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  * $NetBSD: fat.c,v 1.12 2000/10/10 20:24:52 is Exp $
  33  * $FreeBSD: src/sbin/fsck_msdosfs/fat.c,v 1.1.2.1 2001/08/01 05:47:56 obrien Exp $
  34  * $DragonFly: src/sbin/fsck_msdosfs/fat.c,v 1.2 2003/06/17 04:27:32 dillon Exp $
  35  */
  36
  37
  38 #include <sys/cdefs.h>
  39
  40 #include <stdlib.h>
  41 #include <string.h>
  42 #include <ctype.h>
  43 #include <stdio.h>
  44 #include <unistd.h>
  45
  46 #include "ext.h"
  47 #include "fsutil.h"
  48
  49 static int checkclnum __P((struct bootblock *, int, cl_t, cl_t *));
  50 static int clustdiffer __P((cl_t, cl_t *, cl_t *, int));
  51 static int tryclear __P((struct bootblock *, struct fatEntry *, cl_t, cl_t *));
  52 static int _readfat __P((int, struct bootblock *, int, u_char **));
  53
  54 /*
  55  * Check a cluster number for valid value
  56  */
  57 static int
  58 checkclnum(boot, fat, cl, next)
  59         struct bootblock *boot;
  60         int fat;
  61         cl_t cl;
  62         cl_t *next;
  63 {
  64         if (*next >= (CLUST_RSRVD&boot->ClustMask))
  65                 *next |= ~boot->ClustMask;
  66         if (*next == CLUST_FREE) {
  67                 boot->NumFree++;
  68                 return FSOK;
  69         }
  70         if (*next == CLUST_BAD) {
  71                 boot->NumBad++;
  72                 return FSOK;
  73         }
  74         if (*next < CLUST_FIRST
  75             || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
  76                 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
  77                       cl, fat,
  78                       *next < CLUST_RSRVD ? "out of range" : "reserved",
  79                       *next&boot->ClustMask);
  80                 if (ask(0, "Truncate")) {
  81                         *next = CLUST_EOF;
  82                         return FSFATMOD;
  83                 }
  84                 return FSERROR;
  85         }
  86         return FSOK;
  87 }
  88
  89 /*
  90  * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
  91  */
  92 static int
  93 _readfat(fs, boot, no, buffer)
  94         int fs;
  95         struct bootblock *boot;
  96         int no;
  97         u_char **buffer;
  98 {
  99         off_t off;
 100
 101         *buffer = malloc(boot->FATsecs * boot->BytesPerSec);
 102         if (*buffer == NULL) {
 103                 perror("No space for FAT");
 104                 return 0;
 105         }
 106
 107         off = boot->ResSectors + no * boot->FATsecs;
 108         off *= boot->BytesPerSec;
 109
 110         if (lseek(fs, off, SEEK_SET) != off) {
 111                 perror("Unable to read FAT");
 112                 goto err;
 113         }
 114
 115         if (read(fs, *buffer, boot->FATsecs * boot->BytesPerSec)
 116             != boot->FATsecs * boot->BytesPerSec) {
 117                 perror("Unable to read FAT");
 118                 goto err;
 119         }
 120
 121         return 1;
 122
 123     err:
 124         free(*buffer);
 125         return 0;
 126 }
 127
 128 /*
 129  * Read a FAT and decode it into internal format
 130  */
 131 int
 132 readfat(fs, boot, no, fp)
 133         int fs;
 134         struct bootblock *boot;
 135         int no;
 136         struct fatEntry **fp;
 137 {
 138         struct fatEntry *fat;
 139         u_char *buffer, *p;
 140         cl_t cl;
 141         int ret = FSOK;
 142
 143         boot->NumFree = boot->NumBad = 0;
 144
 145         if (!_readfat(fs, boot, no, &buffer))
 146                 return FSFATAL;
 147
 148         fat = calloc(boot->NumClusters, sizeof(struct fatEntry));
 149         if (fat == NULL) {
 150                 perror("No space for FAT");
 151                 free(buffer);
 152                 return FSFATAL;
 153         }
 154
 155         if (buffer[0] != boot->Media
 156             || buffer[1] != 0xff || buffer[2] != 0xff
 157             || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
 158             || (boot->ClustMask == CLUST32_MASK
 159                 && ((buffer[3]&0x0f) != 0x0f
 160                     || buffer[4] != 0xff || buffer[5] != 0xff
 161                     || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
 162
 163                 /* Windows 95 OSR2 (and possibly any later) changes
 164                  * the FAT signature to 0xXXffff7f for FAT16 and to
 165                  * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
 166                  * filesystem is dirty if it doesn't reboot cleanly.
