src/fsck-msdos/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 <stdlib.h>
  35 #include <string.h>
  36 #include <ctype.h>
  37 #include <stdio.h>
  38 #include <unistd.h>
  39
  40 #include "ext.h"
  41 #include "fsutil.h"
  42
  43 static int checkclnum(struct bootblock *, int, cl_t, cl_t *);
  44 static int clustdiffer(cl_t, cl_t *, cl_t *, int);
  45 static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *);
  46 static int _readfat(int, struct bootblock *, int, u_char **);
  47
  48 /*-
  49  * The first 2 FAT entries contain pseudo-cluster numbers with the following
  50  * layout:
  51  *
  52  * 31...... ........ ........ .......0
  53  * rrrr1111 11111111 11111111 mmmmmmmm         FAT32 entry 0
  54  * rrrrsh11 11111111 11111111 11111xxx         FAT32 entry 1
  55  *
  56  *                   11111111 mmmmmmmm         FAT16 entry 0
  57  *                   sh111111 11111xxx         FAT16 entry 1
  58  *
  59  * r = reserved
  60  * m = BPB media ID byte
  61  * s = clean flag (1 = dismounted; 0 = still mounted)
  62  * h = hard error flag (1 = ok; 0 = I/O error)
  63  * x = any value ok
  64  */
  65
  66 int
  67 checkdirty(int fs, struct bootblock *boot)
  68 {
  69         off_t off;
  70         u_char *buffer;
  71         int ret = 0;
  72
  73         if (boot->ClustMask != CLUST16_MASK && boot->ClustMask != CLUST32_MASK)
  74                 return 0;
  75
  76         off = boot->ResSectors;
  77         off *= boot->BytesPerSec;
  78
  79         buffer = malloc(boot->BytesPerSec);
  80         if (buffer == NULL) {
  81                 perror("No space for FAT");
  82                 return 1;
  83         }
  84
  85         if (lseek(fs, off, SEEK_SET) != off) {
  86                 perror("Unable to read FAT");
  87                 goto err;
  88         }
  89
  90         if (read(fs, buffer, boot->BytesPerSec) != boot->BytesPerSec) {
  91                 perror("Unable to read FAT");
  92                 goto err;
  93         }
  94
  95         /*
  96          * If we don't understand the FAT, then the file system must be
  97          * assumed to be unclean.
  98          */
  99         if (buffer[0] != boot->Media || buffer[1] != 0xff)
 100                 goto err;
 101         if (boot->ClustMask == CLUST16_MASK) {
 102                 if ((buffer[2] & 0xf8) != 0xf8 || (buffer[3] & 0x3f) != 0x3f)
 103                         goto err;
 104         } else {
 105                 if (buffer[2] != 0xff || (buffer[3] & 0x0f) != 0x0f
 106                     || (buffer[4] & 0xf8) != 0xf8 || buffer[5] != 0xff
 107                     || buffer[6] != 0xff || (buffer[7] & 0x03) != 0x03)
 108                         goto err;
 109         }
 110
 111         /*
 112          * Now check the actual clean flag (and the no-error flag).
