Import revision 9131ba637f003fb5894e3f6343a27d6322205f18 from FreeBSD.

Change-Id: I8ee418314ea407ca679bcd1bed85bd4cff435c22

10 files changed, 2820 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b101724
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+#	$NetBSD: Makefile,v 1.6 1997/05/08 21:11:11 gwr Exp $
+# $FreeBSD$
+
+FSCK=	${.CURDIR:H}/fsck
+.PATH: ${FSCK}
+
+PACKAGE=runtime
+PROG=	fsck_msdosfs
+MAN=	fsck_msdosfs.8
+SRCS=	main.c check.c boot.c fat.c dir.c fsutil.c
+
+CFLAGS+= -I${FSCK}
+
+.include <bsd.prog.mk>
diff --git a/Makefile.depend b/Makefile.depend
new file mode 100644
index 0000000..6cfaab1
--- /dev/null
+++ b/Makefile.depend
@@ -0,0 +1,17 @@
+# $FreeBSD$
+# Autogenerated - do NOT edit!
+
+DIRDEPS = \
+	gnu/lib/csu \
+	include \
+	include/xlocale \
+	lib/${CSU_DIR} \
+	lib/libc \
+	lib/libcompiler_rt \
+
+
+.include <dirdeps.mk>
+
+.if ${DEP_RELDIR} == ${_DEP_RELDIR}
+# local dependencies - needed for -jN in clean tree
+.endif
diff --git a/boot.c b/boot.c
new file mode 100644
index 0000000..56bd57d
--- /dev/null
+++ b/boot.c
@@ -0,0 +1,297 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 1995, 1997 Wolfgang Solfrank
+ * Copyright (c) 1995 Martin Husemann
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+
+#include <sys/cdefs.h>
+#ifndef lint
+__RCSID("$NetBSD: boot.c,v 1.11 2006/06/05 16:51:18 christos Exp ");
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "ext.h"
+#include "fsutil.h"
+
+int
+readboot(int dosfs, struct bootblock *boot)
+{
+	u_char block[DOSBOOTBLOCKSIZE];
+	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
+	u_char backup[DOSBOOTBLOCKSIZE];
+	int ret = FSOK;
+	int i;
+
+	if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
+		perr("could not read boot block");
+		return FSFATAL;
+	}
+
+	if (block[510] != 0x55 || block[511] != 0xaa) {
+		pfatal("Invalid signature in boot block: %02x%02x",
+		    block[511], block[510]);
+		return FSFATAL;
+	}
+
+	memset(boot, 0, sizeof *boot);
+	boot->ValidFat = -1;
+
+	/* decode bios parameter block */
+	boot->bpbBytesPerSec = block[11] + (block[12] << 8);
+	boot->bpbSecPerClust = block[13];
+	boot->bpbResSectors = block[14] + (block[15] << 8);
+	boot->bpbFATs = block[16];
+	boot->bpbRootDirEnts = block[17] + (block[18] << 8);
+	boot->bpbSectors = block[19] + (block[20] << 8);
+	boot->bpbMedia = block[21];
+	boot->bpbFATsmall = block[22] + (block[23] << 8);
+	boot->SecPerTrack = block[24] + (block[25] << 8);
+	boot->bpbHeads = block[26] + (block[27] << 8);
+	boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
+	    (block[30] << 16) + (block[31] << 24);
+	boot->bpbHugeSectors = block[32] + (block[33] << 8) +
+	    (block[34] << 16) + (block[35] << 24);
+
+	boot->FATsecs = boot->bpbFATsmall;
+
+	if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0 ||
+	    boot->bpbBytesPerSec / DOSBOOTBLOCKSIZE_REAL == 0) {
+		pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
+		return FSFATAL;
+	}
+	if (boot->bpbFATs == 0) {
+		pfatal("Invalid number of FATs: %u", boot->bpbFATs);
+		return FSFATAL;
+	}
+	if (!boot->bpbRootDirEnts)
+		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]);
+			return FSFATAL;
+		}
+		boot->bpbRootClust = block[44] + (block[45] << 8)
+			       + (block[46] << 16) + (block[47] << 24);
+		boot->bpbFSInfo = block[48] + (block[49] << 8);
+		boot->bpbBackup = block[50] + (block[51] << 8);
+
+		/* If the OEM Name field is EXFAT, it's not FAT32, so bail */
+		if (!memcmp(&block[3], "EXFAT   ", 8)) {
+			pfatal("exFAT filesystem is not supported.");
+			return FSFATAL;
+		}
+
+		/* check basic parameters */
+		if ((boot->bpbFSInfo == 0) || (boot->bpbSecPerClust == 0)) {
+			/*
+			 * Either the BIOS Parameter Block has been corrupted,
+			 * or this is not a FAT32 filesystem, most likely an
+			 * exFAT filesystem.
+			 */
+			pfatal("Invalid FAT32 Extended BIOS Parameter Block");
+			return FSFATAL;
+		}
+		if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
+		    SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
+		    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
+			perr("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(0, "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->bpbFSInfo *
+				    boot->bpbBytesPerSec, SEEK_SET)
+				    != boot->bpbFSInfo * boot->bpbBytesPerSec
+				    || write(dosfs, fsinfo, sizeof fsinfo)
+				    != sizeof fsinfo) {
+					perr("Unable to write bpbFSInfo");
+					return FSFATAL;
+				}
+				ret = FSBOOTMOD;
+			} else
+				boot->bpbFSInfo = 0;
+		}
+		if (boot->bpbFSInfo) {
+			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->bpbBackup * boot->bpbBytesPerSec,
+		    SEEK_SET)
+		    != boot->bpbBackup * boot->bpbBytesPerSec
+		    || read(dosfs, backup, sizeof backup) != sizeof  backup) {
+			perr("could not read backup bootblock");
+			return FSFATAL;
+		}
+		backup[65] = block[65];				/* XXX */
+		if (memcmp(block + 11, backup + 11, 79)) {
+			/*
+			 * XXX We require a reference that explains
+			 * that these bytes need to match, or should
+			 * drop the check.  gdt@NetBSD has observed
+			 * filesystems that work fine under Windows XP
+			 * and NetBSD that do not match, so the
+			 * requirement is suspect.  For now, just
+			 * print out useful information and continue.
+			 */
+			pwarn("backup (block %d) mismatch with primary bootblock:\n",
+			        boot->bpbBackup);
+			for (i = 11; i < 11 + 90; i++) {
+				if (block[i] != backup[i])
+					pwarn("\ti=%d\tprimary 0x%02x\tbackup 0x%02x\n",
+					       i, block[i], backup[i]);
+			}
+		}
+		/* Check backup bpbFSInfo?					XXX */
+	}
+
+	if (boot->bpbSecPerClust == 0) {
+		pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
+		return FSFATAL;
+	}
+	if (boot->bpbSectors) {
+		boot->bpbHugeSectors = 0;
+		boot->NumSectors = boot->bpbSectors;
+	} else
+		boot->NumSectors = boot->bpbHugeSectors;
+	boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
+	    boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
+	    boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
+	    CLUST_FIRST * boot->bpbSecPerClust;
+	boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
+	    boot->bpbSecPerClust;
+
+	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->bpbBytesPerSec) / 4;
+		break;
+	case CLUST16_MASK:
+		boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
+		break;
+	default:
+		boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
+		break;
+	}
+
+	if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
+		pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
+		       boot->NumClusters, boot->FATsecs);
+		return FSFATAL;
+	}
+	boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
+
+	boot->NumFiles = 1;
+	boot->NumFree = 0;
+
+	return ret;
+}
+
+int
+writefsinfo(int dosfs, struct bootblock *boot)
+{
+	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
+
+	if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
+	    != boot->bpbFSInfo * boot->bpbBytesPerSec
+	    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
+		perr("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->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
+	    != boot->bpbFSInfo * boot->bpbBytesPerSec
+	    || write(dosfs, fsinfo, sizeof fsinfo)
+	    != sizeof fsinfo) {
+		perr("Unable to write bpbFSInfo");
+		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;
+}
diff --git a/check.c b/check.c
new file mode 100644
index 0000000..2431bd3
--- /dev/null
+++ b/check.c
@@ -0,0 +1,196 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 1995, 1996, 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.
