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
/*
 *      Copyright (C) 1994-1997 Claus-Justus Heine

 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, or (at
 your option) any later version.
 
 This program is distributed in the hope that it will be useful, but
 WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program; see the file COPYING.  If not, write to
 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139,
 USA.
 
 *
 *     This file implements a "generic" interface between the *
 *     zftape-driver and a compression-algorithm. The *
 *     compression-algorithm currently used is a LZ77. I use the *
 *     implementation lzrw3 by Ross N. Williams (Renaissance *
 *     Software). The compression program itself is in the file
 *     lzrw3.c * and lzrw3.h.  To adopt another compression algorithm
 *     the functions * zft_compress() and zft_uncompress() must be
 *     changed * appropriately. See below.
 */

 char zftc_src[] ="$Source: /homes/cvs/ftape-stacked/ftape/compressor/zftape-compress.c,v $";
 char zftc_rev[] = "$Revision: 1.1.6.1 $";
 char zftc_dat[] = "$Date: 1997/11/16 15:15:56 $";

#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/module.h>

#include <linux/zftape.h>

#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,6)
#include <asm/uaccess.h>
#else
#include <asm/segment.h>
#endif

#include "../zftape/zftape-init.h"
#include "../zftape/zftape-eof.h"
#include "../zftape/zftape-ctl.h"
#include "../zftape/zftape-write.h"
#include "../zftape/zftape-read.h"
#include "../zftape/zftape-rw.h"
#include "../compressor/zftape-compress.h"
#include "../zftape/zftape-vtbl.h"
#include "../compressor/lzrw3.h"

/*
 *   global variables
 */

/* I handle the allocation of this buffer as a special case, because
 * it's size varies depending on the tape length inserted.
 */

/* local variables 
 */
static int keep_module_locked = 1;

static void *zftc_wrk_mem = NULL;
static __u8 *zftc_buf     = NULL;
static void *zftc_scratch_buf  = NULL;

/* compression statistics 
 */
static unsigned int zftc_wr_uncompressed = 0;
static unsigned int zftc_wr_compressed   = 0;
static unsigned int zftc_rd_uncompressed = 0;
static unsigned int zftc_rd_compressed   = 0;

/* forward */
static int  zftc_write(int *write_cnt,
		       __u8 *dst_buf, const int seg_sz,
		       const __u8 *src_buf, const int req_len,
		       const zft_position *pos, const zft_volinfo *volume);
static int  zftc_read(int *read_cnt,
		      __u8  *dst_buf, const int to_do,
		      const __u8 *src_buf, const int seg_sz,
		      const zft_position *pos, const zft_volinfo *volume);
static int  zftc_seek(unsigned int new_block_pos, 
		      zft_position *pos, const zft_volinfo *volume,
		      __u8 *buffer);
static void zftc_lock   (void);
static void zftc_reset  (void);
static void zftc_cleanup(void);
static void zftc_stats      (void);

/* compressed segment. This conforms to QIC-80-MC, Revision K.
 * 
 * Rev. K applies to tapes with `fixed length format' which is
 * indicated by format code 2,3 and 5. See below for format code 4 and 6
 *
 * 2 bytes: offset of compression segment structure
 *          29k > offset >= 29k-18: data from previous segment ens in this
 *                                  segment and no compressed block starts
 *                                  in this segment
 *                     offset == 0: data from previous segment occupies entire
 *                                  segment and continues in next segment
 * n bytes: remainder from previous segment
 * 
 * Rev. K:  
 * 4 bytes: 4 bytes: files set byte offset
 * Post Rev. K and QIC-3020/3020:
 * 8 bytes: 8 bytes: files set byte offset
 * 2 bytes: byte count N (amount of data following)
 *          bit 15 is set if data is compressed, bit 15 is not
 *          set if data is uncompressed
 * N bytes: data (as much as specified in the byte count)
 * 2 bytes: byte count N_1 of next cluster
 * N_1 bytes: data of next cluset
 * 2 bytes: byte count N_2 of next cluster
 * N_2 bytes: ...  
 *
 * Note that the `N' byte count accounts only for the bytes that in the
 * current segment if the cluster spans to the next segment.
 */

typedef struct
{
	int cmpr_pos;             /* actual position in compression buffer */
	int cmpr_sz;              /* what is left in the compression buffer
				   * when copying the compressed data to the
				   * deblock buffer
				   */
	unsigned int first_block; /* location of header information in
				   * this segment
				   */
	unsigned int count;       /* amount of data of current block
				   * contained in current segment 
				   */
	unsigned int offset;      /* offset in current segment */
	unsigned int spans:1;     /* might continue in next segment */
	unsigned int uncmpr;      /* 0x8000 if this block contains
				   * uncompressed data 
				   */
	__s64 foffs;              /* file set byte offset, same as in 
				   * compression map segment
				   */
} cmpr_info;

static cmpr_info cseg; /* static data. Must be kept uptodate and shared by 
			* read, write and seek functions
			*/

#define DUMP_CMPR_INFO(level, msg, info)				\
	TRACE(level, msg "\n"						\
	      KERN_INFO "cmpr_pos   : %d\n"				\
	      KERN_INFO "cmpr_sz    : %d\n"				\
	      KERN_INFO "first_block: %d\n"				\
	      KERN_INFO "count      : %d\n"				\
	      KERN_INFO "offset     : %d\n"				\
	      KERN_INFO "spans      : %d\n"				\
	      KERN_INFO "uncmpr     : 0x%04x\n"				\
	      KERN_INFO "foffs      : " LL_X,				\
	      (info)->cmpr_pos, (info)->cmpr_sz, (info)->first_block,	\
	      (info)->count, (info)->offset, (info)->spans == 1,	\
	      (info)->uncmpr, LL((info)->foffs))

