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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
6 No special partition formatter is required. mkdosfs will work fine
7 if you want to format from within Linux.
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.
14 gid=### -- Set the group of all files on this filesystem.
15 The default is the gid of current process.
17 umask=### -- The permission mask (for files and directories, see umask(1)).
18 The default is the umask of current process.
20 dmask=### -- The permission mask for the directory.
21 The default is the umask of current process.
23 fmask=### -- The permission mask for files.
24 The default is the umask of current process.
26 allow_utime=### -- This option controls the permission check of mtime/atime.
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.
32 The default is set from `dmask' option. (If the directory is
33 writable, utime(2) is also allowed. I.e. ~dmask & 022)
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.
41 codepage=### -- Sets the codepage number for converting to shortname
42 characters on FAT filesystem.
43 By default, FAT_DEFAULT_CODEPAGE setting is used.
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.
52 There is also an option of doing UTF-8 translations
53 with the utf8 option.
55 NOTE: "iocharset=utf8" is not recommended. If unsure,
56 you should consider the following option instead.
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.
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.
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'.
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.
88 quiet -- Stops printing certain warning messages.
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
95 nocase -- This was deprecated for vfat. Use shortname=win95 instead.
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'.
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.
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.
128 debug -- Can be set, but unused by the current implementation.
130 sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
131 IMMUTABLE flag on Linux. Not set by default.
133 flush -- If set, the filesystem will try to flush to disk more
134 early than normal. Not set by default.
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).
141 If you want to use ATTR_RO as read-only flag even for
142 the directory, set this option.
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).
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.
153 nfs=stale_rw|nostale_ro
154 Enable this only if you want to export the FAT filesystem
155 over NFS.
157 stale_rw: This option maintains an index (cache) of directory
158 inodes by i_logstart which is used by the nfs-related code to
159 improve look-ups. Full file operations (read/write) over NFS is
160 supported but with cache eviction at NFS server, this could
161 result in ESTALE issues.
163 nostale_ro: This option bases the inode number and filehandle
164 on the on-disk location of a file in the MS-DOS directory entry.
165 This ensures that ESTALE will not be returned after a file is
166 evicted from the inode cache. However, it means that operations
167 such as rename, create and unlink could cause filehandles that
168 previously pointed at one file to point at a different file,
169 potentially causing data corruption. For this reason, this
170 option also mounts the filesystem readonly.
172 To maintain backward compatibility, '-o nfs' is also accepted,
173 defaulting to stale_rw
176 <bool>: 0,1,yes,no,true,false
178 TODO
179 ----------------------------------------------------------------------
180 * Need to get rid of the raw scanning stuff. Instead, always use
181 a get next directory entry approach. The only thing left that uses
182 raw scanning is the directory renaming code.
185 POSSIBLE PROBLEMS
186 ----------------------------------------------------------------------
187 * vfat_valid_longname does not properly checked reserved names.
188 * When a volume name is the same as a directory name in the root
189 directory of the filesystem, the directory name sometimes shows
190 up as an empty file.
191 * autoconv option does not work correctly.
193 BUG REPORTS
194 ----------------------------------------------------------------------
195 If you have trouble with the VFAT filesystem, mail bug reports to
196 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
197 and the operation that gave you trouble.
199 TEST SUITE
200 ----------------------------------------------------------------------
201 If you plan to make any modifications to the vfat filesystem, please
202 get the test suite that comes with the vfat distribution at
204 http://web.archive.org/web/*/http://bmrc.berkeley.edu/
205 people/chaffee/vfat.html
207 This tests quite a few parts of the vfat filesystem and additional
208 tests for new features or untested features would be appreciated.
210 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
211 ----------------------------------------------------------------------
212 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
213 and lightly annotated by Gordon Chaffee).
215 This document presents a very rough, technical overview of my
216 knowledge of the extended FAT file system used in Windows NT 3.5 and
217 Windows 95. I don't guarantee that any of the following is correct,
218 but it appears to be so.
220 The extended FAT file system is almost identical to the FAT
221 file system used in DOS versions up to and including 6.223410239847
222 :-). The significant change has been the addition of long file names.
223 These names support up to 255 characters including spaces and lower
224 case characters as opposed to the traditional 8.3 short names.
