aboutsummaryrefslogtreecommitdiff
path: root/fs/ntfs/runlist.c
blob: 8438fb1da219f61ca464dd6d2f4903d6681d12fd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
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
/**
 * runlist.c - NTFS runlist handling code.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2004 Anton Altaparmakov
 * Copyright (c) 2002 Richard Russon
 *
 * This program/include file 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.
 *
 * This program/include file 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 (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "debug.h"
#include "dir.h"
#include "endian.h"
#include "malloc.h"
#include "ntfs.h"

/**
 * ntfs_rl_mm - runlist memmove
 *
 * It is up to the caller to serialize access to the runlist @base.
 */
static inline void ntfs_rl_mm(runlist_element *base, int dst, int src,
		int size)
{
	if (likely((dst != src) && (size > 0)))
		memmove(base + dst, base + src, size * sizeof (*base));
}

/**
 * ntfs_rl_mc - runlist memory copy
 *
 * It is up to the caller to serialize access to the runlists @dstbase and
 * @srcbase.
 */
static inline void ntfs_rl_mc(runlist_element *dstbase, int dst,
		runlist_element *srcbase, int src, int size)
{
	if (likely(size > 0))
		memcpy(dstbase + dst, srcbase + src, size * sizeof(*dstbase));
}

/**
 * ntfs_rl_realloc - Reallocate memory for runlists
 * @rl:		original runlist
 * @old_size:	number of runlist elements in the original runlist @rl
 * @new_size:	number of runlist elements we need space for
 *
 * As the runlists grow, more memory will be required.  To prevent the
 * kernel having to allocate and reallocate large numbers of small bits of
 * memory, this function returns and entire page of memory.
 *
 * It is up to the caller to serialize access to the runlist @rl.
 *
 * N.B.  If the new allocation doesn't require a different number of pages in
 *       memory, the function will return the original pointer.
 *
 * On success, return a pointer to the newly allocated, or recycled, memory.
 * On error, return -errno. The following error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_realloc(runlist_element *rl,
		int old_size, int new_size)
{
	runlist_element *new_rl;

	old_size = PAGE_ALIGN(old_size * sizeof(*rl));
	new_size = PAGE_ALIGN(new_size * sizeof(*rl));
	if (old_size == new_size)
		return rl;

	new_rl = ntfs_malloc_nofs(new_size);
	if (unlikely(!new_rl))
		return ERR_PTR(-ENOMEM);

	if (likely(rl != NULL)) {
		if (unlikely(old_size > new_size))
			old_size = new_size;
		memcpy(new_rl, rl, old_size);
		ntfs_free(rl);
	}
	return new_rl;
}

/**
 * ntfs_are_rl_mergeable - test if two runlists can be joined together
 * @dst:	original runlist
 * @src:	new runlist to test for mergeability with @dst
 *
 * Test if two runlists can be joined together. For this, their VCNs and LCNs
 * must be adjacent.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * Return: TRUE   Success, the runlists can be merged.
 *	   FALSE  Failure, the runlists cannot be merged.
 */
static inline BOOL ntfs_are_rl_mergeable(runlist_element *dst,
		runlist_element *src)
{
	BUG_ON(!dst);
	BUG_ON(!src);

	if ((dst->lcn < 0) || (src->lcn < 0))     /* Are we merging holes? */
		return FALSE;
	if ((dst->lcn + dst->length) != src->lcn) /* Are the runs contiguous? */
		return FALSE;
	if ((dst->vcn + dst->length) != src->vcn) /* Are the runs misaligned? */
		return FALSE;

	return TRUE;
}

/**
 * __ntfs_rl_merge - merge two runlists without testing if they can be merged
 * @dst:	original, destination runlist
 * @src:	new runlist to merge with @dst
 *
 * Merge the two runlists, writing into the destination runlist @dst. The
 * caller must make sure the runlists can be merged or this will corrupt the
 * destination runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 */
static inline void __ntfs_rl_merge(runlist_element *dst, runlist_element *src)
{
	dst->length += src->length;
}

/**
 * ntfs_rl_append - append a runlist after a given element
 * @dst:	original runlist to be worked on
 * @dsize:	number of elements in @dst (including end marker)
 * @src:	runlist to be inserted into @dst
 * @ssize:	number of elements in @src (excluding end marker)
 * @loc:	append the new runlist @src after this element in @dst
 *
 * Append the runlist @src after element @loc in @dst.  Merge the right end of
 * the new runlist, if necessary. Adjust the size of the hole before the
 * appended runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_append(runlist_element *dst,
		int dsize, runlist_element *src, int ssize, int loc)
{
	BOOL right;
	int magic;

	BUG_ON(!dst);
	BUG_ON(!src);

	/* First, check if the right hand end needs merging. */
	right = ntfs_are_rl_mergeable(src + ssize - 1, dst + loc + 1);

	/* Space required: @dst size + @src size, less one if we merged. */
	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - right);
	if (IS_ERR(dst))
		return dst;
	/*
	 * We are guaranteed to succeed from here so can start modifying the
	 * original runlists.
	 */

	/* First, merge the right hand end, if necessary. */
	if (right)
		__ntfs_rl_merge(src + ssize - 1, dst + loc + 1);

	magic = loc + ssize;

	/* Move the tail of @dst out of the way, then copy in @src. */
	ntfs_rl_mm(dst, magic + 1, loc + 1 + right, dsize - loc - 1 - right);
	ntfs_rl_mc(dst, loc + 1, src, 0, ssize);

	/* Adjust the size of the preceding hole. */
	dst[loc].length = dst[loc + 1].vcn - dst[loc].vcn;

	/* We may have changed the length of the file, so fix the end marker */
	if (dst[magic + 1].lcn == LCN_ENOENT)
		dst[magic + 1].vcn = dst[magic].vcn + dst[magic].length;

	return dst;
}

/**
 * ntfs_rl_insert - insert a runlist into another
 * @dst:	original runlist to be worked on
 * @dsize:	number of elements in @dst (including end marker)
 * @src:	new runlist to be inserted
 * @ssize:	number of elements in @src (excluding end marker)
 * @loc:	insert the new runlist @src before this element in @dst
 *
 * Insert the runlist @src before element @loc in the runlist @dst. Merge the
 * left end of the new runlist, if necessary. Adjust the size of the hole
 * after the inserted runlist.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_insert(runlist_element *dst,
		int dsize, runlist_element *src, int ssize, int loc)
{
	BOOL left = FALSE;
	BOOL disc = FALSE;	/* Discontinuity */
	BOOL hole = FALSE;	/* Following a hole */
	int magic;

