2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank
5 * Copyright (c) 1995 Martin Husemann
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 #include <sys/cdefs.h>
31 __RCSID("$NetBSD: fat.c,v 1.18 2006/06/05 16:51:18 christos Exp $");
32 static const char rcsid[] =
45 static int checkclnum(struct bootblock *, u_int, cl_t, cl_t *);
46 static int clustdiffer(cl_t, cl_t *, cl_t *, u_int);
47 static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *);
48 static int _readfat(int, struct bootblock *, u_int, u_char **);
51 * The first 2 FAT entries contain pseudo-cluster numbers with the following
54 * 31...... ........ ........ .......0
55 * rrrr1111 11111111 11111111 mmmmmmmm FAT32 entry 0
56 * rrrrsh11 11111111 11111111 11111xxx FAT32 entry 1
58 * 11111111 mmmmmmmm FAT16 entry 0
59 * sh111111 11111xxx FAT16 entry 1
62 * m = BPB media ID byte
63 * s = clean flag (1 = dismounted; 0 = still mounted)
64 * h = hard error flag (1 = ok; 0 = I/O error)
69 checkdirty(int fs, struct bootblock *boot)
76 if (boot->ClustMask != CLUST16_MASK && boot->ClustMask != CLUST32_MASK)
79 off = boot->bpbResSectors;
80 off *= boot->bpbBytesPerSec;
82 buffer = malloc(len = boot->bpbBytesPerSec);
84 perr("No space for FAT sectors (%zu)", len);
88 if (lseek(fs, off, SEEK_SET) != off) {
89 perr("Unable to read FAT");
93 if ((size_t)read(fs, buffer, boot->bpbBytesPerSec) !=
94 boot->bpbBytesPerSec) {
95 perr("Unable to read FAT");
100 * If we don't understand the FAT, then the file system must be
101 * assumed to be unclean.
103 if (buffer[0] != boot->bpbMedia || buffer[1] != 0xff)
105 if (boot->ClustMask == CLUST16_MASK) {
106 if ((buffer[2] & 0xf8) != 0xf8 || (buffer[3] & 0x3f) != 0x3f)
109 if (buffer[2] != 0xff || (buffer[3] & 0x0f) != 0x0f
110 || (buffer[4] & 0xf8) != 0xf8 || buffer[5] != 0xff
111 || buffer[6] != 0xff || (buffer[7] & 0x03) != 0x03)
116 * Now check the actual clean flag (and the no-error flag).
118 if (boot->ClustMask == CLUST16_MASK) {
119 if ((buffer[3] & 0xc0) == 0xc0)
122 if ((buffer[7] & 0x0c) == 0x0c)
132 * Check a cluster number for valid value
135 checkclnum(struct bootblock *boot, u_int fat, cl_t cl, cl_t *next)
137 if (*next >= (CLUST_RSRVD&boot->ClustMask))
138 *next |= ~boot->ClustMask;
139 if (*next == CLUST_FREE) {
143 if (*next == CLUST_BAD) {
147 if (*next < CLUST_FIRST
148 || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
149 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
151 *next < CLUST_RSRVD ? "out of range" : "reserved",
152 *next&boot->ClustMask);
153 if (ask(0, "Truncate")) {
163 * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
166 _readfat(int fs, struct bootblock *boot, u_int no, u_char **buffer)
171 *buffer = malloc(len = boot->FATsecs * boot->bpbBytesPerSec);
172 if (*buffer == NULL) {
173 perr("No space for FAT sectors (%zu)", len);
177 off = boot->bpbResSectors + no * boot->FATsecs;
178 off *= boot->bpbBytesPerSec;
180 if (lseek(fs, off, SEEK_SET) != off) {
181 perr("Unable to read FAT");
185 if ((size_t)read(fs, *buffer, boot->FATsecs * boot->bpbBytesPerSec)
186 != boot->FATsecs * boot->bpbBytesPerSec) {
187 perr("Unable to read FAT");
199 * Read a FAT and decode it into internal format
202 readfat(int fs, struct bootblock *boot, u_int no, struct fatEntry **fp)
204 struct fatEntry *fat;
210 boot->NumFree = boot->NumBad = 0;
212 if (!_readfat(fs, boot, no, &buffer))
215 fat = malloc(len = boot->NumClusters * sizeof(struct fatEntry));
217 perr("No space for FAT clusters (%zu)", len);
221 (void)memset(fat, 0, len);
223 if (buffer[0] != boot->bpbMedia
224 || buffer[1] != 0xff || buffer[2] != 0xff
225 || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
226 || (boot->ClustMask == CLUST32_MASK
227 && ((buffer[3]&0x0f) != 0x0f
228 || buffer[4] != 0xff || buffer[5] != 0xff
229 || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
231 /* Windows 95 OSR2 (and possibly any later) changes
232 * the FAT signature to 0xXXffff7f for FAT16 and to
233 * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
234 * file system is dirty if it doesn't reboot cleanly.
