boot.c - platform/external/fsck_msdos - Git at Google

 /*
  * Copyright (C) 1995, 1997 Wolfgang Solfrank
  * Copyright (c) 1995 Martin Husemann
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. All advertising materials mentioning features or use of this software
  *    must display the following acknowledgement:
  *	This product includes software developed by Martin Husemann
  *	and Wolfgang Solfrank.
  * 4. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */


 #include <sys/cdefs.h>
 #ifndef lint
 __RCSID("$NetBSD: boot.c,v 1.9 2003/07/24 19:25:46 ws Exp $");
 static const char rcsid[] =
   "$FreeBSD: src/sbin/fsck_msdosfs/boot.c,v 1.4.28.1 2009/04/15 03:14:26 kensmith Exp $";
 #endif /* not lint */

 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
 #include <stdio.h>
 #include <unistd.h>

 #include "ext.h"
 #include "fsutil.h"

 int
 readboot(dosfs, boot)
 	int dosfs;
 	struct bootblock *boot;
 {
 	u_char block[DOSBOOTBLOCKSIZE];
 	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
 	u_char backup[DOSBOOTBLOCKSIZE];
 	int ret = FSOK;

 	if (read(dosfs, block, sizeof block) < sizeof block) {
 		perror("could not read boot block");
                 exit(2);
 	}

 	if (block[510] != 0x55 || block[511] != 0xaa) {
 		pfatal("Invalid signature in boot block: %02x%02x", block[511], block[510]);
                 exit(2);
 	}

 	memset(boot, 0, sizeof *boot);
 	boot->ValidFat = -1;

 	/* decode bios parameter block */
 	boot->BytesPerSec = block[11] + (block[12] << 8);
 	boot->SecPerClust = block[13];
 	boot->ResSectors = block[14] + (block[15] << 8);
 	boot->FATs = block[16];
 	boot->RootDirEnts = block[17] + (block[18] << 8);
 	boot->Sectors = block[19] + (block[20] << 8);
 	boot->Media = block[21];
 	boot->FATsmall = block[22] + (block[23] << 8);
 	boot->SecPerTrack = block[24] + (block[25] << 8);
 	boot->Heads = block[26] + (block[27] << 8);
 	boot->HiddenSecs = block[28] + (block[29] << 8) + (block[30] << 16) + (block[31] << 24);
 	boot->HugeSectors = block[32] + (block[33] << 8) + (block[34] << 16) + (block[35] << 24);

 	boot->FATsecs = boot->FATsmall;

 	if (!boot->RootDirEnts)
 		boot->flags |= FAT32;
 	if (boot->flags & FAT32) {
 		boot->FATsecs = block[36] + (block[37] << 8)
 				+ (block[38] << 16) + (block[39] << 24);
 		if (block[40] & 0x80)
 			boot->ValidFat = block[40] & 0x0f;

 		/* check version number: */
 		if (block[42] || block[43]) {
 			/* Correct?				XXX */
 			pfatal("Unknown file system version: %x.%x",
 			       block[43], block[42]);
                         exit(2);
 		}
 		boot->RootCl = block[44] + (block[45] << 8)
 			       + (block[46] << 16) + (block[47] << 24);
 		boot->FSInfo = block[48] + (block[49] << 8);
 		boot->Backup = block[50] + (block[51] << 8);

