sbin/fsck_msdosfs/fat.c

   1 /*
   2  * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank
   3  * Copyright (c) 1995 Martin Husemann
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by Martin Husemann
  16  *      and Wolfgang Solfrank.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
  22  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  23  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  24  * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  26  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  27  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  28  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  29  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  30  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  31  */
  32
  33
  34 #include <sys/cdefs.h>
  35 #ifndef lint
  36 __RCSID("$NetBSD: fat.c,v 1.12 2000/10/10 20:24:52 is Exp $");
  37 static const char rcsid[] =
  38   "$FreeBSD: src/sbin/fsck_msdosfs/fat.c,v 1.1.2.1 2001/08/01 05:47:56 obrien Exp $";
  39 #endif /* not lint */
  40
  41 #include <stdlib.h>
  42 #include <string.h>
  43 #include <ctype.h>
  44 #include <stdio.h>
  45 #include <unistd.h>
  46
  47 #include "ext.h"
  48 #include "fsutil.h"
  49
  50 static int checkclnum __P((struct bootblock *, int, cl_t, cl_t *));
  51 static int clustdiffer __P((cl_t, cl_t *, cl_t *, int));
  52 static int tryclear __P((struct bootblock *, struct fatEntry *, cl_t, cl_t *));
  53 static int _readfat __P((int, struct bootblock *, int, u_char **));
  54
  55 /*
  56  * Check a cluster number for valid value
  57  */
  58 static int
  59 checkclnum(boot, fat, cl, next)
  60         struct bootblock *boot;
  61         int fat;
  62         cl_t cl;
  63         cl_t *next;
  64 {
  65         if (*next >= (CLUST_RSRVD&boot->ClustMask))
  66                 *next |= ~boot->ClustMask;
  67         if (*next == CLUST_FREE) {
  68                 boot->NumFree++;
  69                 return FSOK;
  70         }
  71         if (*next == CLUST_BAD) {
  72                 boot->NumBad++;
  73                 return FSOK;
  74         }
  75         if (*next < CLUST_FIRST
  76             || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
  77                 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
  78                       cl, fat,
  79                       *next < CLUST_RSRVD ? "out of range" : "reserved",
  80                       *next&boot->ClustMask);
  81                 if (ask(0, "Truncate")) {
  82                         *next = CLUST_EOF;
  83                         return FSFATMOD;
  84                 }
  85                 return FSERROR;
  86         }
  87         return FSOK;
  88 }
  89
  90 /*
  91  * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
  92  */
  93 static int
  94 _readfat(fs, boot, no, buffer)
  95         int fs;
  96         struct bootblock *boot;
  97         int no;
  98         u_char **buffer;
  99 {
 100         off_t off;
 101
 102         *buffer = malloc(boot->FATsecs * boot->BytesPerSec);
 103         if (*buffer == NULL) {
 104                 perror("No space for FAT");
 105                 return 0;
 106         }
 107
 108         off = boot->ResSectors + no * boot->FATsecs;
 109         off *= boot->BytesPerSec;
 110
 111         if (lseek(fs, off, SEEK_SET) != off) {
 112                 perror("Unable to read FAT");
 113                 goto err;
 114         }
 115
 116         if (read(fs, *buffer, boot->FATsecs * boot->BytesPerSec)
 117             != boot->FATsecs * boot->BytesPerSec) {
 118                 perror("Unable to read FAT");
 119                 goto err;
 120         }
 121
 122         return 1;
 123
 124     err:
 125         free(*buffer);
 126         return 0;
 127 }
 128
 129 /*
 130  * Read a FAT and decode it into internal format
 131  */
 132 int
 133 readfat(fs, boot, no, fp)
 134         int fs;
 135         struct bootblock *boot;
 136         int no;
 137         struct fatEntry **fp;
 138 {
 139         struct fatEntry *fat;
 140         u_char *buffer, *p;
 141         cl_t cl;
 142         int ret = FSOK;
 143
 144         boot->NumFree = boot->NumBad = 0;
 145
 146         if (!_readfat(fs, boot, no, &buffer))
 147                 return FSFATAL;
 148
 149         fat = calloc(boot->NumClusters, sizeof(struct fatEntry));
 150         if (fat == NULL) {
 151                 perror("No space for FAT");
 152                 free(buffer);
 153                 return FSFATAL;
 154         }
 155
 156         if (buffer[0] != boot->Media
 157             || buffer[1] != 0xff || buffer[2] != 0xff
 158             || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
 159             || (boot->ClustMask == CLUST32_MASK
 160                 && ((buffer[3]&0x0f) != 0x0f
 161                     || buffer[4] != 0xff || buffer[5] != 0xff
 162                     || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
 163
 164                 /* Windows 95 OSR2 (and possibly any later) changes
 165                  * the FAT signature to 0xXXffff7f for FAT16 and to
 166                  * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
 167                  * filesystem is dirty if it doesn't reboot cleanly.
