1 /*
2 * volume_id - reads filesystem label and uuid
3 *
4 * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.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_FAT
21 //config: bool "fat filesystem"
22 //config: default y
23 //config: depends on VOLUMEID
24
25 //kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_FAT) += fat.o
26
27 #include "volume_id_internal.h"
28
29 /* linux/msdos_fs.h says: */
30 #define FAT12_MAX 0xff4
31 #define FAT16_MAX 0xfff4
32 #define FAT32_MAX 0x0ffffff6
33
34 #define FAT_ATTR_VOLUME_ID 0x08
35 #define FAT_ATTR_DIR 0x10
36 #define FAT_ATTR_LONG_NAME 0x0f
37 #define FAT_ATTR_MASK 0x3f
38 #define FAT_ENTRY_FREE 0xe5
39
40 struct vfat_super_block {
41 uint8_t boot_jump[3];
42 uint8_t sysid[8];
43 uint16_t sector_size_bytes;
44 uint8_t sectors_per_cluster;
45 uint16_t reserved_sct;
46 uint8_t fats;
47 uint16_t dir_entries;
48 uint16_t sectors;
49 uint8_t media;
50 uint16_t fat_length;
51 uint16_t secs_track;
52 uint16_t heads;
53 uint32_t hidden;
54 uint32_t total_sect;
55 union {
56 struct fat_super_block {
57 uint8_t unknown[3];
58 uint8_t serno[4];
59 uint8_t label[11];
60 uint8_t magic[8];
61 uint8_t dummy2[192];
62 uint8_t pmagic[2];
63 } PACKED fat;
64 struct fat32_super_block {
65 uint32_t fat32_length;
66 uint16_t flags;
67 uint8_t version[2];
68 uint32_t root_cluster;
69 uint16_t insfo_sector;
70 uint16_t backup_boot;
71 uint16_t reserved2[6];
72 uint8_t unknown[3];
73 uint8_t serno[4];
74 uint8_t label[11];
75 uint8_t magic[8];
76 uint8_t dummy2[164];
77 uint8_t pmagic[2];
78 } PACKED fat32;
79 } PACKED type;
80 } PACKED;
81
82 struct vfat_dir_entry {
83 uint8_t name[11];
84 uint8_t attr;
85 uint16_t time_creat;
86 uint16_t date_creat;
87 uint16_t time_acc;
88 uint16_t date_acc;
89 uint16_t cluster_high;
90 uint16_t time_write;
91 uint16_t date_write;
92 uint16_t cluster_low;
93 uint32_t size;
94 } PACKED;
95
get_attr_volume_id(struct vfat_dir_entry * dir,int count)96 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, int count)
97 {
98 for (;--count >= 0; dir++) {
99 /* end marker */
100 if (dir->name[0] == 0x00) {
101 dbg("end of dir");
102 break;
103 }
104
105 /* empty entry */
106 if (dir->name[0] == FAT_ENTRY_FREE)
107 continue;
108
109 /* long name */
110 if ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
111 continue;
112
113 if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
114 /* labels do not have file data */
115 if (dir->cluster_high != 0 || dir->cluster_low != 0)
116 continue;
117
118 dbg("found ATTR_VOLUME_ID id in root dir");
119 return dir->name;
120 }
121
122 dbg("skip dir entry");
123 }
124
125 return NULL;
126 }
127
volume_id_probe_vfat(struct volume_id * id)128 int FAST_FUNC volume_id_probe_vfat(struct volume_id *id /*,uint64_t fat_partition_off*/)
129 {
130 #define fat_partition_off ((uint64_t)0)
131 struct vfat_super_block *vs;
132 struct vfat_dir_entry *dir;
133 uint16_t sector_size_bytes;
134 uint16_t dir_entries;
135 uint32_t sect_count;
136 uint16_t reserved_sct;
137 uint32_t fat_size_sct;
138 uint32_t root_cluster;
139 uint32_t dir_size_sct;
140 uint32_t cluster_count;
141 uint64_t root_start_off;
142 uint32_t start_data_sct;
143 uint8_t *buf;
144 uint32_t buf_size;
145 uint8_t *label = NULL;
146 uint32_t next_cluster;
147 int maxloop;
148
149 dbg("probing at offset 0x%llx", (unsigned long long) fat_partition_off);
150
151 vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
152 if (vs == NULL)
153 return -1;
154
155 /* believe only that's fat, don't trust the version
156 * the cluster_count will tell us
157 */
158 if (memcmp(vs->sysid, "NTFS", 4) == 0)
159 return -1;
160
161 if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
162 goto valid;
163
164 if (memcmp(vs->type.fat32.magic, "FAT32 ", 8) == 0)
165 goto valid;
166
167 if (memcmp(vs->type.fat.magic, "FAT16 ", 8) == 0)
168 goto valid;
169
170 if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
171 goto valid;
172
173 if (memcmp(vs->type.fat.magic, "FAT12 ", 8) == 0)
174 goto valid;
175
176 /*
177 * There are old floppies out there without a magic, so we check
178 * for well known values and guess if it's a fat volume
179 */
180
181 /* boot jump address check */
182 if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90)
183 && vs->boot_jump[0] != 0xe9
184 ) {
185 return -1;
186 }
187
188 /* heads check */
189 if (vs->heads == 0)
190 return -1;
191
192 /* cluster size check */
193 if (vs->sectors_per_cluster == 0
194 || (vs->sectors_per_cluster & (vs->sectors_per_cluster-1))
195 ) {
196 return -1;
197 }
198
199 /* media check */
200 if (vs->media < 0xf8 && vs->media != 0xf0)
201 return -1;
202
203 /* fat count*/
204 if (vs->fats != 2)
205 return -1;
206
207 valid:
208 /* sector size check */
209 sector_size_bytes = le16_to_cpu(vs->sector_size_bytes);
