summaryrefslogtreecommitdiff
path: root/trunk/users/metalab/GCode_Interpreter_SD/fat.cpp
blob: bc9b326d14bb18a2cf814267c07b56d637672615 (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
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317

/* 
 * Copyright (c) 2006-2008 by Roland Riegel <feedback@roland-riegel.de>
 *
 * This file is free software; you can redistribute it and/or modify
 * it under the terms of either the GNU General Public License version 2
 * or the GNU Lesser General Public License version 2.1, both as
 * published by the Free Software Foundation.
 */

#include "byteordering.h"
#include "partition.h"
#include "fat.h"
#include "fat_config.h"
#include "sd-reader_config.h"

#include <string.h>
#include <limits.h>

#if USE_DYNAMIC_MEMORY
    #include <stdlib.h>
#endif

/**
 * \addtogroup fat FAT support
 *
 * This module implements FAT16/FAT32 read and write access.
 * 
 * The following features are supported:
 * - File names up to 31 characters long.
 * - Unlimited depth of subdirectories.
 * - Short 8.3 and long filenames.
 * - Creating and deleting files.
 * - Reading and writing from and to files.
 * - File resizing.
 * - File sizes of up to 4 gigabytes.
 * 
 * @{
 */
/**
 * \file
 * FAT implementation (license: GPLv2 or LGPLv2.1)
 *
 * \author Roland Riegel
 */

/**
 * \addtogroup fat_config FAT configuration
 * Preprocessor defines to configure the FAT implementation.
 */

/**
 * \addtogroup fat_fs FAT access
 * Basic functions for handling a FAT filesystem.
 */

/**
 * \addtogroup fat_file FAT file functions
 * Functions for managing files.
 */

/**
 * \addtogroup fat_dir FAT directory functions
 * Functions for managing directories.
 */

/**
 * @}
 */

#define FAT16_CLUSTER_FREE 0x0000
#define FAT16_CLUSTER_RESERVED_MIN 0xfff0
#define FAT16_CLUSTER_RESERVED_MAX 0xfff6
#define FAT16_CLUSTER_BAD 0xfff7
#define FAT16_CLUSTER_LAST_MIN 0xfff8
#define FAT16_CLUSTER_LAST_MAX 0xffff

#define FAT32_CLUSTER_FREE 0x00000000
#define FAT32_CLUSTER_RESERVED_MIN 0x0ffffff0
#define FAT32_CLUSTER_RESERVED_MAX 0x0ffffff6
#define FAT32_CLUSTER_BAD 0x0ffffff7
#define FAT32_CLUSTER_LAST_MIN 0x0ffffff8
#define FAT32_CLUSTER_LAST_MAX 0x0fffffff

#define FAT_DIRENTRY_DELETED 0xe5
#define FAT_DIRENTRY_LFNLAST (1 << 6)
#define FAT_DIRENTRY_LFNSEQMASK ((1 << 6) - 1)

/* Each entry within the directory table has a size of 32 bytes
 * and either contains a 8.3 DOS-style file name or a part of a
 * long file name, which may consist of several directory table
 * entries at once.
 *
 * multi-byte integer values are stored little-endian!
 *
 * 8.3 file name entry:
 * ====================
 * offset  length  description
 *      0       8  name (space padded)
 *      8       3  extension (space padded)
 *     11       1  attributes (FAT_ATTRIB_*)
 *
 * long file name (lfn) entry ordering for a single file name:
 * ===========================================================
 * LFN entry n
 *     ...
 * LFN entry 2
 * LFN entry 1
 * 8.3 entry (see above)
 * 
 * lfn entry:
 * ==========
 * offset  length  description
 *      0       1  ordinal field
 *      1       2  unicode character 1
 *      3       3  unicode character 2
 *      5       3  unicode character 3
 *      7       3  unicode character 4
 *      9       3  unicode character 5
 *     11       1  attribute (always 0x0f)
 *     12       1  type (reserved, always 0)
 *     13       1  checksum
 *     14       2  unicode character 6
 *     16       2  unicode character 7
 *     18       2  unicode character 8
 *     20       2  unicode character 9
 *     22       2  unicode character 10
 *     24       2  unicode character 11
 *     26       2  cluster (unused, always 0)
 *     28       2  unicode character 12
 *     30       2  unicode character 13
 * 
 * The ordinal field contains a descending number, from n to 1.
 * For the n'th lfn entry the ordinal field is or'ed with 0x40.
 * For deleted lfn entries, the ordinal field is set to 0xe5.
 */

struct fat_header_struct
{
    offset_t size;

    offset_t fat_offset;
    uint32_t fat_size;

    uint16_t sector_size;
    uint16_t cluster_size;

    offset_t cluster_zero_offset;

    offset_t root_dir_offset;
#if FAT_FAT32_SUPPORT
    cluster_t root_dir_cluster;
#endif
};

struct fat_fs_struct
{
    struct partition_struct* partition;
    struct fat_header_struct header;
};

struct fat_file_struct
{
    struct fat_fs_struct* fs;
    struct fat_dir_entry_struct dir_entry;
    offset_t pos;
    cluster_t pos_cluster;
};

struct fat_dir_struct
{
    struct fat_fs_struct* fs;
    struct fat_dir_entry_struct dir_entry;
    cluster_t entry_cluster;
    uint16_t entry_offset;
};

struct fat_read_dir_callback_arg
{
    struct fat_dir_entry_struct* dir_entry;
    uintptr_t bytes_read;
    uint8_t finished;
};

struct fat_usage_count_callback_arg
{
    cluster_t cluster_count;
    uintptr_t buffer_size;
};

#if !USE_DYNAMIC_MEMORY
static struct fat_fs_struct fat_fs_handles[FAT_FS_COUNT];
static struct fat_file_struct fat_file_handles[FAT_FILE_COUNT];
static struct fat_dir_struct fat_dir_handles[FAT_DIR_COUNT];
#endif

static uint8_t fat_read_header(struct fat_fs_struct* fs);
static cluster_t fat_get_next_cluster(const struct fat_fs_struct* fs, cluster_t cluster_num);
static offset_t fat_cluster_offset(const struct fat_fs_struct* fs, cluster_t cluster_num);
static uint8_t fat_dir_entry_read_callback(uint8_t* buffer, offset_t offset, void* p);
static uint8_t fat_interpret_dir_entry(struct fat_dir_entry_struct* dir_entry, const uint8_t* raw_entry);

static uint8_t fat_get_fs_free_16_callback(uint8_t* buffer, offset_t offset, void* p);
#if FAT_FAT32_SUPPORT
static uint8_t fat_get_fs_free_32_callback(uint8_t* buffer, offset_t offset, void* p);
#endif

#if FAT_WRITE_SUPPORT
static cluster_t fat_append_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num, cluster_t count);
static uint8_t fat_free_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num);
static uint8_t fat_terminate_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num);
static uint8_t fat_clear_cluster(const struct fat_fs_struct* fs, cluster_t cluster_num);
static uintptr_t fat_clear_cluster_callback(uint8_t* buffer, offset_t offset, void* p);
static offset_t fat_find_offset_for_dir_entry(const struct fat_fs_struct* fs, const struct fat_dir_struct* parent, const struct fat_dir_entry_struct* dir_entry);
static uint8_t fat_write_dir_entry(const struct fat_fs_struct* fs, struct fat_dir_entry_struct* dir_entry);
#if FAT_DATETIME_SUPPORT
static void fat_set_file_modification_date(struct fat_dir_entry_struct* dir_entry, uint16_t year, uint8_t month, uint8_t day);
static void fat_set_file_modification_time(struct fat_dir_entry_struct* dir_entry, uint8_t hour, uint8_t min, uint8_t sec);
#endif
#endif

/**
 * \ingroup fat_fs
 * Opens a FAT filesystem.
 *
 * \param[in] partition Discriptor of partition on which the filesystem resides.
 * \returns 0 on error, a FAT filesystem descriptor on success.
 * \see fat_close
 */
struct fat_fs_struct* fat_open(struct partition_struct* partition)
{
    if(!partition ||
#if FAT_WRITE_SUPPORT
       !partition->device_write ||
       !partition->device_write_interval
#else
       0
#endif
      )
        return 0;

#if USE_DYNAMIC_MEMORY
    struct fat_fs_struct* fs = malloc(sizeof(*fs));
    if(!fs)
        return 0;
#else
    struct fat_fs_struct* fs = fat_fs_handles;
    uint8_t i;
    for(i = 0; i < FAT_FS_COUNT; ++i)
    {
        if(!fs->partition)
            break;