+ *
+ * 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: check.c,v 1.14 2006/06/05 16:51:18 christos Exp $");
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include "ext.h"
+#include "fsutil.h"
+
+int
+checkfilesys(const char *fname)
+{
+	int dosfs;
+	struct bootblock boot;
+	struct fatEntry *fat = NULL;
+	int finish_dosdirsection=0;
+	u_int i;
+	int mod = 0;
+	int ret = 8;
+
+	rdonly = alwaysno;
+	if (!preen)
+		printf("** %s", fname);
+
+	dosfs = open(fname, rdonly ? O_RDONLY : O_RDWR, 0);
+	if (dosfs < 0 && !rdonly) {
+		dosfs = open(fname, O_RDONLY, 0);
+		if (dosfs >= 0)
+			pwarn(" (NO WRITE)\n");
+		else if (!preen)
+			printf("\n");
+		rdonly = 1;
+	} else if (!preen)
+		printf("\n");
+
+	if (dosfs < 0) {
+		perr("Can't open `%s'", fname);
+		printf("\n");
+		return 8;
+	}
+
+	if (readboot(dosfs, &boot) == FSFATAL) {
+		close(dosfs);
+		printf("\n");
+		return 8;
+	}
+
+	if (skipclean && preen && checkdirty(dosfs, &boot)) {
+		printf("%s: ", fname);
+		printf("FILESYSTEM CLEAN; SKIPPING CHECKS\n");
+		ret = 0;
+		goto out;
+	}
+
+	if (!preen)  {
+		if (boot.ValidFat < 0)
+			printf("** Phase 1 - Read and Compare FATs\n");
+		else
+			printf("** Phase 1 - Read FAT\n");
+	}
+
+	mod |= readfat(dosfs, &boot, boot.ValidFat >= 0 ? boot.ValidFat : 0, &fat);
+	if (mod & FSFATAL) {
+		close(dosfs);
+		return 8;
+	}
+
+	if (boot.ValidFat < 0)
+		for (i = 1; i < boot.bpbFATs; i++) {
+			struct fatEntry *currentFat;
+
+			mod |= readfat(dosfs, &boot, i, &currentFat);
+
+			if (mod & FSFATAL)
+				goto out;
+
+			mod |= comparefat(&boot, fat, currentFat, i);
+			free(currentFat);
+			if (mod & FSFATAL)
+				goto out;
+		}
+
+	if (!preen)
+		printf("** Phase 2 - Check Cluster Chains\n");
+
+	mod |= checkfat(&boot, fat);
+	if (mod & FSFATAL)
+		goto out;
+	/* delay writing FATs */
+
+	if (!preen)
+		printf("** Phase 3 - Checking Directories\n");
+
+	mod |= resetDosDirSection(&boot, fat);
+	finish_dosdirsection = 1;
+	if (mod & FSFATAL)
+		goto out;
+	/* delay writing FATs */
+
+	mod |= handleDirTree(dosfs, &boot, fat);
+	if (mod & FSFATAL)
+		goto out;
+
+	if (!preen)
+		printf("** Phase 4 - Checking for Lost Files\n");
+
+	mod |= checklost(dosfs, &boot, fat);
+	if (mod & FSFATAL)
+		goto out;
+
+	/* now write the FATs */
+	if (mod & (FSFATMOD|FSFIXFAT)) {
+		if (ask(1, "Update FATs")) {
+			mod |= writefat(dosfs, &boot, fat, mod & FSFIXFAT);
+			if (mod & FSFATAL)
+				goto out;
+		} else
+			mod |= FSERROR;
+	}
+
+	if (boot.NumBad)
+		pwarn("%d files, %d free (%d clusters), %d bad (%d clusters)\n",
+		      boot.NumFiles,
+		      boot.NumFree * boot.ClusterSize / 1024, boot.NumFree,
+		      boot.NumBad * boot.ClusterSize / 1024, boot.NumBad);
+	else
+		pwarn("%d files, %d free (%d clusters)\n",
+		      boot.NumFiles,
+		      boot.NumFree * boot.ClusterSize / 1024, boot.NumFree);
+
+	if (mod && (mod & FSERROR) == 0) {
+		if (mod & FSDIRTY) {
+			if (ask(1, "MARK FILE SYSTEM CLEAN") == 0)
+				mod &= ~FSDIRTY;
+
+			if (mod & FSDIRTY) {
+				pwarn("MARKING FILE SYSTEM CLEAN\n");
+				mod |= writefat(dosfs, &boot, fat, 1);
+			} else {
+				pwarn("\n***** FILE SYSTEM IS LEFT MARKED AS DIRTY *****\n");
+				mod |= FSERROR; /* file system not clean */
+			}
+		}
+	}
+
+	if (mod & (FSFATAL | FSERROR))
+		goto out;
+
+	ret = 0;
+
+    out:
+	if (finish_dosdirsection)
+		finishDosDirSection();
+	free(fat);
+	close(dosfs);
+
+	if (mod & (FSFATMOD|FSDIRMOD))
+		pwarn("\n***** FILE SYSTEM WAS MODIFIED *****\n");
+
+	return ret;
+}
diff --git a/dir.c b/dir.c
new file mode 100644
index 0000000..38c7014
--- /dev/null
+++ b/dir.c
@@ -0,0 +1,1016 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank
+ * Copyright (c) 1995 Martin Husemann
+ * Some structure declaration borrowed from Paul Popelka
+ * (paulp@uts.amdahl.com), see /sys/msdosfs/ for reference.
+ *
+ * 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.
+ *
+ * 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: dir.c,v 1.20 2006/06/05 16:51:18 christos Exp $");
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <unistd.h>
+#include <time.h>
+
+#include <sys/param.h>
+
+#include "ext.h"
+#include "fsutil.h"
+
+#define	SLOT_EMPTY	0x00		/* slot has never been used */
+#define	SLOT_E5		0x05		/* the real value is 0xe5 */
+#define	SLOT_DELETED	0xe5		/* file in this slot deleted */
+
+#define	ATTR_NORMAL	0x00		/* normal file */
+#define	ATTR_READONLY	0x01		/* file is readonly */
+#define	ATTR_HIDDEN	0x02		/* file is hidden */
+#define	ATTR_SYSTEM	0x04		/* file is a system file */
+#define	ATTR_VOLUME	0x08		/* entry is a volume label */
+#define	ATTR_DIRECTORY	0x10		/* entry is a directory name */
+#define	ATTR_ARCHIVE	0x20		/* file is new or modified */
+
+#define	ATTR_WIN95	0x0f		/* long name record */
+
+/*
+ * This is the format of the contents of the deTime field in the direntry
+ * structure.
+ * We don't use bitfields because we don't know how compilers for
+ * arbitrary machines will lay them out.
+ */
+#define DT_2SECONDS_MASK	0x1F	/* seconds divided by 2 */
+#define DT_2SECONDS_SHIFT	0
+#define DT_MINUTES_MASK		0x7E0	/* minutes */
+#define DT_MINUTES_SHIFT	5
+#define DT_HOURS_MASK		0xF800	/* hours */
+#define DT_HOURS_SHIFT		11
+
+/*
+ * This is the format of the contents of the deDate field in the direntry
+ * structure.
+ */
+#define DD_DAY_MASK		0x1F	/* day of month */
+#define DD_DAY_SHIFT		0
+#define DD_MONTH_MASK		0x1E0	/* month */
+#define DD_MONTH_SHIFT		5
+#define DD_YEAR_MASK		0xFE00	/* year - 1980 */
+#define DD_YEAR_SHIFT		9
+
+
+/* dir.c */
+static struct dosDirEntry *newDosDirEntry(void);
+static void freeDosDirEntry(struct dosDirEntry *);
+static struct dirTodoNode *newDirTodo(void);
+static void freeDirTodo(struct dirTodoNode *);
+static char *fullpath(struct dosDirEntry *);
+static u_char calcShortSum(u_char *);
+static int delete(int, struct bootblock *, struct fatEntry *, cl_t, int,
+    cl_t, int, int);
+static int removede(int, struct bootblock *, struct fatEntry *, u_char *,
+    u_char *, cl_t, cl_t, cl_t, char *, int);
+static int checksize(struct bootblock *, struct fatEntry *, u_char *,
+    struct dosDirEntry *);
+static int readDosDirSection(int, struct bootblock *, struct fatEntry *,
+    struct dosDirEntry *);
+
+/*
+ * Manage free dosDirEntry structures.
+ */
+static struct dosDirEntry *freede;
+
+static struct dosDirEntry *
+newDosDirEntry(void)
+{
+	struct dosDirEntry *de;
+
+	if (!(de = freede)) {
+		if (!(de = (struct dosDirEntry *)malloc(sizeof *de)))
+			return 0;
+	} else
+		freede = de->next;
+	return de;
+}
+
+static void
+freeDosDirEntry(struct dosDirEntry *de)
+{
+	de->next = freede;
+	freede = de;
+}
+
+/*
+ * The same for dirTodoNode structures.
+ */
+static struct dirTodoNode *freedt;
+
+static struct dirTodoNode *
+newDirTodo(void)
+{
+	struct dirTodoNode *dt;
+
+	if (!(dt = freedt)) {
+		if (!(dt = (struct dirTodoNode *)malloc(sizeof *dt)))
+			return 0;
+	} else
+		freedt = dt->next;
+	return dt;
+}
+
+static void
+freeDirTodo(struct dirTodoNode *dt)
+{
+	dt->next = freedt;
+	freedt = dt;
+}
+
+/*
+ * The stack of unread directories
+ */
+static struct dirTodoNode *pendingDirectories = NULL;
+
+/*
+ * Return the full pathname for a directory entry.
+ */
+static char *
+fullpath(struct dosDirEntry *dir)
+{
+	static char namebuf[MAXPATHLEN + 1];
+	char *cp, *np;
+	int nl;
+
+	cp = namebuf + sizeof namebuf - 1;
+	*cp = '\0';
+	do {
+		np = dir->lname[0] ? dir->lname : dir->name;
+		nl = strlen(np);
+		if ((cp -= nl) <= namebuf + 1)
+			break;
+		memcpy(cp, np, nl);
+		*--cp = '/';
+	} while ((dir = dir->parent) != NULL);
+	if (dir)
+		*--cp = '?';
+	else
+		cp++;
+	return cp;
+}
+
+/*
+ * Calculate a checksum over an 8.3 alias name
+ */
+static u_char
+calcShortSum(u_char *p)
+{
+	u_char sum = 0;
+	int i;
+
+	for (i = 0; i < 11; i++) {
+		sum = (sum << 7)|(sum >> 1);	/* rotate right */
+		sum += p[i];
+	}
+
+	return sum;
+}
+
+/*
+ * Global variables temporarily used during a directory scan
+ */
+static char longName[DOSLONGNAMELEN] = "";
+static u_char *buffer = NULL;
+static u_char *delbuf = NULL;
+
+static struct dosDirEntry *rootDir;
+static struct dosDirEntry *lostDir;
+
+/*
+ * Init internal state for a new directory scan.
+ */
+int
+resetDosDirSection(struct bootblock *boot, struct fatEntry *fat)
+{
+	int b1, b2;
+	cl_t cl;
+	int ret = FSOK;
+	size_t len;
+
+	b1 = boot->bpbRootDirEnts * 32;
+	b2 = boot->bpbSecPerClust * boot->bpbBytesPerSec;
+
+	if ((buffer = malloc(len = MAX(b1, b2))) == NULL) {
+		perr("No space for directory buffer (%zu)", len);
+		return FSFATAL;
+	}
+
+	if ((delbuf = malloc(len = b2)) == NULL) {
+		free(buffer);
+		perr("No space for directory delbuf (%zu)", len);
+		return FSFATAL;
+	}
+
+	if ((rootDir = newDosDirEntry()) == NULL) {
+		free(buffer);
+		free(delbuf);
+		perr("No space for directory entry");
+		return FSFATAL;
+	}
+
+	memset(rootDir, 0, sizeof *rootDir);
+	if (boot->flags & FAT32) {
+		if (boot->bpbRootClust < CLUST_FIRST ||
+		    boot->bpbRootClust >= boot->NumClusters) {
+			pfatal("Root directory starts with cluster out of range(%u)",
+			       boot->bpbRootClust);
+			return FSFATAL;
+		}
+		cl = fat[boot->bpbRootClust].next;
+		if (cl < CLUST_FIRST
+		    || (cl >= CLUST_RSRVD && cl< CLUST_EOFS)
+		    || fat[boot->bpbRootClust].head != boot->bpbRootClust) {
+			if (cl == CLUST_FREE)
+				pwarn("Root directory starts with free cluster\n");
+			else if (cl >= CLUST_RSRVD)
+				pwarn("Root directory starts with cluster marked %s\n",
+				      rsrvdcltype(cl));
+			else {
+				pfatal("Root directory doesn't start a cluster chain");
+				return FSFATAL;
+			}
+			if (ask(1, "Fix")) {
+				fat[boot->bpbRootClust].next = CLUST_FREE;
+				ret = FSFATMOD;
+			} else
+				ret = FSFATAL;
+		}
+
+		fat[boot->bpbRootClust].flags |= FAT_USED;
+		rootDir->head = boot->bpbRootClust;
+	}
+
+	return ret;
+}
+
+/*
+ * Cleanup after a directory scan
+ */
+void
+finishDosDirSection(void)
+{
+	struct dirTodoNode *p, *np;
+	struct dosDirEntry *d, *nd;
+
+	for (p = pendingDirectories; p; p = np) {
+		np = p->next;
+		freeDirTodo(p);
+	}
+	pendingDirectories = NULL;
+	for (d = rootDir; d; d = nd) {
+		if ((nd = d->child) != NULL) {
+			d->child = 0;
+			continue;
+		}
+		if (!(nd = d->next))
+			nd = d->parent;
+		freeDosDirEntry(d);
+	}
+	rootDir = lostDir = NULL;
+	free(buffer);
+	free(delbuf);
+	buffer = NULL;
+	delbuf = NULL;
+}
+
+/*
+ * Delete directory entries between startcl, startoff and endcl, endoff.
