fat.c revision b5e694267142042228a6cac99ecad6c4b4ef8759
/*
* volume_id - reads filesystem label and uuid
*
* Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
*
* 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 version 2 of the License.
*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include "libvolume_id.h"
#include "util.h"
#define FAT12_MAX 0xff5
#define FAT16_MAX 0xfff5
#define FAT_ATTR_VOLUME_ID 0x08
#define FAT_ATTR_DIR 0x10
#define FAT_ATTR_LONG_NAME 0x0f
#define FAT_ATTR_MASK 0x3f
#define FAT_ENTRY_FREE 0xe5
struct vfat_super_block {
uint8_t boot_jump[3];
uint8_t sysid[8];
uint16_t sector_size;
uint8_t sectors_per_cluster;
uint16_t reserved;
uint8_t fats;
uint16_t dir_entries;
uint16_t sectors;
uint8_t media;
uint16_t fat_length;
uint16_t secs_track;
uint16_t heads;
uint32_t hidden;
uint32_t total_sect;
union {
struct fat_super_block {
uint8_t unknown[3];
uint8_t serno[4];
uint8_t label[11];
uint8_t magic[8];
uint8_t dummy2[192];
uint8_t pmagic[2];
} PACKED fat;
struct fat32_super_block {
uint32_t fat32_length;
uint16_t flags;
uint8_t version[2];
uint32_t root_cluster;
uint16_t insfo_sector;
uint16_t backup_boot;
uint16_t reserved2[6];
uint8_t unknown[3];
uint8_t serno[4];
uint8_t label[11];
uint8_t magic[8];
uint8_t dummy2[164];
uint8_t pmagic[2];
} PACKED fat32;
} PACKED type;
} PACKED;
struct vfat_dir_entry {
uint8_t name[11];
uint8_t attr;
uint16_t time_creat;
uint16_t date_creat;
uint16_t time_acc;
uint16_t date_acc;
uint16_t cluster_high;
uint16_t time_write;
uint16_t date_write;
uint16_t cluster_low;
uint32_t size;
} PACKED;
static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, unsigned int count)
{
unsigned int i;
for (i = 0; i < count; i++) {
/* end marker */
if (dir[i].name[0] == 0x00) {
dbg("end of dir");
break;
}
/* empty entry */
if (dir[i].name[0] == FAT_ENTRY_FREE)
continue;
/* long name */
if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
continue;
if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
/* labels do not have file data */
if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
continue;
dbg("found ATTR_VOLUME_ID id in root dir");
return dir[i].name;
}
dbg("skip dir entry");
}
return NULL;
}
int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
{
struct vfat_super_block *vs;
struct vfat_dir_entry *dir;
uint16_t sector_size;
uint16_t dir_entries;
uint32_t sect_count;
uint16_t reserved;
uint32_t fat_size;
uint32_t root_cluster;
uint32_t dir_size;
uint32_t cluster_count;
uint16_t fat_length;
uint32_t fat32_length;
uint64_t root_start;
uint32_t start_data_sect;
uint16_t root_dir_entries;
uint8_t *buf;
uint32_t buf_size;
uint8_t *label = NULL;
uint32_t next;
int maxloop;
dbg("probing at offset 0x%llx", (unsigned long long) off);
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
/* believe only that's fat, don't trust the version
* the cluster_count will tell us
*/
if (memcmp(vs->sysid, "NTFS", 4) == 0)
return -1;
if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
goto magic;
if (memcmp(vs->type.fat32.magic, "FAT32 ", 8) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "FAT16 ", 8) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "FAT12 ", 8) == 0)
goto magic;
/* some old floppies don't have a magic, so we expect the boot code to match */
/* boot jump address check */
if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
vs->boot_jump[0] != 0xe9)
return -1;
magic:
/* reserverd sector count */
if (!vs->reserved)
return -1;
/* fat count*/
if (!vs->fats)
return -1;
/* media check */
if (vs->media < 0xf8 && vs->media != 0xf0)
return -1;
/* cluster size check*/
if (vs->sectors_per_cluster == 0 ||
(vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
return -1;
/* sector size check */
sector_size = le16_to_cpu(vs->sector_size);
if (sector_size != 0x200 && sector_size != 0x400 &&
sector_size != 0x800 && sector_size != 0x1000)
return -1;