210 if (sector_size_bytes != 0x200 && sector_size_bytes != 0x400
211 && sector_size_bytes != 0x800 && sector_size_bytes != 0x1000
212 ) {
213 return -1;
214 }
215
216 dbg("sector_size_bytes 0x%x", sector_size_bytes);
217 dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
218
219 reserved_sct = le16_to_cpu(vs->reserved_sct);
220 dbg("reserved_sct 0x%x", reserved_sct);
221
222 sect_count = le16_to_cpu(vs->sectors);
223 if (sect_count == 0)
224 sect_count = le32_to_cpu(vs->total_sect);
225 dbg("sect_count 0x%x", sect_count);
226
227 fat_size_sct = le16_to_cpu(vs->fat_length);
228 if (fat_size_sct == 0)
229 fat_size_sct = le32_to_cpu(vs->type.fat32.fat32_length);
230 fat_size_sct *= vs->fats;
231 dbg("fat_size_sct 0x%x", fat_size_sct);
232
233 dir_entries = le16_to_cpu(vs->dir_entries);
234 dir_size_sct = ((dir_entries * sizeof(struct vfat_dir_entry)) +
235 (sector_size_bytes-1)) / sector_size_bytes;
236 dbg("dir_size_sct 0x%x", dir_size_sct);
237
238 cluster_count = sect_count - (reserved_sct + fat_size_sct + dir_size_sct);
239 cluster_count /= vs->sectors_per_cluster;
240 dbg("cluster_count 0x%x", cluster_count);
241
242 // if (cluster_count < FAT12_MAX) {
243 // strcpy(id->type_version, "FAT12");
244 // } else if (cluster_count < FAT16_MAX) {
245 // strcpy(id->type_version, "FAT16");
246 // } else {
247 // strcpy(id->type_version, "FAT32");
248 // goto fat32;
249 // }
250 if (cluster_count > FAT16_MAX)
251 goto fat32;
252
253 /* the label may be an attribute in the root directory */
254 root_start_off = (reserved_sct + fat_size_sct) * sector_size_bytes;
255 dbg("root dir start 0x%llx", (unsigned long long) root_start_off);
256 dbg("expected entries 0x%x", dir_entries);
257
258 buf_size = dir_entries * sizeof(struct vfat_dir_entry);
259 buf = volume_id_get_buffer(id, fat_partition_off + root_start_off, buf_size);
260 if (buf == NULL)
261 goto ret;
262
263 label = get_attr_volume_id((struct vfat_dir_entry*) buf, dir_entries);
264
265 vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
266 if (vs == NULL)
267 return -1;
268
269 if (label != NULL && memcmp(label, "NO NAME ", 11) != 0) {
270 // volume_id_set_label_raw(id, label, 11);
271 volume_id_set_label_string(id, label, 11);
272 } else if (memcmp(vs->type.fat.label, "NO NAME ", 11) != 0) {
273 // volume_id_set_label_raw(id, vs->type.fat.label, 11);
274 volume_id_set_label_string(id, vs->type.fat.label, 11);
275 }
276 volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
277 goto ret;
278
279 fat32:
280 /* FAT32 root dir is a cluster chain like any other directory */
281 buf_size = vs->sectors_per_cluster * sector_size_bytes;
282 root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
283 start_data_sct = reserved_sct + fat_size_sct;
284
285 next_cluster = root_cluster;
286 maxloop = 100;
287 while (--maxloop) {
288 uint64_t next_off_sct;
289 uint64_t next_off;
290 uint64_t fat_entry_off;
291 int count;
292
293 dbg("next_cluster 0x%x", (unsigned)next_cluster);
294 next_off_sct = (uint64_t)(next_cluster - 2) * vs->sectors_per_cluster;
295 next_off = (start_data_sct + next_off_sct) * sector_size_bytes;
296 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
297
298 /* get cluster */
299 buf = volume_id_get_buffer(id, fat_partition_off + next_off, buf_size);
300 if (buf == NULL)
301 goto ret;
302
303 dir = (struct vfat_dir_entry*) buf;
304 count = buf_size / sizeof(struct vfat_dir_entry);
305 dbg("expected entries 0x%x", count);
306
307 label = get_attr_volume_id(dir, count);
308 if (label)
309 break;
310
311 /* get FAT entry */
312 fat_entry_off = (reserved_sct * sector_size_bytes) + (next_cluster * sizeof(uint32_t));
313 dbg("fat_entry_off 0x%llx", (unsigned long long)fat_entry_off);
314 buf = volume_id_get_buffer(id, fat_partition_off + fat_entry_off, buf_size);
315 if (buf == NULL)
316 goto ret;
317
318 /* set next cluster */
319 next_cluster = le32_to_cpu(*(uint32_t*)buf) & 0x0fffffff;
320 if (next_cluster < 2 || next_cluster > FAT32_MAX)
321 break;
322 }
323 if (maxloop == 0)
324 dbg("reached maximum follow count of root cluster chain, give up");
325
326 vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
327 if (vs == NULL)
328 return -1;
329
330 if (label != NULL && memcmp(label, "NO NAME ", 11) != 0) {
331 // volume_id_set_label_raw(id, label, 11);
332 volume_id_set_label_string(id, label, 11);
333 } else if (memcmp(vs->type.fat32.label, "NO NAME ", 11) != 0) {
334 // volume_id_set_label_raw(id, vs->type.fat32.label, 11);
335 volume_id_set_label_string(id, vs->type.fat32.label, 11);
336 }
337 volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);
338
339 ret:
340 // volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
341 IF_FEATURE_BLKID_TYPE(id->type = "vfat";)
342
343 return 0;
344 }
345