 113          */
 114         if (boot->ClustMask == CLUST16_MASK) {
 115                 if ((buffer[3] & 0xc0) == 0xc0)
 116                         ret = 1;
 117         } else {
 118                 if ((buffer[7] & 0x0c) == 0x0c)
 119                         ret = 1;
 120         }
 121
 122 err:
 123         free(buffer);
 124         return ret;
 125 }
 126
 127 /*
 128  * Check a cluster number for valid value
 129  */
 130 static int
 131 checkclnum(struct bootblock *boot, int fat, cl_t cl, cl_t *next)
 132 {
 133         if (*next >= (CLUST_RSRVD&boot->ClustMask))
 134                 *next |= ~boot->ClustMask;
 135         if (*next == CLUST_FREE) {
 136                 boot->NumFree++;
 137                 return FSOK;
 138         }
 139         if (*next == CLUST_BAD) {
 140                 boot->NumBad++;
 141                 return FSOK;
 142         }
 143         if (*next < CLUST_FIRST
 144             || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
 145                 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
 146                       cl, fat,
 147                       *next < CLUST_RSRVD ? "out of range" : "reserved",
 148                       *next&boot->ClustMask);
 149                 if (ask(1, "Truncate")) {
 150                         *next = CLUST_EOF;
 151                         return FSFATMOD;
 152                 }
 153                 return FSERROR;
 154         }
 155         return FSOK;
 156 }
 157
 158 /*
 159  * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
 160  */
 161 static int
 162 _readfat(int fs, struct bootblock *boot, int no, u_char **buffer)
 163 {
 164         off_t off;
 165
 166         printf("Attempting to allocate %u KB for FAT\n",
 167                 (boot->FATsecs * boot->BytesPerSec) / 1024);
 168
 169         *buffer = malloc(boot->FATsecs * boot->BytesPerSec);
 170         if (*buffer == NULL) {
 171                 perror("No space for FAT");
 172                 return 0;
 173         }
 174
 175         off = boot->ResSectors + no * boot->FATsecs;
 176         off *= boot->BytesPerSec;
 177
 178         if (lseek(fs, off, SEEK_SET) != off) {
 179                 perror("Unable to read FAT");
 180                 goto err;
 181         }
 182
 183         if (read(fs, *buffer, boot->FATsecs * boot->BytesPerSec)
 184             != boot->FATsecs * boot->BytesPerSec) {
 185                 perror("Unable to read FAT");
 186                 goto err;
 187         }
 188
 189         return 1;
 190
 191     err:
 192         free(*buffer);
 193         return 0;
 194 }
 195
 196 /*
 197  * Read a FAT and decode it into internal format
 198  */
 199 int
 200 readfat(int fs, struct bootblock *boot, int no, struct fatEntry **fp)
 201 {
 202         struct fatEntry *fat;
 203         u_char *buffer, *p;
 204         cl_t cl;
 205         int ret = FSOK;
 206
 207         boot->NumFree = boot->NumBad = 0;
 208
 209         if (!_readfat(fs, boot, no, &buffer))
 210                 return FSFATAL;
 211
 212         fat = calloc(boot->NumClusters, sizeof(struct fatEntry));
 213         if (fat == NULL) {
 214                 perror("No space for FAT");
 215                 free(buffer);
 216                 return FSFATAL;
 217         }
 218
 219         if (buffer[0] != boot->Media
 220             || buffer[1] != 0xff || buffer[2] != 0xff
 221             || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
 222             || (boot->ClustMask == CLUST32_MASK
 223                 && ((buffer[3]&0x0f) != 0x0f
 224                     || buffer[4] != 0xff || buffer[5] != 0xff
 225                     || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
 226
 227                 /* Windows 95 OSR2 (and possibly any later) changes
 228                  * the FAT signature to 0xXXffff7f for FAT16 and to
 229                  * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
 230                  * file system is dirty if it doesn't reboot cleanly.
 231                  * Check this special condition before errorring out.