 167                  * Check this special condition before errorring out.
 168                  */
 169                 if (buffer[0] == boot->Media && buffer[1] == 0xff
 170                     && buffer[2] == 0xff
 171                     && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
 172                         || (boot->ClustMask == CLUST32_MASK
 173                             && buffer[3] == 0x0f && buffer[4] == 0xff
 174                             && buffer[5] == 0xff && buffer[6] == 0xff
 175                             && buffer[7] == 0x07)))
 176                         ret |= FSDIRTY;
 177                 else {
 178                         /* just some odd byte sequence in FAT */
 179
 180                         switch (boot->ClustMask) {
 181                         case CLUST32_MASK:
 182                                 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
 183                                       "FAT starts with odd byte sequence",
 184                                       buffer[0], buffer[1], buffer[2], buffer[3],
 185                                       buffer[4], buffer[5], buffer[6], buffer[7]);
 186                                 break;
 187                         case CLUST16_MASK:
 188                                 pwarn("%s (%02x%02x%02x%02x)\n",
 189                                     "FAT starts with odd byte sequence",
 190                                     buffer[0], buffer[1], buffer[2], buffer[3]);
 191                                 break;
 192                         default:
 193                                 pwarn("%s (%02x%02x%02x)\n",
 194                                     "FAT starts with odd byte sequence",
 195                                     buffer[0], buffer[1], buffer[2]);
 196                                 break;
 197                         }
 198
 199
 200                         if (ask(1, "Correct"))
 201                                 ret |= FSFIXFAT;
 202                 }
 203         }
 204         switch (boot->ClustMask) {
 205         case CLUST32_MASK:
 206                 p = buffer + 8;
 207                 break;
 208         case CLUST16_MASK:
 209                 p = buffer + 4;
 210                 break;
 211         default:
 212                 p = buffer + 3;
 213                 break;
 214         }
 215         for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
 216                 switch (boot->ClustMask) {
 217                 case CLUST32_MASK:
 218                         fat[cl].next = p[0] + (p[1] << 8)
 219                                        + (p[2] << 16) + (p[3] << 24);
 220                         fat[cl].next &= boot->ClustMask;
 221                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 222                         cl++;
 223                         p += 4;
 224                         break;
 225                 case CLUST16_MASK:
 226                         fat[cl].next = p[0] + (p[1] << 8);
 227                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 228                         cl++;
 229                         p += 2;
 230                         break;
 231                 default:
 232                         fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
 233                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 234                         cl++;
 235                         if (cl >= boot->NumClusters)
 236                                 break;
 237                         fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
 238                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 239                         cl++;
 240                         p += 3;
 241                         break;
 242                 }
 243         }
 244
 245         free(buffer);
 246         *fp = fat;
 247         return ret;
 248 }
 249
 250 /*
 251  * Get type of reserved cluster
 252  */
 253 char *
 254 rsrvdcltype(cl)
 255         cl_t cl;
 256 {
 257         if (cl == CLUST_FREE)
 258                 return "free";
 259         if (cl < CLUST_BAD)
 260                 return "reserved";
 261         if (cl > CLUST_BAD)
 262                 return "as EOF";
 263         return "bad";
 264 }
 265
 266 static int
 267 clustdiffer(cl, cp1, cp2, fatnum)
 268         cl_t cl;
 269         cl_t *cp1;
 270         cl_t *cp2;
 271         int fatnum;
 272 {
 273         if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
 274                 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 275                         if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
 276                              && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
 277                             || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
