lib/libstand/dosfs.c

   1 /*
   2  * Copyright (c) 1996, 1998 Robert Nordier
   3  * All rights reserved.
   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
  12  *    the documentation and/or other materials provided with the
  13  *    distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS
  16  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  17  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY
  19  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  21  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  22  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
  23  * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
  25  * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  *
  27  * $FreeBSD: src/lib/libstand/dosfs.c,v 1.4.2.1 2000/05/04 13:47:49 ps Exp $
  28  * $DragonFly: src/lib/libstand/dosfs.c,v 1.2 2003/06/17 04:26:51 dillon Exp $
  29  */
  30
  31 /*
  32  * Readonly filesystem for Microsoft FAT12/FAT16/FAT32 filesystems,
  33  * also supports VFAT.
  34  */
  35
  36 #include <sys/types.h>
  37 #include <string.h>
  38 #include <stddef.h>
  39
  40 #include "stand.h"
  41
  42 #include "dosfs.h"
  43
  44
  45 static int      dos_open(const char *path, struct open_file *fd);
  46 static int      dos_close(struct open_file *fd);
  47 static int      dos_read(struct open_file *fd, void *buf, size_t size, size_t *resid);
  48 static off_t    dos_seek(struct open_file *fd, off_t offset, int whence);
  49 static int      dos_stat(struct open_file *fd, struct stat *sb);
  50 static int      dos_readdir(struct open_file *fd, struct dirent *d);
  51
  52 struct fs_ops dosfs_fsops = {
  53         "dosfs",
  54         dos_open,
  55         dos_close,
  56         dos_read,
  57         null_write,
  58         dos_seek,
  59         dos_stat,
  60         dos_readdir
  61 };
  62
  63 #define SECSIZ  512             /* sector size */
  64 #define SSHIFT    9             /* SECSIZ shift */
  65 #define DEPSEC   16             /* directory entries per sector */
  66 #define DSHIFT    4             /* DEPSEC shift */
  67 #define LOCLUS    2             /* lowest cluster number */
  68
  69 /* DOS "BIOS Parameter Block" */
  70 typedef struct {
  71     u_char secsiz[2];           /* sector size */
  72     u_char spc;                 /* sectors per cluster */
  73     u_char ressec[2];           /* reserved sectors */
  74     u_char fats;                /* FATs */
  75     u_char dirents[2];          /* root directory entries */
  76     u_char secs[2];             /* total sectors */
  77     u_char media;               /* media descriptor */
  78     u_char spf[2];              /* sectors per FAT */
  79     u_char spt[2];              /* sectors per track */
  80     u_char heads[2];            /* drive heads */
  81     u_char hidsec[4];           /* hidden sectors */
  82     u_char lsecs[4];            /* huge sectors */
  83     u_char lspf[4];             /* huge sectors per FAT */
  84     u_char xflg[2];             /* flags */
  85     u_char vers[2];             /* filesystem version */
  86     u_char rdcl[4];             /* root directory start cluster */
  87     u_char infs[2];             /* filesystem info sector */
  88     u_char bkbs[2];             /* backup boot sector */
  89 } DOS_BPB;
  90
  91 /* Initial portion of DOS boot sector */
  92 typedef struct {
  93     u_char jmp[3];              /* usually 80x86 'jmp' opcode */
  94     u_char oem[8];              /* OEM name and version */
  95     DOS_BPB bpb;                /* BPB */
  96 } DOS_BS;
  97
  98 /* Supply missing "." and ".." root directory entries */
  99 static const char *const dotstr[2] = {".", ".."};
