summaryrefslogtreecommitdiffstats
path: root/dosfstools/src/fat.c
blob: 5a92f568410d2ad895f450c83ff0de5e6d2b8fd6 (plain) (blame)
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
/* fat.c - Read/write access to the FAT

   Copyright (C) 1993 Werner Almesberger <werner.almesberger@lrc.di.epfl.ch>
   Copyright (C) 1998 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
   Copyright (C) 2008-2014 Daniel Baumann <mail@daniel-baumann.ch>

   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 3 of the License, 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. If not, see <http://www.gnu.org/licenses/>.

   The complete text of the GNU General Public License
   can be found in /usr/share/common-licenses/GPL-3 file.
*/

/* FAT32, VFAT, Atari format support, and various fixes additions May 1998
 * by Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de> */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "common.h"
#include "fsck.fat.h"
#include "io.h"
#include "check.h"
#include "fat.h"

/**
 * Fetch the FAT entry for a specified cluster.
 *
 * @param[out]  entry	    Cluster to which cluster of interest is linked
 * @param[in]	fat	    FAT table for the partition
 * @param[in]	cluster     Cluster of interest
 * @param[in]	fs          Information from the FAT boot sectors (bits per FAT entry)
 */
void get_fat(FAT_ENTRY * entry, void *fat, uint32_t cluster, DOS_FS * fs)
{
    unsigned char *ptr;

    switch (fs->fat_bits) {
    case 12:
	ptr = &((unsigned char *)fat)[cluster * 3 / 2];
	entry->value = 0xfff & (cluster & 1 ? (ptr[0] >> 4) | (ptr[1] << 4) :
				(ptr[0] | ptr[1] << 8));
	break;
    case 16:
	entry->value = le16toh(((unsigned short *)fat)[cluster]);
	break;
    case 32:
	/* According to M$, the high 4 bits of a FAT32 entry are reserved and
	 * are not part of the cluster number. So we cut them off. */
	{
	    uint32_t e = le32toh(((unsigned int *)fat)[cluster]);
	    entry->value = e & 0xfffffff;
	    entry->reserved = e >> 28;
	}
	break;
    default:
	die("Bad FAT entry size: %d bits.", fs->fat_bits);
    }
}

/**
 * Build a bookkeeping structure from the partition's FAT table.
 * If the partition has multiple FATs and they don't agree, try to pick a winner,
 * and queue a command to overwrite the loser.
 * One error that is fixed here is a cluster that links to something out of range.
 *
 * @param[inout]    fs      Information about the filesystem
 */
void read_fat(DOS_FS * fs)
{
    int eff_size, alloc_size;
    uint32_t i;
    void *first, *second = NULL;
    int first_ok, second_ok;
    uint32_t total_num_clusters;

    /* Clean up from previous pass */
    if (fs->fat)
	free(fs->fat);
    if (fs->cluster_owner)
	free(fs->cluster_owner);
    fs->fat = NULL;
    fs->cluster_owner = NULL;

    total_num_clusters = fs->clusters + 2UL;
    eff_size = (total_num_clusters * fs->fat_bits + 7) / 8ULL;

    if (fs->fat_bits != 12)
	    alloc_size = eff_size;
    else
	    /* round up to an even number of FAT entries to avoid special
	     * casing the last entry in get_fat() */
	    alloc_size = (total_num_clusters * 12 + 23) / 24 * 3;

    first = alloc(alloc_size);
    fs_read(fs->fat_start, eff_size, first);
    if (fs->nfats > 1) {
	second = alloc(alloc_size);
	fs_read(fs->fat_start + fs->fat_size, eff_size, second);
    }
    if (second && memcmp(first, second, eff_size) != 0) {
	FAT_ENTRY first_media, second_media;
	get_fat(&first_media, first, 0, fs);
	get_fat(&second_media, second, 0, fs);
	first_ok = (first_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
	second_ok = (second_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
	if (first_ok && !second_ok) {
	    printf("FATs differ - using first FAT.\n");
	    fs_write(fs->fat_start + fs->fat_size, eff_size, first);
	}
	if (!first_ok && second_ok) {
	    printf("FATs differ - using second FAT.\n");
	    fs_write(fs->fat_start, eff_size, second);
	    memcpy(first, second, eff_size);
	}
	if (first_ok && second_ok) {
	    if (interactive) {
		printf("FATs differ but appear to be intact. Use which FAT ?\n"
		       "1) Use first FAT\n2) Use second FAT\n");
		if (get_key("12", "?") == '1') {
		    fs_write(fs->fat_start + fs->fat_size, eff_size, first);
		} else {
		    fs_write(fs->fat_start, eff_size, second);
		    memcpy(first, second, eff_size);
		}
	    } else {
		printf("FATs differ but appear to be intact. Using first "
		       "FAT.\n");
		fs_write(fs->fat_start + fs->fat_size, eff_size, first);
	    }
	}
	if (!first_ok && !second_ok) {
	    printf("Both FATs appear to be corrupt. Giving up.\n");
	    exit(1);
	}
    }
    if (second) {
	free(second);
    }
    fs->fat = (unsigned char *)first;

    fs->cluster_owner = alloc(total_num_clusters * sizeof(DOS_FILE *));
    memset(fs->cluster_owner, 0, (total_num_clusters * sizeof(DOS_FILE *)));

