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1 USING VFAT
2 ----------------------------------------------------------------------
3 To use the vfat filesystem, use the filesystem type 'vfat'. i.e.
4 mount -t vfat /dev/fd0 /mnt
5
6 No special partition formatter is required. mkdosfs will work fine
7 if you want to format from within Linux.
8
9 VFAT MOUNT OPTIONS
10 ----------------------------------------------------------------------
11 uid=### -- Set the owner of all files on this filesystem.
12 The default is the uid of current process.
13
14 gid=### -- Set the group of all files on this filesystem.
15 The default is the gid of current process.
16
17 umask=### -- The permission mask (for files and directories, see umask(1)).
18 The default is the umask of current process.
19
20 dmask=### -- The permission mask for the directory.
21 The default is the umask of current process.
22
23 fmask=### -- The permission mask for files.
24 The default is the umask of current process.
25
26 allow_utime=### -- This option controls the permission check of mtime/atime.
27
28 20 - If current process is in group of file's group ID,
29 you can change timestamp.
30 2 - Other users can change timestamp.
31
32 The default is set from `dmask' option. (If the directory is
33 writable, utime(2) is also allowed. I.e. ~dmask & 022)
34
35 Normally utime(2) checks current process is owner of
36 the file, or it has CAP_FOWNER capability. But FAT
37 filesystem doesn't have uid/gid on disk, so normal
38 check is too unflexible. With this option you can
39 relax it.
40
41 codepage=### -- Sets the codepage number for converting to shortname
42 characters on FAT filesystem.
43 By default, FAT_DEFAULT_CODEPAGE setting is used.
44
45 iocharset=<name> -- Character set to use for converting between the
46 encoding is used for user visible filename and 16 bit
47 Unicode characters. Long filenames are stored on disk
48 in Unicode format, but Unix for the most part doesn't
49 know how to deal with Unicode.
50 By default, FAT_DEFAULT_IOCHARSET setting is used.
51
52 There is also an option of doing UTF-8 translations
53 with the utf8 option.
54
55 NOTE: "iocharset=utf8" is not recommended. If unsure,
56 you should consider the following option instead.
57
58 utf8=<bool> -- UTF-8 is the filesystem safe version of Unicode that
59 is used by the console. It can be enabled for the
60 filesystem with this option. If 'uni_xlate' gets set,
61 UTF-8 gets disabled.
62
63 uni_xlate=<bool> -- Translate unhandled Unicode characters to special
64 escaped sequences. This would let you backup and
65 restore filenames that are created with any Unicode
66 characters. Until Linux supports Unicode for real,
67 this gives you an alternative. Without this option,
68 a '?' is used when no translation is possible. The
69 escape character is ':' because it is otherwise
70 illegal on the vfat filesystem. The escape sequence
71 that gets used is ':' and the four digits of hexadecimal
72 unicode.
73
74 nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will
75 end in '~1' or tilde followed by some number. If this
76 option is set, then if the filename is
77 "longfilename.txt" and "longfile.txt" does not
78 currently exist in the directory, 'longfile.txt' will
79 be the short alias instead of 'longfi~1.txt'.
80
81 usefree -- Use the "free clusters" value stored on FSINFO. It'll
82 be used to determine number of free clusters without
83 scanning disk. But it's not used by default, because
84 recent Windows don't update it correctly in some
85 case. If you are sure the "free clusters" on FSINFO is
86 correct, by this option you can avoid scanning disk.
87
88 quiet -- Stops printing certain warning messages.
89
90 check=s|r|n -- Case sensitivity checking setting.
91 s: strict, case sensitive
92 r: relaxed, case insensitive
93 n: normal, default setting, currently case insensitive
94
95 nocase -- This was deprecated for vfat. Use shortname=win95 instead.
96
97 shortname=lower|win95|winnt|mixed
98 -- Shortname display/create setting.
99 lower: convert to lowercase for display,
100 emulate the Windows 95 rule for create.
101 win95: emulate the Windows 95 rule for display/create.
102 winnt: emulate the Windows NT rule for display/create.
103 mixed: emulate the Windows NT rule for display,
104 emulate the Windows 95 rule for create.
105 Default setting is `mixed'.
106
107 tz=UTC -- Interpret timestamps as UTC rather than local time.