/*   dispatch compression segment info, return error code
 *  
 *   afterwards, cseg->offset points to start of data of the NEXT
 *   compressed block, and cseg->count contains the amount of data
 *   left in the actual compressed block. cseg->spans is set to 1 if
 *   the block is continued in the following segment. Otherwise it is
 *   set to 0. 
 */
static int get_cseg (cmpr_info *cinfo, const __u8 *buff, 
		     const unsigned int seg_sz,
		     const zft_volinfo *volume)
{
	TRACE_FUN(ft_t_flow);

 	cinfo->first_block = GET2(buff, 0);
	if (cinfo->first_block == 0) { /* data spans to next segment */
		cinfo->count  = seg_sz - sizeof(__u16);
		cinfo->offset = seg_sz;
		cinfo->spans = 1;
	} else { /* cluster definetely ends in this segment */
		if (cinfo->first_block > seg_sz) {
			/* data corrupted */
			TRACE_ABORT(-EIO, ft_t_err, "corrupted data:\n"
				    KERN_INFO "segment size: %d\n"
				    KERN_INFO "first block : %d",
				    seg_sz, cinfo->first_block);
		}
	        cinfo->count  = cinfo->first_block - sizeof(__u16);
		cinfo->offset = cinfo->first_block;
		cinfo->spans = 0;
	}
	/* now get the offset the first block should have in the
	 * uncompressed data stream.
	 *
	 * For this magic `18' refer to CRF-3 standard or QIC-80MC,
	 * Rev. K.  
	 */
	if ((seg_sz - cinfo->offset) > 18) {
		if (volume->qic113) { /* > revision K */
			TRACE(ft_t_data_flow, "New QIC-113 compliance");
			cinfo->foffs = GET8(buff, cinfo->offset);
			cinfo->offset += sizeof(__s64); 
		} else {
			TRACE(/* ft_t_data_flow */ ft_t_noise, "pre QIC-113 version");
			cinfo->foffs   = (__s64)GET4(buff, cinfo->offset);
			cinfo->offset += sizeof(__u32); 
		}
	}
	if (cinfo->foffs > volume->size) {
		TRACE_ABORT(-EIO, ft_t_err, "Inconsistency:\n"
			    KERN_INFO "offset in current volume: %d\n"
			    KERN_INFO "size of current volume  : %d",
			    (int)(cinfo->foffs>>10), (int)(volume->size>>10));
	}
	if (cinfo->cmpr_pos + cinfo->count > volume->blk_sz) {
		TRACE_ABORT(-EIO, ft_t_err, "Inconsistency:\n"
			    KERN_INFO "block size : %d\n"
			    KERN_INFO "data record: %d",
			    volume->blk_sz, cinfo->cmpr_pos + cinfo->count);
	}
	DUMP_CMPR_INFO(ft_t_noise /* ft_t_any */, "", cinfo);
	TRACE_EXIT 0;
}

/*  This one is called, when a new cluster starts in same segment.
 *  
 *  Note: if this is the first cluster in the current segment, we must
 *  not check whether there are more than 18 bytes available because
 *  this have already been done in get_cseg() and there may be less
 *  than 18 bytes available due to header information.
 * 
 */
static void get_next_cluster(cmpr_info *cluster, const __u8 *buff, 
			     const int seg_sz, const int finish)
{
	TRACE_FUN(ft_t_flow);

	if (seg_sz - cluster->offset > 18 || cluster->foffs != 0) {
		cluster->count   = GET2(buff, cluster->offset);
		cluster->uncmpr  = cluster->count & 0x8000;
		cluster->count  -= cluster->uncmpr;
		cluster->offset += sizeof(__u16);
		cluster->foffs   = 0;
		if ((cluster->offset + cluster->count) < seg_sz) {
			cluster->spans = 0;
		} else if (cluster->offset + cluster->count == seg_sz) {
			cluster->spans = !finish;
		} else {
			/* either an error or a volume written by an 
			 * old version. If this is a data error, then we'll
			 * catch it later.
			 */
			TRACE(ft_t_data_flow, "Either error or old volume");
			cluster->spans = 1;
			cluster->count = seg_sz - cluster->offset;
		}
	} else {
		cluster->count = 0;
		cluster->spans = 0;
		cluster->foffs = 0;
	}
	DUMP_CMPR_INFO(ft_t_noise /* ft_t_any */ , "", cluster);
	TRACE_EXIT;
}

static void zftc_lock(void)
{
#if LINUX_VERSION_CODE < KERNEL_VER(2,1,18)
	if (!MOD_IN_USE) {
		MOD_INC_USE_COUNT;
	}
#else
	MOD_INC_USE_COUNT; /*  sets MOD_VISITED and MOD_USED_ONCE,
			    *  locking is done with can_unload()
			    */
#endif
	keep_module_locked = 1;
}

/*  this function is needed for zftape_reset_position in zftape-io.c 
 */
static void zftc_reset(void)
{
	TRACE_FUN(ft_t_flow);

	memset((void *)&cseg, '\0', sizeof(cseg));
	zftc_stats();
#if LINUX_VERSION_CODE < KERNEL_VER(2,1,18)
	if (MOD_IN_USE) {
		MOD_DEC_USE_COUNT;
	}
#endif
	keep_module_locked = 0;
	TRACE_EXIT;
}

static int cmpr_mem_initialized = 0;
static unsigned int alloc_blksz = 0;

static int zft_allocate_cmpr_mem(unsigned int blksz)
{
	TRACE_FUN(ft_t_flow);

	if (cmpr_mem_initialized && blksz == alloc_blksz) {
		TRACE_EXIT 0;
	}
	TRACE_CATCH(zft_vmalloc_once(&zftc_wrk_mem, CMPR_WRK_MEM_SIZE),
		    zftc_cleanup());
	TRACE_CATCH(zft_vmalloc_always(&zftc_buf, blksz + CMPR_OVERRUN),
		    zftc_cleanup());
	alloc_blksz = blksz;
	TRACE_CATCH(zft_vmalloc_always(&zftc_scratch_buf, blksz+CMPR_OVERRUN),
		    zftc_cleanup());
	cmpr_mem_initialized = 1;
	TRACE_EXIT 0;
}

static void zftc_cleanup(void)
{
	TRACE_FUN(ft_t_flow);

	zft_vfree(&zftc_wrk_mem, CMPR_WRK_MEM_SIZE);
	zft_vfree(&zftc_buf, alloc_blksz + CMPR_OVERRUN);
	zft_vfree(&zftc_scratch_buf, alloc_blksz + CMPR_OVERRUN);
	cmpr_mem_initialized = alloc_blksz = 0;
	TRACE_EXIT;
}

