2 * volume_id - reads filesystem label and uuid
4 * Copyright (C) 2012 S-G Bergh <sgb@systemasis.org>
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.
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.
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
21 //kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_EXFAT) += exfat.o
23 //config:config FEATURE_VOLUMEID_EXFAT
24 //config: bool "exFAT filesystem"
26 //config: depends on VOLUMEID
28 //config: exFAT (extended FAT) is a proprietary file system designed especially
29 //config: for flash drives. It has many features from NTFS, but with less
30 //config: overhead. exFAT is used on most SDXC cards for consumer electronics.
32 #include "volume_id_internal.h"
34 #define EXFAT_SB_OFFSET 0
35 #define EXFAT_DIR_ENTRY_SZ 32
36 #define EXFAT_MAX_DIR_ENTRIES 100
38 struct exfat_super_block {
39 /* 0x00 */ uint8_t boot_jump[3];
40 /* 0x03 */ uint8_t fs_name[8];
41 /* 0x0B */ uint8_t must_be_zero[53];
42 /* 0x40 */ uint64_t partition_offset;
43 /* 0x48 */ uint64_t volume_length;
44 /* 0x50 */ uint32_t fat_offset; // Sector address of 1st FAT
45 /* 0x54 */ uint32_t fat_size; // In sectors
46 /* 0x58 */ uint32_t cluster_heap_offset; // Sector address of Data Region
47 /* 0x5C */ uint32_t cluster_count;
48 /* 0x60 */ uint32_t root_dir; // Cluster address of Root Directory
49 /* 0x64 */ uint8_t vol_serial_nr[4]; // Volume ID
50 /* 0x68 */ uint16_t fs_revision; // VV.MM
51 /* 0x6A */ uint16_t vol_flags;
52 /* 0x6C */ uint8_t bytes_per_sector; // Power of 2: 9 => 512, 12 => 4096
53 /* 0x6D */ uint8_t sectors_per_cluster; // Power of 2
54 /* 0x6E */ uint8_t nr_of_fats; // 2 for TexFAT
58 struct exfat_dir_entry {
59 /* 0x00 */ uint8_t entry_type;
62 /* 0x01 */ uint8_t char_count; // Length of label
63 /* 0x02 */ uint16_t vol_label[11]; // UTF16 string without null termination
64 /* 0x18 */ uint8_t reserved[8];
65 /* 0x20 */ } PACKED label;
67 /* 0x01 */ uint8_t sec_count;
68 /* 0x02 */ uint16_t set_checksum;
69 /* 0x04 */ uint16_t flags;
70 /* 0x06 */ uint8_t vol_guid[16];
71 /* 0x16 */ uint8_t reserved[10];
72 /* 0x20 */ } PACKED guid;
76 int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/)
78 struct exfat_super_block *sb;
79 struct exfat_dir_entry *de;
82 uint64_t root_dir_off;
84 unsigned need_lbl_guid;
86 // Primary super block
87 dbg("exFAT: probing at offset 0x%x", EXFAT_SB_OFFSET);
88 sb = volume_id_get_buffer(id, EXFAT_SB_OFFSET, sizeof(*sb));
93 if (memcmp(sb->fs_name, "EXFAT ", 8) != 0)
96 sector_sz = 1 << sb->bytes_per_sector;
97 cluster_sz = sector_sz << sb->sectors_per_cluster;
98 // There are no clusters 0 and 1, so the first cluster is 2.
99 root_dir_off = (uint64_t)EXFAT_SB_OFFSET +
100 // Hmm... should we cast sector_sz/cluster_sz to uint64_t?
101 (le32_to_cpu(sb->cluster_heap_offset)) * sector_sz +
102 (le32_to_cpu(sb->root_dir) - 2) * cluster_sz;
103 dbg("exFAT: sector size 0x%x bytes", sector_sz);
104 dbg("exFAT: cluster size 0x%x bytes", cluster_sz);
105 dbg("exFAT: root dir is at 0x%llx", (long long)root_dir_off);
107 // Use DOS uuid as fallback, if no GUID set
108 volume_id_set_uuid(id, sb->vol_serial_nr, UUID_DOS);
110 // EXFAT_MAX_DIR_ENTRIES is used as a safety belt.
111 // The Root Directory may hold an unlimited number of entries,
112 // so we do not want to check all. Usually label and GUID
113 // are in the beginning, but there are no guarantees.
114 need_lbl_guid = (1 << 0) | (1 << 1);
115 for (count = 0; count < EXFAT_MAX_DIR_ENTRIES; count++) {
116 de = volume_id_get_buffer(id, root_dir_off + (count * EXFAT_DIR_ENTRY_SZ), EXFAT_DIR_ENTRY_SZ);
119 if (de->entry_type == 0x00) {
120 // End of Directory Marker
121 dbg("exFAT: End of root directory reached after %u entries", count);
124 if (de->entry_type == 0x83) {
125 // Volume Label Directory Entry
126 volume_id_set_label_unicode16(id, (uint8_t *)de->type.label.vol_label,
127 LE, 2 * de->type.label.char_count);
128 need_lbl_guid &= ~(1 << 0);
130 if (de->entry_type == 0xA0) {
131 // Volume GUID Directory Entry
132 volume_id_set_uuid(id, de->type.guid.vol_guid, UUID_DCE);
133 need_lbl_guid &= ~(1 << 1);
139 IF_FEATURE_BLKID_TYPE(id->type = "exfat";)