/* 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>
Copyright (C) 2008-2014 Daniel Baumann <mail@daniel-baumann.ch>
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/>.
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 "fsck.fat.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, uint32_t 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 = le16toh(((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. */
{
uint32_t e = le32toh(((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, alloc_size;
uint32_t i;
void *first, *second = NULL;
int first_ok, second_ok;
uint32_t total_num_clusters;
/* Clean up from previous pass */
if (fs->fat)
free(fs->fat);
if (fs->cluster_owner)
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;
if (fs->fat_bits != 12)
alloc_size = eff_size;
else
/* round up to an even number of FAT entries to avoid special
* casing the last entry in get_fat() */
alloc_size = (total_num_clusters * 12 + 23) / 24 * 3;
first = alloc(alloc_size);
fs_read(fs->fat_start, eff_size, first);
if (fs->nfats > 1) {
second = alloc(alloc_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", (long)(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",
(long)(i - 2), (long)curEntry.value, (long)(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, uint32_t cluster, int32_t new)
{
unsigned char *data = NULL;
int size;
loff_t offs;
if (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 = htole16(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. */
*(uint32_t *)data = htole32((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, uint32_t 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
*/
uint32_t next_cluster(DOS_FS * fs, uint32_t cluster)
{
uint32_t 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, uint32_t cluster)
{
return fs->data_start + ((loff_t) cluster -
2) * (uint64_t)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, uint32_t 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, uint32_t cluster)
{
if (fs->cluster_owner == NULL)
return NULL;
else
return fs->cluster_owner[cluster];
}
void fix_bad(DOS_FS * fs)
{
uint32_t 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", (unsigned long)i);
set_fat(fs, i, -2);
}
}
}
void reclaim_free(DOS_FS * fs)
{
int reclaimed;
uint32_t 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", (int)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, uint32_t *num_refs,
uint32_t start_cluster)
{
int prev;
uint32_t 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;
uint32_t i, next, walk;
uint32_t *num_refs = NULL; /* Only for orphaned clusters */
uint32_t total_num_clusters;
if (verbose)
printf("Reclaiming unconnected clusters.\n");
total_num_clusters = fs->clusters + 2UL;
num_refs = alloc(total_num_clusters * sizeof(uint32_t));
memset(num_refs, 0, (total_num_clusters * sizeof(uint32_t)));
/* 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", (unsigned long)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%04dREC");
de.start = htole16(i & 0xffff);
if (fs->fat_bits == 32)
de.starthi = htole16(i >> 16);
for (walk = i; walk > 0 && walk != -1;
walk = next_cluster(fs, walk)) {
de.size = htole32(le32toh(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);
}
uint32_t update_free(DOS_FS * fs)
{
uint32_t i;
uint32_t 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",
(long)fs->free_clusters, (long)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", (long)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) {
uint32_t le_free = htole32(free);
fs->free_clusters = free;
fs_write(fs->fsinfo_start + offsetof(struct info_sector, free_clusters),
sizeof(le_free), &le_free);
}
return free;
}
