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