1 /* $NetBSD: dosfs.c,v 1.19 2013/10/20 17:15:42 christos Exp $ */ 2 3 /* 4 * Copyright (c) 1996, 1998 Robert Nordier 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in 14 * the documentation and/or other materials provided with the 15 * distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS 18 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY 21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE 23 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 24 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER 25 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 26 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN 27 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30 /* 31 * Readonly filesystem for Microsoft FAT12/FAT16/FAT32 filesystems, 32 * also supports VFAT. 33 */ 34 35 /* 36 * XXX DOES NOT SUPPORT: 37 * 38 * LIBSA_FS_SINGLECOMPONENT 39 */ 40 41 #include <sys/param.h> 42 43 #include <fs/msdosfs/bpb.h> 44 #include <fs/msdosfs/direntry.h> 45 46 #ifdef _STANDALONE 47 #include <lib/libkern/libkern.h> 48 #else 49 #include <string.h> 50 #include <stddef.h> 51 #endif 52 53 #include "stand.h" 54 #include "dosfs.h" 55 56 #define SECSIZ 512 /* sector size */ 57 #define SSHIFT 9 /* SECSIZ shift */ 58 #define DEPSEC 16 /* directory entries per sector */ 59 #define DSHIFT 4 /* DEPSEC shift */ 60 #define LOCLUS 2 /* lowest cluster number */ 61 62 typedef union { 63 struct direntry de; /* standard directory entry */ 64 struct winentry xde; /* extended directory entry */ 65 } DOS_DIR; 66 67 typedef struct { 68 struct open_file *fd; /* file descriptor */ 69 u_char *buf; /* buffer */ 70 u_int bufsec; /* buffered sector */ 71 u_int links; /* active links to structure */ 72 u_int spc; /* sectors per cluster */ 73 u_int bsize; /* cluster size in bytes */ 74 u_int bshift; /* cluster conversion shift */ 75 u_int dirents; /* root directory entries */ 76 u_int spf; /* sectors per fat */ 77 u_int rdcl; /* root directory start cluster */ 78 u_int lsnfat; /* start of fat */ 79 u_int lsndir; /* start of root dir */ 80 u_int lsndta; /* start of data area */ 81 u_int fatsz; /* FAT entry size */ 82 u_int xclus; /* maximum cluster number */ 83 } DOS_FS; 84 85 typedef struct { 86 DOS_FS *fs; /* associated filesystem */ 87 struct direntry de; /* directory entry */ 88 u_int offset; /* current offset */ 89 u_int c; /* last cluster read */ 90 } DOS_FILE; 91 92 /* Initial portion of DOS boot sector */ 93 typedef struct { 94 u_char jmp[3]; /* usually 80x86 'jmp' opcode */ 95 u_char oem[8]; /* OEM name and version */ 96 struct byte_bpb710 bpb; /* BPB */ 97 } DOS_BS; 98 99 /* Supply missing "." and ".." root directory entries */ 100 static const char *const dotstr[2] = {".", ".."