diff --git a/dosfstools/src/fat.c b/dosfstools/src/fat.c
new file mode 100644
index 0000000..5a0dfb0
--- /dev/null
+++ b/dosfstools/src/fat.c
@@ -0,0 +1,547 @@
+/* fat.c - Read/write access to the FAT
+
+   Copyright (C) 1993 Werner Almesberger <werner.almesberger@lrc.di.epfl.ch>
+   Copyright (C) 1998 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+   On Debian systems, the complete text of the GNU General Public License
+   can be found in /usr/share/common-licenses/GPL-3 file.
+*/
+
+/* FAT32, VFAT, Atari format support, and various fixes additions May 1998
+ * by Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de> */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "dosfsck.h"
+#include "io.h"
+#include "check.h"
+#include "fat.h"
+
+/**
+ * Fetch the FAT entry for a specified cluster.
+ *
+ * @param[out]  entry	    Cluster to which cluster of interest is linked
+ * @param[in]	fat	    FAT table for the partition
+ * @param[in]	cluster     Cluster of interest
+ * @param[in]	fs          Information from the FAT boot sectors (bits per FAT entry)
+ */
+void get_fat(FAT_ENTRY * entry, void *fat, unsigned long cluster, DOS_FS * fs)
+{
+    unsigned char *ptr;
+
+    switch (fs->fat_bits) {
+    case 12:
+	ptr = &((unsigned char *)fat)[cluster * 3 / 2];
+	entry->value = 0xfff & (cluster & 1 ? (ptr[0] >> 4) | (ptr[1] << 4) :
+				(ptr[0] | ptr[1] << 8));
+	break;
+    case 16:
+	entry->value = CF_LE_W(((unsigned short *)fat)[cluster]);
+	break;
+    case 32:
+	/* According to M$, the high 4 bits of a FAT32 entry are reserved and
+	 * are not part of the cluster number. So we cut them off. */
+	{
+	    unsigned long e = CF_LE_L(((unsigned int *)fat)[cluster]);
+	    entry->value = e & 0xfffffff;
+	    entry->reserved = e >> 28;
+	}
+	break;
+    default:
+	die("Bad FAT entry size: %d bits.", fs->fat_bits);
+    }
+}
+
+/**
+ * Build a bookkeeping structure from the partition's FAT table.
+ * If the partition has multiple FATs and they don't agree, try to pick a winner,
+ * and queue a command to overwrite the loser.
+ * One error that is fixed here is a cluster that links to something out of range.
+ *
+ * @param[inout]    fs      Information about the filesystem
+ */
+void read_fat(DOS_FS * fs)
+{
+    int eff_size;
+    unsigned long i;
+    void *first, *second = NULL;
+    int first_ok, second_ok;
+    unsigned long total_num_clusters;
+
+    /* Clean up from previous pass */
+    free(fs->fat);
+    free(fs->cluster_owner);
+    fs->fat = NULL;
+    fs->cluster_owner = NULL;
+
+    total_num_clusters = fs->clusters + 2UL;
+    eff_size = (total_num_clusters * fs->fat_bits + 7) / 8ULL;
+    first = alloc(eff_size);
+    fs_read(fs->fat_start, eff_size, first);
+    if (fs->nfats > 1) {
+	second = alloc(eff_size);
+	fs_read(fs->fat_start + fs->fat_size, eff_size, second);
+    }
+    if (second && memcmp(first, second, eff_size) != 0) {
+	FAT_ENTRY first_media, second_media;
+	get_fat(&first_media, first, 0, fs);
+	get_fat(&second_media, second, 0, fs);
+	first_ok = (first_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
+	second_ok = (second_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
+	if (first_ok && !second_ok) {
+	    printf("FATs differ - using first FAT.\n");
+	    fs_write(fs->fat_start + fs->fat_size, eff_size, first);
+	}
+	if (!first_ok && second_ok) {
+	    printf("FATs differ - using second FAT.\n");
+	    fs_write(fs->fat_start, eff_size, second);
+	    memcpy(first, second, eff_size);
+	}
+	if (first_ok && second_ok) {
+	    if (interactive) {
+		printf("FATs differ but appear to be intact. Use which FAT ?\n"