        ++fs;
    }
    if(i >= FAT_FS_COUNT)
        return 0;
#endif

    memset(fs, 0, sizeof(*fs));

    fs->partition = partition;
    if(!fat_read_header(fs))
    {
#if USE_DYNAMIC_MEMORY
        free(fs);
#else
        fs->partition = 0;
#endif
        return 0;
    }
    
    return fs;
}

/**
 * \ingroup fat_fs
 * Closes a FAT filesystem.
 *
 * When this function returns, the given filesystem descriptor
 * will be invalid.
 *
 * \param[in] fs The filesystem to close.
 * \see fat_open
 */
void fat_close(struct fat_fs_struct* fs)
{
    if(!fs)
        return;

#if USE_DYNAMIC_MEMORY
    free(fs);
#else
    fs->partition = 0;
#endif
}

/**
 * \ingroup fat_fs
 * Reads and parses the header of a FAT filesystem.
 *
 * \param[inout] fs The filesystem for which to parse the header.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat_read_header(struct fat_fs_struct* fs)
{
    if(!fs)
        return 0;

    struct partition_struct* partition = fs->partition;
    if(!partition)
        return 0;

    /* read fat parameters */
#if FAT_FAT32_SUPPORT
    uint8_t buffer[37];
#else
    uint8_t buffer[25];
#endif
    offset_t partition_offset = (offset_t) partition->offset * 512;
    if(!partition->device_read(partition_offset + 0x0b, buffer, sizeof(buffer)))
        return 0;

    uint16_t bytes_per_sector = ltoh16(*((uint16_t*) &buffer[0x00]));
    uint16_t reserved_sectors = ltoh16(*((uint16_t*) &buffer[0x03]));
    uint8_t sectors_per_cluster = buffer[0x02];
    uint8_t fat_copies = buffer[0x05];
    uint16_t max_root_entries = ltoh16(*((uint16_t*) &buffer[0x06]));
    uint16_t sector_count_16 = ltoh16(*((uint16_t*) &buffer[0x08]));
    uint16_t sectors_per_fat = ltoh16(*((uint16_t*) &buffer[0x0b]));
    uint32_t sector_count = ltoh32(*((uint32_t*) &buffer[0x15]));
#if FAT_FAT32_SUPPORT
    uint32_t sectors_per_fat32 = ltoh32(*((uint32_t*) &buffer[0x19]));
    uint32_t cluster_root_dir = ltoh32(*((uint32_t*) &buffer[0x21]));
#endif

    if(sector_count == 0)
    {
        if(sector_count_16 == 0)
            /* illegal volume size */
            return 0;
        else
            sector_count = sector_count_16;
    }
#if FAT_FAT32_SUPPORT
    if(sectors_per_fat != 0)
        sectors_per_fat32 = sectors_per_fat;
    else if(sectors_per_fat32 == 0)
        /* this is neither FAT16 nor FAT32 */
        return 0;
#else
    if(sectors_per_fat == 0)
        /* this is not a FAT16 */
        return 0;
#endif

    /* determine the type of FAT we have here */
    uint32_t data_sector_count = sector_count
                                 - reserved_sectors
#if FAT_FAT32_SUPPORT
                                 - sectors_per_fat32 * fat_copies
#else
                                 - (uint32_t) sectors_per_fat * fat_copies
#endif
                                 - ((max_root_entries * 32 + bytes_per_sector - 1) / bytes_per_sector);
    uint32_t data_cluster_count = data_sector_count / sectors_per_cluster;
    if(data_cluster_count < 4085)
        /* this is a FAT12, not supported */
        return 0;
    else if(data_cluster_count < 65525)
        /* this is a FAT16 */
        partition->type = PARTITION_TYPE_FAT16;
    else
        /* this is a FAT32 */
        partition->type = PARTITION_TYPE_FAT32;

    /* fill header information */
    struct fat_header_struct* header = &fs->header;
    memset(header, 0, sizeof(*header));
    
    header->size = (offset_t) sector_count * bytes_per_sector;

    header->fat_offset = /* jump to partition */
                         partition_offset +
                         /* jump to fat */
                         (offset_t) reserved_sectors * bytes_per_sector;
    header->fat_size = (data_cluster_count + 2) * sizeof(cluster_t);

    header->sector_size = bytes_per_sector;
    header->cluster_size = (uint16_t) bytes_per_sector * sectors_per_cluster;

#if FAT_FAT32_SUPPORT
    if(partition->type == PARTITION_TYPE_FAT16)
#endif
    {
        header->root_dir_offset = /* jump to fats */
                                  header->fat_offset +
                                  /* jump to root directory entries */
                                  (offset_t) fat_copies * sectors_per_fat * bytes_per_sector;

        header->cluster_zero_offset = /* jump to root directory entries */
                                      header->root_dir_offset +
                                      /* skip root directory entries */
                                      (offset_t) max_root_entries * 32;
    }
#if FAT_FAT32_SUPPORT
    else
    {
        header->cluster_zero_offset = /* jump to fats */
                                      header->fat_offset +
                                      /* skip fats */
                                      (offset_t) fat_copies * sectors_per_fat32 * bytes_per_sector;

        header->root_dir_cluster = cluster_root_dir;
    }
#endif

    return 1;
}

/**
 * \ingroup fat_fs
 * Retrieves the next following cluster of a given cluster.
 *
 * Using the filesystem file allocation table, this function returns
 * the number of the cluster containing the data directly following
 * the data within the cluster with the given number.
 *
 * \param[in] fs The filesystem for which to determine the next cluster.
 * \param[in] cluster_num The number of the cluster for which to determine its successor.
 * \returns The wanted cluster number, or 0 on error.
 */
cluster_t fat_get_next_cluster(const struct fat_fs_struct* fs, cluster_t cluster_num)
{
    if(!fs || cluster_num < 2)
        return 0;

#if FAT_FAT32_SUPPORT
    if(fs->partition->type == PARTITION_TYPE_FAT32)
    {
        /* read appropriate fat entry */
        uint32_t fat_entry;
        if(!fs->partition->device_read(fs->header.fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
            return 0;

        /* determine next cluster from fat */
        cluster_num = ltoh32(fat_entry);
        
        if(cluster_num == FAT32_CLUSTER_FREE ||
           cluster_num == FAT32_CLUSTER_BAD ||
           (cluster_num >= FAT32_CLUSTER_RESERVED_MIN && cluster_num <= FAT32_CLUSTER_RESERVED_MAX) ||
           (cluster_num >= FAT32_CLUSTER_LAST_MIN && cluster_num <= FAT32_CLUSTER_LAST_MAX))
            return 0;
    }
    else
#endif
    {
        /* read appropriate fat entry */
        uint16_t fat_entry;
        if(!fs->partition->device_read(fs->header.fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
            return 0;

        /* determine next cluster from fat */
        cluster_num = ltoh16(fat_entry);
        
        if(cluster_num == FAT16_CLUSTER_FREE ||
           cluster_num == FAT16_CLUSTER_BAD ||
           (cluster_num >= FAT16_CLUSTER_RESERVED_MIN && cluster_num <= FAT16_CLUSTER_RESERVED_MAX) ||
           (cluster_num >= FAT16_CLUSTER_LAST_MIN && cluster_num <= FAT16_CLUSTER_LAST_MAX))
            return 0;
    }

    return cluster_num;
}

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Appends a new cluster chain to an existing one.
 *
 * Set cluster_num to zero to create a completely new one.
 *
 * \param[in] fs The file system on which to operate.
 * \param[in] cluster_num The cluster to which to append the new chain.
 * \param[in] count The number of clusters to allocate.
 * \returns 0 on failure, the number of the first new cluster on success.
 */
cluster_t fat_append_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num, cluster_t count)
{
    if(!fs)
        return 0;

    device_read_t device_read = fs->partition->device_read;
    device_write_t device_write = fs->partition->device_write;
    offset_t fat_offset = fs->header.fat_offset;
    cluster_t count_left = count;
    cluster_t cluster_next = 0;
    cluster_t cluster_max;
    uint16_t fat_entry16;
#if FAT_FAT32_SUPPORT
    uint32_t fat_entry32;
    uint8_t is_fat32 = (fs->partition->type == PARTITION_TYPE_FAT32);

    if(is_fat32)
        cluster_max = fs->header.fat_size / sizeof(fat_entry32);
    else
#endif
        cluster_max = fs->header.fat_size / sizeof(fat_entry16);

    for(cluster_t cluster_new = 2; cluster_new < cluster_max; ++cluster_new)
    {
#if FAT_FAT32_SUPPORT
        if(is_fat32)
        {
            if(!device_read(fat_offset + cluster_new * sizeof(fat_entry32), (uint8_t*) &fat_entry32, sizeof(fat_entry32)))
                return 0;
        }
        else
#endif
        {
            if(!device_read(fat_offset + cluster_new * sizeof(fat_entry16), (uint8_t*) &fat_entry16, sizeof(fat_entry16)))
                return 0;
        }