+ */
+static int
+delete(int f, struct bootblock *boot, struct fatEntry *fat, cl_t startcl,
+    int startoff, cl_t endcl, int endoff, int notlast)
+{
+	u_char *s, *e;
+	off_t off;
+	int clsz = boot->bpbSecPerClust * boot->bpbBytesPerSec;
+
+	s = delbuf + startoff;
+	e = delbuf + clsz;
+	while (startcl >= CLUST_FIRST && startcl < boot->NumClusters) {
+		if (startcl == endcl) {
+			if (notlast)
+				break;
+			e = delbuf + endoff;
+		}
+		off = startcl * boot->bpbSecPerClust + boot->ClusterOffset;
+		off *= boot->bpbBytesPerSec;
+		if (lseek(f, off, SEEK_SET) != off
+		    || read(f, delbuf, clsz) != clsz) {
+			perr("Unable to read directory");
+			return FSFATAL;
+		}
+		while (s < e) {
+			*s = SLOT_DELETED;
+			s += 32;
+		}
+		if (lseek(f, off, SEEK_SET) != off
+		    || write(f, delbuf, clsz) != clsz) {
+			perr("Unable to write directory");
+			return FSFATAL;
+		}
+		if (startcl == endcl)
+			break;
+		startcl = fat[startcl].next;
+		s = delbuf;
+	}
+	return FSOK;
+}
+
+static int
+removede(int f, struct bootblock *boot, struct fatEntry *fat, u_char *start,
+    u_char *end, cl_t startcl, cl_t endcl, cl_t curcl, char *path, int type)
+{
+	switch (type) {
+	case 0:
+		pwarn("Invalid long filename entry for %s\n", path);
+		break;
+	case 1:
+		pwarn("Invalid long filename entry at end of directory %s\n",
+		    path);
+		break;
+	case 2:
+		pwarn("Invalid long filename entry for volume label\n");
+		break;
+	}
+	if (ask(0, "Remove")) {
+		if (startcl != curcl) {
+			if (delete(f, boot, fat,
+				   startcl, start - buffer,
+				   endcl, end - buffer,
+				   endcl == curcl) == FSFATAL)
+				return FSFATAL;
+			start = buffer;
+		}
+		/* startcl is < CLUST_FIRST for !fat32 root */
+		if ((endcl == curcl) || (startcl < CLUST_FIRST))
+			for (; start < end; start += 32)
+				*start = SLOT_DELETED;
+		return FSDIRMOD;
+	}
+	return FSERROR;
+}
+
+/*
+ * Check an in-memory file entry
+ */
+static int
+checksize(struct bootblock *boot, struct fatEntry *fat, u_char *p,
+    struct dosDirEntry *dir)
+{
+	/*
+	 * Check size on ordinary files
+	 */
+	u_int32_t physicalSize;
+
+	if (dir->head == CLUST_FREE)
+		physicalSize = 0;
+	else {
+		if (dir->head < CLUST_FIRST || dir->head >= boot->NumClusters)
+			return FSERROR;
+		physicalSize = fat[dir->head].length * boot->ClusterSize;
+	}
+	if (physicalSize < dir->size) {
+		pwarn("size of %s is %u, should at most be %u\n",
+		      fullpath(dir), dir->size, physicalSize);
+		if (ask(1, "Truncate")) {
+			dir->size = physicalSize;
+			p[28] = (u_char)physicalSize;
+			p[29] = (u_char)(physicalSize >> 8);
+			p[30] = (u_char)(physicalSize >> 16);
+			p[31] = (u_char)(physicalSize >> 24);
+			return FSDIRMOD;
+		} else
+			return FSERROR;
+	} else if (physicalSize - dir->size >= boot->ClusterSize) {
+		pwarn("%s has too many clusters allocated\n",
+		      fullpath(dir));
+		if (ask(1, "Drop superfluous clusters")) {
+			cl_t cl;
+			u_int32_t sz, len;
+
+			for (cl = dir->head, len = sz = 0;
+			    (sz += boot->ClusterSize) < dir->size; len++)
+				cl = fat[cl].next;
+			clearchain(boot, fat, fat[cl].next);
+			fat[cl].next = CLUST_EOF;
+			fat[dir->head].length = len;
+			return FSFATMOD;
+		} else
+			return FSERROR;
+	}
+	return FSOK;
+}
+
+/*
+ * Read a directory and
+ *   - resolve long name records
+ *   - enter file and directory records into the parent's list
+ *   - push directories onto the todo-stack
+ */
+static int
+readDosDirSection(int f, struct bootblock *boot, struct fatEntry *fat,
+    struct dosDirEntry *dir)
+{
+	struct dosDirEntry dirent, *d;
+	u_char *p, *vallfn, *invlfn, *empty;
+	off_t off;
+	int i, j, k, last;
+	cl_t cl, valcl = ~0, invcl = ~0, empcl = ~0;
+	char *t;
+	u_int lidx = 0;
+	int shortSum;
+	int mod = FSOK;
+#define	THISMOD	0x8000			/* Only used within this routine */
+
+	cl = dir->head;
+	if (dir->parent && (cl < CLUST_FIRST || cl >= boot->NumClusters)) {
+		/*
+		 * Already handled somewhere else.
+		 */
+		return FSOK;
+	}
+	shortSum = -1;
+	vallfn = invlfn = empty = NULL;
+	do {
+		if (!(boot->flags & FAT32) && !dir->parent) {
+			last = boot->bpbRootDirEnts * 32;
+			off = boot->bpbResSectors + boot->bpbFATs *
+			    boot->FATsecs;
+		} else {
+			last = boot->bpbSecPerClust * boot->bpbBytesPerSec;
+			off = cl * boot->bpbSecPerClust + boot->ClusterOffset;
+		}
+
+		off *= boot->bpbBytesPerSec;
+		if (lseek(f, off, SEEK_SET) != off
+		    || read(f, buffer, last) != last) {
+			perr("Unable to read directory");
+			return FSFATAL;
+		}
+		last /= 32;
+		/*
+		 * Check `.' and `..' entries here?			XXX
+		 */
+		for (p = buffer, i = 0; i < last; i++, p += 32) {
+			if (dir->fsckflags & DIREMPWARN) {
+				*p = SLOT_EMPTY;
+				continue;
+			}
+
+			if (*p == SLOT_EMPTY || *p == SLOT_DELETED) {
+				if (*p == SLOT_EMPTY) {
+					dir->fsckflags |= DIREMPTY;
+					empty = p;
+					empcl = cl;
+				}
+				continue;
+			}
+
+			if (dir->fsckflags & DIREMPTY) {
+				if (!(dir->fsckflags & DIREMPWARN)) {
+					pwarn("%s has entries after end of directory\n",
+					      fullpath(dir));
+					if (ask(1, "Extend")) {
+						u_char *q;
+
+						dir->fsckflags &= ~DIREMPTY;
+						if (delete(f, boot, fat,
+							   empcl, empty - buffer,
+							   cl, p - buffer, 1) == FSFATAL)
+							return FSFATAL;
+						q = empcl == cl ? empty : buffer;
+						for (; q < p; q += 32)
+							*q = SLOT_DELETED;
+						mod |= THISMOD|FSDIRMOD;
+					} else if (ask(0, "Truncate"))
+						dir->fsckflags |= DIREMPWARN;
+				}
+				if (dir->fsckflags & DIREMPWARN) {
+					*p = SLOT_DELETED;
+					mod |= THISMOD|FSDIRMOD;
+					continue;
+				} else if (dir->fsckflags & DIREMPTY)
+					mod |= FSERROR;
+				empty = NULL;
+			}
+
+			if (p[11] == ATTR_WIN95) {
+				if (*p & LRFIRST) {
+					if (shortSum != -1) {
+						if (!invlfn) {
+							invlfn = vallfn;
+							invcl = valcl;
+						}
+					}
+					memset(longName, 0, sizeof longName);
+					shortSum = p[13];
+					vallfn = p;
+					valcl = cl;
+				} else if (shortSum != p[13]
+					   || lidx != (*p & LRNOMASK)) {
+					if (!invlfn) {
+						invlfn = vallfn;
+						invcl = valcl;
+					}
+					if (!invlfn) {
+						invlfn = p;
+						invcl = cl;
+					}
+					vallfn = NULL;
+				}
+				lidx = *p & LRNOMASK;
+				t = longName + --lidx * 13;
+				for (k = 1; k < 11 && t < longName +
+				    sizeof(longName); k += 2) {
+					if (!p[k] && !p[k + 1])
+						break;
+					*t++ = p[k];
+					/*
+					 * Warn about those unusable chars in msdosfs here?	XXX
+					 */
+					if (p[k + 1])
+						t[-1] = '?';
+				}
+				if (k >= 11)
+					for (k = 14; k < 26 && t < longName + sizeof(longName); k += 2) {
+						if (!p[k] && !p[k + 1])
+							break;
+						*t++ = p[k];
+						if (p[k + 1])
+							t[-1] = '?';
+					}
+				if (k >= 26)
+					for (k = 28; k < 32 && t < longName + sizeof(longName); k += 2) {
+						if (!p[k] && !p[k + 1])
+							break;
+						*t++ = p[k];
+						if (p[k + 1])
+							t[-1] = '?';
+					}
+				if (t >= longName + sizeof(longName)) {
+					pwarn("long filename too long\n");
+					if (!invlfn) {
+						invlfn = vallfn;
+						invcl = valcl;
+					}
+					vallfn = NULL;
+				}
+				if (p[26] | (p[27] << 8)) {
+					pwarn("long filename record cluster start != 0\n");
+					if (!invlfn) {
+						invlfn = vallfn;
+						invcl = cl;
+					}
+					vallfn = NULL;
+				}
+				continue;	/* long records don't carry further
+						 * information */
+			}
+
+			/*
+			 * This is a standard msdosfs directory entry.
