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 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 27#include <stdlib.h> 28#include <string.h> 29#include <ctype.h> 30#include <stdio.h> 31#include <unistd.h> 32 33#include "ext.h" 34 35static int checkclnum(struct bootblock *, u_int, cl_t, cl_t *); 36static int clustdiffer(cl_t, cl_t *, cl_t *, u_int); 37static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *); 38static int _readfat(int, struct bootblock *, u_int, u_char **); 39 40/*- 41 * The first 2 FAT entries contain pseudo-cluster numbers with the following 42 * layout: 43 * 44 * 31...... ........ ........ .......0 45 * rrrr1111 11111111 11111111 mmmmmmmm FAT32 entry 0 46 * rrrrsh11 11111111 11111111 11111xxx FAT32 entry 1 47 * 48 * 11111111 mmmmmmmm FAT16 entry 0 49 * sh111111 11111xxx FAT16 entry 1 50 * 51 * r = reserved 52 * m = BPB media ID byte 53 * s = clean flag (1 = dismounted; 0 = still mounted) 54 * h = hard error flag (1 = ok; 0 = I/O error) 55 * x = any value ok 56 */ 57 58int 59checkdirty(int fs, struct bootblock *boot) 60{ 61 off_t off; 62 u_char *buffer; 63 int ret = 0; 64 size_t len; 65 66 if (boot->ClustMask != CLUST16_MASK && boot->ClustMask != CLUST32_MASK) 67 return 0; 68 69 off = boot->bpbResSectors; 70 off *= boot->bpbBytesPerSec; 71 72 buffer = malloc(len = boot->bpbBytesPerSec); 73 if (buffer == NULL) { 74 perr("No space for FAT sectors (%zu)", len); 75 return 1; 76 } 77 78 if (lseek(fs, off, SEEK_SET) != off) { 79 perr("Unable to read FAT"); 80 goto err; 81 } 82 83 if ((size_t)read(fs, buffer, boot->bpbBytesPerSec) != 84 boot->bpbBytesPerSec) { 85 perr("Unable to read FAT"); 86 goto err; 87 } 88 89 /* 90 * If we don't understand the FAT, then the file system must be 91 * assumed to be unclean. 92 */ 93 if (buffer[0] != boot->bpbMedia || buffer[1] != 0xff) 94 goto err; 95 if (boot->ClustMask == CLUST16_MASK) { 96 if ((buffer[2] & 0xf8) != 0xf8 || (buffer[3] & 0x3f) != 0x3f) 97 goto err; 98 } else { 99 if (buffer[2] != 0xff || (buffer[3] & 0x0f) != 0x0f 100 || (buffer[4] & 0xf8) != 0xf8 || buffer[5] != 0xff 101 || buffer[6] != 0xff || (buffer[7] & 0x03) != 0x03) 102 goto err; 103 } 104 105 /* 106 * Now check the actual clean flag (and the no-error flag). 107 */ 108 if (boot->ClustMask == CLUST16_MASK) { 109 if ((buffer[3] & 0xc0) == 0xc0) 110 ret = 1; 111 } else { 112 if ((buffer[7] & 0x0c) == 0x0c) 113 ret = 1; 114 } 115 116err: 117 free(buffer); 118 return ret; 119} 120 121/* 122 * Check a cluster number for valid value 123 */ 124static int 125checkclnum(struct bootblock *boot, u_int fat, cl_t cl, cl_t *next) 126{ 127 if (*next >= (CLUST_RSRVD&boot->ClustMask)) 128 *next |= ~boot->ClustMask; 129 if (*next == CLUST_FREE) { 130 boot->NumFree++; 131 return FSOK; 132 } 133 if (*next == CLUST_BAD) { 134 boot->NumBad++; 135 return FSOK; 136 } 137 if (*next < CLUST_FIRST 138 || (*next >= boot->NumClusters && *next < CLUST_EOFS)) { 139 pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n", 140 cl, fat, 141 *next < CLUST_RSRVD ? "out of range" : "reserved", 142 *next&boot->ClustMask); 143 if (ask(0, "Truncate")) { 144 *next = CLUST_EOF; 145 return FSFATMOD; 146 } 147 return FSERROR; 148 } 149 return FSOK; 150} 151 152/* 153 * Read a FAT from disk. Returns 1 if successful, 0 otherwise. 