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)
170 *buffer = calloc(boot->FATsecs, boot->bpbBytesPerSec);
171 if (*buffer == NULL) {
172 perr("No space for FAT sectors (%zu)",
173 (size_t)boot->FATsecs);
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;
209 boot->NumFree = boot->NumBad = 0;
211 if (!_readfat(fs, boot, no, &buffer))
214 fat = calloc(boot->NumClusters, sizeof(struct fatEntry));
216 perr("No space for FAT clusters (%zu)",
217 (size_t)boot->NumClusters);
222 if (buffer[0] != boot->bpbMedia
223 || buffer[1] != 0xff || buffer[2] != 0xff
224 || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
225 || (boot->ClustMask == CLUST32_MASK
226 && ((buffer[3]&0x0f) != 0x0f
227 || buffer[4] != 0xff || buffer[5] != 0xff
228 || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
230 /* Windows 95 OSR2 (and possibly any later) changes
231 * the FAT signature to 0xXXffff7f for FAT16 and to
232 * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
233 * file system is dirty if it doesn't reboot cleanly.
234 * Check this special condition before errorring out.
236 if (buffer[0] == boot->bpbMedia && buffer[1] == 0xff
238 && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
239 || (boot->ClustMask == CLUST32_MASK
240 && buffer[3] == 0x0f && buffer[4] == 0xff
241 && buffer[5] == 0xff && buffer[6] == 0xff
242 && buffer[7] == 0x07)))
245 /* just some odd byte sequence in FAT */
247 switch (boot->ClustMask) {
249 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
250 "FAT starts with odd byte sequence",
251 buffer[0], buffer[1], buffer[2], buffer[3],
252 buffer[4], buffer[5], buffer[6], buffer[7]);
255 pwarn("%s (%02x%02x%02x%02x)\n",
256 "FAT starts with odd byte sequence",
257 buffer[0], buffer[1], buffer[2], buffer[3]);
260 pwarn("%s (%02x%02x%02x)\n",
261 "FAT starts with odd byte sequence",
262 buffer[0], buffer[1], buffer[2]);
267 if (ask(1, "Correct"))
271 switch (boot->ClustMask) {
282 for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
283 switch (boot->ClustMask) {
285 fat[cl].next = p[0] + (p[1] << 8)
286 + (p[2] << 16) + (p[3] << 24);
287 fat[cl].next &= boot->ClustMask;
288 ret |= checkclnum(boot, no, cl, &fat[cl].next);
293 fat[cl].next = p[0] + (p[1] << 8);
294 ret |= checkclnum(boot, no, cl, &fat[cl].next);
299 fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
300 ret |= checkclnum(boot, no, cl, &fat[cl].next);
302 if (cl >= boot->NumClusters)
304 fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
305 ret |= checkclnum(boot, no, cl, &fat[cl].next);
322 * Get type of reserved cluster
327 if (cl == CLUST_FREE)
337 clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum)
339 if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
340 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
341 if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
342 && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
343 || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
344 pwarn("Cluster %u is marked %s with different indicators\n",
345 cl, rsrvdcltype(*cp1));
352 pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n",
353 cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
354 if (ask(0, "Use FAT 0's entry")) {
358 if (ask(0, "Use FAT %u's entry", fatnum)) {
364 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
365 cl, rsrvdcltype(*cp1), *cp2, fatnum);
366 if (ask(0, "Use continuation from FAT %u", fatnum)) {
370 if (ask(0, "Use mark from FAT 0")) {
376 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
377 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n",
378 cl, *cp1, rsrvdcltype(*cp2), fatnum);
379 if (ask(0, "Use continuation from FAT 0")) {
383 if (ask(0, "Use mark from FAT %d", fatnum)) {
389 pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n",
390 cl, *cp1, *cp2, fatnum);
391 if (ask(0, "Use continuation from FAT 0")) {
395 if (ask(0, "Use continuation from FAT %u", fatnum)) {
403 * Compare two FAT copies in memory. Resolve any conflicts and merge them
404 * into the first one.
407 comparefat(struct bootblock *boot, struct fatEntry *first,
408 struct fatEntry *second, u_int fatnum)
413 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
414 if (first[cl].next != second[cl].next)
415 ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
420 clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head)
424 for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
425 if (fat[p].head != head)
428 fat[p].next = fat[p].head = CLUST_FREE;
434 tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp)
436 if (ask(0, "Clear chain starting at %u", head)) {
437 clearchain(boot, fat, head);
439 } else if (ask(0, "Truncate")) {
443 for (p = head, len = 0;
444 p >= CLUST_FIRST && p < boot->NumClusters;
445 p = fat[p].next, len++)
448 fat[head].length = len;
455 * Check a complete FAT in-memory for crosslinks
458 checkfat(struct bootblock *boot, struct fatEntry *fat)
466 * pass 1: figure out the cluster chains.
