summaryrefslogtreecommitdiffhomepage
path: root/util-linux/mkfs_vfat.c
blob: 6a6dc652fb87c4188680a6d5637ab32775c9abd9 (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
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
/* vi: set sw=4 ts=4: */
/*
 * mkfs_vfat: utility to create FAT32 filesystem
 * inspired by dosfstools
 *
 * Busybox'ed (2009) by Vladimir Dronnikov <dronnikov@gmail.com>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config MKDOSFS
//config:	bool "mkdosfs (6.8 kb)"
//config:	default y
//config:	select PLATFORM_LINUX
//config:	help
//config:	Utility to create FAT32 filesystems.
//config:
//config:config MKFS_VFAT
//config:	bool "mkfs.vfat (6.8 kb)"
//config:	default y
//config:	select PLATFORM_LINUX
//config:	help
//config:	Alias to "mkdosfs".

//                    APPLET_ODDNAME:name       main       location     suid_type     help
//applet:IF_MKDOSFS(  APPLET_ODDNAME(mkdosfs,   mkfs_vfat, BB_DIR_SBIN, BB_SUID_DROP, mkfs_vfat))
//applet:IF_MKFS_VFAT(APPLET_ODDNAME(mkfs.vfat, mkfs_vfat, BB_DIR_SBIN, BB_SUID_DROP, mkfs_vfat))

//kbuild:lib-$(CONFIG_MKDOSFS) += mkfs_vfat.o
//kbuild:lib-$(CONFIG_MKFS_VFAT) += mkfs_vfat.o

//usage:#define mkfs_vfat_trivial_usage
//usage:       "[-v] [-n LABEL] BLOCKDEV [KBYTES]"
/* Accepted but ignored:
       "[-c] [-C] [-I] [-l bad-block-file] [-b backup-boot-sector] "
       "[-m boot-msg-file] [-i volume-id] "
       "[-s sectors-per-cluster] [-S logical-sector-size] [-f number-of-FATs] "
       "[-h hidden-sectors] [-F fat-size] [-r root-dir-entries] [-R reserved-sectors] "
*/
//usage:#define mkfs_vfat_full_usage "\n\n"
//usage:       "Make a FAT32 filesystem\n"
/* //usage:  "\n	-c	Check device for bad blocks" */
//usage:     "\n	-v	Verbose"
/* //usage:  "\n	-I	Allow to use entire disk device (e.g. /dev/hda)" */
//usage:     "\n	-n LBL	Volume label"

#include "libbb.h"

#include <linux/hdreg.h> /* HDIO_GETGEO */
#include <linux/fd.h>    /* FDGETPRM */
#include <sys/mount.h>   /* BLKSSZGET */
#if !defined(BLKSSZGET)
# define BLKSSZGET _IO(0x12, 104)
#endif
//#include <linux/msdos_fs.h>

#define SECTOR_SIZE             512

#define SECTORS_PER_BLOCK	(BLOCK_SIZE / SECTOR_SIZE)

// M$ says the high 4 bits of a FAT32 FAT entry are reserved
#define EOF_FAT32       0x0FFFFFF8
#define BAD_FAT32       0x0FFFFFF7
#define MAX_CLUST_32    0x0FFFFFF0

#define ATTR_VOLUME     8

#define NUM_FATS        2

/* FAT32 filesystem looks like this:
 * sector -nn...-1: "hidden" sectors, all sectors before this partition
 * (-h hidden-sectors sets it. Useful only for boot loaders,
 *  they need to know _disk_ offset in order to be able to correctly
 *  address sectors relative to start of disk)
 * sector 0: boot sector
 * sector 1: info sector
 * sector 2: set aside for boot code which didn't fit into sector 0
 * ...(zero-filled sectors)...
 * sector B: backup copy of sector 0 [B set by -b backup-boot-sector]
 * sector B+1: backup copy of sector 1
 * sector B+2: backup copy of sector 2
 * ...(zero-filled sectors)...
 * sector R: FAT#1 [R set by -R reserved-sectors]
 * ...(FAT#1)...
 * sector R+fat_size: FAT#2
 * ...(FAT#2)...
 * sector R+fat_size*2: cluster #2
 * ...(cluster #2)...
 * sector R+fat_size*2+clust_size: cluster #3
 * ...(the rest is filled by clusters till the end)...
 */

enum {
// Perhaps this should remain constant
	info_sector_number = 1,
// TODO: make these cmdline options
// dont forget sanity check: backup_boot_sector + 3 <= reserved_sect
	backup_boot_sector = 3,
	reserved_sect      = 6,
};