+			 */
+			memset(&dirent, 0, sizeof dirent);
+
+			/*
+			 * it's a short name record, but we need to know
+			 * more, so get the flags first.
+			 */
+			dirent.flags = p[11];
+
+			/*
+			 * Translate from 850 to ISO here		XXX
+			 */
+			for (j = 0; j < 8; j++)
+				dirent.name[j] = p[j];
+			dirent.name[8] = '\0';
+			for (k = 7; k >= 0 && dirent.name[k] == ' '; k--)
+				dirent.name[k] = '\0';
+			if (k < 0 || dirent.name[k] != '\0')
+				k++;
+			if (dirent.name[0] == SLOT_E5)
+				dirent.name[0] = 0xe5;
+
+			if (dirent.flags & ATTR_VOLUME) {
+				if (vallfn || invlfn) {
+					mod |= removede(f, boot, fat,
+							invlfn ? invlfn : vallfn, p,
+							invlfn ? invcl : valcl, -1, 0,
+							fullpath(dir), 2);
+					vallfn = NULL;
+					invlfn = NULL;
+				}
+				continue;
+			}
+
+			if (p[8] != ' ')
+				dirent.name[k++] = '.';
+			for (j = 0; j < 3; j++)
+				dirent.name[k++] = p[j+8];
+			dirent.name[k] = '\0';
+			for (k--; k >= 0 && dirent.name[k] == ' '; k--)
+				dirent.name[k] = '\0';
+
+			if (vallfn && shortSum != calcShortSum(p)) {
+				if (!invlfn) {
+					invlfn = vallfn;
+					invcl = valcl;
+				}
+				vallfn = NULL;
+			}
+			dirent.head = p[26] | (p[27] << 8);
+			if (boot->ClustMask == CLUST32_MASK)
+				dirent.head |= (p[20] << 16) | (p[21] << 24);
+			dirent.size = p[28] | (p[29] << 8) | (p[30] << 16) | (p[31] << 24);
+			if (vallfn) {
+				strlcpy(dirent.lname, longName,
+				    sizeof(dirent.lname));
+				longName[0] = '\0';
+				shortSum = -1;
+			}
+
+			dirent.parent = dir;
+			dirent.next = dir->child;
+
+			if (invlfn) {
+				mod |= k = removede(f, boot, fat,
+						    invlfn, vallfn ? vallfn : p,
+						    invcl, vallfn ? valcl : cl, cl,
+						    fullpath(&dirent), 0);
+				if (mod & FSFATAL)
+					return FSFATAL;
+				if (vallfn
+				    ? (valcl == cl && vallfn != buffer)
+				    : p != buffer)
+					if (k & FSDIRMOD)
+						mod |= THISMOD;
+			}
+
+			vallfn = NULL; /* not used any longer */
+			invlfn = NULL;
+
+			if (dirent.size == 0 && !(dirent.flags & ATTR_DIRECTORY)) {
+				if (dirent.head != 0) {
+					pwarn("%s has clusters, but size 0\n",
+					      fullpath(&dirent));
+					if (ask(1, "Drop allocated clusters")) {
+						p[26] = p[27] = 0;
+						if (boot->ClustMask == CLUST32_MASK)
+							p[20] = p[21] = 0;
+						clearchain(boot, fat, dirent.head);
+						dirent.head = 0;
+						mod |= THISMOD|FSDIRMOD|FSFATMOD;
+					} else
+						mod |= FSERROR;
+				}
+			} else if (dirent.head == 0
+				   && !strcmp(dirent.name, "..")
+				   && dir->parent			/* XXX */
+				   && !dir->parent->parent) {
+				/*
+				 *  Do nothing, the parent is the root
+				 */
+			} else if (dirent.head < CLUST_FIRST
+				   || dirent.head >= boot->NumClusters
+				   || fat[dirent.head].next == CLUST_FREE
+				   || (fat[dirent.head].next >= CLUST_RSRVD
+				       && fat[dirent.head].next < CLUST_EOFS)
+				   || fat[dirent.head].head != dirent.head) {
+				if (dirent.head == 0)
+					pwarn("%s has no clusters\n",
+					      fullpath(&dirent));
+				else if (dirent.head < CLUST_FIRST
+					 || dirent.head >= boot->NumClusters)
+					pwarn("%s starts with cluster out of range(%u)\n",
+					      fullpath(&dirent),
+					      dirent.head);
+				else if (fat[dirent.head].next == CLUST_FREE)
+					pwarn("%s starts with free cluster\n",
+					      fullpath(&dirent));
+				else if (fat[dirent.head].next >= CLUST_RSRVD)
+					pwarn("%s starts with cluster marked %s\n",
+					      fullpath(&dirent),
+					      rsrvdcltype(fat[dirent.head].next));
+				else
+					pwarn("%s doesn't start a cluster chain\n",
+					      fullpath(&dirent));
+				if (dirent.flags & ATTR_DIRECTORY) {
+					if (ask(0, "Remove")) {
+						*p = SLOT_DELETED;
+						mod |= THISMOD|FSDIRMOD;
+					} else
+						mod |= FSERROR;
+					continue;
+				} else {
+					if (ask(1, "Truncate")) {
+						p[28] = p[29] = p[30] = p[31] = 0;
+						p[26] = p[27] = 0;
+						if (boot->ClustMask == CLUST32_MASK)
+							p[20] = p[21] = 0;
+						dirent.size = 0;
+						mod |= THISMOD|FSDIRMOD;
+					} else
+						mod |= FSERROR;
+				}
+			}
+
+			if (dirent.head >= CLUST_FIRST && dirent.head < boot->NumClusters)
+				fat[dirent.head].flags |= FAT_USED;
+
+			if (dirent.flags & ATTR_DIRECTORY) {
+				/*
+				 * gather more info for directories
+				 */
+				struct dirTodoNode *n;
+
+				if (dirent.size) {
+					pwarn("Directory %s has size != 0\n",
+					      fullpath(&dirent));
+					if (ask(1, "Correct")) {
+						p[28] = p[29] = p[30] = p[31] = 0;
+						dirent.size = 0;
+						mod |= THISMOD|FSDIRMOD;
+					} else
+						mod |= FSERROR;
+				}
+				/*
+				 * handle `.' and `..' specially
+				 */
+				if (strcmp(dirent.name, ".") == 0) {
+					if (dirent.head != dir->head) {
+						pwarn("`.' entry in %s has incorrect start cluster\n",
+						      fullpath(dir));
+						if (ask(1, "Correct")) {
+							dirent.head = dir->head;
+							p[26] = (u_char)dirent.head;
+							p[27] = (u_char)(dirent.head >> 8);
+							if (boot->ClustMask == CLUST32_MASK) {
+								p[20] = (u_char)(dirent.head >> 16);
+								p[21] = (u_char)(dirent.head >> 24);
+							}
+							mod |= THISMOD|FSDIRMOD;
+						} else
+							mod |= FSERROR;
+					}
+					continue;
+				}
+				if (strcmp(dirent.name, "..") == 0) {
+					if (dir->parent) {		/* XXX */
+						if (!dir->parent->parent) {
+							if (dirent.head) {
+								pwarn("`..' entry in %s has non-zero start cluster\n",
+								      fullpath(dir));
+								if (ask(1, "Correct")) {
+									dirent.head = 0;
+									p[26] = p[27] = 0;
+									if (boot->ClustMask == CLUST32_MASK)
+										p[20] = p[21] = 0;
+									mod |= THISMOD|FSDIRMOD;
+								} else
+									mod |= FSERROR;
+							}
+						} else if (dirent.head != dir->parent->head) {
+							pwarn("`..' entry in %s has incorrect start cluster\n",
+							      fullpath(dir));
+							if (ask(1, "Correct")) {
+								dirent.head = dir->parent->head;
+								p[26] = (u_char)dirent.head;
+								p[27] = (u_char)(dirent.head >> 8);
+								if (boot->ClustMask == CLUST32_MASK) {
+									p[20] = (u_char)(dirent.head >> 16);
+									p[21] = (u_char)(dirent.head >> 24);
+								}
+								mod |= THISMOD|FSDIRMOD;
+							} else
+								mod |= FSERROR;
+						}
+					}
+					continue;
+				}
+
+				/* create directory tree node */
+				if (!(d = newDosDirEntry())) {
+					perr("No space for directory");
+					return FSFATAL;
+				}
+				memcpy(d, &dirent, sizeof(struct dosDirEntry));
+				/* link it into the tree */
+				dir->child = d;
+
+				/* Enter this directory into the todo list */
+				if (!(n = newDirTodo())) {
+					perr("No space for todo list");
+					return FSFATAL;
+				}
+				n->next = pendingDirectories;
+				n->dir = d;
+				pendingDirectories = n;
+			} else {
+				mod |= k = checksize(boot, fat, p, &dirent);
+				if (k & FSDIRMOD)
+					mod |= THISMOD;
+			}
+			boot->NumFiles++;
+		}
+
+		if (!(boot->flags & FAT32) && !dir->parent)
+			break;
+
+		if (mod & THISMOD) {
+			last *= 32;
+			if (lseek(f, off, SEEK_SET) != off
+			    || write(f, buffer, last) != last) {
+				perr("Unable to write directory");
+				return FSFATAL;
+			}
+			mod &= ~THISMOD;
+		}
+	} while ((cl = fat[cl].next) >= CLUST_FIRST && cl < boot->NumClusters);
+	if (invlfn || vallfn)
+		mod |= removede(f, boot, fat,
+				invlfn ? invlfn : vallfn, p,
+				invlfn ? invcl : valcl, -1, 0,
+				fullpath(dir), 1);
+
+	/* The root directory of non fat32 filesystems is in a special
+	 * area and may have been modified above without being written out.