 		if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
 		    != boot->FSInfo * boot->BytesPerSec
 		    || read(dosfs, fsinfo, sizeof fsinfo)
 		    != sizeof fsinfo) {
 			perror("could not read fsinfo block");
 			return FSFATAL;
 		}
 		if (memcmp(fsinfo, "RRaA", 4)
 		    || memcmp(fsinfo + 0x1e4, "rrAa", 4)
 		    || fsinfo[0x1fc]
 		    || fsinfo[0x1fd]
 		    || fsinfo[0x1fe] != 0x55
 		    || fsinfo[0x1ff] != 0xaa
 		    || fsinfo[0x3fc]
 		    || fsinfo[0x3fd]
 		    || fsinfo[0x3fe] != 0x55
 		    || fsinfo[0x3ff] != 0xaa) {
 			pwarn("Invalid signature in fsinfo block\n");
 			if (ask(1, "fix")) {
 				memcpy(fsinfo, "RRaA", 4);
 				memcpy(fsinfo + 0x1e4, "rrAa", 4);
 				fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
 				fsinfo[0x1fe] = 0x55;
 				fsinfo[0x1ff] = 0xaa;
 				fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
 				fsinfo[0x3fe] = 0x55;
 				fsinfo[0x3ff] = 0xaa;
 				if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
 				    != boot->FSInfo * boot->BytesPerSec
 				    || write(dosfs, fsinfo, sizeof fsinfo)
 				    != sizeof fsinfo) {
 					perror("Unable to write FSInfo");
 					return FSFATAL;
 				}
 				ret = FSBOOTMOD;
 			} else
 				boot->FSInfo = 0;
 		}
 		if (boot->FSInfo) {
 			boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
 				       + (fsinfo[0x1ea] << 16)
 				       + (fsinfo[0x1eb] << 24);
 			boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
 				       + (fsinfo[0x1ee] << 16)
 				       + (fsinfo[0x1ef] << 24);
 		}

 		if (lseek(dosfs, boot->Backup * boot->BytesPerSec, SEEK_SET)
 		    != boot->Backup * boot->BytesPerSec
 		    || read(dosfs, backup, sizeof backup) != sizeof  backup) {
 			perror("could not read backup bootblock");
 			return FSFATAL;
 		}
 		backup[65] = block[65];				/* XXX */
 		if (memcmp(block + 11, backup + 11, 79)) {
                         char tmp[255];
                         int i;

 			/*
 			 * For now, lets not bail out if they don't match
 			 * It seems a lot of sdcards are formatted with
 			 * the backup either empty or containing garbage.
 			 */

 			pwarn("Primary/Backup bootblock miscompare\n");

                         strcpy(tmp, "");
                         pwarn("Primary:\n");
 			for (i = 0; i < 79; i++) {
 				char tmp2[16];
                                 snprintf(tmp2, sizeof(tmp2), "%.2x ", block[11 + i]);
 				strcat(tmp, tmp2);
                         }
                         pwarn("%s\n", tmp);

 			strcpy(tmp, "");
                         pwarn("Backup:\n");
 			for (i = 0; i < 79; i++) {
 				char tmp2[16];
                                 snprintf(tmp2, sizeof(tmp2), "%.2x ", backup[11 + i]);
 				strcat(tmp, tmp2);
                         }
                         pwarn("%s\n", tmp);
 		}
 		/* Check backup FSInfo?					XXX */
 	}

 	if (boot->BytesPerSec % DOSBOOTBLOCKSIZE != 0) {
 		pfatal("Invalid sector size: %u", boot->BytesPerSec);
 		return FSFATAL;
 	}
 	if (boot->SecPerClust == 0) {
 		pfatal("Invalid cluster size: %u", boot->SecPerClust);
 		return FSFATAL;
 	}
 	if (boot->BytesPerSec == 0) {
 		pfatal("Invalid sector size: %u", boot->BytesPerSec);
 		return FSFATAL;
 	}
 	if (boot->FATs == 0) {
 		pfatal("Invalid number of FATs: %u", boot->FATs);
 		return FSFATAL;
 	}
 	if (boot->Sectors) {
 		boot->HugeSectors = 0;
 		boot->NumSectors = boot->Sectors;
 	} else
 		boot->NumSectors = boot->HugeSectors;

 	boot->ClusterOffset = (boot->RootDirEnts * 32 + boot->BytesPerSec - 1)
 	    / boot->BytesPerSec
 	    + boot->ResSectors
 	    + boot->FATs * boot->FATsecs
 	    - CLUST_FIRST * boot->SecPerClust;

 	boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) / boot->SecPerClust;