/*****************************************************************************
 *                                                                           *
 *  The following two functions "ftape_compress()" and                       *
 *  "ftape_uncompress()" are the interface to the actual compression         *
 *  algorithm (i.e. they are calling the "compress()" function from          *
 *  the lzrw3 package for now). These routines could quite easily be         *
 *  changed to adopt another compression algorithm instead of lzrw3,         *
 *  which currently is used.                                                 *
 *                                                                           *
 *****************************************************************************/

/* called by zft_compress_write() to perform the compression. Must
 * return the size of the compressed data.
 *
 * NOTE: The size of the compressed data should not exceed the size of
 *       the uncompressed data. Most compression algorithms have means
 *       to store data unchanged if the "compressed" data amount would
 *       exceed the original one. Mostly this is done by storing some
 *       flag-bytes in front of the compressed data to indicate if it
 *       is compressed or not. Thus the worst compression result
 *       length is the original length plus those flag-bytes.
 *
 *       We don't want that, as the QIC-80 standard provides a means
 *       of marking uncompressed blocks by simply setting bit 15 of
 *       the compressed block's length. Thus a compessed block can
 *       have at most a length of 2^15-1 bytes. The QIC-80 standard
 *       restricts the block-length even further, allowing only 29k -
 *       6 bytes.
 *
 *       Currently, the maximum blocksize used by zftape is 28k.
 *
 *       In short: don't exceed the length of the input-package, set
 *       bit 15 of the compressed size to 1 if you have copied data
 *       instead of compressing it.
 */
static int zft_compress(__u8 *in_buffer, unsigned int in_sz, __u8 *out_buffer)
{ 
	__s32 compressed_sz;
	TRACE_FUN(ft_t_flow);
	

	lzrw3_compress(COMPRESS_ACTION_COMPRESS, zftc_wrk_mem,
		       in_buffer, in_sz, out_buffer, &compressed_sz);
	if (TRACE_LEVEL >= ft_t_info) {
		/*  the compiler will optimize this away when
		 *  compiled with NO_TRACE_AT_ALL option
		 */
		TRACE(ft_t_data_flow, "\n"
		      KERN_INFO "before compression: %d bytes\n"
		      KERN_INFO "after compresison : %d bytes", 
		      in_sz, 
		      (int)(compressed_sz < 0 
		      ? -compressed_sz : compressed_sz));
		/*  for statistical purposes
		 */
		zftc_wr_compressed   += (compressed_sz < 0 
					   ? -compressed_sz : compressed_sz);
		zftc_wr_uncompressed += in_sz;
	}
	TRACE_EXIT (int)compressed_sz;
}

/* called by zft_compress_read() to decompress the data. Must
 * return the size of the decompressed data for sanity checks
 * (compared with zft_blk_sz)
 *
 * NOTE: Read the note for zft_compress() above!  If bit 15 of the
 *       parameter in_sz is set, then the data in in_buffer isn't
 *       compressed, which must be handled by the un-compression
 *       algorithm. (I changed lzrw3 to handle this.)
 *
 *  The parameter max_out_sz is needed to prevent buffer overruns when 
 *  uncompressing corrupt data.
 */
static unsigned int zft_uncompress(__u8 *in_buffer, 
				   int in_sz, 
				   __u8 *out_buffer,
				   unsigned int max_out_sz)
{ 
	TRACE_FUN(ft_t_flow);
	
	lzrw3_compress(COMPRESS_ACTION_DECOMPRESS, zftc_wrk_mem,
		       in_buffer, (__s32)in_sz,
		       out_buffer, (__u32 *)&max_out_sz);
	
	if (TRACE_LEVEL >= ft_t_info) {
		TRACE(ft_t_data_flow, "\n"
		      KERN_INFO "before decompression: %d bytes\n"
		      KERN_INFO "after decompression : %d bytes", 
		      in_sz < 0 ? -in_sz : in_sz,(int)max_out_sz);
		/*  for statistical purposes
		 */
		zftc_rd_compressed   += in_sz < 0 ? -in_sz : in_sz;
		zftc_rd_uncompressed += max_out_sz;
	}
	TRACE_EXIT (unsigned int)max_out_sz;
}

/* print some statistics about the efficiency of the compression to
 * the kernel log 
 */
static void zftc_stats(void)
{
	TRACE_FUN(ft_t_flow);

	if (TRACE_LEVEL < ft_t_info) {
		TRACE_EXIT;
	}
	if (zftc_wr_uncompressed != 0) {
		if (zftc_wr_compressed > (1<<14)) {
			TRACE(ft_t_info, "compression statistics (writing):\n"
			      KERN_INFO " compr./uncmpr.   : %3d %%",
			      (((zftc_wr_compressed>>10) * 100)
			       / (zftc_wr_uncompressed>>10)));
		} else {
			TRACE(ft_t_info, "compression statistics (writing):\n"
			      KERN_INFO " compr./uncmpr.   : %3d %%",
			      ((zftc_wr_compressed * 100)
			       / zftc_wr_uncompressed));
		}
	}
	if (zftc_rd_uncompressed != 0) {
		if (zftc_rd_compressed > (1<<14)) {
			TRACE(ft_t_info, "compression statistics (reading):\n"
			      KERN_INFO " compr./uncmpr.   : %3d %%",
			      (((zftc_rd_compressed>>10) * 100)
			       / (zftc_rd_uncompressed>>10)));
		} else {
			TRACE(ft_t_info, "compression statistics (reading):\n"
			      KERN_INFO " compr./uncmpr.   : %3d %%",
			      ((zftc_rd_compressed * 100)
			       / zftc_rd_uncompressed));
		}
	}
	/* only print it once: */
	zftc_wr_uncompressed = 
		zftc_wr_compressed  =
		zftc_rd_uncompressed =
		zftc_rd_compressed   = 0;
	TRACE_EXIT;
}