+	 */
+	if ((mod & FSDIRMOD) && !(boot->flags & FAT32) && !dir->parent) {
+		last *= 32;
+		if (lseek(f, off, SEEK_SET) != off
+		    || write(f, buffer, last) != last) {
+			perr("Unable to write directory");
+			return FSFATAL;
+		}
+		mod &= ~THISMOD;
+	}
+	return mod & ~THISMOD;
+}
+
+int
+handleDirTree(int dosfs, struct bootblock *boot, struct fatEntry *fat)
+{
+	int mod;
+
+	mod = readDosDirSection(dosfs, boot, fat, rootDir);
+	if (mod & FSFATAL)
+		return FSFATAL;
+
+	/*
+	 * process the directory todo list
+	 */
+	while (pendingDirectories) {
+		struct dosDirEntry *dir = pendingDirectories->dir;
+		struct dirTodoNode *n = pendingDirectories->next;
+
+		/*
+		 * remove TODO entry now, the list might change during
+		 * directory reads
+		 */
+		freeDirTodo(pendingDirectories);
+		pendingDirectories = n;
+
+		/*
+		 * handle subdirectory
+		 */
+		mod |= readDosDirSection(dosfs, boot, fat, dir);
+		if (mod & FSFATAL)
+			return FSFATAL;
+	}
+
+	return mod;
+}
+
+/*
+ * Try to reconnect a FAT chain into dir
+ */
+static u_char *lfbuf;
+static cl_t lfcl;
+static off_t lfoff;
+
+int
+reconnect(int dosfs, struct bootblock *boot, struct fatEntry *fat, cl_t head)
+{
+	struct dosDirEntry d;
+	int len;
+	u_char *p;
+
+	if (!ask(1, "Reconnect"))
+		return FSERROR;
+
+	if (!lostDir) {
+		for (lostDir = rootDir->child; lostDir; lostDir = lostDir->next) {
+			if (!strcmp(lostDir->name, LOSTDIR))
+				break;
+		}
+		if (!lostDir) {		/* Create LOSTDIR?		XXX */
+			pwarn("No %s directory\n", LOSTDIR);
+			return FSERROR;
+		}
+	}
+	if (!lfbuf) {
+		lfbuf = malloc(boot->ClusterSize);
+		if (!lfbuf) {
+			perr("No space for buffer");
+			return FSFATAL;
+		}
+		p = NULL;
+	} else
+		p = lfbuf;
+	while (1) {
+		if (p)
+			for (; p < lfbuf + boot->ClusterSize; p += 32)
+				if (*p == SLOT_EMPTY
+				    || *p == SLOT_DELETED)
+					break;
+		if (p && p < lfbuf + boot->ClusterSize)
+			break;
+		lfcl = p ? fat[lfcl].next : lostDir->head;
+		if (lfcl < CLUST_FIRST || lfcl >= boot->NumClusters) {
+			/* Extend LOSTDIR?				XXX */
+			pwarn("No space in %s\n", LOSTDIR);
+			return FSERROR;
+		}
+		lfoff = lfcl * boot->ClusterSize
+		    + boot->ClusterOffset * boot->bpbBytesPerSec;
+		if (lseek(dosfs, lfoff, SEEK_SET) != lfoff
+		    || (size_t)read(dosfs, lfbuf, boot->ClusterSize) != boot->ClusterSize) {
+			perr("could not read LOST.DIR");
+			return FSFATAL;
+		}
+		p = lfbuf;
+	}
+
+	boot->NumFiles++;
+	/* Ensure uniqueness of entry here!				XXX */
+	memset(&d, 0, sizeof d);
+	/* worst case -1 = 4294967295, 10 digits */
+	len = snprintf(d.name, sizeof(d.name), "%u", head);
+	d.flags = 0;
+	d.head = head;
+	d.size = fat[head].length * boot->ClusterSize;
+
+	memcpy(p, d.name, len);
+	memset(p + len, ' ', 11 - len);
+	memset(p + 11, 0, 32 - 11);
+	p[26] = (u_char)d.head;
+	p[27] = (u_char)(d.head >> 8);
+	if (boot->ClustMask == CLUST32_MASK) {
+		p[20] = (u_char)(d.head >> 16);
+		p[21] = (u_char)(d.head >> 24);
+	}
+	p[28] = (u_char)d.size;
+	p[29] = (u_char)(d.size >> 8);
+	p[30] = (u_char)(d.size >> 16);
+	p[31] = (u_char)(d.size >> 24);
+	fat[head].flags |= FAT_USED;
+	if (lseek(dosfs, lfoff, SEEK_SET) != lfoff
+	    || (size_t)write(dosfs, lfbuf, boot->ClusterSize) != boot->ClusterSize) {
+		perr("could not write LOST.DIR");
+		return FSFATAL;
+	}
+	return FSDIRMOD;
+}
+
+void
+finishlf(void)
+{
+	if (lfbuf)
+		free(lfbuf);
+	lfbuf = NULL;
+}
diff --git a/dosfs.h b/dosfs.h
new file mode 100644
index 0000000..3d84ea0
--- /dev/null
+++ b/dosfs.h
@@ -0,0 +1,141 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank
+ * Copyright (c) 1995 Martin Husemann
+ * Some structure declaration borrowed from Paul Popelka
+ * (paulp@uts.amdahl.com), see /sys/msdosfs/ for reference.
+ *
+ * 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.
+ *
+ * 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.
+ *	$NetBSD: dosfs.h,v 1.4 1997/01/03 14:32:48 ws Exp $
+ * $FreeBSD$
+ */
+
+#ifndef DOSFS_H
+#define DOSFS_H
+
+/* support 4Kn disk reads */
+#define DOSBOOTBLOCKSIZE_REAL 512
+#define DOSBOOTBLOCKSIZE 4096
+
+typedef	u_int32_t	cl_t;	/* type holding a cluster number */
+
+/*
+ * architecture independent description of all the info stored in a
+ * FAT boot block.
+ */
+struct bootblock {
+	u_int	bpbBytesPerSec;		/* bytes per sector */
+	u_int	bpbSecPerClust;		/* sectors per cluster */
+	u_int	bpbResSectors;		/* number of reserved sectors */
+	u_int	bpbFATs;		/* number of bpbFATs */
+	u_int	bpbRootDirEnts;		/* number of root directory entries */
+	u_int32_t bpbSectors;		/* total number of sectors */
+	u_int	bpbMedia;		/* media descriptor */
+	u_int	bpbFATsmall;		/* number of sectors per FAT */
+	u_int	SecPerTrack;		/* sectors per track */
+	u_int	bpbHeads;		/* number of heads */
+	u_int32_t bpbHiddenSecs;	/* # of hidden sectors */
+	u_int32_t bpbHugeSectors;	/* # of sectors if bpbbpbSectors == 0 */
+	cl_t	bpbRootClust;		/* Start of Root Directory */
+	u_int	bpbFSInfo;		/* FSInfo sector */
+	u_int	bpbBackup;		/* Backup of Bootblocks */
+	cl_t	FSFree;			/* Number of free clusters acc. FSInfo */
+	cl_t	FSNext;			/* Next free cluster acc. FSInfo */
+
+	/* and some more calculated values */
+	u_int	flags;			/* some flags: */
+#define	FAT32		1		/* this is a FAT32 file system */
+					/*
+					 * Maybe, we should separate out
+					 * various parts of FAT32?	XXX
+					 */
+	int	ValidFat;		/* valid fat if FAT32 non-mirrored */
+	cl_t	ClustMask;		/* mask for entries in FAT */
+	cl_t	NumClusters;		/* # of entries in a FAT */
+	u_int32_t NumSectors;		/* how many sectors are there */
+	u_int32_t FATsecs;		/* how many sectors are in FAT */
+	u_int32_t NumFatEntries;	/* how many entries really are there */
+	u_int	ClusterOffset;		/* at what sector would sector 0 start */
+	u_int	ClusterSize;		/* Cluster size in bytes */
+
+	/* Now some statistics: */
+	u_int	NumFiles;		/* # of plain files */
+	u_int	NumFree;		/* # of free clusters */
+	u_int	NumBad;			/* # of bad clusters */
+};
+
+struct fatEntry {
+	cl_t	next;			/* pointer to next cluster */
+	cl_t	head;			/* pointer to start of chain */
+	u_int32_t length;		/* number of clusters on chain */
+	int	flags;			/* see below */
+};
+
+#define	CLUST_FREE	0		/* 0 means cluster is free */
+#define	CLUST_FIRST	2		/* 2 is the minimum valid cluster number */
+#define	CLUST_RSRVD	0xfffffff6	/* start of reserved clusters */
+#define	CLUST_BAD	0xfffffff7	/* a cluster with a defect */
+#define	CLUST_EOFS	0xfffffff8	/* start of EOF indicators */
+#define	CLUST_EOF	0xffffffff	/* standard value for last cluster */
+
+/*
+ * Masks for cluster values
+ */
+#define	CLUST12_MASK	0xfff
+#define	CLUST16_MASK	0xffff
+#define	CLUST32_MASK	0xfffffff
+
+#define	FAT_USED	1		/* This fat chain is used in a file */
+
+#define	DOSLONGNAMELEN	256		/* long name maximal length */
+#define LRFIRST		0x40		/* first long name record */
+#define	LRNOMASK	0x1f		/* mask to extract long record
+					 * sequence number */
+
+/*
+ * Architecture independent description of a directory entry
+ */
+struct dosDirEntry {
+	struct dosDirEntry
+		*parent,		/* previous tree level */
+		*next,			/* next brother */
+		*child;			/* if this is a directory */
+	char name[8+1+3+1];		/* alias name first part */
+	char lname[DOSLONGNAMELEN];	/* real name */
+	uint flags;			/* attributes */
+	cl_t head;			/* cluster no */
+	u_int32_t size;			/* filesize in bytes */
+	uint fsckflags;			/* flags during fsck */
+};
+/* Flags in fsckflags: */
+#define	DIREMPTY	1
+#define	DIREMPWARN	2
+
+/*
+ *  TODO-list of unread directories
+ */
+struct dirTodoNode {
+	struct dosDirEntry *dir;
+	struct dirTodoNode *next;
+};
+
+#endif
diff --git a/ext.h b/ext.h
new file mode 100644
index 0000000..ebc9467
--- /dev/null
+++ b/ext.h
@@ -0,0 +1,143 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 1995, 1996, 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.
+ *
+ * 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.
+ *	$NetBSD: ext.h,v 1.6 2000/04/25 23:02:51 jdolecek Exp $
+ * $FreeBSD$
+ */
+
+#ifndef EXT_H
+#define	EXT_H
+
+#include <sys/types.h>
+
+#include "dosfs.h"
+
+#define	LOSTDIR	"LOST.DIR"
+
+/*
+ * Options:
+ */
+extern int alwaysno;	/* assume "no" for all questions */
+extern int alwaysyes;	/* assume "yes" for all questions */
+extern int preen;	/* we are preening */
+extern int rdonly;	/* device is opened read only (supersedes above) */
+extern int skipclean;	/* skip clean file systems if preening */
+
+/*
+ * function declarations
+ */
+int ask(int, const char *, ...) __printflike(2, 3);
+
+/*
+ * Check the dirty flag.  If the file system is clean, then return 1.
+ * Otherwise, return 0 (this includes the case of FAT12 file systems --
+ * they have no dirty flag, so they must be assumed to be unclean).