 232                  */
 233                 if (buffer[0] == boot->Media && buffer[1] == 0xff
 234                     && buffer[2] == 0xff
 235                     && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
 236                         || (boot->ClustMask == CLUST32_MASK
 237                             && buffer[3] == 0x0f && buffer[4] == 0xff
 238                             && buffer[5] == 0xff && buffer[6] == 0xff
 239                             && buffer[7] == 0x07)))
 240                         ret |= FSDIRTY;
 241                 else {
 242                         /* just some odd byte sequence in FAT */
 243
 244                         switch (boot->ClustMask) {
 245                         case CLUST32_MASK:
 246                                 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
 247                                       "FAT starts with odd byte sequence",
 248                                       buffer[0], buffer[1], buffer[2], buffer[3],
 249                                       buffer[4], buffer[5], buffer[6], buffer[7]);
 250                                 break;
 251                         case CLUST16_MASK:
 252                                 pwarn("%s (%02x%02x%02x%02x)\n",
 253                                     "FAT starts with odd byte sequence",
 254                                     buffer[0], buffer[1], buffer[2], buffer[3]);
 255                                 break;
 256                         default:
 257                                 pwarn("%s (%02x%02x%02x)\n",
 258                                     "FAT starts with odd byte sequence",
 259                                     buffer[0], buffer[1], buffer[2]);
 260                                 break;
 261                         }
 262
 263
 264                         if (ask(1, "Correct"))
 265                                 ret |= FSFIXFAT;
 266                 }
 267         }
 268         switch (boot->ClustMask) {
 269         case CLUST32_MASK:
 270                 p = buffer + 8;
 271                 break;
 272         case CLUST16_MASK:
 273                 p = buffer + 4;
 274                 break;
 275         default:
 276                 p = buffer + 3;
 277                 break;
 278         }
 279         for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
 280                 switch (boot->ClustMask) {
 281                 case CLUST32_MASK:
 282                         fat[cl].next = p[0] + (p[1] << 8)
 283                                        + (p[2] << 16) + (p[3] << 24);
 284                         fat[cl].next &= boot->ClustMask;
 285                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 286                         cl++;
 287                         p += 4;
 288                         break;
 289                 case CLUST16_MASK:
 290                         fat[cl].next = p[0] + (p[1] << 8);
 291                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 292                         cl++;
 293                         p += 2;
 294                         break;
 295                 default:
 296                         fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
 297                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 298                         cl++;
 299                         if (cl >= boot->NumClusters)
 300                                 break;
 301                         fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
 302                         ret |= checkclnum(boot, no, cl, &fat[cl].next);
 303                         cl++;
 304                         p += 3;
 305                         break;
 306                 }
 307         }
 308
 309         free(buffer);
 310         *fp = fat;
 311         return ret;
 312 }
 313
 314 /*
 315  * Get type of reserved cluster
 316  */
 317 char *
 318 rsrvdcltype(cl_t cl)
 319 {
 320         if (cl == CLUST_FREE)
 321                 return "free";
 322         if (cl < CLUST_BAD)
 323                 return "reserved";
 324         if (cl > CLUST_BAD)
 325                 return "as EOF";
 326         return "bad";
 327 }
 328
 329 static int
 330 clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, int fatnum)
 331 {
 332         if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
 333                 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 334                         if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
 335                              && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
 336                             || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
 337                                 pwarn("Cluster %u is marked %s with different indicators\n",
 338                                       cl, rsrvdcltype(*cp1));
 339                                 if (ask(1, "Fix")) {
 340                                         *cp2 = *cp1;
 341                                         return FSFATMOD;
 342                                 }
 343                                 return FSFATAL;
 344                         }
 345                         pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %d\n",
 346                               cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
 347                         if (ask(1, "Use FAT 0's entry")) {
 348                                 *cp2 = *cp1;
 349                                 return FSFATMOD;
 350                         }
 351                         if (ask(1, "Use FAT %d's entry", fatnum)) {
 352                                 *cp1 = *cp2;
 353                                 return FSFATMOD;
 354                         }
 355                         return FSFATAL;
 356                 }
 357                 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
 358                       cl, rsrvdcltype(*cp1), *cp2, fatnum);
 359                 if (ask(1, "Use continuation from FAT %d", fatnum)) {
 360                         *cp1 = *cp2;
 361                         return FSFATMOD;
 362                 }
 363                 if (ask(1, "Use mark from FAT 0")) {
 364                         *cp2 = *cp1;
 365                         return FSFATMOD;
 366                 }
 367                 return FSFATAL;
 368         }
 369         if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
 370                 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %d\n",
 371                       cl, *cp1, rsrvdcltype(*cp2), fatnum);
 372                 if (ask(1, "Use continuation from FAT 0")) {
 373                         *cp2 = *cp1;
 374                         return FSFATMOD;
 375                 }
 376                 if (ask(1, "Use mark from FAT %d", fatnum)) {
 377                         *cp1 = *cp2;
 378                         return FSFATMOD;
 379                 }
 380                 return FSERROR;
 381         }
 382         pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %d\n",
 383               cl, *cp1, *cp2, fatnum);
 384         if (ask(1, "Use continuation from FAT 0")) {
 385                 *cp2 = *cp1;
 386                 return FSFATMOD;
 387         }
 388         if (ask(1, "Use continuation from FAT %d", fatnum)) {
 389                 *cp1 = *cp2;
 390                 return FSFATMOD;
 391         }
 392         return FSERROR;
 393 }
 394
 395 /*
 396  * Compare two FAT copies in memory. Resolve any conflicts and merge them
 397  * into the first one.