#if FAT_FAT32_SUPPORT
        if(is_fat32)
        {
            /* check if this is a free cluster */
            if(fat_entry32 != HTOL32(FAT32_CLUSTER_FREE))
                continue;

            /* allocate cluster */
            if(cluster_next == 0)
                fat_entry32 = HTOL32(FAT32_CLUSTER_LAST_MAX);
            else
                fat_entry32 = htol32(cluster_next);

            if(!device_write(fat_offset + cluster_new * sizeof(fat_entry32), (uint8_t*) &fat_entry32, sizeof(fat_entry32)))
                break;
        }
        else
#endif
        {
            /* check if this is a free cluster */
            if(fat_entry16 != HTOL16(FAT16_CLUSTER_FREE))
                continue;

            /* allocate cluster */
            if(cluster_next == 0)
                fat_entry16 = HTOL16(FAT16_CLUSTER_LAST_MAX);
            else
                fat_entry16 = htol16((uint16_t) cluster_next);

            if(!device_write(fat_offset + cluster_new * sizeof(fat_entry16), (uint8_t*) &fat_entry16, sizeof(fat_entry16)))
                break;
        }

        cluster_next = cluster_new;
        if(--count_left == 0)
            break;
    }

    do
    {
        if(count_left > 0)
            break;

        /* We allocated a new cluster chain. Now join
         * it with the existing one (if any).
         */
        if(cluster_num >= 2)
        {
#if FAT_FAT32_SUPPORT
            if(is_fat32)
            {
                fat_entry32 = htol32(cluster_next);

                if(!device_write(fat_offset + cluster_num * sizeof(fat_entry32), (uint8_t*) &fat_entry32, sizeof(fat_entry32)))
                    break;
            }
            else
#endif
            {
                fat_entry16 = htol16((uint16_t) cluster_next);

                if(!device_write(fat_offset + cluster_num * sizeof(fat_entry16), (uint8_t*) &fat_entry16, sizeof(fat_entry16)))
                    break;
            }
        }

        return cluster_next;

    } while(0);

    /* No space left on device or writing error.
     * Free up all clusters already allocated.
     */
    fat_free_clusters(fs, cluster_next);

    return 0;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Frees a cluster chain, or a part thereof.
 *
 * Marks the specified cluster and all clusters which are sequentially
 * referenced by it as free. They may then be used again for future
 * file allocations.
 *
 * \note If this function is used for freeing just a part of a cluster
 *       chain, the new end of the chain is not correctly terminated
 *       within the FAT. Use fat_terminate_clusters() instead.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] cluster_num The starting cluster of the chain which to free.
 * \returns 0 on failure, 1 on success.
 * \see fat_terminate_clusters
 */
uint8_t fat_free_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num)
{
    if(!fs || cluster_num < 2)
        return 0;

    offset_t fat_offset = fs->header.fat_offset;
#if FAT_FAT32_SUPPORT
    if(fs->partition->type == PARTITION_TYPE_FAT32)
    {
        uint32_t fat_entry;
        while(cluster_num)
        {
            if(!fs->partition->device_read(fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
                return 0;

            /* get next cluster of current cluster before freeing current cluster */
            uint32_t cluster_num_next = ltoh32(fat_entry);

            if(cluster_num_next == FAT32_CLUSTER_FREE)
                return 1;
            if(cluster_num_next == FAT32_CLUSTER_BAD ||
               (cluster_num_next >= FAT32_CLUSTER_RESERVED_MIN &&
                cluster_num_next <= FAT32_CLUSTER_RESERVED_MAX
               )
              )
                return 0;
            if(cluster_num_next >= FAT32_CLUSTER_LAST_MIN && cluster_num_next <= FAT32_CLUSTER_LAST_MAX)
                cluster_num_next = 0;

            /* free cluster */
            fat_entry = HTOL32(FAT32_CLUSTER_FREE);
            fs->partition->device_write(fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry));

            /* We continue in any case here, even if freeing the cluster failed.
             * The cluster is lost, but maybe we can still free up some later ones.
             */

            cluster_num = cluster_num_next;
        }
    }
    else
#endif
    {
        uint16_t fat_entry;
        while(cluster_num)
        {
            if(!fs->partition->device_read(fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
                return 0;

            /* get next cluster of current cluster before freeing current cluster */
            uint16_t cluster_num_next = ltoh16(fat_entry);

            if(cluster_num_next == FAT16_CLUSTER_FREE)
                return 1;
            if(cluster_num_next == FAT16_CLUSTER_BAD ||
               (cluster_num_next >= FAT16_CLUSTER_RESERVED_MIN &&
                cluster_num_next <= FAT16_CLUSTER_RESERVED_MAX
               )
              )
                return 0;
            if(cluster_num_next >= FAT16_CLUSTER_LAST_MIN && cluster_num_next <= FAT16_CLUSTER_LAST_MAX)
                cluster_num_next = 0;

            /* free cluster */
            fat_entry = HTOL16(FAT16_CLUSTER_FREE);
            fs->partition->device_write(fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry));

            /* We continue in any case here, even if freeing the cluster failed.
             * The cluster is lost, but maybe we can still free up some later ones.
             */

            cluster_num = cluster_num_next;
        }
    }

    return 1;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Frees a part of a cluster chain and correctly terminates the rest.
 *
 * Marks the specified cluster as the new end of a cluster chain and
 * frees all following clusters.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] cluster_num The new end of the cluster chain.
 * \returns 0 on failure, 1 on success.
 * \see fat_free_clusters
 */
uint8_t fat_terminate_clusters(const struct fat_fs_struct* fs, cluster_t cluster_num)
{
    if(!fs || cluster_num < 2)
        return 0;

    /* fetch next cluster before overwriting the cluster entry */
    cluster_t cluster_num_next = fat_get_next_cluster(fs, cluster_num);

    /* mark cluster as the last one */
#if FAT_FAT32_SUPPORT
    if(fs->partition->type == PARTITION_TYPE_FAT32)
    {
        uint32_t fat_entry = HTOL32(FAT32_CLUSTER_LAST_MAX);
        if(!fs->partition->device_write(fs->header.fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
            return 0;
    }
    else
#endif
    {
        uint16_t fat_entry = HTOL16(FAT16_CLUSTER_LAST_MAX);
        if(!fs->partition->device_write(fs->header.fat_offset + cluster_num * sizeof(fat_entry), (uint8_t*) &fat_entry, sizeof(fat_entry)))
            return 0;
    }

    /* free remaining clusters */
    if(cluster_num_next)
        return fat_free_clusters(fs, cluster_num_next);
    else
        return 1;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Clears a single cluster.
 *
 * The complete cluster is filled with zeros.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] cluster_num The cluster to clear.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat_clear_cluster(const struct fat_fs_struct* fs, cluster_t cluster_num)
{
    if(cluster_num < 2)
        return 0;

    offset_t cluster_offset = fat_cluster_offset(fs, cluster_num);

    uint8_t zero[16];
    memset(zero, 0, sizeof(zero));
    return fs->partition->device_write_interval(cluster_offset,
                                                zero,
                                                fs->header.cluster_size,
                                                fat_clear_cluster_callback,
                                                0
                                               );
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Callback function for clearing a cluster.
 */
uintptr_t fat_clear_cluster_callback(uint8_t* buffer, offset_t offset, void* p)
{
    return 16;
}
#endif

/**
 * \ingroup fat_fs
 * Calculates the offset of the specified cluster.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] cluster_num The cluster whose offset to calculate.
 * \returns The cluster offset.
 */
offset_t fat_cluster_offset(const struct fat_fs_struct* fs, cluster_t cluster_num)
{
    if(!fs || cluster_num < 2)
        return 0;

    return fs->header.cluster_zero_offset + (offset_t) (cluster_num - 2) * fs->header.cluster_size;
}

/**
 * \ingroup fat_file
 * Retrieves the directory entry of a path.
 *
 * The given path may both describe a file or a directory.
 *
 * \param[in] fs The FAT filesystem on which to search.
 * \param[in] path The path of which to read the directory entry.
 * \param[out] dir_entry The directory entry to fill.
 * \returns 0 on failure, 1 on success.
 * \see fat_read_dir
 */
uint8_t fat_get_dir_entry_of_path(struct fat_fs_struct* fs, const char* path, struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !path || path[0] == '\0' || !dir_entry)
        return 0;

    if(path[0] == '/')
        ++path;

    /* begin with the root directory */
    memset(dir_entry, 0, sizeof(*dir_entry));
    dir_entry->attributes = FAT_ATTRIB_DIR;

    while(1)
    {
        if(path[0] == '\0')
            return 1;

        struct fat_dir_struct* dd = fat_open_dir(fs, dir_entry);
        if(!dd)
            break;

