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/*
* volume_id - reads filesystem label and uuid
*
* Copyright (C) 2012 S-G Bergh <sgb@systemasis.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
*/
//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_EXFAT) += exfat.o
//config:
//config:config FEATURE_VOLUMEID_EXFAT
//config: bool "exFAT filesystem"
//config: default y
//config: depends on VOLUMEID
//config: help
//config: exFAT (extended FAT) is a proprietary file system designed especially
//config: for flash drives. It has many features from NTFS, but with less
//config: overhead. exFAT is used on most SDXC cards for consumer electronics.
//config:
#include "volume_id_internal.h"
#define EXFAT_SB_OFFSET 0
#define EXFAT_DIR_ENTRY_SZ 32
#define EXFAT_MAX_DIR_ENTRIES 100
struct exfat_super_block {
/* 0x00 */ uint8_t boot_jump[3];
/* 0x03 */ uint8_t fs_name[8];
/* 0x0B */ uint8_t must_be_zero[53];
/* 0x40 */ uint64_t partition_offset;
/* 0x48 */ uint64_t volume_length;
/* 0x50 */ uint32_t fat_offset; // Sector address of 1st FAT
/* 0x54 */ uint32_t fat_size; // In sectors
/* 0x58 */ uint32_t cluster_heap_offset; // Sector address of Data Region
/* 0x5C */ uint32_t cluster_count;
/* 0x60 */ uint32_t root_dir; // Cluster address of Root Directory
/* 0x64 */ uint8_t vol_serial_nr[4]; // Volume ID
/* 0x68 */ uint16_t fs_revision; // VV.MM
/* 0x6A */ uint16_t vol_flags;
/* 0x6C */ uint8_t bytes_per_sector; // Power of 2: 9 => 512, 12 => 4096
/* 0x6D */ uint8_t sectors_per_cluster; // Power of 2
/* 0x6E */ uint8_t nr_of_fats; // 2 for TexFAT
/* 0x6F */ // ...
} PACKED;
struct exfat_dir_entry {
/* 0x00 */ uint8_t entry_type;
union {
struct volume_label {
/* 0x01 */ uint8_t char_count; // Length of label
/* 0x02 */ uint16_t vol_label[11]; // UTF16 string without null termination
/* 0x18 */ uint8_t reserved[8];
/* 0x20 */ } PACKED label;
struct volume_guid {
/* 0x01 */ uint8_t sec_count;
/* 0x02 */ uint16_t set_checksum;
/* 0x04 */ uint16_t flags;
/* 0x06 */ uint8_t vol_guid[16];
/* 0x16 */ uint8_t reserved[10];
/* 0x20 */ } PACKED guid;
} PACKED type;
} PACKED;
int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/)
{
struct exfat_super_block *sb;
struct exfat_dir_entry *de;
unsigned sector_sz;
unsigned cluster_sz;
uint64_t root_dir_off;
unsigned count;
unsigned need_lbl_guid;
// Primary super block
dbg("exFAT: probing at offset 0x%x", EXFAT_SB_OFFSET);
sb = volume_id_get_buffer(id, EXFAT_SB_OFFSET, sizeof(*sb));
if (!sb)
return -1;
if (memcmp(sb->fs_name, "EXFAT ", 8) != 0)
return -1;
sector_sz = 1 << sb->bytes_per_sector;
cluster_sz = sector_sz << sb->sectors_per_cluster;
// There are no clusters 0 and 1, so the first cluster is 2.
root_dir_off = (uint64_t)EXFAT_SB_OFFSET +
// Hmm... should we cast sector_sz/cluster_sz to uint64_t?
(le32_to_cpu(sb->cluster_heap_offset)) * sector_sz +
(le32_to_cpu(sb->root_dir) - 2) * cluster_sz;
dbg("exFAT: sector size 0x%x bytes", sector_sz);
dbg("exFAT: cluster size 0x%x bytes", cluster_sz);
dbg("exFAT: root dir is at 0x%llx", (long long)root_dir_off);
// Use DOS uuid as fallback, if no GUID set
volume_id_set_uuid(id, sb->vol_serial_nr, UUID_DOS);
// EXFAT_MAX_DIR_ENTRIES is used as a safety belt.
// The Root Directory may hold an unlimited number of entries,
// so we do not want to check all. Usually label and GUID
// are in the beginning, but there are no guarantees.
need_lbl_guid = (1 << 0) | (1 << 1);
for (count = 0; count < EXFAT_MAX_DIR_ENTRIES; count++) {
de = volume_id_get_buffer(id, root_dir_off + (count * EXFAT_DIR_ENTRY_SZ), EXFAT_DIR_ENTRY_SZ);
if (de == NULL)
break;
if (de->entry_type == 0x00) {
// End of Directory Marker
dbg("exFAT: End of root directory reached after %u entries", count);
break;
}
if (de->entry_type == 0x83) {
// Volume Label Directory Entry
volume_id_set_label_unicode16(id, (uint8_t *)de->type.label.vol_label,
LE, 2 * de->type.label.char_count);
need_lbl_guid &= ~(1 << 0);
}
if (de->entry_type == 0xA0) {
// Volume GUID Directory Entry
volume_id_set_uuid(id, de->type.guid.vol_guid, UUID_DCE);
need_lbl_guid &= ~(1 << 1);
}
if (!need_lbl_guid)
break;
}
IF_FEATURE_BLKID_TYPE(id->type = "exfat";)
return 0;
}
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