summaryrefslogtreecommitdiff
path: root/util-linux/volume_id/fat.c
blob: 816d69d4c6e909d6490deb09c74b1d9b2fedb473 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
/*
 * volume_id - reads filesystem label and uuid
 *
 * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
 *
 *	This library is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU Lesser General Public
 *	License as published by the Free Software Foundation; either
 *	version 2.1 of the License, or (at your option) any later version.
 *
 *	This library is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *	Lesser General Public License for more details.
 *
 *	You should have received a copy of the GNU Lesser General Public
 *	License along with this library; if not, write to the Free Software
 *	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include "volume_id_internal.h"

/* linux/msdos_fs.h says: */
#define FAT12_MAX			0xff4
#define FAT16_MAX			0xfff4
#define FAT32_MAX			0x0ffffff6

#define FAT_ATTR_VOLUME_ID		0x08
#define FAT_ATTR_DIR			0x10
#define FAT_ATTR_LONG_NAME		0x0f
#define FAT_ATTR_MASK			0x3f
#define FAT_ENTRY_FREE			0xe5

struct vfat_super_block {
	uint8_t		boot_jump[3];
	uint8_t		sysid[8];
	uint16_t	sector_size_bytes;
	uint8_t		sectors_per_cluster;
	uint16_t	reserved_sct;
	uint8_t		fats;
	uint16_t	dir_entries;
	uint16_t	sectors;
	uint8_t		media;
	uint16_t	fat_length;
	uint16_t	secs_track;
	uint16_t	heads;
	uint32_t	hidden;
	uint32_t	total_sect;
	union {
		struct fat_super_block {
			uint8_t		unknown[3];
			uint8_t		serno[4];
			uint8_t		label[11];
			uint8_t		magic[8];
			uint8_t		dummy2[192];
			uint8_t		pmagic[2];
		} __attribute__((__packed__)) fat;
		struct fat32_super_block {
			uint32_t	fat32_length;
			uint16_t	flags;
			uint8_t		version[2];
			uint32_t	root_cluster;
			uint16_t	insfo_sector;
			uint16_t	backup_boot;
			uint16_t	reserved2[6];
			uint8_t		unknown[3];
			uint8_t		serno[4];
			uint8_t		label[11];
			uint8_t		magic[8];
			uint8_t		dummy2[164];
			uint8_t		pmagic[2];
		} __attribute__((__packed__)) fat32;
	} __attribute__((__packed__)) type;
} __attribute__((__packed__));

struct vfat_dir_entry {
	uint8_t		name[11];
	uint8_t		attr;
	uint16_t	time_creat;
	uint16_t	date_creat;
	uint16_t	time_acc;
	uint16_t	date_acc;
	uint16_t	cluster_high;
	uint16_t	time_write;
	uint16_t	date_write;
	uint16_t	cluster_low;
	uint32_t	size;
} __attribute__((__packed__));

static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, int count)
{
	for (;--count >= 0; dir++) {
		/* end marker */
		if (dir->name[0] == 0x00) {
			dbg("end of dir");
			break;
		}

		/* empty entry */
		if (dir->name[0] == FAT_ENTRY_FREE)
			continue;

		/* long name */
		if ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
			continue;

		if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
			/* labels do not have file data */
			if (dir->cluster_high != 0 || dir->cluster_low != 0)
				continue;

			dbg("found ATTR_VOLUME_ID id in root dir");
			return dir->name;
		}

		dbg("skip dir entry");
	}

	return NULL;
}

int volume_id_probe_vfat(struct volume_id *id, uint64_t fat_partition_off)
{
	struct vfat_super_block *vs;
	struct vfat_dir_entry *dir;
	uint16_t sector_size_bytes;
	uint16_t dir_entries;
	uint32_t sect_count;
	uint16_t reserved_sct;
	uint32_t fat_size_sct;
	uint32_t root_cluster;
	uint32_t dir_size_sct;
	uint32_t cluster_count;
	uint64_t root_start_off;
	uint32_t start_data_sct;
	uint8_t *buf;
	uint32_t buf_size;
	uint8_t *label = NULL;
	uint32_t next_cluster;
	int maxloop;

	dbg("probing at offset 0x%llx", (unsigned long long) fat_partition_off);

	vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
	if (vs == NULL)
		return -1;

	/* believe only that's fat, don't trust the version
	 * the cluster_count will tell us
	 */
	if (memcmp(vs->sysid, "NTFS", 4) == 0)
		return -1;

	if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
		goto valid;

	if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
		goto valid;

	if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
		goto valid;

	if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
		goto valid;

	if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
		goto valid;

	/*
	 * There are old floppies out there without a magic, so we check
	 * for well known values and guess if it's a fat volume
	 */

	/* boot jump address check */
	if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
	     vs->boot_jump[0] != 0xe9)
		return -1;

	/* heads check */
	if (vs->heads == 0)
		return -1;

	/* cluster size check */
	if (vs->sectors_per_cluster == 0 ||
	    (vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
		return -1;

	/* media check */
	if (vs->media < 0xf8 && vs->media != 0xf0)
		return -1;

