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1da177e4 LT |
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 | umask=### -- The permission mask (for files and directories, see umask(1)). | |
12 | The default is the umask of current process. | |
13 | ||
14 | dmask=### -- The permission mask for the directory. | |
15 | The default is the umask of current process. | |
16 | ||
17 | fmask=### -- The permission mask for files. | |
18 | The default is the umask of current process. | |
19 | ||
20 | codepage=### -- Sets the codepage number for converting to shortname | |
21 | characters on FAT filesystem. | |
22 | By default, FAT_DEFAULT_CODEPAGE setting is used. | |
23 | ||
24 | iocharset=name -- Character set to use for converting between the | |
25 | encoding is used for user visible filename and 16 bit | |
26 | Unicode characters. Long filenames are stored on disk | |
27 | in Unicode format, but Unix for the most part doesn't | |
28 | know how to deal with Unicode. | |
29 | By default, FAT_DEFAULT_IOCHARSET setting is used. | |
30 | ||
31 | There is also an option of doing UTF8 translations | |
32 | with the utf8 option. | |
33 | ||
34 | NOTE: "iocharset=utf8" is not recommended. If unsure, | |
35 | you should consider the following option instead. | |
36 | ||
37 | utf8=<bool> -- UTF8 is the filesystem safe version of Unicode that | |
38 | is used by the console. It can be be enabled for the | |
39 | filesystem with this option. If 'uni_xlate' gets set, | |
40 | UTF8 gets disabled. | |
41 | ||
42 | uni_xlate=<bool> -- Translate unhandled Unicode characters to special | |
43 | escaped sequences. This would let you backup and | |
44 | restore filenames that are created with any Unicode | |
45 | characters. Until Linux supports Unicode for real, | |
46 | this gives you an alternative. Without this option, | |
47 | a '?' is used when no translation is possible. The | |
48 | escape character is ':' because it is otherwise | |
49 | illegal on the vfat filesystem. The escape sequence | |
50 | that gets used is ':' and the four digits of hexadecimal | |
51 | unicode. | |
52 | ||
53 | nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will | |
54 | end in '~1' or tilde followed by some number. If this | |
55 | option is set, then if the filename is | |
56 | "longfilename.txt" and "longfile.txt" does not | |
57 | currently exist in the directory, 'longfile.txt' will | |
58 | be the short alias instead of 'longfi~1.txt'. | |
59 | ||
60 | quiet -- Stops printing certain warning messages. | |
61 | ||
62 | check=s|r|n -- Case sensitivity checking setting. | |
63 | s: strict, case sensitive | |
64 | r: relaxed, case insensitive | |
65 | n: normal, default setting, currently case insensitive | |
66 | ||
67 | shortname=lower|win95|winnt|mixed | |
68 | -- Shortname display/create setting. | |
69 | lower: convert to lowercase for display, | |
70 | emulate the Windows 95 rule for create. | |
71 | win95: emulate the Windows 95 rule for display/create. | |
72 | winnt: emulate the Windows NT rule for display/create. | |
73 | mixed: emulate the Windows NT rule for display, | |
74 | emulate the Windows 95 rule for create. | |
75 | Default setting is `lower'. | |
76 | ||
77 | <bool>: 0,1,yes,no,true,false | |
78 | ||
79 | TODO | |
80 | ---------------------------------------------------------------------- | |
81 | * Need to get rid of the raw scanning stuff. Instead, always use | |
82 | a get next directory entry approach. The only thing left that uses | |
83 | raw scanning is the directory renaming code. | |
84 | ||
85 | ||
86 | POSSIBLE PROBLEMS | |
87 | ---------------------------------------------------------------------- | |
88 | * vfat_valid_longname does not properly checked reserved names. | |
89 | * When a volume name is the same as a directory name in the root | |
90 | directory of the filesystem, the directory name sometimes shows | |
91 | up as an empty file. | |
92 | * autoconv option does not work correctly. | |
93 | ||
94 | BUG REPORTS | |
95 | ---------------------------------------------------------------------- | |
96 | If you have trouble with the VFAT filesystem, mail bug reports to | |
97 | chaffee@bmrc.cs.berkeley.edu. Please specify the filename | |
98 | and the operation that gave you trouble. | |
99 | ||
100 | TEST SUITE | |
101 | ---------------------------------------------------------------------- | |
102 | If you plan to make any modifications to the vfat filesystem, please | |
103 | get the test suite that comes with the vfat distribution at | |
104 | ||
105 | http://bmrc.berkeley.edu/people/chaffee/vfat.html | |
106 | ||
107 | This tests quite a few parts of the vfat filesystem and additional | |
108 | tests for new features or untested features would be appreciated. | |
109 | ||
110 | NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM | |
111 | ---------------------------------------------------------------------- | |
112 | (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu> | |
113 | and lightly annotated by Gordon Chaffee). | |
114 | ||
115 | This document presents a very rough, technical overview of my | |
116 | knowledge of the extended FAT file system used in Windows NT 3.5 and | |
117 | Windows 95. I don't guarantee that any of the following is correct, | |
118 | but it appears to be so. | |
119 | ||
120 | The extended FAT file system is almost identical to the FAT | |
121 | file system used in DOS versions up to and including 6.223410239847 | |
122 | :-). The significant change has been the addition of long file names. | |
123 | These names support up to 255 characters including spaces and lower | |