468 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
469 /* find next untravelled chain */
470 if (fat[head].head != 0 /* cluster already belongs to some chain */
471 || fat[head].next == CLUST_FREE
472 || fat[head].next == CLUST_BAD)
473 continue; /* skip it. */
475 /* follow the chain and mark all clusters on the way */
476 for (len = 0, p = head;
477 p >= CLUST_FIRST && p < boot->NumClusters &&
484 /* the head record gets the length */
485 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
489 * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
490 * we didn't know the real start of the chain then - would have treated partial
491 * chains as interlinked with their main chain)
493 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
494 /* find next untravelled chain */
495 if (fat[head].head != head)
498 /* follow the chain to its end (hopefully) */
499 for (len = fat[head].length, p = head;
500 (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
502 if (fat[n].head != head || len-- < 2)
507 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
508 pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
509 head, rsrvdcltype(n));
511 ret |= tryclear(boot, fat, head, &fat[p].next);
514 if (n < CLUST_FIRST || n >= boot->NumClusters) {
515 pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
519 if (head == fat[n].head) {
520 pwarn("Cluster chain starting at %u loops at cluster %u\n",
524 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
525 head, fat[n].head, n);
526 conf = tryclear(boot, fat, head, &fat[p].next);
527 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
528 if (conf == FSERROR) {
530 * Transfer the common chain to the one not cleared above.
533 p >= CLUST_FIRST && p < boot->NumClusters;
535 if (h != fat[p].head) {
537 * Have to reexamine this chain.
545 clearchain(boot, fat, h);
555 * Write out FATs encoding them from the internal format
558 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
567 fatsz = boot->FATsecs * boot->bpbBytesPerSec;
568 buffer = calloc(boot->FATsecs, boot->bpbBytesPerSec);
569 if (buffer == NULL) {
570 perr("No space for FAT sectors (%zu)",
571 (size_t)boot->FATsecs);
577 *p++ = (u_char)boot->bpbMedia;
580 switch (boot->ClustMask) {
593 /* use same FAT signature as the old FAT has */
597 switch (boot->ClustMask) {
609 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
615 memcpy(p, old_fat, count);
620 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
621 switch (boot->ClustMask) {
623 if (fat[cl].next == CLUST_FREE)
625 *p++ = (u_char)fat[cl].next;
626 *p++ = (u_char)(fat[cl].next >> 8);
627 *p++ = (u_char)(fat[cl].next >> 16);
629 *p++ |= (fat[cl].next >> 24)&0x0f;
632 if (fat[cl].next == CLUST_FREE)
634 *p++ = (u_char)fat[cl].next;
635 *p++ = (u_char)(fat[cl].next >> 8);
638 if (fat[cl].next == CLUST_FREE)
640 *p++ = (u_char)fat[cl].next;
641 *p = (u_char)((fat[cl].next >> 8) & 0xf);
643 if (cl >= boot->NumClusters)
645 if (fat[cl].next == CLUST_FREE)
647 *p++ |= (u_char)(fat[cl].next << 4);
648 *p++ = (u_char)(fat[cl].next >> 4);
652 for (i = 0; i < boot->bpbFATs; i++) {
653 off = boot->bpbResSectors + i * boot->FATsecs;
654 off *= boot->bpbBytesPerSec;
655 if (lseek(fs, off, SEEK_SET) != off
656 || (size_t)write(fs, buffer, fatsz) != fatsz) {
657 perr("Unable to write FAT");
658 ret = FSFATAL; /* Return immediately? XXX */
666 * Check a complete in-memory FAT for lost cluster chains
669 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
675 for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
676 /* find next untravelled chain */
677 if (fat[head].head != head
678 || fat[head].next == CLUST_FREE
679 || (fat[head].next >= CLUST_RSRVD
680 && fat[head].next < CLUST_EOFS)
681 || (fat[head].flags & FAT_USED))
684 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
685 head, fat[head].length);
686 mod |= ret = reconnect(dosfs, boot, fat, head);
689 if (ret == FSERROR && ask(0, "Clear")) {
690 clearchain(boot, fat, head);
696 if (boot->bpbFSInfo) {
698 if (boot->FSFree != 0xffffffffU &&
699 boot->FSFree != boot->NumFree) {
700 pwarn("Free space in FSInfo block (%u) not correct (%u)\n",
701 boot->FSFree, boot->NumFree);
703 boot->FSFree = boot->NumFree;
707 if (boot->FSNext != 0xffffffffU &&
708 (boot->FSNext >= boot->NumClusters ||
709 (boot->NumFree && fat[boot->FSNext].next != CLUST_FREE))) {
710 pwarn("Next free cluster in FSInfo block (%u) %s\n",
712 (boot->FSNext >= boot->NumClusters) ? "invalid" : "not free");
714 for (head = CLUST_FIRST; head < boot->NumClusters; head++)
715 if (fat[head].next == CLUST_FREE) {
722 mod |= writefsinfo(dosfs, boot);