+		       "1) Use first FAT\n2) Use second FAT\n");
+		if (get_key("12", "?") == '1') {
+		    fs_write(fs->fat_start + fs->fat_size, eff_size, first);
+		} else {
+		    fs_write(fs->fat_start, eff_size, second);
+		    memcpy(first, second, eff_size);
+		}
+	    } else {
+		printf("FATs differ but appear to be intact. Using first "
+		       "FAT.\n");
+		fs_write(fs->fat_start + fs->fat_size, eff_size, first);
+	    }
+	}
+	if (!first_ok && !second_ok) {
+	    printf("Both FATs appear to be corrupt. Giving up.\n");
+	    exit(1);
+	}
+    }
+    if (second) {
+	free(second);
+    }
+    fs->fat = (unsigned char *)first;
+
+    fs->cluster_owner = alloc(total_num_clusters * sizeof(DOS_FILE *));
+    memset(fs->cluster_owner, 0, (total_num_clusters * sizeof(DOS_FILE *)));
+
+    /* Truncate any cluster chains that link to something out of range */
+    for (i = 2; i < fs->clusters + 2; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+	if (curEntry.value == 1) {
+	    printf("Cluster %ld out of range (1). Setting to EOF.\n", i - 2);
+	    set_fat(fs, i, -1);
+	}
+	if (curEntry.value >= fs->clusters + 2 &&
+	    (curEntry.value < FAT_MIN_BAD(fs))) {
+	    printf("Cluster %ld out of range (%ld > %ld). Setting to EOF.\n",
+		   i - 2, curEntry.value, fs->clusters + 2 - 1);
+	    set_fat(fs, i, -1);
+	}
+    }
+}
+
+/**
+ * Update the FAT entry for a specified cluster
+ * (i.e., change the cluster it links to).
+ * Queue a command to write out this change.
+ *
+ * @param[in,out]   fs          Information about the filesystem
+ * @param[in]	    cluster     Cluster to change
+ * @param[in]       new	        Cluster to link to
+ *				Special values:
+ *				   0 == free cluster
+ *				  -1 == end-of-chain
+ *				  -2 == bad cluster
+ */
+void set_fat(DOS_FS * fs, unsigned long cluster, unsigned long new)
+{
+    unsigned char *data = NULL;
+    int size;
+    loff_t offs;
+
+    if ((long)new == -1)
+	new = FAT_EOF(fs);
+    else if ((long)new == -2)
+	new = FAT_BAD(fs);
+    switch (fs->fat_bits) {
+    case 12:
+	data = fs->fat + cluster * 3 / 2;
+	offs = fs->fat_start + cluster * 3 / 2;
+	if (cluster & 1) {
+	    FAT_ENTRY prevEntry;
+	    get_fat(&prevEntry, fs->fat, cluster - 1, fs);
+	    data[0] = ((new & 0xf) << 4) | (prevEntry.value >> 8);
+	    data[1] = new >> 4;
+	} else {
+	    FAT_ENTRY subseqEntry;
+	    get_fat(&subseqEntry, fs->fat, cluster + 1, fs);
+	    data[0] = new & 0xff;
+	    data[1] = (new >> 8) | (cluster == fs->clusters - 1 ? 0 :
+				    (0xff & subseqEntry.value) << 4);
+	}
+	size = 2;
+	break;
+    case 16:
+	data = fs->fat + cluster * 2;
+	offs = fs->fat_start + cluster * 2;
+	*(unsigned short *)data = CT_LE_W(new);
+	size = 2;
+	break;
+    case 32:
+	{
+	    FAT_ENTRY curEntry;
+	    get_fat(&curEntry, fs->fat, cluster, fs);
+
+	    data = fs->fat + cluster * 4;
+	    offs = fs->fat_start + cluster * 4;
+	    /* According to M$, the high 4 bits of a FAT32 entry are reserved and
+	     * are not part of the cluster number. So we never touch them. */
+	    *(unsigned long *)data = CT_LE_L((new & 0xfffffff) |
+					     (curEntry.reserved << 28));
+	    size = 4;
+	}
+	break;
+    default:
+	die("Bad FAT entry size: %d bits.", fs->fat_bits);
+    }
+    fs_write(offs, size, data);
+    if (fs->nfats > 1) {
+	fs_write(offs + fs->fat_size, size, data);
+    }
+}
+
+int bad_cluster(DOS_FS * fs, unsigned long cluster)
+{
+    FAT_ENTRY curEntry;
+    get_fat(&curEntry, fs->fat, cluster, fs);
+
+    return FAT_IS_BAD(fs, curEntry.value);
+}
+
+/**
+ * Get the cluster to which the specified cluster is linked.