    /* Truncate any cluster chains that link to something out of range */
    for (i = 2; i < fs->clusters + 2; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);
	if (curEntry.value == 1) {
	    printf("Cluster %ld out of range (1). Setting to EOF.\n", (long)(i - 2));
	    set_fat(fs, i, -1);
	}
	if (curEntry.value >= fs->clusters + 2 &&
	    (curEntry.value < FAT_MIN_BAD(fs))) {
	    printf("Cluster %ld out of range (%ld > %ld). Setting to EOF.\n",
		   (long)(i - 2), (long)curEntry.value, (long)(fs->clusters + 2 - 1));
	    set_fat(fs, i, -1);
	}
    }
}

/**
 * Update the FAT entry for a specified cluster
 * (i.e., change the cluster it links to).
 * Queue a command to write out this change.
 *
 * @param[in,out]   fs          Information about the filesystem
 * @param[in]	    cluster     Cluster to change
 * @param[in]       new	        Cluster to link to
 *				Special values:
 *				   0 == free cluster
 *				  -1 == end-of-chain
 *				  -2 == bad cluster
 */
void set_fat(DOS_FS * fs, uint32_t cluster, int32_t new)
{
    unsigned char *data = NULL;
    int size;
    loff_t offs;

    if (new == -1)
	new = FAT_EOF(fs);
    else if ((long)new == -2)
	new = FAT_BAD(fs);
    switch (fs->fat_bits) {
    case 12:
	data = fs->fat + cluster * 3 / 2;
	offs = fs->fat_start + cluster * 3 / 2;
	if (cluster & 1) {
	    FAT_ENTRY prevEntry;
	    get_fat(&prevEntry, fs->fat, cluster - 1, fs);
	    data[0] = ((new & 0xf) << 4) | (prevEntry.value >> 8);
	    data[1] = new >> 4;
	} else {
	    FAT_ENTRY subseqEntry;
	    get_fat(&subseqEntry, fs->fat, cluster + 1, fs);
	    data[0] = new & 0xff;
	    data[1] = (new >> 8) | (cluster == fs->clusters - 1 ? 0 :
				    (0xff & subseqEntry.value) << 4);
	}
	size = 2;
	break;
    case 16:
	data = fs->fat + cluster * 2;
	offs = fs->fat_start + cluster * 2;
	*(unsigned short *)data = htole16(new);
	size = 2;
	break;
    case 32:
	{
	    FAT_ENTRY curEntry;
	    get_fat(&curEntry, fs->fat, cluster, fs);

	    data = fs->fat + cluster * 4;
	    offs = fs->fat_start + cluster * 4;
	    /* According to M$, the high 4 bits of a FAT32 entry are reserved and
	     * are not part of the cluster number. So we never touch them. */
	    *(uint32_t *)data = htole32((new & 0xfffffff) |
					     (curEntry.reserved << 28));
	    size = 4;
	}
	break;
    default:
	die("Bad FAT entry size: %d bits.", fs->fat_bits);
    }
    fs_write(offs, size, data);
    if (fs->nfats > 1) {
	fs_write(offs + fs->fat_size, size, data);
    }
}

int bad_cluster(DOS_FS * fs, uint32_t cluster)
{
    FAT_ENTRY curEntry;
    get_fat(&curEntry, fs->fat, cluster, fs);

    return FAT_IS_BAD(fs, curEntry.value);
}

/**
 * Get the cluster to which the specified cluster is linked.
 * If the linked cluster is marked bad, abort.
 *
 * @param[in]   fs          Information about the filesystem
 * @param[in]	cluster     Cluster to follow
 *
 * @return  -1              'cluster' is at the end of the chain
 * @return  Other values    Next cluster in this chain
 */
uint32_t next_cluster(DOS_FS * fs, uint32_t cluster)
{
    uint32_t value;
    FAT_ENTRY curEntry;

    get_fat(&curEntry, fs->fat, cluster, fs);

    value = curEntry.value;
    if (FAT_IS_BAD(fs, value))
	die("Internal error: next_cluster on bad cluster");
    return FAT_IS_EOF(fs, value) ? -1 : value;
}

loff_t cluster_start(DOS_FS * fs, uint32_t cluster)
{
    return fs->data_start + ((loff_t) cluster -
			     2) * (uint64_t)fs->cluster_size;
}