 168                  * Check this special condition before errorring out.
 169                  */
 170                 if (buffer[0] == boot->Media && buffer[1] == 0xff
 171                     && buffer[2] == 0xff
 172                     && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
 173                         || (boot->ClustMask == CLUST32_MASK
 174                             && buffer[3] == 0x0f && buffer[4] == 0xff
 175                             && buffer[5] == 0xff && buffer[6] == 0xff
 176                             && buffer[7] == 0x07)))
 177                         ret |= FSDIRTY;
 178                 else {
 179                         /* just some odd byte sequence in FAT */
 180
 181                         switch (boot->ClustMask) {
 182                         case CLUST32_MASK:
 183                                 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
 184                                       "FAT starts with odd byte sequence",
 185                                       buffer[0], buffer[1], buffer[2], buffer[3],
 186                                       buffer[4], buffer[5], buffer[6], buffer[7]);
 187                                 break;
 188                         case CLUST16_MASK:
 189                                 pwarn("%s (%02x%02x%02x%02x)\n",
 190                                     "FAT starts with odd byte sequence",
 191                                     buffer[0], buffer[1], buffer[2], buffer[3]);
 192                                 break;
 193                         default:
 194                                 pwarn("%s (%02x%02x%02x)\n",
 195                                     "FAT starts with odd byte sequence",
 196                                     buffer[0], buffer[1], buffer[2]);
 197                                 break;
 198                         }
 199
 200
 201                         if (ask(1, "Correct"))
 202                                 ret |= FSFIXFAT;
 203                 }
 204         }
 205         switch (boot->ClustMask) {
 206         case CLUST32_MASK:
 207                 p = buffer + 8;
 208                 break;
 209         case CLUST16_MASK:
 210                 p = buffer + 4;
 211                 break;
 212         default:
 213                 p = buffer + 3;
 214                 break;
 215         }
 216         for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
 217                 switch (boot->ClustMask) {
 218                 case CLUST32_MASK:
 219                         fat[cl].next = p[0] + (p[1] << 8)
 220                                        + (p[2] << 16) + (p[3] << 24);
 221                         fat[cl].next &= boot->ClustMask;
 222                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 223                         cl++;
 224                         p += 4;
 225                         break;
 226                 case CLUST16_MASK:
 227                         fat[cl].next = p[0] + (p[1] << 8);
 228                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 229                         cl++;
 230                         p += 2;
 231                         break;
 232                 default:
 233                         fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
 234                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 235                         cl++;
 236                         if (cl >= boot->NumClusters)
 237                                 break;
 238                         fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
 239                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 240                         cl++;
 241                         p += 3;
 242                         break;
 243                 }
 244         }
 245
 246         free(buffer);
 247         *fp = fat;
 248         return ret;
 249 }
 250
 251 /*
 252  * Get type of reserved cluster
 253  */
 254 char *
 255 rsrvdcltype(cl)
 256         cl_t cl;
 257 {
 258         if (cl == CLUST_FREE)
 259                 return "free";
 260         if (cl < CLUST_BAD)
 261                 return "reserved";
 262         if (cl > CLUST_BAD)
 263                 return "as EOF";
 264         return "bad";
 265 }
 266
 267 static int
 268 clustdiffer(cl, cp1, cp2, fatnum)
 269         cl_t cl;
 270         cl_t *cp1;
 271         cl_t *cp2;
 272         int fatnum;
 273 {
 274         if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
 275                 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 276                         if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
 277                              && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
 278                             || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