dbg("sector_size 0x%x", sector_size);
dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
dir_entries = le16_to_cpu(vs->dir_entries);
reserved = le16_to_cpu(vs->reserved);
dbg("reserved 0x%x", reserved);
sect_count = le16_to_cpu(vs->sectors);
if (sect_count == 0)
sect_count = le32_to_cpu(vs->total_sect);
dbg("sect_count 0x%x", sect_count);
fat_length = le16_to_cpu(vs->fat_length);
dbg("fat_length 0x%x", fat_length);
fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
dbg("fat32_length 0x%x", fat32_length);
if (fat_length)
fat_size = fat_length * vs->fats;
else if (fat32_length)
fat_size = fat32_length * vs->fats;
else
return -1;
dbg("fat_size 0x%x", fat_size);
dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
(sector_size-1)) / sector_size;
dbg("dir_size 0x%x", dir_size);
cluster_count = sect_count - (reserved + fat_size + dir_size);
cluster_count /= vs->sectors_per_cluster;
dbg("cluster_count 0x%x", cluster_count);
/* must be FAT32 */
if (!fat_length && fat32_length)
goto fat32;
/* cluster_count tells us the format */
if (cluster_count < FAT12_MAX)
strcpy(id->type_version, "FAT12");
else if (cluster_count < FAT16_MAX)
strcpy(id->type_version, "FAT16");
else
goto fat32;
/* the label may be an attribute in the root directory */
root_start = (reserved + fat_size) * sector_size;
dbg("root dir start 0x%llx", (unsigned long long) root_start);
root_dir_entries = le16_to_cpu(vs->dir_entries);
dbg("expected entries 0x%x", root_dir_entries);
buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
buf = volume_id_get_buffer(id, off + root_start, buf_size);
if (buf == NULL)
goto found;
dir = (struct vfat_dir_entry*) buf;
label = get_attr_volume_id(dir, root_dir_entries);
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
if (label != NULL && memcmp(label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, label, 11);
volume_id_set_label_string(id, label, 11);
} else if (memcmp(vs->type.fat.label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, vs->type.fat.label, 11);
volume_id_set_label_string(id, vs->type.fat.label, 11);
}
volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
goto found;
fat32:
strcpy(id->type_version, "FAT32");
/* FAT32 root dir is a cluster chain like any other directory */
buf_size = vs->sectors_per_cluster * sector_size;
root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
dbg("root dir cluster %u", root_cluster);
start_data_sect = reserved + fat_size;
next = root_cluster;
maxloop = 100;
while (--maxloop) {
uint32_t next_sect_off;
uint64_t next_off;
uint64_t fat_entry_off;
int count;
dbg("next cluster %u", next);
next_sect_off = (next - 2) * vs->sectors_per_cluster;
next_off = (start_data_sect + next_sect_off) * sector_size;
dbg("cluster offset 0x%llx", (unsigned long long) next_off);
/* get cluster */
buf = volume_id_get_buffer(id, off + next_off, buf_size);
if (buf == NULL)
goto found;
dir = (struct vfat_dir_entry*) buf;
count = buf_size / sizeof(struct vfat_dir_entry);
dbg("expected entries 0x%x", count);
label = get_attr_volume_id(dir, count);
if (label)
break;
/* get FAT entry */
fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
if (buf == NULL)
goto found;
/* set next cluster */
next = le32_to_cpu(*((uint32_t *) buf) & 0x0fffffff);
if (next == 0)
break;
}
if (maxloop == 0)
dbg("reached maximum follow count of root cluster chain, give up");
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
if (label != NULL && memcmp(label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, label, 11);
volume_id_set_label_string(id, label, 11);
} else if (memcmp(vs->type.fat32.label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, vs->type.fat32.label, 11);
volume_id_set_label_string(id, vs->type.fat32.label, 11);
}
volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);
found:
volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
id->type = "vfat";
return 0;
}