	BUG_ON(!dst);
	BUG_ON(!src);

	/* disc => Discontinuity between the end of @dst and the start of @src.
	 *	   This means we might need to insert a hole.
	 * hole => @dst ends with a hole or an unmapped region which we can
	 *	   extend to match the discontinuity. */
	if (loc == 0)
		disc = (src[0].vcn > 0);
	else {
		s64 merged_length;

		left = ntfs_are_rl_mergeable(dst + loc - 1, src);

		merged_length = dst[loc - 1].length;
		if (left)
			merged_length += src->length;

		disc = (src[0].vcn > dst[loc - 1].vcn + merged_length);
		if (disc)
			hole = (dst[loc - 1].lcn == LCN_HOLE);
	}

	/* Space required: @dst size + @src size, less one if we merged, plus
	 * one if there was a discontinuity, less one for a trailing hole. */
	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left + disc - hole);
	if (IS_ERR(dst))
		return dst;
	/*
	 * We are guaranteed to succeed from here so can start modifying the
	 * original runlist.
	 */

	if (left)
		__ntfs_rl_merge(dst + loc - 1, src);

	magic = loc + ssize - left + disc - hole;

	/* Move the tail of @dst out of the way, then copy in @src. */
	ntfs_rl_mm(dst, magic, loc, dsize - loc);
	ntfs_rl_mc(dst, loc + disc - hole, src, left, ssize - left);

	/* Adjust the VCN of the last run ... */
	if (dst[magic].lcn <= LCN_HOLE)
		dst[magic].vcn = dst[magic - 1].vcn + dst[magic - 1].length;
	/* ... and the length. */
	if (dst[magic].lcn == LCN_HOLE || dst[magic].lcn == LCN_RL_NOT_MAPPED)
		dst[magic].length = dst[magic + 1].vcn - dst[magic].vcn;

	/* Writing beyond the end of the file and there's a discontinuity. */
	if (disc) {
		if (hole)
			dst[loc - 1].length = dst[loc].vcn - dst[loc - 1].vcn;
		else {
			if (loc > 0) {
				dst[loc].vcn = dst[loc - 1].vcn +
						dst[loc - 1].length;
				dst[loc].length = dst[loc + 1].vcn -
						dst[loc].vcn;
			} else {
				dst[loc].vcn = 0;
				dst[loc].length = dst[loc + 1].vcn;
			}
			dst[loc].lcn = LCN_RL_NOT_MAPPED;
		}

		magic += hole;

		if (dst[magic].lcn == LCN_ENOENT)
			dst[magic].vcn = dst[magic - 1].vcn +
					dst[magic - 1].length;
	}
	return dst;
}

/**
 * ntfs_rl_replace - overwrite a runlist element with another runlist
 * @dst:	original runlist to be worked on
 * @dsize:	number of elements in @dst (including end marker)
 * @src:	new runlist to be inserted
 * @ssize:	number of elements in @src (excluding end marker)
 * @loc:	index in runlist @dst to overwrite with @src
 *
 * Replace the runlist element @dst at @loc with @src. Merge the left and
 * right ends of the inserted runlist, if necessary.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
		int dsize, runlist_element *src, int ssize, int loc)
{
	BOOL left = FALSE;
	BOOL right;
	int magic;

	BUG_ON(!dst);
	BUG_ON(!src);

	/* First, merge the left and right ends, if necessary. */
	right = ntfs_are_rl_mergeable(src + ssize - 1, dst + loc + 1);
	if (loc > 0)
		left = ntfs_are_rl_mergeable(dst + loc - 1, src);

	/* Allocate some space. We'll need less if the left, right, or both
	 * ends were merged. */
	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left - right);
	if (IS_ERR(dst))
		return dst;
	/*
	 * We are guaranteed to succeed from here so can start modifying the
	 * original runlists.
	 */
	if (right)
		__ntfs_rl_merge(src + ssize - 1, dst + loc + 1);
	if (left)
		__ntfs_rl_merge(dst + loc - 1, src);

	/* FIXME: What does this mean? (AIA) */
	magic = loc + ssize - left;

	/* Move the tail of @dst out of the way, then copy in @src. */
	ntfs_rl_mm(dst, magic, loc + right + 1, dsize - loc - right - 1);
	ntfs_rl_mc(dst, loc, src, left, ssize - left);

	/* We may have changed the length of the file, so fix the end marker */
	if (dst[magic].lcn == LCN_ENOENT)
		dst[magic].vcn = dst[magic - 1].vcn + dst[magic - 1].length;
	return dst;
}

/**
 * ntfs_rl_split - insert a runlist into the centre of a hole
 * @dst:	original runlist to be worked on
 * @dsize:	number of elements in @dst (including end marker)
 * @src:	new runlist to be inserted
 * @ssize:	number of elements in @src (excluding end marker)
 * @loc:	index in runlist @dst at which to split and insert @src
 *
 * Split the runlist @dst at @loc into two and insert @new in between the two
 * fragments. No merging of runlists is necessary. Adjust the size of the
 * holes either side.
 *
 * It is up to the caller to serialize access to the runlists @dst and @src.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @dst and @src are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 */
static inline runlist_element *ntfs_rl_split(runlist_element *dst, int dsize,
		runlist_element *src, int ssize, int loc)
{
	BUG_ON(!dst);
	BUG_ON(!src);

	/* Space required: @dst size + @src size + one new hole. */
	dst = ntfs_rl_realloc(dst, dsize, dsize + ssize + 1);
	if (IS_ERR(dst))
		return dst;
	/*
	 * We are guaranteed to succeed from here so can start modifying the
	 * original runlists.
	 */

	/* Move the tail of @dst out of the way, then copy in @src. */
	ntfs_rl_mm(dst, loc + 1 + ssize, loc, dsize - loc);
	ntfs_rl_mc(dst, loc + 1, src, 0, ssize);