        /* extract the next hierarchy we will search for */
        const char* sub_path = strchr(path, '/');
        uint8_t length_to_sep;
        if(sub_path)
        {
            length_to_sep = sub_path - path;
            ++sub_path;
        }
        else
        {
            length_to_sep = strlen(path);
            sub_path = path + length_to_sep;
        }
        
        /* read directory entries */
        while(fat_read_dir(dd, dir_entry))
        {
            /* check if we have found the next hierarchy */
            if((strlen(dir_entry->long_name) != length_to_sep ||
                strncmp(path, dir_entry->long_name, length_to_sep) != 0))
                continue;

            fat_close_dir(dd);
            dd = 0;

            if(path[length_to_sep] == '\0')
                /* we iterated through the whole path and have found the file */
                return 1;

            if(dir_entry->attributes & FAT_ATTRIB_DIR)
            {
                /* we found a parent directory of the file we are searching for */
                path = sub_path;
                break;
            }

            /* a parent of the file exists, but not the file itself */
            return 0;
        }

        fat_close_dir(dd);
    }
    
    return 0;
}

/**
 * \ingroup fat_file
 * Opens a file on a FAT filesystem.
 *
 * \param[in] fs The filesystem on which the file to open lies.
 * \param[in] dir_entry The directory entry of the file to open.
 * \returns The file handle, or 0 on failure.
 * \see fat_close_file
 */
struct fat_file_struct* fat_open_file(struct fat_fs_struct* fs, const struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry || (dir_entry->attributes & FAT_ATTRIB_DIR))
        return 0;

#if USE_DYNAMIC_MEMORY
    struct fat_file_struct* fd = malloc(sizeof(*fd));
    if(!fd)
        return 0;
#else
    struct fat_file_struct* fd = fat_file_handles;
    uint8_t i;
    for(i = 0; i < FAT_FILE_COUNT; ++i)
    {
        if(!fd->fs)
            break;

        ++fd;
    }
    if(i >= FAT_FILE_COUNT)
        return 0;
#endif
    
    memcpy(&fd->dir_entry, dir_entry, sizeof(*dir_entry));
    fd->fs = fs;
    fd->pos = 0;
    fd->pos_cluster = dir_entry->cluster;

    return fd;
}

/**
 * \ingroup fat_file
 * Closes a file.
 *
 * \param[in] fd The file handle of the file to close.
 * \see fat_open_file
 */
void fat_close_file(struct fat_file_struct* fd)
{
    if(fd)
#if USE_DYNAMIC_MEMORY
        free(fd);
#else
        fd->fs = 0;
#endif
}

/**
 * \ingroup fat_file
 * Reads data from a file.
 * 
 * The data requested is read from the current file location.
 *
 * \param[in] fd The file handle of the file from which to read.
 * \param[out] buffer The buffer into which to write.
 * \param[in] buffer_len The amount of data to read.
 * \returns The number of bytes read, 0 on end of file, or -1 on failure.
 * \see fat_write_file
 */
intptr_t fat_read_file(struct fat_file_struct* fd, uint8_t* buffer, uintptr_t buffer_len)
{
    /* check arguments */
    if(!fd || !buffer || buffer_len < 1)
        return -1;

    /* determine number of bytes to read */
    if(fd->pos + buffer_len > fd->dir_entry.file_size)
        buffer_len = fd->dir_entry.file_size - fd->pos;
    if(buffer_len == 0)
        return 0;
    
    uint16_t cluster_size = fd->fs->header.cluster_size;
    cluster_t cluster_num = fd->pos_cluster;
    uintptr_t buffer_left = buffer_len;
    uint16_t first_cluster_offset = (uint16_t) (fd->pos & (cluster_size - 1));

    /* find cluster in which to start reading */
    if(!cluster_num)
    {
        cluster_num = fd->dir_entry.cluster;
        
        if(!cluster_num)
        {
            if(!fd->pos)
                return 0;
            else
                return -1;
        }

        if(fd->pos)
        {
            uint32_t pos = fd->pos;
            while(pos >= cluster_size)
            {
                pos -= cluster_size;
                cluster_num = fat_get_next_cluster(fd->fs, cluster_num);
                if(!cluster_num)
                    return -1;
            }
        }
    }
    
    /* read data */
    do
    {
        /* calculate data size to copy from cluster */
        offset_t cluster_offset = fat_cluster_offset(fd->fs, cluster_num) + first_cluster_offset;
        uint16_t copy_length = cluster_size - first_cluster_offset;
        if(copy_length > buffer_left)
            copy_length = buffer_left;

        /* read data */
        if(!fd->fs->partition->device_read(cluster_offset, buffer, copy_length))
            return buffer_len - buffer_left;

        /* calculate new file position */
        buffer += copy_length;
        buffer_left -= copy_length;
        fd->pos += copy_length;

        if(first_cluster_offset + copy_length >= cluster_size)
        {
            /* we are on a cluster boundary, so get the next cluster */
            if((cluster_num = fat_get_next_cluster(fd->fs, cluster_num)))
            {
                first_cluster_offset = 0;
            }
            else
            {
                fd->pos_cluster = 0;
                return buffer_len - buffer_left;
            }
        }

        fd->pos_cluster = cluster_num;

    } while(buffer_left > 0); /* check if we are done */

    return buffer_len;
}

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_file
 * Writes data to a file.
 * 
 * The data is written to the current file location.
 *
 * \param[in] fd The file handle of the file to which to write.
 * \param[in] buffer The buffer from which to read the data to be written.
 * \param[in] buffer_len The amount of data to write.
 * \returns The number of bytes written, 0 on disk full, or -1 on failure.
 * \see fat_read_file
 */
intptr_t fat_write_file(struct fat_file_struct* fd, const uint8_t* buffer, uintptr_t buffer_len)
{
    /* check arguments */
    if(!fd || !buffer || buffer_len < 1)
        return -1;
    if(fd->pos > fd->dir_entry.file_size)
        return -1;

    uint16_t cluster_size = fd->fs->header.cluster_size;
    cluster_t cluster_num = fd->pos_cluster;
    uintptr_t buffer_left = buffer_len;
    uint16_t first_cluster_offset = (uint16_t) (fd->pos & (cluster_size - 1));

    /* find cluster in which to start writing */
    if(!cluster_num)
    {
        cluster_num = fd->dir_entry.cluster;
        
        if(!cluster_num)
        {
            if(!fd->pos)
            {
                /* empty file */
                fd->dir_entry.cluster = cluster_num = fat_append_clusters(fd->fs, 0, 1);
                if(!cluster_num)
                    return -1;
            }
            else
            {
                return -1;
            }
        }

        if(fd->pos)
        {
            uint32_t pos = fd->pos;
            cluster_t cluster_num_next;
            while(pos >= cluster_size)
            {
                pos -= cluster_size;
                cluster_num_next = fat_get_next_cluster(fd->fs, cluster_num);
                if(!cluster_num_next && pos == 0)
                    /* the file exactly ends on a cluster boundary, and we append to it */
                    cluster_num_next = fat_append_clusters(fd->fs, cluster_num, 1);
                if(!cluster_num_next)
                    return -1;

                cluster_num = cluster_num_next;
            }
        }
    }
    
    /* write data */
    do
    {
        /* calculate data size to write to cluster */
        offset_t cluster_offset = fat_cluster_offset(fd->fs, cluster_num) + first_cluster_offset;
        uint16_t write_length = cluster_size - first_cluster_offset;
        if(write_length > buffer_left)
            write_length = buffer_left;

        /* write data which fits into the current cluster */
        if(!fd->fs->partition->device_write(cluster_offset, buffer, write_length))
            break;

        /* calculate new file position */
        buffer += write_length;
        buffer_left -= write_length;
        fd->pos += write_length;

        if(first_cluster_offset + write_length >= cluster_size)
        {
            /* we are on a cluster boundary, so get the next cluster */
            cluster_t cluster_num_next = fat_get_next_cluster(fd->fs, cluster_num);
            if(!cluster_num_next && buffer_left > 0)
                /* we reached the last cluster, append a new one */
                cluster_num_next = fat_append_clusters(fd->fs, cluster_num, 1);
            if(!cluster_num_next)
            {
                fd->pos_cluster = 0;
                break;
            }

            cluster_num = cluster_num_next;
            first_cluster_offset = 0;
        }

        fd->pos_cluster = cluster_num;

    } while(buffer_left > 0); /* check if we are done */

    /* update directory entry */
    if(fd->pos > fd->dir_entry.file_size)
    {
        uint32_t size_old = fd->dir_entry.file_size;