/* start new compressed block 
 */
static int start_new_cseg(cmpr_info *cluster, 
			  char *dst_buf, 
			  const zft_position *pos,
			  const unsigned int blk_sz,
			  const char *src_buf,
			  const int this_segs_sz,
			  const int qic113)
{
	int size_left;
	int cp_cnt;
	int buf_pos;
	TRACE_FUN(ft_t_flow);

	size_left = this_segs_sz - sizeof(__u16) - cluster->cmpr_sz;
	TRACE(ft_t_data_flow,"\n" 
	      KERN_INFO "segment size   : %d\n"
	      KERN_INFO "compressed_sz: %d\n"
	      KERN_INFO "size_left      : %d",
	      this_segs_sz, cluster->cmpr_sz, size_left);
	if (size_left > 18) { /* start a new cluseter */
		cp_cnt = cluster->cmpr_sz;
		cluster->cmpr_sz = 0;
		buf_pos = cp_cnt + sizeof(__u16);
		PUT2(dst_buf, 0, buf_pos);

		if (qic113) {
			__s64 foffs = pos->volume_pos;
			if (cp_cnt) foffs += (__s64)blk_sz;

			TRACE(ft_t_data_flow, "new style QIC-113 header");
			PUT8(dst_buf, buf_pos, foffs);
			buf_pos += sizeof(__s64);
		} else {
			__u32 foffs = (__u32)pos->volume_pos;
			if (cp_cnt) foffs += (__u32)blk_sz;
			
			TRACE(ft_t_data_flow, "old style QIC-80MC header");
			PUT4(dst_buf, buf_pos, foffs);
			buf_pos += sizeof(__u32);
		}
	} else if (size_left >= 0) {
		cp_cnt = cluster->cmpr_sz;
		cluster->cmpr_sz = 0;
		buf_pos = cp_cnt + sizeof(__u16);
		PUT2(dst_buf, 0, buf_pos);  
		/* zero unused part of segment. */
		memset(dst_buf + buf_pos, '\0', size_left);
		buf_pos = this_segs_sz;
	} else { /* need entire segment and more space */
		PUT2(dst_buf, 0, 0); 
		cp_cnt = this_segs_sz - sizeof(__u16);
		cluster->cmpr_sz  -= cp_cnt;
		buf_pos = this_segs_sz;
	}
	memcpy(dst_buf + sizeof(__u16), src_buf + cluster->cmpr_pos, cp_cnt);
	cluster->cmpr_pos += cp_cnt;
	TRACE_EXIT buf_pos;
}

/* return-value: the number of bytes removed from the user-buffer
 *               `src_buf' or error code
 *
 *  int *write_cnt           : how much actually has been moved to the
 *                             dst_buf. Need not be initialized when
 *                             function returns with an error code
 *                             (negativ return value) 
 *  __u8 *dst_buf            : kernel space buffer where the has to be
 *                             copied to. The contents of this buffers
 *                             goes to a specific segment.
 *  const int seg_sz         : the size of the segment dst_buf will be
 *                             copied to.
 *  const zft_position *pos  : struct containing the coordinates in
 *                             the current volume (byte position,
 *                             segment id of current segment etc)
 *  const zft_volinfo *volume: information about the current volume,
 *                             size etc.
 *  const __u8 *src_buf      : user space buffer that contains the
 *                             data the user wants to be written to
 *                             tape.
 *  const int req_len        : the amount of data the user wants to be
 *                             written to tape.
 */
static int zftc_write(int *write_cnt,
		      __u8 *dst_buf, const int seg_sz,
		      const __u8 *src_buf, const int req_len,
		      const zft_position *pos, const zft_volinfo *volume)
{
	int req_len_left = req_len;
	int result;
	int len_left;
	int buf_pos_write = pos->seg_byte_pos;
	TRACE_FUN(ft_t_flow);
	
	keep_module_locked = 1;
#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,18)
	MOD_INC_USE_COUNT; /*  sets MOD_VISITED and MOD_USED_ONCE,
			    *  locking is done with can_unload()
			    */
#else
	if (!MOD_IN_USE) {
		MOD_INC_USE_COUNT;
	}
#endif
	/* Note: we do not unlock the module because
	 * there are some values cached in that `cseg' variable.  We
	 * don't don't want to use this information when being
	 * unloaded by kerneld even when the tape is full or when we
	 * cannot allocate enough memory.
	 */
	if (pos->tape_pos > (volume->size-volume->blk_sz-ZFT_CMPR_OVERHEAD)) {
		TRACE_EXIT -ENOSPC;
	}    
	if (zft_allocate_cmpr_mem(volume->blk_sz) < 0) {
		/* should we unlock the module? But it shouldn't 
		 * be locked anyway ...
		 */
		TRACE_EXIT -ENOMEM;
	}
	if (buf_pos_write == 0) { /* fill a new segment */
		*write_cnt = buf_pos_write = start_new_cseg(&cseg,
							    dst_buf,
							    pos,
							    volume->blk_sz,
							    zftc_buf, 
							    seg_sz,
							    volume->qic113);
		if (cseg.cmpr_sz == 0 && cseg.cmpr_pos != 0) {
			req_len_left -= result = volume->blk_sz;
			cseg.cmpr_pos  = 0;
		} else {
			result = 0;
		}
	} else {
		*write_cnt = result = 0;
	}
	
	len_left = seg_sz - buf_pos_write;
	while ((req_len_left > 0) && (len_left > 18)) {
		/* now we have some size left for a new compressed
		 * block.  We know, that the compression buffer is
		 * empty (else there wouldn't be any space left).  
		 */
#if LINUX_VERSION_CODE > KERNEL_VER(2,1,3)
		if (copy_from_user(zftc_scratch_buf, src_buf + result, 
				   volume->blk_sz) != 0) {
			TRACE_EXIT -EFAULT;
		}
#else
		TRACE_CATCH(verify_area(VERIFY_READ, src_buf + result, 
					volume->blk_sz),);
		memcpy_fromfs(zftc_scratch_buf, src_buf + result, 
			      volume->blk_sz);
#endif
		req_len_left -= volume->blk_sz;
		cseg.cmpr_sz = zft_compress(zftc_scratch_buf, volume->blk_sz, 
					    zftc_buf);
		if (cseg.cmpr_sz < 0) {
			cseg.uncmpr = 0x8000;
			cseg.cmpr_sz = -cseg.cmpr_sz;
		} else {
			cseg.uncmpr = 0;
		}
		/* increment "result" iff we copied the entire
		 * compressed block to the zft_deblock_buf 
		 */
		len_left -= sizeof(__u16);
		if (len_left >= cseg.cmpr_sz) {
			len_left -= cseg.count = cseg.cmpr_sz;
			cseg.cmpr_pos = cseg.cmpr_sz = 0;
			result += volume->blk_sz;
		} else {
			cseg.cmpr_sz       -= 
				cseg.cmpr_pos =
				cseg.count    = len_left;
			len_left = 0;
		}
		PUT2(dst_buf, buf_pos_write, cseg.uncmpr | cseg.count);
		buf_pos_write += sizeof(__u16);
		memcpy(dst_buf + buf_pos_write, zftc_buf, cseg.count);
		buf_pos_write += cseg.count;
		*write_cnt    += cseg.count + sizeof(__u16);
		FT_SIGNAL_EXIT(_DONT_BLOCK);
	}
	/* erase the remainder of the segment if less than 18 bytes
	 * left (18 bytes is due to the QIC-80 standard) 
	 */
	if (len_left <= 18) {
		memset(dst_buf + buf_pos_write, '\0', len_left);
		(*write_cnt) += len_left;
	}
	TRACE(ft_t_data_flow, "returning %d", result);
	TRACE_EXIT result;
}   