	/* Adjust the size of the holes either size of @src. */
	dst[loc].length		= dst[loc+1].vcn       - dst[loc].vcn;
	dst[loc+ssize+1].vcn    = dst[loc+ssize].vcn   + dst[loc+ssize].length;
	dst[loc+ssize+1].length = dst[loc+ssize+2].vcn - dst[loc+ssize+1].vcn;

	return dst;
}

/**
 * ntfs_runlists_merge - merge two runlists into one
 * @drl:	original runlist to be worked on
 * @srl:	new runlist to be merged into @drl
 *
 * First we sanity check the two runlists @srl and @drl to make sure that they
 * are sensible and can be merged. The runlist @srl must be either after the
 * runlist @drl or completely within a hole (or unmapped region) in @drl.
 *
 * It is up to the caller to serialize access to the runlists @drl and @srl.
 *
 * Merging of runlists is necessary in two cases:
 *   1. When attribute lists are used and a further extent is being mapped.
 *   2. When new clusters are allocated to fill a hole or extend a file.
 *
 * There are four possible ways @srl can be merged. It can:
 *	- be inserted at the beginning of a hole,
 *	- split the hole in two and be inserted between the two fragments,
 *	- be appended at the end of a hole, or it can
 *	- replace the whole hole.
 * It can also be appended to the end of the runlist, which is just a variant
 * of the insert case.
 *
 * On success, return a pointer to the new, combined, runlist. Note, both
 * runlists @drl and @srl are deallocated before returning so you cannot use
 * the pointers for anything any more. (Strictly speaking the returned runlist
 * may be the same as @dst but this is irrelevant.)
 *
 * On error, return -errno. Both runlists are left unmodified. The following
 * error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EINVAL	- Invalid parameters were passed in.
 *	-ERANGE	- The runlists overlap and cannot be merged.
 */
runlist_element *ntfs_runlists_merge(runlist_element *drl,
		runlist_element *srl)
{
	int di, si;		/* Current index into @[ds]rl. */
	int sstart;		/* First index with lcn > LCN_RL_NOT_MAPPED. */
	int dins;		/* Index into @drl at which to insert @srl. */
	int dend, send;		/* Last index into @[ds]rl. */
	int dfinal, sfinal;	/* The last index into @[ds]rl with
				   lcn >= LCN_HOLE. */
	int marker = 0;
	VCN marker_vcn = 0;

#ifdef DEBUG
	ntfs_debug("dst:");
	ntfs_debug_dump_runlist(drl);
	ntfs_debug("src:");
	ntfs_debug_dump_runlist(srl);
#endif

	/* Check for silly calling... */
	if (unlikely(!srl))
		return drl;
	if (IS_ERR(srl) || IS_ERR(drl))
		return ERR_PTR(-EINVAL);

	/* Check for the case where the first mapping is being done now. */
	if (unlikely(!drl)) {
		drl = srl;
		/* Complete the source runlist if necessary. */
		if (unlikely(drl[0].vcn)) {
			/* Scan to the end of the source runlist. */
			for (dend = 0; likely(drl[dend].length); dend++)
				;
			drl = ntfs_rl_realloc(drl, dend, dend + 1);
			if (IS_ERR(drl))
				return drl;
			/* Insert start element at the front of the runlist. */
			ntfs_rl_mm(drl, 1, 0, dend);
			drl[0].vcn = 0;
			drl[0].lcn = LCN_RL_NOT_MAPPED;
			drl[0].length = drl[1].vcn;
		}
		goto finished;
	}

	si = di = 0;

	/* Skip any unmapped start element(s) in the source runlist. */
	while (srl[si].length && srl[si].lcn < LCN_HOLE)
		si++;

	/* Can't have an entirely unmapped source runlist. */
	BUG_ON(!srl[si].length);

	/* Record the starting points. */
	sstart = si;

	/*
	 * Skip forward in @drl until we reach the position where @srl needs to
	 * be inserted. If we reach the end of @drl, @srl just needs to be
	 * appended to @drl.
	 */
	for (; drl[di].length; di++) {
		if (drl[di].vcn + drl[di].length > srl[sstart].vcn)
			break;
	}
	dins = di;

	/* Sanity check for illegal overlaps. */
	if ((drl[di].vcn == srl[si].vcn) && (drl[di].lcn >= 0) &&
			(srl[si].lcn >= 0)) {
		ntfs_error(NULL, "Run lists overlap. Cannot merge!");
		return ERR_PTR(-ERANGE);
	}

	/* Scan to the end of both runlists in order to know their sizes. */
	for (send = si; srl[send].length; send++)
		;
	for (dend = di; drl[dend].length; dend++)
		;

	if (srl[send].lcn == LCN_ENOENT)
		marker_vcn = srl[marker = send].vcn;

	/* Scan to the last element with lcn >= LCN_HOLE. */
	for (sfinal = send; sfinal >= 0 && srl[sfinal].lcn < LCN_HOLE; sfinal--)
		;
	for (dfinal = dend; dfinal >= 0 && drl[dfinal].lcn < LCN_HOLE; dfinal--)
		;

	{
	BOOL start;
	BOOL finish;
	int ds = dend + 1;		/* Number of elements in drl & srl */
	int ss = sfinal - sstart + 1;

	start  = ((drl[dins].lcn <  LCN_RL_NOT_MAPPED) ||    /* End of file   */
		  (drl[dins].vcn == srl[sstart].vcn));	     /* Start of hole */
	finish = ((drl[dins].lcn >= LCN_RL_NOT_MAPPED) &&    /* End of file   */
		 ((drl[dins].vcn + drl[dins].length) <=      /* End of hole   */
		  (srl[send - 1].vcn + srl[send - 1].length)));

	/* Or we'll lose an end marker */
	if (start && finish && (drl[dins].length == 0))
		ss++;
	if (marker && (drl[dins].vcn + drl[dins].length > srl[send - 1].vcn))
		finish = FALSE;
#if 0
	ntfs_debug("dfinal = %i, dend = %i", dfinal, dend);
	ntfs_debug("sstart = %i, sfinal = %i, send = %i", sstart, sfinal, send);
	ntfs_debug("start = %i, finish = %i", start, finish);
	ntfs_debug("ds = %i, ss = %i, dins = %i", ds, ss, dins);
#endif
	if (start) {
		if (finish)
			drl = ntfs_rl_replace(drl, ds, srl + sstart, ss, dins);
		else
			drl = ntfs_rl_insert(drl, ds, srl + sstart, ss, dins);
	} else {
		if (finish)
			drl = ntfs_rl_append(drl, ds, srl + sstart, ss, dins);
		else
			drl = ntfs_rl_split(drl, ds, srl + sstart, ss, dins);
	}
	if (IS_ERR(drl)) {
		ntfs_error(NULL, "Merge failed.");
		return drl;
	}
	ntfs_free(srl);
	if (marker) {
		ntfs_debug("Triggering marker code.");
		for (ds = dend; drl[ds].length; ds++)
			;
		/* We only need to care if @srl ended after @drl. */
		if (drl[ds].vcn <= marker_vcn) {
			int slots = 0;

