dos/syslinux.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 1998-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   9  *   Boston MA 02111-1307, USA; either version 2 of the License, or
  10  *   (at your option) any later version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * syslinux.c - Linux installer program for SYSLINUX
  16  *
  17  * Hacked up for DOS.
  18  */
  19
  20 #include <errno.h>
  21 #include <getopt.h>
  22 #include <stdio.h>
  23 #include <string.h>
  24 #include <stdlib.h>
  25 #include <stdarg.h>
  26 #include "mystuff.h"
  27
  28 #include "syslinux.h"
  29 #include "libfat.h"
  30 #include "setadv.h"
  31 #include "sysexits.h"
  32 #include "syslxopt.h"
  33 #include "syslxint.h"
  34 #include "syslxfs.h"
  35
  36 char *program = "syslinux.com";         /* Name of program */
  37 uint16_t dos_version;
  38
  39 #ifdef DEBUG
  40 # define dprintf printf
  41 void pause(void)
  42 {
  43     uint16_t ax;
  44
  45     asm volatile("int $0x16" : "=a" (ax) : "a" (0));
  46 }
  47 #else
  48 # define dprintf(...) ((void)0)
  49 # define pause() ((void)0)
  50 #endif
  51
  52 void unlock_device(int);
  53
  54 void __attribute__ ((noreturn)) die(const char *msg)
  55 {
  56     unlock_device(0);
  57     puts("syslinux: ");
  58     puts(msg);
  59     putchar('\n');
  60     exit(1);
  61 }
  62
  63 void warning(const char *msg)
  64 {
  65     puts("syslinux: warning: ");
  66     puts(msg);
  67     putchar('\n');
  68 }
  69
  70 /*
  71  * read/write wrapper functions
  72  */
  73 int creat(const char *filename, int mode)
  74 {
  75     uint16_t rv;
  76     uint8_t err;
  77
  78     dprintf("creat(\"%s\", 0x%x)\n", filename, mode);
  79
  80     rv = 0x3C00;
  81     asm volatile ("int $0x21 ; setc %0"
  82                   : "=bcdm" (err), "+a" (rv)
  83                   : "c" (mode), "d" (filename));
  84     if (err) {
  85         dprintf("rv = %d\n", rv);
  86         die("cannot open ldlinux.sys");
  87     }
  88
  89     return rv;
  90 }
  91
  92 void close(int fd)
  93 {
  94     uint16_t rv = 0x3E00;
  95
  96     dprintf("close(%d)\n", fd);
  97
  98     asm volatile ("int $0x21":"+a" (rv)
  99                   :"b"(fd));
 100
 101     /* The only error MS-DOS returns for close is EBADF,
 102        and we really don't care... */
 103 }
 104
 105 int rename(const char *oldname, const char *newname)
 106 {
 107     uint16_t rv = 0x5600;       /* Also support 43FFh? */
 108     uint8_t err;
 109
 110     dprintf("rename(\"%s\", \"%s\")\n", oldname, newname);
 111
 112     asm volatile ("int $0x21 ; setc %0":"=bcdm" (err), "+a"(rv)
 113                   :"d"(oldname), "D"(newname));
 114
 115     if (err) {
 116         dprintf("rv = %d\n", rv);
 117         warning("cannot move ldlinux.sys");
 118         return rv;
 119     }
 120
 121     return 0;
 122 }
 123
 124 ssize_t write_file_seg(int fd, unsigned char *buf, const unsigned int len)
 125 {
 126     uint16_t seg = ((size_t)buf >> 4) + ds();
 127     uint32_t offset = 0;
 128     uint16_t rv;
 129     uint8_t err;
 130
 131     while (offset < len) {
 132         uint32_t chunk = len - offset;
 133         if (chunk > 32768)
 134             chunk = 32768;
 135         asm volatile ("pushw %%ds ; "
 136                       "movw %6,%%ds ; "
 137                       "int $0x21 ; "
 138                       "popw %%ds ; " "setc %0":"=bcdm" (err), "=a"(rv)
 139                       :"a"(0x4000), "b"(fd), "c"(chunk), "d" (offset & 15),
