blob: 223c32171dcc2b562ee0995a708e87ba1829cc8c [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001USING VFAT
2----------------------------------------------------------------------
3To use the vfat filesystem, use the filesystem type 'vfat'. i.e.
4 mount -t vfat /dev/fd0 /mnt
5
6No special partition formatter is required. mkdosfs will work fine
7if you want to format from within Linux.
8
9VFAT MOUNT OPTIONS
10----------------------------------------------------------------------
Bart Trojanowski8986ab52008-11-06 12:53:44 -080011uid=### -- Set the owner of all files on this filesystem.
12 The default is the uid of current process.
13
14gid=### -- Set the group of all files on this filesystem.
15 The default is the gid of current process.
16
Linus Torvalds1da177e2005-04-16 15:20:36 -070017umask=### -- The permission mask (for files and directories, see umask(1)).
18 The default is the umask of current process.
19
20dmask=### -- The permission mask for the directory.
21 The default is the umask of current process.
22
23fmask=### -- The permission mask for files.
24 The default is the umask of current process.
25
OGAWA Hirofumi1ae43f82008-04-28 02:16:26 -070026allow_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
Linus Torvalds1da177e2005-04-16 15:20:36 -070041codepage=### -- Sets the codepage number for converting to shortname
42 characters on FAT filesystem.
43 By default, FAT_DEFAULT_CODEPAGE setting is used.
44
Bart Trojanowski8986ab52008-11-06 12:53:44 -080045iocharset=<name> -- Character set to use for converting between the
Linus Torvalds1da177e2005-04-16 15:20:36 -070046 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
Alexey Dobriyan4de151d2006-03-22 00:13:35 +010052 There is also an option of doing UTF-8 translations
Linus Torvalds1da177e2005-04-16 15:20:36 -070053 with the utf8 option.
54
55 NOTE: "iocharset=utf8" is not recommended. If unsure,
56 you should consider the following option instead.
57
Alexey Dobriyan4de151d2006-03-22 00:13:35 +010058utf8=<bool> -- UTF-8 is the filesystem safe version of Unicode that
Paolo Ornati670e9f32006-10-03 22:57:56 +020059 is used by the console. It can be enabled for the
Linus Torvalds1da177e2005-04-16 15:20:36 -070060 filesystem with this option. If 'uni_xlate' gets set,
Alexey Dobriyan4de151d2006-03-22 00:13:35 +010061 UTF-8 gets disabled.
Linus Torvalds1da177e2005-04-16 15:20:36 -070062
63uni_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
74nonumtail=<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
OGAWA Hirofumi28ec0392007-05-08 00:31:01 -070081usefree -- 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
Linus Torvalds1da177e2005-04-16 15:20:36 -070088quiet -- Stops printing certain warning messages.
89
90check=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
Bart Trojanowski8986ab52008-11-06 12:53:44 -080095nocase -- This was deprecated for vfat. Use shortname=win95 instead.
96
Linus Torvalds1da177e2005-04-16 15:20:36 -070097shortname=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.
Paul Wise95523472009-08-01 21:30:31 +0900105 Default setting is `mixed'.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700106
Joe Peterson41003cd2008-07-25 01:46:48 -0700107tz=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
Bart Trojanowski8986ab52008-11-06 12:53:44 -0800110 (which Linux uses internally). This is particularly
Joe Peterson41003cd2008-07-25 01:46:48 -0700111 useful when mounting devices (like digital cameras)
112 that are set to UTC in order to avoid the pitfalls of
113 local time.
Jan Kara58156c82012-12-17 16:02:58 -0800114time_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.
Joe Peterson41003cd2008-07-25 01:46:48 -0700123
Bart Trojanowski8986ab52008-11-06 12:53:44 -0800124showexec -- 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
128debug -- Can be set, but unused by the current implementation.
129
130sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
131 IMMUTABLE flag on Linux. Not set by default.
132
133flush -- If set, the filesystem will try to flush to disk more
134 early than normal. Not set by default.
135
Matt LaPlante19f59462009-04-27 15:06:31 +0200136rodir -- 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).