			if (drl[ds].vcn == marker_vcn) {
				ntfs_debug("Old marker = 0x%llx, replacing "
						"with LCN_ENOENT.",
						(unsigned long long)
						drl[ds].lcn);
				drl[ds].lcn = LCN_ENOENT;
				goto finished;
			}
			/*
			 * We need to create an unmapped runlist element in
			 * @drl or extend an existing one before adding the
			 * ENOENT terminator.
			 */
			if (drl[ds].lcn == LCN_ENOENT) {
				ds--;
				slots = 1;
			}
			if (drl[ds].lcn != LCN_RL_NOT_MAPPED) {
				/* Add an unmapped runlist element. */
				if (!slots) {
					/* FIXME/TODO: We need to have the
					 * extra memory already! (AIA) */
					drl = ntfs_rl_realloc(drl, ds, ds + 2);
					if (!drl)
						goto critical_error;
					slots = 2;
				}
				ds++;
				/* Need to set vcn if it isn't set already. */
				if (slots != 1)
					drl[ds].vcn = drl[ds - 1].vcn +
							drl[ds - 1].length;
				drl[ds].lcn = LCN_RL_NOT_MAPPED;
				/* We now used up a slot. */
				slots--;
			}
			drl[ds].length = marker_vcn - drl[ds].vcn;
			/* Finally add the ENOENT terminator. */
			ds++;
			if (!slots) {
				/* FIXME/TODO: We need to have the extra
				 * memory already! (AIA) */
				drl = ntfs_rl_realloc(drl, ds, ds + 1);
				if (!drl)
					goto critical_error;
			}
			drl[ds].vcn = marker_vcn;
			drl[ds].lcn = LCN_ENOENT;
			drl[ds].length = (s64)0;
		}
	}
	}

finished:
	/* The merge was completed successfully. */
	ntfs_debug("Merged runlist:");
	ntfs_debug_dump_runlist(drl);
	return drl;

critical_error:
	/* Critical error! We cannot afford to fail here. */
	ntfs_error(NULL, "Critical error! Not enough memory.");
	panic("NTFS: Cannot continue.");
}

/**
 * ntfs_mapping_pairs_decompress - convert mapping pairs array to runlist
 * @vol:	ntfs volume on which the attribute resides
 * @attr:	attribute record whose mapping pairs array to decompress
 * @old_rl:	optional runlist in which to insert @attr's runlist
 *
 * It is up to the caller to serialize access to the runlist @old_rl.
 *
 * Decompress the attribute @attr's mapping pairs array into a runlist. On
 * success, return the decompressed runlist.
 *
 * If @old_rl is not NULL, decompressed runlist is inserted into the
 * appropriate place in @old_rl and the resultant, combined runlist is
 * returned. The original @old_rl is deallocated.
 *
 * On error, return -errno. @old_rl is left unmodified in that case.
 *
 * The following error codes are defined:
 *	-ENOMEM	- Not enough memory to allocate runlist array.
 *	-EIO	- Corrupt runlist.
 *	-EINVAL	- Invalid parameters were passed in.
 *	-ERANGE	- The two runlists overlap.
 *
 * FIXME: For now we take the conceptionally simplest approach of creating the
 * new runlist disregarding the already existing one and then splicing the
 * two into one, if that is possible (we check for overlap and discard the new
 * runlist if overlap present before returning ERR_PTR(-ERANGE)).
 */
runlist_element *ntfs_mapping_pairs_decompress(const ntfs_volume *vol,
		const ATTR_RECORD *attr, runlist_element *old_rl)
{
	VCN vcn;		/* Current vcn. */
	LCN lcn;		/* Current lcn. */
	s64 deltaxcn;		/* Change in [vl]cn. */
	runlist_element *rl;	/* The output runlist. */
	u8 *buf;		/* Current position in mapping pairs array. */
	u8 *attr_end;		/* End of attribute. */
	int rlsize;		/* Size of runlist buffer. */
	u16 rlpos;		/* Current runlist position in units of
				   runlist_elements. */
	u8 b;			/* Current byte offset in buf. */

#ifdef DEBUG
	/* Make sure attr exists and is non-resident. */
	if (!attr || !attr->non_resident || sle64_to_cpu(
			attr->data.non_resident.lowest_vcn) < (VCN)0) {
		ntfs_error(vol->sb, "Invalid arguments.");
		return ERR_PTR(-EINVAL);
	}
#endif
	/* Start at vcn = lowest_vcn and lcn 0. */
	vcn = sle64_to_cpu(attr->data.non_resident.lowest_vcn);
	lcn = 0;
	/* Get start of the mapping pairs array. */
	buf = (u8*)attr + le16_to_cpu(
			attr->data.non_resident.mapping_pairs_offset);
	attr_end = (u8*)attr + le32_to_cpu(attr->length);
	if (unlikely(buf < (u8*)attr || buf > attr_end)) {
		ntfs_error(vol->sb, "Corrupt attribute.");
		return ERR_PTR(-EIO);
	}
	/* Current position in runlist array. */
	rlpos = 0;
	/* Allocate first page and set current runlist size to one page. */
	rl = ntfs_malloc_nofs(rlsize = PAGE_SIZE);
	if (unlikely(!rl))
		return ERR_PTR(-ENOMEM);
	/* Insert unmapped starting element if necessary. */
	if (vcn) {
		rl->vcn = 0;
		rl->lcn = LCN_RL_NOT_MAPPED;
		rl->length = vcn;
		rlpos++;
	}
	while (buf < attr_end && *buf) {
		/*
		 * Allocate more memory if needed, including space for the
		 * not-mapped and terminator elements. ntfs_malloc_nofs()
		 * operates on whole pages only.
		 */
		if (((rlpos + 3) * sizeof(*old_rl)) > rlsize) {
			runlist_element *rl2;