 140                       "SD" ((uint16_t)(seg + (offset >> 4))));
 141         if (err || rv == 0)
 142             die("file write error");
 143         offset += rv;
 144     }
 145
 146     return offset;
 147 }
 148
 149 ssize_t write_file(int fd, const void *buf, size_t count)
 150 {
 151     uint16_t rv;
 152     ssize_t done = 0;
 153     uint8_t err;
 154
 155     dprintf("write_file(%d,%p,%u)\n", fd, buf, count);
 156
 157     while (count) {
 158         asm volatile ("int $0x21 ; setc %0":"=bcdm" (err), "=a"(rv)
 159                       :"a"(0x4000), "b"(fd), "c"(count), "d"(buf));
 160         if (err || rv == 0)
 161             die("file write error");
 162
 163         done += rv;
 164         count -= rv;
 165     }
 166
 167     return done;
 168 }
 169
 170 static inline __attribute__ ((const))
 171 uint16_t data_segment(void)
 172 {
 173     uint16_t ds;
 174
 175     asm("movw %%ds,%0" : "=rm"(ds));
 176     return ds;
 177 }
 178
 179 void write_device(int drive, const void *buf, size_t nsecs, unsigned int sector)
 180 {
 181     uint16_t errnum = 0x0001;
 182     struct diskio dio;
 183
 184     dprintf("write_device(%d,%p,%u,%u)\n", drive, buf, nsecs, sector);
 185
 186     dio.startsector = sector;
 187     dio.sectors = nsecs;
 188     dio.bufoffs = (uintptr_t) buf;
 189     dio.bufseg = data_segment();
 190
 191     if (dos_version >= 0x070a) {
 192         /* Try FAT32-aware system call first */
 193         asm volatile("int $0x21 ; jc 1f ; xorw %0,%0\n"
 194                      "1:"
 195                      : "=a" (errnum)
 196                      : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
 197                        "S" (1), "m" (dio)
 198                      : "memory");
 199         dprintf(" rv(7305) = %04x", errnum);
 200     }
 201
 202     /* If not supported, try the legacy system call (int2526.S) */
 203     if (errnum == 0x0001)
 204         errnum = int26_write_sector(drive, &dio);
 205
 206     if (errnum) {
 207         dprintf("rv = %04x\n", errnum);
 208         die("sector write error");
 209     }
 210 }
 211
 212 void read_device(int drive, void *buf, size_t nsecs, unsigned int sector)
 213 {
 214     uint16_t errnum = 0x0001;
 215     struct diskio dio;
 216
 217     dprintf("read_device(%d,%p,%u,%u)\n", drive, buf, nsecs, sector);
 218
 219     dio.startsector = sector;
 220     dio.sectors = nsecs;
 221     dio.bufoffs = (uintptr_t) buf;
 222     dio.bufseg = data_segment();
 223
 224     if (dos_version >= 0x070a) {
 225         /* Try FAT32-aware system call first */
 226         asm volatile("int $0x21 ; jc 1f ; xorw %0,%0\n"
 227                      "1:"
 228                      : "=a" (errnum)
 229                      : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
 230                        "S" (0), "m" (dio));
 231         dprintf(" rv(7305) = %04x", errnum);
 232     }
 233
 234     /* If not supported, try the legacy system call (int2526.S) */
 235     if (errnum == 0x0001)
 236         errnum = int25_read_sector(drive, &dio);
 237
 238     if (errnum) {
 239         dprintf("rv = %04x\n", errnum);
 240         die("sector read error");
 241     }
 242 }
 243
 244 /* Both traditional DOS and FAT32 DOS return this structure, but
 245    FAT32 return a lot more data, so make sure we have plenty of space */
 246 struct deviceparams {
 247     uint8_t specfunc;
 248     uint8_t devtype;
 249     uint16_t devattr;
 250     uint16_t cylinders;
 251     uint8_t mediatype;
 252     uint16_t bytespersec;
 253     uint8_t secperclust;