OGAWA Hirofumidfc209c2008-11-06 12:53:55 -0800140
141 If you want to use ATTR_RO as read-only flag even for
142 the directory, set this option.
143
Denis Karpov85c78592009-06-04 02:34:22 +0900144errors=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
Namjae Jeond65226e2012-08-21 16:15:46 -0700149discard -- 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
Namjae Jeon27cf10e2013-04-29 16:21:15 -0700153nfs=stale_rw|nostale_ro
154 Enable this only if you want to export the FAT filesystem
155 over NFS.
Namjae Jeond65226e2012-08-21 16:15:46 -0700156
Namjae Jeon27cf10e2013-04-29 16:21:15 -0700157 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.
162
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.
171
172 To maintain backward compatibility, '-o nfs' is also accepted,
173 defaulting to stale_rw
174
Conrad Meyer190a8842014-06-06 14:36:37 -0700175dos1xfloppy -- If set, use a fallback default BIOS Parameter Block
176 configuration, determined by backing device size. These static
177 parameters match defaults assumed by DOS 1.x for 160 kiB,
178 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
179
Namjae Jeond65226e2012-08-21 16:15:46 -0700180
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181<bool>: 0,1,yes,no,true,false
182
Namjae Jeon28016122016-01-20 14:59:49 -0800183LIMITATION
184---------------------------------------------------------------------
185* The fallocated region of file is discarded at umount/evict time
186 when using fallocate with FALLOC_FL_KEEP_SIZE.
187 So, User should assume that fallocated region can be discarded at
188 last close if there is memory pressure resulting in eviction of
189 the inode from the memory. As a result, for any dependency on
190 the fallocated region, user should make sure to recheck fallocate
191 after reopening the file.
192
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193TODO
194----------------------------------------------------------------------
195* Need to get rid of the raw scanning stuff. Instead, always use
196 a get next directory entry approach. The only thing left that uses
197 raw scanning is the directory renaming code.
198
199
200POSSIBLE PROBLEMS
201----------------------------------------------------------------------
202* vfat_valid_longname does not properly checked reserved names.
203* When a volume name is the same as a directory name in the root
204 directory of the filesystem, the directory name sometimes shows
205 up as an empty file.
206* autoconv option does not work correctly.
207
208BUG REPORTS
209----------------------------------------------------------------------
210If you have trouble with the VFAT filesystem, mail bug reports to
211chaffee@bmrc.cs.berkeley.edu. Please specify the filename
212and the operation that gave you trouble.
213
214TEST SUITE
215----------------------------------------------------------------------
216If you plan to make any modifications to the vfat filesystem, please
217get the test suite that comes with the vfat distribution at
218
Justin P. Mattock0ea6e612010-07-23 20:51:24 -0700219 http://web.archive.org/web/*/http://bmrc.berkeley.edu/
220 people/chaffee/vfat.html
Linus Torvalds1da177e2005-04-16 15:20:36 -0700221
222This tests quite a few parts of the vfat filesystem and additional
223tests for new features or untested features would be appreciated.
224
225NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
226----------------------------------------------------------------------
227(This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
228 and lightly annotated by Gordon Chaffee).
229
230This document presents a very rough, technical overview of my
231knowledge of the extended FAT file system used in Windows NT 3.5 and
232Windows 95. I don't guarantee that any of the following is correct,
233but it appears to be so.
234
235The extended FAT file system is almost identical to the FAT
236file system used in DOS versions up to and including 6.223410239847
237:-). The significant change has been the addition of long file names.
238These names support up to 255 characters including spaces and lower
239case characters as opposed to the traditional 8.3 short names.
