	if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
		return feat_num - 1;

	/*
	 * Other features: add cases for new feature types here after adding
	 * them to the above table.
	 */
	switch (feat_num) {
	case DCCPF_SEND_LEV_RATE:
			return DCCP_FEAT_SUPPORTED_MAX - 1;
	}
	return -1;
}

static u8 dccp_feat_type(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);

	if (idx < 0)
		return FEAT_UNKNOWN;
	return dccp_feat_table[idx].reconciliation;
}

static int dccp_feat_default_value(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);
	/*
	 * There are no default values for unknown features, so encountering a
	 * negative index here indicates a serious problem somewhere else.
	 */
	DCCP_BUG_ON(idx < 0);

	return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
}

/*
 *	Debugging and verbose-printing section
 */
static const char *dccp_feat_fname(const u8 feat)
{
	static const char *const feature_names[] = {
		[DCCPF_RESERVED]	= "Reserved",
		[DCCPF_CCID]		= "CCID",
		[DCCPF_SHORT_SEQNOS]	= "Allow Short Seqnos",
		[DCCPF_SEQUENCE_WINDOW]	= "Sequence Window",
		[DCCPF_ECN_INCAPABLE]	= "ECN Incapable",
		[DCCPF_ACK_RATIO]	= "Ack Ratio",
		[DCCPF_SEND_ACK_VECTOR]	= "Send ACK Vector",
		[DCCPF_SEND_NDP_COUNT]	= "Send NDP Count",
		[DCCPF_MIN_CSUM_COVER]	= "Min. Csum Coverage",
		[DCCPF_DATA_CHECKSUM]	= "Send Data Checksum",
	};
	if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
		return feature_names[DCCPF_RESERVED];

	if (feat ==  DCCPF_SEND_LEV_RATE)
		return "Send Loss Event Rate";
	if (feat >= DCCPF_MIN_CCID_SPECIFIC)
		return "CCID-specific";

	return feature_names[feat];
}

static const char *const dccp_feat_sname[] = {
	"DEFAULT", "INITIALISING", "CHANGING", "UNSTABLE", "STABLE",
};

#ifdef CONFIG_IP_DCCP_DEBUG
static const char *dccp_feat_oname(const u8 opt)
{
	switch (opt) {
	case DCCPO_CHANGE_L:  return "Change_L";
	case DCCPO_CONFIRM_L: return "Confirm_L";
	case DCCPO_CHANGE_R:  return "Change_R";
	case DCCPO_CONFIRM_R: return "Confirm_R";
	}
	return NULL;
}

static void dccp_feat_printval(u8 feat_num, dccp_feat_val const *val)
{
	u8 i, type = dccp_feat_type(feat_num);

	if (val == NULL || (type == FEAT_SP && val->sp.vec == NULL))
		dccp_pr_debug_cat("(NULL)");
	else if (type == FEAT_SP)
		for (i = 0; i < val->sp.len; i++)
			dccp_pr_debug_cat("%s%u", i ? " " : "", val->sp.vec[i]);
	else if (type == FEAT_NN)
		dccp_pr_debug_cat("%llu", (unsigned long long)val->nn);
	else
		dccp_pr_debug_cat("unknown type %u", type);
}

static void dccp_feat_printvals(u8 feat_num, u8 *list, u8 len)
{
	u8 type = dccp_feat_type(feat_num);
	dccp_feat_val fval = { .sp.vec = list, .sp.len = len };

	if (type == FEAT_NN)
		fval.nn = dccp_decode_value_var(list, len);
	dccp_feat_printval(feat_num, &fval);
}

static void dccp_feat_print_entry(struct dccp_feat_entry const *entry)
{
	dccp_debug("   * %s %s = ", entry->is_local ? "local" : "remote",
				    dccp_feat_fname(entry->feat_num));
	dccp_feat_printval(entry->feat_num, &entry->val);
	dccp_pr_debug_cat(", state=%s %s\n", dccp_feat_sname[entry->state],
			  entry->needs_confirm ? "(Confirm pending)" : "");
}

#define dccp_feat_print_opt(opt, feat, val, len, mandatory)	do {	      \
	dccp_pr_debug("%s(%s, ", dccp_feat_oname(opt), dccp_feat_fname(feat));\
	dccp_feat_printvals(feat, val, len);				      \
	dccp_pr_debug_cat(") %s\n", mandatory ? "!" : "");	} while (0)

#define dccp_feat_print_fnlist(fn_list)  {		\
	const struct dccp_feat_entry *___entry;		\
							\
	dccp_pr_debug("List Dump:\n");			\
	list_for_each_entry(___entry, fn_list, node)	\
		dccp_feat_print_entry(___entry);	\
}
#else	/* ! CONFIG_IP_DCCP_DEBUG */
#define dccp_feat_print_opt(opt, feat, val, len, mandatory)
#define dccp_feat_print_fnlist(fn_list)
#endif

static int __dccp_feat_activate(struct sock *sk, const int idx,
				const bool is_local, dccp_feat_val const *fval)
{
	bool rx;
	u64 val;

	if (idx < 0 || idx >= DCCP_FEAT_SUPPORTED_MAX)
		return -1;
	if (dccp_feat_table[idx].activation_hdlr == NULL)
		return 0;

	if (fval == NULL) {
		val = dccp_feat_table[idx].default_value;
	} else if (dccp_feat_table[idx].reconciliation == FEAT_SP) {
		if (fval->sp.vec == NULL) {
			/*
			 * This can happen when an empty Confirm is sent
			 * for an SP (i.e. known) feature. In this case
			 * we would be using the default anyway.
			 */
			DCCP_CRIT("Feature #%d undefined: using default", idx);
			val = dccp_feat_table[idx].default_value;
		} else {
			val = fval->sp.vec[0];
		}
	} else {
		val = fval->nn;
	}