 279                                 pwarn("Cluster %u is marked %s with different indicators, ",
 280                                       cl, rsrvdcltype(*cp1));
 281                                 if (ask(1, "fix")) {
 282                                         *cp2 = *cp1;
 283                                         return FSFATMOD;
 284                                 }
 285                                 return FSFATAL;
 286                         }
 287                         pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %d\n",
 288                               cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
 289                         if (ask(0, "use FAT 0's entry")) {
 290                                 *cp2 = *cp1;
 291                                 return FSFATMOD;
 292                         }
 293                         if (ask(0, "use FAT %d's entry", fatnum)) {
 294                                 *cp1 = *cp2;
 295                                 return FSFATMOD;
 296                         }
 297                         return FSFATAL;
 298                 }
 299                 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
 300                       cl, rsrvdcltype(*cp1), *cp2, fatnum);
 301                 if (ask(0, "Use continuation from FAT %d", fatnum)) {
 302                         *cp1 = *cp2;
 303                         return FSFATMOD;
 304                 }
 305                 if (ask(0, "Use mark from FAT 0")) {
 306                         *cp2 = *cp1;
 307                         return FSFATMOD;
 308                 }
 309                 return FSFATAL;
 310         }
 311         if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 312                 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %d\n",
 313                       cl, *cp1, rsrvdcltype(*cp2), fatnum);
 314                 if (ask(0, "Use continuation from FAT 0")) {
 315                         *cp2 = *cp1;
 316                         return FSFATMOD;
 317                 }
 318                 if (ask(0, "Use mark from FAT %d", fatnum)) {
 319                         *cp1 = *cp2;
 320                         return FSFATMOD;
 321                 }
 322                 return FSERROR;
 323         }
 324         pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %d\n",
 325               cl, *cp1, *cp2, fatnum);
 326         if (ask(0, "Use continuation from FAT 0")) {
 327                 *cp2 = *cp1;
 328                 return FSFATMOD;
 329         }
 330         if (ask(0, "Use continuation from FAT %d", fatnum)) {
 331                 *cp1 = *cp2;
 332                 return FSFATMOD;
 333         }
 334         return FSERROR;
 335 }
 336
 337 /*
 338  * Compare two FAT copies in memory. Resolve any conflicts and merge them
 339  * into the first one.
 340  */
 341 int
 342 comparefat(boot, first, second, fatnum)
 343         struct bootblock *boot;
 344         struct fatEntry *first;
 345         struct fatEntry *second;
 346         int fatnum;
 347 {
 348         cl_t cl;
 349         int ret = FSOK;
 350
 351         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
 352                 if (first[cl].next != second[cl].next)
 353                         ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
 354         return ret;
 355 }
 356
 357 void
 358 clearchain(boot, fat, head)
 359         struct bootblock *boot;
 360         struct fatEntry *fat;
 361         cl_t head;
 362 {
 363         cl_t p, q;
 364
 365         for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
 366                 if (fat[p].head != head)
 367                         break;
 368                 q = fat[p].next;
 369                 fat[p].next = fat[p].head = CLUST_FREE;
 370                 fat[p].length = 0;
 371         }
 372 }
 373
 374 int
 375 tryclear(boot, fat, head, trunc)
 376         struct bootblock *boot;
 377         struct fatEntry *fat;
 378         cl_t head;
 379         cl_t *trunc;
 380 {
 381         if (ask(0, "Clear chain starting at %u", head)) {
 382                 clearchain(boot, fat, head);
 383                 return FSFATMOD;
 384         } else if (ask(0, "Truncate")) {
 385                 *trunc = CLUST_EOF;
 386                 return FSFATMOD;
 387         } else
 388                 return FSERROR;
 389 }
 390
 391 /*
 392  * Check a complete FAT in-memory for crosslinks
 393  */
 394 int
 395 checkfat(boot, fat)
 396         struct bootblock *boot;
 397         struct fatEntry *fat;
 398 {
 399         cl_t head, p, h, n;
 400         u_int len;
 401         int ret = 0;
 402         int conf;
 403
 404         /*
 405          * pass 1: figure out the cluster chains.