// how many blocks we try to read while testing
#define TEST_BUFFER_BLOCKS      16

struct msdos_dir_entry {
	char     name[11];       /* 000 name and extension */
	uint8_t  attr;           /* 00b attribute bits */
	uint8_t  lcase;          /* 00c case for base and extension */
	uint8_t  ctime_cs;       /* 00d creation time, centiseconds (0-199) */
	uint16_t ctime;          /* 00e creation time */
	uint16_t cdate;          /* 010 creation date */
	uint16_t adate;          /* 012 last access date */
	uint16_t starthi;        /* 014 high 16 bits of cluster in FAT32 */
	uint16_t time;           /* 016 time */
	uint16_t date;           /* 018 date */
	uint16_t start;          /* 01a first cluster */
	uint32_t size;           /* 01c file size in bytes */
} PACKED;

/* Example of boot sector's beginning:
0000  eb 58 90 4d 53 57 49 4e  34 2e 31 00 02 08 26 00  |...MSWIN4.1...&.|
0010  02 00 00 00 00 f8 00 00  3f 00 ff 00 3f 00 00 00  |........?...?...|
0020  54 9b d0 00 0d 34 00 00  00 00 00 00 02 00 00 00  |T....4..........|
0030  01 00 06 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
0040  80 00 29 71 df 51 e0 4e  4f 20 4e 41 4d 45 20 20  |..)q.Q.NO NAME  |
0050  20 20 46 41 54 33 32 20  20 20 33 c9 8e d1 bc f4  |  FAT32   3.....|
*/
struct msdos_volume_info { /* (offsets are relative to start of boot sector) */
	uint8_t  drive_number;    /* 040 BIOS drive number */
	uint8_t  reserved;        /* 041 unused */
	uint8_t  ext_boot_sign;	  /* 042 0x29 if fields below exist (DOS 3.3+) */
	uint32_t volume_id32;     /* 043 volume ID number */
	char     volume_label[11];/* 047 volume label */
	char     fs_type[8];      /* 052 typically "FATnn" */
} PACKED;                         /* 05a end. Total size 26 (0x1a) bytes */

struct msdos_boot_sector {
	/* We use strcpy to fill both, and gcc-4.4.x complains if they are separate */
	char     boot_jump_and_sys_id[3+8]; /* 000 short or near jump instruction */
	/*char   system_id[8];*/     /* 003 name - can be used to special case partition manager volumes */
	uint16_t bytes_per_sect;     /* 00b bytes per logical sector */
	uint8_t  sect_per_clust;     /* 00d sectors/cluster */
	uint16_t reserved_sect;      /* 00e reserved sectors (sector offset of 1st FAT relative to volume start) */
	uint8_t  fats;               /* 010 number of FATs */
	uint16_t dir_entries;        /* 011 root directory entries */
	uint16_t volume_size_sect;   /* 013 volume size in sectors */
	uint8_t  media_byte;         /* 015 media code */
	uint16_t sect_per_fat;       /* 016 sectors/FAT */
	uint16_t sect_per_track;     /* 018 sectors per track */
	uint16_t heads;              /* 01a number of heads */
	uint32_t hidden;             /* 01c hidden sectors (sector offset of volume within physical disk) */
	uint32_t fat32_volume_size_sect; /* 020 volume size in sectors (if volume_size_sect == 0) */
	uint32_t fat32_sect_per_fat; /* 024 sectors/FAT */
	uint16_t fat32_flags;        /* 028 bit 8: fat mirroring, low 4: active fat */
	uint8_t  fat32_version[2];   /* 02a major, minor filesystem version (I see 0,0) */
	uint32_t fat32_root_cluster; /* 02c first cluster in root directory */
	uint16_t fat32_info_sector;  /* 030 filesystem info sector (usually 1) */
	uint16_t fat32_backup_boot;  /* 032 backup boot sector (usually 6) */
	uint32_t reserved2[3];       /* 034 unused */
	struct msdos_volume_info vi; /* 040 */
	char     boot_code[0x200 - 0x5a - 2]; /* 05a */
#define BOOT_SIGN 0xAA55
	uint16_t boot_sign;          /* 1fe */
} PACKED;

