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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 or disabled
60 for the filesystem with this option.
61 If 'uni_xlate' gets set, UTF-8 gets disabled.
62 By default, FAT_DEFAULT_UTF8 setting is used.
64 uni_xlate=<bool> -- Translate unhandled Unicode characters to special
65 escaped sequences. This would let you backup and
66 restore filenames that are created with any Unicode
67 characters. Until Linux supports Unicode for real,
68 this gives you an alternative. Without this option,
69 a '?' is used when no translation is possible. The
70 escape character is ':' because it is otherwise
71 illegal on the vfat filesystem. The escape sequence
72 that gets used is ':' and the four digits of hexadecimal
73 unicode.
75 nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will
76 end in '~1' or tilde followed by some number. If this
77 option is set, then if the filename is
78 "longfilename.txt" and "longfile.txt" does not
79 currently exist in the directory, 'longfile.txt' will
80 be the short alias instead of 'longfi~1.txt'.
82 usefree -- Use the "free clusters" value stored on FSINFO. It'll
83 be used to determine number of free clusters without
84 scanning disk. But it's not used by default, because
85 recent Windows don't update it correctly in some
86 case. If you are sure the "free clusters" on FSINFO is
87 correct, by this option you can avoid scanning disk.
89 quiet -- Stops printing certain warning messages.
91 check=s|r|n -- Case sensitivity checking setting.
92 s: strict, case sensitive
93 r: relaxed, case insensitive
94 n: normal, default setting, currently case insensitive
96 nocase -- This was deprecated for vfat. Use shortname=win95 instead.
98 shortname=lower|win95|winnt|mixed
99 -- Shortname display/create setting.
100 lower: convert to lowercase for display,
101 emulate the Windows 95 rule for create.
102 win95: emulate the Windows 95 rule for display/create.
103 winnt: emulate the Windows NT rule for display/create.
104 mixed: emulate the Windows NT rule for display,
105 emulate the Windows 95 rule for create.
106 Default setting is `mixed'.
108 tz=UTC -- Interpret timestamps as UTC rather than local time.
109 This option disables the conversion of timestamps
110 between local time (as used by Windows on FAT) and UTC
111 (which Linux uses internally). This is particularly
112 useful when mounting devices (like digital cameras)
113 that are set to UTC in order to avoid the pitfalls of
114 local time.
115 time_offset=minutes
116 -- Set offset for conversion of timestamps from local time
117 used by FAT to UTC. I.e. <minutes> minutes will be subtracted
118 from each timestamp to convert it to UTC used internally by
119 Linux. This is useful when time zone set in sys_tz is
120 not the time zone used by the filesystem. Note that this
121 option still does not provide correct time stamps in all
122 cases in presence of DST - time stamps in a different DST
123 setting will be off by one hour.
125 showexec -- If set, the execute permission bits of the file will be
126 allowed only if the extension part of the name is .EXE,
127 .COM, or .BAT. Not set by default.
129 debug -- Can be set, but unused by the current implementation.
131 sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
132 IMMUTABLE flag on Linux. Not set by default.
134 flush -- If set, the filesystem will try to flush to disk more
135 early than normal. Not set by default.
137 rodir -- FAT has the ATTR_RO (read-only) attribute. On Windows,
138 the ATTR_RO of the directory will just be ignored,
139 and is used only by applications as a flag (e.g. it's set
140 for the customized folder).
142 If you want to use ATTR_RO as read-only flag even for
143 the directory, set this option.
145 errors=panic|continue|remount-ro
146 -- specify FAT behavior on critical errors: panic, continue
147 without doing anything or remount the partition in
148 read-only mode (default behavior).
150 discard -- If set, issues discard/TRIM commands to the block
151 device when blocks are freed. This is useful for SSD devices
152 and sparse/thinly-provisoned LUNs.
154 nfs=stale_rw|nostale_ro
155 Enable this only if you want to export the FAT filesystem
156 over NFS.