/* out:
 *
 * int *read_cnt: the number of bytes we removed from the zft_deblock_buf
 *                (result)
 * int *to_do   : the remaining size of the read-request.
 *
 * in:
 *
 * char *buff          : buff is the address of the upper part of the user
 *                       buffer, that hasn't been filled with data yet.

 * int buf_pos_read    : copy of from _ftape_read()
 * int buf_len_read    : copy of buf_len_rd from _ftape_read()
 * char *zft_deblock_buf: zft_deblock_buf
 * unsigned short blk_sz: the block size valid for this volume, may differ
 *                            from zft_blk_sz.
 * int finish: if != 0 means that this is the last segment belonging
 *  to this volume
 * returns the amount of data actually copied to the user-buffer
 *
 * to_do MUST NOT SHRINK except to indicate an EOF. In this case *to_do has to
 * be set to 0 
 */
static int zftc_read (int *read_cnt, 
		      __u8  *dst_buf, const int to_do, 
		      const __u8 *src_buf, const int seg_sz, 
		      const zft_position *pos, const zft_volinfo *volume)
{          
	int uncompressed_sz;         
	int result = 0;
	int remaining = to_do;
	TRACE_FUN(ft_t_flow);

	keep_module_locked = 1;
#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,18)
	MOD_INC_USE_COUNT; /*  sets MOD_VISITED and MOD_USED_ONCE,
			    *  locking is done with can_unload()
			    */
#else
	if (!MOD_IN_USE) {
		MOD_INC_USE_COUNT;
	}
#endif
	TRACE_CATCH(zft_allocate_cmpr_mem(volume->blk_sz),);
	if (pos->seg_byte_pos == 0) {
		/* new segment just read
		 */
		TRACE_CATCH(get_cseg(&cseg, src_buf, seg_sz, volume),
			    *read_cnt = 0);
		memcpy(zftc_buf + cseg.cmpr_pos, src_buf + sizeof(__u16), 
		       cseg.count);
		cseg.cmpr_pos += cseg.count;
		*read_cnt      = cseg.offset;
		DUMP_CMPR_INFO(ft_t_noise /* ft_t_any */, "", &cseg);
	} else {
		*read_cnt = 0;
	}
	/* loop and uncompress until user buffer full or
	 * deblock-buffer empty 
	 */
	TRACE(ft_t_data_flow, "compressed_sz: %d, compos : %d, *read_cnt: %d",
	      cseg.cmpr_sz, cseg.cmpr_pos, *read_cnt);
	while ((cseg.spans == 0) && (remaining > 0)) {
		if (cseg.cmpr_pos  != 0) { /* cmpr buf is not empty */
			uncompressed_sz = 
				zft_uncompress(zftc_buf,
					       cseg.uncmpr == 0x8000 ?
					       -cseg.cmpr_pos : cseg.cmpr_pos,
					       zftc_scratch_buf,
					       volume->blk_sz);
			if (uncompressed_sz != volume->blk_sz) {
				*read_cnt = 0;
				TRACE_ABORT(-EIO, ft_t_warn,
				      "Uncompressed blk (%d) != blk size (%d)",
				      uncompressed_sz, volume->blk_sz);
			}       
#if LINUX_VERSION_CODE > KERNEL_VER(2,1,3)
			if (copy_to_user(dst_buf + result, 
					 zftc_scratch_buf, 
					 uncompressed_sz) != 0 ) {
				TRACE_EXIT -EFAULT;
			}
#else
			memcpy_tofs(dst_buf + result, zftc_scratch_buf, 
				    uncompressed_sz);
#endif
			remaining      -= uncompressed_sz;
			result     += uncompressed_sz;
			cseg.cmpr_pos  = 0;
		}                                              
		if (remaining > 0) {
			get_next_cluster(&cseg, src_buf, seg_sz, 
					 volume->end_seg == pos->seg_pos);
			if (cseg.count != 0) {
				memcpy(zftc_buf, src_buf + cseg.offset,
				       cseg.count);
				cseg.cmpr_pos = cseg.count;
				cseg.offset  += cseg.count;
				*read_cnt += cseg.count + sizeof(__u16);
			} else {
				remaining = 0;
			}
		}
		TRACE(ft_t_data_flow, "\n" 
		      KERN_INFO "compressed_sz: %d\n"
		      KERN_INFO "compos       : %d\n"
		      KERN_INFO "*read_cnt    : %d",
		      cseg.cmpr_sz, cseg.cmpr_pos, *read_cnt);
	}
	if (seg_sz - cseg.offset <= 18) {
		*read_cnt += seg_sz - cseg.offset;
		TRACE(ft_t_data_flow, "expanding read cnt to: %d", *read_cnt);
	}
	TRACE(ft_t_data_flow, "\n"
	      KERN_INFO "segment size   : %d\n"
	      KERN_INFO "read count     : %d\n"
	      KERN_INFO "buf_pos_read   : %d\n"
	      KERN_INFO "remaining      : %d",
		seg_sz, *read_cnt, pos->seg_byte_pos, 
		seg_sz - *read_cnt - pos->seg_byte_pos);
	TRACE(ft_t_data_flow, "returning: %d", result);
	TRACE_EXIT result;
}                