#define FAT_FSINFO_SIG1 0x41615252
#define FAT_FSINFO_SIG2 0x61417272
struct fat32_fsinfo {
	uint32_t signature1;         /* 0x52,0x52,0x41,0x61, "RRaA" */
	uint32_t reserved1[128 - 8];
	uint32_t signature2;         /* 0x72,0x72,0x61,0x41, "rrAa" */
	uint32_t free_clusters;      /* free cluster count.  -1 if unknown */
	uint32_t next_cluster;       /* most recently allocated cluster */
	uint32_t reserved2[3];
	uint16_t reserved3;          /* 1fc */
	uint16_t boot_sign;          /* 1fe */
} PACKED;

struct bug_check {
	char BUG1[sizeof(struct msdos_dir_entry  ) == 0x20 ? 1 : -1];
	char BUG2[sizeof(struct msdos_volume_info) == 0x1a ? 1 : -1];
	char BUG3[sizeof(struct msdos_boot_sector) == 0x200 ? 1 : -1];
	char BUG4[sizeof(struct fat32_fsinfo     ) == 0x200 ? 1 : -1];
};

static const char boot_code[] ALIGN1 =
	"\x0e"          /* 05a:         push  cs */
	"\x1f"          /* 05b:         pop   ds */
	"\xbe\x77\x7c"  /*  write_msg:  mov   si, offset message_txt */
	"\xac"          /* 05f:         lodsb */
	"\x22\xc0"      /* 060:         and   al, al */
	"\x74\x0b"      /* 062:         jz    key_press */
	"\x56"          /* 064:         push  si */
	"\xb4\x0e"      /* 065:         mov   ah, 0eh */
	"\xbb\x07\x00"  /* 067:         mov   bx, 0007h */
	"\xcd\x10"      /* 06a:         int   10h */
	"\x5e"          /* 06c:         pop   si */
	"\xeb\xf0"      /* 06d:         jmp   write_msg */
	"\x32\xe4"      /*  key_press:  xor   ah, ah */
	"\xcd\x16"      /* 071:         int   16h */
	"\xcd\x19"      /* 073:         int   19h */
	"\xeb\xfe"      /*  foo:        jmp   foo */
	/* 077: message_txt: */
	"This is not a bootable disk\r\n";


#define MARK_CLUSTER(cluster, value) \
	((uint32_t *)fat)[cluster] = SWAP_LE32(value)

/* compat:
 * mkdosfs 2.11 (12 Mar 2005)
 * Usage: mkdosfs [-A] [-c] [-C] [-v] [-I] [-l bad-block-file]
 *        [-b backup-boot-sector]
 *        [-m boot-msg-file] [-n volume-name] [-i volume-id]
 *        [-s sectors-per-cluster] [-S logical-sector-size]
 *        [-f number-of-FATs]
 *        [-h hidden-sectors] [-F fat-size] [-r root-dir-entries]
 *        [-R reserved-sectors]
 *        /dev/name [blocks]
 */
int mkfs_vfat_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
{
	struct stat st;
	const char *volume_label = "";
	char *buf;
	char *device_name;
	uoff_t volume_size_bytes;
	uoff_t volume_size_sect;
	uint32_t total_clust;
	uint32_t volume_id;
	int dev;
	unsigned bytes_per_sect;
	unsigned sect_per_fat;
	unsigned opts;
	uint16_t sect_per_track;
	uint8_t media_byte;
	uint8_t sect_per_clust;
	uint8_t heads;
	enum {
		OPT_A = 1 << 0,  // [IGNORED] atari format
		OPT_b = 1 << 1,	 // [IGNORED] location of backup boot sector
		OPT_c = 1 << 2,	 // [IGNORED] check filesystem
		OPT_C = 1 << 3,	 // [IGNORED] create a new file
		OPT_f = 1 << 4,	 // [IGNORED] number of FATs
		OPT_F = 1 << 5,	 // [IGNORED, implied 32] choose FAT size
		OPT_h = 1 << 6,	 // [IGNORED] number of hidden sectors
		OPT_I = 1 << 7,	 // [IGNORED] don't bark at entire disk devices
		OPT_i = 1 << 8,	 // [IGNORED] volume ID
		OPT_l = 1 << 9,	 // [IGNORED] bad block filename
		OPT_m = 1 << 10, // [IGNORED] message file
		OPT_n = 1 << 11, // volume label
		OPT_r = 1 << 12, // [IGNORED] root directory entries
		OPT_R = 1 << 13, // [IGNORED] number of reserved sectors
		OPT_s = 1 << 14, // [IGNORED] sectors per cluster
		OPT_S = 1 << 15, // [IGNORED] sector size
		OPT_v = 1 << 16, // verbose
	};