 100 static DOS_DE dot[2] = {
 101     {".       ", "   ", FA_DIR, {0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}},
 102      {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}},
 103     {"..      ", "   ", FA_DIR, {0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}},
 104      {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}}
 105 };
 106
 107 /* The usual conversion macros to avoid multiplication and division */
 108 #define bytsec(n)      ((n) >> SSHIFT)
 109 #define secbyt(s)      ((s) << SSHIFT)
 110 #define entsec(e)      ((e) >> DSHIFT)
 111 #define bytblk(fs, n)  ((n) >> (fs)->bshift)
 112 #define blkbyt(fs, b)  ((b) << (fs)->bshift)
 113 #define secblk(fs, s)  ((s) >> ((fs)->bshift - SSHIFT))
 114 #define blksec(fs, b)  ((b) << ((fs)->bshift - SSHIFT))
 115
 116 /* Convert cluster number to offset within filesystem */
 117 #define blkoff(fs, b) (secbyt((fs)->lsndta) + blkbyt(fs, (b) - LOCLUS))
 118
 119 /* Convert cluster number to logical sector number */
 120 #define blklsn(fs, b)  ((fs)->lsndta + blksec(fs, (b) - LOCLUS))
 121
 122 /* Convert cluster number to offset within FAT */
 123 #define fatoff(sz, c)  ((sz) == 12 ? (c) + ((c) >> 1) :  \
 124                         (sz) == 16 ? (c) << 1 :          \
 125                         (c) << 2)
 126
 127 /* Does cluster number reference a valid data cluster? */
 128 #define okclus(fs, c)  ((c) >= LOCLUS && (c) <= (fs)->xclus)
 129
 130 /* Get start cluster from directory entry */
 131 #define stclus(sz, de)  ((sz) != 32 ? cv2((de)->clus) :          \
 132                          ((u_int)cv2((de)->dex.h_clus) << 16) |  \
 133                          cv2((de)->clus))
 134
 135 static int dosunmount(DOS_FS *);
 136 static int parsebs(DOS_FS *, DOS_BS *);
 137 static int namede(DOS_FS *, const char *, DOS_DE **);
 138 static int lookup(DOS_FS *, u_int, const char *, DOS_DE **);
 139 static void cp_xdnm(u_char *, DOS_XDE *);
 140 static void cp_sfn(u_char *, DOS_DE *);
 141 static off_t fsize(DOS_FS *, DOS_DE *);
 142 static int fatcnt(DOS_FS *, u_int);
 143 static int fatget(DOS_FS *, u_int *);
 144 static int fatend(u_int, u_int);
 145 static int ioread(DOS_FS *, u_int, void *, u_int);
 146 static int iobuf(DOS_FS *, u_int);
 147 static int ioget(struct open_file *, u_int, void *, u_int);
 148
 149 /*
 150  * Mount DOS filesystem
 151  */
 152 static int
 153 dos_mount(DOS_FS *fs, struct open_file *fd)
 154 {
 155     int err;
 156
 157     bzero(fs, sizeof(DOS_FS));
 158     fs->fd = fd;
 159     if ((err = !(fs->buf = malloc(SECSIZ)) ? errno : 0) ||
 160         (err = ioget(fs->fd, 0, fs->buf, 1)) ||
 161         (err = parsebs(fs, (DOS_BS *)fs->buf))) {
 162         (void)dosunmount(fs);
 163         return(err);
 164     }
 165     fs->root = dot[0];
 166     fs->root.name[0] = ' ';
 167     if (fs->fatsz == 32) {
 168         fs->root.clus[0] = fs->rdcl & 0xff;
 169         fs->root.clus[1] = (fs->rdcl >> 8) & 0xff;
 170         fs->root.dex.h_clus[0] = (fs->rdcl >> 16) & 0xff;
 171         fs->root.dex.h_clus[1] = (fs->rdcl >> 24) & 0xff;
 172     }
 173     return 0;
 174 }
 175
 176 /*
 177  * Unmount mounted filesystem
 178  */
 179 static int
 180 dos_unmount(DOS_FS *fs)
 181 {
 182     int err;
 183
 184     if (fs->links)
 185         return(EBUSY);
 186     if ((err = dosunmount(fs)))
 187         return(err);
 188     return 0;
 189 }
 190
 191 /*
 192  * Common code shared by dos_mount() and dos_unmount()
 193  */
 194 static int
 195 dosunmount(DOS_FS *fs)
 196 {
 197     if (fs->buf)
 198         free(fs->buf);
 199     free(fs);
 200     return(0);
 201 }
 202
 203 /*
 204  * Open DOS file
 205  */
 206 static int