+ * If the linked cluster is marked bad, abort.
+ *
+ * @param[in]   fs          Information about the filesystem
+ * @param[in]	cluster     Cluster to follow
+ *
+ * @return  -1              'cluster' is at the end of the chain
+ * @return  Other values    Next cluster in this chain
+ */
+unsigned long next_cluster(DOS_FS * fs, unsigned long cluster)
+{
+    unsigned long value;
+    FAT_ENTRY curEntry;
+
+    get_fat(&curEntry, fs->fat, cluster, fs);
+
+    value = curEntry.value;
+    if (FAT_IS_BAD(fs, value))
+	die("Internal error: next_cluster on bad cluster");
+    return FAT_IS_EOF(fs, value) ? -1 : value;
+}
+
+loff_t cluster_start(DOS_FS * fs, unsigned long cluster)
+{
+    return fs->data_start + ((loff_t) cluster -
+			     2) * (unsigned long long)fs->cluster_size;
+}
+
+/**
+ * Update internal bookkeeping to show that the specified cluster belongs
+ * to the specified dentry.
+ *
+ * @param[in,out]   fs          Information about the filesystem
+ * @param[in]	    cluster     Cluster being assigned
+ * @param[in]	    owner       Information on dentry that owns this cluster
+ *                              (may be NULL)
+ */
+void set_owner(DOS_FS * fs, unsigned long cluster, DOS_FILE * owner)
+{
+    if (fs->cluster_owner == NULL)
+	die("Internal error: attempt to set owner in non-existent table");
+
+    if (owner && fs->cluster_owner[cluster]
+	&& (fs->cluster_owner[cluster] != owner))
+	die("Internal error: attempt to change file owner");
+    fs->cluster_owner[cluster] = owner;
+}
+
+DOS_FILE *get_owner(DOS_FS * fs, unsigned long cluster)
+{
+    if (fs->cluster_owner == NULL)
+	return NULL;
+    else
+	return fs->cluster_owner[cluster];
+}
+
+void fix_bad(DOS_FS * fs)
+{
+    unsigned long i;
+
+    if (verbose)
+	printf("Checking for bad clusters.\n");
+    for (i = 2; i < fs->clusters + 2; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+
+	if (!get_owner(fs, i) && !FAT_IS_BAD(fs, curEntry.value))
+	    if (!fs_test(cluster_start(fs, i), fs->cluster_size)) {
+		printf("Cluster %lu is unreadable.\n", i);
+		set_fat(fs, i, -2);
+	    }
+    }
+}
+
+void reclaim_free(DOS_FS * fs)
+{
+    int reclaimed;
+    unsigned long i;
+
+    if (verbose)
+	printf("Checking for unused clusters.\n");
+    reclaimed = 0;
+    for (i = 2; i < fs->clusters + 2; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+
+	if (!get_owner(fs, i) && curEntry.value &&
+	    !FAT_IS_BAD(fs, curEntry.value)) {
+	    set_fat(fs, i, 0);
+	    reclaimed++;
+	}
+    }
+    if (reclaimed)
+	printf("Reclaimed %d unused cluster%s (%llu bytes).\n", reclaimed,
+	       reclaimed == 1 ? "" : "s",
+	       (unsigned long long)reclaimed * fs->cluster_size);
+}
+
+/**
+ * Assign the specified owner to all orphan chains (except cycles).