226 Here is the description of the traditional FAT entry in the current
227 Windows 95 filesystem:
229 struct directory { // Short 8.3 names
230 unsigned char name[8]; // file name
231 unsigned char ext[3]; // file extension
232 unsigned char attr; // attribute byte
233 unsigned char lcase; // Case for base and extension
234 unsigned char ctime_ms; // Creation time, milliseconds
235 unsigned char ctime[2]; // Creation time
236 unsigned char cdate[2]; // Creation date
237 unsigned char adate[2]; // Last access date
238 unsigned char reserved[2]; // reserved values (ignored)
239 unsigned char time[2]; // time stamp
240 unsigned char date[2]; // date stamp
241 unsigned char start[2]; // starting cluster number
242 unsigned char size[4]; // size of the file
243 };
245 The lcase field specifies if the base and/or the extension of an 8.3
246 name should be capitalized. This field does not seem to be used by
247 Windows 95 but it is used by Windows NT. The case of filenames is not
248 completely compatible from Windows NT to Windows 95. It is not completely
249 compatible in the reverse direction, however. Filenames that fit in
250 the 8.3 namespace and are written on Windows NT to be lowercase will
251 show up as uppercase on Windows 95.
253 Note that the "start" and "size" values are actually little
254 endian integer values. The descriptions of the fields in this
255 structure are public knowledge and can be found elsewhere.
257 With the extended FAT system, Microsoft has inserted extra
258 directory entries for any files with extended names. (Any name which
259 legally fits within the old 8.3 encoding scheme does not have extra
260 entries.) I call these extra entries slots. Basically, a slot is a
261 specially formatted directory entry which holds up to 13 characters of
262 a file's extended name. Think of slots as additional labeling for the
263 directory entry of the file to which they correspond. Microsoft
264 prefers to refer to the 8.3 entry for a file as its alias and the
265 extended slot directory entries as the file name.
267 The C structure for a slot directory entry follows:
269 struct slot { // Up to 13 characters of a long name
270 unsigned char id; // sequence number for slot
271 unsigned char name0_4[10]; // first 5 characters in name
272 unsigned char attr; // attribute byte
273 unsigned char reserved; // always 0
274 unsigned char alias_checksum; // checksum for 8.3 alias
275 unsigned char name5_10[12]; // 6 more characters in name
276 unsigned char start[2]; // starting cluster number
277 unsigned char name11_12[4]; // last 2 characters in name
278 };
280 If the layout of the slots looks a little odd, it's only
281 because of Microsoft's efforts to maintain compatibility with old
282 software. The slots must be disguised to prevent old software from
283 panicking. To this end, a number of measures are taken:
285 1) The attribute byte for a slot directory entry is always set
286 to 0x0f. This corresponds to an old directory entry with
287 attributes of "hidden", "system", "read-only", and "volume
288 label". Most old software will ignore any directory
289 entries with the "volume label" bit set. Real volume label
290 entries don't have the other three bits set.
292 2) The starting cluster is always set to 0, an impossible
293 value for a DOS file.
295 Because the extended FAT system is backward compatible, it is
296 possible for old software to modify directory entries. Measures must
297 be taken to ensure the validity of slots. An extended FAT system can
298 verify that a slot does in fact belong to an 8.3 directory entry by
299 the following:
301 1) Positioning. Slots for a file always immediately proceed
302 their corresponding 8.3 directory entry. In addition, each
303 slot has an id which marks its order in the extended file
304 name. Here is a very abbreviated view of an 8.3 directory
305 entry and its corresponding long name slots for the file
306 "My Big File.Extension which is long":
308 <proceeding files...>
309 <slot #3, id = 0x43, characters = "h is long">
310 <slot #2, id = 0x02, characters = "xtension whic">
311 <slot #1, id = 0x01, characters = "My Big File.E">
312 <directory entry, name = "MYBIGFIL.EXT">
314 Note that the slots are stored from last to first. Slots
315 are numbered from 1 to N. The Nth slot is or'ed with 0x40
316 to mark it as the last one.
318 2) Checksum. Each slot has an "alias_checksum" value. The
319 checksum is calculated from the 8.3 name using the
320 following algorithm:
322 for (sum = i = 0; i < 11; i++) {
323 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
324 }
326 3) If there is free space in the final slot, a Unicode NULL (0x0000)
327 is stored after the final character. After that, all unused
328 characters in the final slot are set to Unicode 0xFFFF.
330 Finally, note that the extended name is stored in Unicode. Each Unicode
331 character takes two bytes.