108 This option disables the conversion of timestamps
109 between local time (as used by Windows on FAT) and UTC
110 (which Linux uses internally). This is particularly
111 useful when mounting devices (like digital cameras)
112 that are set to UTC in order to avoid the pitfalls of
113 local time.
114 time_offset=minutes
115 -- Set offset for conversion of timestamps from local time
116 used by FAT to UTC. I.e. <minutes> minutes will be subtracted
117 from each timestamp to convert it to UTC used internally by
118 Linux. This is useful when time zone set in sys_tz is
119 not the time zone used by the filesystem. Note that this
120 option still does not provide correct time stamps in all
121 cases in presence of DST - time stamps in a different DST
122 setting will be off by one hour.
123
124 showexec -- If set, the execute permission bits of the file will be
125 allowed only if the extension part of the name is .EXE,
126 .COM, or .BAT. Not set by default.
127
128 debug -- Can be set, but unused by the current implementation.
129
130 sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
131 IMMUTABLE flag on Linux. Not set by default.
132
133 flush -- If set, the filesystem will try to flush to disk more
134 early than normal. Not set by default.
135
136 rodir -- FAT has the ATTR_RO (read-only) attribute. On Windows,
137 the ATTR_RO of the directory will just be ignored,
138 and is used only by applications as a flag (e.g. it's set
139 for the customized folder).
140
141 If you want to use ATTR_RO as read-only flag even for
142 the directory, set this option.
143
144 errors=panic|continue|remount-ro
145 -- specify FAT behavior on critical errors: panic, continue
146 without doing anything or remount the partition in
147 read-only mode (default behavior).
148
149 discard -- If set, issues discard/TRIM commands to the block
150 device when blocks are freed. This is useful for SSD devices
151 and sparse/thinly-provisoned LUNs.
152
153 nfs -- This option maintains an index (cache) of directory
154 inodes by i_logstart which is used by the nfs-related code to
155 improve look-ups.
156
157 Enable this only if you want to export the FAT filesystem
158 over NFS
159
160 <bool>: 0,1,yes,no,true,false
161
162 TODO
163 ----------------------------------------------------------------------
164 * Need to get rid of the raw scanning stuff. Instead, always use
165 a get next directory entry approach. The only thing left that uses
166 raw scanning is the directory renaming code.
167
168
169 POSSIBLE PROBLEMS
170 ----------------------------------------------------------------------
171 * vfat_valid_longname does not properly checked reserved names.
172 * When a volume name is the same as a directory name in the root
173 directory of the filesystem, the directory name sometimes shows
174 up as an empty file.
175 * autoconv option does not work correctly.
176
177 BUG REPORTS
178 ----------------------------------------------------------------------
179 If you have trouble with the VFAT filesystem, mail bug reports to
180 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
181 and the operation that gave you trouble.
182
183 TEST SUITE
184 ----------------------------------------------------------------------
185 If you plan to make any modifications to the vfat filesystem, please
186 get the test suite that comes with the vfat distribution at
187
188 http://web.archive.org/web/*/http://bmrc.berkeley.edu/
189 people/chaffee/vfat.html
190
191 This tests quite a few parts of the vfat filesystem and additional
192 tests for new features or untested features would be appreciated.
193
194 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
195 ----------------------------------------------------------------------
196 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
197 and lightly annotated by Gordon Chaffee).
198
199 This document presents a very rough, technical overview of my
200 knowledge of the extended FAT file system used in Windows NT 3.5 and
201 Windows 95. I don't guarantee that any of the following is correct,
202 but it appears to be so.
203
204 The extended FAT file system is almost identical to the FAT
205 file system used in DOS versions up to and including 6.223410239847
206 :-). The significant change has been the addition of long file names.
207 These names support up to 255 characters including spaces and lower
208 case characters as opposed to the traditional 8.3 short names.