	/* Location is RX if this is a local-RX or remote-TX feature */
	rx = (is_local == (dccp_feat_table[idx].rxtx == FEAT_AT_RX));

	dccp_debug("   -> activating %s %s, %sval=%llu\n", rx ? "RX" : "TX",
		   dccp_feat_fname(dccp_feat_table[idx].feat_num),
		   fval ? "" : "default ",  (unsigned long long)val);

	return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
}

/**
 * dccp_feat_activate  -  Activate feature value on socket
 * @sk: fully connected DCCP socket (after handshake is complete)
 * @feat_num: feature to activate, one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is meant
 * @fval: the value (SP or NN) to activate, or NULL to use the default value
 *
 * For general use this function is preferable over __dccp_feat_activate().
 */
static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local,
			      dccp_feat_val const *fval)
{
	return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval);
}

/* Test for "Req'd" feature (RFC 4340, 6.4) */
static inline int dccp_feat_must_be_understood(u8 feat_num)
{
	return	feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
		feat_num == DCCPF_SEQUENCE_WINDOW;
}

/* copy constructor, fval must not already contain allocated memory */
static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
{
	fval->sp.len = len;
	if (fval->sp.len > 0) {
		fval->sp.vec = kmemdup(val, len, gfp_any());
		if (fval->sp.vec == NULL) {
			fval->sp.len = 0;
			return -ENOBUFS;
		}
	}
	return 0;
}

static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
{
	if (unlikely(val == NULL))
		return;
	if (dccp_feat_type(feat_num) == FEAT_SP)
		kfree(val->sp.vec);
	memset(val, 0, sizeof(*val));
}

static struct dccp_feat_entry *
	      dccp_feat_clone_entry(struct dccp_feat_entry const *original)
{
	struct dccp_feat_entry *new;
	u8 type = dccp_feat_type(original->feat_num);

	if (type == FEAT_UNKNOWN)
		return NULL;

	new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
	if (new == NULL)
		return NULL;

	if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
						      original->val.sp.vec,
						      original->val.sp.len)) {
		kfree(new);
		return NULL;
	}
	return new;
}

static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
{
	if (entry != NULL) {
		dccp_feat_val_destructor(entry->feat_num, &entry->val);
		kfree(entry);
	}
}

/*
 * List management functions
 *
 * Feature negotiation lists rely on and maintain the following invariants:
 * - each feat_num in the list is known, i.e. we know its type and default value
 * - each feat_num/is_local combination is unique (old entries are overwritten)
 * - SP values are always freshly allocated
 * - list is sorted in increasing order of feature number (faster lookup)
 */
static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
						     u8 feat_num, bool is_local)
{
	struct dccp_feat_entry *entry;

	list_for_each_entry(entry, fn_list, node) {
		if (entry->feat_num == feat_num && entry->is_local == is_local)
			return entry;
		else if (entry->feat_num > feat_num)
			break;
	}
	return NULL;
}

/**
 * dccp_feat_entry_new  -  Central list update routine (called by all others)
 * @head:  list to add to
 * @feat:  feature number
 * @local: whether the local (1) or remote feature with number @feat is meant
 *
 * This is the only constructor and serves to ensure the above invariants.
 */
static struct dccp_feat_entry *
	      dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
{
	struct dccp_feat_entry *entry;

	list_for_each_entry(entry, head, node)
		if (entry->feat_num == feat && entry->is_local == local) {
			dccp_feat_val_destructor(entry->feat_num, &entry->val);
			return entry;
		} else if (entry->feat_num > feat) {
			head = &entry->node;
			break;
		}

	entry = kmalloc(sizeof(*entry), gfp_any());
	if (entry != NULL) {
		entry->feat_num = feat;
		entry->is_local = local;
		list_add_tail(&entry->node, head);
	}
	return entry;
}

/**
 * dccp_feat_push_change  -  Add/overwrite a Change option in the list
 * @fn_list: feature-negotiation list to update
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is meant
 * @mandatory: whether to use Mandatory feature negotiation options
 * @fval: pointer to NN/SP value to be inserted (will be copied)
 */
static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
				 u8 mandatory, dccp_feat_val *fval)
{
	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

	if (new == NULL)
		return -ENOMEM;

	new->feat_num	     = feat;
	new->is_local	     = local;
	new->state	     = FEAT_INITIALISING;
	new->needs_confirm   = false;
	new->empty_confirm   = false;
	new->val	     = *fval;
	new->needs_mandatory = mandatory;

	return 0;
}

/**
 * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
 * @fn_list: feature-negotiation list to add to
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is being confirmed
 * @fval: pointer to NN/SP value to be inserted or NULL
 *
 * Returns 0 on success, a Reset code for further processing otherwise.
 */
static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
				  dccp_feat_val *fval)
{
	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

	if (new == NULL)
		return DCCP_RESET_CODE_TOO_BUSY;