 398  */
 399 int
 400 comparefat(struct bootblock *boot, struct fatEntry *first,
 401     struct fatEntry *second, int fatnum)
 402 {
 403         cl_t cl;
 404         int ret = FSOK;
 405
 406         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
 407                 if (first[cl].next != second[cl].next)
 408                         ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
 409         return ret;
 410 }
 411
 412 void
 413 clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head)
 414 {
 415         cl_t p, q;
 416
 417         for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
 418                 if (fat[p].head != head)
 419                         break;
 420                 q = fat[p].next;
 421                 fat[p].next = fat[p].head = CLUST_FREE;
 422                 fat[p].length = 0;
 423         }
 424 }
 425
 426 int
 427 tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *trunc)
 428 {
 429         if (ask(1, "Clear chain starting at %u", head)) {
 430                 clearchain(boot, fat, head);
 431                 return FSFATMOD;
 432         } else if (ask(1, "Truncate")) {
 433                 *trunc = CLUST_EOF;
 434                 return FSFATMOD;
 435         } else
 436                 return FSERROR;
 437 }
 438
 439 /*
 440  * Check a complete FAT in-memory for crosslinks
 441  */
 442 int
 443 checkfat(struct bootblock *boot, struct fatEntry *fat)
 444 {
 445         cl_t head, p, h, n, wdk;
 446         u_int len;
 447         int ret = 0;
 448         int conf;
 449
 450         /*
 451          * pass 1: figure out the cluster chains.
 452          */
 453         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 454                 /* find next untravelled chain */
 455                 if (fat[head].head != 0         /* cluster already belongs to some chain */
 456                     || fat[head].next == CLUST_FREE
 457                     || fat[head].next == CLUST_BAD)
 458                         continue;               /* skip it. */
 459
 460                 /* follow the chain and mark all clusters on the way */
 461                 for (len = 0, p = head;
 462                          p >= CLUST_FIRST && p < boot->NumClusters;
 463                          p = fat[p].next) {
 464                                 /* we have to check the len, to avoid infinite loop */
 465                                 if (len > boot->NumClusters) {
 466                                         printf("detect cluster chain loop: head %u for p %u\n", head, p);
 467                                         break;
 468                         }
 469
 470                         fat[p].head = head;
 471                         len++;
 472                 }
 473
 474                 /* the head record gets the length */
 475                 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
 476         }
 477
 478         /*
 479          * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
 480          * we didn't know the real start of the chain then - would have treated partial
 481          * chains as interlinked with their main chain)
 482          */
 483         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 484                 /* find next untravelled chain */
 485                 if (fat[head].head != head)
 486                         continue;
 487
 488                 /* follow the chain to its end (hopefully) */
 489                 /* also possible infinite loop, that's why I insert wdk counter */
 490                 for (p = head,wdk=boot->NumClusters;
 491                      (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters && wdk;
 492                                  p = n,wdk--) {
 493                         if (fat[n].head != head)
 494                                 break;
 495                 }
 496
 497                 if (n >= CLUST_EOFS)
 498                         continue;
 499
 500                 if (n == CLUST_FREE || n >= CLUST_RSRVD) {
 501                         pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
 502                               head, rsrvdcltype(n));
 503                         ret |= tryclear(boot, fat, head, &fat[p].next);
 504                         continue;
 505                 }
 506                 if (n < CLUST_FIRST || n >= boot->NumClusters) {
 507                         pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
 508                               head, n);
 509                         ret |= tryclear(boot, fat, head, &fat[p].next);
 510                         continue;
 511                 }
 512                 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
 513                       head, fat[n].head, n);
 514                 conf = tryclear(boot, fat, head, &fat[p].next);
 515                 if (ask(1, "Clear chain starting at %u", h = fat[n].head)) {
 516                         if (conf == FSERROR) {
 517                                 /*
 518                                  * Transfer the common chain to the one not cleared above.