 207 dos_open(const char *path, struct open_file *fd)
 208 {
 209     DOS_DE *de;
 210     DOS_FILE *f;
 211     DOS_FS *fs;
 212     u_int size, clus;
 213     int err = 0;
 214
 215     /* Allocate mount structure, associate with open */
 216     fs = malloc(sizeof(DOS_FS));
 217
 218     if ((err = dos_mount(fs, fd)))
 219         goto out;
 220
 221     if ((err = namede(fs, path, &de)))
 222         goto out;
 223
 224     clus = stclus(fs->fatsz, de);
 225     size = cv4(de->size);
 226
 227     if ((!(de->attr & FA_DIR) && (!clus != !size)) ||
 228         ((de->attr & FA_DIR) && size) ||
 229         (clus && !okclus(fs, clus))) {
 230         err = EINVAL;
 231         goto out;
 232     }
 233     f = malloc(sizeof(DOS_FILE));
 234     bzero(f, sizeof(DOS_FILE));
 235     f->fs = fs;
 236     fs->links++;
 237     f->de = *de;
 238     fd->f_fsdata = (void *)f;
 239
 240  out:
 241     return(err);
 242 }
 243
 244 /*
 245  * Read from file
 246  */
 247 static int
 248 dos_read(struct open_file *fd, void *buf, size_t nbyte, size_t *resid)
 249 {
 250     off_t size;
 251     u_int nb, off, clus, c, cnt, n;
 252     DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
 253     int err = 0;
 254
 255     nb = (u_int)nbyte;
 256     if ((size = fsize(f->fs, &f->de)) == -1)
 257         return EINVAL;
 258     if (nb > (n = size - f->offset))
 259         nb = n;
 260     off = f->offset;
 261     if ((clus = stclus(f->fs->fatsz, &f->de)))
 262         off &= f->fs->bsize - 1;
 263     c = f->c;
 264     cnt = nb;
 265     while (cnt) {
 266         n = 0;
 267         if (!c) {
 268             if ((c = clus))
 269                 n = bytblk(f->fs, f->offset);
 270         } else if (!off)
 271             n++;
 272         while (n--) {
 273             if ((err = fatget(f->fs, &c)))
 274                 goto out;
 275             if (!okclus(f->fs, c)) {
 276                 err = EINVAL;
 277                 goto out;
 278             }
 279         }
 280         if (!clus || (n = f->fs->bsize - off) > cnt)
 281             n = cnt;
 282         if ((err = ioread(f->fs, (c ? blkoff(f->fs, c) :
 283                                       secbyt(f->fs->lsndir)) + off,
 284                           buf, n)))
 285             goto out;
 286         f->offset += n;
 287         f->c = c;
 288         off = 0;
 289         buf += n;
 290         cnt -= n;
 291     }
 292  out:
 293     if (resid)
 294         *resid = nbyte - nb + cnt;
 295     return(err);
 296 }
 297
 298 /*
 299  * Reposition within file
 300  */
 301 static off_t
 302 dos_seek(struct open_file *fd, off_t offset, int whence)
 303 {
 304     off_t off;
 305     u_int size;
 306     DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
 307
 308     size = cv4(f->de.size);
 309     switch (whence) {
 310     case SEEK_SET:
 311         off = 0;
 312         break;
 313     case SEEK_CUR:
 314         off = f->offset;
 315         break;
 316     case SEEK_END:
 317         off = size;
 318         break;
 319     default:
 320         return(-1);
 321     }
 322     off += offset;
 323     if (off < 0 || off > size)
 324         return(-1);
 325     f->offset = (u_int)off;
 326     f->c = 0;
 327     return(off);
 328 }
 329
 330 /*
 331  * Close open file
 332  */
 333 static int
 334 dos_close(struct open_file *fd)
 335 {
 336     DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
 337     DOS_FS *fs;
 338
 339     fd->f_fsdata = NULL;
 340     if (f) {
 341         fs = f->fs;
 342         f->fs = NULL;
 343         fs->links--;
 344         free(f);
 345         dos_unmount(fs);
 346     }
 347     return 0;
 348 }
 349
 350 /*
 351  * Return some stat information on a file.