	opts = getopt32(argv, "^"
		"Ab:cCf:F:h:Ii:l:m:n:r:R:s:S:v"
		"\0" "-1", //:b+:f+:F+:h+:r+:R+:s+:S+:vv:c--l:l--c
		NULL, NULL, NULL, NULL, NULL,
		NULL, NULL, &volume_label, NULL, NULL, NULL, NULL);
	argv += optind;

	// cache device name
	device_name = argv[0];
	// default volume ID = creation time
	volume_id = time(NULL);

	dev = xopen(device_name, O_RDWR);
	xfstat(dev, &st, device_name);

	//
	// Get image size and sector size
	//
	bytes_per_sect = SECTOR_SIZE;
	if (!S_ISBLK(st.st_mode)) {
		if (!S_ISREG(st.st_mode)) {
			if (!argv[1])
				bb_error_msg_and_die("image size must be specified");
		}
		// not a block device, skip bad sectors check
		opts &= ~OPT_c;
	} else {
		int min_bytes_per_sect;
#if 0
		unsigned device_num;
		// for true block devices we do check sanity
		device_num = st.st_rdev & 0xff3f;
		// do we allow to format the whole disk device?
		if (!(opts & OPT_I) && (
			device_num == 0x0300 || // hda, hdb
			(device_num & 0xff0f) == 0x0800 || // sd
			device_num == 0x0d00 || // xd
			device_num == 0x1600 )  // hdc, hdd
		)
			bb_error_msg_and_die("will not try to make filesystem on full-disk device (use -I if wanted)");
		// can't work on mounted filesystems
		if (find_mount_point(device_name, 0))
			bb_error_msg_and_die("can't format mounted filesystem");
#endif
		// get true sector size
		// (parameter must be int*, not long* or size_t*)
		xioctl(dev, BLKSSZGET, &min_bytes_per_sect);
		if (min_bytes_per_sect > SECTOR_SIZE) {
			bytes_per_sect = min_bytes_per_sect;
			bb_error_msg("for this device sector size is %u", min_bytes_per_sect);
		}
	}
	volume_size_bytes = get_volume_size_in_bytes(dev, argv[1], 1024, /*extend:*/ 1);
	volume_size_sect = volume_size_bytes / bytes_per_sect;

	//
	// Find out or guess media parameters
	//
	media_byte = 0xf8;
	heads = 255;
	sect_per_track = 63;
	sect_per_clust = 1;
	{
		struct hd_geometry geometry;
		// size (in sectors), sect (per track), head
		struct floppy_struct param;

		// N.B. whether to use HDIO_GETGEO or HDIO_REQ?
		if (ioctl(dev, HDIO_GETGEO, &geometry) == 0
		 && geometry.sectors
		 && geometry.heads
		) {
			// hard drive
			sect_per_track = geometry.sectors;
			heads = geometry.heads;

