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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.
115 showexec -- If set, the execute permission bits of the file will be
116 allowed only if the extension part of the name is .EXE,
117 .COM, or .BAT. Not set by default.
119 debug -- Can be set, but unused by the current implementation.
121 sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
122 IMMUTABLE flag on Linux. Not set by default.
124 flush -- If set, the filesystem will try to flush to disk more
125 early than normal. Not set by default.
127 rodir -- FAT has the ATTR_RO (read-only) attribute. On Windows,
128 the ATTR_RO of the directory will just be ignored,
129 and is used only by applications as a flag (e.g. it's set
130 for the customized folder).
132 If you want to use ATTR_RO as read-only flag even for
133 the directory, set this option.
135 errors=panic|continue|remount-ro
136 -- specify FAT behavior on critical errors: panic, continue
137 without doing anything or remount the partition in
138 read-only mode (default behavior).
140 <bool>: 0,1,yes,no,true,false
142 TODO
143 ----------------------------------------------------------------------
144 * Need to get rid of the raw scanning stuff. Instead, always use
145 a get next directory entry approach. The only thing left that uses
146 raw scanning is the directory renaming code.
149 POSSIBLE PROBLEMS
150 ----------------------------------------------------------------------
151 * vfat_valid_longname does not properly checked reserved names.
152 * When a volume name is the same as a directory name in the root
153 directory of the filesystem, the directory name sometimes shows
154 up as an empty file.
155 * autoconv option does not work correctly.
157 BUG REPORTS
158 ----------------------------------------------------------------------
159 If you have trouble with the VFAT filesystem, mail bug reports to
160 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
161 and the operation that gave you trouble.
163 TEST SUITE
164 ----------------------------------------------------------------------
165 If you plan to make any modifications to the vfat filesystem, please
166 get the test suite that comes with the vfat distribution at
168 http://bmrc.berkeley.edu/people/chaffee/vfat.html
170 This tests quite a few parts of the vfat filesystem and additional
171 tests for new features or untested features would be appreciated.
173 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
174 ----------------------------------------------------------------------
175 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
176 and lightly annotated by Gordon Chaffee).
178 This document presents a very rough, technical overview of my
179 knowledge of the extended FAT file system used in Windows NT 3.5 and
180 Windows 95. I don't guarantee that any of the following is correct,
181 but it appears to be so.
183 The extended FAT file system is almost identical to the FAT
184 file system used in DOS versions up to and including 6.223410239847
185 :-). The significant change has been the addition of long file names.
186 These names support up to 255 characters including spaces and lower
187 case characters as opposed to the traditional 8.3 short names.
189 Here is the description of the traditional FAT entry in the current
190 Windows 95 filesystem:
192 struct directory { // Short 8.3 names
193 unsigned char name[8]; // file name
194 unsigned char ext[3]; // file extension
195 unsigned char attr; // attribute byte
196 unsigned char lcase; // Case for base and extension
197 unsigned char ctime_ms; // Creation time, milliseconds
198 unsigned char ctime[2]; // Creation time
199 unsigned char cdate[2]; // Creation date
200 unsigned char adate[2]; // Last access date
201 unsigned char reserved[2]; // reserved values (ignored)
202 unsigned char time[2]; // time stamp
203 unsigned char date[2]; // date stamp
204 unsigned char start[2]; // starting cluster number
205 unsigned char size[4]; // size of the file
206 };
208 The lcase field specifies if the base and/or the extension of an 8.3
209 name should be capitalized. This field does not seem to be used by
210 Windows 95 but it is used by Windows NT. The case of filenames is not
211 completely compatible from Windows NT to Windows 95. It is not completely
212 compatible in the reverse direction, however. Filenames that fit in
213 the 8.3 namespace and are written on Windows NT to be lowercase will
214 show up as uppercase on Windows 95.
216 Note that the "start" and "size" values are actually little
217 endian integer values. The descriptions of the fields in this
218 structure are public knowledge and can be found elsewhere.
220 With the extended FAT system, Microsoft has inserted extra
221 directory entries for any files with extended names. (Any name which
222 legally fits within the old 8.3 encoding scheme does not have extra
223 entries.) I call these extra entries slots. Basically, a slot is a
224 specially formatted directory entry which holds up to 13 characters of
225 a file's extended name. Think of slots as additional labeling for the
226 directory entry of the file to which they correspond. Microsoft
227 prefers to refer to the 8.3 entry for a file as its alias and the
228 extended slot directory entries as the file name.
230 The C structure for a slot directory entry follows:
232 struct slot { // Up to 13 characters of a long name
233 unsigned char id; // sequence number for slot
234 unsigned char name0_4[10]; // first 5 characters in name
235 unsigned char attr; // attribute byte
236 unsigned char reserved; // always 0
237 unsigned char alias_checksum; // checksum for 8.3 alias
238 unsigned char name5_10[12]; // 6 more characters in name
239 unsigned char start[2]; // starting cluster number
240 unsigned char name11_12[4]; // last 2 characters in name
241 };
243 If the layout of the slots looks a little odd, it's only
244 because of Microsoft's efforts to maintain compatibility with old
245 software. The slots must be disguised to prevent old software from
246 panicking. To this end, a number of measures are taken:
248 1) The attribute byte for a slot directory entry is always set
249 to 0x0f. This corresponds to an old directory entry with
250 attributes of "hidden", "system", "read-only", and "volume
251 label". Most old software will ignore any directory
252 entries with the "volume label" bit set. Real volume label
253 entries don't have the other three bits set.
255 2) The starting cluster is always set to 0, an impossible
256 value for a DOS file.
258 Because the extended FAT system is backward compatible, it is
259 possible for old software to modify directory entries. Measures must
260 be taken to ensure the validity of slots. An extended FAT system can
261 verify that a slot does in fact belong to an 8.3 directory entry by
262 the following:
264 1) Positioning. Slots for a file always immediately proceed
265 their corresponding 8.3 directory entry. In addition, each
266 slot has an id which marks its order in the extended file
267 name. Here is a very abbreviated view of an 8.3 directory
268 entry and its corresponding long name slots for the file
269 "My Big File.Extension which is long":
271 <proceeding files...>
272 <slot #3, id = 0x43, characters = "h is long">
273 <slot #2, id = 0x02, characters = "xtension whic">
274 <slot #1, id = 0x01, characters = "My Big File.E">
275 <directory entry, name = "MYBIGFIL.EXT">
277 Note that the slots are stored from last to first. Slots
278 are numbered from 1 to N. The Nth slot is or'ed with 0x40
279 to mark it as the last one.
281 2) Checksum. Each slot has an "alias_checksum" value. The
282 checksum is calculated from the 8.3 name using the
283 following algorithm:
285 for (sum = i = 0; i < 11; i++) {
286 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
287 }
289 3) If there is free space in the final slot, a Unicode NULL (0x0000)
290 is stored after the final character. After that, all unused
291 characters in the final slot are set to Unicode 0xFFFF.
293 Finally, note that the extended name is stored in Unicode. Each Unicode
294 character takes two bytes.