 352  */
 353 static int
 354 dos_stat(struct open_file *fd, struct stat *sb)
 355 {
 356     DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
 357
 358     /* only important stuff */
 359     sb->st_mode = f->de.attr & FA_DIR ? S_IFDIR | 0555 : S_IFREG | 0444;
 360     sb->st_nlink = 1;
 361     sb->st_uid = 0;
 362     sb->st_gid = 0;
 363     if ((sb->st_size = fsize(f->fs, &f->de)) == -1)
 364         return EINVAL;
 365     return (0);
 366 }
 367
 368 static int
 369 dos_readdir(struct open_file *fd, struct dirent *d)
 370 {
 371     /* DOS_FILE *f = (DOS_FILE *)fd->f_fsdata; */
 372     u_char fn[261];
 373     DOS_DIR dd;
 374     size_t res;
 375     u_int chk, i, x, xdn;
 376     int err;
 377
 378     x = chk = 0;
 379     while (1) {
 380         xdn = x;
 381         x = 0;
 382         err = dos_read(fd, &dd, sizeof(dd), &res);
 383         if (err)
 384             return (err);
 385         if (res == sizeof(dd))
 386             return (ENOENT);
 387         if (dd.de.name[0] == 0)
 388             return (ENOENT);
 389
 390         /* Skip deleted entries */
 391         if (dd.de.name[0] == 0xe5)
 392             continue;
 393
 394         /* Check if directory entry is volume label */
 395         if (dd.de.attr & FA_LABEL) {
 396             /*
 397              * If volume label set, check if the current entry is
 398              * extended entry (FA_XDE) for long file names.
 399              */
 400             if ((dd.de.attr & FA_MASK) == FA_XDE) {
 401                 /*
 402                  * Read through all following extended entries
 403                  * to get the long file name. 0x40 marks the
 404                  * last entry containing part of long file name.
 405                  */
 406                 if (dd.xde.seq & 0x40)
 407                     chk = dd.xde.chk;
 408                 else if (dd.xde.seq != xdn - 1 || dd.xde.chk != chk)
 409                     continue;
 410                 x = dd.xde.seq & ~0x40;
 411                 if (x < 1 || x > 20) {
 412                     x = 0;
 413                     continue;
 414                 }
 415                 cp_xdnm(fn, &dd.xde);
 416             } else {
 417                 /* skip only volume label entries */
 418                 continue;
 419             }
 420         } else {
 421             if (xdn == 1) {
 422                 x = 0;
 423                 for (i = 0; i < 11; i++) {
 424                     x = ((x & 1) << 7) | (x >> 1);
 425                     x += (i < 8) ? dd.de.name[i] : dd.de.ext[i-8];
 426                     x &= 0xff;
 427                 }
 428                 if (x == chk)
 429                     break;
 430             } else {
 431                 cp_sfn(fn, &dd.de);
 432                 break;
 433             }
 434             x = 0;
 435         }
 436     }
 437
 438     d->d_fileno = (dd.de.clus[1] << 8) + dd.de.clus[0];
 439     d->d_type = (dd.de.attr & FA_DIR) ? DT_DIR : DT_REG;
 440     memcpy(d->d_name, fn, sizeof(d->d_name));
 441     return(0);
 442 }
 443
 444 /*
 445  * Parse DOS boot sector
 446  */
 447 static int
 448 parsebs(DOS_FS *fs, DOS_BS *bs)
 449 {
 450     u_int sc;
 451
 452     if ((bs->jmp[0] != 0x69 &&
 453          bs->jmp[0] != 0xe9 &&
 454          (bs->jmp[0] != 0xeb || bs->jmp[2] != 0x90)) ||
 455         bs->bpb.media < 0xf0)
 456         return EINVAL;
 457     if (cv2(bs->bpb.secsiz) != SECSIZ)
