LXR busybox/util-linux/volume

   1/*
   2 * volume_id - reads filesystem label and uuid
   3 *
   4 * Copyright (C) 2012 S-G Bergh <sgb@systemasis.org>
   5 *
   6 *      This library is free software; you can redistribute it and/or
   7 *      modify it under the terms of the GNU Lesser General Public
   8 *      License as published by the Free Software Foundation; either
   9 *      version 2.1 of the License, or (at your option) any later version.
  10 *
  11 *      This library is distributed in the hope that it will be useful,
  12 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14 *      Lesser General Public License for more details.
  15 *
  16 *      You should have received a copy of the GNU Lesser General Public
  17 *      License along with this library; if not, write to the Free Software
  18 *      Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  19 */
  20
  21//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_EXFAT) += exfat.o
  22
  23//config:
  24//config:config FEATURE_VOLUMEID_EXFAT
  25//config:       bool "exFAT filesystem"
  26//config:       default y
  27//config:       depends on VOLUMEID
  28//config:       help
  29//config:         exFAT (extended FAT) is a proprietary file system designed especially
  30//config:         for flash drives. It has many features from NTFS, but with less
  31//config:         overhead. exFAT is used on most SDXC cards for consumer electronics.
  32//config:
  33
  34#include "volume_id_internal.h"
  35
  36#define EXFAT_SB_OFFSET         0
  37#define EXFAT_DIR_ENTRY_SZ      32
  38#define EXFAT_MAX_DIR_ENTRIES   100
  39
  40struct exfat_super_block {
  41/* 0x00 */      uint8_t         boot_jump[3];
  42/* 0x03 */      uint8_t         fs_name[8];
  43/* 0x0B */      uint8_t         must_be_zero[53];
  44/* 0x40 */      uint64_t        partition_offset;
  45/* 0x48 */      uint64_t        volume_length;
  46/* 0x50 */      uint32_t        fat_offset;             // Sector address of 1st FAT
  47/* 0x54 */      uint32_t        fat_size;               // In sectors
  48/* 0x58 */      uint32_t        cluster_heap_offset;    // Sector address of Data Region
  49/* 0x5C */      uint32_t        cluster_count;
  50/* 0x60 */      uint32_t        root_dir;               // Cluster address of Root Directory
  51/* 0x64 */      uint8_t         vol_serial_nr[4];       // Volume ID
  52/* 0x68 */      uint16_t        fs_revision;            // VV.MM
  53/* 0x6A */      uint16_t        vol_flags;
  54/* 0x6C */      uint8_t         bytes_per_sector;       // Power of 2: 9 => 512, 12 => 4096
  55/* 0x6D */      uint8_t         sectors_per_cluster;    // Power of 2
  56/* 0x6E */      uint8_t         nr_of_fats;             // 2 for TexFAT
  57/* 0x6F */      // ...
  58} PACKED;
  59
  60struct exfat_dir_entry {
  61/* 0x00 */      uint8_t         entry_type;
  62                union {
  63                        struct volume_label {
  64/* 0x01 */                      uint8_t         char_count;             // Length of label
  65/* 0x02 */                      uint16_t        vol_label[11];          // UTF16 string without null termination
  66/* 0x18 */                      uint8_t         reserved[8];
  67/* 0x20 */              } PACKED label;
  68                        struct volume_guid {
  69/* 0x01 */                      uint8_t         sec_count;
  70/* 0x02 */                      uint16_t        set_checksum;
  71/* 0x04 */                      uint16_t        flags;
  72/* 0x06 */                      uint8_t         vol_guid[16];
  73/* 0x16 */                      uint8_t         reserved[10];
  74/* 0x20 */              } PACKED guid;
  75                } PACKED type;
  76} PACKED;
  77
  78int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/)
  79{
  80        struct exfat_super_block *sb;
  81        struct exfat_dir_entry *de;
  82        unsigned        sector_sz;
  83        unsigned        cluster_sz;
  84        uint64_t        root_dir_off;
  85        unsigned        count;
  86        unsigned        need_lbl_guid;
  87
  88        // Primary super block
  89        dbg("exFAT: probing at offset 0x%x", EXFAT_SB_OFFSET);
  90        sb = volume_id_get_buffer(id, EXFAT_SB_OFFSET, sizeof(*sb));
  91
  92        if (!sb)
  93                return -1;
  94
  95        if (memcmp(sb->fs_name, "EXFAT   ", 8) != 0)
  96                return -1;
  97
  98        sector_sz = 1 << sb->bytes_per_sector;
  99        cluster_sz = sector_sz << sb->sectors_per_cluster;
 100        // There are no clusters 0 and 1, so the first cluster is 2.
 101        root_dir_off = (uint64_t)EXFAT_SB_OFFSET +
 102                // Hmm... should we cast sector_sz/cluster_sz to uint64_t?
 103                (le32_to_cpu(sb->cluster_heap_offset)) * sector_sz +
 104                (le32_to_cpu(sb->root_dir) - 2) * cluster_sz;
 105        dbg("exFAT: sector size 0x%x bytes", sector_sz);
 106        dbg("exFAT: cluster size 0x%x bytes", cluster_sz);
 107        dbg("exFAT: root dir is at 0x%llx", (long long)root_dir_off);
 108
 109        // Use DOS uuid as fallback, if no GUID set
 110        volume_id_set_uuid(id, sb->vol_serial_nr, UUID_DOS);
 111
 112        // EXFAT_MAX_DIR_ENTRIES is used as a safety belt.
 113        // The Root Directory may hold an unlimited number of entries,
 114        // so we do not want to check all. Usually label and GUID
 115        // are in the beginning, but there are no guarantees.
 116        need_lbl_guid = (1 << 0) | (1 << 1);
 117        for (count = 0; count < EXFAT_MAX_DIR_ENTRIES; count++) {
 118                de = volume_id_get_buffer(id, root_dir_off + (count * EXFAT_DIR_ENTRY_SZ), EXFAT_DIR_ENTRY_SZ);
 119                if (de == NULL)
 120                        break;
 121                if (de->entry_type == 0x00) {
 122                        // End of Directory Marker
 123                        dbg("exFAT: End of root directory reached after %u entries", count);
 124                        break;
 125                }
 126                if (de->entry_type == 0x83) {
 127                        // Volume Label Directory Entry
 128                        volume_id_set_label_unicode16(id, (uint8_t *)de->type.label.vol_label,
 129                                                LE, 2 * de->type.label.char_count);
 130                        need_lbl_guid &= ~(1 << 0);
 131                }
 132                if (de->entry_type == 0xA0) {
 133                        // Volume GUID Directory Entry
 134                        volume_id_set_uuid(id, de->type.guid.vol_guid, UUID_DCE);
 135                        need_lbl_guid &= ~(1 << 1);
 136                }
 137                if (!need_lbl_guid)
 138                        break;
 139        }
 140
 141        IF_FEATURE_BLKID_TYPE(id->type = "exfat";)
 142        return 0;
 143}
 144