158 stale_rw: This option maintains an index (cache) of directory
159 inodes by i_logstart which is used by the nfs-related code to
160 improve look-ups. Full file operations (read/write) over NFS is
161 supported but with cache eviction at NFS server, this could
162 result in ESTALE issues.
164 nostale_ro: This option bases the inode number and filehandle
165 on the on-disk location of a file in the MS-DOS directory entry.
166 This ensures that ESTALE will not be returned after a file is
167 evicted from the inode cache. However, it means that operations
168 such as rename, create and unlink could cause filehandles that
169 previously pointed at one file to point at a different file,
170 potentially causing data corruption. For this reason, this
171 option also mounts the filesystem readonly.
173 To maintain backward compatibility, '-o nfs' is also accepted,
174 defaulting to stale_rw
176 dos1xfloppy -- If set, use a fallback default BIOS Parameter Block
177 configuration, determined by backing device size. These static
178 parameters match defaults assumed by DOS 1.x for 160 kiB,
179 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
182 <bool>: 0,1,yes,no,true,false
184 LIMITATION
185 ---------------------------------------------------------------------
186 * The fallocated region of file is discarded at umount/evict time
187 when using fallocate with FALLOC_FL_KEEP_SIZE.
188 So, User should assume that fallocated region can be discarded at
189 last close if there is memory pressure resulting in eviction of
190 the inode from the memory. As a result, for any dependency on
191 the fallocated region, user should make sure to recheck fallocate
192 after reopening the file.
194 TODO
195 ----------------------------------------------------------------------
196 * Need to get rid of the raw scanning stuff. Instead, always use
197 a get next directory entry approach. The only thing left that uses
198 raw scanning is the directory renaming code.
201 POSSIBLE PROBLEMS
202 ----------------------------------------------------------------------
203 * vfat_valid_longname does not properly checked reserved names.
204 * When a volume name is the same as a directory name in the root
205 directory of the filesystem, the directory name sometimes shows
206 up as an empty file.
207 * autoconv option does not work correctly.
209 BUG REPORTS
210 ----------------------------------------------------------------------
211 If you have trouble with the VFAT filesystem, mail bug reports to
212 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
213 and the operation that gave you trouble.
215 TEST SUITE
216 ----------------------------------------------------------------------
217 If you plan to make any modifications to the vfat filesystem, please
218 get the test suite that comes with the vfat distribution at
220 http://web.archive.org/web/*/http://bmrc.berkeley.edu/
221 people/chaffee/vfat.html
223 This tests quite a few parts of the vfat filesystem and additional
224 tests for new features or untested features would be appreciated.
226 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
227 ----------------------------------------------------------------------
228 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
229 and lightly annotated by Gordon Chaffee).
231 This document presents a very rough, technical overview of my
232 knowledge of the extended FAT file system used in Windows NT 3.5 and
233 Windows 95. I don't guarantee that any of the following is correct,
234 but it appears to be so.
236 The extended FAT file system is almost identical to the FAT
237 file system used in DOS versions up to and including 6.223410239847
238 :-). The significant change has been the addition of long file names.
239 These names support up to 255 characters including spaces and lower
240 case characters as opposed to the traditional 8.3 short names.
242 Here is the description of the traditional FAT entry in the current
243 Windows 95 filesystem:
245 struct directory { // Short 8.3 names
246 unsigned char name[8]; // file name
247 unsigned char ext[3]; // file extension
248 unsigned char attr; // attribute byte
249 unsigned char lcase; // Case for base and extension
250 unsigned char ctime_ms; // Creation time, milliseconds
251 unsigned char ctime[2]; // Creation time
252 unsigned char cdate[2]; // Creation date
253 unsigned char adate[2]; // Last access date
254 unsigned char reserved[2]; // reserved values (ignored)
255 unsigned char time[2]; // time stamp
256 unsigned char date[2]; // date stamp
257 unsigned char start[2]; // starting cluster number
258 unsigned char size[4]; // size of the file
259 };
261 The lcase field specifies if the base and/or the extension of an 8.3
262 name should be capitalized. This field does not seem to be used by
263 Windows 95 but it is used by Windows NT. The case of filenames is not
264 completely compatible from Windows NT to Windows 95. It is not completely
265 compatible in the reverse direction, however. Filenames that fit in
266 the 8.3 namespace and are written on Windows NT to be lowercase will
267 show up as uppercase on Windows 95.