 278                                 pwarn("Cluster %u is marked %s with different indicators, ",
 279                                       cl, rsrvdcltype(*cp1));
 280                                 if (ask(1, "fix")) {
 281                                         *cp2 = *cp1;
 282                                         return FSFATMOD;
 283                                 }
 284                                 return FSFATAL;
 285                         }
 286                         pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %d\n",
 287                               cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
 288                         if (ask(0, "use FAT 0's entry")) {
 289                                 *cp2 = *cp1;
 290                                 return FSFATMOD;
 291                         }
 292                         if (ask(0, "use FAT %d's entry", fatnum)) {
 293                                 *cp1 = *cp2;
 294                                 return FSFATMOD;
 295                         }
 296                         return FSFATAL;
 297                 }
 298                 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
 299                       cl, rsrvdcltype(*cp1), *cp2, fatnum);
 300                 if (ask(0, "Use continuation from FAT %d", fatnum)) {
 301                         *cp1 = *cp2;
 302                         return FSFATMOD;
 303                 }
 304                 if (ask(0, "Use mark from FAT 0")) {
 305                         *cp2 = *cp1;
 306                         return FSFATMOD;
 307                 }
 308                 return FSFATAL;
 309         }
 310         if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 311                 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %d\n",
 312                       cl, *cp1, rsrvdcltype(*cp2), fatnum);
 313                 if (ask(0, "Use continuation from FAT 0")) {
 314                         *cp2 = *cp1;
 315                         return FSFATMOD;
 316                 }
 317                 if (ask(0, "Use mark from FAT %d", fatnum)) {
 318                         *cp1 = *cp2;
 319                         return FSFATMOD;
 320                 }
 321                 return FSERROR;
 322         }
 323         pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %d\n",
 324               cl, *cp1, *cp2, fatnum);
 325         if (ask(0, "Use continuation from FAT 0")) {
 326                 *cp2 = *cp1;
 327                 return FSFATMOD;
 328         }
 329         if (ask(0, "Use continuation from FAT %d", fatnum)) {
 330                 *cp1 = *cp2;
 331                 return FSFATMOD;
 332         }
 333         return FSERROR;
 334 }
 335
 336 /*
 337  * Compare two FAT copies in memory. Resolve any conflicts and merge them
 338  * into the first one.
 339  */
 340 int
 341 comparefat(boot, first, second, fatnum)
 342         struct bootblock *boot;
 343         struct fatEntry *first;
 344         struct fatEntry *second;
 345         int fatnum;
 346 {
 347         cl_t cl;
 348         int ret = FSOK;
 349
 350         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
 351                 if (first[cl].next != second[cl].next)
 352                         ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
 353         return ret;
 354 }
 355
 356 void
 357 clearchain(boot, fat, head)
 358         struct bootblock *boot;
 359         struct fatEntry *fat;
 360         cl_t head;
 361 {
 362         cl_t p, q;
 363
 364         for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
 365                 if (fat[p].head != head)
 366                         break;
 367                 q = fat[p].next;
 368                 fat[p].next = fat[p].head = CLUST_FREE;
 369                 fat[p].length = 0;
 370         }
 371 }
 372
 373 int
 374 tryclear(boot, fat, head, trunc)
 375         struct bootblock *boot;
 376         struct fatEntry *fat;
 377         cl_t head;
 378         cl_t *trunc;
 379 {
 380         if (ask(0, "Clear chain starting at %u", head)) {
 381                 clearchain(boot, fat, head);
 382                 return FSFATMOD;
 383         } else if (ask(0, "Truncate")) {
 384                 *trunc = CLUST_EOF;
 385                 return FSFATMOD;
 386         } else
 387                 return FSERROR;
 388 }
 389
 390 /*
 391  * Check a complete FAT in-memory for crosslinks
 392  */
 393 int
 394 checkfat(boot, fat)
 395         struct bootblock *boot;
 396         struct fatEntry *fat;
 397 {
 398         cl_t head, p, h, n;
 399         u_int len;
 400         int ret = 0;
 401         int conf;
 402
 403         /*
 404          * pass 1: figure out the cluster chains.