        /* update file size */
        fd->dir_entry.file_size = fd->pos;
        /* write directory entry */
        if(!fat_write_dir_entry(fd->fs, &fd->dir_entry))
        {
            /* We do not return an error here since we actually wrote
             * some data to disk. So we calculate the amount of data
             * we wrote to disk and which lies within the old file size.
             */
            buffer_left = fd->pos - size_old;
            fd->pos = size_old;
        }
    }

    return buffer_len - buffer_left;
}
#endif

/**
 * \ingroup fat_file
 * Repositions the read/write file offset.
 *
 * Changes the file offset where the next call to fat_read_file()
 * or fat_write_file() starts reading/writing.
 *
 * If the new offset is beyond the end of the file, fat_resize_file()
 * is implicitly called, i.e. the file is expanded.
 *
 * The new offset can be given in different ways determined by
 * the \c whence parameter:
 * - \b FAT_SEEK_SET: \c *offset is relative to the beginning of the file.
 * - \b FAT_SEEK_CUR: \c *offset is relative to the current file position.
 * - \b FAT_SEEK_END: \c *offset is relative to the end of the file.
 *
 * The resulting absolute offset is written to the location the \c offset
 * parameter points to.
 * 
 * \param[in] fd The file decriptor of the file on which to seek.
 * \param[in,out] offset A pointer to the new offset, as affected by the \c whence
 *                   parameter. The function writes the new absolute offset
 *                   to this location before it returns.
 * \param[in] whence Affects the way \c offset is interpreted, see above.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat_seek_file(struct fat_file_struct* fd, int32_t* offset, uint8_t whence)
{
    if(!fd || !offset)
        return 0;

    uint32_t new_pos = fd->pos;
    switch(whence)
    {
        case FAT_SEEK_SET:
            new_pos = *offset;
            break;
        case FAT_SEEK_CUR:
            new_pos += *offset;
            break;
        case FAT_SEEK_END:
            new_pos = fd->dir_entry.file_size + *offset;
            break;
        default:
            return 0;
    }

    if(new_pos > fd->dir_entry.file_size
#if FAT_WRITE_SUPPORT
       && !fat_resize_file(fd, new_pos)
#endif
       )
        return 0;

    fd->pos = new_pos;
    fd->pos_cluster = 0;

    *offset = (int32_t) new_pos;
    return 1;
}

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_file
 * Resizes a file to have a specific size.
 *
 * Enlarges or shrinks the file pointed to by the file descriptor to have
 * exactly the specified size.
 *
 * If the file is truncated, all bytes having an equal or larger offset
 * than the given size are lost. If the file is expanded, the additional
 * bytes are allocated.
 *
 * \note Please be aware that this function just allocates or deallocates disk
 * space, it does not explicitely clear it. To avoid data leakage, this
 * must be done manually.
 *
 * \param[in] fd The file decriptor of the file which to resize.
 * \param[in] size The new size of the file.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat_resize_file(struct fat_file_struct* fd, uint32_t size)
{
    if(!fd)
        return 0;

    cluster_t cluster_num = fd->dir_entry.cluster;
    uint16_t cluster_size = fd->fs->header.cluster_size;
    uint32_t size_new = size;

    do
    {
        if(cluster_num == 0 && size_new == 0)
            /* the file stays empty */
            break;

        /* seek to the next cluster as long as we need the space */
        while(size_new > cluster_size)
        {
            /* get next cluster of file */
            cluster_t cluster_num_next = fat_get_next_cluster(fd->fs, cluster_num);
            if(cluster_num_next)
            {
                cluster_num = cluster_num_next;
                size_new -= cluster_size;
            }
            else
            {
                break;
            }
        }

        if(size_new > cluster_size || cluster_num == 0)
        {
            /* Allocate new cluster chain and append
             * it to the existing one, if available.
             */
            cluster_t cluster_count = (size_new + cluster_size - 1) / cluster_size;
            cluster_t cluster_new_chain = fat_append_clusters(fd->fs, cluster_num, cluster_count);
            if(!cluster_new_chain)
                return 0;

            if(!cluster_num)
            {
                cluster_num = cluster_new_chain;
                fd->dir_entry.cluster = cluster_num;
            }
        }

        /* write new directory entry */
        fd->dir_entry.file_size = size;
        if(size == 0)
            fd->dir_entry.cluster = 0;
        if(!fat_write_dir_entry(fd->fs, &fd->dir_entry))
            return 0;

        if(size == 0)
        {
            /* free all clusters of file */
            fat_free_clusters(fd->fs, cluster_num);
        }
        else if(size_new <= cluster_size)
        {
            /* free all clusters no longer needed */
            fat_terminate_clusters(fd->fs, cluster_num);
        }

    } while(0);

    /* correct file position */
    if(size < fd->pos)
    {
        fd->pos = size;
        fd->pos_cluster = 0;
    }

    return 1;
}
#endif

/**
 * \ingroup fat_dir
 * Opens a directory.
 *
 * \param[in] fs The filesystem on which the directory to open resides.
 * \param[in] dir_entry The directory entry which stands for the directory to open.
 * \returns An opaque directory descriptor on success, 0 on failure.
 * \see fat_close_dir
 */
struct fat_dir_struct* fat_open_dir(struct fat_fs_struct* fs, const struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry || !(dir_entry->attributes & FAT_ATTRIB_DIR))
        return 0;

#if USE_DYNAMIC_MEMORY
    struct fat_dir_struct* dd = malloc(sizeof(*dd));
    if(!dd)
        return 0;
#else
    struct fat_dir_struct* dd = fat_dir_handles;
    uint8_t i;
    for(i = 0; i < FAT_DIR_COUNT; ++i)
    {
        if(!dd->fs)
            break;

        ++dd;
    }
    if(i >= FAT_DIR_COUNT)
        return 0;
#endif
    
    memcpy(&dd->dir_entry, dir_entry, sizeof(*dir_entry));
    dd->fs = fs;
    dd->entry_cluster = dir_entry->cluster;
    dd->entry_offset = 0;

    return dd;
}

/**
 * \ingroup fat_dir
 * Closes a directory descriptor.
 *
 * This function destroys a directory descriptor which was
 * previously obtained by calling fat_open_dir(). When this
 * function returns, the given descriptor will be invalid.
 *
 * \param[in] dd The directory descriptor to close.
 * \see fat_open_dir
 */
void fat_close_dir(struct fat_dir_struct* dd)
{
    if(dd)
#if USE_DYNAMIC_MEMORY
        free(dd);
#else
        dd->fs = 0;
#endif
}

/**
 * \ingroup fat_dir
 * Reads the next directory entry contained within a parent directory.
 *
 * \param[in] dd The descriptor of the parent directory from which to read the entry.
 * \param[out] dir_entry Pointer to a buffer into which to write the directory entry information.
 * \returns 0 on failure, 1 on success.
 * \see fat_reset_dir
 */
uint8_t fat_read_dir(struct fat_dir_struct* dd, struct fat_dir_entry_struct* dir_entry)
{
    if(!dd || !dir_entry)
        return 0;

    /* get current position of directory handle */
    struct fat_fs_struct* fs = dd->fs;
    const struct fat_header_struct* header = &fs->header;
    uint16_t cluster_size = header->cluster_size;
    cluster_t cluster_num = dd->entry_cluster;
    uint16_t cluster_offset = dd->entry_offset;
    struct fat_read_dir_callback_arg arg;

    /* reset directory entry */
    memset(dir_entry, 0, sizeof(*dir_entry));

    /* reset callback arguments */
    memset(&arg, 0, sizeof(arg));
    arg.dir_entry = dir_entry;

    /* check if we read from the root directory */
    if(cluster_num == 0)
    {
#if FAT_FAT32_SUPPORT
        if(fs->partition->type == PARTITION_TYPE_FAT32)
            cluster_num = header->root_dir_cluster;
        else
#endif
            cluster_size = header->cluster_zero_offset - header->root_dir_offset;
    }

    /* read entries */
    uint8_t buffer[32];
    while(!arg.finished)
    {
        /* read directory entries up to the cluster border */
        uint16_t cluster_left = cluster_size - cluster_offset;
        uint32_t pos = cluster_offset;
        if(cluster_num == 0)
            pos += header->root_dir_offset;
        else
            pos += fat_cluster_offset(fs, cluster_num);

        arg.bytes_read = 0;
        if(!fs->partition->device_read_interval(pos,
                                                buffer,
                                                sizeof(buffer),
                                                cluster_left,
                                                fat_dir_entry_read_callback,
                                                &arg)
          )
            return 0;

        cluster_offset += arg.bytes_read;

        if(cluster_offset >= cluster_size)
        {
            /* we reached the cluster border and switch to the next cluster */
            cluster_offset = 0;

