util-linux/volume_id/exfat.c

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