diff options
Diffstat (limited to 'dosfstools/src/fat.c')
| -rw-r--r-- | dosfstools/src/fat.c | 547 |
1 files changed, 547 insertions, 0 deletions
diff --git a/dosfstools/src/fat.c b/dosfstools/src/fat.c new file mode 100644 index 000000000..5a0dfb0f2 --- /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; +} |