            /* get number of next cluster */
            if(!(cluster_num = fat_get_next_cluster(fs, cluster_num)))
            {
                /* directory entry not found, reset directory handle */
                cluster_num = dd->dir_entry.cluster;
                break;
            }
        }
    }

    dd->entry_cluster = cluster_num;
    dd->entry_offset = cluster_offset;

    return dir_entry->long_name[0] != '\0' ? 1 : 0;
}

/**
 * \ingroup fat_dir
 * Resets a directory handle.
 *
 * Resets the directory handle such that reading restarts
 * with the first directory entry.
 *
 * \param[in] dd The directory handle to reset.
 * \returns 0 on failure, 1 on success.
 * \see fat_read_dir
 */
uint8_t fat_reset_dir(struct fat_dir_struct* dd)
{
    if(!dd)
        return 0;

    dd->entry_cluster = dd->dir_entry.cluster;
    dd->entry_offset = 0;
    return 1;
}

/**
 * \ingroup fat_fs
 * Callback function for reading a directory entry.
 */
uint8_t fat_dir_entry_read_callback(uint8_t* buffer, offset_t offset, void* p)
{
  struct fat_read_dir_callback_arg* arg = (fat_read_dir_callback_arg *)p;
    struct fat_dir_entry_struct* dir_entry = arg->dir_entry;

    arg->bytes_read += 32;

    /* skip deleted or empty entries */
    if(buffer[0] == FAT_DIRENTRY_DELETED || !buffer[0])
        return 1;

    if(!dir_entry->entry_offset)
        dir_entry->entry_offset = offset;
    
    switch(fat_interpret_dir_entry(dir_entry, buffer))
    {
        case 0: /* failure */
        {
            return 0;
        }
        case 1: /* buffer successfully parsed, continue */
        {
            return 1;
        }
        case 2: /* directory entry complete, finish */
        {
            arg->finished = 1;
            return 0;
        }
    }

    return 0;
}

/**
 * \ingroup fat_fs
 * Interprets a raw directory entry and puts the contained
 * information into the directory entry.
 * 
 * For a single file there may exist multiple directory
 * entries. All except the last one are lfn entries, which
 * contain parts of the long filename. The last directory
 * entry is a traditional 8.3 style one. It contains all
 * other information like size, cluster, date and time.
 * 
 * \param[in,out] dir_entry The directory entry to fill.
 * \param[in] raw_entry A pointer to 32 bytes of raw data.
 * \returns 0 on failure, 1 on success and 2 if the
 *          directory entry is complete.
 */
uint8_t fat_interpret_dir_entry(struct fat_dir_entry_struct* dir_entry, const uint8_t* raw_entry)
{
    if(!dir_entry || !raw_entry || !raw_entry[0])
        return 0;

    char* long_name = dir_entry->long_name;
    if(raw_entry[11] == 0x0f)
    {
        /* Lfn supports unicode, but we do not, for now.
         * So we assume pure ascii and read only every
         * second byte.
         */
        uint16_t char_offset = ((raw_entry[0] & 0x3f) - 1) * 13;
        const uint8_t char_mapping[] = { 1, 3, 5, 7, 9, 14, 16, 18, 20, 22, 24, 28, 30 };
        for(uint8_t i = 0; i <= 12 && char_offset + i < sizeof(dir_entry->long_name) - 1; ++i)
            long_name[char_offset + i] = raw_entry[char_mapping[i]];

        return 1;
    }
    else
    {
        /* if we do not have a long name, take the short one */
        if(long_name[0] == '\0')
        {
            uint8_t i;
            for(i = 0; i < 8; ++i)
            {
                if(raw_entry[i] == ' ')
                    break;
                long_name[i] = raw_entry[i];
            }
            if(long_name[0] == 0x05)
                long_name[0] = (char) FAT_DIRENTRY_DELETED;

            if(raw_entry[8] != ' ')
            {
                long_name[i++] = '.';

                uint8_t j = 8;
                for(; j < 11; ++j)
                {
                    if(raw_entry[j] != ' ')
                    {
                        long_name[i++] = raw_entry[j];
                    }
                    else
                    {
                        break;
                    }
                }
            } 

            long_name[i] = '\0';
        }
        
        /* extract properties of file and store them within the structure */
        dir_entry->attributes = raw_entry[11];
        dir_entry->cluster = ltoh16(*((uint16_t*) &raw_entry[26]));
#if FAT_FAT32_SUPPORT
        dir_entry->cluster |= ((cluster_t) ltoh16(*((uint16_t*) &raw_entry[20]))) << 16;
#endif
        dir_entry->file_size = ltoh32(*((uint32_t*) &raw_entry[28]));

#if FAT_DATETIME_SUPPORT
        dir_entry->modification_time = ltoh16(*((uint16_t*) &raw_entry[22]));
        dir_entry->modification_date = ltoh16(*((uint16_t*) &raw_entry[24]));
#endif

        return 2;
    }
}

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Searches for space where to store a directory entry.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] parent The directory in which to search.
 * \param[in] dir_entry The directory entry for which to search space.
 * \returns 0 on failure, a device offset on success.
 */
offset_t fat_find_offset_for_dir_entry(const struct fat_fs_struct* fs, const struct fat_dir_struct* parent, const struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry)
        return 0;

    /* search for a place where to write the directory entry to disk */
    uint8_t free_dir_entries_needed = (strlen(dir_entry->long_name) + 12) / 13 + 1;
    uint8_t free_dir_entries_found = 0;
    cluster_t cluster_num = parent->dir_entry.cluster;
    offset_t dir_entry_offset = 0;
    offset_t offset = 0;
    offset_t offset_to = 0;
#if FAT_FAT32_SUPPORT
    uint8_t is_fat32 = (fs->partition->type == PARTITION_TYPE_FAT32);
#endif

    if(cluster_num == 0)
    {
#if FAT_FAT32_SUPPORT
        if(is_fat32)
        {
            cluster_num = fs->header.root_dir_cluster;
        }
        else
#endif
        {
            /* we read/write from the root directory entry */
            offset = fs->header.root_dir_offset;
            offset_to = fs->header.cluster_zero_offset;
            dir_entry_offset = offset;
        }
    }
    
    while(1)
    {
        if(offset == offset_to)
        {
            if(cluster_num == 0)
                /* We iterated through the whole root directory and
                 * could not find enough space for the directory entry.
                 */
                return 0;

            if(offset)
            {
                /* We reached a cluster boundary and have to
                 * switch to the next cluster.
                 */

                cluster_t cluster_next = fat_get_next_cluster(fs, cluster_num);
                if(!cluster_next)
                {
                    cluster_next = fat_append_clusters(fs, cluster_num, 1);
                    if(!cluster_next)
                        return 0;

                    /* we appended a new cluster and know it is free */
                    dir_entry_offset = fs->header.cluster_zero_offset +
                                       (offset_t) (cluster_next - 2) * fs->header.cluster_size;

                    /* clear cluster to avoid garbage directory entries */
                    fat_clear_cluster(fs, cluster_next);

                    break;
                }
                cluster_num = cluster_next;
            }

            offset = fat_cluster_offset(fs, cluster_num);
            offset_to = offset + fs->header.cluster_size;
            dir_entry_offset = offset;
            free_dir_entries_found = 0;
        }
        
        /* read next lfn or 8.3 entry */
        uint8_t first_char;
        if(!fs->partition->device_read(offset, &first_char, sizeof(first_char)))
            return 0;

        /* check if we found a free directory entry */
        if(first_char == FAT_DIRENTRY_DELETED || !first_char)
        {
            /* check if we have the needed number of available entries */
            ++free_dir_entries_found;
            if(free_dir_entries_found >= free_dir_entries_needed)
                break;

            offset += 32;
        }
        else
        {
            offset += 32;
            dir_entry_offset = offset;
            free_dir_entries_found = 0;
        }
    }

    return dir_entry_offset;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_fs
 * Writes a directory entry to disk.
 *
 * \note The file name is not checked for invalid characters.
 *
 * \note The generation of the short 8.3 file name is quite
 * simple. The first eight characters are used for the filename.
 * The extension, if any, is made up of the first three characters
 * following the last dot within the long filename. If the
 * filename (without the extension) is longer than eight characters,
 * the lower byte of the cluster number replaces the last two
 * characters to avoid name clashes. In any other case, it is your
 * responsibility to avoid name clashes.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] dir_entry The directory entry to write.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat_write_dir_entry(const struct fat_fs_struct* fs, struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry)
        return 0;
    
#if FAT_DATETIME_SUPPORT
    {
        uint16_t year;
        uint8_t month;
        uint8_t day;
        uint8_t hour;
        uint8_t min;
        uint8_t sec;

        fat_get_datetime(&year, &month, &day, &hour, &min, &sec);
        fat_set_file_modification_date(dir_entry, year, month, day);
        fat_set_file_modification_time(dir_entry, hour, min, sec);
    }
#endif

    device_write_t device_write = fs->partition->device_write;
    offset_t offset = dir_entry->entry_offset;
    const char* name = dir_entry->long_name;
    uint8_t name_len = strlen(name);
    uint8_t lfn_entry_count = (name_len + 12) / 13;
    uint8_t buffer[32];