 458         return EINVAL;
 459     if (!(fs->spc = bs->bpb.spc) || fs->spc & (fs->spc - 1))
 460         return EINVAL;
 461     fs->bsize = secbyt(fs->spc);
 462     fs->bshift = ffs(fs->bsize) - 1;
 463     if ((fs->spf = cv2(bs->bpb.spf))) {
 464         if (bs->bpb.fats != 2)
 465             return EINVAL;
 466         if (!(fs->dirents = cv2(bs->bpb.dirents)))
 467             return EINVAL;
 468     } else {
 469         if (!(fs->spf = cv4(bs->bpb.lspf)))
 470             return EINVAL;
 471         if (!bs->bpb.fats || bs->bpb.fats > 16)
 472             return EINVAL;
 473         if ((fs->rdcl = cv4(bs->bpb.rdcl)) < LOCLUS)
 474             return EINVAL;
 475     }
 476     if (!(fs->lsnfat = cv2(bs->bpb.ressec)))
 477         return EINVAL;
 478     fs->lsndir = fs->lsnfat + fs->spf * bs->bpb.fats;
 479     fs->lsndta = fs->lsndir + entsec(fs->dirents);
 480     if (!(sc = cv2(bs->bpb.secs)) && !(sc = cv4(bs->bpb.lsecs)))
 481         return EINVAL;
 482     if (fs->lsndta > sc)
 483         return EINVAL;
 484     if ((fs->xclus = secblk(fs, sc - fs->lsndta) + 1) < LOCLUS)
 485         return EINVAL;
 486     fs->fatsz = fs->dirents ? fs->xclus < 0xff6 ? 12 : 16 : 32;
 487     sc = (secbyt(fs->spf) << 1) / (fs->fatsz >> 2) - 1;
 488     if (fs->xclus > sc)
 489         fs->xclus = sc;
 490     return 0;
 491 }
 492
 493 /*
 494  * Return directory entry from path
 495  */
 496 static int
 497 namede(DOS_FS *fs, const char *path, DOS_DE **dep)
 498 {
 499     char name[256];
 500     DOS_DE *de;
 501     char *s;
 502     size_t n;
 503     int err;
 504
 505     err = 0;
 506     de = &fs->root;
 507     while (*path) {
 508         while (*path == '/')
 509             path++;
 510         if (*path == '\0')
 511             break;
 512         if (!(s = strchr(path, '/')))
 513             s = strchr(path, 0);
 514         if ((n = s - path) > 255)
 515             return ENAMETOOLONG;
 516         memcpy(name, path, n);
 517         name[n] = 0;
 518         path = s;
 519         if (!(de->attr & FA_DIR))
 520             return ENOTDIR;
 521         if ((err = lookup(fs, stclus(fs->fatsz, de), name, &de)))
 522             return err;
 523     }
 524     *dep = de;
 525     return 0;
 526 }
 527
 528 /*
 529  * Lookup path segment
 530  */
 531 static int
 532 lookup(DOS_FS *fs, u_int clus, const char *name, DOS_DE **dep)
 533 {
 534     static DOS_DIR dir[DEPSEC];
 535     u_char lfn[261];
 536     u_char sfn[13];
 537     u_int nsec, lsec, xdn, chk, sec, ent, x;
 538     int err, ok, i;
 539
 540     if (!clus)
 541         for (ent = 0; ent < 2; ent++)
 542             if (!strcasecmp(name, dotstr[ent])) {
 543                 *dep = dot + ent;
 544                 return 0;
 545             }
 546     if (!clus && fs->fatsz == 32)
 547         clus = fs->rdcl;
 548     nsec = !clus ? entsec(fs->dirents) : fs->spc;
 549     lsec = 0;
 550     xdn = chk = 0;
 551     for (;;) {
 552         if (!clus && !lsec)
 553             lsec = fs->lsndir;
 554         else if (okclus(fs, clus))
 555             lsec = blklsn(fs, clus);
 556         else
 557             return EINVAL;
 558         for (sec = 0; sec < nsec; sec++) {
 559             if ((err = ioget(fs->fd, lsec + sec, dir, 1)))
 560                 return err;
 561             for (ent = 0; ent < DEPSEC; ent++) {
 562                 if (!*dir[ent].de.name)
 563                     return ENOENT;