 519                                  */
 520                                 for (p = n;
 521                                      p >= CLUST_FIRST && p < boot->NumClusters;
 522                                      p = fat[p].next) {
 523                                         if (h != fat[p].head) {
 524                                                 /*
 525                                                  * Have to reexamine this chain.
 526                                                  */
 527                                                 head--;
 528                                                 break;
 529                                         }
 530                                         fat[p].head = head;
 531                                 }
 532                         }
 533                         clearchain(boot, fat, h);
 534                         conf |= FSFATMOD;
 535                 }
 536                 ret |= conf;
 537         }
 538
 539         return ret;
 540 }
 541
 542 /*
 543  * Write out FATs encoding them from the internal format
 544  */
 545 int
 546 writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
 547 {
 548         u_char *buffer, *p;
 549         cl_t cl;
 550         int i;
 551         u_int32_t fatsz;
 552         off_t off;
 553         int ret = FSOK;
 554
 555         buffer = malloc(fatsz = boot->FATsecs * boot->BytesPerSec);
 556         if (buffer == NULL) {
 557                 perror("No space for FAT");
 558                 return FSFATAL;
 559         }
 560         memset(buffer, 0, fatsz);
 561         boot->NumFree = 0;
 562         p = buffer;
 563         if (correct_fat) {
 564                 *p++ = (u_char)boot->Media;
 565                 *p++ = 0xff;
 566                 *p++ = 0xff;
 567                 switch (boot->ClustMask) {
 568                 case CLUST16_MASK:
 569                         *p++ = 0xff;
 570                         break;
 571                 case CLUST32_MASK:
 572                         *p++ = 0x0f;
 573                         *p++ = 0xff;
 574                         *p++ = 0xff;
 575                         *p++ = 0xff;
 576                         *p++ = 0x0f;
 577                         break;
 578                 }
 579         } else {
 580                 /* use same FAT signature as the old FAT has */
 581                 int count;
 582                 u_char *old_fat;
 583
 584                 switch (boot->ClustMask) {
 585                 case CLUST32_MASK:
 586                         count = 8;
 587                         break;
 588                 case CLUST16_MASK:
 589                         count = 4;
 590                         break;
 591                 default:
 592                         count = 3;
 593                         break;
 594                 }
 595
 596                 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
 597                                          &old_fat)) {
 598                         free(buffer);
 599                         return FSFATAL;
 600                 }
 601
 602                 memcpy(p, old_fat, count);
 603                 free(old_fat);
 604                 p += count;
 605         }
 606
 607         for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
 608                 switch (boot->ClustMask) {
 609                 case CLUST32_MASK:
 610                         if (fat[cl].next == CLUST_FREE)
 611                                 boot->NumFree++;
 612                         *p++ = (u_char)fat[cl].next;
 613                         *p++ = (u_char)(fat[cl].next >> 8);
 614                         *p++ = (u_char)(fat[cl].next >> 16);
 615                         *p &= 0xf0;
 616                         *p++ |= (fat[cl].next >> 24)&0x0f;
 617                         break;
 618                 case CLUST16_MASK:
 619                         if (fat[cl].next == CLUST_FREE)
 620                                 boot->NumFree++;
 621                         *p++ = (u_char)fat[cl].next;
 622                         *p++ = (u_char)(fat[cl].next >> 8);
 623                         break;
 624                 default:
 625                         if (fat[cl].next == CLUST_FREE)
 626                                 boot->NumFree++;
 627                         if (cl + 1 < boot->NumClusters
 628                             && fat[cl + 1].next == CLUST_FREE)
 629                                 boot->NumFree++;
 630                         *p++ = (u_char)fat[cl].next;
 631                         *p++ = (u_char)((fat[cl].next >> 8) & 0xf)
 632                                |(u_char)(fat[cl+1].next << 4);
 633                         *p++ = (u_char)(fat[++cl].next >> 4);