 254     uint16_t ressectors;
 255     uint8_t fats;
 256     uint16_t rootdirents;
 257     uint16_t sectors;
 258     uint8_t media;
 259     uint16_t fatsecs;
 260     uint16_t secpertrack;
 261     uint16_t heads;
 262     uint32_t hiddensecs;
 263     uint32_t hugesectors;
 264     uint8_t lotsofpadding[224];
 265 } __attribute__ ((packed));
 266
 267 uint32_t get_partition_offset(int drive)
 268 {
 269     uint8_t err;
 270     uint16_t rv;
 271     struct deviceparams dp;
 272
 273     dp.specfunc = 1;            /* Get current information */
 274
 275     rv = 0x440d;
 276     asm volatile ("int $0x21 ; setc %0"
 277                   :"=abcdm" (err), "+a"(rv), "=m"(dp)
 278                   :"b" (drive), "c" (0x0860), "d" (&dp));
 279
 280     if (!err)
 281         return dp.hiddensecs;
 282
 283     rv = 0x440d;
 284     asm volatile ("int $0x21 ; setc %0"
 285                   : "=abcdm" (err), "+a" (rv), "=m" (dp)
 286                   : "b" (drive), "c" (0x4860), "d" (&dp));
 287
 288     if (!err)
 289         return dp.hiddensecs;
 290
 291     die("could not find partition start offset");
 292 }
 293
 294 struct rwblock {
 295     uint8_t special;
 296     uint16_t head;
 297     uint16_t cylinder;
 298     uint16_t firstsector;
 299     uint16_t sectors;
 300     uint16_t bufferoffset;
 301     uint16_t bufferseg;
 302 } __attribute__ ((packed));
 303
 304 static struct rwblock mbr = {
 305     .special = 0,
 306     .head = 0,
 307     .cylinder = 0,
 308     .firstsector = 0,           /* MS-DOS, unlike the BIOS, zero-base sectors */
 309     .sectors = 1,
 310     .bufferoffset = 0,
 311     .bufferseg = 0
 312 };
 313
 314 void write_mbr(int drive, const void *buf)
 315 {
 316     uint16_t rv;
 317     uint8_t err;
 318
 319     dprintf("write_mbr(%d,%p)", drive, buf);
 320
 321     mbr.bufferoffset = (uintptr_t) buf;
 322     mbr.bufferseg = data_segment();
 323
 324     rv = 0x440d;
 325     asm volatile ("int $0x21 ; setc %0" : "=bcdm" (err), "+a"(rv)
 326                   :"c"(0x0841), "d"(&mbr), "b"(drive), "m"(mbr));
 327
 328     dprintf(" rv(0841) = %04x", rv);
 329     if (!err) {
 330         dprintf("\n");
 331         return;
 332     }
 333
 334     rv = 0x440d;
 335     asm volatile ("int $0x21 ; setc %0" : "=bcdm" (err), "+a"(rv)
 336                   :"c"(0x4841), "d"(&mbr), "b"(drive), "m"(mbr));
 337
 338     dprintf(" rv(4841) = %04x\n", rv);
 339     if (err)
 340         die("mbr write error");
 341 }
 342
 343 void read_mbr(int drive, const void *buf)
 344 {
 345     uint16_t rv;
 346     uint8_t err;
 347
 348     dprintf("read_mbr(%d,%p)", drive, buf);
 349
 350     mbr.bufferoffset = (uintptr_t) buf;
 351     mbr.bufferseg = data_segment();
 352
 353     rv = 0x440d;
 354     asm volatile ("int $0x21 ; setc %0":"=abcdm" (err), "+a"(rv)
 355                   :"c"(0x0861), "d"(&mbr), "b"(drive), "m"(mbr));
 356
 357     dprintf(" rv(0861) = %04x", rv);
 358     if (!err) {
 359         dprintf("\n");
 360         return;
 361     }
 362
 363     rv = 0x440d;
 364     asm volatile ("int $0x21 ; setc %0":"=abcdm" (err), "+a"(rv)
 365                   :"c"(0x4861), "d"(&mbr), "b"(drive), "m"(mbr));
 366
 367     dprintf(" rv(4841) = %04x\n", rv);
 368     if (err)
 369         die("mbr read error");
 370
 371     dprintf("Bytes: %02x %02x %02x %02x %02x %02x %02x %02x\n",
 372             ((const uint8_t *)buf)[0],
 373             ((const uint8_t *)buf)[1],
 374             ((const uint8_t *)buf)[2],
 375             ((const uint8_t *)buf)[3],