}; 101 static const struct direntry dot[2] = { 102 {". ", " ", ATTR_DIRECTORY, 103 0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}, 104 {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}}, 105 106 {".. ", " ", ATTR_DIRECTORY, 107 0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}, 108 {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}} 109 }; 110 111 /* The usual conversion macros to avoid multiplication and division */ 112 #define bytsec(n) ((n) >> SSHIFT) 113 #define secbyt(s) ((s) << SSHIFT) 114 #define entsec(e) ((e) >> DSHIFT) 115 #define bytblk(fs, n) ((n) >> (fs)->bshift) 116 #define blkbyt(fs, b) ((b) << (fs)->bshift) 117 #define secblk(fs, s) ((s) >> ((fs)->bshift - SSHIFT)) 118 #define blksec(fs, b) ((b) << ((fs)->bshift - SSHIFT)) 119 120 /* Convert cluster number to offset within filesystem */ 121 #define blkoff(fs, b) (secbyt((fs)->lsndta) + blkbyt(fs, (b) - LOCLUS)) 122 123 /* Convert cluster number to logical sector number */ 124 #define blklsn(fs, b) ((fs)->lsndta + blksec(fs, (b) - LOCLUS)) 125 126 /* Convert cluster number to offset within FAT */ 127 #define fatoff(sz, c) ((sz) == 12 ? (c) + ((c) >> 1) : \ 128 (sz) == 16 ? (c) << 1 : \ 129 (c) << 2) 130 131 /* Does cluster number reference a valid data cluster? */ 132 #define okclus(fs, c) ((c) >= LOCLUS && (c) <= (fs)->xclus) 133 134 /* Get start cluster from directory entry */ 135 #define stclus(sz, de) ((sz) != 32 ? (u_int)getushort((de)->deStartCluster) : \ 136 ((u_int)getushort((de)->deHighClust) << 16) | \ 137 (u_int)getushort((de)->deStartCluster)) 138 139 static int dosunmount(DOS_FS *); 140 static int parsebs(DOS_FS *, DOS_BS *); 141 static int namede(DOS_FS *, const char *, const struct direntry **); 142 static int lookup(DOS_FS *, u_int, const char *, const struct direntry **); 143 static void cp_xdnm(u_char *, struct winentry *); 144 static void cp_sfn(u_char *, struct direntry *); 145 static off_t fsize(DOS_FS *, struct direntry *); 146 static int fatcnt(DOS_FS *, u_int); 147 static int fatget(DOS_FS *, u_int *); 148 static int fatend(u_int, u_int); 149 static int ioread(DOS_FS *, u_int, void *, u_int); 150 static int iobuf(DOS_FS *, u_int); 151 static int ioget(struct open_file *, u_int, void *, u_int); 152 153 #define strcasecmp(s1, s2) dos_strcasecmp(s1, s2) 154 static int 155 strcasecmp(const char *s1, const char *s2) 156 { 157 char c1, c2; 158 #define TO_UPPER(c) ((c) >= 'a' && (c) <= 'z' ? (c) - ('a' - 'A') : (c)) 159 for (;;) { 160 c1 = *s1++; 161 c2 = *s2++; 162 if (TO_UPPER(c1) != TO_UPPER(c2)) 163 return 1; 164 if (c1 == 0) 165 return 0; 166 } 167 #undef TO_UPPER 168 } 169 170 /* 171 * Mount DOS filesystem 172 */ 173 static int 174 dos_mount(DOS_FS *fs, struct open_file *fd) 175 { 176 int err; 177 178 (void)memset(fs, 0, sizeof(DOS_FS)); 179 fs->fd = fd; 180 if ((err = !(fs->buf = alloc(SECSIZ)) ? errno : 0) || 181 (err = ioget(fs->fd, 0, fs->buf, 1)) || 182 (err = parsebs(fs, (DOS_BS *)fs->buf))) { 183 (void) dosunmount(fs); 184 return err; 185 } 186 return 0; 187 } 188 189 #ifndef LIBSA_NO_FS_CLOSE 190 /* 191 * Unmount mounted filesystem 192 */ 193 static int 194 dos_unmount(DOS_FS *fs) 195 { 196 int err; 197 198 if (fs->links) 199 return EBUSY; 200 if ((err = dosunmount(fs))) 201 return err; 202 return 0; 203 } 204 #endif 205 206 /* 207 * Common code shared by dos_mount() and dos_unmount() 208 */ 209 static int 210 dosunmount(DOS_FS *fs) 211 { 212 if (fs->buf) 213 dealloc(fs->buf, SECSIZ); 214 dealloc(fs, sizeof(DOS_FS)); 215 return 0; 216 } 217 218 /* 219 * Open DOS file 220 */ 221 __compactcall int 222 dosfs_open(const char *path, struct open_file *fd) 223 { 224 const struct direntry *de; 225 DOS_FILE *f; 226 DOS_FS *fs; 227 u_int size, clus; 228 int err = 0; 229 230 /* Allocate mount structure, associate with open */ 231 fs = alloc(sizeof(DOS_FS)); 232 233 if ((err = dos_mount(fs, fd))) 234 goto out; 235 236 if ((err = namede(fs, path, &de))) 237 goto out; 238 239 clus = stclus(fs->fatsz, de); 240 size = getulong(de->deFileSize); 241 242 if ((!