 634                         break;
 635                 }
 636         }
 637         for (i = 0; i < boot->FATs; i++) {
 638                 off = boot->ResSectors + i * boot->FATsecs;
 639                 off *= boot->BytesPerSec;
 640                 if (lseek(fs, off, SEEK_SET) != off
 641                     || write(fs, buffer, fatsz) != fatsz) {
 642                         perror("Unable to write FAT");
 643                         ret = FSFATAL; /* Return immediately?           XXX */
 644                 }
 645         }
 646         free(buffer);
 647         return ret;
 648 }
 649
 650 /*
 651  * Check a complete in-memory FAT for lost cluster chains
 652  */
 653 int
 654 checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
 655 {
 656         cl_t head;
 657         int mod = FSOK;
 658         int ret;
 659
 660         for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
 661                 /* find next untravelled chain */
 662                 if (fat[head].head != head
 663                     || fat[head].next == CLUST_FREE
 664                     || (fat[head].next >= CLUST_RSRVD
 665                         && fat[head].next < CLUST_EOFS)
 666                     || (fat[head].flags & FAT_USED))
 667                         continue;
 668
 669                 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
 670                       head, fat[head].length);
 671                 mod |= ret = reconnect(dosfs, boot, fat, head);
 672                 if (mod & FSFATAL) {
 673                         /* If the reconnect failed, then just clear the chain */
 674                         pwarn("Error reconnecting chain - clearing\n");
 675                         mod &= ~FSFATAL;
 676                         clearchain(boot, fat, head);
 677                         mod |= FSFATMOD;
 678                         continue;
 679                 }
 680                 if (ret == FSERROR && ask(1, "Clear")) {
 681                         clearchain(boot, fat, head);
 682                         mod |= FSFATMOD;
 683                 }
 684         }
 685         finishlf();
 686
 687         if (boot->FSInfo) {
 688                 ret = 0;
 689                 if (boot->FSFree != boot->NumFree) {
 690                         pwarn("Free space in FSInfo block (%d) not correct (%d)\n",
 691                               boot->FSFree, boot->NumFree);
 692                         if (ask(1, "Fix")) {
 693                                 boot->FSFree = boot->NumFree;
 694                                 ret = 1;
 695                         }
 696                 }
 697
 698                 if (boot->NumFree) {
 699                         if ((boot->FSNext >= boot->NumClusters) || (fat[boot->FSNext].next != CLUST_FREE)) {
 700                                 pwarn("Next free cluster in FSInfo block (%u) not free\n",
 701                                       boot->FSNext);
 702                                 if (ask(1, "Fix"))
 703                                         for (head = CLUST_FIRST; head < boot->NumClusters; head++)
 704                                                 if (fat[head].next == CLUST_FREE) {
 705                                                         boot->FSNext = head;
 706                                                         ret = 1;
 707                                                         break;
 708                                                 }
 709                         }
 710         }
 711
 712                 if (boot->FSNext > boot->NumClusters  ) {
 713                         pwarn("FSNext block (%d) not correct NumClusters (%d)\n",
 714                                         boot->FSNext, boot->NumClusters);
 715                         boot->FSNext=CLUST_FIRST; // boot->FSNext can have -1 value.
 716             }
 717
 718                 if (boot->NumFree && fat[boot->FSNext].next != CLUST_FREE) {
 719                         pwarn("Next free cluster in FSInfo block (%u) not free\n",
 720                                         boot->FSNext);
 721                         if (ask(1, "Fix"))
 722                                 for (head = CLUST_FIRST; head < boot->NumClusters; head++)
 723                                         if (fat[head].next == CLUST_FREE) {
 724                                                 boot->FSNext = head;
 725                                                 ret = 1;
 726                                                 break;
 727                                         }
 728             }
 729
 730                 if (ret)
 731                         mod |= writefsinfo(dosfs, boot);
 732         }
 733
 734         return mod;
 735 }