 376             ((const uint8_t *)buf)[4],
 377             ((const uint8_t *)buf)[5],
 378             ((const uint8_t *)buf)[6],
 379             ((const uint8_t *)buf)[7]);
 380 }
 381
 382 /* This call can legitimately fail, and we don't care, so ignore error return */
 383 void set_attributes(const char *file, int attributes)
 384 {
 385     uint16_t rv = 0x4301;
 386
 387     dprintf("set_attributes(\"%s\", 0x%02x)\n", file, attributes);
 388
 389     asm volatile ("int $0x21":"+a" (rv)
 390                   :"c"(attributes), "d"(file));
 391 }
 392
 393 /*
 394  * Version of the read_device function suitable for libfat
 395  */
 396 int libfat_xpread(intptr_t pp, void *buf, size_t secsize,
 397                   libfat_sector_t sector)
 398 {
 399     read_device(pp, buf, 1, sector);
 400     return secsize;
 401 }
 402
 403 static inline void get_dos_version(void)
 404 {
 405     dprintf("DOS version %d.%d\n", (dos_version >> 8), dos_version & 0xff);
 406 }
 407
 408 /* The locking interface relies on static variables.  A massive hack :( */
 409 static uint8_t lock_level, lock_drive;
 410
 411 static inline void set_lock_device(uint8_t device)
 412 {
 413     lock_level  = 0;
 414     lock_drive = device;
 415 }
 416
 417 static int do_lock(uint8_t level)
 418 {
 419     uint16_t level_arg = lock_drive + (level << 8);
 420     uint16_t rv;
 421     uint8_t err;
 422 #if 0
 423     /* DOS 7.10 = Win95 OSR2 = first version with FAT32 */
 424     uint16_t lock_call = (dos_version >= 0x070a) ? 0x484A : 0x084A;
 425 #else
 426     uint16_t lock_call = 0x084A; /* MSDN says this is OK for all filesystems */
 427 #endif
 428
 429     dprintf("Trying lock %04x... ", level_arg);
 430     asm volatile ("int $0x21 ; setc %0"
 431                   : "=bcdm" (err), "=a" (rv)
 432                   : "a" (0x440d), "b" (level_arg),
 433                     "c" (lock_call), "d" (0x0001));
 434     dprintf("%s %04x\n", err ? "err" : "ok", rv);
 435
 436     return err ? rv : 0;
 437 }
 438
 439 void lock_device(int level)
 440 {
 441     static int hard_lock = 0;
 442     int err;
 443
 444     if (dos_version < 0x0700)
 445         return;                 /* Win9x/NT only */
 446
 447     if (!hard_lock) {
 448         /* Assume hierarchial "soft" locking supported */
 449
 450         while (lock_level < level) {
 451             int new_level = lock_level + 1;
 452             err = do_lock(new_level);
 453             if (err) {
 454                 if (err == 0x0001) {
 455                     /* Try hard locking next */
 456                     hard_lock = 1;
 457                 }
 458                 goto soft_fail;
 459             }
 460
 461             lock_level = new_level;
 462         }
 463         return;
 464     }
 465
 466 soft_fail:
 467     if (hard_lock) {
 468         /* Hard locking, only level 4 supported */
 469         /* This is needed for Win9x in DOS mode */
 470
 471         err = do_lock(4);
 472         if (err) {
 473             if (err == 0x0001) {
 474                 /* Assume locking is not needed */
 475                 return;
 476             }
 477             goto hard_fail;
 478         }
 479
 480         lock_level = 4;
 481         return;
 482     }
 483
 484 hard_fail:
 485     die("could not lock device");
 486 }
 487
 488 void unlock_device(int level)
 489 {
 490     uint16_t rv;
 491     uint8_t err;
 492     uint16_t unlock_call;
 493
 494     if (dos_version < 0x0700)
 495         return;                 /* Win9x/NT only */
 496
