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.
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
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,
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
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'.
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
51 shortname=lower|win95|winnt|mixed
52 -- Shortname display/create setting.
53 lower: convert to lowercase for display,
54 emulate the Windows 95 rule for create.
55 win95: emulate the Windows 95 rule for display/create.
56 winnt: emulate the Windows NT rule for display/create.
57 mixed: emulate the Windows NT rule for display,
58 emulate the Windows 95 rule for create.
59 Default setting is `lower'.
61 <bool>: 0,1,yes,no,true,false
64 ----------------------------------------------------------------------
65 * Need to get rid of the raw scanning stuff. Instead, always use
66 a get next directory entry approach. The only thing left that uses
67 raw scanning is the directory renaming code.
69 * Fix the POSIX filesystem support to work in 8.3 space. This involves
70 renaming aliases if a conflict occurs between a new filename and
71 an old alias. This is quite a mess.
75 ----------------------------------------------------------------------
76 * vfat_valid_longname does not properly checked reserved names.
77 * When a volume name is the same as a directory name in the root
78 directory of the filesystem, the directory name sometimes shows
80 * autoconv option does not work correctly.
83 ----------------------------------------------------------------------
84 If you have trouble with the VFAT filesystem, mail bug reports to
85 chaffee@bmrc.cs.berkeley.edu. Please specify the filename
86 and the operation that gave you trouble.
89 ----------------------------------------------------------------------
90 If you plan to make any modifications to the vfat filesystem, please
91 get the test suite that comes with the vfat distribution at
93 http://bmrc.berkeley.edu/people/chaffee/vfat.html
95 This tests quite a few parts of the vfat filesystem and additional
96 tests for new features or untested features would be appreciated.
98 NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
99 ----------------------------------------------------------------------
100 (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
101 and lightly annotated by Gordon Chaffee).
103 This document presents a very rough, technical overview of my
104 knowledge of the extended FAT file system used in Windows NT 3.5 and
105 Windows 95. I don't guarantee that any of the following is correct,
106 but it appears to be so.
108 The extended FAT file system is almost identical to the FAT
109 file system used in DOS versions up to and including 6.223410239847
110 :-). The significant change has been the addition of long file names.
111 These names support up to 255 characters including spaces and lower
112 case characters as opposed to the traditional 8.3 short names.
114 Here is the description of the traditional FAT entry in the current
115 Windows 95 filesystem:
117 struct directory { // Short 8.3 names
118 unsigned char name[8]; // file name
119 unsigned char ext[3]; // file extension
120 unsigned char attr; // attribute byte
121 unsigned char lcase; // Case for base and extension
122 unsigned char ctime_ms; // Creation time, milliseconds
123 unsigned char ctime[2]; // Creation time
124 unsigned char cdate[2]; // Creation date
125 unsigned char adate[2]; // Last access date
126 unsigned char reserved[2]; // reserved values (ignored)
127 unsigned char time[2]; // time stamp
128 unsigned char date[2]; // date stamp
129 unsigned char start[2]; // starting cluster number
130 unsigned char size[4]; // size of the file
133 The lcase field specifies if the base and/or the extension of an 8.3
134 name should be capitalized. This field does not seem to be used by
135 Windows 95 but it is used by Windows NT. The case of filenames is not
136 completely compatible from Windows NT to Windows 95. It is not completely
137 compatible in the reverse direction, however. Filenames that fit in
138 the 8.3 namespace and are written on Windows NT to be lowercase will
139 show up as uppercase on Windows 95.
141 Note that the "start" and "size" values are actually little
142 endian integer values. The descriptions of the fields in this
143 structure are public knowledge and can be found elsewhere.
145 With the extended FAT system, Microsoft has inserted extra
146 directory entries for any files with extended names. (Any name which
147 legally fits within the old 8.3 encoding scheme does not have extra
148 entries.) I call these extra entries slots. Basically, a slot is a
149 specially formatted directory entry which holds up to 13 characters of
150 a file's extended name. Think of slots as additional labeling for the
151 directory entry of the file to which they correspond. Microsoft
152 prefers to refer to the 8.3 entry for a file as its alias and the
153 extended slot directory entries as the file name.
155 The C structure for a slot directory entry follows:
157 struct slot { // Up to 13 characters of a long name
158 unsigned char id; // sequence number for slot
159 unsigned char name0_4[10]; // first 5 characters in name
160 unsigned char attr; // attribute byte
161 unsigned char reserved; // always 0
162 unsigned char alias_checksum; // checksum for 8.3 alias
163 unsigned char name5_10[12]; // 6 more characters in name
164 unsigned char start[2]; // starting cluster number
165 unsigned char name11_12[4]; // last 2 characters in name
168 If the layout of the slots looks a little odd, it's only
169 because of Microsoft's efforts to maintain compatibility with old
170 software. The slots must be disguised to prevent old software from
171 panicking. To this end, a number of measures are taken:
173 1) The attribute byte for a slot directory entry is always set
174 to 0x0f. This corresponds to an old directory entry with
175 attributes of "hidden", "system", "read-only", and "volume
176 label". Most old software will ignore any directory
177 entries with the "volume label" bit set. Real volume label
178 entries don't have the other three bits set.
180 2) The starting cluster is always set to 0, an impossible
181 value for a DOS file.
183 Because the extended FAT system is backward compatible, it is
184 possible for old software to modify directory entries. Measures must
185 be taken to ensure the validity of slots. An extended FAT system can
186 verify that a slot does in fact belong to an 8.3 directory entry by
189 1) Positioning. Slots for a file always immediately proceed
190 their corresponding 8.3 directory entry. In addition, each
191 slot has an id which marks its order in the extended file
192 name. Here is a very abbreviated view of an 8.3 directory
193 entry and its corresponding long name slots for the file
194 "My Big File.Extension which is long":
196 <proceeding files...>
197 <slot #3, id = 0x43, characters = "h is long">
198 <slot #2, id = 0x02, characters = "xtension whic">
199 <slot #1, id = 0x01, characters = "My Big File.E">
200 <directory entry, name = "MYBIGFIL.EXT">
202 Note that the slots are stored from last to first. Slots
203 are numbered from 1 to N. The Nth slot is or'ed with 0x40
204 to mark it as the last one.
206 2) Checksum. Each slot has an "alias_checksum" value. The
207 checksum is calculated from the 8.3 name using the
210 for (sum = i = 0; i < 11; i++) {
211 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
214 3) If there is free space in the final slot, a Unicode NULL (0x0000)
215 is stored after the final character. After that, all unused
216 characters in the final slot are set to Unicode 0xFFFF.
218 Finally, note that the extended name is stored in Unicode. Each Unicode
219 character takes two bytes.