 406          */
 407         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 408                 /* find next untravelled chain */
 409                 if (fat[head].head != 0         /* cluster already belongs to some chain */
 410                     || fat[head].next == CLUST_FREE
 411                     || fat[head].next == CLUST_BAD)
 412                         continue;               /* skip it. */
 413
 414                 /* follow the chain and mark all clusters on the way */
 415                 for (len = 0, p = head;
 416                      p >= CLUST_FIRST && p < boot->NumClusters;
 417                      p = fat[p].next) {
 418                         fat[p].head = head;
 419                         len++;
 420                 }
 421
 422                 /* the head record gets the length */
 423                 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
 424         }
 425
 426         /*
 427          * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
 428          * we didn't know the real start of the chain then - would have treated partial
 429          * chains as interlinked with their main chain)
 430          */
 431         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 432                 /* find next untravelled chain */
 433                 if (fat[head].head != head)
 434                         continue;
 435
 436                 /* follow the chain to its end (hopefully) */
 437                 for (p = head;
 438                      (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
 439                      p = n)
 440                         if (fat[n].head != head)
 441                                 break;
 442                 if (n >= CLUST_EOFS)
 443                         continue;
 444
 445                 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
 446                         pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
 447                               head, rsrvdcltype(n));
 448                         ret |= tryclear(boot, fat, head, &fat[p].next);
 449                         continue;
 450                 }
 451                 if (n < CLUST_FIRST || n >= boot->NumClusters) {
 452                         pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
 453                               head, n);
 454                         ret |= tryclear(boot, fat, head, &fat[p].next);
 455                         continue;
 456                 }
 457                 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
 458                       head, fat[n].head, n);
 459                 conf = tryclear(boot, fat, head, &fat[p].next);
 460                 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
 461                         if (conf == FSERROR) {
 462                                 /*
 463                                  * Transfer the common chain to the one not cleared above.
 464                                  */
 465                                 for (p = n;
 466                                      p >= CLUST_FIRST && p < boot->NumClusters;
 467                                      p = fat[p].next) {
 468                                         if (h != fat[p].head) {
 469                                                 /*
 470                                                  * Have to reexamine this chain.
 471                                                  */
 472                                                 head--;
 473                                                 break;
 474                                         }
 475                                         fat[p].head = head;
 476                                 }
 477                         }
 478                         clearchain(boot, fat, h);
 479                         conf |= FSFATMOD;
 480                 }
 481                 ret |= conf;
 482         }
 483
 484         return ret;
 485 }
 486
 487 /*
 488  * Write out FATs encoding them from the internal format
 489  */
 490 int
 491 writefat(fs, boot, fat, correct_fat)
 492         int fs;
 493         struct bootblock *boot;
 494         struct fatEntry *fat;
 495         int correct_fat;
 496 {
 497         u_char *buffer, *p;
 498         cl_t cl;
 499         int i;
 500         u_int32_t fatsz;
 501         off_t off;
 502         int ret = FSOK;
 503
 504         buffer = malloc(fatsz = boot->FATsecs * boot->BytesPerSec);
 505         if (buffer == NULL) {
 506                 perror("No space for FAT");
 507                 return FSFATAL;
 508         }
 509         memset(buffer, 0, fatsz);
 510         boot->NumFree = 0;
 511         p = buffer;
 512         if (correct_fat) {
 513                 *p++ = (u_char)boot->Media;
 514                 *p++ = 0xff;
 515                 *p++ = 0xff;
 516                 switch (boot->ClustMask) {
 517                 case CLUST16_MASK:
 518                         *p++ = 0xff;
 519                         break;
 520                 case CLUST32_MASK:
 521                         *p++ = 0x0f;
 522                         *p++ = 0xff;
 523                         *p++ = 0xff;
 524                         *p++ = 0xff;
 525                         *p++ = 0x0f;
 526                         break;
 527                 }
 528         } else {
 529                 /* use same FAT signature as the old FAT has */
 530                 int count;
 531                 u_char *old_fat;
 532