 405          */
 406         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 407                 /* find next untravelled chain */
 408                 if (fat[head].head != 0         /* cluster already belongs to some chain */
 409                     || fat[head].next == CLUST_FREE
 410                     || fat[head].next == CLUST_BAD)
 411                         continue;               /* skip it. */
 412
 413                 /* follow the chain and mark all clusters on the way */
 414                 for (len = 0, p = head;
 415                      p >= CLUST_FIRST && p < boot->NumClusters;
 416                      p = fat[p].next) {
 417                         fat[p].head = head;
 418                         len++;
 419                 }
 420
 421                 /* the head record gets the length */
 422                 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
 423         }
 424
 425         /*
 426          * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
 427          * we didn't know the real start of the chain then - would have treated partial
 428          * chains as interlinked with their main chain)
 429          */
 430         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 431                 /* find next untravelled chain */
 432                 if (fat[head].head != head)
 433                         continue;
 434
 435                 /* follow the chain to its end (hopefully) */
 436                 for (p = head;
 437                      (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
 438                      p = n)
 439                         if (fat[n].head != head)
 440                                 break;
 441                 if (n >= CLUST_EOFS)
 442                         continue;
 443
 444                 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
 445                         pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
 446                               head, rsrvdcltype(n));
 447                         ret |= tryclear(boot, fat, head, &fat[p].next);
 448                         continue;
 449                 }
 450                 if (n < CLUST_FIRST || n >= boot->NumClusters) {
 451                         pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
 452                               head, n);
 453                         ret |= tryclear(boot, fat, head, &fat[p].next);
 454                         continue;
 455                 }
 456                 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
 457                       head, fat[n].head, n);
 458                 conf = tryclear(boot, fat, head, &fat[p].next);
 459                 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
 460                         if (conf == FSERROR) {
 461                                 /*
 462                                  * Transfer the common chain to the one not cleared above.
 463                                  */
 464                                 for (p = n;
 465                                      p >= CLUST_FIRST && p < boot->NumClusters;
 466                                      p = fat[p].next) {
 467                                         if (h != fat[p].head) {
 468                                                 /*
 469                                                  * Have to reexamine this chain.
 470                                                  */
 471                                                 head--;
 472                                                 break;
 473                                         }
 474                                         fat[p].head = head;
 475                                 }
 476                         }
 477                         clearchain(boot, fat, h);
 478                         conf |= FSFATMOD;
 479                 }
 480                 ret |= conf;
 481         }
 482
 483         return ret;
 484 }
 485
 486 /*
 487  * Write out FATs encoding them from the internal format
 488  */
 489 int
 490 writefat(fs, boot, fat, correct_fat)
 491         int fs;
 492         struct bootblock *boot;
 493         struct fatEntry *fat;
 494         int correct_fat;
 495 {
 496         u_char *buffer, *p;
 497         cl_t cl;
 498         int i;
 499         u_int32_t fatsz;
 500         off_t off;
 501         int ret = FSOK;
 502
 503         buffer = malloc(fatsz = boot->FATsecs * boot->BytesPerSec);
 504         if (buffer == NULL) {
 505                 perror("No space for FAT");
 506                 return FSFATAL;
 507         }
 508         memset(buffer, 0, fatsz);
 509         boot->NumFree = 0;
 510         p = buffer;
 511         if (correct_fat) {
 512                 *p++ = (u_char)boot->Media;
 513                 *p++ = 0xff;
 514                 *p++ = 0xff;
 515                 switch (boot->ClustMask) {
 516                 case CLUST16_MASK:
 517                         *p++ = 0xff;
 518                         break;
 519                 case CLUST32_MASK:
 520                         *p++ = 0x0f;
 521                         *p++ = 0xff;
 522                         *p++ = 0xff;
 523                         *p++ = 0xff;
 524                         *p++ = 0x0f;
 525                         break;
 526                 }
 527         } else {
 528                 /* use same FAT signature as the old FAT has */
 529                 int count;
 530                 u_char *old_fat;
 531