	/* fat count*/
	if (vs->fats != 2)
		return -1;

 valid:
	/* sector size check */
	sector_size_bytes = le16_to_cpu(vs->sector_size_bytes);
	if (sector_size_bytes != 0x200 && sector_size_bytes != 0x400 &&
	    sector_size_bytes != 0x800 && sector_size_bytes != 0x1000)
		return -1;

	dbg("sector_size_bytes 0x%x", sector_size_bytes);
	dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);

	reserved_sct = le16_to_cpu(vs->reserved_sct);
	dbg("reserved_sct 0x%x", reserved_sct);

	sect_count = le16_to_cpu(vs->sectors);
	if (sect_count == 0)
		sect_count = le32_to_cpu(vs->total_sect);
	dbg("sect_count 0x%x", sect_count);

	fat_size_sct = le16_to_cpu(vs->fat_length);
	if (fat_size_sct == 0)
		fat_size_sct = le32_to_cpu(vs->type.fat32.fat32_length);
	fat_size_sct *= vs->fats;
	dbg("fat_size_sct 0x%x", fat_size_sct);

	dir_entries = le16_to_cpu(vs->dir_entries);
	dir_size_sct = ((dir_entries * sizeof(struct vfat_dir_entry)) +
			(sector_size_bytes-1)) / sector_size_bytes;
	dbg("dir_size_sct 0x%x", dir_size_sct);

	cluster_count = sect_count - (reserved_sct + fat_size_sct + dir_size_sct);
	cluster_count /= vs->sectors_per_cluster;
	dbg("cluster_count 0x%x", cluster_count);

//	if (cluster_count < FAT12_MAX) {
//		strcpy(id->type_version, "FAT12");
//	} else if (cluster_count < FAT16_MAX) {
//		strcpy(id->type_version, "FAT16");
//	} else {
//		strcpy(id->type_version, "FAT32");
//		goto fat32;
//	}
	if (cluster_count >= FAT16_MAX)
		goto fat32;

	/* the label may be an attribute in the root directory */
	root_start_off = (reserved_sct + fat_size_sct) * sector_size_bytes;
	dbg("root dir start 0x%llx", (unsigned long long) root_start_off);
	dbg("expected entries 0x%x", dir_entries);

	buf_size = dir_entries * sizeof(struct vfat_dir_entry);
	buf = volume_id_get_buffer(id, fat_partition_off + root_start_off, buf_size);
	if (buf == NULL)
		goto found;

	label = get_attr_volume_id((struct vfat_dir_entry*) buf, dir_entries);

	vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
	if (vs == NULL)
		return -1;

	if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
//		volume_id_set_label_raw(id, label, 11);
		volume_id_set_label_string(id, label, 11);
	} else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
//		volume_id_set_label_raw(id, vs->type.fat.label, 11);
		volume_id_set_label_string(id, vs->type.fat.label, 11);
	}
	volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
	goto found;

 fat32:
	/* FAT32 root dir is a cluster chain like any other directory */
	buf_size = vs->sectors_per_cluster * sector_size_bytes;
	root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
	start_data_sct = reserved_sct + fat_size_sct;

	next_cluster = root_cluster;
	maxloop = 100;
	while (--maxloop) {
		uint32_t next_off_sct;
		uint64_t next_off;
		uint64_t fat_entry_off;
		int count;

		dbg("next_cluster 0x%x", (unsigned)next_cluster);
		next_off_sct = (next_cluster - 2) * vs->sectors_per_cluster;
		next_off = (start_data_sct + next_off_sct) * sector_size_bytes;
		dbg("cluster offset 0x%llx", (unsigned long long) next_off);

		/* get cluster */
		buf = volume_id_get_buffer(id, fat_partition_off + next_off, buf_size);
		if (buf == NULL)
			goto found;

		dir = (struct vfat_dir_entry*) buf;
		count = buf_size / sizeof(struct vfat_dir_entry);
		dbg("expected entries 0x%x", count);

		label = get_attr_volume_id(dir, count);
		if (label)
			break;

		/* get FAT entry */
		fat_entry_off = (reserved_sct * sector_size_bytes) + (next_cluster * sizeof(uint32_t));
		dbg("fat_entry_off 0x%llx", (unsigned long long)fat_entry_off);
		buf = volume_id_get_buffer(id, fat_partition_off + fat_entry_off, buf_size);
		if (buf == NULL)
			goto found;

		/* set next cluster */
		next_cluster = le32_to_cpu(*(uint32_t*)buf) & 0x0fffffff;
		if (next_cluster < 2 || next_cluster > FAT32_MAX)
			break;
	}
	if (maxloop == 0)
		dbg("reached maximum follow count of root cluster chain, give up");

	vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
	if (vs == NULL)
		return -1;

	if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
//		volume_id_set_label_raw(id, label, 11);
		volume_id_set_label_string(id, label, 11);
	} else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
//		volume_id_set_label_raw(id, vs->type.fat32.label, 11);
		volume_id_set_label_string(id, vs->type.fat32.label, 11);
	}
	volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);

 found:
//	volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
//	id->type = "vfat";

	return 0;
}