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 codepage=### -- Sets the codepage for converting to shortname characters
12 on FAT and VFAT filesystems. By default, codepage 437
13 is used. This is the default for the U.S. and some
14 European countries.
15 iocharset=name -- Character set to use for converting between 8 bit characters
16 and 16 bit Unicode characters. Long filenames are stored on
17 disk in Unicode format, but Unix for the most part doesn't
18 know how to deal with Unicode. There is also an option of
19 doing UTF8 translations with the utf8 option.
20 utf8=<bool> -- UTF8 is the filesystem safe version of Unicode that
21 is used by the console. It can be be enabled for the
22 filesystem with this option. If 'uni_xlate' gets set,
23 UTF8 gets disabled.
24 uni_xlate=<bool> -- Translate unhandled Unicode characters to special
25 escaped sequences. This would let you backup and
26 restore filenames that are created with any Unicode
27 characters. Until Linux supports Unicode for real,
28 this gives you an alternative. Without this option,
29 a '?' is used when no translation is possible. The
30 escape character is ':' because it is otherwise
31 illegal on the vfat filesystem. The escape sequence
32 that gets used is ':' and the four digits of hexadecimal
33 unicode.
34 posix=<bool> -- Allow names of same letters, different case such as
35 'LongFileName' and 'longfilename' to coexist. This has some
36 problems currently because 8.3 conflicts are not handled
37 correctly for POSIX filesystem compliance.
38 nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will
39 end in '~1' or tilde followed by some number. If this
40 option is set, then if the filename is
41 "longfilename.txt" and "longfile.txt" does not
42 currently exist in the directory, 'longfile.txt' will
43 be the short alias instead of 'longfi~1.txt'.
44
45 quiet -- Stops printing certain warning messages.
46 check=s|r|n -- Case sensitivity checking setting.
47 s: strict, case sensitive
48 r: relaxed, case insensitive
49 n: normal, default setting, currently case insensitive
50
51 <bool>: 0,1,yes,no,true,false
52
53 TODO
54 ----------------------------------------------------------------------
55 * Need to get rid of the raw scanning stuff. Instead, always use
56 a get next directory entry approach. The only thing left that uses
57 raw scanning is the directory renaming code.
58
59 * Fix the POSIX filesystem support to work in 8.3 space. This involves
60 renaming aliases if a conflict occurs between a new filename and
61 an old alias. This is quite a mess.
62
63
64 POSSIBLE PROBLEMS
65 ----------------------------------------------------------------------
66 * vfat_valid_longname does not properly checked reserved names.
67 * When a volume name is the same as a directory name in the root
68 directory of the filesystem, the directory name sometimes shows
69 up as an empty file.
70 * autoconv option does not work correctly.
71
72 BUG REPORTS
73 ----------------------------------------------------------------------
74 If you have trouble with the VFAT filesystem, mail bug reports to
75 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
76 and the operation that gave you trouble.
77
78 TEST SUITE
79 ----------------------------------------------------------------------
80 If you plan to make any modifications to the vfat filesystem, please
81 get the test suite that comes with the vfat distribution at
82
83 http://bmrc.berkeley.edu/people/chaffee/vfat.html
84
85 This tests quite a few parts of the vfat filesystem and additional
86 tests for new features or untested features would be appreciated.
87
88 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
89 ----------------------------------------------------------------------
90 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
91 and lightly annotated by Gordon Chaffee).
92
93 This document presents a very rough, technical overview of my
94 knowledge of the extended FAT file system used in Windows NT 3.5 and
95 Windows 95. I don't guarantee that any of the following is correct,
96 but it appears to be so.
97
98 The extended FAT file system is almost identical to the FAT
99 file system used in DOS versions up to and including 6.223410239847
100 :-). The significant change has been the addition of long file names.
101 These names support up to 255 characters including spaces and lower
102 case characters as opposed to the traditional 8.3 short names.