 532                 switch (boot->ClustMask) {
 533                 case CLUST32_MASK:
 534                         count = 8;
 535                         break;
 536                 case CLUST16_MASK:
 537                         count = 4;
 538                         break;
 539                 default:
 540                         count = 3;
 541                         break;
 542                 }
 543
 544                 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
 545                                          &old_fat)) {
 546                         free(buffer);
 547                         return FSFATAL;
 548                 }
 549
 550                 memcpy(p, old_fat, count);
 551                 free(old_fat);
 552                 p += count;
 553         }
 554
 555         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
 556                 switch (boot->ClustMask) {
 557                 case CLUST32_MASK:
 558                         if (fat[cl].next == CLUST_FREE)
 559                                 boot->NumFree++;
 560                         *p++ = (u_char)fat[cl].next;
 561                         *p++ = (u_char)(fat[cl].next >> 8);
 562                         *p++ = (u_char)(fat[cl].next >> 16);
 563                         *p &= 0xf0;
 564                         *p++ |= (fat[cl].next >> 24)&0x0f;
 565                         break;
 566                 case CLUST16_MASK:
 567                         if (fat[cl].next == CLUST_FREE)
 568                                 boot->NumFree++;
 569                         *p++ = (u_char)fat[cl].next;
 570                         *p++ = (u_char)(fat[cl].next >> 8);
 571                         break;
 572                 default:
 573                         if (fat[cl].next == CLUST_FREE)
 574                                 boot->NumFree++;
 575                         if (cl + 1 < boot->NumClusters
 576                             && fat[cl + 1].next == CLUST_FREE)
 577                                 boot->NumFree++;
 578                         *p++ = (u_char)fat[cl].next;
 579                         *p++ = (u_char)((fat[cl].next >> 8) & 0xf)
 580                                |(u_char)(fat[cl+1].next << 4);
 581                         *p++ = (u_char)(fat[++cl].next >> 4);
 582                         break;
 583                 }
 584         }
 585         for (i = 0; i < boot->FATs; i++) {
 586                 off = boot->ResSectors + i * boot->FATsecs;
 587                 off *= boot->BytesPerSec;
 588                 if (lseek(fs, off, SEEK_SET) != off
 589                     || write(fs, buffer, fatsz) != fatsz) {
 590                         perror("Unable to write FAT");
 591                         ret = FSFATAL; /* Return immediately?           XXX */
 592                 }
 593         }
 594         free(buffer);
 595         return ret;
 596 }
 597
 598 /*
 599  * Check a complete in-memory FAT for lost cluster chains
 600  */
 601 int
 602 checklost(dosfs, boot, fat)
 603         int dosfs;
 604         struct bootblock *boot;
 605         struct fatEntry *fat;
 606 {
 607         cl_t head;
 608         int mod = FSOK;
 609         int ret;
 610
 611         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 612                 /* find next untravelled chain */
 613                 if (fat[head].head != head
 614                     || fat[head].next == CLUST_FREE
 615                     || (fat[head].next >= CLUST_RSRVD
 616                         && fat[head].next < CLUST_EOFS)
 617                     || (fat[head].flags & FAT_USED))
 618                         continue;
 619
 620                 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
 621                       head, fat[head].length);
 622                 mod |= ret = reconnect(dosfs, boot, fat, head);
 623                 if (mod & FSFATAL)
 624                         break;
 625                 if (ret == FSERROR && ask(0, "Clear")) {
 626                         clearchain(boot, fat, head);
 627                         mod |= FSFATMOD;
 628                 }
 629         }
 630         finishlf();
 631
 632         if (boot->FSInfo) {
 633                 ret = 0;
 634                 if (boot->FSFree != boot->NumFree) {
 635                         pwarn("Free space in FSInfo block (%d) not correct (%d)\n",
 636                               boot->FSFree, boot->NumFree);
 637                         if (ask(1, "fix")) {
 638                                 boot->FSFree = boot->NumFree;
 639                                 ret = 1;
 640                         }
 641                 }
 642                 if (boot->NumFree && fat[boot->FSNext].next != CLUST_FREE) {
 643                         pwarn("Next free cluster in FSInfo block (%u) not free\n",
 644                               boot->FSNext);
 645                         if (ask(1, "fix"))
 646                                 for (head = CLUST_FIRST; head < boot->NumClusters; head++)
 647                                         if (fat[head].next == CLUST_FREE) {
 648                                                 boot->FSNext = head;
 649                                                 ret = 1;
 650                                                 break;
 651                                         }
 652                 }
 653                 if (ret)
 654                         mod |= writefsinfo(dosfs, boot);
 655         }
 656
 657         return mod;
 658 }