 	if (boot->flags&FAT32)
 		boot->ClustMask = CLUST32_MASK;
 	else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
 		boot->ClustMask = CLUST12_MASK;
 	else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
 		boot->ClustMask = CLUST16_MASK;
 	else {
 		pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
 		       boot->NumClusters);
 		return FSFATAL;
 	}

 	switch (boot->ClustMask) {
 	case CLUST32_MASK:
 		boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec) / 4;
 		break;
 	case CLUST16_MASK:
 		boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec) / 2;
 		break;
 	default:
 		boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec * 2) / 3;
 		break;
 	}

 	if (boot->NumFatEntries < boot->NumClusters) {
 		pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
 		       boot->NumClusters, boot->FATsecs);
 		return FSFATAL;
 	}
 	boot->ClusterSize = boot->BytesPerSec * boot->SecPerClust;

 	boot->NumFiles = 1;
 	boot->NumFree = 0;

 	return ret;
 }

 int
 writefsinfo(dosfs, boot)
 	int dosfs;
 	struct bootblock *boot;
 {
 	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];

 	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
 	    != boot->FSInfo * boot->BytesPerSec
 	    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 		perror("could not read fsinfo block");
 		return FSFATAL;
 	}
 	fsinfo[0x1e8] = (u_char)boot->FSFree;
 	fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
 	fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
 	fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
 	fsinfo[0x1ec] = (u_char)boot->FSNext;
 	fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
 	fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
 	fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
 	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
 	    != boot->FSInfo * boot->BytesPerSec
 	    || write(dosfs, fsinfo, sizeof fsinfo)
 	    != sizeof fsinfo) {
 		perror("Unable to write FSInfo");
 		return FSFATAL;
 	}
 	/*
 	 * Technically, we should return FSBOOTMOD here.
 	 *
 	 * However, since Win95 OSR2 (the first M$ OS that has
 	 * support for FAT32) doesn't maintain the FSINFO block
 	 * correctly, it has to be fixed pretty often.
 	 *
 	 * Therefor, we handle the FSINFO block only informally,
 	 * fixing it if necessary, but otherwise ignoring the
 	 * fact that it was incorrect.
 	 */
 	return 0;
 }
	/*
	* Copyright (C) 1995, 1997 Wolfgang Solfrank
	* Copyright (c) 1995 Martin Husemann
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	* 3. All advertising materials mentioning features or use of this software
	* must display the following acknowledgement:
	* This product includes software developed by Martin Husemann
	* and Wolfgang Solfrank.
	* 4. Neither the name of the University nor the names of its contributors
	* may be used to endorse or promote products derived from this software
	* without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	* IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/


	#include <sys/cdefs.h>
	#ifndef lint
	__RCSID("$NetBSD: boot.c,v 1.9 2003/07/24 19:25:46 ws Exp $");
	static const char rcsid[] =
	"$FreeBSD: src/sbin/fsck_msdosfs/boot.c,v 1.4.28.1 2009/04/15 03:14:26 kensmith Exp $";
	#endif /* not lint */

	#include <stdlib.h>
	#include <string.h>
	#include <ctype.h>
	#include <stdio.h>
	#include <unistd.h>

	#include "ext.h"
	#include "fsutil.h"

	int
	readboot(dosfs, boot)
	int dosfs;
	struct bootblock *boot;
	{
	u_char block[DOSBOOTBLOCKSIZE];
	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
	u_char backup[DOSBOOTBLOCKSIZE];
	int ret = FSOK;

	if (read(dosfs, block, sizeof block) < sizeof block) {
	perror("could not read boot block");
	exit(2);
	}

	if (block[510] != 0x55 \|\| block[511] != 0xaa) {
	pfatal("Invalid signature in boot block: %02x%02x", block[511], block[510]);
	exit(2);
	}

	memset(boot, 0, sizeof *boot);
	boot->ValidFat = -1;