			rl2 = ntfs_malloc_nofs(rlsize + (int)PAGE_SIZE);
			if (unlikely(!rl2)) {
				ntfs_free(rl);
				return ERR_PTR(-ENOMEM);
			}
			memcpy(rl2, rl, rlsize);
			ntfs_free(rl);
			rl = rl2;
			rlsize += PAGE_SIZE;
		}
		/* Enter the current vcn into the current runlist element. */
		rl[rlpos].vcn = vcn;
		/*
		 * Get the change in vcn, i.e. the run length in clusters.
		 * Doing it this way ensures that we signextend negative values.
		 * A negative run length doesn't make any sense, but hey, I
		 * didn't make up the NTFS specs and Windows NT4 treats the run
		 * length as a signed value so that's how it is...
		 */
		b = *buf & 0xf;
		if (b) {
			if (unlikely(buf + b > attr_end))
				goto io_error;
			for (deltaxcn = (s8)buf[b--]; b; b--)
				deltaxcn = (deltaxcn << 8) + buf[b];
		} else { /* The length entry is compulsory. */
			ntfs_error(vol->sb, "Missing length entry in mapping "
					"pairs array.");
			deltaxcn = (s64)-1;
		}
		/*
		 * Assume a negative length to indicate data corruption and
		 * hence clean-up and return NULL.
		 */
		if (unlikely(deltaxcn < 0)) {
			ntfs_error(vol->sb, "Invalid length in mapping pairs "
					"array.");
			goto err_out;
		}
		/*
		 * Enter the current run length into the current runlist
		 * element.
		 */
		rl[rlpos].length = deltaxcn;
		/* Increment the current vcn by the current run length. */
		vcn += deltaxcn;
		/*
		 * There might be no lcn change at all, as is the case for
		 * sparse clusters on NTFS 3.0+, in which case we set the lcn
		 * to LCN_HOLE.
		 */
		if (!(*buf & 0xf0))
			rl[rlpos].lcn = LCN_HOLE;
		else {
			/* Get the lcn change which really can be negative. */
			u8 b2 = *buf & 0xf;
			b = b2 + ((*buf >> 4) & 0xf);
			if (buf + b > attr_end)
				goto io_error;
			for (deltaxcn = (s8)buf[b--]; b > b2; b--)
				deltaxcn = (deltaxcn << 8) + buf[b];
			/* Change the current lcn to its new value. */
			lcn += deltaxcn;
#ifdef DEBUG
			/*
			 * On NTFS 1.2-, apparently can have lcn == -1 to
			 * indicate a hole. But we haven't verified ourselves
			 * whether it is really the lcn or the deltaxcn that is
			 * -1. So if either is found give us a message so we
			 * can investigate it further!
			 */
			if (vol->major_ver < 3) {
				if (unlikely(deltaxcn == (LCN)-1))
					ntfs_error(vol->sb, "lcn delta == -1");
				if (unlikely(lcn == (LCN)-1))
					ntfs_error(vol->sb, "lcn == -1");
			}
#endif
			/* Check lcn is not below -1. */
			if (unlikely(lcn < (LCN)-1)) {
				ntfs_error(vol->sb, "Invalid LCN < -1 in "
						"mapping pairs array.");
				goto err_out;
			}
			/* Enter the current lcn into the runlist element. */
			rl[rlpos].lcn = lcn;
		}
		/* Get to the next runlist element. */
		rlpos++;
		/* Increment the buffer position to the next mapping pair. */
		buf += (*buf & 0xf) + ((*buf >> 4) & 0xf) + 1;
	}
	if (unlikely(buf >= attr_end))
		goto io_error;
	/*
	 * If there is a highest_vcn specified, it must be equal to the final
	 * vcn in the runlist - 1, or something has gone badly wrong.
	 */
	deltaxcn = sle64_to_cpu(attr->data.non_resident.highest_vcn);
	if (unlikely(deltaxcn && vcn - 1 != deltaxcn)) {
mpa_err:
		ntfs_error(vol->sb, "Corrupt mapping pairs array in "
				"non-resident attribute.");
		goto err_out;
	}
	/* Setup not mapped runlist element if this is the base extent. */
	if (!attr->data.non_resident.lowest_vcn) {
		VCN max_cluster;

		max_cluster = (sle64_to_cpu(
				attr->data.non_resident.allocated_size) +
				vol->cluster_size - 1) >>
				vol->cluster_size_bits;
		/*
		 * If there is a difference between the highest_vcn and the
		 * highest cluster, the runlist is either corrupt or, more
		 * likely, there are more extents following this one.
		 */
		if (deltaxcn < --max_cluster) {
			ntfs_debug("More extents to follow; deltaxcn = 0x%llx, "
					"max_cluster = 0x%llx",
					(unsigned long long)deltaxcn,
					(unsigned long long)max_cluster);
			rl[rlpos].vcn = vcn;
			vcn += rl[rlpos].length = max_cluster - deltaxcn;
			rl[rlpos].lcn = LCN_RL_NOT_MAPPED;
			rlpos++;
		} else if (unlikely(deltaxcn > max_cluster)) {
			ntfs_error(vol->sb, "Corrupt attribute. deltaxcn = "
					"0x%llx, max_cluster = 0x%llx",
					(unsigned long long)deltaxcn,
					(unsigned long long)max_cluster);
			goto mpa_err;
		}
		rl[rlpos].lcn = LCN_ENOENT;
	} else /* Not the base extent. There may be more extents to follow. */
		rl[rlpos].lcn = LCN_RL_NOT_MAPPED;

	/* Setup terminating runlist element. */
	rl[rlpos].vcn = vcn;
	rl[rlpos].length = (s64)0;
	/* If no existing runlist was specified, we are done. */
	if (!old_rl) {
		ntfs_debug("Mapping pairs array successfully decompressed:");
		ntfs_debug_dump_runlist(rl);
		return rl;
	}
	/* Now combine the new and old runlists checking for overlaps. */
	old_rl = ntfs_runlists_merge(old_rl, rl);
	if (likely(!IS_ERR(old_rl)))
		return old_rl;
	ntfs_free(rl);
	ntfs_error(vol->sb, "Failed to merge runlists.");
	return old_rl;
io_error:
	ntfs_error(vol->sb, "Corrupt attribute.");
err_out:
	ntfs_free(rl);
	return ERR_PTR(-EIO);
}