154 */ 155static int 156_readfat(int fs, struct bootblock *boot, u_int no, u_char **buffer) 157{ 158 off_t off; 159 size_t len; 160 161 *buffer = malloc(len = boot->FATsecs * boot->bpbBytesPerSec); 162 if (*buffer == NULL) { 163 perr("No space for FAT sectors (%zu)", len); 164 return 0; 165 } 166 167 off = boot->bpbResSectors + no * boot->FATsecs; 168 off *= boot->bpbBytesPerSec; 169 170 if (lseek(fs, off, SEEK_SET) != off) { 171 perr("Unable to read FAT"); 172 goto err; 173 } 174 175 if ((size_t)read(fs, *buffer, boot->FATsecs * boot->bpbBytesPerSec) 176 != boot->FATsecs * boot->bpbBytesPerSec) { 177 perr("Unable to read FAT"); 178 goto err; 179 } 180 181 return 1; 182 183 err: 184 free(*buffer); 185 return 0; 186} 187 188/* 189 * Read a FAT and decode it into internal format 190 */ 191int 192readfat(int fs, struct bootblock *boot, u_int no, struct fatEntry **fp) 193{ 194 struct fatEntry *fat; 195 u_char *buffer, *p; 196 cl_t cl; 197 int ret = FSOK; 198 size_t len; 199 200 boot->NumFree = boot->NumBad = 0; 201 202 if (!_readfat(fs, boot, no, &buffer)) 203 return FSFATAL; 204 205 fat = malloc(len = boot->NumClusters * sizeof(struct fatEntry)); 206 if (fat == NULL) { 207 perr("No space for FAT clusters (%zu)", len); 208 free(buffer); 209 return FSFATAL; 210 } 211 (void)memset(fat, 0, len); 212 213 if (buffer[0] != boot->bpbMedia 214 || buffer[1] != 0xff || buffer[2] != 0xff 215 || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff) 216 || (boot->ClustMask == CLUST32_MASK 217 && ((buffer[3]&0x0f) != 0x0f 218 || buffer[4] != 0xff || buffer[5] != 0xff 219 || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) { 220 221 /* Windows 95 OSR2 (and possibly any later) changes 222 * the FAT signature to 0xXXffff7f for FAT16 and to 223 * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the 224 * file system is dirty if it doesn't reboot cleanly. 225 * Check this special condition before errorring out. 226 */ 227 if (buffer[0] == boot->bpbMedia && buffer[1] == 0xff 228 && buffer[2] == 0xff 229 && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f) 230 || (boot->ClustMask == CLUST32_MASK 231 && buffer[3] == 0x0f && buffer[4] == 0xff 232 && buffer[5] == 0xff && buffer[6] == 0xff 233 && buffer[7] == 0x07))) 234 ret |= FSDIRTY; 235 else { 236 /* just some odd byte sequence in FAT */ 237 238 switch (boot->ClustMask) { 239 case CLUST32_MASK: 240 pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n", 241 "FAT starts with odd byte sequence", 242 buffer[0], buffer[1], buffer[2], buffer[3], 243 buffer[4], buffer[5], buffer[6], buffer[7]); 244 break; 245 case CLUST16_MASK: 246 pwarn("%s (%02x%02x%02x%02x)\n", 247 "FAT starts with odd byte sequence", 248 buffer[0], buffer[1], buffer[2], buffer[3]); 249 break; 250 default: 251 pwarn("%s (%02x%02x%02x)\n", 252 "FAT starts with odd byte sequence", 253 buffer[0], buffer[1], buffer[2]); 254 break; 255 } 256 257 258 if (ask(1, "Correct")) 259 ret |= FSFIXFAT; 260 } 261 } 262 switch (boot->ClustMask) { 263 case CLUST32_MASK: 264 p = buffer + 8; 265 break; 266 case CLUST16_MASK: 267 p = buffer + 4; 268 break; 269 default: 270 p = buffer + 3; 271 break; 272 } 273 for (cl = CLUST_FIRST; cl < boot->NumClusters;) { 274 switch (boot->ClustMask) { 275 case CLUST32_MASK: 276 fat[cl].next = p[0] + (p[1] << 8) 277 + (p[2] << 16) + (p[3] << 24); 278 fat[cl].next &= boot->ClustMask; 279 ret |= checkclnum(boot, no, cl, &fat[cl].next); 280 cl++; 281 p += 4; 282 break; 283 case CLUST16_MASK: 284 fat[cl].next = p[0] + (p[1] << 8); 285 ret |= checkclnum(boot, no, cl, &fat[cl].next); 286 cl++; 287 p += 2; 288 break; 289 default: 290 fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff; 291 ret |= checkclnum(boot, no, cl, &fat[cl].next); 292 cl++; 293 if (cl >= boot->NumClusters) 294 break; 295 fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff; 296 ret |= checkclnum(boot, no, cl, &fat[cl].next); 297 cl++; 298 p += 3; 299 break; 300 } 301 } 302 303 free(buffer); 304 if (ret & FSFATAL) { 305 free(fat); 306 *fp = NULL; 307 } else 308 *fp = fat; 309 return ret; 310} 311 312/* 313 * Get type of reserved cluster 314 */ 315const char * 316rsrvdcltype(cl_t cl) 317{ 318 if (cl == CLUST_FREE) 319 return "free"; 320 if (cl < CLUST_BAD) 321 return "reserved"; 322 if (cl > CLUST_BAD) 323 return "as EOF"; 324 return "bad"; 325} 326 327static int 328clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum) 329{ 330 if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) { 331 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) { 332 if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD 333 && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD) 334 || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) { 335 pwarn("Cluster %u is marked %s with different indicators\n", 336 cl, rsrvdcltype(*cp1)); 337 if (ask(1, "Fix")) { 338 *cp2 = *cp1; 339 return FSFATMOD; 340 } 341 return FSFATAL; 342 } 343 pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n", 344 cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum); 345 if (ask(0, "Use FAT 0's entry")) { 346 *cp2 = *cp1; 347 return FSFATMOD; 348 } 349 if (ask(0, "Use FAT %u's entry", fatnum)) { 350 *cp1 = *cp2; 351 return FSFATMOD; 352 } 353 return FSFATAL; 354 } 355 pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n", 356 cl, rsrvdcltype(*cp1), *cp2, fatnum); 357 if (ask(0, "Use continuation from FAT %u", fatnum)) { 358 *cp1 = *cp2; 359 return FSFATMOD; 360 } 361 if (ask(0, "Use mark from FAT 0")) { 362 *cp2 = *cp1; 363 return FSFATMOD; 364 } 365 return FSFATAL; 366 } 367 if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) { 368 pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n", 369 cl, *cp1, rsrvdcltype(*cp2), fatnum); 370 if (ask(0, "Use continuation from FAT 0")) { 371 *cp2 = *cp1; 372 return FSFATMOD; 373 } 374 if (ask(0, "Use mark from FAT %d", fatnum)) { 375 *cp1 = *cp2; 376 return FSFATMOD; 377 } 378 return FSERROR; 379 } 380 pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n", 381 cl, *cp1, *cp2, fatnum); 382 if (ask(0, "Use continuation from FAT 0")) { 383 *cp2 = *cp1; 384 return FSFATMOD; 385 } 386 if (ask(0, "Use continuation from FAT %u", fatnum)) { 387 *cp1 = *cp2; 388 return FSFATMOD; 389 } 390 return FSERROR; 391} 392 393/* 394 * Compare two FAT copies in memory. Resolve any conflicts and merge them 395 * into the first one. 396 */ 397int 398comparefat(struct bootblock *boot, struct fatEntry *first, 399 struct fatEntry *second, u_int fatnum) 400{ 401 cl_t cl; 402 int ret = FSOK; 403 404 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) 405 if (first[cl].next != second[cl].next) 406 ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum); 407 return ret; 408} 409 410void 411clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head) 412{ 413 cl_t p, q; 414 415 for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) { 416 if (fat[p].head != head) 417 break; 418 q = fat[p].next; 419 fat[p].next = fat[p].head = CLUST_FREE; 420 fat[p].length = 0; 421 } 422} 423 424int 425tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp) 426{ 427 if (ask(0, "Clear chain starting at %u", head)) { 428 clearchain(boot, fat, head); 429 return FSFATMOD; 430 } else if (ask(0, "Truncate")) { 431 uint32_t len; 432 cl_t p; 433 434 for (p = head, len = 0; 435 p >= CLUST_FIRST && p < boot->NumClusters; 436 p = fat[p].next, len++) 437 continue; 438 *truncp = CLUST_EOF; 439 fat[head].length = len; 440 return FSFATMOD; 441 } else 442 return FSERROR; 443} 444 445/* 446 * Check a complete FAT in-memory for crosslinks 447 */ 448int 449checkfat(struct bootblock *boot, struct fatEntry *fat) 450{ 451 cl_t head, p, h, n; 452 u_int len; 453 int ret = 0; 454 int conf; 455 456 /* 457 * pass 1: figure out the cluster chains. 458 */ 459 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 460 /* find next untravelled chain */ 461 if (fat[head].head != 0 /* cluster already belongs to some chain */ 462 || fat[head].next == CLUST_FREE 463 || fat[head].next == CLUST_BAD) 464 continue; /* skip it. */ 465 466 /* follow the chain and mark all clusters on the way */ 467 for (len = 0, p = head; 468 p >= CLUST_FIRST && p < boot->NumClusters && 469 fat[p].head != head; 470 p = fat[p].next) { 471 fat[p].head = head; 472 len++; 473 } 474 475 /* the head record gets the length */ 476 fat[head].length = fat[head].next == CLUST_FREE ? 0 : len; 477 } 478 479 /* 480 * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because 481 * we didn't know the real start of the chain then - would have treated partial 482 * chains as interlinked with their main chain) 483 */ 484 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 485 /* find next untravelled chain */ 486 if (fat[head].head != head) 487 continue; 488 489 /* follow the chain to its end (hopefully) */ 490 for (len = fat[head].length, p = head; 491 (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters; 492 p = n) 493 if (fat[n].head != head || len-- < 2) 494 break; 495 if (n >= CLUST_EOFS) 496 continue; 497 498 if (n == CLUST_FREE || n >= CLUST_RSRVD) { 499 pwarn("Cluster chain starting at %u ends with cluster marked %s\n", 500 head, rsrvdcltype(n)); 501clear: 502 ret |= tryclear(boot, fat, head, &fat[p].next); 503 continue; 504 } 505 if (n < CLUST_FIRST || n >= boot->NumClusters) { 506 pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n", 507 head, n); 508 goto clear; 509 } 510 if (head == fat[n].head) { 511 pwarn("Cluster chain starting at %u loops at cluster %u\n", 512 513 head, p); 514 goto clear; 515 } 516 pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n", 517 head, fat[n].head, n); 518 conf = tryclear(boot, fat, head, &fat[p].next); 519 if (ask(0, "Clear chain starting at %u", h = fat[n].head)) { 520 if (conf == FSERROR) { 521 /* 522 * Transfer the common chain to the one not cleared above. 523 */ 524 for (p = n; 525 p >= CLUST_FIRST && p < boot->NumClusters; 526 p = fat[p].next) { 527 if (h != fat[p].head) { 528 /* 529 * Have to reexamine this chain. 