+ * Break cross-links between orphan chains.
+ *
+ * @param[in,out]   fs             Information about the filesystem
+ * @param[in]	    owner          dentry to be assigned ownership of orphans
+ * @param[in,out]   num_refs	   For each orphan cluster [index], how many
+ *				   clusters link to it.
+ * @param[in]	    start_cluster  Where to start scanning for orphans
+ */
+static void tag_free(DOS_FS * fs, DOS_FILE * owner, unsigned long *num_refs,
+		     unsigned long start_cluster)
+{
+    int prev;
+    unsigned long i, walk;
+
+    if (start_cluster == 0)
+	start_cluster = 2;
+
+    for (i = start_cluster; i < fs->clusters + 2; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+
+	/* If the current entry is the head of an un-owned chain... */
+	if (curEntry.value && !FAT_IS_BAD(fs, curEntry.value) &&
+	    !get_owner(fs, i) && !num_refs[i]) {
+	    prev = 0;
+	    /* Walk the chain, claiming ownership as we go */
+	    for (walk = i; walk != -1; walk = next_cluster(fs, walk)) {
+		if (!get_owner(fs, walk)) {
+		    set_owner(fs, walk, owner);
+		} else {
+		    /* We've run into cross-links between orphaned chains,
+		     * or a cycle with a tail.
+		     * Terminate this orphan chain (break the link)
+		     */
+		    set_fat(fs, prev, -1);
+
+		    /* This is not necessary because 'walk' is owned and thus
+		     * will never become the head of a chain (the only case
+		     * that would matter during reclaim to files).
+		     * It's easier to decrement than to prove that it's
+		     * unnecessary.
+		     */
+		    num_refs[walk]--;
+		    break;
+		}
+		prev = walk;
+	    }
+	}
+    }
+}
+
+/**
+ * Recover orphan chains to files, handling any cycles or cross-links.
+ *
+ * @param[in,out]   fs             Information about the filesystem
+ */
+void reclaim_file(DOS_FS * fs)
+{
+    DOS_FILE orphan;
+    int reclaimed, files;
+    int changed = 0;
+    unsigned long i, next, walk;
+    unsigned long *num_refs = NULL;	/* Only for orphaned clusters */
+    unsigned long total_num_clusters;
+
+    if (verbose)
+	printf("Reclaiming unconnected clusters.\n");
+
+    total_num_clusters = fs->clusters + 2UL;
+    num_refs = alloc(total_num_clusters * sizeof(unsigned long));
+    memset(num_refs, 0, (total_num_clusters * sizeof(unsigned long)));
+
+    /* Guarantee that all orphan chains (except cycles) end cleanly
+     * with an end-of-chain mark.
+     */
+
+    for (i = 2; i < total_num_clusters; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+
+	next = curEntry.value;
+	if (!get_owner(fs, i) && next && next < fs->clusters + 2) {
+	    /* Cluster is linked, but not owned (orphan) */
+	    FAT_ENTRY nextEntry;
+	    get_fat(&nextEntry, fs->fat, next, fs);
+
+	    /* Mark it end-of-chain if it links into an owned cluster,
+	     * a free cluster, or a bad cluster.