	new->feat_num	     = feat;
	new->is_local	     = local;
	new->state	     = FEAT_STABLE;	/* transition in 6.6.2 */
	new->needs_confirm   = true;
	new->empty_confirm   = (fval == NULL);
	new->val.nn	     = 0;		/* zeroes the whole structure */
	if (!new->empty_confirm)
		new->val     = *fval;
	new->needs_mandatory = false;

	return 0;
}

static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
{
	return dccp_feat_push_confirm(fn_list, feat, local, NULL);
}

static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
{
	list_del(&entry->node);
	dccp_feat_entry_destructor(entry);
}

void dccp_feat_list_purge(struct list_head *fn_list)
{
	struct dccp_feat_entry *entry, *next;

	list_for_each_entry_safe(entry, next, fn_list, node)
		dccp_feat_entry_destructor(entry);
	INIT_LIST_HEAD(fn_list);
}
EXPORT_SYMBOL_GPL(dccp_feat_list_purge);

/* generate @to as full clone of @from - @to must not contain any nodes */
int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
{
	struct dccp_feat_entry *entry, *new;

	INIT_LIST_HEAD(to);
	list_for_each_entry(entry, from, node) {
		new = dccp_feat_clone_entry(entry);
		if (new == NULL)
			goto cloning_failed;
		list_add_tail(&new->node, to);
	}
	return 0;

cloning_failed:
	dccp_feat_list_purge(to);
	return -ENOMEM;
}

/**
 * dccp_feat_valid_nn_length  -  Enforce length constraints on NN options
 * Length is between 0 and %DCCP_OPTVAL_MAXLEN. Used for outgoing packets only,
 * incoming options are accepted as long as their values are valid.
 */
static u8 dccp_feat_valid_nn_length(u8 feat_num)
{
	if (feat_num == DCCPF_ACK_RATIO)	/* RFC 4340, 11.3 and 6.6.8 */
		return 2;
	if (feat_num == DCCPF_SEQUENCE_WINDOW)	/* RFC 4340, 7.5.2 and 6.5  */
		return 6;
	return 0;
}

static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
{
	switch (feat_num) {
	case DCCPF_ACK_RATIO:
		return val <= DCCPF_ACK_RATIO_MAX;
	case DCCPF_SEQUENCE_WINDOW:
		return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
	}
	return 0;	/* feature unknown - so we can't tell */
}

/* check that SP values are within the ranges defined in RFC 4340 */
static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
{
	switch (feat_num) {
	case DCCPF_CCID:
		return val == DCCPC_CCID2 || val == DCCPC_CCID3;
	/* Type-check Boolean feature values: */
	case DCCPF_SHORT_SEQNOS:
	case DCCPF_ECN_INCAPABLE:
	case DCCPF_SEND_ACK_VECTOR:
	case DCCPF_SEND_NDP_COUNT:
	case DCCPF_DATA_CHECKSUM:
	case DCCPF_SEND_LEV_RATE:
		return val < 2;
	case DCCPF_MIN_CSUM_COVER:
		return val < 16;
	}
	return 0;			/* feature unknown */
}

static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
{
	if (sp_list == NULL || sp_len < 1)
		return 0;
	while (sp_len--)
		if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
			return 0;
	return 1;
}

/**
 * dccp_feat_insert_opts  -  Generate FN options from current list state
 * @skb: next sk_buff to be sent to the peer
 * @dp: for client during handshake and general negotiation
 * @dreq: used by the server only (all Changes/Confirms in LISTEN/RESPOND)
 */
int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq,
			  struct sk_buff *skb)
{
	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
	struct dccp_feat_entry *pos, *next;
	u8 opt, type, len, *ptr, nn_in_nbo[DCCP_OPTVAL_MAXLEN];
	bool rpt;

	/* put entries into @skb in the order they appear in the list */
	list_for_each_entry_safe_reverse(pos, next, fn, node) {
		opt  = dccp_feat_genopt(pos);
		type = dccp_feat_type(pos->feat_num);
		rpt  = false;

		if (pos->empty_confirm) {
			len = 0;
			ptr = NULL;
		} else {
			if (type == FEAT_SP) {
				len = pos->val.sp.len;
				ptr = pos->val.sp.vec;
				rpt = pos->needs_confirm;
			} else if (type == FEAT_NN) {
				len = dccp_feat_valid_nn_length(pos->feat_num);
				ptr = nn_in_nbo;
				dccp_encode_value_var(pos->val.nn, ptr, len);
			} else {
				DCCP_BUG("unknown feature %u", pos->feat_num);
				return -1;
			}
		}
		dccp_feat_print_opt(opt, pos->feat_num, ptr, len, 0);

		if (dccp_insert_fn_opt(skb, opt, pos->feat_num, ptr, len, rpt))
			return -1;
		if (pos->needs_mandatory && dccp_insert_option_mandatory(skb))
			return -1;

		if (skb->sk->sk_state == DCCP_OPEN &&
		    (opt == DCCPO_CONFIRM_R || opt == DCCPO_CONFIRM_L)) {
			/*
			 * Confirms don't get retransmitted (6.6.3) once the
			 * connection is in state OPEN
			 */
			dccp_feat_list_pop(pos);
		} else {
			/*
			 * Enter CHANGING after transmitting the Change
			 * option (6.6.2).
			 */
			if (pos->state == FEAT_INITIALISING)
				pos->state = FEAT_CHANGING;
		}
	}
	return 0;
}