/**
 * ntfs_rl_vcn_to_lcn - convert a vcn into a lcn given a runlist
 * @rl:		runlist to use for conversion
 * @vcn:	vcn to convert
 *
 * Convert the virtual cluster number @vcn of an attribute into a logical
 * cluster number (lcn) of a device using the runlist @rl to map vcns to their
 * corresponding lcns.
 *
 * It is up to the caller to serialize access to the runlist @rl.
 *
 * Since lcns must be >= 0, we use negative return values with special meaning:
 *
 * Return value			Meaning / Description
 * ==================================================
 *  -1 = LCN_HOLE		Hole / not allocated on disk.
 *  -2 = LCN_RL_NOT_MAPPED	This is part of the runlist which has not been
 *				inserted into the runlist yet.
 *  -3 = LCN_ENOENT		There is no such vcn in the attribute.
 *
 * Locking: - The caller must have locked the runlist (for reading or writing).
 *	    - This function does not touch the lock.
 */
LCN ntfs_rl_vcn_to_lcn(const runlist_element *rl, const VCN vcn)
{
	int i;

	BUG_ON(vcn < 0);
	/*
	 * If rl is NULL, assume that we have found an unmapped runlist. The
	 * caller can then attempt to map it and fail appropriately if
	 * necessary.
	 */
	if (unlikely(!rl))
		return LCN_RL_NOT_MAPPED;

	/* Catch out of lower bounds vcn. */
	if (unlikely(vcn < rl[0].vcn))
		return LCN_ENOENT;

	for (i = 0; likely(rl[i].length); i++) {
		if (unlikely(vcn < rl[i+1].vcn)) {
			if (likely(rl[i].lcn >= (LCN)0))
				return rl[i].lcn + (vcn - rl[i].vcn);
			return rl[i].lcn;
		}
	}
	/*
	 * The terminator element is setup to the correct value, i.e. one of
	 * LCN_HOLE, LCN_RL_NOT_MAPPED, or LCN_ENOENT.
	 */
	if (likely(rl[i].lcn < (LCN)0))
		return rl[i].lcn;
	/* Just in case... We could replace this with BUG() some day. */
	return LCN_ENOENT;
}

/**
 * ntfs_get_nr_significant_bytes - get number of bytes needed to store a number
 * @n:		number for which to get the number of bytes for
 *
 * Return the number of bytes required to store @n unambiguously as
 * a signed number.
 *
 * This is used in the context of the mapping pairs array to determine how
 * many bytes will be needed in the array to store a given logical cluster
 * number (lcn) or a specific run length.
 *
 * Return the number of bytes written.  This function cannot fail.
 */
static inline int ntfs_get_nr_significant_bytes(const s64 n)
{
	s64 l = n;
	int i;
	s8 j;

	i = 0;
	do {
		l >>= 8;
		i++;
	} while (l != 0 && l != -1);
	j = (n >> 8 * (i - 1)) & 0xff;
	/* If the sign bit is wrong, we need an extra byte. */
	if ((n < 0 && j >= 0) || (n > 0 && j < 0))
		i++;
	return i;
}

/**
 * ntfs_get_size_for_mapping_pairs - get bytes needed for mapping pairs array
 * @vol:	ntfs volume (needed for the ntfs version)
 * @rl:		locked runlist to determine the size of the mapping pairs of
 * @start_vcn:	vcn at which to start the mapping pairs array
 *
 * Walk the locked runlist @rl and calculate the size in bytes of the mapping
 * pairs array corresponding to the runlist @rl, starting at vcn @start_vcn.
 * This for example allows us to allocate a buffer of the right size when
 * building the mapping pairs array.
 *
 * If @rl is NULL, just return 1 (for the single terminator byte).
 *
 * Return the calculated size in bytes on success.  On error, return -errno.
 * The following error codes are defined:
 *	-EINVAL	- Run list contains unmapped elements.  Make sure to only pass
 *		  fully mapped runlists to this function.
 *	-EIO	- The runlist is corrupt.
 *
 * Locking: @rl must be locked on entry (either for reading or writing), it
 *	    remains locked throughout, and is left locked upon return.
 */
int ntfs_get_size_for_mapping_pairs(const ntfs_volume *vol,
		const runlist_element *rl, const VCN start_vcn)
{
	LCN prev_lcn;
	int rls;

	BUG_ON(start_vcn < 0);
	if (!rl) {
		BUG_ON(start_vcn);
		return 1;
	}
	/* Skip to runlist element containing @start_vcn. */
	while (rl->length && start_vcn >= rl[1].vcn)
		rl++;
	if ((!rl->length && start_vcn > rl->vcn) || start_vcn < rl->vcn)
		return -EINVAL;
	prev_lcn = 0;
	/* Always need the termining zero byte. */
	rls = 1;
	/* Do the first partial run if present. */
	if (start_vcn > rl->vcn) {
		s64 delta;

		/* We know rl->length != 0 already. */
		if (rl->length < 0 || rl->lcn < LCN_HOLE)
			goto err_out;
		delta = start_vcn - rl->vcn;
		/* Header byte + length. */
		rls += 1 + ntfs_get_nr_significant_bytes(rl->length - delta);
		/*
		 * If the logical cluster number (lcn) denotes a hole and we
		 * are on NTFS 3.0+, we don't store it at all, i.e. we need
		 * zero space.  On earlier NTFS versions we just store the lcn.
		 * Note: this assumes that on NTFS 1.2-, holes are stored with
		 * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
		 */
		if (rl->lcn >= 0 || vol->major_ver < 3) {
			prev_lcn = rl->lcn;
			if (rl->lcn >= 0)
				prev_lcn += delta;
			/* Change in lcn. */
			rls += ntfs_get_nr_significant_bytes(prev_lcn);
		}
		/* Go to next runlist element. */
		rl++;
	}
	/* Do the full runs. */
	for (; rl->length; rl++) {
		if (rl->length < 0 || rl->lcn < LCN_HOLE)
			goto err_out;
		/* Header byte + length. */
		rls += 1 + ntfs_get_nr_significant_bytes(rl->length);
		/*
		 * If the logical cluster number (lcn) denotes a hole and we
		 * are on NTFS 3.0+, we don't store it at all, i.e. we need
		 * zero space.  On earlier NTFS versions we just store the lcn.
		 * Note: this assumes that on NTFS 1.2-, holes are stored with
		 * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
		 */
		if (rl->lcn >= 0 || vol->major_ver < 3) {
			/* Change in lcn. */
			rls += ntfs_get_nr_significant_bytes(rl->lcn -
					prev_lcn);
			prev_lcn = rl->lcn;
		}
	}
	return rls;
err_out:
	if (rl->lcn == LCN_RL_NOT_MAPPED)
		rls = -EINVAL;
	else
		rls = -EIO;
	return rls;
}