530 */ 531 head--; 532 break; 533 } 534 fat[p].head = head; 535 } 536 } 537 clearchain(boot, fat, h); 538 conf |= FSFATMOD; 539 } 540 ret |= conf; 541 } 542 543 return ret; 544} 545 546/* 547 * Write out FATs encoding them from the internal format 548 */ 549int 550writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat) 551{ 552 u_char *buffer, *p; 553 cl_t cl; 554 u_int i; 555 size_t fatsz; 556 off_t off; 557 int ret = FSOK; 558 559 buffer = malloc(fatsz = boot->FATsecs * boot->bpbBytesPerSec); 560 if (buffer == NULL) { 561 perr("No space for FAT sectors (%zu)", fatsz); 562 return FSFATAL; 563 } 564 memset(buffer, 0, fatsz); 565 boot->NumFree = 0; 566 p = buffer; 567 if (correct_fat) { 568 *p++ = (u_char)boot->bpbMedia; 569 *p++ = 0xff; 570 *p++ = 0xff; 571 switch (boot->ClustMask) { 572 case CLUST16_MASK: 573 *p++ = 0xff; 574 break; 575 case CLUST32_MASK: 576 *p++ = 0x0f; 577 *p++ = 0xff; 578 *p++ = 0xff; 579 *p++ = 0xff; 580 *p++ = 0x0f; 581 break; 582 } 583 } else { 584 /* use same FAT signature as the old FAT has */ 585 int count; 586 u_char *old_fat; 587 588 switch (boot->ClustMask) { 589 case CLUST32_MASK: 590 count = 8; 591 break; 592 case CLUST16_MASK: 593 count = 4; 594 break; 595 default: 596 count = 3; 597 break; 598 } 599 600 if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0, 601 &old_fat)) { 602 free(buffer); 603 return FSFATAL; 604 } 605 606 memcpy(p, old_fat, count); 607 free(old_fat); 608 p += count; 609 } 610 611 for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) { 612 switch (boot->ClustMask) { 613 case CLUST32_MASK: 614 if (fat[cl].next == CLUST_FREE) 615 boot->NumFree++; 616 *p++ = (u_char)fat[cl].next; 617 *p++ = (u_char)(fat[cl].next >> 8); 618 *p++ = (u_char)(fat[cl].next >> 16); 619 *p &= 0xf0; 620 *p++ |= (fat[cl].next >> 24)&0x0f; 621 break; 622 case CLUST16_MASK: 623 if (fat[cl].next == CLUST_FREE) 624 boot->NumFree++; 625 *p++ = (u_char)fat[cl].next; 626 *p++ = (u_char)(fat[cl].next >> 8); 627 break; 628 default: 629 if (fat[cl].next == CLUST_FREE) 630 boot->NumFree++; 631 *p++ = (u_char)fat[cl].next; 632 *p = (u_char)((fat[cl].next >> 8) & 0xf); 633 cl++; 634 if (cl >= boot->NumClusters) 635 break; 636 if (fat[cl].next == CLUST_FREE) 637 boot->NumFree++; 638 *p++ |= (u_char)(fat[cl + 1].next << 4); 639 *p++ = (u_char)(fat[cl + 1].next >> 4); 640 break; 641 } 642 } 643 for (i = 0; i < boot->bpbFATs; i++) { 644 off = boot->bpbResSectors + i * boot->FATsecs; 645 off *= boot->bpbBytesPerSec; 646 if (lseek(fs, off, SEEK_SET) != off 647 || (size_t)write(fs, buffer, fatsz) != fatsz) { 648 perr("Unable to write FAT"); 649 ret = FSFATAL; /* Return immediately? XXX */ 650 } 651 } 652 free(buffer); 653 return ret; 654} 655 656/* 657 * Check a complete in-memory FAT for lost cluster chains 658 */ 659int 660checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat) 661{ 662 cl_t head; 663 int mod = FSOK; 664 int ret; 665 666 for (head = CLUST_FIRST; head < boot->NumClusters; head++) { 667 /* find next untravelled chain */ 668 if (fat[head].head != head 669 || fat[head].next == CLUST_FREE 670 || (fat[head].next >= CLUST_RSRVD 671 && fat[head].next < CLUST_EOFS) 672 || (fat[head].flags & FAT_USED)) 673 continue; 674 675 pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n", 676 head, fat[head].length); 677 mod |= ret = reconnect(dosfs, boot, fat, head); 678 if (mod & FSFATAL) 679 break; 680 if (ret == FSERROR && ask(0, "Clear")) { 681 clearchain(boot, fat, head); 682 mod |= FSFATMOD; 683 } 684 } 685 finishlf(); 686 687 if (boot->bpbFSInfo) { 688 ret = 0; 689 if (boot->FSFree != 0xffffffffU && 690 boot->FSFree != boot->NumFree) { 691 pwarn("Free space in FSInfo block (%u) not correct (%u)\n", 692 boot->FSFree, boot->NumFree); 693 if (ask(1, "Fix")) { 694 boot->FSFree = boot->NumFree; 695 ret = 1; 696 } 697 } 698 if (ret) 699 mod |= writefsinfo(dosfs, boot); 700 } 701 702 return mod; 703} 704