/**
 * __feat_register_nn  -  Register new NN value on socket
 * @fn: feature-negotiation list to register with
 * @feat: an NN feature from %dccp_feature_numbers
 * @mandatory: use Mandatory option if 1
 * @nn_val: value to register (restricted to 4 bytes)
 *
 * Note that NN features are local by definition (RFC 4340, 6.3.2).
 */
static int __feat_register_nn(struct list_head *fn, u8 feat,
			      u8 mandatory, u64 nn_val)
{
	dccp_feat_val fval = { .nn = nn_val };

	if (dccp_feat_type(feat) != FEAT_NN ||
	    !dccp_feat_is_valid_nn_val(feat, nn_val))
		return -EINVAL;

	/* Don't bother with default values, they will be activated anyway. */
	if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
		return 0;

	return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
}

/**
 * __feat_register_sp  -  Register new SP value/list on socket
 * @fn: feature-negotiation list to register with
 * @feat: an SP feature from %dccp_feature_numbers
 * @is_local: whether the local (1) or the remote (0) @feat is meant
 * @mandatory: use Mandatory option if 1
 * @sp_val: SP value followed by optional preference list
 * @sp_len: length of @sp_val in bytes
 */
static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
			      u8 mandatory, u8 const *sp_val, u8 sp_len)
{
	dccp_feat_val fval;

	if (dccp_feat_type(feat) != FEAT_SP ||
	    !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
		return -EINVAL;

	/* Avoid negotiating alien CCIDs by only advertising supported ones */
	if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
		return -EOPNOTSUPP;

	if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
		return -ENOMEM;

	return dccp_feat_push_change(fn, feat, is_local, mandatory, &fval);
}

/**
 * dccp_feat_register_sp  -  Register requests to change SP feature values
 * @sk: client or listening socket
 * @feat: one of %dccp_feature_numbers
 * @is_local: whether the local (1) or remote (0) @feat is meant
 * @list: array of preferred values, in descending order of preference
 * @len: length of @list in bytes
 */
int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
			  u8 const *list, u8 len)
{	 /* any changes must be registered before establishing the connection */
	if (sk->sk_state != DCCP_CLOSED)
		return -EISCONN;
	if (dccp_feat_type(feat) != FEAT_SP)
		return -EINVAL;
	return __feat_register_sp(&dccp_sk(sk)->dccps_featneg, feat, is_local,
				  0, list, len);
}

/**
 * dccp_feat_nn_get  -  Query current/pending value of NN feature
 * @sk: DCCP socket of an established connection
 * @feat: NN feature number from %dccp_feature_numbers
 *
 * For a known NN feature, returns value currently being negotiated, or
 * current (confirmed) value if no negotiation is going on.
 */
u64 dccp_feat_nn_get(struct sock *sk, u8 feat)
{
	if (dccp_feat_type(feat) == FEAT_NN) {
		struct dccp_sock *dp = dccp_sk(sk);
		struct dccp_feat_entry *entry;

		entry = dccp_feat_list_lookup(&dp->dccps_featneg, feat, 1);
		if (entry != NULL)
			return entry->val.nn;

		switch (feat) {
		case DCCPF_ACK_RATIO:
			return dp->dccps_l_ack_ratio;
		case DCCPF_SEQUENCE_WINDOW:
			return dp->dccps_l_seq_win;
		}
	}
	DCCP_BUG("attempt to look up unsupported feature %u", feat);
	return 0;
}
EXPORT_SYMBOL_GPL(dccp_feat_nn_get);

/**
 * dccp_feat_signal_nn_change  -  Update NN values for an established connection
 * @sk: DCCP socket of an established connection
 * @feat: NN feature number from %dccp_feature_numbers
 * @nn_val: the new value to use
 *
 * This function is used to communicate NN updates out-of-band.
 */
int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val)
{
	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
	dccp_feat_val fval = { .nn = nn_val };
	struct dccp_feat_entry *entry;

	if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN)
		return 0;

	if (dccp_feat_type(feat) != FEAT_NN ||
	    !dccp_feat_is_valid_nn_val(feat, nn_val))
		return -EINVAL;

	if (nn_val == dccp_feat_nn_get(sk, feat))
		return 0;	/* already set or negotiation under way */

	entry = dccp_feat_list_lookup(fn, feat, 1);
	if (entry != NULL) {
		dccp_pr_debug("Clobbering existing NN entry %llu -> %llu\n",
			      (unsigned long long)entry->val.nn,
			      (unsigned long long)nn_val);
		dccp_feat_list_pop(entry);
	}

	inet_csk_schedule_ack(sk);
	return dccp_feat_push_change(fn, feat, 1, 0, &fval);
}
EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change);