/* seeks to the new data-position. Reads sometimes a segment.
 *  
 * start_seg and end_seg give the boundaries of the current volume
 * blk_sz is the blk_sz of the current volume as stored in the
 * volume label
 *
 * We don't allow blocksizes less than 1024 bytes, therefore we don't need
 * a 64 bit argument for new_block_pos.
 */

static int seek_in_segment(const unsigned int to_do, cmpr_info  *c_info,
			   const char *src_buf, const int seg_sz, 
			   const int seg_pos, const zft_volinfo *volume);
static int slow_seek_forward_until_error(const unsigned int distance,
					 cmpr_info *c_info, zft_position *pos, 
					 const zft_volinfo *volume, __u8 *buf);
static int search_valid_segment(unsigned int segment,
				const unsigned int end_seg,
				const unsigned int max_foffs,
				zft_position *pos, cmpr_info *c_info,
				const zft_volinfo *volume, __u8 *buf);
static int slow_seek_forward(unsigned int dest, cmpr_info *c_info,
			     zft_position *pos, const zft_volinfo *volume,
			     __u8 *buf);
static int compute_seg_pos(unsigned int dest, zft_position *pos,
			   const zft_volinfo *volume);

#define ZFT_SLOW_SEEK_THRESHOLD  10 /* segments */
#define ZFT_FAST_SEEK_MAX_TRIALS 10 /* times */
#define ZFT_FAST_SEEK_BACKUP     10 /* segments */

static int zftc_seek(unsigned int new_block_pos,
		     zft_position *pos, const zft_volinfo *volume, __u8 *buf)
{
	unsigned int dest;
	int limit;
	int distance;
	int result = 0;
	int seg_dist;
	int new_seg;
	int old_seg = 0;
	int fast_seek_trials = 0;
	TRACE_FUN(ft_t_flow);

	keep_module_locked = 1;
#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,18)
	MOD_INC_USE_COUNT; /*  sets MOD_VISITED and MOD_USED_ONCE,
			    *  locking is done with can_unload()
			    */
#else
	if (!MOD_IN_USE) {
		MOD_INC_USE_COUNT;
	}
#endif
	if (new_block_pos == 0) {
		pos->seg_pos      = volume->start_seg;
		pos->seg_byte_pos = 0;
		pos->volume_pos   = 0;
		zftc_reset();
		TRACE_EXIT 0;
	}
	dest = new_block_pos * (volume->blk_sz >> 10);
	distance = dest - (pos->volume_pos >> 10);
	while (distance != 0) {
		seg_dist = compute_seg_pos(dest, pos, volume);
		TRACE(ft_t_noise, "\n"
		      KERN_INFO "seg_dist: %d\n"
		      KERN_INFO "distance: %d\n"
		      KERN_INFO "dest    : %d\n"
		      KERN_INFO "vpos    : %d\n"
		      KERN_INFO "seg_pos : %d\n"
		      KERN_INFO "trials  : %d",
		      seg_dist, distance, dest,
		      (unsigned int)(pos->volume_pos>>10), pos->seg_pos,
		      fast_seek_trials);
		if (distance > 0) {
			if (seg_dist < 0) {
				TRACE(ft_t_bug, "BUG: distance %d > 0, "
				      "segment difference %d < 0",
				      distance, seg_dist);
				result = -EIO;
				break;
			}
			new_seg = pos->seg_pos + seg_dist;
			if (new_seg > volume->end_seg) {
				new_seg = volume->end_seg;
			}
			if (old_seg == new_seg || /* loop */
			    seg_dist <= ZFT_SLOW_SEEK_THRESHOLD ||
			    fast_seek_trials >= ZFT_FAST_SEEK_MAX_TRIALS) {
				TRACE(ft_t_noise, "starting slow seek:\n"
				   KERN_INFO "fast seek failed too often: %s\n"
				   KERN_INFO "near target position      : %s\n"
				   KERN_INFO "looping between two segs  : %s",
				      (fast_seek_trials >= 
				       ZFT_FAST_SEEK_MAX_TRIALS)
				      ? "yes" : "no",
				      (seg_dist <= ZFT_SLOW_SEEK_THRESHOLD) 
				      ? "yes" : "no",
				      (old_seg == new_seg)
				      ? "yes" : "no");
				result = slow_seek_forward(dest, &cseg, 
							   pos, volume, buf);
				break;
			}
			old_seg = new_seg;
			limit = volume->end_seg;
			fast_seek_trials ++;
			for (;;) {
				result = search_valid_segment(new_seg, limit,
							      volume->size,
							      pos, &cseg,
							      volume, buf);
				if (result == 0 || result == -EINTR) {
					break;
				}
				if (new_seg == volume->start_seg) {
					result = -EIO; /* set errror 
							* condition
							*/
					break;
				}
				limit    = new_seg;
				new_seg -= ZFT_FAST_SEEK_BACKUP;
				if (new_seg < volume->start_seg) {
					new_seg = volume->start_seg;
				}
			}
			if (result < 0) {
				TRACE(ft_t_warn,
				      "Couldn't find a readable segment");
				break;
			}
		} else /* if (distance < 0) */ {
			if (seg_dist > 0) {
				TRACE(ft_t_bug, "BUG: distance %d < 0, "
				      "segment difference %d >0",
				      distance, seg_dist);
				result = -EIO;
				break;
			}
			new_seg = pos->seg_pos + seg_dist;
			if (fast_seek_trials > 0 && seg_dist == 0) {
				/* this avoids sticking to the same
				 * segment all the time. On the other hand:
				 * if we got here for the first time, and the
				 * deblock_buffer still contains a valid
				 * segment, then there is no need to skip to 
				 * the previous segment if the desired position
				 * is inside this segment.
				 */
				new_seg --;
			}
			if (new_seg < volume->start_seg) {
				new_seg = volume->start_seg;
			}
			limit   = pos->seg_pos;
			fast_seek_trials ++;
			for (;;) {
				result = search_valid_segment(new_seg, limit,
							      pos->volume_pos,
							      pos, &cseg,
							      volume, buf);
				if (result == 0 || result == -EINTR) {
					break;
				}
				if (new_seg == volume->start_seg) {
					result = -EIO; /* set errror 
							* condition
							*/
					break;
				}
				limit    = new_seg;
				new_seg -= ZFT_FAST_SEEK_BACKUP;
				if (new_seg < volume->start_seg) {
					new_seg = volume->start_seg;
				}
			}
			if (result < 0) {
				TRACE(ft_t_warn,
				      "Couldn't find a readable segment");
				break;
			}
		}
		distance = dest - (pos->volume_pos >> 10);
	}
	TRACE_EXIT result;
}