235 * Check this special condition before errorring out.
237 if (buffer[0] == boot->bpbMedia && buffer[1] == 0xff
239 && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
240 || (boot->ClustMask == CLUST32_MASK
241 && buffer[3] == 0x0f && buffer[4] == 0xff
242 && buffer[5] == 0xff && buffer[6] == 0xff
243 && buffer[7] == 0x07)))
246 /* just some odd byte sequence in FAT */
248 switch (boot->ClustMask) {
250 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
251 "FAT starts with odd byte sequence",
252 buffer[0], buffer[1], buffer[2], buffer[3],
253 buffer[4], buffer[5], buffer[6], buffer[7]);
256 pwarn("%s (%02x%02x%02x%02x)\n",
257 "FAT starts with odd byte sequence",
258 buffer[0], buffer[1], buffer[2], buffer[3]);
261 pwarn("%s (%02x%02x%02x)\n",
262 "FAT starts with odd byte sequence",
263 buffer[0], buffer[1], buffer[2]);
268 if (ask(1, "Correct"))
272 switch (boot->ClustMask) {
283 for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
284 switch (boot->ClustMask) {
286 fat[cl].next = p[0] + (p[1] << 8)
287 + (p[2] << 16) + (p[3] << 24);
288 fat[cl].next &= boot->ClustMask;
289 ret |= checkclnum(boot, no, cl, &fat[cl].next);
294 fat[cl].next = p[0] + (p[1] << 8);
295 ret |= checkclnum(boot, no, cl, &fat[cl].next);
300 fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
301 ret |= checkclnum(boot, no, cl, &fat[cl].next);
303 if (cl >= boot->NumClusters)
305 fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
306 ret |= checkclnum(boot, no, cl, &fat[cl].next);
323 * Get type of reserved cluster
328 if (cl == CLUST_FREE)
338 clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum)
340 if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
341 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
342 if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
343 && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
344 || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
345 pwarn("Cluster %u is marked %s with different indicators\n",
346 cl, rsrvdcltype(*cp1));
353 pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n",
354 cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
355 if (ask(0, "Use FAT 0's entry")) {
359 if (ask(0, "Use FAT %u's entry", fatnum)) {
365 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
366 cl, rsrvdcltype(*cp1), *cp2, fatnum);
367 if (ask(0, "Use continuation from FAT %u", fatnum)) {
371 if (ask(0, "Use mark from FAT 0")) {
377 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
378 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n",
379 cl, *cp1, rsrvdcltype(*cp2), fatnum);
380 if (ask(0, "Use continuation from FAT 0")) {
384 if (ask(0, "Use mark from FAT %d", fatnum)) {
390 pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n",
391 cl, *cp1, *cp2, fatnum);
392 if (ask(0, "Use continuation from FAT 0")) {
396 if (ask(0, "Use continuation from FAT %u", fatnum)) {
404 * Compare two FAT copies in memory. Resolve any conflicts and merge them
405 * into the first one.
408 comparefat(struct bootblock *boot, struct fatEntry *first,
409 struct fatEntry *second, u_int fatnum)
414 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
415 if (first[cl].next != second[cl].next)
416 ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
421 clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head)
425 for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
426 if (fat[p].head != head)
429 fat[p].next = fat[p].head = CLUST_FREE;
435 tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp)
437 if (ask(0, "Clear chain starting at %u", head)) {
438 clearchain(boot, fat, head);
440 } else if (ask(0, "Truncate")) {
444 for (p = head, len = 0;
445 p >= CLUST_FIRST && p < boot->NumClusters;
446 p = fat[p].next, len++)
449 fat[head].length = len;
456 * Check a complete FAT in-memory for crosslinks
459 checkfat(struct bootblock *boot, struct fatEntry *fat)
467 * pass 1: figure out the cluster chains.