269 Note that the "start" and "size" values are actually little
270 endian integer values. The descriptions of the fields in this
271 structure are public knowledge and can be found elsewhere.
273 With the extended FAT system, Microsoft has inserted extra
274 directory entries for any files with extended names. (Any name which
275 legally fits within the old 8.3 encoding scheme does not have extra
276 entries.) I call these extra entries slots. Basically, a slot is a
277 specially formatted directory entry which holds up to 13 characters of
278 a file's extended name. Think of slots as additional labeling for the
279 directory entry of the file to which they correspond. Microsoft
280 prefers to refer to the 8.3 entry for a file as its alias and the
281 extended slot directory entries as the file name.
283 The C structure for a slot directory entry follows:
285 struct slot { // Up to 13 characters of a long name
286 unsigned char id; // sequence number for slot
287 unsigned char name0_4[10]; // first 5 characters in name
288 unsigned char attr; // attribute byte
289 unsigned char reserved; // always 0
290 unsigned char alias_checksum; // checksum for 8.3 alias
291 unsigned char name5_10[12]; // 6 more characters in name
292 unsigned char start[2]; // starting cluster number
293 unsigned char name11_12[4]; // last 2 characters in name
294 };
296 If the layout of the slots looks a little odd, it's only
297 because of Microsoft's efforts to maintain compatibility with old
298 software. The slots must be disguised to prevent old software from
299 panicking. To this end, a number of measures are taken:
301 1) The attribute byte for a slot directory entry is always set
302 to 0x0f. This corresponds to an old directory entry with
303 attributes of "hidden", "system", "read-only", and "volume
304 label". Most old software will ignore any directory
305 entries with the "volume label" bit set. Real volume label
306 entries don't have the other three bits set.
308 2) The starting cluster is always set to 0, an impossible
309 value for a DOS file.
311 Because the extended FAT system is backward compatible, it is
312 possible for old software to modify directory entries. Measures must
313 be taken to ensure the validity of slots. An extended FAT system can
314 verify that a slot does in fact belong to an 8.3 directory entry by
315 the following:
317 1) Positioning. Slots for a file always immediately proceed
318 their corresponding 8.3 directory entry. In addition, each
319 slot has an id which marks its order in the extended file
320 name. Here is a very abbreviated view of an 8.3 directory
321 entry and its corresponding long name slots for the file
322 "My Big File.Extension which is long":
324 <proceeding files...>
325 <slot #3, id = 0x43, characters = "h is long">
326 <slot #2, id = 0x02, characters = "xtension whic">
327 <slot #1, id = 0x01, characters = "My Big File.E">
328 <directory entry, name = "MYBIGFIL.EXT">
330 Note that the slots are stored from last to first. Slots
331 are numbered from 1 to N. The Nth slot is or'ed with 0x40
332 to mark it as the last one.
334 2) Checksum. Each slot has an "alias_checksum" value. The
335 checksum is calculated from the 8.3 name using the
336 following algorithm:
338 for (sum = i = 0; i < 11; i++) {
339 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
340 }
342 3) If there is free space in the final slot, a Unicode NULL (0x0000)
343 is stored after the final character. After that, all unused
344 characters in the final slot are set to Unicode 0xFFFF.
346 Finally, note that the extended name is stored in Unicode. Each Unicode
347 character takes two bytes.