	/* decode bios parameter block */
	boot->BytesPerSec = block[11] + (block[12] << 8);
	boot->SecPerClust = block[13];
	boot->ResSectors = block[14] + (block[15] << 8);
	boot->FATs = block[16];
	boot->RootDirEnts = block[17] + (block[18] << 8);
	boot->Sectors = block[19] + (block[20] << 8);
	boot->Media = block[21];
	boot->FATsmall = block[22] + (block[23] << 8);
	boot->SecPerTrack = block[24] + (block[25] << 8);
	boot->Heads = block[26] + (block[27] << 8);
	boot->HiddenSecs = block[28] + (block[29] << 8) + (block[30] << 16) + (block[31] << 24);
	boot->HugeSectors = block[32] + (block[33] << 8) + (block[34] << 16) + (block[35] << 24);

	boot->FATsecs = boot->FATsmall;

	if (!boot->RootDirEnts)
	boot->flags \|= FAT32;
	if (boot->flags & FAT32) {
	boot->FATsecs = block[36] + (block[37] << 8)
	+ (block[38] << 16) + (block[39] << 24);
	if (block[40] & 0x80)
	boot->ValidFat = block[40] & 0x0f;

	/* check version number: */
	if (block[42] \|\| block[43]) {
	/* Correct? XXX */
	pfatal("Unknown file system version: %x.%x",
	block[43], block[42]);
	exit(2);
	}
	boot->RootCl = block[44] + (block[45] << 8)
	+ (block[46] << 16) + (block[47] << 24);
	boot->FSInfo = block[48] + (block[49] << 8);
	boot->Backup = block[50] + (block[51] << 8);

	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
	!= boot->FSInfo * boot->BytesPerSec
	\|\| read(dosfs, fsinfo, sizeof fsinfo)
	!= sizeof fsinfo) {
	perror("could not read fsinfo block");
	return FSFATAL;
	}
	if (memcmp(fsinfo, "RRaA", 4)
	\|\| memcmp(fsinfo + 0x1e4, "rrAa", 4)
	\|\| fsinfo[0x1fc]
	\|\| fsinfo[0x1fd]
	\|\| fsinfo[0x1fe] != 0x55
	\|\| fsinfo[0x1ff] != 0xaa
	\|\| fsinfo[0x3fc]
	\|\| fsinfo[0x3fd]
	\|\| fsinfo[0x3fe] != 0x55
	\|\| fsinfo[0x3ff] != 0xaa) {
	pwarn("Invalid signature in fsinfo block\n");
	if (ask(1, "fix")) {
	memcpy(fsinfo, "RRaA", 4);
	memcpy(fsinfo + 0x1e4, "rrAa", 4);
	fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
	fsinfo[0x1fe] = 0x55;
	fsinfo[0x1ff] = 0xaa;
	fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
	fsinfo[0x3fe] = 0x55;
	fsinfo[0x3ff] = 0xaa;
	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
	!= boot->FSInfo * boot->BytesPerSec
	\|\| write(dosfs, fsinfo, sizeof fsinfo)
	!= sizeof fsinfo) {
	perror("Unable to write FSInfo");
	return FSFATAL;
	}
	ret = FSBOOTMOD;
	} else
	boot->FSInfo = 0;
	}
	if (boot->FSInfo) {
	boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
	+ (fsinfo[0x1ea] << 16)
	+ (fsinfo[0x1eb] << 24);
	boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
	+ (fsinfo[0x1ee] << 16)
	+ (fsinfo[0x1ef] << 24);
	}

	if (lseek(dosfs, boot->Backup * boot->BytesPerSec, SEEK_SET)
	!= boot->Backup * boot->BytesPerSec
	\|\| read(dosfs, backup, sizeof backup) != sizeof backup) {
	perror("could not read backup bootblock");
	return FSFATAL;
	}
	backup[65] = block[65]; /* XXX */
	if (memcmp(block + 11, backup + 11, 79)) {
	char tmp[255];
	int i;