103
104 Here is the description of the traditional FAT entry in the current
105 Windows 95 filesystem:
106
107 struct directory { // Short 8.3 names
108 unsigned char name[8]; // file name
109 unsigned char ext[3]; // file extension
110 unsigned char attr; // attribute byte
111 unsigned char lcase; // Case for base and extension
112 unsigned char ctime_ms; // Creation time, milliseconds
113 unsigned char ctime[2]; // Creation time
114 unsigned char cdate[2]; // Creation date
115 unsigned char adate[2]; // Last access date
116 unsigned char reserved[2]; // reserved values (ignored)
117 unsigned char time[2]; // time stamp
118 unsigned char date[2]; // date stamp
119 unsigned char start[2]; // starting cluster number
120 unsigned char size[4]; // size of the file
121 };
122
123 The lcase field specifies if the base and/or the extension of an 8.3
124 name should be capitalized. This field does not seem to be used by
125 Windows 95 but it is used by Windows NT. The case of filenames is not
126 completely compatible from Windows NT to Windows 95. It is not completely
127 compatible in the reverse direction, however. Filenames that fit in
128 the 8.3 namespace and are written on Windows NT to be lowercase will
129 show up as uppercase on Windows 95.
130
131 Note that the "start" and "size" values are actually little
132 endian integer values. The descriptions of the fields in this
133 structure are public knowledge and can be found elsewhere.
134
135 With the extended FAT system, Microsoft has inserted extra
136 directory entries for any files with extended names. (Any name which
137 legally fits within the old 8.3 encoding scheme does not have extra
138 entries.) I call these extra entries slots. Basically, a slot is a
139 specially formatted directory entry which holds up to 13 characters of
140 a file's extended name. Think of slots as additional labeling for the
141 directory entry of the file to which they correspond. Microsoft
142 prefers to refer to the 8.3 entry for a file as its alias and the
143 extended slot directory entries as the file name.
144
145 The C structure for a slot directory entry follows:
146
147 struct slot { // Up to 13 characters of a long name
148 unsigned char id; // sequence number for slot
149 unsigned char name0_4[10]; // first 5 characters in name
150 unsigned char attr; // attribute byte
151 unsigned char reserved; // always 0
152 unsigned char alias_checksum; // checksum for 8.3 alias
153 unsigned char name5_10[12]; // 6 more characters in name
154 unsigned char start[2]; // starting cluster number
155 unsigned char name11_12[4]; // last 2 characters in name
156 };
157
158 If the layout of the slots looks a little odd, it's only
159 because of Microsoft's efforts to maintain compatibility with old
160 software. The slots must be disguised to prevent old software from
161 panicking. To this end, a number of measures are taken:
162
163 1) The attribute byte for a slot directory entry is always set
164 to 0x0f. This corresponds to an old directory entry with
165 attributes of "hidden", "system", "read-only", and "volume
166 label". Most old software will ignore any directory
167 entries with the "volume label" bit set. Real volume label
168 entries don't have the other three bits set.
169
170 2) The starting cluster is always set to 0, an impossible
171 value for a DOS file.
172
173 Because the extended FAT system is backward compatible, it is
174 possible for old software to modify directory entries. Measures must
175 be taken to ensure the validity of slots. An extended FAT system can
176 verify that a slot does in fact belong to an 8.3 directory entry by
177 the following:
178
179 1) Positioning. Slots for a file always immediately proceed
180 their corresponding 8.3 directory entry. In addition, each
181 slot has an id which marks its order in the extended file
182 name. Here is a very abbreviated view of an 8.3 directory
183 entry and its corresponding long name slots for the file
184 "My Big File.Extension which is long":
185
186 <proceeding files...>
187 <slot #3, id = 0x43, characters = "h is long">
188 <slot #2, id = 0x02, characters = "xtension whic">
189 <slot #1, id = 0x01, characters = "My Big File.E">
190 <directory entry, name = "MYBIGFIL.EXT">
191
192 Note that the slots are stored from last to first. Slots
193 are numbered from 1 to N. The Nth slot is or'ed with 0x40
194 to mark it as the last one.
195
196 2) Checksum. Each slot has an "alias_checksum" value. The
197 checksum is calculated from the 8.3 name using the
198 following algorithm:
199
200 for (sum = i = 0; i < 11; i++) {
201 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
202 }
203
204 3) If there is free space in the final slot, a Unicode NULL (0x0000)
205 is stored after the final character. After that, all unused
206 characters in the final slot are set to Unicode 0xFFFF.
207
208 Finally, note that the extended name is stored in Unicode. Each Unicode
209 character takes two bytes.
This page was automatically generated by the
LXR engine.
Visit the LXR main site for more
information.