 set_cluster_size:
			/* For FAT32, try to do the same as M$'s format command
			 * (see http://www.win.tue.nl/~aeb/linux/fs/fat/fatgen103.pdf p. 20):
			 * fs size <= 260M: 0.5k clusters
			 * fs size <=   8G: 4k clusters
			 * fs size <=  16G: 8k clusters
			 * fs size >   16G: 16k clusters
			 */
			sect_per_clust = 1;
			if (volume_size_bytes >= 260*1024*1024) {
				sect_per_clust = 8;
				/* fight gcc: */
				/* "error: integer overflow in expression" */
				/* "error: right shift count >= width of type" */
				if (sizeof(off_t) > 4) {
					unsigned t = (volume_size_bytes >> 31 >> 1);
					if (t >= 8/4)
						sect_per_clust = 16;
					if (t >= 16/4)
						sect_per_clust = 32;
				}
			}
		} else {
			// floppy, loop, or regular file
			int not_floppy = ioctl(dev, FDGETPRM, &param);
			if (not_floppy == 0) {
				// floppy disk
				sect_per_track = param.sect;
				heads = param.head;
				volume_size_sect = param.size;
				volume_size_bytes = param.size * SECTOR_SIZE;
			}
			// setup the media descriptor byte
			switch (volume_size_sect) {
			case 2*360:	// 5.25", 2, 9, 40 - 360K
				media_byte = 0xfd;
				break;
			case 2*720:	// 3.5", 2, 9, 80 - 720K
			case 2*1200:	// 5.25", 2, 15, 80 - 1200K
				media_byte = 0xf9;
				break;
			default:	// anything else
				if (not_floppy)
					goto set_cluster_size;
			case 2*1440:	// 3.5", 2, 18, 80 - 1440K
			case 2*2880:	// 3.5", 2, 36, 80 - 2880K
				media_byte = 0xf0;
				break;
			}
			// not floppy, but size matches floppy exactly.
			// perhaps it is a floppy image.
			// we already set media_byte as if it is a floppy,
			// now set sect_per_track and heads.
			heads = 2;
			sect_per_track = (unsigned)volume_size_sect / 160;
			if (sect_per_track < 9)
				sect_per_track = 9;
		}
	}

	//
	// Calculate number of clusters, sectors/cluster, sectors/FAT
	// (an initial guess for sect_per_clust should already be set)
	//
	// "mkdosfs -v -F 32 image5k 5" is the minimum:
	// 2 sectors for FATs and 2 data sectors
	if ((off_t)(volume_size_sect - reserved_sect) < 4)
		bb_error_msg_and_die("the image is too small for FAT32");
	sect_per_fat = 1;
	while (1) {
		while (1) {
			int spf_adj;
			uoff_t tcl = (volume_size_sect - reserved_sect - NUM_FATS * sect_per_fat) / sect_per_clust;
			// tcl may be > MAX_CLUST_32 here, but it may be
			// because sect_per_fat is underestimated,
			// and with increased sect_per_fat it still may become
			// <= MAX_CLUST_32. Therefore, we do not check
			// against MAX_CLUST_32, but against a bigger const:
			if (tcl > 0x80ffffff)
				goto next;
			total_clust = tcl; // fits in uint32_t
			// Every cluster needs 4 bytes in FAT. +2 entries since
			// FAT has space for non-existent clusters 0 and 1.
			// Let's see how many sectors that needs.
			//May overflow at "*4":
			//spf_adj = ((total_clust+2) * 4 + bytes_per_sect-1) / bytes_per_sect - sect_per_fat;
			//Same in the more obscure, non-overflowing form:
			spf_adj = ((total_clust+2) + (bytes_per_sect/4)-1) / (bytes_per_sect/4) - sect_per_fat;
#if 0
			bb_error_msg("sect_per_clust:%u sect_per_fat:%u total_clust:%u",
					sect_per_clust, sect_per_fat, (int)tcl);
			bb_error_msg("adjust to sect_per_fat:%d", spf_adj);
#endif
			if (spf_adj <= 0) {
				// do not need to adjust sect_per_fat.
				// so, was total_clust too big after all?
				if (total_clust <= MAX_CLUST_32)
					goto found_total_clust; // no
				// yes, total_clust is _a bit_ too big
				goto next;
			}
			// adjust sect_per_fat, go back and recalc total_clust
			// (note: just "sect_per_fat += spf_adj" isn't ok)
			sect_per_fat += ((unsigned)spf_adj / 2) | 1;
		}
 next:
		if (sect_per_clust == 128)
			bb_error_msg_and_die("can't make FAT32 with >128 sectors/cluster");
		sect_per_clust *= 2;
		sect_per_fat = (sect_per_fat / 2) | 1;
	}
 found_total_clust:

	//
	// Print info
	//
	if (opts & OPT_v) {
		fprintf(stderr,
			"Device '%s':\n"
			"heads:%u, sectors/track:%u, bytes/sector:%u\n"
			"media descriptor:%02x\n"
			"total sectors:%"OFF_FMT"u, clusters:%u, sectors/cluster:%u\n"
			"FATs:2, sectors/FAT:%u\n"
			"volumeID:%08x, label:'%s'\n",
			device_name,
			heads, sect_per_track, bytes_per_sect,
			(int)media_byte,
			volume_size_sect, (int)total_clust, (int)sect_per_clust,
			sect_per_fat,
			(int)volume_id, volume_label
		);
	}

	//
	// Write filesystem image sequentially (no seeking)
	//
	{
		// (a | b) is poor man's max(a, b)
		unsigned bufsize = reserved_sect;
		//bufsize |= sect_per_fat; // can be quite large
		bufsize |= 2; // use this instead
		bufsize |= sect_per_clust;
		buf = xzalloc(bufsize * bytes_per_sect);
	}

	{ // boot and fsinfo sectors, and their copies
		struct msdos_boot_sector *boot_blk = (void*)buf;
		struct fat32_fsinfo *info = (void*)(buf + bytes_per_sect);

		strcpy(boot_blk->boot_jump_and_sys_id, "\xeb\x58\x90" "mkdosfs");
		STORE_LE(boot_blk->bytes_per_sect, bytes_per_sect);
		STORE_LE(boot_blk->sect_per_clust, sect_per_clust);
		// cast in needed on big endian to suppress a warning
		STORE_LE(boot_blk->reserved_sect, (uint16_t)reserved_sect);
		STORE_LE(boot_blk->fats, 2);
		//STORE_LE(boot_blk->dir_entries, 0); // for FAT32, stays 0
		if (volume_size_sect <= 0xffff)
			STORE_LE(boot_blk->volume_size_sect, volume_size_sect);
		STORE_LE(boot_blk->media_byte, media_byte);
		// wrong: this would make Linux think that it's fat12/16:
		//if (sect_per_fat <= 0xffff)
		//	STORE_LE(boot_blk->sect_per_fat, sect_per_fat);
		// works:
		//STORE_LE(boot_blk->sect_per_fat, 0);
		STORE_LE(boot_blk->sect_per_track, sect_per_track);
		STORE_LE(boot_blk->heads, heads);
		//STORE_LE(boot_blk->hidden, 0);
		STORE_LE(boot_blk->fat32_volume_size_sect, volume_size_sect);
		STORE_LE(boot_blk->fat32_sect_per_fat, sect_per_fat);
		//STORE_LE(boot_blk->fat32_flags, 0);
		//STORE_LE(boot_blk->fat32_version[2], 0,0);
		STORE_LE(boot_blk->fat32_root_cluster, 2);
		STORE_LE(boot_blk->fat32_info_sector, info_sector_number);
		STORE_LE(boot_blk->fat32_backup_boot, backup_boot_sector);
		//STORE_LE(boot_blk->reserved2[3], 0,0,0);
		STORE_LE(boot_blk->vi.ext_boot_sign, 0x29);
		STORE_LE(boot_blk->vi.volume_id32, volume_id);
		memcpy(boot_blk->vi.fs_type, "FAT32   ", sizeof(boot_blk->vi.fs_type));
		strncpy(boot_blk->vi.volume_label, volume_label, sizeof(boot_blk->vi.volume_label));
		memcpy(boot_blk->boot_code, boot_code, sizeof(boot_code));
		STORE_LE(boot_blk->boot_sign, BOOT_SIGN);

		STORE_LE(info->signature1, FAT_FSINFO_SIG1);
		STORE_LE(info->signature2, FAT_FSINFO_SIG2);
		// we've allocated cluster 2 for the root dir
		STORE_LE(info->free_clusters, (total_clust - 1));
		STORE_LE(info->next_cluster, 2);
		STORE_LE(info->boot_sign, BOOT_SIGN);

		// 1st copy
		xwrite(dev, buf, bytes_per_sect * backup_boot_sector);
		// 2nd copy and possibly zero sectors
		xwrite(dev, buf, bytes_per_sect * (reserved_sect - backup_boot_sector));
	}