/**
 * Update internal bookkeeping to show that the specified cluster belongs
 * to the specified dentry.
 *
 * @param[in,out]   fs          Information about the filesystem
 * @param[in]	    cluster     Cluster being assigned
 * @param[in]	    owner       Information on dentry that owns this cluster
 *                              (may be NULL)
 */
void set_owner(DOS_FS * fs, uint32_t cluster, DOS_FILE * owner)
{
    if (fs->cluster_owner == NULL)
	die("Internal error: attempt to set owner in non-existent table");

    if (owner && fs->cluster_owner[cluster]
	&& (fs->cluster_owner[cluster] != owner))
	die("Internal error: attempt to change file owner");
    fs->cluster_owner[cluster] = owner;
}

DOS_FILE *get_owner(DOS_FS * fs, uint32_t cluster)
{
    if (fs->cluster_owner == NULL)
	return NULL;
    else
	return fs->cluster_owner[cluster];
}

void fix_bad(DOS_FS * fs)
{
    uint32_t i;

    if (verbose)
	printf("Checking for bad clusters.\n");
    for (i = 2; i < fs->clusters + 2; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);

	if (!get_owner(fs, i) && !FAT_IS_BAD(fs, curEntry.value))
	    if (!fs_test(cluster_start(fs, i), fs->cluster_size)) {
		printf("Cluster %lu is unreadable.\n", (unsigned long)i);
		set_fat(fs, i, -2);
	    }
    }
}

void reclaim_free(DOS_FS * fs)
{
    int reclaimed;
    uint32_t i;

    if (verbose)
	printf("Checking for unused clusters.\n");
    reclaimed = 0;
    for (i = 2; i < fs->clusters + 2; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);

	if (!get_owner(fs, i) && curEntry.value &&
	    !FAT_IS_BAD(fs, curEntry.value)) {
	    set_fat(fs, i, 0);
	    reclaimed++;
	}
    }
    if (reclaimed)
	printf("Reclaimed %d unused cluster%s (%llu bytes).\n", (int)reclaimed,
	       reclaimed == 1 ? "" : "s",
	       (unsigned long long)reclaimed * fs->cluster_size);
}

/**
 * Assign the specified owner to all orphan chains (except cycles).
 * Break cross-links between orphan chains.
 *
 * @param[in,out]   fs             Information about the filesystem
 * @param[in]	    owner          dentry to be assigned ownership of orphans
 * @param[in,out]   num_refs	   For each orphan cluster [index], how many
 *				   clusters link to it.
 * @param[in]	    start_cluster  Where to start scanning for orphans
 */
static void tag_free(DOS_FS * fs, DOS_FILE * owner, uint32_t *num_refs,
		     uint32_t start_cluster)
{
    int prev;
    uint32_t i, walk;

    if (start_cluster == 0)
	start_cluster = 2;

    for (i = start_cluster; i < fs->clusters + 2; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);

	/* If the current entry is the head of an un-owned chain... */
	if (curEntry.value && !FAT_IS_BAD(fs, curEntry.value) &&
	    !get_owner(fs, i) && !num_refs[i]) {
	    prev = 0;
	    /* Walk the chain, claiming ownership as we go */
	    for (walk = i; walk != -1; walk = next_cluster(fs, walk)) {
		if (!get_owner(fs, walk)) {
		    set_owner(fs, walk, owner);
		} else {
		    /* We've run into cross-links between orphaned chains,
		     * or a cycle with a tail.
		     * Terminate this orphan chain (break the link)
		     */
		    set_fat(fs, prev, -1);

		    /* This is not necessary because 'walk' is owned and thus
		     * will never become the head of a chain (the only case
		     * that would matter during reclaim to files).
		     * It's easier to decrement than to prove that it's
		     * unnecessary.
		     */
		    num_refs[walk]--;
		    break;
		}
		prev = walk;
	    }
	}
    }
}

/**
 * Recover orphan chains to files, handling any cycles or cross-links.
 *
 * @param[in,out]   fs             Information about the filesystem
 */
void reclaim_file(DOS_FS * fs)
{
    DOS_FILE orphan;
    int reclaimed, files;
    int changed = 0;
    uint32_t i, next, walk;
    uint32_t *num_refs = NULL;	/* Only for orphaned clusters */
    uint32_t total_num_clusters;

    if (verbose)
	printf("Reclaiming unconnected clusters.\n");

    total_num_clusters = fs->clusters + 2UL;
    num_refs = alloc(total_num_clusters * sizeof(uint32_t));
    memset(num_refs, 0, (total_num_clusters * sizeof(uint32_t)));