(de->deAttributes & ATTR_DIRECTORY) && (!clus != !size)) || 243 ((de->deAttributes & ATTR_DIRECTORY) && size) || 244 (clus && !okclus(fs, clus))) { 245 err = EINVAL; 246 goto out; 247 } 248 249 f = alloc(sizeof(DOS_FILE)); 250 #ifdef BOOTXX 251 /* due to __internal_memset_ causing all sorts of register spillage 252 (and being completely unoptimized for zeroing small amounts of 253 memory), if we hand-initialize the remaining members of f to zero, 254 the code size drops 68 bytes. This makes no sense, admittedly. */ 255 f->offset = 0; 256 f->c = 0; 257 #else 258 (void)memset(f, 0, sizeof(DOS_FILE)); 259 #endif 260 f->fs = fs; 261 fs->links++; 262 f->de = *de; 263 fd->f_fsdata = (void *)f; 264 fsmod = "msdos"; 265 266 out: 267 return err; 268 } 269 270 /* 271 * Read from file 272 */ 273 __compactcall int 274 dosfs_read(struct open_file *fd, void *vbuf, size_t nbyte, size_t *resid) 275 { 276 off_t size; 277 u_int8_t *buf = vbuf; 278 u_int nb, off, clus, c, cnt, n; 279 DOS_FILE *f = (DOS_FILE *)fd->f_fsdata; 280 int err = 0; 281 282 nb = (u_int) nbyte; 283 if ((size = fsize(f->fs, &f->de)) == -1) 284 return EINVAL; 285 if (nb > (n = size - f->offset)) 286 nb = n; 287 off = f->offset; 288 if ((clus = stclus(f->fs->fatsz, &f->de))) 289 off &= f->fs->bsize - 1; 290 c = f->c; 291 cnt = nb; 292 while (cnt) { 293 n = 0; 294 if (!c) { 295 if ((c = clus)) 296 n = bytblk(f->fs, f->offset); 297 } else if (!off) { 298 n++; 299 } 300 while (n--) { 301 if ((err = fatget(f->fs, &c))) 302 goto out; 303 if (!okclus(f->fs, c)) { 304 err = EINVAL; 305 goto out; 306 } 307 } 308 if (!clus || (n = f->fs->bsize - off) > cnt) 309 n = cnt; 310 if ((err = ioread(f->fs, (c ? blkoff(f->fs, c) : 311 secbyt(f->fs->lsndir)) + off, 312 buf, n))) 313 goto out; 314 f->offset += n; 315 f->c = c; 316 off = 0; 317 buf += n; 318 cnt -= n; 319 } 320 out: 321 if (resid) 322 *resid = nbyte - nb + cnt; 323 return err; 324 } 325 326 #ifndef LIBSA_NO_FS_WRITE 327 /* 328 * Not implemented. 329 */ 330 __compactcall int 331 dosfs_write(struct open_file *fd, void *start, size_t size, size_t *resid) 332 { 333 334 return EROFS; 335 } 336 #endif /* !LIBSA_NO_FS_WRITE */ 337 338 #ifndef LIBSA_NO_FS_SEEK 339 /* 340 * Reposition within file 341 */ 342 __compactcall off_t 343 dosfs_seek(struct open_file *fd, off_t offset, int whence) 344 { 345 off_t off; 346 u_int size; 347 DOS_FILE *f = (DOS_FILE *)fd->f_fsdata; 348 349 size = getulong(f->de.deFileSize); 350 switch (whence) { 351 case SEEK_SET: 352 off = 0; 353 break; 354 case SEEK_CUR: 355 off = f->offset; 356 break; 357 case SEEK_END: 358 off = size; 359 break; 360 default: 361 return -1; 362 } 363 off += offset; 364 if (off < 0 || off > size) 365 return -1; 366 f->offset = (u_int) off; 367 f->c = 0; 368 return off; 369 } 370 #endif /* !LIBSA_NO_FS_SEEK */ 371 372 #ifndef LIBSA_NO_FS_CLOSE 373 /* 374 * Close open file 375 */ 376 __compactcall int 377 dosfs_close(struct open_file *fd) 378 { 379 DOS_FILE *f = (DOS_FILE *)fd->f_fsdata; 380 DOS_FS *fs = f->fs; 381 382 f->fs->links--; 383 dealloc(f, sizeof(DOS_FILE)); 384 dos_unmount(fs); 385 return 0; 386 } 387 #endif /* !LIBSA_NO_FS_CLOSE */ 388 389 /* 390 * Return some stat information on a file. 391 */ 392 __compactcall int 393 dosfs_stat(struct open_file *fd, struct stat *sb) 394 { 395 DOS_FILE *f = (DOS_FILE *)fd->f_fsdata; 396 397 /* only important stuff */ 398 sb->st_mode = (f->de.deAttributes & ATTR_DIRECTORY) ? 399 (S_IFDIR | 0555) : (S_IFREG | 0444); 400 sb->st_nlink = 1; 401 sb->st_uid = 0; 402 sb->st_gid = 0; 403 if ((sb->st_size = fsize(f->fs, &f->de)) == -1) 404 return EINVAL; 405 return 0; 406 } 407 408 #if defined(LIBSA_ENABLE_LS_OP) 409 __compactcall void 410 dosfs_ls(struct open_file *f, const char *pattern, 411 void (*funcp)(char* arg), char* path) 412 { 413 printf("Currently ls command is unsupported by dosfs\n"); 414 return; 415 } 416 #endif 417 418 /* 419 * Parse DOS boot sector 420 */ 421 static int 422 parsebs(DOS_FS *fs, DOS_BS *bs) 423 { 424 u_int sc; 425 426 if ((bs->jmp[0] != 0x69 && 427 bs->jmp[0] != 0xe9 && 428 (bs->jmp[0] != 0xeb || bs->jmp[2] != 0x90)) || 429 bs->bpb.bpbMedia < 0xf0) 430 return EINVAL; 431 if (getushort(bs->bpb.bpbBytesPerSec) != SECSIZ) 432 return EINVAL; 433 if (!(fs->spc = bs->bpb.bpbSecPerClust) || fs->spc & (fs->spc - 1)) 434 return EINVAL; 435 fs->bsize = secbyt(fs->spc); 436 fs->bshift = ffs(fs->bsize) - 1; 437 if ((fs->spf = getushort(bs->bpb.bpbFATsecs))) { 438 if (bs->bpb.bpbFATs != 2) 439 return EINVAL; 440 if (!(fs->dirents = getushort(bs->bpb.bpbRootDirEnts))) 441 return EINVAL; 442 } else { 443 if (!(fs->spf = getulong(bs->bpb.bpbBigFATsecs))) 444 return EINVAL; 445 if (!bs->bpb.bpbFATs || bs->bpb.bpbFATs > 16) 446 return EINVAL; 447 if ((fs->rdcl = getulong(bs->bpb.bpbRootClust)) < LOCLUS) 448 return EINVAL; 449 } 450 if (!(fs->lsnfat = getushort(bs->bpb.bpbResSectors))) 451 return EINVAL; 452 fs->lsndir = fs->lsnfat + fs->spf * bs->bpb.bpbFATs; 453 fs->lsndta = fs->lsndir + entsec(fs->dirents); 454 if (!(sc = getushort(bs->bpb.bpbSectors)) && 455 !(sc = getulong(bs->bpb.bpbHugeSectors))) 456 return EINVAL; 457 if (fs->lsndta > sc) 458 return EINVAL; 459 if ((fs->xclus = secblk(fs, sc - fs->lsndta) + 1) < LOCLUS) 460 return EINVAL; 461 fs->fatsz = fs->dirents ? fs->xclus < 0xff6 ? 12 : 16 : 32; 462 sc = (secbyt(fs->spf) << 1) / (fs->fatsz >> 2) - 1; 463 if (fs->xclus > sc) 464 fs->xclus = sc; 465 return 0; 466 } 467 468 /* 469 * Return directory entry from path 470 */ 471 static int 472 namede(DOS_FS *fs, const char *path, const struct direntry **dep) 473 { 474 char name[256]; 475 const struct direntry *de; 476 char *s; 477 size_t n; 478 int err; 479 480 err = 0; 481 de = dot; 482 if (*path == '/') 483 path++; 484 while (*path) { 485 if (!(s = strchr(path, '/'))) 486 s = strchr(path, 0); 487 if ((n = s - path) > 255) 488 return ENAMETOOLONG; 489 memcpy(name, path, n); 490 name[n] = 0; 491 path = s; 492 if (!