124 | case characters as opposed to the traditional 8.3 short names. | |
125 | ||
126 | Here is the description of the traditional FAT entry in the current | |
127 | Windows 95 filesystem: | |
128 | ||
129 | struct directory { // Short 8.3 names | |
130 | unsigned char name[8]; // file name | |
131 | unsigned char ext[3]; // file extension | |
132 | unsigned char attr; // attribute byte | |
133 | unsigned char lcase; // Case for base and extension | |
134 | unsigned char ctime_ms; // Creation time, milliseconds | |
135 | unsigned char ctime[2]; // Creation time | |
136 | unsigned char cdate[2]; // Creation date | |
137 | unsigned char adate[2]; // Last access date | |
138 | unsigned char reserved[2]; // reserved values (ignored) | |
139 | unsigned char time[2]; // time stamp | |
140 | unsigned char date[2]; // date stamp | |
141 | unsigned char start[2]; // starting cluster number | |
142 | unsigned char size[4]; // size of the file | |
143 | }; | |
144 | ||
145 | The lcase field specifies if the base and/or the extension of an 8.3 | |
146 | name should be capitalized. This field does not seem to be used by | |
147 | Windows 95 but it is used by Windows NT. The case of filenames is not | |
148 | completely compatible from Windows NT to Windows 95. It is not completely | |
149 | compatible in the reverse direction, however. Filenames that fit in | |
150 | the 8.3 namespace and are written on Windows NT to be lowercase will | |
151 | show up as uppercase on Windows 95. | |
152 | ||
153 | Note that the "start" and "size" values are actually little | |
154 | endian integer values. The descriptions of the fields in this | |
155 | structure are public knowledge and can be found elsewhere. | |
156 | ||
157 | With the extended FAT system, Microsoft has inserted extra | |
158 | directory entries for any files with extended names. (Any name which | |
159 | legally fits within the old 8.3 encoding scheme does not have extra | |
160 | entries.) I call these extra entries slots. Basically, a slot is a | |
161 | specially formatted directory entry which holds up to 13 characters of | |
162 | a file's extended name. Think of slots as additional labeling for the | |
163 | directory entry of the file to which they correspond. Microsoft | |
164 | prefers to refer to the 8.3 entry for a file as its alias and the | |
165 | extended slot directory entries as the file name. | |
166 | ||
167 | The C structure for a slot directory entry follows: | |
168 | ||
169 | struct slot { // Up to 13 characters of a long name | |
170 | unsigned char id; // sequence number for slot | |
171 | unsigned char name0_4[10]; // first 5 characters in name | |
172 | unsigned char attr; // attribute byte | |
173 | unsigned char reserved; // always 0 | |
174 | unsigned char alias_checksum; // checksum for 8.3 alias | |
175 | unsigned char name5_10[12]; // 6 more characters in name | |
176 | unsigned char start[2]; // starting cluster number | |
177 | unsigned char name11_12[4]; // last 2 characters in name | |
178 | }; | |
179 | ||
180 | If the layout of the slots looks a little odd, it's only | |
181 | because of Microsoft's efforts to maintain compatibility with old | |
182 | software. The slots must be disguised to prevent old software from | |
183 | panicking. To this end, a number of measures are taken: | |
184 | ||
185 | 1) The attribute byte for a slot directory entry is always set | |
186 | to 0x0f. This corresponds to an old directory entry with | |
187 | attributes of "hidden", "system", "read-only", and "volume | |
188 | label". Most old software will ignore any directory | |
189 | entries with the "volume label" bit set. Real volume label | |
190 | entries don't have the other three bits set. | |
191 | ||
192 | 2) The starting cluster is always set to 0, an impossible | |
193 | value for a DOS file. | |
194 | ||
195 | Because the extended FAT system is backward compatible, it is | |
196 | possible for old software to modify directory entries. Measures must | |
197 | be taken to ensure the validity of slots. An extended FAT system can | |
198 | verify that a slot does in fact belong to an 8.3 directory entry by | |
199 | the following: | |
200 | ||
201 | 1) Positioning. Slots for a file always immediately proceed | |
202 | their corresponding 8.3 directory entry. In addition, each | |
203 | slot has an id which marks its order in the extended file | |
204 | name. Here is a very abbreviated view of an 8.3 directory | |
205 | entry and its corresponding long name slots for the file | |
206 | "My Big File.Extension which is long": | |
207 | ||
208 | <proceeding files...> | |
209 | <slot #3, id = 0x43, characters = "h is long"> | |
210 | <slot #2, id = 0x02, characters = "xtension whic"> | |
211 | <slot #1, id = 0x01, characters = "My Big File.E"> | |
212 | <directory entry, name = "MYBIGFIL.EXT"> | |
213 | ||
214 | Note that the slots are stored from last to first. Slots | |
215 | are numbered from 1 to N. The Nth slot is or'ed with 0x40 | |
216 | to mark it as the last one. | |
217 | ||
218 | 2) Checksum. Each slot has an "alias_checksum" value. The | |
219 | checksum is calculated from the 8.3 name using the | |
220 | following algorithm: | |
221 | ||
222 | for (sum = i = 0; i < 11; i++) { | |
223 | sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i] | |
224 | } | |
225 | ||
226 | 3) If there is free space in the final slot, a Unicode NULL (0x0000) | |
227 | is stored after the final character. After that, all unused | |
228 | characters in the final slot are set to Unicode 0xFFFF. | |
229 | ||
230 | Finally, note that the extended name is stored in Unicode. Each Unicode | |
231 | character takes two bytes. |