 497 #if 0
 498     /* DOS 7.10 = Win95 OSR2 = first version with FAT32 */
 499     unlock_call = (dos_version >= 0x070a) ? 0x486A : 0x086A;
 500 #else
 501     unlock_call = 0x086A;       /* MSDN says this is OK for all filesystems */
 502 #endif
 503
 504     if (lock_level == 4 && level > 0)
 505         return;                 /* Only drop the hard lock at the end */
 506
 507     while (lock_level > level) {
 508         uint8_t new_level = (lock_level == 4) ? 0 : lock_level - 1;
 509         uint16_t level_arg = (new_level << 8) + lock_drive;
 510         rv = 0x440d;
 511         dprintf("Trying unlock %04x... ", new_level);
 512         asm volatile ("int $0x21 ; setc %0"
 513                       : "=bcdm" (err), "+a" (rv)
 514                       : "b" (level_arg), "c" (unlock_call));
 515         dprintf("%s %04x\n", err ? "err" : "ok", rv);
 516         lock_level = new_level;
 517     }
 518 }
 519
 520 /*
 521  * This function does any desired MBR manipulation; called with the device lock held.
 522  */
 523 struct mbr_entry {
 524     uint8_t active;             /* Active flag */
 525     uint8_t bhead;              /* Begin head */
 526     uint8_t bsector;            /* Begin sector */
 527     uint8_t bcylinder;          /* Begin cylinder */
 528     uint8_t filesystem;         /* Filesystem value */
 529     uint8_t ehead;              /* End head */
 530     uint8_t esector;            /* End sector */
 531     uint8_t ecylinder;          /* End cylinder */
 532     uint32_t startlba;          /* Start sector LBA */
 533     uint32_t sectors;           /* Length in sectors */
 534 } __attribute__ ((packed));
 535
 536 static void adjust_mbr(int device, int writembr, int set_active)
 537 {
 538     static unsigned char sectbuf[SECTOR_SIZE];
 539     int i;
 540
 541     if (!writembr && !set_active)
 542         return;                 /* Nothing to do */
 543
 544     read_mbr(device, sectbuf);
 545
 546     if (writembr) {
 547         memcpy(sectbuf, syslinux_mbr, syslinux_mbr_len);
 548         *(uint16_t *) (sectbuf + 510) = 0xaa55;
 549     }
 550
 551     if (set_active) {
 552         uint32_t offset = get_partition_offset(device);
 553         struct mbr_entry *me = (struct mbr_entry *)(sectbuf + 446);
 554         int found = 0;
 555
 556         dprintf("Searching for partition offset: %08x\n", offset);
 557
 558         for (i = 0; i < 4; i++) {
 559             if (me->startlba == offset) {
 560                 me->active = 0x80;
 561                 found++;
 562             } else {
 563                 me->active = 0;
 564             }
 565             me++;
 566         }
 567
 568         if (found < 1) {
 569             die("partition not found (-a is not implemented for logical partitions)");
 570         } else if (found > 1) {
 571             die("multiple aliased partitions found");
 572         }
 573     }
 574
 575     write_mbr(device, sectbuf);
 576 }
 577
 578 static void move_file(int dev_fd, char *pathname, char *filename)
 579 {
 580     char new_name[160];
 581     char *cp = new_name + 3;
 582     const char *sd;
 583     int slash = 1;
 584
 585     new_name[0] = dev_fd | 0x40;
 586     new_name[1] = ':';
 587     new_name[2] = '\\';
 588
 589     for (sd = opt.directory; *sd; sd++) {
 590         char c = *sd;
 591
 592         if (c == '/' || c == '\\') {
 593             if (slash)
 594                 continue;
 595             c = '\\';
 596             slash = 1;
 597         } else {
 598             slash = 0;
 599         }