(de->deAttributes & ATTR_DIRECTORY)) 493 return ENOTDIR; 494 if ((err = lookup(fs, stclus(fs->fatsz, de), name, &de))) 495 return err; 496 if (*path == '/') 497 path++; 498 } 499 *dep = de; 500 return 0; 501 } 502 503 /* 504 * Lookup path segment 505 */ 506 static int 507 lookup(DOS_FS *fs, u_int clus, const char *name, const struct direntry **dep) 508 { 509 static DOS_DIR *dir = NULL; 510 u_char lfn[261]; 511 u_char sfn[13]; 512 u_int nsec, lsec, xdn, chk, sec, ent, x; 513 int err = 0, ok, i; 514 515 if (!clus) 516 for (ent = 0; ent < 2; ent++) 517 if (!strcasecmp(name, dotstr[ent])) { 518 *dep = dot + ent; 519 return 0; 520 } 521 522 if (dir == NULL) { 523 dir = alloc(sizeof(DOS_DIR) * DEPSEC); 524 if (dir == NULL) 525 return ENOMEM; 526 } 527 528 if (!clus && fs->fatsz == 32) 529 clus = fs->rdcl; 530 nsec = !clus ? entsec(fs->dirents) : fs->spc; 531 lsec = 0; 532 xdn = chk = 0; 533 for (;;) { 534 if (!clus && !lsec) 535 lsec = fs->lsndir; 536 else if (okclus(fs, clus)) 537 lsec = blklsn(fs, clus); 538 else { 539 err = EINVAL; 540 goto out; 541 } 542 for (sec = 0; sec < nsec; sec++) { 543 if ((err = ioget(fs->fd, lsec + sec, dir, 1))) 544 goto out; 545 for (ent = 0; ent < DEPSEC; ent++) { 546 if (!*dir[ent].de.deName) { 547 err = ENOENT; 548 goto out; 549 } 550 if (*dir[ent].de.deName != 0xe5) { 551 if (dir[ent].de.deAttributes == 552 ATTR_WIN95) { 553 x = dir[ent].xde.weCnt; 554 if (x & WIN_LAST || 555 (x + 1 == xdn && 556 dir[ent].xde.weChksum == 557 chk)) { 558 if (x & WIN_LAST) { 559 chk = dir[ent].xde.weChksum; 560 x &= WIN_CNT; 561 } 562 if (x >= 1 && x <= 20) { 563 cp_xdnm(lfn, &dir[ent].xde); 564 xdn = x; 565 continue; 566 } 567 } 568 } else if (!(dir[ent].de.deAttributes & 569 ATTR_VOLUME)) { 570 if ((ok = xdn == 1)) { 571 for (x = 0, i = 0; 572 i < 11; i++) 573 x = ((((x & 1) << 7) | (x >> 1)) + 574 msdos_dirchar(&dir[ent].de,i)) & 0xff; 575 ok = chk == x && 576 !strcasecmp(name, (const char *)lfn); 577 } 578 if (!ok) { 579 cp_sfn(sfn, &dir[ent].de); 580 ok = !strcasecmp(name, (const char *)sfn); 581 } 582 if (ok) { 583 *dep = &dir[ent].de; 584 goto out2; 585 } 586 } 587 } 588 xdn = 0; 589 } 590 } 591 if (!clus) 592 break; 593 if ((err = fatget(fs, &clus))) 594 goto out; 595 if (fatend(fs->fatsz, clus)) 596 break; 597 } 598 err = ENOENT; 599 out: 600 dealloc(dir, sizeof(DOS_DIR) * DEPSEC); 601 dir = NULL; 602 out2: 603 return err; 604 } 605 606 /* 607 * Copy name from extended directory entry 608 */ 609 static void 610 cp_xdnm(u_char *lfn, struct winentry *xde) 611 { 612 static const struct { 613 u_int off; 614 u_int dim; 615 } ix[3] = { 616 { offsetof(struct winentry, wePart1), 617 sizeof(xde->wePart1) / 2 }, 618 { offsetof(struct winentry, wePart2), 619 sizeof(xde->wePart2) / 2 }, 620 { offsetof(struct winentry, wePart3), 621 sizeof(xde->wePart3) / 2 } 622 }; 623 u_char *p; 624 u_int n, x, c; 625 626 lfn += 13 * ((xde->weCnt & WIN_CNT) - 1); 627 for (n = 0; n < 3; n++) 628 for (p = (u_char *)xde + ix[n].off, x = ix[n].dim; x; 629 p += 2, x--) { 630 if ((c = getushort(p)) && (c < 32 || c > 127)) 631 c = '?'; 632 if (!