+	     */
+	    if (get_owner(fs, next) || !nextEntry.value ||
+		FAT_IS_BAD(fs, nextEntry.value))
+		set_fat(fs, i, -1);
+	    else
+		num_refs[next]++;
+	}
+    }
+
+    /* Scan until all the orphans are accounted for,
+     * and all cycles and cross-links are broken
+     */
+    do {
+	tag_free(fs, &orphan, num_refs, changed);
+	changed = 0;
+
+	/* Any unaccounted-for orphans must be part of a cycle */
+	for (i = 2; i < total_num_clusters; i++) {
+	    FAT_ENTRY curEntry;
+	    get_fat(&curEntry, fs->fat, i, fs);
+
+	    if (curEntry.value && !FAT_IS_BAD(fs, curEntry.value) &&
+		!get_owner(fs, i)) {
+		if (!num_refs[curEntry.value]--)
+		    die("Internal error: num_refs going below zero");
+		set_fat(fs, i, -1);
+		changed = curEntry.value;
+		printf("Broke cycle at cluster %lu in free chain.\n", i);
+
+		/* If we've created a new chain head,
+		 * tag_free() can claim it
+		 */
+		if (num_refs[curEntry.value] == 0)
+		    break;
+	    }
+	}
+    }
+    while (changed);
+
+    /* Now we can start recovery */
+    files = reclaimed = 0;
+    for (i = 2; i < total_num_clusters; i++)
+	/* If this cluster is the head of an orphan chain... */
+	if (get_owner(fs, i) == &orphan && !num_refs[i]) {
+	    DIR_ENT de;
+	    loff_t offset;
+	    files++;
+	    offset = alloc_rootdir_entry(fs, &de, "FSCK%04d");
+	    de.start = CT_LE_W(i & 0xffff);
+	    if (fs->fat_bits == 32)
+		de.starthi = CT_LE_W(i >> 16);
+	    for (walk = i; walk > 0 && walk != -1;
+		 walk = next_cluster(fs, walk)) {
+		de.size = CT_LE_L(CF_LE_L(de.size) + fs->cluster_size);
+		reclaimed++;
+	    }
+	    fs_write(offset, sizeof(DIR_ENT), &de);
+	}
+    if (reclaimed)
+	printf("Reclaimed %d unused cluster%s (%llu bytes) in %d chain%s.\n",
+	       reclaimed, reclaimed == 1 ? "" : "s",
+	       (unsigned long long)reclaimed * fs->cluster_size, files,
+	       files == 1 ? "" : "s");
+
+    free(num_refs);
+}
+
+unsigned long update_free(DOS_FS * fs)
+{
+    unsigned long i;
+    unsigned long free = 0;
+    int do_set = 0;
+
+    for (i = 2; i < fs->clusters + 2; i++) {
+	FAT_ENTRY curEntry;
+	get_fat(&curEntry, fs->fat, i, fs);
+
+	if (!get_owner(fs, i) && !FAT_IS_BAD(fs, curEntry.value))
+	    ++free;
+    }
+
+    if (!fs->fsinfo_start)
+	return free;
+
+    if (verbose)
+	printf("Checking free cluster summary.\n");
+    if (fs->free_clusters != 0xFFFFFFFF) {
+	if (free != fs->free_clusters) {
+	    printf("Free cluster summary wrong (%ld vs. really %ld)\n",
+		   fs->free_clusters, free);
+	    if (interactive)
+		printf("1) Correct\n2) Don't correct\n");
+	    else
+		printf("  Auto-correcting.\n");
+	    if (!interactive || get_key("12", "?") == '1')
+		do_set = 1;
+	}
+    } else {
+	printf("Free cluster summary uninitialized (should be %ld)\n", free);
+	if (rw) {
+	    if (interactive)
+		printf("1) Set it\n2) Leave it uninitialized\n");
+	    else
+		printf("  Auto-setting.\n");
+	    if (!interactive || get_key("12", "?") == '1')
+		do_set = 1;
+	}
+    }
+
+    if (do_set) {
+	unsigned long le_free = CT_LE_L(free);
+	fs->free_clusters = free;
+	fs_write(fs->fsinfo_start + offsetof(struct info_sector, free_clusters),
+		 sizeof(le_free), &le_free);
+    }
+
+    return free;
+}