/*  advance inside the given segment at most to_do bytes.
 *  of kilobytes moved
 */

static int seek_in_segment(const unsigned int to_do,
			   cmpr_info  *c_info,
			   const char *src_buf, 
			   const int seg_sz, 
			   const int seg_pos,
			   const zft_volinfo *volume)
{
	int result = 0;
	int blk_sz = volume->blk_sz >> 10;
	int remaining = to_do;
	TRACE_FUN(ft_t_flow);

	if (c_info->offset == 0) {
		/* new segment just read
		 */
		TRACE_CATCH(get_cseg(c_info, src_buf, seg_sz, volume),);
		c_info->cmpr_pos += c_info->count;
		DUMP_CMPR_INFO(ft_t_noise, "", c_info);
	}
	/* loop and uncompress until user buffer full or
	 * deblock-buffer empty 
	 */
	TRACE(ft_t_noise, "compressed_sz: %d, compos : %d",
	      c_info->cmpr_sz, c_info->cmpr_pos);
	while (c_info->spans == 0 && remaining > 0) {
		if (c_info->cmpr_pos  != 0) { /* cmpr buf is not empty */
			result       += blk_sz;
			remaining    -= blk_sz;
			c_info->cmpr_pos = 0;
		}
		if (remaining > 0) {
			get_next_cluster(c_info, src_buf, seg_sz, 
					 volume->end_seg == seg_pos);
			if (c_info->count != 0) {
				c_info->cmpr_pos = c_info->count;
				c_info->offset  += c_info->count;
			} else {
				break;
			}
		}
		/*  Allow escape from this loop on signal!
		 */
		FT_SIGNAL_EXIT(_DONT_BLOCK);
		DUMP_CMPR_INFO(ft_t_noise, "", c_info);
		TRACE(ft_t_noise, "to_do: %d", remaining);
	}
	if (seg_sz - c_info->offset <= 18) {
		c_info->offset = seg_sz;
	}
	TRACE(ft_t_noise, "\n"
	      KERN_INFO "segment size   : %d\n"
	      KERN_INFO "buf_pos_read   : %d\n"
	      KERN_INFO "remaining      : %d",
	      seg_sz, c_info->offset,
	      seg_sz - c_info->offset);
	TRACE_EXIT result;
}                

static int slow_seek_forward_until_error(const unsigned int distance,
					 cmpr_info *c_info,
					 zft_position *pos, 
					 const zft_volinfo *volume,
					 __u8 *buf)
{
	unsigned int remaining = distance;
	int seg_sz;
	int seg_pos;
	int result;
	TRACE_FUN(ft_t_flow);
	
	seg_pos = pos->seg_pos;
	do {
		TRACE_CATCH(seg_sz = zft_fetch_segment(seg_pos, buf, 
						       FT_RD_AHEAD),);
		/* now we have the contents of the actual segment in
		 * the deblock buffer
		 */
		TRACE_CATCH(result = seek_in_segment(remaining, c_info, buf,
						     seg_sz, seg_pos,volume),);
		remaining        -= result;
		pos->volume_pos  += result<<10;
		pos->seg_pos      = seg_pos;
		pos->seg_byte_pos = c_info->offset;
		seg_pos ++;
		if (seg_pos <= volume->end_seg && c_info->offset == seg_sz) {
			pos->seg_pos ++;
			pos->seg_byte_pos = 0;
			c_info->offset = 0;
		}
		/*  Allow escape from this loop on signal!
		 */
		FT_SIGNAL_EXIT(_DONT_BLOCK);
		TRACE(ft_t_noise, "\n"
		      KERN_INFO "remaining:  %d\n"
		      KERN_INFO "seg_pos:    %d\n"
		      KERN_INFO "end_seg:    %d\n"
		      KERN_INFO "result:     %d",
		      remaining, seg_pos, volume->end_seg, result);  
	} while (remaining > 0 && seg_pos <= volume->end_seg);
	TRACE_EXIT 0;
}

/* return segment id of next segment containing valid data, -EIO otherwise
 */
static int search_valid_segment(unsigned int segment,
				const unsigned int end_seg,
				const unsigned int max_foffs,
				zft_position *pos,
				cmpr_info *c_info,
				const zft_volinfo *volume,
				__u8 *buf)
{
	cmpr_info tmp_info;
	int seg_sz;
	TRACE_FUN(ft_t_flow);
	
	memset(&tmp_info, 0, sizeof(cmpr_info));
	while (segment <= end_seg) {
		FT_SIGNAL_EXIT(_DONT_BLOCK);
		TRACE(ft_t_noise,
		      "Searching readable segment between %d and %d",
		      segment, end_seg);
		seg_sz = zft_fetch_segment(segment, buf, FT_RD_AHEAD);
		if ((seg_sz > 0) &&
		    (get_cseg (&tmp_info, buf, seg_sz, volume) >= 0) &&
		    (tmp_info.foffs != 0 || segment == volume->start_seg)) {
			if ((tmp_info.foffs>>10) > max_foffs) {
				TRACE_ABORT(-EIO, ft_t_noise, "\n"
					    KERN_INFO "cseg.foff: %d\n"
					    KERN_INFO "dest     : %d",
					    (int)(tmp_info.foffs >> 10),
					    max_foffs);
			}
			DUMP_CMPR_INFO(ft_t_noise, "", &tmp_info);
			*c_info           = tmp_info;
			pos->seg_pos      = segment;
			pos->volume_pos   = c_info->foffs;
			pos->seg_byte_pos = c_info->offset;
			TRACE(ft_t_noise, "found segment at %d", segment);
			TRACE_EXIT 0;
		}
		segment++;
	}
	TRACE_EXIT -EIO;
}

static int slow_seek_forward(unsigned int dest,
			     cmpr_info *c_info,
			     zft_position *pos,
			     const zft_volinfo *volume,
			     __u8 *buf)
{
	unsigned int distance;
	int result = 0;
	TRACE_FUN(ft_t_flow);
		