 564                 if (*dir[ent].de.name != 0xe5) {
 565                     if ((dir[ent].de.attr & FA_MASK) == FA_XDE) {
 566                         x = dir[ent].xde.seq;
 567                         if (x & 0x40 || (x + 1 == xdn &&
 568                                          dir[ent].xde.chk == chk)) {
 569                             if (x & 0x40) {
 570                                 chk = dir[ent].xde.chk;
 571                                 x &= ~0x40;
 572                             }
 573                             if (x >= 1 && x <= 20) {
 574                                 cp_xdnm(lfn, &dir[ent].xde);
 575                                 xdn = x;
 576                                 continue;
 577                             }
 578                         }
 579                     } else if (!(dir[ent].de.attr & FA_LABEL)) {
 580                         if ((ok = xdn == 1)) {
 581                             for (x = 0, i = 0; i < 11; i++)
 582                                 x = ((((x & 1) << 7) | (x >> 1)) +
 583                                      ((i < 8) ? dir[ent].de.name[i] :
 584                                                 dir[ent].de.ext[i - 8])
 585                                      ) & 0xff;
 586                             ok = chk == x &&
 587                                 !strcasecmp(name, (const char *)lfn);
 588                         }
 589                         if (!ok) {
 590                             cp_sfn(sfn, &dir[ent].de);
 591                             ok = !strcasecmp(name, (const char *)sfn);
 592                         }
 593                         if (ok) {
 594                             *dep = &dir[ent].de;
 595                             return 0;
 596                         }
 597                     }
 598                 }
 599                 xdn = 0;
 600             }
 601         }
 602         if (!clus)
 603             break;
 604         if ((err = fatget(fs, &clus)))
 605             return err;
 606         if (fatend(fs->fatsz, clus))
 607             break;
 608     }
 609     return ENOENT;
 610 }
 611
 612 /*
 613  * Copy name from extended directory entry
 614  */
 615 static void
 616 cp_xdnm(u_char *lfn, DOS_XDE *xde)
 617 {
 618     static struct {
 619         u_int off;
 620         u_int dim;
 621     } ix[3] = {
 622         {offsetof(DOS_XDE, name1), sizeof(xde->name1) / 2},
 623         {offsetof(DOS_XDE, name2), sizeof(xde->name2) / 2},
 624         {offsetof(DOS_XDE, name3), sizeof(xde->name3) / 2}
 625     };
 626     u_char *p;
 627     u_int n, x, c;
 628
 629     lfn += 13 * ((xde->seq & ~0x40) - 1);
 630     for (n = 0; n < 3; n++)
 631         for (p = (u_char *)xde + ix[n].off, x = ix[n].dim; x;
 632              p += 2, x--) {
 633             if ((c = cv2(p)) && (c < 32 || c > 127))
 634                 c = '?';
 635             if (!(*lfn++ = c))
 636                 return;
 637         }
 638     if (xde->seq & 0x40)
 639         *lfn = 0;
 640 }
 641
 642 /*
 643  * Copy short filename
 644  */
 645 static void
 646 cp_sfn(u_char *sfn, DOS_DE *de)
 647 {
 648     u_char *p;
 649     int j, i;
 650
 651     p = sfn;
 652     if (*de->name != ' ') {
 653         for (j = 7; de->name[j] == ' '; j--);
 654         for (i = 0; i <= j; i++)
 655             *p++ = de->name[i];
 656         if (*de->ext != ' ') {
 657             *p++ = '.';