+ */
+int checkdirty(int, struct bootblock *);
+
+/*
+ * Check file system given as arg
+ */
+int checkfilesys(const char *);
+
+/*
+ * Return values of various functions
+ */
+#define	FSOK		0		/* Check was OK */
+#define	FSBOOTMOD	1		/* Boot block was modified */
+#define	FSDIRMOD	2		/* Some directory was modified */
+#define	FSFATMOD	4		/* The FAT was modified */
+#define	FSERROR		8		/* Some unrecovered error remains */
+#define	FSFATAL		16		/* Some unrecoverable error occurred */
+#define	FSDIRTY		32		/* File system is dirty */
+#define	FSFIXFAT	64		/* Fix file system FAT */
+
+/*
+ * read a boot block in a machine independent fashion and translate
+ * it into our struct bootblock.
+ */
+int readboot(int, struct bootblock *);
+
+/*
+ * Correct the FSInfo block.
+ */
+int writefsinfo(int, struct bootblock *);
+
+/*
+ * Read one of the FAT copies and return a pointer to the new
+ * allocated array holding our description of it.
+ */
+int readfat(int, struct bootblock *, u_int, struct fatEntry **);
+
+/*
+ * Check two FAT copies for consistency and merge changes into the
+ * first if necessary.
+ */
+int comparefat(struct bootblock *, struct fatEntry *, struct fatEntry *, u_int);
+
+/*
+ * Check a FAT
+ */
+int checkfat(struct bootblock *, struct fatEntry *);
+
+/*
+ * Write back FAT entries
+ */
+int writefat(int, struct bootblock *, struct fatEntry *, int);
+
+/*
+ * Read a directory
+ */
+int resetDosDirSection(struct bootblock *, struct fatEntry *);
+void finishDosDirSection(void);
+int handleDirTree(int, struct bootblock *, struct fatEntry *);
+
+/*
+ * Cross-check routines run after everything is completely in memory
+ */
+/*
+ * Check for lost cluster chains
+ */
+int checklost(int, struct bootblock *, struct fatEntry *);
+/*
+ * Try to reconnect a lost cluster chain
+ */
+int reconnect(int, struct bootblock *, struct fatEntry *, cl_t);
+void finishlf(void);
+
+/*
+ * Small helper functions
+ */
+/*
+ * Return the type of a reserved cluster as text
+ */
+const char *rsrvdcltype(cl_t);
+
+/*
+ * Clear a cluster chain in a FAT
+ */
+void clearchain(struct bootblock *, struct fatEntry *, cl_t);
+
+#endif
diff --git a/fat.c b/fat.c
new file mode 100644
index 0000000..8a54837
--- /dev/null
+++ b/fat.c
@@ -0,0 +1,713 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (C) 1995, 1996, 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.
+ *
+ * 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: fat.c,v 1.18 2006/06/05 16:51:18 christos Exp $");
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "ext.h"
+#include "fsutil.h"
+
+static int checkclnum(struct bootblock *, u_int, cl_t, cl_t *);
+static int clustdiffer(cl_t, cl_t *, cl_t *, u_int);
+static int tryclear(struct bootblock *, struct fatEntry *, cl_t, cl_t *);
+static int _readfat(int, struct bootblock *, u_int, u_char **);
+
+/*-
+ * The first 2 FAT entries contain pseudo-cluster numbers with the following
+ * layout:
+ *
+ * 31...... ........ ........ .......0
+ * rrrr1111 11111111 11111111 mmmmmmmm         FAT32 entry 0
+ * rrrrsh11 11111111 11111111 11111xxx         FAT32 entry 1
+ * 
+ *                   11111111 mmmmmmmm         FAT16 entry 0
+ *                   sh111111 11111xxx         FAT16 entry 1
+ * 
+ * r = reserved
+ * m = BPB media ID byte
+ * s = clean flag (1 = dismounted; 0 = still mounted)
+ * h = hard error flag (1 = ok; 0 = I/O error)
+ * x = any value ok
+ */
+
+int
+checkdirty(int fs, struct bootblock *boot)
+{
+	off_t off;
+	u_char *buffer;
+	int ret = 0;
+	size_t len;
+
+	if (boot->ClustMask != CLUST16_MASK && boot->ClustMask != CLUST32_MASK)
+		return 0;
+
+	off = boot->bpbResSectors;
+	off *= boot->bpbBytesPerSec;
+
+	buffer = malloc(len = boot->bpbBytesPerSec);
+	if (buffer == NULL) {
+		perr("No space for FAT sectors (%zu)", len);
+		return 1;
+	}
+
+	if (lseek(fs, off, SEEK_SET) != off) {
+		perr("Unable to read FAT");
+		goto err;
+	}
+
+	if ((size_t)read(fs, buffer, boot->bpbBytesPerSec) !=
+	    boot->bpbBytesPerSec) {
+		perr("Unable to read FAT");
+		goto err;
+	}
+
+	/*
+	 * If we don't understand the FAT, then the file system must be
+	 * assumed to be unclean.
+	 */
+	if (buffer[0] != boot->bpbMedia || buffer[1] != 0xff)
+		goto err;
+	if (boot->ClustMask == CLUST16_MASK) {
+		if ((buffer[2] & 0xf8) != 0xf8 || (buffer[3] & 0x3f) != 0x3f)
+			goto err;
+	} else {
+		if (buffer[2] != 0xff || (buffer[3] & 0x0f) != 0x0f
+		    || (buffer[4] & 0xf8) != 0xf8 || buffer[5] != 0xff
+		    || buffer[6] != 0xff || (buffer[7] & 0x03) != 0x03)
+			goto err;
+	}
+
+	/*
+	 * Now check the actual clean flag (and the no-error flag).
+	 */
+	if (boot->ClustMask == CLUST16_MASK) {
+		if ((buffer[3] & 0xc0) == 0xc0)
+			ret = 1;
+	} else {
+		if ((buffer[7] & 0x0c) == 0x0c)
+			ret = 1;
+	}
+
+err:
+	free(buffer);
+	return ret;
+}
+
+/*
+ * Check a cluster number for valid value
+ */
+static int
+checkclnum(struct bootblock *boot, u_int fat, cl_t cl, cl_t *next)
+{
+	if (*next >= (CLUST_RSRVD&boot->ClustMask))
+		*next |= ~boot->ClustMask;
+	if (*next == CLUST_FREE) {
+		boot->NumFree++;
+		return FSOK;
+	}
+	if (*next == CLUST_BAD) {
+		boot->NumBad++;
+		return FSOK;
+	}
+	if (*next < CLUST_FIRST
+	    || (*next >= boot->NumClusters && *next < CLUST_EOFS)) {
+		pwarn("Cluster %u in FAT %d continues with %s cluster number %u\n",
+		      cl, fat,
+		      *next < CLUST_RSRVD ? "out of range" : "reserved",
+		      *next&boot->ClustMask);
+		if (ask(0, "Truncate")) {
+			*next = CLUST_EOF;
+			return FSFATMOD;
+		}
+		return FSERROR;
+	}
+	return FSOK;
+}
+
+/*
+ * Read a FAT from disk. Returns 1 if successful, 0 otherwise.
+ */
+static int
+_readfat(int fs, struct bootblock *boot, u_int no, u_char **buffer)
+{
+	off_t off;
+	size_t len;
+
+	*buffer = malloc(len = boot->FATsecs * boot->bpbBytesPerSec);
+	if (*buffer == NULL) {
+		perr("No space for FAT sectors (%zu)", len);
+		return 0;
+	}
+
+	off = boot->bpbResSectors + no * boot->FATsecs;
+	off *= boot->bpbBytesPerSec;
+
+	if (lseek(fs, off, SEEK_SET) != off) {
+		perr("Unable to read FAT");
+		goto err;
+	}
+
+	if ((size_t)read(fs, *buffer, boot->FATsecs * boot->bpbBytesPerSec)
+	    != boot->FATsecs * boot->bpbBytesPerSec) {
+		perr("Unable to read FAT");
+		goto err;
+	}
+
+	return 1;
+
+    err:
+	free(*buffer);
+	return 0;
+}
+
+/*
+ * Read a FAT and decode it into internal format
+ */
+int
+readfat(int fs, struct bootblock *boot, u_int no, struct fatEntry **fp)
+{
+	struct fatEntry *fat;
+	u_char *buffer, *p;
+	cl_t cl;
+	int ret = FSOK;
+	size_t len;
+
+	boot->NumFree = boot->NumBad = 0;
+
+	if (!_readfat(fs, boot, no, &buffer))
+		return FSFATAL;
+
+	fat = malloc(len = boot->NumClusters * sizeof(struct fatEntry));
+	if (fat == NULL) {
+		perr("No space for FAT clusters (%zu)", len);
+		free(buffer);
+		return FSFATAL;
+	}
+	(void)memset(fat, 0, len);
+
+	if (buffer[0] != boot->bpbMedia
+	    || buffer[1] != 0xff || buffer[2] != 0xff
+	    || (boot->ClustMask == CLUST16_MASK && buffer[3] != 0xff)
+	    || (boot->ClustMask == CLUST32_MASK
+		&& ((buffer[3]&0x0f) != 0x0f
+		    || buffer[4] != 0xff || buffer[5] != 0xff
+		    || buffer[6] != 0xff || (buffer[7]&0x0f) != 0x0f))) {
+
+		/* Windows 95 OSR2 (and possibly any later) changes
+		 * the FAT signature to 0xXXffff7f for FAT16 and to
+		 * 0xXXffff0fffffff07 for FAT32 upon boot, to know that the
+		 * file system is dirty if it doesn't reboot cleanly.
+		 * Check this special condition before errorring out.