    /* Guarantee that all orphan chains (except cycles) end cleanly
     * with an end-of-chain mark.
     */

    for (i = 2; i < total_num_clusters; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);

	next = curEntry.value;
	if (!get_owner(fs, i) && next && next < fs->clusters + 2) {
	    /* Cluster is linked, but not owned (orphan) */
	    FAT_ENTRY nextEntry;
	    get_fat(&nextEntry, fs->fat, next, fs);

	    /* Mark it end-of-chain if it links into an owned cluster,
	     * a free cluster, or a bad cluster.
	     */
	    if (get_owner(fs, next) || !nextEntry.value ||
		FAT_IS_BAD(fs, nextEntry.value))
		set_fat(fs, i, -1);
	    else
		num_refs[next]++;
	}
    }

    /* Scan until all the orphans are accounted for,
     * and all cycles and cross-links are broken
     */
    do {
	tag_free(fs, &orphan, num_refs, changed);
	changed = 0;

	/* Any unaccounted-for orphans must be part of a cycle */
	for (i = 2; i < total_num_clusters; i++) {
	    FAT_ENTRY curEntry;
	    get_fat(&curEntry, fs->fat, i, fs);

	    if (curEntry.value && !FAT_IS_BAD(fs, curEntry.value) &&
		!get_owner(fs, i)) {
		if (!num_refs[curEntry.value]--)
		    die("Internal error: num_refs going below zero");
		set_fat(fs, i, -1);
		changed = curEntry.value;
		printf("Broke cycle at cluster %lu in free chain.\n", (unsigned long)i);

		/* If we've created a new chain head,
		 * tag_free() can claim it
		 */
		if (num_refs[curEntry.value] == 0)
		    break;
	    }
	}
    }
    while (changed);

    /* Now we can start recovery */
    files = reclaimed = 0;
    for (i = 2; i < total_num_clusters; i++)
	/* If this cluster is the head of an orphan chain... */
	if (get_owner(fs, i) == &orphan && !num_refs[i]) {
	    DIR_ENT de;
	    loff_t offset;
	    files++;
	    offset = alloc_rootdir_entry(fs, &de, "FSCK%04dREC");
	    de.start = htole16(i & 0xffff);
	    if (fs->fat_bits == 32)
		de.starthi = htole16(i >> 16);
	    for (walk = i; walk > 0 && walk != -1;
		 walk = next_cluster(fs, walk)) {
		de.size = htole32(le32toh(de.size) + fs->cluster_size);
		reclaimed++;
	    }
	    fs_write(offset, sizeof(DIR_ENT), &de);
	}
    if (reclaimed)
	printf("Reclaimed %d unused cluster%s (%llu bytes) in %d chain%s.\n",
	       reclaimed, reclaimed == 1 ? "" : "s",
	       (unsigned long long)reclaimed * fs->cluster_size, files,
	       files == 1 ? "" : "s");

    free(num_refs);
}

uint32_t update_free(DOS_FS * fs)
{
    uint32_t i;
    uint32_t free = 0;
    int do_set = 0;

    for (i = 2; i < fs->clusters + 2; i++) {
	FAT_ENTRY curEntry;
	get_fat(&curEntry, fs->fat, i, fs);

	if (!get_owner(fs, i) && !FAT_IS_BAD(fs, curEntry.value))
	    ++free;
    }

    if (!fs->fsinfo_start)
	return free;

    if (verbose)
	printf("Checking free cluster summary.\n");
    if (fs->free_clusters != 0xFFFFFFFF) {
	if (free != fs->free_clusters) {
	    printf("Free cluster summary wrong (%ld vs. really %ld)\n",
		   (long)fs->free_clusters, (long)free);
	    if (interactive)
		printf("1) Correct\n2) Don't correct\n");
	    else
		printf("  Auto-correcting.\n");
	    if (!interactive || get_key("12", "?") == '1')
		do_set = 1;
	}
    } else {
	printf("Free cluster summary uninitialized (should be %ld)\n", (long)free);
	if (rw) {
	    if (interactive)
		printf("1) Set it\n2) Leave it uninitialized\n");
	    else
		printf("  Auto-setting.\n");
	    if (!interactive || get_key("12", "?") == '1')
		do_set = 1;
	}
    }

    if (do_set) {
	uint32_t le_free = htole32(free);
	fs->free_clusters = free;
	fs_write(fs->fsinfo_start + offsetof(struct info_sector, free_clusters),
		 sizeof(le_free), &le_free);
    }

    return free;
}