 533                 switch (boot->ClustMask) {
 534                 case CLUST32_MASK:
 535                         count = 8;
 536                         break;
 537                 case CLUST16_MASK:
 538                         count = 4;
 539                         break;
 540                 default:
 541                         count = 3;
 542                         break;
 543                 }
 544
 545                 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
 546                                          &old_fat)) {
 547                         free(buffer);
 548                         return FSFATAL;
 549                 }
 550
 551                 memcpy(p, old_fat, count);
 552                 free(old_fat);
 553                 p += count;
 554         }
 555
 556         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
 557                 switch (boot->ClustMask) {
 558                 case CLUST32_MASK:
 559                         if (fat[cl].next == CLUST_FREE)
 560                                 boot->NumFree++;
 561                         *p++ = (u_char)fat[cl].next;
 562                         *p++ = (u_char)(fat[cl].next >> 8);
 563                         *p++ = (u_char)(fat[cl].next >> 16);
 564                         *p &= 0xf0;
 565                         *p++ |= (fat[cl].next >> 24)&0x0f;
 566                         break;
 567                 case CLUST16_MASK:
 568                         if (fat[cl].next == CLUST_FREE)
 569                                 boot->NumFree++;
 570                         *p++ = (u_char)fat[cl].next;
 571                         *p++ = (u_char)(fat[cl].next >> 8);
 572                         break;
 573                 default:
 574                         if (fat[cl].next == CLUST_FREE)
 575                                 boot->NumFree++;
 576                         if (cl + 1 < boot->NumClusters
 577                             && fat[cl + 1].next == CLUST_FREE)
 578                                 boot->NumFree++;
 579                         *p++ = (u_char)fat[cl].next;
 580                         *p++ = (u_char)((fat[cl].next >> 8) & 0xf)
 581                                |(u_char)(fat[cl+1].next << 4);
 582                         *p++ = (u_char)(fat[++cl].next >> 4);
 583                         break;
 584                 }
 585         }
 586         for (i = 0; i < boot->FATs; i++) {
 587                 off = boot->ResSectors + i * boot->FATsecs;
 588                 off *= boot->BytesPerSec;
 589                 if (lseek(fs, off, SEEK_SET) != off
 590                     || write(fs, buffer, fatsz) != fatsz) {
 591                         perror("Unable to write FAT");
 592                         ret = FSFATAL; /* Return immediately?           XXX */
 593                 }
 594         }
 595         free(buffer);
 596         return ret;
 597 }
 598
 599 /*
 600  * Check a complete in-memory FAT for lost cluster chains
 601  */
 602 int
 603 checklost(dosfs, boot, fat)
 604         int dosfs;
 605         struct bootblock *boot;
 606         struct fatEntry *fat;
 607 {
 608         cl_t head;
 609         int mod = FSOK;
 610         int ret;
 611
 612         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 613                 /* find next untravelled chain */
 614                 if (fat[head].head != head
 615                     || fat[head].next == CLUST_FREE
 616                     || (fat[head].next >= CLUST_RSRVD
 617                         && fat[head].next < CLUST_EOFS)
 618                     || (fat[head].flags & FAT_USED))
 619                         continue;
 620
 621                 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
 622                       head, fat[head].length);
 623                 mod |= ret = reconnect(dosfs, boot, fat, head);
 624                 if (mod & FSFATAL)
 625                         break;
 626                 if (ret == FSERROR && ask(0, "Clear")) {
 627                         clearchain(boot, fat, head);
 628                         mod |= FSFATMOD;
 629                 }
 630         }
 631         finishlf();
 632
 633         if (boot->FSInfo) {
 634                 ret = 0;
 635                 if (boot->FSFree != boot->NumFree) {
 636                         pwarn("Free space in FSInfo block (%d) not correct (%d)\n",
 637                               boot->FSFree, boot->NumFree);
 638                         if (ask(1, "fix")) {
 639                                 boot->FSFree = boot->NumFree;
 640                                 ret = 1;
 641                         }
 642                 }
 643                 if (boot->NumFree && fat[boot->FSNext].next != CLUST_FREE) {
 644                         pwarn("Next free cluster in FSInfo block (%u) not free\n",
 645                               boot->FSNext);
 646                         if (ask(1, "fix"))
 647                                 for (head = CLUST_FIRST; head < boot->NumClusters; head++)
 648                                         if (fat[head].next == CLUST_FREE) {
 649                                                 boot->FSNext = head;
 650                                                 ret = 1;
 651                                                 break;
 652                                         }
 653                 }
 654                 if (ret)
 655                         mod |= writefsinfo(dosfs, boot);
 656         }
 657
 658         return mod;
 659 }