209
210 Here is the description of the traditional FAT entry in the current
211 Windows 95 filesystem:
212
213 struct directory { // Short 8.3 names
214 unsigned char name[8]; // file name
215 unsigned char ext[3]; // file extension
216 unsigned char attr; // attribute byte
217 unsigned char lcase; // Case for base and extension
218 unsigned char ctime_ms; // Creation time, milliseconds
219 unsigned char ctime[2]; // Creation time
220 unsigned char cdate[2]; // Creation date
221 unsigned char adate[2]; // Last access date
222 unsigned char reserved[2]; // reserved values (ignored)
223 unsigned char time[2]; // time stamp
224 unsigned char date[2]; // date stamp
225 unsigned char start[2]; // starting cluster number
226 unsigned char size[4]; // size of the file
227 };
228
229 The lcase field specifies if the base and/or the extension of an 8.3
230 name should be capitalized. This field does not seem to be used by
231 Windows 95 but it is used by Windows NT. The case of filenames is not
232 completely compatible from Windows NT to Windows 95. It is not completely
233 compatible in the reverse direction, however. Filenames that fit in
234 the 8.3 namespace and are written on Windows NT to be lowercase will
235 show up as uppercase on Windows 95.
236
237 Note that the "start" and "size" values are actually little
238 endian integer values. The descriptions of the fields in this
239 structure are public knowledge and can be found elsewhere.
240
241 With the extended FAT system, Microsoft has inserted extra
242 directory entries for any files with extended names. (Any name which
243 legally fits within the old 8.3 encoding scheme does not have extra
244 entries.) I call these extra entries slots. Basically, a slot is a
245 specially formatted directory entry which holds up to 13 characters of
246 a file's extended name. Think of slots as additional labeling for the
247 directory entry of the file to which they correspond. Microsoft
248 prefers to refer to the 8.3 entry for a file as its alias and the
249 extended slot directory entries as the file name.
250
251 The C structure for a slot directory entry follows:
252
253 struct slot { // Up to 13 characters of a long name
254 unsigned char id; // sequence number for slot
255 unsigned char name0_4[10]; // first 5 characters in name
256 unsigned char attr; // attribute byte
257 unsigned char reserved; // always 0
258 unsigned char alias_checksum; // checksum for 8.3 alias
259 unsigned char name5_10[12]; // 6 more characters in name
260 unsigned char start[2]; // starting cluster number
261 unsigned char name11_12[4]; // last 2 characters in name
262 };
263
264 If the layout of the slots looks a little odd, it's only
265 because of Microsoft's efforts to maintain compatibility with old
266 software. The slots must be disguised to prevent old software from
267 panicking. To this end, a number of measures are taken:
268
269 1) The attribute byte for a slot directory entry is always set
270 to 0x0f. This corresponds to an old directory entry with
271 attributes of "hidden", "system", "read-only", and "volume
272 label". Most old software will ignore any directory
273 entries with the "volume label" bit set. Real volume label
274 entries don't have the other three bits set.
275
276 2) The starting cluster is always set to 0, an impossible
277 value for a DOS file.
278
279 Because the extended FAT system is backward compatible, it is
280 possible for old software to modify directory entries. Measures must
281 be taken to ensure the validity of slots. An extended FAT system can
282 verify that a slot does in fact belong to an 8.3 directory entry by
283 the following:
284
285 1) Positioning. Slots for a file always immediately proceed
286 their corresponding 8.3 directory entry. In addition, each
287 slot has an id which marks its order in the extended file
288 name. Here is a very abbreviated view of an 8.3 directory
289 entry and its corresponding long name slots for the file
290 "My Big File.Extension which is long":
291
292 <proceeding files...>
293 <slot #3, id = 0x43, characters = "h is long">
294 <slot #2, id = 0x02, characters = "xtension whic">
295 <slot #1, id = 0x01, characters = "My Big File.E">
296 <directory entry, name = "MYBIGFIL.EXT">
297
298 Note that the slots are stored from last to first. Slots
299 are numbered from 1 to N. The Nth slot is or'ed with 0x40
300 to mark it as the last one.
301
302 2) Checksum. Each slot has an "alias_checksum" value. The
303 checksum is calculated from the 8.3 name using the
304 following algorithm:
305
306 for (sum = i = 0; i < 11; i++) {
307 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
308 }
309
310 3) If there is free space in the final slot, a Unicode NULL (0x0000)
311 is stored after the final character. After that, all unused
312 characters in the final slot are set to Unicode 0xFFFF.
313
314 Finally, note that the extended name is stored in Unicode. Each Unicode
315 character takes two bytes.