	{ // file allocation tables
		unsigned i,j;
		unsigned char *fat = (void*)buf;

		memset(buf, 0, bytes_per_sect * 2);
		// initial FAT entries
		MARK_CLUSTER(0, 0x0fffff00 | media_byte);
		MARK_CLUSTER(1, 0xffffffff);
		// mark cluster 2 as EOF (used for root dir)
		MARK_CLUSTER(2, EOF_FAT32);
		for (i = 0; i < NUM_FATS; i++) {
			xwrite(dev, buf, bytes_per_sect);
			for (j = 1; j < sect_per_fat; j++)
				xwrite(dev, buf + bytes_per_sect, bytes_per_sect);
		}
	}

	// root directory
	// empty directory is just a set of zero bytes
	memset(buf, 0, sect_per_clust * bytes_per_sect);
	if (volume_label[0]) {
		// create dir entry for volume_label
		struct msdos_dir_entry *de;
#if 0
		struct tm tm_time;
		uint16_t t, d;
#endif
		de = (void*)buf;
		strncpy(de->name, volume_label, sizeof(de->name));
		STORE_LE(de->attr, ATTR_VOLUME);
#if 0
		localtime_r(&create_time, &tm_time);
		t = (tm_time.tm_sec >> 1) + (tm_time.tm_min << 5) + (tm_time.tm_hour << 11);
		d = tm_time.tm_mday + ((tm_time.tm_mon+1) << 5) + ((tm_time.tm_year-80) << 9);
		STORE_LE(de->time, t);
		STORE_LE(de->date, d);
		//STORE_LE(de->ctime_cs, 0);
		de->ctime = de->time;
		de->cdate = de->date;
		de->adate = de->date;
#endif
	}
	xwrite(dev, buf, sect_per_clust * bytes_per_sect);

#if 0
	if (opts & OPT_c) {
		uoff_t volume_size_blocks;
		unsigned start_data_sector;
		unsigned start_data_block;
		unsigned badblocks = 0;
		int try, got;
		off_t currently_testing;
		char *blkbuf = xmalloc(BLOCK_SIZE * TEST_BUFFER_BLOCKS);

		volume_size_blocks = (volume_size_bytes >> BLOCK_SIZE_BITS);
		// N.B. the two following vars are in hard sectors, i.e. SECTOR_SIZE byte sectors!
		start_data_sector = (reserved_sect + NUM_FATS * sect_per_fat) * (bytes_per_sect / SECTOR_SIZE);
		start_data_block = (start_data_sector + SECTORS_PER_BLOCK - 1) / SECTORS_PER_BLOCK;

		bb_error_msg("searching for bad blocks");
		currently_testing = 0;
		try = TEST_BUFFER_BLOCKS;
		while (currently_testing < volume_size_blocks) {
			if (currently_testing + try > volume_size_blocks)
				try = volume_size_blocks - currently_testing;
			// perform a test on a block. return the number of blocks
			// that could be read successfully.
			// seek to the correct location
			xlseek(dev, currently_testing * BLOCK_SIZE, SEEK_SET);
			// try reading
			got = read(dev, blkbuf, try * BLOCK_SIZE);
			if (got < 0)
				got = 0;
			if (got & (BLOCK_SIZE - 1))
				bb_error_msg("unexpected values in do_check: probably bugs");
			got /= BLOCK_SIZE;
			currently_testing += got;
			if (got == try) {
				try = TEST_BUFFER_BLOCKS;
				continue;
			}
			try = 1;
			if (currently_testing < start_data_block)
				bb_error_msg_and_die("bad blocks before data-area: cannot make fs");

			// mark all of the sectors in the block as bad
			for (i = 0; i < SECTORS_PER_BLOCK; i++) {
				int cluster = (currently_testing * SECTORS_PER_BLOCK + i - start_data_sector) / (int) (sect_per_clust) / (bytes_per_sect / SECTOR_SIZE);
				if (cluster < 0)
					bb_error_msg_and_die("invalid cluster number in mark_sector: probably bug!");
				MARK_CLUSTER(cluster, BAD_FAT32);
			}
			badblocks++;
			currently_testing++;
		}
		free(blkbuf);
		if (badblocks)
			bb_error_msg("%d bad block(s)", badblocks);
	}
#endif

	// cleanup
	if (ENABLE_FEATURE_CLEAN_UP) {
		free(buf);
		close(dev);
	}

	return 0;
}