/*
 *	Tracking features whose value depend on the choice of CCID
 *
 * This is designed with an extension in mind so that a list walk could be done
 * before activating any features. However, the existing framework was found to
 * work satisfactorily up until now, the automatic verification is left open.
 * When adding new CCIDs, add a corresponding dependency table here.
 */
static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
{
	static const struct ccid_dependency ccid2_dependencies[2][2] = {
		/*
		 * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
		 * feature and Send Ack Vector is an RX feature, `is_local'
		 * needs to be reversed.
		 */
		{	/* Dependencies of the receiver-side (remote) CCID2 */
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= true,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		},
		{	/* Dependencies of the sender-side (local) CCID2 */
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		}
	};
	static const struct ccid_dependency ccid3_dependencies[2][5] = {
		{	/*
			 * Dependencies of the receiver-side CCID3
			 */
			{	/* locally disable Ack Vectors */
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 0
			},
			{	/* see below why Send Loss Event Rate is on */
				.dependent_feat	= DCCPF_SEND_LEV_RATE,
				.is_local	= true,
				.is_mandatory	= true,
				.val		= 1
			},
			{	/* NDP Count is needed as per RFC 4342, 6.1.1 */
				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 },
		},
		{	/*
			 * CCID3 at the TX side: we request that the HC-receiver
			 * will not send Ack Vectors (they will be ignored, so
			 * Mandatory is not set); we enable Send Loss Event Rate
			 * (Mandatory since the implementation does not support
			 * the Loss Intervals option of RFC 4342, 8.6).
			 * The last two options are for peer's information only.
			*/
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= false,
				.is_mandatory	= false,
				.val		= 0
			},
			{
				.dependent_feat	= DCCPF_SEND_LEV_RATE,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{	/* this CCID does not support Ack Ratio */
				.dependent_feat	= DCCPF_ACK_RATIO,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 0
			},
			{	/* tell receiver we are sending NDP counts */
				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		}
	};
	switch (ccid) {
	case DCCPC_CCID2:
		return ccid2_dependencies[is_local];
	case DCCPC_CCID3:
		return ccid3_dependencies[is_local];
	default:
		return NULL;
	}
}

/**
 * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
 * @fn: feature-negotiation list to update
 * @id: CCID number to track
 * @is_local: whether TX CCID (1) or RX CCID (0) is meant
 *
 * This function needs to be called after registering all other features.
 */
static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
{
	const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
	int i, rc = (table == NULL);

	for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
		if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
			rc = __feat_register_sp(fn, table[i].dependent_feat,
						    table[i].is_local,
						    table[i].is_mandatory,
						    &table[i].val, 1);
		else
			rc = __feat_register_nn(fn, table[i].dependent_feat,
						    table[i].is_mandatory,
						    table[i].val);
	return rc;
}

/**
 * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
 * @dp: client or listening socket (settings will be inherited)
 *
 * This is called after all registrations (socket initialisation, sysctls, and
 * sockopt calls), and before sending the first packet containing Change options
 * (ie. client-Request or server-Response), to ensure internal consistency.
 */
int dccp_feat_finalise_settings(struct dccp_sock *dp)
{
	struct list_head *fn = &dp->dccps_featneg;
	struct dccp_feat_entry *entry;
	int i = 2, ccids[2] = { -1, -1 };

	/*
	 * Propagating CCIDs:
	 * 1) not useful to propagate CCID settings if this host advertises more
	 *    than one CCID: the choice of CCID  may still change - if this is
	 *    the client, or if this is the server and the client sends
	 *    singleton CCID values.
	 * 2) since is that propagate_ccid changes the list, we defer changing
	 *    the sorted list until after the traversal.
	 */
	list_for_each_entry(entry, fn, node)
		if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
			ccids[entry->is_local] = entry->val.sp.vec[0];
	while (i--)
		if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
			return -1;
	dccp_feat_print_fnlist(fn);
	return 0;
}

/**
 * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
 * It is the server which resolves the dependencies once the CCID has been
 * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
 */
int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
{
	struct list_head *fn = &dreq->dreq_featneg;
	struct dccp_feat_entry *entry;
	u8 is_local, ccid;

	for (is_local = 0; is_local <= 1; is_local++) {
		entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);

		if (entry != NULL && !entry->empty_confirm)
			ccid = entry->val.sp.vec[0];
		else
			ccid = dccp_feat_default_value(DCCPF_CCID);

		if (dccp_feat_propagate_ccid(fn, ccid, is_local))
			return -1;
	}
	return 0;
}

/* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
{
	u8 c, s;

	for (s = 0; s < slen; s++)
		for (c = 0; c < clen; c++)
			if (servlist[s] == clilist[c])
				return servlist[s];
	return -1;
}

/**
 * dccp_feat_prefer  -  Move preferred entry to the start of array
 * Reorder the @array_len elements in @array so that @preferred_value comes
 * first. Returns >0 to indicate that @preferred_value does occur in @array.
 */
static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
{
	u8 i, does_occur = 0;

	if (array != NULL) {
		for (i = 0; i < array_len; i++)
			if (array[i] == preferred_value) {
				array[i] = array[0];
				does_occur++;
			}
		if (does_occur)
			array[0] = preferred_value;
	}
	return does_occur;
}

/**
 * dccp_feat_reconcile  -  Reconcile SP preference lists
 *  @fv: SP list to reconcile into
 *  @arr: received SP preference list
 *  @len: length of @arr in bytes
 *  @is_server: whether this side is the server (and @fv is the server's list)
 *  @reorder: whether to reorder the list in @fv after reconciling with @arr
 * When successful, > 0 is returned and the reconciled list is in @fval.
 * A value of 0 means that negotiation failed (no shared entry).
 */
static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
			       bool is_server, bool reorder)
{
	int rc;

	if (!fv->sp.vec || !arr) {
		DCCP_CRIT("NULL feature value or array");
		return 0;
	}

	if (is_server)
		rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
	else
		rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);

	if (!reorder)
		return rc;
	if (rc < 0)
		return 0;