240
241Here is the description of the traditional FAT entry in the current
242Windows 95 filesystem:
243
244 struct directory { // Short 8.3 names
245 unsigned char name[8]; // file name
246 unsigned char ext[3]; // file extension
247 unsigned char attr; // attribute byte
248 unsigned char lcase; // Case for base and extension
249 unsigned char ctime_ms; // Creation time, milliseconds
250 unsigned char ctime[2]; // Creation time
251 unsigned char cdate[2]; // Creation date
252 unsigned char adate[2]; // Last access date
253 unsigned char reserved[2]; // reserved values (ignored)
254 unsigned char time[2]; // time stamp
255 unsigned char date[2]; // date stamp
256 unsigned char start[2]; // starting cluster number
257 unsigned char size[4]; // size of the file
258 };
259
260The lcase field specifies if the base and/or the extension of an 8.3
261name should be capitalized. This field does not seem to be used by
262Windows 95 but it is used by Windows NT. The case of filenames is not
263completely compatible from Windows NT to Windows 95. It is not completely
264compatible in the reverse direction, however. Filenames that fit in
265the 8.3 namespace and are written on Windows NT to be lowercase will
266show up as uppercase on Windows 95.
267
268Note that the "start" and "size" values are actually little
269endian integer values. The descriptions of the fields in this
270structure are public knowledge and can be found elsewhere.
271
272With the extended FAT system, Microsoft has inserted extra
273directory entries for any files with extended names. (Any name which
274legally fits within the old 8.3 encoding scheme does not have extra
275entries.) I call these extra entries slots. Basically, a slot is a
276specially formatted directory entry which holds up to 13 characters of
277a file's extended name. Think of slots as additional labeling for the
278directory entry of the file to which they correspond. Microsoft
279prefers to refer to the 8.3 entry for a file as its alias and the
280extended slot directory entries as the file name.
281
282The C structure for a slot directory entry follows:
283
284 struct slot { // Up to 13 characters of a long name
285 unsigned char id; // sequence number for slot
286 unsigned char name0_4[10]; // first 5 characters in name
287 unsigned char attr; // attribute byte
288 unsigned char reserved; // always 0
289 unsigned char alias_checksum; // checksum for 8.3 alias
290 unsigned char name5_10[12]; // 6 more characters in name
291 unsigned char start[2]; // starting cluster number
292 unsigned char name11_12[4]; // last 2 characters in name
293 };
294
295If the layout of the slots looks a little odd, it's only
296because of Microsoft's efforts to maintain compatibility with old
297software. The slots must be disguised to prevent old software from
298panicking. To this end, a number of measures are taken:
299
300 1) The attribute byte for a slot directory entry is always set
301 to 0x0f. This corresponds to an old directory entry with
302 attributes of "hidden", "system", "read-only", and "volume
303 label". Most old software will ignore any directory
304 entries with the "volume label" bit set. Real volume label
305 entries don't have the other three bits set.
306
307 2) The starting cluster is always set to 0, an impossible
308 value for a DOS file.
309
310Because the extended FAT system is backward compatible, it is
311possible for old software to modify directory entries. Measures must
312be taken to ensure the validity of slots. An extended FAT system can
313verify that a slot does in fact belong to an 8.3 directory entry by
314the following:
315
316 1) Positioning. Slots for a file always immediately proceed
317 their corresponding 8.3 directory entry. In addition, each
318 slot has an id which marks its order in the extended file
319 name. Here is a very abbreviated view of an 8.3 directory
320 entry and its corresponding long name slots for the file
321 "My Big File.Extension which is long":
322
323 <proceeding files...>
324 <slot #3, id = 0x43, characters = "h is long">
Luis Ortega Perez de Villar965fd292013-11-12 15:11:10 -0800325 <slot #2, id = 0x02, characters = "xtension whic">
Linus Torvalds1da177e2005-04-16 15:20:36 -0700326 <slot #1, id = 0x01, characters = "My Big File.E">
327 <directory entry, name = "MYBIGFIL.EXT">
328
329 Note that the slots are stored from last to first. Slots
330 are numbered from 1 to N. The Nth slot is or'ed with 0x40
331 to mark it as the last one.
332
333 2) Checksum. Each slot has an "alias_checksum" value. The
334 checksum is calculated from the 8.3 name using the
335 following algorithm:
336
337 for (sum = i = 0; i < 11; i++) {
338 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
339 }
340
341 3) If there is free space in the final slot, a Unicode NULL (0x0000)
342 is stored after the final character. After that, all unused
343 characters in the final slot are set to Unicode 0xFFFF.
344
345Finally, note that the extended name is stored in Unicode. Each Unicode
346character takes two bytes.