/**
 * ntfs_write_significant_bytes - write the significant bytes of a number
 * @dst:	destination buffer to write to
 * @dst_max:	pointer to last byte of destination buffer for bounds checking
 * @n:		number whose significant bytes to write
 *
 * Store in @dst, the minimum bytes of the number @n which are required to
 * identify @n unambiguously as a signed number, taking care not to exceed
 * @dest_max, the maximum position within @dst to which we are allowed to
 * write.
 *
 * This is used when building the mapping pairs array of a runlist to compress
 * a given logical cluster number (lcn) or a specific run length to the minumum
 * size possible.
 *
 * Return the number of bytes written on success.  On error, i.e. the
 * destination buffer @dst is too small, return -ENOSPC.
 */
static inline int ntfs_write_significant_bytes(s8 *dst, const s8 *dst_max,
		const s64 n)
{
	s64 l = n;
	int i;
	s8 j;

	i = 0;
	do {
		if (dst > dst_max)
			goto err_out;
		*dst++ = l & 0xffll;
		l >>= 8;
		i++;
	} while (l != 0 && l != -1);
	j = (n >> 8 * (i - 1)) & 0xff;
	/* If the sign bit is wrong, we need an extra byte. */
	if (n < 0 && j >= 0) {
		if (dst > dst_max)
			goto err_out;
		i++;
		*dst = (s8)-1;
	} else if (n > 0 && j < 0) {
		if (dst > dst_max)
			goto err_out;
		i++;
		*dst = (s8)0;
	}
	return i;
err_out:
	return -ENOSPC;
}

/**
 * ntfs_mapping_pairs_build - build the mapping pairs array from a runlist
 * @vol:	ntfs volume (needed for the ntfs version)
 * @dst:	destination buffer to which to write the mapping pairs array
 * @dst_len:	size of destination buffer @dst in bytes
 * @rl:		locked runlist for which to build the mapping pairs array
 * @start_vcn:	vcn at which to start the mapping pairs array
 * @stop_vcn:	first vcn outside destination buffer on success or -ENOSPC
 *
 * Create the mapping pairs array from the locked runlist @rl, starting at vcn
 * @start_vcn and save the array in @dst.  @dst_len is the size of @dst in
 * bytes and it should be at least equal to the value obtained by calling
 * ntfs_get_size_for_mapping_pairs().
 *
 * If @rl is NULL, just write a single terminator byte to @dst.
 *
 * On success or -ENOSPC error, if @stop_vcn is not NULL, *@stop_vcn is set to
 * the first vcn outside the destination buffer.  Note that on error, @dst has
 * been filled with all the mapping pairs that will fit, thus it can be treated
 * as partial success, in that a new attribute extent needs to be created or
 * the next extent has to be used and the mapping pairs build has to be
 * continued with @start_vcn set to *@stop_vcn.
 *
 * Return 0 on success and -errno on error.  The following error codes are
 * defined:
 *	-EINVAL	- Run list contains unmapped elements.  Make sure to only pass
 *		  fully mapped runlists to this function.
 *	-EIO	- The runlist is corrupt.
 *	-ENOSPC	- The destination buffer is too small.
 *
 * Locking: @rl must be locked on entry (either for reading or writing), it
 *	    remains locked throughout, and is left locked upon return.
 */
int ntfs_mapping_pairs_build(const ntfs_volume *vol, s8 *dst,
		const int dst_len, const runlist_element *rl,
		const VCN start_vcn, VCN *const stop_vcn)
{
	LCN prev_lcn;
	s8 *dst_max, *dst_next;
	int err = -ENOSPC;
	s8 len_len, lcn_len;

	BUG_ON(start_vcn < 0);
	BUG_ON(dst_len < 1);
	if (!rl) {
		BUG_ON(start_vcn);
		if (stop_vcn)
			*stop_vcn = 0;
		/* Terminator byte. */
		*dst = 0;
		return 0;
	}
	/* Skip to runlist element containing @start_vcn. */
	while (rl->length && start_vcn >= rl[1].vcn)
		rl++;
	if ((!rl->length && start_vcn > rl->vcn) || start_vcn < rl->vcn)
		return -EINVAL;
	/*
	 * @dst_max is used for bounds checking in
	 * ntfs_write_significant_bytes().
	 */
	dst_max = dst + dst_len - 1;
	prev_lcn = 0;
	/* Do the first partial run if present. */
	if (start_vcn > rl->vcn) {
		s64 delta;