+		 */
+		if (buffer[0] == boot->bpbMedia && buffer[1] == 0xff
+		    && buffer[2] == 0xff
+		    && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
+			|| (boot->ClustMask == CLUST32_MASK
+			    && buffer[3] == 0x0f && buffer[4] == 0xff
+			    && buffer[5] == 0xff && buffer[6] == 0xff
+			    && buffer[7] == 0x07)))
+			ret |= FSDIRTY;
+		else {
+			/* just some odd byte sequence in FAT */
+
+			switch (boot->ClustMask) {
+			case CLUST32_MASK:
+				pwarn("%s (%02x%02x%02x%02x%02x%02x%02x%02x)\n",
+				      "FAT starts with odd byte sequence",
+				      buffer[0], buffer[1], buffer[2], buffer[3],
+				      buffer[4], buffer[5], buffer[6], buffer[7]);
+				break;
+			case CLUST16_MASK:
+				pwarn("%s (%02x%02x%02x%02x)\n",
+				    "FAT starts with odd byte sequence",
+				    buffer[0], buffer[1], buffer[2], buffer[3]);
+				break;
+			default:
+				pwarn("%s (%02x%02x%02x)\n",
+				    "FAT starts with odd byte sequence",
+				    buffer[0], buffer[1], buffer[2]);
+				break;
+			}
+
+
+			if (ask(1, "Correct"))
+				ret |= FSFIXFAT;
+		}
+	}
+	switch (boot->ClustMask) {
+	case CLUST32_MASK:
+		p = buffer + 8;
+		break;
+	case CLUST16_MASK:
+		p = buffer + 4;
+		break;
+	default:
+		p = buffer + 3;
+		break;
+	}
+	for (cl = CLUST_FIRST; cl < boot->NumClusters;) {
+		switch (boot->ClustMask) {
+		case CLUST32_MASK:
+			fat[cl].next = p[0] + (p[1] << 8)
+				       + (p[2] << 16) + (p[3] << 24);
+			fat[cl].next &= boot->ClustMask;
+			ret |= checkclnum(boot, no, cl, &fat[cl].next);
+			cl++;
+			p += 4;
+			break;
+		case CLUST16_MASK:
+			fat[cl].next = p[0] + (p[1] << 8);
+			ret |= checkclnum(boot, no, cl, &fat[cl].next);
+			cl++;
+			p += 2;
+			break;
+		default:
+			fat[cl].next = (p[0] + (p[1] << 8)) & 0x0fff;
+			ret |= checkclnum(boot, no, cl, &fat[cl].next);
+			cl++;
+			if (cl >= boot->NumClusters)
+				break;
+			fat[cl].next = ((p[1] >> 4) + (p[2] << 4)) & 0x0fff;
+			ret |= checkclnum(boot, no, cl, &fat[cl].next);
+			cl++;
+			p += 3;
+			break;
+		}
+	}
+
+	free(buffer);
+	if (ret & FSFATAL) {
+		free(fat);
+		*fp = NULL;
+	} else
+		*fp = fat;
+	return ret;
+}
+
+/*
+ * Get type of reserved cluster
+ */
+const char *
+rsrvdcltype(cl_t cl)
+{
+	if (cl == CLUST_FREE)
+		return "free";
+	if (cl < CLUST_BAD)
+		return "reserved";
+	if (cl > CLUST_BAD)
+		return "as EOF";
+	return "bad";
+}
+
+static int
+clustdiffer(cl_t cl, cl_t *cp1, cl_t *cp2, u_int fatnum)
+{
+	if (*cp1 == CLUST_FREE || *cp1 >= CLUST_RSRVD) {
+		if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
+			if ((*cp1 != CLUST_FREE && *cp1 < CLUST_BAD
+			     && *cp2 != CLUST_FREE && *cp2 < CLUST_BAD)
+			    || (*cp1 > CLUST_BAD && *cp2 > CLUST_BAD)) {
+				pwarn("Cluster %u is marked %s with different indicators\n",
+				      cl, rsrvdcltype(*cp1));
+				if (ask(1, "Fix")) {
+					*cp2 = *cp1;
+					return FSFATMOD;
+				}
+				return FSFATAL;
+			}
+			pwarn("Cluster %u is marked %s in FAT 0, %s in FAT %u\n",
+			      cl, rsrvdcltype(*cp1), rsrvdcltype(*cp2), fatnum);
+			if (ask(0, "Use FAT 0's entry")) {
+				*cp2 = *cp1;
+				return FSFATMOD;
+			}
+			if (ask(0, "Use FAT %u's entry", fatnum)) {
+				*cp1 = *cp2;
+				return FSFATMOD;
+			}
+			return FSFATAL;
+		}
+		pwarn("Cluster %u is marked %s in FAT 0, but continues with cluster %u in FAT %d\n",
+		      cl, rsrvdcltype(*cp1), *cp2, fatnum);
+		if (ask(0, "Use continuation from FAT %u", fatnum)) {
+			*cp1 = *cp2;
+			return FSFATMOD;
+		}
+		if (ask(0, "Use mark from FAT 0")) {
+			*cp2 = *cp1;
+			return FSFATMOD;
+		}
+		return FSFATAL;
+	}
+	if (*cp2 == CLUST_FREE || *cp2 >= CLUST_RSRVD) {
+		pwarn("Cluster %u continues with cluster %u in FAT 0, but is marked %s in FAT %u\n",
+		      cl, *cp1, rsrvdcltype(*cp2), fatnum);
+		if (ask(0, "Use continuation from FAT 0")) {
+			*cp2 = *cp1;
+			return FSFATMOD;
+		}
+		if (ask(0, "Use mark from FAT %d", fatnum)) {
+			*cp1 = *cp2;
+			return FSFATMOD;
+		}
+		return FSERROR;
+	}
+	pwarn("Cluster %u continues with cluster %u in FAT 0, but with cluster %u in FAT %u\n",
+	      cl, *cp1, *cp2, fatnum);
+	if (ask(0, "Use continuation from FAT 0")) {
+		*cp2 = *cp1;
+		return FSFATMOD;
+	}
+	if (ask(0, "Use continuation from FAT %u", fatnum)) {
+		*cp1 = *cp2;
+		return FSFATMOD;
+	}
+	return FSERROR;
+}
+
+/*
+ * Compare two FAT copies in memory. Resolve any conflicts and merge them
+ * into the first one.
+ */
+int
+comparefat(struct bootblock *boot, struct fatEntry *first,
+    struct fatEntry *second, u_int fatnum)
+{
+	cl_t cl;
+	int ret = FSOK;
+
+	for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++)
+		if (first[cl].next != second[cl].next)
+			ret |= clustdiffer(cl, &first[cl].next, &second[cl].next, fatnum);
+	return ret;
+}
+
+void
+clearchain(struct bootblock *boot, struct fatEntry *fat, cl_t head)
+{
+	cl_t p, q;
+
+	for (p = head; p >= CLUST_FIRST && p < boot->NumClusters; p = q) {
+		if (fat[p].head != head)
+			break;
+		q = fat[p].next;
+		fat[p].next = fat[p].head = CLUST_FREE;
+		fat[p].length = 0;
+	}
+}
+
+int
+tryclear(struct bootblock *boot, struct fatEntry *fat, cl_t head, cl_t *truncp)
+{
+	if (ask(0, "Clear chain starting at %u", head)) {
+		clearchain(boot, fat, head);
+		return FSFATMOD;
+	} else if (ask(0, "Truncate")) {
+		uint32_t len;
+		cl_t p;
+
+		for (p = head, len = 0;
+		    p >= CLUST_FIRST && p < boot->NumClusters;
+		    p = fat[p].next, len++)
+			continue;
+		*truncp = CLUST_EOF;
+		fat[head].length = len;
+		return FSFATMOD;
+	} else
+		return FSERROR;
+}
+
+/*
+ * Check a complete FAT in-memory for crosslinks
+ */
+int
+checkfat(struct bootblock *boot, struct fatEntry *fat)
+{
+	cl_t head, p, h, n;
+	u_int len;
+	int ret = 0;
+	int conf;
+
+	/*
+	 * pass 1: figure out the cluster chains.
+	 */
+	for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
+		/* find next untravelled chain */
+		if (fat[head].head != 0		/* cluster already belongs to some chain */
+		    || fat[head].next == CLUST_FREE
+		    || fat[head].next == CLUST_BAD)
+			continue;		/* skip it. */
+
+		/* follow the chain and mark all clusters on the way */
+		for (len = 0, p = head;
+		     p >= CLUST_FIRST && p < boot->NumClusters &&
+		     fat[p].head != head;
+		     p = fat[p].next) {
+			fat[p].head = head;
+			len++;
+		}
+
+		/* the head record gets the length */
+		fat[head].length = fat[head].next == CLUST_FREE ? 0 : len;
+	}
+
+	/*
+	 * pass 2: check for crosslinked chains (we couldn't do this in pass 1 because
+	 * we didn't know the real start of the chain then - would have treated partial
+	 * chains as interlinked with their main chain)
+	 */
+	for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
+		/* find next untravelled chain */
+		if (fat[head].head != head)
+			continue;
+
+		/* follow the chain to its end (hopefully) */
+		for (len = fat[head].length, p = head;
+		     (n = fat[p].next) >= CLUST_FIRST && n < boot->NumClusters;
+		     p = n)
+			if (fat[n].head != head || len-- < 2)
+				break;
+		if (n >= CLUST_EOFS)
+			continue;
+
+		if (n == CLUST_FREE || n >= CLUST_RSRVD) {
+			pwarn("Cluster chain starting at %u ends with cluster marked %s\n",
+			      head, rsrvdcltype(n));
+clear:
+			ret |= tryclear(boot, fat, head, &fat[p].next);
+			continue;
+		}
+		if (n < CLUST_FIRST || n >= boot->NumClusters) {
+			pwarn("Cluster chain starting at %u ends with cluster out of range (%u)\n",
+			    head, n);
+			goto clear;
+		}
+		if (head == fat[n].head) {
+			pwarn("Cluster chain starting at %u loops at cluster %u\n",
+			
+			    head, p);
+			goto clear;
+		}
+		pwarn("Cluster chains starting at %u and %u are linked at cluster %u\n",
+		      head, fat[n].head, n);
+		conf = tryclear(boot, fat, head, &fat[p].next);
+		if (ask(0, "Clear chain starting at %u", h = fat[n].head)) {
+			if (conf == FSERROR) {
+				/*
+				 * Transfer the common chain to the one not cleared above.
+				 */
+				for (p = n;
+				     p >= CLUST_FIRST && p < boot->NumClusters;
+				     p = fat[p].next) {
+					if (h != fat[p].head) {
+						/*
+						 * Have to reexamine this chain.