	/*
	 * Reorder list: used for activating features and in dccp_insert_fn_opt.
	 */
	return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
}

/**
 * dccp_feat_change_recv  -  Process incoming ChangeL/R options
 * @fn: feature-negotiation list to update
 * @is_mandatory: whether the Change was preceded by a Mandatory option
 * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
 * @feat: one of %dccp_feature_numbers
 * @val: NN value or SP value/preference list
 * @len: length of @val in bytes
 * @server: whether this node is the server (1) or the client (0)
 */
static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
				u8 feat, u8 *val, u8 len, const bool server)
{
	u8 defval, type = dccp_feat_type(feat);
	const bool local = (opt == DCCPO_CHANGE_R);
	struct dccp_feat_entry *entry;
	dccp_feat_val fval;

	if (len == 0 || type == FEAT_UNKNOWN)		/* 6.1 and 6.6.8 */
		goto unknown_feature_or_value;

	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);

	/*
	 *	Negotiation of NN features: Change R is invalid, so there is no
	 *	simultaneous negotiation; hence we do not look up in the list.
	 */
	if (type == FEAT_NN) {
		if (local || len > sizeof(fval.nn))
			goto unknown_feature_or_value;

		/* 6.3.2: "The feature remote MUST accept any valid value..." */
		fval.nn = dccp_decode_value_var(val, len);
		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
			goto unknown_feature_or_value;

		return dccp_feat_push_confirm(fn, feat, local, &fval);
	}

	/*
	 *	Unidirectional/simultaneous negotiation of SP features (6.3.1)
	 */
	entry = dccp_feat_list_lookup(fn, feat, local);
	if (entry == NULL) {
		/*
		 * No particular preferences have been registered. We deal with
		 * this situation by assuming that all valid values are equally
		 * acceptable, and apply the following checks:
		 * - if the peer's list is a singleton, we accept a valid value;
		 * - if we are the server, we first try to see if the peer (the
		 *   client) advertises the default value. If yes, we use it,
		 *   otherwise we accept the preferred value;
		 * - else if we are the client, we use the first list element.
		 */
		if (dccp_feat_clone_sp_val(&fval, val, 1))
			return DCCP_RESET_CODE_TOO_BUSY;

		if (len > 1 && server) {
			defval = dccp_feat_default_value(feat);
			if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
				fval.sp.vec[0] = defval;
		} else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
			kfree(fval.sp.vec);
			goto unknown_feature_or_value;
		}

		/* Treat unsupported CCIDs like invalid values */
		if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
			kfree(fval.sp.vec);
			goto not_valid_or_not_known;
		}

		return dccp_feat_push_confirm(fn, feat, local, &fval);

	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
		return 0;
	}

	if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
		entry->empty_confirm = false;
	} else if (is_mandatory) {
		return DCCP_RESET_CODE_MANDATORY_ERROR;
	} else if (entry->state == FEAT_INITIALISING) {
		/*
		 * Failed simultaneous negotiation (server only): try to `save'
		 * the connection by checking whether entry contains the default
		 * value for @feat. If yes, send an empty Confirm to signal that
		 * the received Change was not understood - which implies using
		 * the default value.
		 * If this also fails, we use Reset as the last resort.
		 */
		WARN_ON(!server);
		defval = dccp_feat_default_value(feat);
		if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
			return DCCP_RESET_CODE_OPTION_ERROR;
		entry->empty_confirm = true;
	}
	entry->needs_confirm   = true;
	entry->needs_mandatory = false;
	entry->state	       = FEAT_STABLE;
	return 0;

unknown_feature_or_value:
	if (!is_mandatory)
		return dccp_push_empty_confirm(fn, feat, local);

not_valid_or_not_known:
	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
			    : DCCP_RESET_CODE_OPTION_ERROR;
}

/**
 * dccp_feat_confirm_recv  -  Process received Confirm options
 * @fn: feature-negotiation list to update
 * @is_mandatory: whether @opt was preceded by a Mandatory option
 * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_R
 * @feat: one of %dccp_feature_numbers
 * @val: NN value or SP value/preference list
 * @len: length of @val in bytes
 * @server: whether this node is server (1) or client (0)
 */
static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
				 u8 feat, u8 *val, u8 len, const bool server)
{
	u8 *plist, plen, type = dccp_feat_type(feat);
	const bool local = (opt == DCCPO_CONFIRM_R);
	struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);

	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);

	if (entry == NULL) {	/* nothing queued: ignore or handle error */
		if (is_mandatory && type == FEAT_UNKNOWN)
			return DCCP_RESET_CODE_MANDATORY_ERROR;

		if (!local && type == FEAT_NN)		/* 6.3.2 */
			goto confirmation_failed;
		return 0;
	}

	if (entry->state != FEAT_CHANGING)		/* 6.6.2 */
		return 0;

	if (len == 0) {
		if (dccp_feat_must_be_understood(feat))	/* 6.6.7 */
			goto confirmation_failed;
		/*
		 * Empty Confirm during connection setup: this means reverting
		 * to the `old' value, which in this case is the default. Since
		 * we handle default values automatically when no other values
		 * have been set, we revert to the old value by removing this
		 * entry from the list.
		 */
		dccp_feat_list_pop(entry);
		return 0;
	}

	if (type == FEAT_NN) {
		if (len > sizeof(entry->val.nn))
			goto confirmation_failed;

		if (entry->val.nn == dccp_decode_value_var(val, len))
			goto confirmation_succeeded;