469 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
470 /* find next untravelled chain */
471 if (fat[head].head != 0 /* cluster already belongs to some chain */
472 || fat[head].next == CLUST_FREE
473 || fat[head].next == CLUST_BAD)
474 continue; /* skip it. */
476 /* follow the chain and mark all clusters on the way */
477 for (len = 0, p = head;
478 p >= CLUST_FIRST && p < boot->NumClusters &&
485 /* the head record gets the length */
486 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
490 * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
491 * we didn't know the real start of the chain then - would have treated partial
492 * chains as interlinked with their main chain)
494 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
495 /* find next untravelled chain */
496 if (fat[head].head != head)
499 /* follow the chain to its end (hopefully) */
500 for (len = fat[head].length, p = head;
501 (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
503 if (fat[n].head != head || len-- < 2)
508 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
509 pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
510 head, rsrvdcltype(n));
512 ret |= tryclear(boot, fat, head, &fat[p].next);
515 if (n < CLUST_FIRST || n >= boot->NumClusters) {
516 pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
520 if (head == fat[n].head) {
521 pwarn("Cluster chain starting at %u loops at cluster %u\n",
526 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
527 head, fat[n].head, n);
528 conf = tryclear(boot, fat, head, &fat[p].next);
529 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
530 if (conf == FSERROR) {
532 * Transfer the common chain to the one not cleared above.
535 p >= CLUST_FIRST && p < boot->NumClusters;
537 if (h != fat[p].head) {
539 * Have to reexamine this chain.
547 clearchain(boot, fat, h);
557 * Write out FATs encoding them from the internal format
560 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
569 buffer = malloc(fatsz = boot->FATsecs * boot->bpbBytesPerSec);
570 if (buffer == NULL) {
571 perr("No space for FAT sectors (%zu)", fatsz);
574 memset(buffer, 0, fatsz);
578 *p++ = (u_char)boot->bpbMedia;
581 switch (boot->ClustMask) {
594 /* use same FAT signature as the old FAT has */
598 switch (boot->ClustMask) {
610 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
616 memcpy(p, old_fat, count);
621 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
622 switch (boot->ClustMask) {
624 if (fat[cl].next == CLUST_FREE)
626 *p++ = (u_char)fat[cl].next;
627 *p++ = (u_char)(fat[cl].next >> 8);
628 *p++ = (u_char)(fat[cl].next >> 16);
630 *p++ |= (fat[cl].next >> 24)&0x0f;
633 if (fat[cl].next == CLUST_FREE)
635 *p++ = (u_char)fat[cl].next;
636 *p++ = (u_char)(fat[cl].next >> 8);
639 if (fat[cl].next == CLUST_FREE)
641 *p++ = (u_char)fat[cl].next;
642 *p = (u_char)((fat[cl].next >> 8) & 0xf);
644 if (cl >= boot->NumClusters)
646 if (fat[cl].next == CLUST_FREE)
648 *p++ |= (u_char)(fat[cl + 1].next << 4);
649 *p++ = (u_char)(fat[cl + 1].next >> 4);
653 for (i = 0; i < boot->bpbFATs; i++) {
654 off = boot->bpbResSectors + i * boot->FATsecs;
655 off *= boot->bpbBytesPerSec;
656 if (lseek(fs, off, SEEK_SET) != off
657 || (size_t)write(fs, buffer, fatsz) != fatsz) {
658 perr("Unable to write FAT");
659 ret = FSFATAL; /* Return immediately? XXX */
667 * Check a complete in-memory FAT for lost cluster chains
670 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
676 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
677 /* find next untravelled chain */
678 if (fat[head].head != head
679 || fat[head].next == CLUST_FREE
680 || (fat[head].next >= CLUST_RSRVD
681 && fat[head].next < CLUST_EOFS)
682 || (fat[head].flags & FAT_USED))
685 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
686 head, fat[head].length);
687 mod |= ret = reconnect(dosfs, boot, fat, head);
690 if (ret == FSERROR && ask(0, "Clear")) {
691 clearchain(boot, fat, head);
697 if (boot->bpbFSInfo) {
699 if (boot->FSFree != 0xffffffffU &&
700 boot->FSFree != boot->NumFree) {
701 pwarn("Free space in FSInfo block (%u) not correct (%u)\n",
702 boot->FSFree, boot->NumFree);
704 boot->FSFree = boot->NumFree;
709 mod |= writefsinfo(dosfs, boot);