	/*
	* For now, lets not bail out if they don't match
	* It seems a lot of sdcards are formatted with
	* the backup either empty or containing garbage.
	*/

	pwarn("Primary/Backup bootblock miscompare\n");

	strcpy(tmp, "");
	pwarn("Primary:\n");
	for (i = 0; i < 79; i++) {
	char tmp2[16];
	snprintf(tmp2, sizeof(tmp2), "%.2x ", block[11 + i]);
	strcat(tmp, tmp2);
	}
	pwarn("%s\n", tmp);

	strcpy(tmp, "");
	pwarn("Backup:\n");
	for (i = 0; i < 79; i++) {
	char tmp2[16];
	snprintf(tmp2, sizeof(tmp2), "%.2x ", backup[11 + i]);
	strcat(tmp, tmp2);
	}
	pwarn("%s\n", tmp);
	}
	/* Check backup FSInfo? XXX */
	}

	if (boot->BytesPerSec % DOSBOOTBLOCKSIZE != 0) {
	pfatal("Invalid sector size: %u", boot->BytesPerSec);
	return FSFATAL;
	}
	if (boot->SecPerClust == 0) {
	pfatal("Invalid cluster size: %u", boot->SecPerClust);
	return FSFATAL;
	}
	if (boot->BytesPerSec == 0) {
	pfatal("Invalid sector size: %u", boot->BytesPerSec);
	return FSFATAL;
	}
	if (boot->FATs == 0) {
	pfatal("Invalid number of FATs: %u", boot->FATs);
	return FSFATAL;
	}
	if (boot->Sectors) {
	boot->HugeSectors = 0;
	boot->NumSectors = boot->Sectors;
	} else
	boot->NumSectors = boot->HugeSectors;

	boot->ClusterOffset = (boot->RootDirEnts * 32 + boot->BytesPerSec - 1)
	/ boot->BytesPerSec
	+ boot->ResSectors
	+ boot->FATs * boot->FATsecs
	- CLUST_FIRST * boot->SecPerClust;

	boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) / boot->SecPerClust;

	if (boot->flags&FAT32)
	boot->ClustMask = CLUST32_MASK;
	else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
	boot->ClustMask = CLUST12_MASK;
	else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
	boot->ClustMask = CLUST16_MASK;
	else {
	pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
	boot->NumClusters);
	return FSFATAL;
	}

	switch (boot->ClustMask) {
	case CLUST32_MASK:
	boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec) / 4;
	break;
	case CLUST16_MASK:
	boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec) / 2;
	break;
	default:
	boot->NumFatEntries = (boot->FATsecs * boot->BytesPerSec * 2) / 3;
	break;
	}

	if (boot->NumFatEntries < boot->NumClusters) {
	pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
	boot->NumClusters, boot->FATsecs);
	return FSFATAL;
	}
	boot->ClusterSize = boot->BytesPerSec * boot->SecPerClust;

	boot->NumFiles = 1;
	boot->NumFree = 0;

	return ret;
	}

	int
	writefsinfo(dosfs, boot)
	int dosfs;
	struct bootblock *boot;
	{
	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];

	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
	!= boot->FSInfo * boot->BytesPerSec
	\|\| read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
	perror("could not read fsinfo block");
	return FSFATAL;
	}
	fsinfo[0x1e8] = (u_char)boot->FSFree;
	fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
	fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
	fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
	fsinfo[0x1ec] = (u_char)boot->FSNext;
	fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
	fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
	fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
	if (lseek(dosfs, boot->FSInfo * boot->BytesPerSec, SEEK_SET)
	!= boot->FSInfo * boot->BytesPerSec
	\|\| write(dosfs, fsinfo, sizeof fsinfo)
	!= sizeof fsinfo) {
	perror("Unable to write FSInfo");
	return FSFATAL;
	}
	/*
	* Technically, we should return FSBOOTMOD here.
	*
	* However, since Win95 OSR2 (the first M$ OS that has
	* support for FAT32) doesn't maintain the FSINFO block
	* correctly, it has to be fixed pretty often.
	*
	* Therefor, we handle the FSINFO block only informally,
	* fixing it if necessary, but otherwise ignoring the
	* fact that it was incorrect.
	*/
	return 0;
	}