	distance = dest - (pos->volume_pos >> 10);
	while ((distance > 0) &&
	       (result = slow_seek_forward_until_error(distance,
						       c_info,
						       pos,
						       volume,
						       buf)) < 0) {
		if (result == -EINTR) {
			break;
		}
		TRACE(ft_t_noise, "seg_pos: %d", pos->seg_pos);
		/* the failing segment is either pos->seg_pos or
		 * pos->seg_pos + 1. There is no need to further try
		 * that segment, because ftape_read_segment() already
		 * has tried very much to read it. So we start with
		 * following segment, which is pos->seg_pos + 1
		 */
		if(search_valid_segment(pos->seg_pos+1, volume->end_seg, dest,
					pos, c_info,
					volume, buf) < 0) {
			TRACE(ft_t_noise, "search_valid_segment() failed");
			result = -EIO;
			break;
		}
		distance = dest - (pos->volume_pos >> 10);
		result = 0;
		TRACE(ft_t_noise, "segment: %d", pos->seg_pos);
		/* found valid segment, retry the seek */
	}
	TRACE_EXIT result;
}

static int compute_seg_pos(const unsigned int dest,
			   zft_position *pos,
			   const zft_volinfo *volume)
{
	int segment;
	int distance = dest - (pos->volume_pos >> 10);
	unsigned int raw_size;
	unsigned int virt_size;
	unsigned int factor;
	TRACE_FUN(ft_t_flow);

	if (distance >= 0) {
		raw_size  = volume->end_seg - pos->seg_pos + 1;
		virt_size = ((unsigned int)(volume->size>>10) 
			     - (unsigned int)(pos->volume_pos>>10)
			     + FT_SECTORS_PER_SEGMENT - FT_ECC_SECTORS - 1);
		virt_size /= FT_SECTORS_PER_SEGMENT - FT_ECC_SECTORS;
		if (virt_size == 0 || raw_size == 0) {
			TRACE_EXIT 0;
		}
		if (raw_size >= (1<<25)) {
			factor = raw_size/(virt_size>>7);
		} else {
			factor = (raw_size<<7)/virt_size;
		}
		segment = distance/(FT_SECTORS_PER_SEGMENT-FT_ECC_SECTORS);
		segment = (segment * factor)>>7;
	} else {
		raw_size  = pos->seg_pos - volume->start_seg + 1;
		virt_size = ((unsigned int)(pos->volume_pos>>10)
			     + FT_SECTORS_PER_SEGMENT - FT_ECC_SECTORS - 1);
		virt_size /= FT_SECTORS_PER_SEGMENT - FT_ECC_SECTORS;
		if (virt_size == 0 || raw_size == 0) {
			TRACE_EXIT 0;
		}
		if (raw_size >= (1<<25)) {
			factor = raw_size/(virt_size>>7);
		} else {
			factor = (raw_size<<7)/virt_size;
		}
		segment = distance/(FT_SECTORS_PER_SEGMENT-FT_ECC_SECTORS);
	}
	TRACE(ft_t_noise, "factor: %d/%d", factor, 1<<7);
	TRACE_EXIT segment;
}

static struct zft_cmpr_ops cmpr_ops = {
	zftc_write,
	zftc_read,
	zftc_seek,
	zftc_lock,
	zftc_reset,
	zftc_cleanup
};

int zft_compressor_init(void)
{
	TRACE_FUN(ft_t_flow);
	
#ifdef MODULE
	printk(KERN_INFO "zftape compressor v1.00a 970514 for " FTAPE_VERSION "\n");
        if (TRACE_LEVEL >= ft_t_info) {
		printk(
KERN_INFO "(c) 1997 Claus-Justus Heine (claus@momo.math.rwth-aachen.de)\n"
KERN_INFO "Compressor for zftape (lzrw3 algorithm)\n"
KERN_INFO "Compiled for kernel version %s"
#ifdef MODVERSIONS
		" with versioned symbols"
#endif
		"\n", UTS_RELEASE);
        }
#else /* !MODULE */
	/* print a short no-nonsense boot message */
	printk("zftape compressor v1.00a 970514 for Linux " UTS_RELEASE "\n");
	printk("For use with " FTAPE_VERSION "\n");
#endif /* MODULE */
	TRACE(ft_t_info, "zft_compressor_init @ 0x%p", zft_compressor_init);
	TRACE(ft_t_info, "installing compressor for zftape ...");
	TRACE_CATCH(zft_cmpr_register(&cmpr_ops),);
	TRACE_EXIT 0;
}


#ifdef MODULE
#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,18)
MODULE_AUTHOR(
	"(c) 1996, 1997 Claus-Justus Heine (claus@momo.math.rwth-aachen.de");
MODULE_DESCRIPTION(
"Compression routines for zftape. Uses the lzrw3 algorithm by Ross Williams");
#endif

#if LINUX_VERSION_CODE <= KERNEL_VER(1,2,13)
char kernel_version[] = UTS_RELEASE;
#endif
#if LINUX_VERSION_CODE >= KERNEL_VER(2,1,18)
static int can_unload(void)
{
	return keep_module_locked ? -EBUSY : 0;
}
#endif

/* Called by modules package when installing the driver
 */
int init_module(void)
{
	int result;

#if LINUX_VERSION_CODE >= KERNEL_VER(1,1,85)
# if LINUX_VERSION_CODE < KERNEL_VER(2,1,18)
	register_symtab(0); /* remove global ftape symbols */
# else
	if (!mod_member_present(&__this_module, can_unload))
		return -EBUSY;
	__this_module.can_unload = can_unload;
	EXPORT_NO_SYMBOLS;
# endif
#endif
	result = zft_compressor_init();
	keep_module_locked = 0;
	return result;
}

/* Called by modules package when removing the driver 
 */
void cleanup_module(void)
{
	TRACE_FUN(ft_t_flow);

	if (zft_cmpr_unregister() != &cmpr_ops) {
		TRACE(ft_t_info, "failed");
	} else {
		TRACE(ft_t_info, "successful");
	}
	zftc_cleanup();
        printk(KERN_INFO "zft-compressor successfully unloaded.\n");
	TRACE_EXIT;
}
#endif /* MODULE */