    /* write 8.3 entry */

    /* generate 8.3 file name */
    memset(&buffer[0], ' ', 11);
    char* name_ext = strrchr(name, '.');
    if(name_ext && *++name_ext)
    {
        uint8_t name_ext_len = strlen(name_ext);
        name_len -= name_ext_len + 1;

        if(name_ext_len > 3)
            name_ext_len = 3;
        
        memcpy(&buffer[8], name_ext, name_ext_len);
    }
    
    if(name_len <= 8)
    {
        memcpy(buffer, name, name_len);

        /* For now, we create lfn entries for all files,
         * except the "." and ".." directory references.
         * This is to avoid difficulties with capitalization,
         * as 8.3 filenames allow uppercase letters only.
         *
         * Theoretically it would be possible to leave
         * the 8.3 entry alone if the basename and the
         * extension have no mixed capitalization.
         */
        if(name[0] == '.' &&
           ((name[1] == '.' && name[2] == '\0') ||
            name[1] == '\0')
          )
            lfn_entry_count = 0;
    }
    else
    {
        memcpy(buffer, name, 8);

        /* Minimize 8.3 name clashes by appending
         * the lower byte of the cluster number.
         */
        uint8_t num = dir_entry->cluster & 0xff;

        buffer[6] = (num < 0xa0) ? ('0' + (num >> 4)) : ('a' + (num >> 4));
        num &= 0x0f;
        buffer[7] = (num < 0x0a) ? ('0' + num) : ('a' + num);
    }
    if(buffer[0] == FAT_DIRENTRY_DELETED)
        buffer[0] = 0x05;

    /* fill directory entry buffer */
    memset(&buffer[11], 0, sizeof(buffer) - 11);
    buffer[0x0b] = dir_entry->attributes;
#if FAT_DATETIME_SUPPORT
    *((uint16_t*) &buffer[0x16]) = htol16(dir_entry->modification_time);
    *((uint16_t*) &buffer[0x18]) = htol16(dir_entry->modification_date);
#endif
#if FAT_FAT32_SUPPORT
    *((uint16_t*) &buffer[0x14]) = htol16((uint16_t) (dir_entry->cluster >> 16));
#endif
    *((uint16_t*) &buffer[0x1a]) = htol16(dir_entry->cluster);
    *((uint32_t*) &buffer[0x1c]) = htol32(dir_entry->file_size);

    /* write to disk */
    if(!device_write(offset + (uint16_t) lfn_entry_count * 32, buffer, sizeof(buffer)))
        return 0;
    
    /* calculate checksum of 8.3 name */
    uint8_t checksum = buffer[0];
    for(uint8_t i = 1; i < 11; ++i)
        checksum = ((checksum >> 1) | (checksum << 7)) + buffer[i];
    
    /* write lfn entries */
    for(uint8_t lfn_entry = lfn_entry_count; lfn_entry > 0; --lfn_entry)
    {
        memset(buffer, 0xff, sizeof(buffer));
        
        /* set file name */
        const char* long_name_curr = name + (lfn_entry - 1) * 13;
        uint8_t i = 1;
        while(i < 0x1f)
        {
            buffer[i++] = *long_name_curr;
            buffer[i++] = 0;

            switch(i)
            {
                case 0x0b:
                    i = 0x0e;
                    break;
                case 0x1a:
                    i = 0x1c;
                    break;
            }

            if(!*long_name_curr++)
                break;
        }
        
        /* set index of lfn entry */
        buffer[0x00] = lfn_entry;
        if(lfn_entry == lfn_entry_count)
            buffer[0x00] |= FAT_DIRENTRY_LFNLAST;

        /* mark as lfn entry */
        buffer[0x0b] = 0x0f;

        /* set 8.3 checksum */
        buffer[0x0d] = checksum;

        /* clear reserved bytes */
        buffer[0x0c] = 0;
        buffer[0x1a] = 0;
        buffer[0x1b] = 0;

        /* write entry */
        device_write(offset, buffer, sizeof(buffer));
    
        offset += sizeof(buffer);
    }
    
    return 1;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_file
 * Creates a file.
 *
 * Creates a file and obtains the directory entry of the
 * new file. If the file to create already exists, the
 * directory entry of the existing file will be returned
 * within the dir_entry parameter.
 *
 * \note The file name is not checked for invalid characters.
 *
 * \note The generation of the short 8.3 file name is quite
 * simple. The first eight characters are used for the filename.
 * The extension, if any, is made up of the first three characters
 * following the last dot within the long filename. If the
 * filename (without the extension) is longer than eight characters,
 * the lower byte of the cluster number replaces the last two
 * characters to avoid name clashes. In any other case, it is your
 * responsibility to avoid name clashes.
 *
 * \param[in] parent The handle of the directory in which to create the file.
 * \param[in] file The name of the file to create.
 * \param[out] dir_entry The directory entry to fill for the new file.
 * \returns 0 on failure, 1 on success.
 * \see fat_delete_file
 */
uint8_t fat_create_file(struct fat_dir_struct* parent, const char* file, struct fat_dir_entry_struct* dir_entry)
{
    if(!parent || !file || !file[0] || !dir_entry)
        return 0;

    /* check if the file already exists */
    while(1)
    {
        if(!fat_read_dir(parent, dir_entry))
            break;

        if(strcmp(file, dir_entry->long_name) == 0)
        {
            fat_reset_dir(parent);
            return 0;
        }
    }

    struct fat_fs_struct* fs = parent->fs;

    /* prepare directory entry with values already known */
    memset(dir_entry, 0, sizeof(*dir_entry));
    strncpy(dir_entry->long_name, file, sizeof(dir_entry->long_name) - 1);

    /* find place where to store directory entry */
    if(!(dir_entry->entry_offset = fat_find_offset_for_dir_entry(fs, parent, dir_entry)))
        return 0;
    
    /* write directory entry to disk */
    if(!fat_write_dir_entry(fs, dir_entry))
        return 0;
    
    return 1;
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_file
 * Deletes a file or directory.
 *
 * If a directory is deleted without first deleting its
 * subdirectories and files, disk space occupied by these
 * files will get wasted as there is no chance to release
 * it and mark it as free.
 * 
 * \param[in] fs The filesystem on which to operate.
 * \param[in] dir_entry The directory entry of the file to delete.
 * \returns 0 on failure, 1 on success.
 * \see fat_create_file
 */
uint8_t fat_delete_file(struct fat_fs_struct* fs, struct fat_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry)
        return 0;

    /* get offset of the file's directory entry */
    offset_t dir_entry_offset = dir_entry->entry_offset;
    if(!dir_entry_offset)
        return 0;

    uint8_t buffer[12];
    while(1)
    {
        /* read directory entry */
        if(!fs->partition->device_read(dir_entry_offset, buffer, sizeof(buffer)))
            return 0;
        
        /* mark the directory entry as deleted */
        buffer[0] = FAT_DIRENTRY_DELETED;
        
        /* write back entry */
        if(!fs->partition->device_write(dir_entry_offset, buffer, sizeof(buffer)))
            return 0;

        /* check if we deleted the whole entry */
        if(buffer[11] != 0x0f)
            break;

        dir_entry_offset += 32;
    }

    /* We deleted the directory entry. The next thing to do is
     * marking all occupied clusters as free.
     */
    return (dir_entry->cluster == 0 || fat_free_clusters(fs, dir_entry->cluster));
}
#endif

#if DOXYGEN || FAT_WRITE_SUPPORT
/**
 * \ingroup fat_dir
 * Creates a directory.
 *
 * Creates a directory and obtains its directory entry.
 * If the directory to create already exists, its
 * directory entry will be returned within the dir_entry
 * parameter.
 *
 * \note The notes which apply to fat_create_file also
 * apply to this function.
 *
 * \param[in] parent The handle of the parent directory of the new directory.
 * \param[in] dir The name of the directory to create.
 * \param[out] dir_entry The directory entry to fill for the new directory.
 * \returns 0 on failure, 1 on success.
 * \see fat_delete_dir
 */
uint8_t fat_create_dir(struct fat_dir_struct* parent, const char* dir, struct fat_dir_entry_struct* dir_entry)
{
    if(!parent || !dir || !dir[0] || !dir_entry)
        return 0;

    /* check if the file or directory already exists */
    while(fat_read_dir(parent, dir_entry))
    {
        if(strcmp(dir, dir_entry->long_name) == 0)
        {
            fat_reset_dir(parent);
            return 0;
        }
    }

    struct fat_fs_struct* fs = parent->fs;

    /* allocate cluster which will hold directory entries */
    cluster_t dir_cluster = fat_append_clusters(fs, 0, 1);
    if(!dir_cluster)
        return 0;

    /* clear cluster to prevent bogus directory entries */
    fat_clear_cluster(fs, dir_cluster);
    
    memset(dir_entry, 0, sizeof(*dir_entry));
    dir_entry->attributes = FAT_ATTRIB_DIR;