+						 */
+						head--;
+						break;
+					}
+					fat[p].head = head;
+				}
+			}
+			clearchain(boot, fat, h);
+			conf |= FSFATMOD;
+		}
+		ret |= conf;
+	}
+
+	return ret;
+}
+
+/*
+ * Write out FATs encoding them from the internal format
+ */
+int
+writefat(int fs, struct bootblock *boot, struct fatEntry *fat, int correct_fat)
+{
+	u_char *buffer, *p;
+	cl_t cl;
+	u_int i;
+	size_t fatsz;
+	off_t off;
+	int ret = FSOK;
+
+	buffer = malloc(fatsz = boot->FATsecs * boot->bpbBytesPerSec);
+	if (buffer == NULL) {
+		perr("No space for FAT sectors (%zu)", fatsz);
+		return FSFATAL;
+	}
+	memset(buffer, 0, fatsz);
+	boot->NumFree = 0;
+	p = buffer;
+	if (correct_fat) {
+		*p++ = (u_char)boot->bpbMedia;
+		*p++ = 0xff;
+		*p++ = 0xff;
+		switch (boot->ClustMask) {
+		case CLUST16_MASK:
+			*p++ = 0xff;
+			break;
+		case CLUST32_MASK:
+			*p++ = 0x0f;
+			*p++ = 0xff;
+			*p++ = 0xff;
+			*p++ = 0xff;
+			*p++ = 0x0f;
+			break;
+		}
+	} else {
+		/* use same FAT signature as the old FAT has */
+		int count;
+		u_char *old_fat;
+
+		switch (boot->ClustMask) {
+		case CLUST32_MASK:
+			count = 8;
+			break;
+		case CLUST16_MASK:
+			count = 4;
+			break;
+		default:
+			count = 3;
+			break;
+		}
+
+		if (!_readfat(fs, boot, boot->ValidFat >= 0 ? boot->ValidFat :0,
+					 &old_fat)) {
+			free(buffer);
+			return FSFATAL;
+		}
+
+		memcpy(p, old_fat, count);
+		free(old_fat);
+		p += count;
+	}
+
+	for (cl = CLUST_FIRST; cl < boot->NumClusters; cl++) {
+		switch (boot->ClustMask) {
+		case CLUST32_MASK:
+			if (fat[cl].next == CLUST_FREE)
+				boot->NumFree++;
+			*p++ = (u_char)fat[cl].next;
+			*p++ = (u_char)(fat[cl].next >> 8);
+			*p++ = (u_char)(fat[cl].next >> 16);
+			*p &= 0xf0;
+			*p++ |= (fat[cl].next >> 24)&0x0f;
+			break;
+		case CLUST16_MASK:
+			if (fat[cl].next == CLUST_FREE)
+				boot->NumFree++;
+			*p++ = (u_char)fat[cl].next;
+			*p++ = (u_char)(fat[cl].next >> 8);
+			break;
+		default:
+			if (fat[cl].next == CLUST_FREE)
+				boot->NumFree++;
+			*p++ = (u_char)fat[cl].next;
+			*p = (u_char)((fat[cl].next >> 8) & 0xf);
+			cl++;
+			if (cl >= boot->NumClusters)
+				break;
+			if (fat[cl].next == CLUST_FREE)
+				boot->NumFree++;
+			*p++ |= (u_char)(fat[cl + 1].next << 4);
+			*p++ = (u_char)(fat[cl + 1].next >> 4);
+			break;
+		}
+	}
+	for (i = 0; i < boot->bpbFATs; i++) {
+		off = boot->bpbResSectors + i * boot->FATsecs;
+		off *= boot->bpbBytesPerSec;
+		if (lseek(fs, off, SEEK_SET) != off
+		    || (size_t)write(fs, buffer, fatsz) != fatsz) {
+			perr("Unable to write FAT");
+			ret = FSFATAL; /* Return immediately?		XXX */
+		}
+	}
+	free(buffer);
+	return ret;
+}
+
+/*
+ * Check a complete in-memory FAT for lost cluster chains
+ */
+int
+checklost(int dosfs, struct bootblock *boot, struct fatEntry *fat)
+{
+	cl_t head;
+	int mod = FSOK;
+	int ret;
+
+	for (head = CLUST_FIRST; head < boot->NumClusters; head++) {
+		/* find next untravelled chain */
+		if (fat[head].head != head
+		    || fat[head].next == CLUST_FREE
+		    || (fat[head].next >= CLUST_RSRVD
+			&& fat[head].next < CLUST_EOFS)
+		    || (fat[head].flags & FAT_USED))
+			continue;
+
+		pwarn("Lost cluster chain at cluster %u\n%d Cluster(s) lost\n",
+		      head, fat[head].length);
+		mod |= ret = reconnect(dosfs, boot, fat, head);
+		if (mod & FSFATAL)
+			break;
+		if (ret == FSERROR && ask(0, "Clear")) {
+			clearchain(boot, fat, head);
+			mod |= FSFATMOD;
+		}
+	}
+	finishlf();
+
+	if (boot->bpbFSInfo) {
+		ret = 0;
+		if (boot->FSFree != 0xffffffffU &&
+		    boot->FSFree != boot->NumFree) {
+			pwarn("Free space in FSInfo block (%u) not correct (%u)\n",
+			      boot->FSFree, boot->NumFree);
+			if (ask(1, "Fix")) {
+				boot->FSFree = boot->NumFree;
+				ret = 1;
+			}
+		}
+		if (ret)
+			mod |= writefsinfo(dosfs, boot);
+	}
+
+	return mod;
+}
diff --git a/fsck_msdosfs.8 b/fsck_msdosfs.8
new file mode 100644
index 0000000..f953dbd
--- /dev/null
+++ b/fsck_msdosfs.8
@@ -0,0 +1,126 @@
+.\"	$NetBSD: fsck_msdos.8,v 1.9 1997/10/17 11:19:58 ws Exp $
+.\"
+.\" Copyright (C) 1995 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.
+.\"
+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd October 3, 2016
+.Dt FSCK_MSDOSFS 8
+.Os
+.Sh NAME
+.Nm fsck_msdosfs
+.Nd DOS/Windows (FAT) file system consistency checker
+.Sh SYNOPSIS
+.Nm
+.Fl p
+.Op Fl Cf
+.Ar filesystem ...
+.Nm
+.Op Fl Cny
+.Ar filesystem ...
+.Sh DESCRIPTION
+The
+.Nm
+utility verifies and repairs
+.Tn FAT
+file systems (more commonly known
+as
+.Tn DOS
+file systems).
+.Pp
+The first form of
+.Nm
+preens the specified file systems.
+It is normally started by
+.Xr fsck 8
+run from
+.Pa /etc/rc
+during automatic reboot, when a FAT file system is detected.
+When preening file systems,
+.Nm
+will fix common inconsistencies non-interactively.
+If more serious problems are found,
+.Nm
+does not try to fix them, indicates that it was not
+successful, and exits.
+.Pp
+The second form of
+.Nm
+checks the specified file systems and tries to repair all
+detected inconsistencies, requesting confirmation before
+making any changes.
+.Pp
+The options are as follows:
+.Bl -tag -width indent
+.It Fl C
+Compatibility with the corresponding
+.Xr fsck 8
+option (skip check if clean), defined to no-op.
+.It Fl F
+Compatibility with the wrapper
+.Xr fsck 8
+which seeks to determine whether the file system needs to be cleaned
+immediately in foreground, or if its cleaning can be deferred to background.
+FAT (MS-DOS) file systems must always be cleaned in the foreground.
+A non-zero exit code is always returned for this option.
+.It Fl f
+Force
+.Nm
+to check
+.Dq clean
+file systems when preening.
+.It Fl n
+Causes
+.Nm
+to assume
+.Dq Li no
+as the answer to all operator
+questions, except
+.Dq Li CONTINUE? .
+.It Fl p
+Preen the specified file systems.
+.It Fl y
+Causes
+.Nm
+to assume
+.Dq Li yes
+as the answer to all operator questions.
+.El
+.Sh SEE ALSO
+.Xr fsck 8 ,
+.Xr fsck_ffs 8 ,
+.Xr mount_msdosfs 8
+.Sh HISTORY
+The
+.Nm
+utility appeared in
+.Nx 1.2 .
+.Nm
+first appeared in
+.Fx 4.4 .
+.Sh BUGS
+The
+.Nm
+utility is
+.Ud
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..8425d8a
--- /dev/null
+++ b/main.c
@@ -0,0 +1,157 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (C) 1995 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.
+ *
+ * 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: main.c,v 1.10 1997/10/01 02:18:14 enami Exp $");
+static const char rcsid[] =
+  "$FreeBSD$";
+#endif /* not lint */
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdarg.h>
+
+#include "fsutil.h"
+#include "ext.h"
+
+int alwaysno;		/* assume "no" for all questions */
+int alwaysyes;		/* assume "yes" for all questions */
+int preen;		/* set when preening */
+int rdonly;		/* device is opened read only (supersedes above) */
+int skipclean;		/* skip clean file systems if preening */
+
+static void usage(void) __dead2;
+
+static void
+usage(void)
+{
+
+	fprintf(stderr, "%s\n%s\n",
+	    "usage: fsck_msdosfs -p [-f] filesystem ...",
+	    "       fsck_msdosfs [-ny] filesystem ...");
+	exit(1);
+}
+
+int
+main(int argc, char **argv)
+{
+	int ret = 0, erg;
+	int ch;
+
+	skipclean = 1;
+	while ((ch = getopt(argc, argv, "CfFnpy")) != -1) {
+		switch (ch) {
+		case 'C': /* for fsck_ffs compatibility */
+			break;
+		case 'f':
+			skipclean = 0;
+			break;
+		case 'F':
+			/*
+			 * We can never run in the background.  We must exit
+			 * silently with a nonzero exit code so that fsck(8)
+			 * can probe our support for -F.  The exit code
+			 * doesn't really matter, but we use an unusual one
+			 * in case someone tries -F directly.  The -F flag
+			 * is intentionally left out of the usage message.
+			 */
+			exit(5);
+		case 'n':
+			alwaysno = 1;
+			alwaysyes = preen = 0;
+			break;
+		case 'y':
+			alwaysyes = 1;
+			alwaysno = preen = 0;
+			break;
+
+		case 'p':
+			preen = 1;
+			alwaysyes = alwaysno = 0;
+			break;
+
+		default:
+			usage();
+			break;
+		}
+	}
+	argc -= optind;
+	argv += optind;
+
+	if (!argc)
+		usage();
+
+	while (--argc >= 0) {
+		setcdevname(*argv, preen);
+		erg = checkfilesys(*argv++);
+		if (erg > ret)
+			ret = erg;
+	}
+
+	return ret;
+}
+
+
+/*VARARGS*/
+int
+ask(int def, const char *fmt, ...)
+{
+	va_list ap;
+
+	char prompt[256];
+	int c;
+
+	if (preen) {
+		if (rdonly)
+			def = 0;
+		if (def)
+			printf("FIXED\n");
+		return def;
+	}
+
+	va_start(ap, fmt);
+	vsnprintf(prompt, sizeof(prompt), fmt, ap);
+	va_end(ap);
+	if (alwaysyes || rdonly) {
+		printf("%s? %s\n", prompt, rdonly ? "no" : "yes");
+		return !rdonly;
+	}
+	do {
+		printf("%s? [yn] ", prompt);
+		fflush(stdout);
+		c = getchar();
+		while (c != '\n' && getchar() != '\n')
+			if (feof(stdin))
+				return 0;
+	} while (c != 'y' && c != 'Y' && c != 'n' && c != 'N');
+	return c == 'y' || c == 'Y';
+}