(*lfn++ = c)) 633 return; 634 } 635 if (xde->weCnt & WIN_LAST) 636 *lfn = 0; 637 } 638 639 /* 640 * Copy short filename 641 */ 642 static void 643 cp_sfn(u_char *sfn, struct direntry *de) 644 { 645 u_char *p; 646 int j, i; 647 648 p = sfn; 649 if (*de->deName != ' ') { 650 for (j = 7; de->deName[j] == ' '; j--); 651 for (i = 0; i <= j; i++) 652 *p++ = de->deName[i]; 653 if (*de->deExtension != ' ') { 654 *p++ = '.'; 655 for (j = 2; de->deExtension[j] == ' '; j--); 656 for (i = 0; i <= j; i++) 657 *p++ = de->deExtension[i]; 658 } 659 } 660 *p = 0; 661 if (*sfn == 5) 662 *sfn = 0xe5; 663 } 664 665 /* 666 * Return size of file in bytes 667 */ 668 static off_t 669 fsize(DOS_FS *fs, struct direntry *de) 670 { 671 u_long size; 672 u_int c; 673 int n; 674 675 if (!(size = getulong(de->deFileSize)) && 676 de->deAttributes & ATTR_DIRECTORY) { 677 if (!(c = getushort(de->deStartCluster))) { 678 size = fs->dirents * sizeof(struct direntry); 679 } else { 680 if ((n = fatcnt(fs, c)) == -1) 681 return n; 682 size = blkbyt(fs, n); 683 } 684 } 685 return size; 686 } 687 688 /* 689 * Count number of clusters in chain 690 */ 691 static int 692 fatcnt(DOS_FS *fs, u_int c) 693 { 694 int n; 695 696 for (n = 0; okclus(fs, c); n++) 697 if (fatget(fs, &c)) 698 return -1; 699 return fatend(fs->fatsz, c) ? n : -1; 700 } 701 702 /* 703 * Get next cluster in cluster chain 704 */ 705 static int 706 fatget(DOS_FS *fs, u_int *c) 707 { 708 u_char buf[4]; 709 u_int x; 710 int err; 711 712 err = ioread(fs, secbyt(fs->lsnfat) + fatoff(fs->fatsz, *c), buf, 713 fs->fatsz != 32 ? 2 : 4); 714 if (err) 715 return err; 716 x = fs->fatsz != 32 ? getushort(buf) : getulong(buf); 717 *c = fs->fatsz == 12 ? *c & 1 ? x >> 4 : x & 0xfff : x; 718 return 0; 719 } 720 721 /* 722 * Is cluster an end-of-chain marker? 723 */ 724 static int 725 fatend(u_int sz, u_int c) 726 { 727 return c > (sz == 12 ? 0xff7U : sz == 16 ? 0xfff7U : 0xffffff7); 728 } 729 730 /* 731 * Offset-based I/O primitive 732 */ 733 static int 734 ioread(DOS_FS *fs, u_int offset, void *buf, u_int nbyte) 735 { 736 char *s; 737 u_int off, n; 738 int err; 739 740 s = buf; 741 if ((off = offset & (SECSIZ - 1))) { 742 offset -= off; 743 if ((err = iobuf(fs, bytsec(offset)))) 744 return err; 745 offset += SECSIZ; 746 if ((n = SECSIZ - off) > nbyte) 747 n = nbyte; 748 memcpy(s, fs->buf + off, n); 749 s += n; 750 nbyte -= n; 751 } 752 n = nbyte & (SECSIZ - 1); 753 if (nbyte -= n) { 754 if ((err = ioget(fs->fd, bytsec(offset), s, bytsec(nbyte)))) 755 return err; 756 offset += nbyte; 757 s += nbyte; 758 } 759 if (n) { 760 if ((err = iobuf(fs, bytsec(offset)))) 761 return err; 762 memcpy(s, fs->buf, n); 763 } 764 return 0; 765 } 766 767 /* 768 * Buffered sector-based I/O primitive 769 */ 770 static int 771 iobuf(DOS_FS *fs, u_int lsec) 772 { 773 int err; 774 775 if (fs->bufsec != lsec) { 776 if ((err = ioget(fs->fd, lsec, fs->buf, 1))) 777 return err; 778 fs->bufsec = lsec; 779 } 780 return 0; 781 } 782 783 /* 784 * Sector-based I/O primitive 785 */ 786 static int 787 ioget(struct open_file *fd, u_int lsec, void *buf, u_int nsec) 788 { 789 size_t rsize; 790 int err; 791 792 #ifndef LIBSA_NO_TWIDDLE 793 twiddle(); 794 #endif 795 err = DEV_STRATEGY(fd->f_dev)(fd->f_devdata, F_READ, lsec, 796 secbyt(nsec), buf, &rsize); 797 return err; 798 } 799