    /* create "." directory self reference */
    dir_entry->entry_offset = fs->header.cluster_zero_offset +
                              (offset_t) (dir_cluster - 2) * fs->header.cluster_size;
    dir_entry->long_name[0] = '.';
    dir_entry->cluster = dir_cluster;
    if(!fat_write_dir_entry(fs, dir_entry))
    {
        fat_free_clusters(fs, dir_cluster);
        return 0;
    }

    /* create ".." parent directory reference */
    dir_entry->entry_offset += 32;
    dir_entry->long_name[1] = '.';
    dir_entry->cluster = parent->dir_entry.cluster;
    if(!fat_write_dir_entry(fs, dir_entry))
    {
        fat_free_clusters(fs, dir_cluster);
        return 0;
    }

    /* fill directory entry */
    strncpy(dir_entry->long_name, dir, sizeof(dir_entry->long_name) - 1);
    dir_entry->cluster = dir_cluster;

    /* find place where to store directory entry */
    if(!(dir_entry->entry_offset = fat_find_offset_for_dir_entry(fs, parent, dir_entry)))
    {
        fat_free_clusters(fs, dir_cluster);
        return 0;
    }

    /* write directory to disk */
    if(!fat_write_dir_entry(fs, dir_entry))
    {
        fat_free_clusters(fs, dir_cluster);
        return 0;
    }

    return 1;
}
#endif

/**
 * \ingroup fat_dir
 * Deletes a directory.
 *
 * This is just a synonym for fat_delete_file().
 * If a directory is deleted without first deleting its
 * subdirectories and files, disk space occupied by these
 * files will get wasted as there is no chance to release
 * it and mark it as free.
 * 
 * \param[in] fs The filesystem on which to operate.
 * \param[in] dir_entry The directory entry of the directory to delete.
 * \returns 0 on failure, 1 on success.
 * \see fat_create_dir
 */
#ifdef DOXYGEN
uint8_t fat_delete_dir(struct fat_fs_struct* fs, struct fat_dir_entry_struct* dir_entry);
#endif

#if DOXYGEN || FAT_DATETIME_SUPPORT
/**
 * \ingroup fat_file
 * Returns the modification date of a file.
 *
 * \param[in] dir_entry The directory entry of which to return the modification date.
 * \param[out] year The year the file was last modified.
 * \param[out] month The month the file was last modified.
 * \param[out] day The day the file was last modified.
 */
void fat_get_file_modification_date(const struct fat_dir_entry_struct* dir_entry, uint16_t* year, uint8_t* month, uint8_t* day)
{
    if(!dir_entry)
        return;

    *year = 1980 + ((dir_entry->modification_date >> 9) & 0x7f);
    *month = (dir_entry->modification_date >> 5) & 0x0f;
    *day = (dir_entry->modification_date >> 0) & 0x1f;
}
#endif

#if DOXYGEN || FAT_DATETIME_SUPPORT
/**
 * \ingroup fat_file
 * Returns the modification time of a file.
 *
 * \param[in] dir_entry The directory entry of which to return the modification time.
 * \param[out] hour The hour the file was last modified.
 * \param[out] min The min the file was last modified.
 * \param[out] sec The sec the file was last modified.
 */
void fat_get_file_modification_time(const struct fat_dir_entry_struct* dir_entry, uint8_t* hour, uint8_t* min, uint8_t* sec)
{
    if(!dir_entry)
        return;

    *hour = (dir_entry->modification_time >> 11) & 0x1f;
    *min = (dir_entry->modification_time >> 5) & 0x3f;
    *sec = ((dir_entry->modification_time >> 0) & 0x1f) * 2;
}
#endif

#if DOXYGEN || (FAT_WRITE_SUPPORT && FAT_DATETIME_SUPPORT)
/**
 * \ingroup fat_file
 * Sets the modification time of a date.
 *
 * \param[in] dir_entry The directory entry for which to set the modification date.
 * \param[in] year The year the file was last modified.
 * \param[in] month The month the file was last modified.
 * \param[in] day The day the file was last modified.
 */
void fat_set_file_modification_date(struct fat_dir_entry_struct* dir_entry, uint16_t year, uint8_t month, uint8_t day)
{
    if(!dir_entry)
        return;

    dir_entry->modification_date =
        ((year - 1980) << 9) |
        ((uint16_t) month << 5) |
        ((uint16_t) day << 0);
}
#endif

#if DOXYGEN || (FAT_WRITE_SUPPORT && FAT_DATETIME_SUPPORT)
/**
 * \ingroup fat_file
 * Sets the modification time of a file.
 *
 * \param[in] dir_entry The directory entry for which to set the modification time.
 * \param[in] hour The year the file was last modified.
 * \param[in] min The month the file was last modified.
 * \param[in] sec The day the file was last modified.
 */
void fat_set_file_modification_time(struct fat_dir_entry_struct* dir_entry, uint8_t hour, uint8_t min, uint8_t sec)
{
    if(!dir_entry)
        return;

    dir_entry->modification_time =
        ((uint16_t) hour << 11) |
        ((uint16_t) min << 5) |
        ((uint16_t) sec >> 1) ;
}
#endif

/**
 * \ingroup fat_fs
 * Returns the amount of total storage capacity of the filesystem in bytes.
 *
 * \param[in] fs The filesystem on which to operate.
 * \returns 0 on failure, the filesystem size in bytes otherwise.
 */
offset_t fat_get_fs_size(const struct fat_fs_struct* fs)
{
    if(!fs)
        return 0;

#if FAT_FAT32_SUPPORT
    if(fs->partition->type == PARTITION_TYPE_FAT32)
        return (offset_t) (fs->header.fat_size / 4 - 2) * fs->header.cluster_size;
    else
#endif
        return (offset_t) (fs->header.fat_size / 2 - 2) * fs->header.cluster_size;
}

/**
 * \ingroup fat_fs
 * Returns the amount of free storage capacity on the filesystem in bytes.
 *
 * \note As the FAT filesystem is cluster based, this function does not
 *       return continuous values but multiples of the cluster size.
 *
 * \param[in] fs The filesystem on which to operate.
 * \returns 0 on failure, the free filesystem space in bytes otherwise.
 */
offset_t fat_get_fs_free(const struct fat_fs_struct* fs)
{
    if(!fs)
        return 0;

    uint8_t fat[32];
    struct fat_usage_count_callback_arg count_arg;
    count_arg.cluster_count = 0;
    count_arg.buffer_size = sizeof(fat);

    offset_t fat_offset = fs->header.fat_offset;
    uint32_t fat_size = fs->header.fat_size;
    while(fat_size > 0)
    {
        uintptr_t length = UINT_MAX - 1;
        if(fat_size < length)
            length = fat_size;

        if(!fs->partition->device_read_interval(fat_offset,
                                                fat,
                                                sizeof(fat),
                                                length,
#if FAT_FAT32_SUPPORT
                                                (fs->partition->type == PARTITION_TYPE_FAT16) ?
                                                    fat_get_fs_free_16_callback :
                                                    fat_get_fs_free_32_callback,
#else
                                                fat_get_fs_free_16_callback,
#endif
                                                &count_arg
                                               )
          )
            return 0;

        fat_offset += length;
        fat_size -= length;
    }

    return (offset_t) count_arg.cluster_count * fs->header.cluster_size;
}

/**
 * \ingroup fat_fs
 * Callback function used for counting free clusters in a FAT.
 */
uint8_t fat_get_fs_free_16_callback(uint8_t* buffer, offset_t offset, void* p)
{
    struct fat_usage_count_callback_arg* count_arg = (struct fat_usage_count_callback_arg*) p;
    uintptr_t buffer_size = count_arg->buffer_size;

    for(uintptr_t i = 0; i < buffer_size; i += 2, buffer += 2)
    {
        uint16_t cluster = *((uint16_t*) &buffer[0]);
        if(cluster == HTOL16(FAT16_CLUSTER_FREE))
            ++(count_arg->cluster_count);
    }

    return 1;
}

#if DOXYGEN || FAT_FAT32_SUPPORT
/**
 * \ingroup fat_fs
 * Callback function used for counting free clusters in a FAT32.
 */
uint8_t fat_get_fs_free_32_callback(uint8_t* buffer, offset_t offset, void* p)
{
    struct fat_usage_count_callback_arg* count_arg = (struct fat_usage_count_callback_arg*) p;
    uintptr_t buffer_size = count_arg->buffer_size;

    for(uintptr_t i = 0; i < buffer_size; i += 4, buffer += 4)
    {
        uint32_t cluster = *((uint32_t*) &buffer[0]);
        if(cluster == HTOL32(FAT32_CLUSTER_FREE))
            ++(count_arg->cluster_count);
    }

    return 1;
}
#endif