 658             for (j = 2; de->ext[j] == ' '; j--);
 659             for (i = 0; i <= j; i++)
 660                 *p++ = de->ext[i];
 661         }
 662     }
 663     *p = 0;
 664     if (*sfn == 5)
 665         *sfn = 0xe5;
 666 }
 667
 668 /*
 669  * Return size of file in bytes
 670  */
 671 static off_t
 672 fsize(DOS_FS *fs, DOS_DE *de)
 673 {
 674    u_long size;
 675    u_int c;
 676    int n;
 677
 678    if (!(size = cv4(de->size)) && de->attr & FA_DIR) {
 679       if (!(c = cv2(de->clus)))
 680          size = fs->dirents * sizeof(DOS_DE);
 681       else {
 682          if ((n = fatcnt(fs, c)) == -1)
 683             return n;
 684          size = blkbyt(fs, n);
 685       }
 686    }
 687    return size;
 688 }
 689
 690 /*
 691  * Count number of clusters in chain
 692  */
 693 static int
 694 fatcnt(DOS_FS *fs, u_int c)
 695 {
 696    int n;
 697
 698    for (n = 0; okclus(fs, c); n++)
 699       if (fatget(fs, &c))
 700           return -1;
 701    return fatend(fs->fatsz, c) ? n : -1;
 702 }
 703
 704 /*
 705  * Get next cluster in cluster chain
 706  */
 707 static int
 708 fatget(DOS_FS *fs, u_int *c)
 709 {
 710     u_char buf[4];
 711     u_int x;
 712     int err;
 713
 714     err = ioread(fs, secbyt(fs->lsnfat) + fatoff(fs->fatsz, *c), buf,
 715                  fs->fatsz != 32 ? 2 : 4);
 716     if (err)
 717         return err;
 718     x = fs->fatsz != 32 ? cv2(buf) : cv4(buf);
 719     *c = fs->fatsz == 12 ? *c & 1 ? x >> 4 : x & 0xfff : x;
 720     return 0;
 721 }
 722
 723 /*
 724  * Is cluster an end-of-chain marker?
 725  */
 726 static int
 727 fatend(u_int sz, u_int c)
 728 {
 729     return c > (sz == 12 ? 0xff7U : sz == 16 ? 0xfff7U : 0xffffff7);
 730 }
 731
 732 /*
 733  * Offset-based I/O primitive
 734  */
 735 static int
 736 ioread(DOS_FS *fs, u_int offset, void *buf, u_int nbyte)
 737 {
 738     char *s;
 739     u_int off, n;
 740     int err;
 741
 742     s = buf;
 743     if ((off = offset & (SECSIZ - 1))) {
 744         offset -= off;
 745         if ((err = iobuf(fs, bytsec(offset))))
 746             return err;
 747         offset += SECSIZ;
 748         if ((n = SECSIZ - off) > nbyte)
 749             n = nbyte;
 750         memcpy(s, fs->buf + off, n);
 751         s += n;
 752         nbyte -= n;
 753     }
 754     n = nbyte & (SECSIZ - 1);
 755     if (nbyte -= n) {
 756         if ((err = ioget(fs->fd, bytsec(offset), s, bytsec(nbyte))))
 757             return err;
 758         offset += nbyte;
 759         s += nbyte;
 760     }
 761     if (n) {
 762         if ((err = iobuf(fs, bytsec(offset))))
 763             return err;
 764         memcpy(s, fs->buf, n);
 765     }
 766     return 0;
 767 }
 768
 769 /*
 770  * Buffered sector-based I/O primitive
 771  */
 772 static int
 773 iobuf(DOS_FS *fs, u_int lsec)
 774 {
 775     int err;
 776
 777     if (fs->bufsec != lsec) {
 778         if ((err = ioget(fs->fd, lsec, fs->buf, 1)))
 779             return err;
 780         fs->bufsec = lsec;
 781     }
 782     return 0;
 783 }
 784
 785 /*
 786  * Sector-based I/O primitive
 787  */
 788 static int
 789 ioget(struct open_file *fd, u_int lsec, void *buf, u_int nsec)
 790 {
 791     int err;
 792
 793     twiddle();
 794     if ((err = (fd->f_dev->dv_strategy)(fd->f_devdata, F_READ, lsec,
 795                                         secbyt(nsec), buf, NULL)))
 796         return(err);
 797     return(0);
 798 }