		DCCP_WARN("Bogus Confirm for non-existing value\n");
		goto confirmation_failed;
	}

	/*
	 * Parsing SP Confirms: the first element of @val is the preferred
	 * SP value which the peer confirms, the remainder depends on @len.
	 * Note that only the confirmed value need to be a valid SP value.
	 */
	if (!dccp_feat_is_valid_sp_val(feat, *val))
		goto confirmation_failed;

	if (len == 1) {		/* peer didn't supply a preference list */
		plist = val;
		plen  = len;
	} else {		/* preferred value + preference list */
		plist = val + 1;
		plen  = len - 1;
	}

	/* Check whether the peer got the reconciliation right (6.6.8) */
	if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
		DCCP_WARN("Confirm selected the wrong value %u\n", *val);
		return DCCP_RESET_CODE_OPTION_ERROR;
	}
	entry->val.sp.vec[0] = *val;

confirmation_succeeded:
	entry->state = FEAT_STABLE;
	return 0;

confirmation_failed:
	DCCP_WARN("Confirmation failed\n");
	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
			    : DCCP_RESET_CODE_OPTION_ERROR;
}

/**
 * dccp_feat_handle_nn_established  -  Fast-path reception of NN options
 * @sk:		socket of an established DCCP connection
 * @mandatory:	whether @opt was preceded by a Mandatory option
 * @opt:	%DCCPO_CHANGE_L | %DCCPO_CONFIRM_R (NN only)
 * @feat:	NN number, one of %dccp_feature_numbers
 * @val:	NN value
 * @len:	length of @val in bytes
 *
 * This function combines the functionality of change_recv/confirm_recv, with
 * the following differences (reset codes are the same):
 *    - cleanup after receiving the Confirm;
 *    - values are directly activated after successful parsing;
 *    - deliberately restricted to NN features.
 * The restriction to NN features is essential since SP features can have non-
 * predictable outcomes (depending on the remote configuration), and are inter-
 * dependent (CCIDs for instance cause further dependencies).
 */
static u8 dccp_feat_handle_nn_established(struct sock *sk, u8 mandatory, u8 opt,
					  u8 feat, u8 *val, u8 len)
{
	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
	const bool local = (opt == DCCPO_CONFIRM_R);
	struct dccp_feat_entry *entry;
	u8 type = dccp_feat_type(feat);
	dccp_feat_val fval;

	dccp_feat_print_opt(opt, feat, val, len, mandatory);

	/* Ignore non-mandatory unknown and non-NN features */
	if (type == FEAT_UNKNOWN) {
		if (local && !mandatory)
			return 0;
		goto fast_path_unknown;
	} else if (type != FEAT_NN) {
		return 0;
	}

	/*
	 * We don't accept empty Confirms, since in fast-path feature
	 * negotiation the values are enabled immediately after sending
	 * the Change option.
	 * Empty Changes on the other hand are invalid (RFC 4340, 6.1).
	 */
	if (len == 0 || len > sizeof(fval.nn))
		goto fast_path_unknown;

	if (opt == DCCPO_CHANGE_L) {
		fval.nn = dccp_decode_value_var(val, len);
		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
			goto fast_path_unknown;

		if (dccp_feat_push_confirm(fn, feat, local, &fval) ||
		    dccp_feat_activate(sk, feat, local, &fval))
			return DCCP_RESET_CODE_TOO_BUSY;

		/* set the `Ack Pending' flag to piggyback a Confirm */
		inet_csk_schedule_ack(sk);

	} else if (opt == DCCPO_CONFIRM_R) {
		entry = dccp_feat_list_lookup(fn, feat, local);
		if (entry == NULL || entry->state != FEAT_CHANGING)
			return 0;

		fval.nn = dccp_decode_value_var(val, len);
		/*
		 * Just ignore a value that doesn't match our current value.
		 * If the option changes twice within two RTTs, then at least
		 * one CONFIRM will be received for the old value after a
		 * new CHANGE was sent.
		 */
		if (fval.nn != entry->val.nn)
			return 0;

		/* Only activate after receiving the Confirm option (6.6.1). */
		dccp_feat_activate(sk, feat, local, &fval);

		/* It has been confirmed - so remove the entry */
		dccp_feat_list_pop(entry);

	} else {
		DCCP_WARN("Received illegal option %u\n", opt);
		goto fast_path_failed;
	}
	return 0;

fast_path_unknown:
	if (!mandatory)
		return dccp_push_empty_confirm(fn, feat, local);

fast_path_failed:
	return mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
			 : DCCP_RESET_CODE_OPTION_ERROR;
}

