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
volume_id_probe_exfat(struct volume_id * id)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 }
141