		/* We know rl->length != 0 already. */
		if (rl->length < 0 || rl->lcn < LCN_HOLE)
			goto err_out;
		delta = start_vcn - rl->vcn;
		/* Write length. */
		len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
				rl->length - delta);
		if (len_len < 0)
			goto size_err;
		/*
		 * If the logical cluster number (lcn) denotes a hole and we
		 * are on NTFS 3.0+, we don't store it at all, i.e. we need
		 * zero space.  On earlier NTFS versions we just write the lcn
		 * change.  FIXME: Do we need to write the lcn change or just
		 * the lcn in that case?  Not sure as I have never seen this
		 * case on NT4. - We assume that we just need to write the lcn
		 * change until someone tells us otherwise... (AIA)
		 */
		if (rl->lcn >= 0 || vol->major_ver < 3) {
			prev_lcn = rl->lcn;
			if (rl->lcn >= 0)
				prev_lcn += delta;
			/* Write change in lcn. */
			lcn_len = ntfs_write_significant_bytes(dst + 1 +
					len_len, dst_max, prev_lcn);
			if (lcn_len < 0)
				goto size_err;
		} else
			lcn_len = 0;
		dst_next = dst + len_len + lcn_len + 1;
		if (dst_next > dst_max)
			goto size_err;
		/* Update header byte. */
		*dst = lcn_len << 4 | len_len;
		/* Position at next mapping pairs array element. */
		dst = dst_next;
		/* Go to next runlist element. */
		rl++;
	}
	/* Do the full runs. */
	for (; rl->length; rl++) {
		if (rl->length < 0 || rl->lcn < LCN_HOLE)
			goto err_out;
		/* Write length. */
		len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
				rl->length);
		if (len_len < 0)
			goto size_err;
		/*
		 * If the logical cluster number (lcn) denotes a hole and we
		 * are on NTFS 3.0+, we don't store it at all, i.e. we need
		 * zero space.  On earlier NTFS versions we just write the lcn
		 * change.  FIXME: Do we need to write the lcn change or just
		 * the lcn in that case?  Not sure as I have never seen this
		 * case on NT4. - We assume that we just need to write the lcn
		 * change until someone tells us otherwise... (AIA)
		 */
		if (rl->lcn >= 0 || vol->major_ver < 3) {
			/* Write change in lcn. */
			lcn_len = ntfs_write_significant_bytes(dst + 1 +
					len_len, dst_max, rl->lcn - prev_lcn);
			if (lcn_len < 0)
				goto size_err;
			prev_lcn = rl->lcn;
		} else
			lcn_len = 0;
		dst_next = dst + len_len + lcn_len + 1;
		if (dst_next > dst_max)
			goto size_err;
		/* Update header byte. */
		*dst = lcn_len << 4 | len_len;
		/* Position at next mapping pairs array element. */
		dst = dst_next;
	}
	/* Success. */
	err = 0;
size_err:
	/* Set stop vcn. */
	if (stop_vcn)
		*stop_vcn = rl->vcn;
	/* Add terminator byte. */
	*dst = 0;
	return err;
err_out:
	if (rl->lcn == LCN_RL_NOT_MAPPED)
		err = -EINVAL;
	else
		err = -EIO;
	return err;
}

/**
 * ntfs_rl_truncate_nolock - truncate a runlist starting at a specified vcn
 * @runlist:	runlist to truncate
 * @new_length:	the new length of the runlist in VCNs
 *
 * Truncate the runlist described by @runlist as well as the memory buffer
 * holding the runlist elements to a length of @new_length VCNs.
 *
 * If @new_length lies within the runlist, the runlist elements with VCNs of
 * @new_length and above are discarded.
 *
 * If @new_length lies beyond the runlist, a sparse runlist element is added to
 * the end of the runlist @runlist or if the last runlist element is a sparse
 * one already, this is extended.
 *
 * Return 0 on success and -errno on error.
 *
 * Locking: The caller must hold @runlist->lock for writing.
 */
int ntfs_rl_truncate_nolock(const ntfs_volume *vol, runlist *const runlist,
		const s64 new_length)
{
	runlist_element *rl;
	int old_size;

	ntfs_debug("Entering for new_length 0x%llx.", (long long)new_length);
	BUG_ON(!runlist);
	BUG_ON(new_length < 0);
	rl = runlist->rl;
	if (unlikely(!rl)) {
		/*
		 * Create a runlist consisting of a sparse runlist element of
		 * length @new_length followed by a terminator runlist element.
		 */
		rl = ntfs_malloc_nofs(PAGE_SIZE);
		if (unlikely(!rl)) {
			ntfs_error(vol->sb, "Not enough memory to allocate "
					"runlist element buffer.");
			return -ENOMEM;
		}
		runlist->rl = rl;
		rl[1].length = rl->vcn = 0;
		rl->lcn = LCN_HOLE;
		rl[1].vcn = rl->length = new_length;
		rl[1].lcn = LCN_ENOENT;
		return 0;
	}
	BUG_ON(new_length < rl->vcn);
	/* Find @new_length in the runlist. */
	while (likely(rl->length && new_length >= rl[1].vcn))
		rl++;
	/*
	 * If not at the end of the runlist we need to shrink it.
	 * If at the end of the runlist we need to expand it.
	 */
	if (rl->length) {
		runlist_element *trl;
		BOOL is_end;

		ntfs_debug("Shrinking runlist.");
		/* Determine the runlist size. */
		trl = rl + 1;
		while (likely(trl->length))
			trl++;
		old_size = trl - runlist->rl + 1;
		/* Truncate the run. */
		rl->length = new_length - rl->vcn;
		/*
		 * If a run was partially truncated, make the following runlist
		 * element a terminator.
		 */
		is_end = FALSE;
		if (rl->length) {
			rl++;
			if (!rl->length)
				is_end = TRUE;
			rl->vcn = new_length;
			rl->length = 0;
		}
		rl->lcn = LCN_ENOENT;
		/* Reallocate memory if necessary. */
		if (!is_end) {
			int new_size = rl - runlist->rl + 1;
			rl = ntfs_rl_realloc(runlist->rl, old_size, new_size);
			if (IS_ERR(rl))
				ntfs_warning(vol->sb, "Failed to shrink "
						"runlist buffer.  This just "
						"wastes a bit of memory "
						"temporarily so we ignore it "
						"and return success.");
			else
				runlist->rl = rl;
		}
	} else if (likely(/* !rl->length && */ new_length > rl->vcn)) {
		ntfs_debug("Expanding runlist.");
		/*
		 * If there is a previous runlist element and it is a sparse
		 * one, extend it.  Otherwise need to add a new, sparse runlist
		 * element.
		 */
		if ((rl > runlist->rl) && ((rl - 1)->lcn == LCN_HOLE))
			(rl - 1)->length = new_length - (rl - 1)->vcn;
		else {
			/* Determine the runlist size. */
			old_size = rl - runlist->rl + 1;
			/* Reallocate memory if necessary. */
			rl = ntfs_rl_realloc(runlist->rl, old_size,
					old_size + 1);
			if (IS_ERR(rl)) {
				ntfs_error(vol->sb, "Failed to expand runlist "
						"buffer, aborting.");
				return PTR_ERR(rl);
			}
			runlist->rl = rl;
			/*
			 * Set @rl to the same runlist element in the new
			 * runlist as before in the old runlist.
			 */
			rl += old_size - 1;
			/* Add a new, sparse runlist element. */
			rl->lcn = LCN_HOLE;
			rl->length = new_length - rl->vcn;
			/* Add a new terminator runlist element. */
			rl++;
			rl->length = 0;
		}
		rl->vcn = new_length;
		rl->lcn = LCN_ENOENT;
	} else /* if (unlikely(!rl->length && new_length == rl->vcn)) */ {
		/* Runlist already has same size as requested. */
		rl->lcn = LCN_ENOENT;
	}
	ntfs_debug("Done.");
	return 0;
}