/**
 * dccp_feat_parse_options  -  Process Feature-Negotiation Options
 * @sk: for general use and used by the client during connection setup
 * @dreq: used by the server during connection setup
 * @mandatory: whether @opt was preceded by a Mandatory option
 * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
 * @feat: one of %dccp_feature_numbers
 * @val: value contents of @opt
 * @len: length of @val in bytes
 *
 * Returns 0 on success, a Reset code for ending the connection otherwise.
 */
int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
			    u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
	bool server = false;

	switch (sk->sk_state) {
	/*
	 *	Negotiation during connection setup
	 */
	case DCCP_LISTEN:
		server = true;			/* fall through */
	case DCCP_REQUESTING:
		switch (opt) {
		case DCCPO_CHANGE_L:
		case DCCPO_CHANGE_R:
			return dccp_feat_change_recv(fn, mandatory, opt, feat,
						     val, len, server);
		case DCCPO_CONFIRM_R:
		case DCCPO_CONFIRM_L:
			return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
						      val, len, server);
		}
		break;
	/*
	 *	Support for exchanging NN options on an established connection.
	 */
	case DCCP_OPEN:
	case DCCP_PARTOPEN:
		return dccp_feat_handle_nn_established(sk, mandatory, opt, feat,
						       val, len);
	}
	return 0;	/* ignore FN options in all other states */
}

/**
 * dccp_feat_init  -  Seed feature negotiation with host-specific defaults
 * This initialises global defaults, depending on the value of the sysctls.
 * These can later be overridden by registering changes via setsockopt calls.
 * The last link in the chain is finalise_settings, to make sure that between
 * here and the start of actual feature negotiation no inconsistencies enter.
 *
 * All features not appearing below use either defaults or are otherwise
 * later adjusted through dccp_feat_finalise_settings().
 */
int dccp_feat_init(struct sock *sk)
{
	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
	u8 on = 1, off = 0;
	int rc;
	struct {
		u8 *val;
		u8 len;
	} tx, rx;

	/* Non-negotiable (NN) features */
	rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
				    sysctl_dccp_sequence_window);
	if (rc)
		return rc;

	/* Server-priority (SP) features */

	/* Advertise that short seqnos are not supported (7.6.1) */
	rc = __feat_register_sp(fn, DCCPF_SHORT_SEQNOS, true, true, &off, 1);
	if (rc)
		return rc;

	/* RFC 4340 12.1: "If a DCCP is not ECN capable, ..." */
	rc = __feat_register_sp(fn, DCCPF_ECN_INCAPABLE, true, true, &on, 1);
	if (rc)
		return rc;

	/*
	 * We advertise the available list of CCIDs and reorder according to
	 * preferences, to avoid failure resulting from negotiating different
	 * singleton values (which always leads to failure).
	 * These settings can still (later) be overridden via sockopts.
	 */
	if (ccid_get_builtin_ccids(&tx.val, &tx.len))
		return -ENOBUFS;
	if (ccid_get_builtin_ccids(&rx.val, &rx.len)) {
		kfree(tx.val);
		return -ENOBUFS;
	}

	if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
	    !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
		goto free_ccid_lists;

	rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);
	if (rc)
		goto free_ccid_lists;

	rc = __feat_register_sp(fn, DCCPF_CCID, false, false, rx.val, rx.len);

free_ccid_lists:
	kfree(tx.val);
	kfree(rx.val);
	return rc;
}

int dccp_feat_activate_values(struct sock *sk, struct list_head *fn_list)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dccp_feat_entry *cur, *next;
	int idx;
	dccp_feat_val *fvals[DCCP_FEAT_SUPPORTED_MAX][2] = {
		 [0 ... DCCP_FEAT_SUPPORTED_MAX-1] = { NULL, NULL }
	};

	list_for_each_entry(cur, fn_list, node) {
		/*
		 * An empty Confirm means that either an unknown feature type
		 * or an invalid value was present. In the first case there is
		 * nothing to activate, in the other the default value is used.
		 */
		if (cur->empty_confirm)
			continue;

		idx = dccp_feat_index(cur->feat_num);
		if (idx < 0) {
			DCCP_BUG("Unknown feature %u", cur->feat_num);
			goto activation_failed;
		}
		if (cur->state != FEAT_STABLE) {
			DCCP_CRIT("Negotiation of %s %s failed in state %s",
				  cur->is_local ? "local" : "remote",
				  dccp_feat_fname(cur->feat_num),
				  dccp_feat_sname[cur->state]);
			goto activation_failed;
		}
		fvals[idx][cur->is_local] = &cur->val;
	}

	/*
	 * Activate in decreasing order of index, so that the CCIDs are always
	 * activated as the last feature. This avoids the case where a CCID
	 * relies on the initialisation of one or more features that it depends
	 * on (e.g. Send NDP Count, Send Ack Vector, and Ack Ratio features).
	 */
	for (idx = DCCP_FEAT_SUPPORTED_MAX; --idx >= 0;)
		if (__dccp_feat_activate(sk, idx, 0, fvals[idx][0]) ||
		    __dccp_feat_activate(sk, idx, 1, fvals[idx][1])) {
			DCCP_CRIT("Could not activate %d", idx);
			goto activation_failed;
		}

	/* Clean up Change options which have been confirmed already */
	list_for_each_entry_safe(cur, next, fn_list, node)
		if (!cur->needs_confirm)
			dccp_feat_list_pop(cur);

	dccp_pr_debug("Activation OK\n");
	return 0;

activation_failed:
	/*
	 * We clean up everything that may have been allocated, since
	 * it is difficult to track at which stage negotiation failed.
	 * This is ok, since all allocation functions below are robust
	 * against NULL arguments.
	 */
	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
	ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
	dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
	dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
	dp->dccps_hc_rx_ackvec = NULL;
	return -1;
}