 600
 601         *cp++ = c;
 602     }
 603
 604     /* Skip if subdirectory == root */
 605     if (cp > new_name + 3) {
 606         if (!slash)
 607             *cp++ = '\\';
 608
 609         memcpy(cp, filename, 12);
 610
 611         set_attributes(pathname, 0);
 612         if (rename(pathname, new_name))
 613             set_attributes(pathname, 0x07);
 614         else
 615             set_attributes(new_name, 0x07);
 616     }
 617 }
 618
 619 int main(int argc, char *argv[])
 620 {
 621     static unsigned char sectbuf[SECTOR_SIZE];
 622     int dev_fd, fd;
 623     static char ldlinux_name[] = "@:\\ldlinux.sys";
 624     static char ldlinuxc32_name[] = "@:\\ldlinux.c32";
 625     struct libfat_filesystem *fs;
 626     libfat_sector_t s, *secp;
 627     libfat_sector_t *sectors;
 628     int ldlinux_sectors;
 629     int32_t ldlinux_cluster;
 630     int nsectors;
 631     const char *errmsg;
 632     int i;
 633     int patch_sectors;
 634     unsigned char *dp;
 635
 636     dprintf("argv = %p\n", argv);
 637     for (i = 0; i <= argc; i++)
 638         dprintf("argv[%d] = %p = \"%s\"\n", i, argv[i], argv[i]);
 639
 640     get_dos_version();
 641
 642     argv[0] = program;
 643     parse_options(argc, argv, MODE_SYSLINUX_DOSWIN);
 644
 645     if (!opt.device)
 646         usage(EX_USAGE, MODE_SYSLINUX_DOSWIN);
 647     if (opt.sectors || opt.heads || opt.reset_adv || opt.set_once
 648         || (opt.update_only > 0) || opt.menu_save || opt.offset) {
 649         fprintf(stderr,
 650                 "At least one specified option not yet implemented"
 651                 " for this installer.\n");
 652         exit(1);
 653     }
 654
 655     /*
 656      * Create an ADV in memory... this should be smarter.
 657      */
 658     syslinux_reset_adv(syslinux_adv);
 659
 660     /*
 661      * Figure out which drive we're talking to
 662      */
 663     dev_fd = (opt.device[0] & ~0x20) - 0x40;
 664     if (dev_fd < 1 || dev_fd > 26 || opt.device[1] != ':' || opt.device[2])
 665         usage(EX_USAGE, MODE_SYSLINUX_DOSWIN);
 666
 667     set_lock_device(dev_fd);
 668
 669     lock_device(2);             /* Make sure we can lock the device */
 670     read_device(dev_fd, sectbuf, 1, 0);
 671     unlock_device(1);
 672
 673     /*
 674      * Check to see that what we got was indeed an MS-DOS boot sector/superblock
 675      */
 676     if ((errmsg = syslinux_check_bootsect(sectbuf, NULL))) {
 677         unlock_device(0);
 678         puts(errmsg);
 679         putchar('\n');
 680         exit(1);
 681     }
 682
 683     ldlinux_name[0] = dev_fd | 0x40;
 684     ldlinuxc32_name[0] = dev_fd | 0x40;
 685
 686     set_attributes(ldlinux_name, 0);
 687     fd = creat(ldlinux_name, 0);        /* SYSTEM HIDDEN READONLY */
 688     write_file_seg(fd, syslinux_ldlinux, syslinux_ldlinux_len);
 689     write_file(fd, syslinux_adv, 2 * ADV_SIZE);
 690     close(fd);
 691     set_attributes(ldlinux_name, 0x07); /* SYSTEM HIDDEN READONLY */
 692
 693     set_attributes(ldlinuxc32_name, 0);
 694     fd = creat(ldlinuxc32_name, 0);             /* SYSTEM HIDDEN READONLY */
 695     write_file_seg(fd, syslinux_ldlinuxc32, syslinux_ldlinuxc32_len);
 696     close(fd);
 697     set_attributes(ldlinuxc32_name, 0x07);      /* SYSTEM HIDDEN READONLY */
 698
 699     /*
 700      * Now, use libfat to create a block map.  This probably
 701      * should be changed to use ioctl(...,FIBMAP,...) since
 702      * this is supposed to be a simple, privileged version
 703      * of the installer.
