busybox/util-linux/volume_id/fat.c
Denis Vlasenko 28ea4298e3 volume_id: abort early on read failures.
should help with probing missing fdd's
2009-02-15 05:51:19 +00:00

333 lines
9.1 KiB
C

/*
* volume_id - reads filesystem label and uuid
*
* Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "volume_id_internal.h"
/* linux/msdos_fs.h says: */
#define FAT12_MAX 0xff4
#define FAT16_MAX 0xfff4
#define FAT32_MAX 0x0ffffff6
#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_bytes;
uint8_t sectors_per_cluster;
uint16_t reserved_sct;
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];
} __attribute__((__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];
} __attribute__((__packed__)) fat32;
} __attribute__((__packed__)) type;
} __attribute__((__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;
} __attribute__((__packed__));
static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, int count)
{
for (;--count >= 0; dir++) {
/* end marker */
if (dir->name[0] == 0x00) {
dbg("end of dir");
break;
}
/* empty entry */
if (dir->name[0] == FAT_ENTRY_FREE)
continue;
/* long name */
if ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
continue;
if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
/* labels do not have file data */
if (dir->cluster_high != 0 || dir->cluster_low != 0)
continue;
dbg("found ATTR_VOLUME_ID id in root dir");
return dir->name;
}
dbg("skip dir entry");
}
return NULL;
}
int volume_id_probe_vfat(struct volume_id *id /*,uint64_t fat_partition_off*/)
{
#define fat_partition_off ((uint64_t)0)
struct vfat_super_block *vs;
struct vfat_dir_entry *dir;
uint16_t sector_size_bytes;
uint16_t dir_entries;
uint32_t sect_count;
uint16_t reserved_sct;
uint32_t fat_size_sct;
uint32_t root_cluster;
uint32_t dir_size_sct;
uint32_t cluster_count;
uint64_t root_start_off;
uint32_t start_data_sct;
uint8_t *buf;
uint32_t buf_size;
uint8_t *label = NULL;
uint32_t next_cluster;
int maxloop;
dbg("probing at offset 0x%llx", (unsigned long long) fat_partition_off);
vs = volume_id_get_buffer(id, fat_partition_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 valid;
if (memcmp(vs->type.fat32.magic, "FAT32 ", 8) == 0)
goto valid;
if (memcmp(vs->type.fat.magic, "FAT16 ", 8) == 0)
goto valid;
if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
goto valid;
if (memcmp(vs->type.fat.magic, "FAT12 ", 8) == 0)
goto valid;
/*
* There are old floppies out there without a magic, so we check
* for well known values and guess if it's a fat volume
*/
/* boot jump address check */
if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
vs->boot_jump[0] != 0xe9)
return -1;
/* heads check */
if (vs->heads == 0)
return -1;
/* cluster size check */
if (vs->sectors_per_cluster == 0 ||
(vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
return -1;
/* media check */
if (vs->media < 0xf8 && vs->media != 0xf0)
return -1;
/* fat count*/
if (vs->fats != 2)
return -1;
valid:
/* sector size check */
sector_size_bytes = le16_to_cpu(vs->sector_size_bytes);
if (sector_size_bytes != 0x200 && sector_size_bytes != 0x400 &&
sector_size_bytes != 0x800 && sector_size_bytes != 0x1000)
return -1;
dbg("sector_size_bytes 0x%x", sector_size_bytes);
dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
reserved_sct = le16_to_cpu(vs->reserved_sct);
dbg("reserved_sct 0x%x", reserved_sct);
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_size_sct = le16_to_cpu(vs->fat_length);
if (fat_size_sct == 0)
fat_size_sct = le32_to_cpu(vs->type.fat32.fat32_length);
fat_size_sct *= vs->fats;
dbg("fat_size_sct 0x%x", fat_size_sct);
dir_entries = le16_to_cpu(vs->dir_entries);
dir_size_sct = ((dir_entries * sizeof(struct vfat_dir_entry)) +
(sector_size_bytes-1)) / sector_size_bytes;
dbg("dir_size_sct 0x%x", dir_size_sct);
cluster_count = sect_count - (reserved_sct + fat_size_sct + dir_size_sct);
cluster_count /= vs->sectors_per_cluster;
dbg("cluster_count 0x%x", cluster_count);
// if (cluster_count < FAT12_MAX) {
// strcpy(id->type_version, "FAT12");
// } else if (cluster_count < FAT16_MAX) {
// strcpy(id->type_version, "FAT16");
// } else {
// strcpy(id->type_version, "FAT32");
// goto fat32;
// }
if (cluster_count >= FAT16_MAX)
goto fat32;
/* the label may be an attribute in the root directory */
root_start_off = (reserved_sct + fat_size_sct) * sector_size_bytes;
dbg("root dir start 0x%llx", (unsigned long long) root_start_off);
dbg("expected entries 0x%x", dir_entries);
buf_size = dir_entries * sizeof(struct vfat_dir_entry);
buf = volume_id_get_buffer(id, fat_partition_off + root_start_off, buf_size);
if (buf == NULL)
goto ret;
label = get_attr_volume_id((struct vfat_dir_entry*) buf, dir_entries);
vs = volume_id_get_buffer(id, fat_partition_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 ret;
fat32:
/* FAT32 root dir is a cluster chain like any other directory */
buf_size = vs->sectors_per_cluster * sector_size_bytes;
root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
start_data_sct = reserved_sct + fat_size_sct;
next_cluster = root_cluster;
maxloop = 100;
while (--maxloop) {
uint64_t next_off_sct;
uint64_t next_off;
uint64_t fat_entry_off;
int count;
dbg("next_cluster 0x%x", (unsigned)next_cluster);
next_off_sct = (uint64_t)(next_cluster - 2) * vs->sectors_per_cluster;
next_off = (start_data_sct + next_off_sct) * sector_size_bytes;
dbg("cluster offset 0x%llx", (unsigned long long) next_off);
/* get cluster */
buf = volume_id_get_buffer(id, fat_partition_off + next_off, buf_size);
if (buf == NULL)
goto ret;
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_sct * sector_size_bytes) + (next_cluster * sizeof(uint32_t));
dbg("fat_entry_off 0x%llx", (unsigned long long)fat_entry_off);
buf = volume_id_get_buffer(id, fat_partition_off + fat_entry_off, buf_size);
if (buf == NULL)
goto ret;
/* set next cluster */
next_cluster = le32_to_cpu(*(uint32_t*)buf) & 0x0fffffff;
if (next_cluster < 2 || next_cluster > FAT32_MAX)
break;
}
if (maxloop == 0)
dbg("reached maximum follow count of root cluster chain, give up");
vs = volume_id_get_buffer(id, fat_partition_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);
ret:
// volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
// id->type = "vfat";
return 0;
}