 704      */
 705     ldlinux_sectors = (syslinux_ldlinux_len + 2 * ADV_SIZE
 706                        + SECTOR_SIZE - 1) >> SECTOR_SHIFT;
 707     sectors = calloc(ldlinux_sectors, sizeof *sectors);
 708     lock_device(2);
 709     fs = libfat_open(libfat_xpread, dev_fd);
 710     ldlinux_cluster = libfat_searchdir(fs, 0, "LDLINUX SYS", NULL);
 711     secp = sectors;
 712     nsectors = 0;
 713     s = libfat_clustertosector(fs, ldlinux_cluster);
 714     while (s && nsectors < ldlinux_sectors) {
 715         *secp++ = s;
 716         nsectors++;
 717         s = libfat_nextsector(fs, s);
 718     }
 719     libfat_close(fs);
 720
 721     /*
 722      * If requested, move ldlinux.sys
 723      */
 724     if (opt.directory) {
 725         move_file(dev_fd, ldlinux_name, "ldlinux.sys");
 726         move_file(dev_fd, ldlinuxc32_name, "ldlinux.c32");
 727     }
 728
 729     /*
 730      * Patch ldlinux.sys and the boot sector
 731      */
 732     i = syslinux_patch(sectors, nsectors, opt.stupid_mode, opt.raid_mode, opt.directory, NULL);
 733     patch_sectors = (i + SECTOR_SIZE - 1) >> SECTOR_SHIFT;
 734
 735     /*
 736      * Overwrite the now-patched ldlinux.sys
 737      */
 738     /* lock_device(3); -- doesn't seem to be needed */
 739     dp = syslinux_ldlinux;
 740     for (i = 0; i < patch_sectors; i++) {
 741         memcpy_from_sl(sectbuf, dp, SECTOR_SIZE);
 742         dp += SECTOR_SIZE;
 743         write_device(dev_fd, sectbuf, 1, sectors[i]);
 744     }
 745
 746     /*
 747      * Muck with the MBR, if desired, while we hold the lock
 748      */
 749     adjust_mbr(dev_fd, opt.install_mbr, opt.activate_partition);
 750
 751     /*
 752      * To finish up, write the boot sector
 753      */
 754
 755     /* Read the superblock again since it might have changed while mounted */
 756     read_device(dev_fd, sectbuf, 1, 0);
 757
 758     /* Copy the syslinux code into the boot sector */
 759     syslinux_make_bootsect(sectbuf, VFAT);
 760
 761     /* Write new boot sector */
 762     if (opt.bootsecfile) {
 763         unlock_device(0);
 764         fd = creat(opt.bootsecfile, 0x20);      /* ARCHIVE */
 765         write_file(fd, sectbuf, SECTOR_SIZE);
 766         close(fd);
 767     } else {
 768         write_device(dev_fd, sectbuf, 1, 0);
 769         unlock_device(0);
 770     }
 771
 772     /* Done! */
 773
 774     return 0;
 775 }