Root/
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 | uid=### -- Set the owner of all files on this filesystem. |
12 | The default is the uid of current process. |
13 | |
14 | gid=### -- Set the group of all files on this filesystem. |
15 | The default is the gid of current process. |
16 | |
17 | umask=### -- The permission mask (for files and directories, see umask(1)). |
18 | The default is the umask of current process. |
19 | |
20 | dmask=### -- The permission mask for the directory. |
21 | The default is the umask of current process. |
22 | |
23 | fmask=### -- The permission mask for files. |
24 | The default is the umask of current process. |
25 | |
26 | allow_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 | |
41 | codepage=### -- Sets the codepage number for converting to shortname |
42 | characters on FAT filesystem. |
43 | By default, FAT_DEFAULT_CODEPAGE setting is used. |
44 | |
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. |
51 | |
52 | There is also an option of doing UTF-8 translations |
53 | with the utf8 option. |
54 | |
55 | NOTE: "iocharset=utf8" is not recommended. If unsure, |
56 | you should consider the following option instead. |
57 | |
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. |
62 | |
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. |
73 | |
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'. |
80 | |
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. |
87 | |
88 | quiet -- Stops printing certain warning messages. |
89 | |
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 |
94 | |
95 | nocase -- This was deprecated for vfat. Use shortname=win95 instead. |
96 | |
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'. |
106 | |
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. |
114 | |
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. |
118 | |
119 | debug -- Can be set, but unused by the current implementation. |
120 | |
121 | sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as |
122 | IMMUTABLE flag on Linux. Not set by default. |
123 | |
124 | flush -- If set, the filesystem will try to flush to disk more |
125 | early than normal. Not set by default. |
126 | |
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). |
131 | |
132 | If you want to use ATTR_RO as read-only flag even for |
133 | the directory, set this option. |
134 | |
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). |
139 | |
140 | <bool>: 0,1,yes,no,true,false |
141 | |
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. |
147 | |
148 | |
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. |
156 | |
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. |
162 | |
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 |
167 | |
168 | http://web.archive.org/web/*/http://bmrc.berkeley.edu/ |
169 | people/chaffee/vfat.html |
170 | |
171 | This tests quite a few parts of the vfat filesystem and additional |
172 | tests for new features or untested features would be appreciated. |
173 | |
174 | NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM |
175 | ---------------------------------------------------------------------- |
176 | (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu> |
177 | and lightly annotated by Gordon Chaffee). |
178 | |
179 | This document presents a very rough, technical overview of my |
180 | knowledge of the extended FAT file system used in Windows NT 3.5 and |
181 | Windows 95. I don't guarantee that any of the following is correct, |
182 | but it appears to be so. |
183 | |
184 | The extended FAT file system is almost identical to the FAT |
185 | file system used in DOS versions up to and including 6.223410239847 |
186 | :-). The significant change has been the addition of long file names. |
187 | These names support up to 255 characters including spaces and lower |
188 | case characters as opposed to the traditional 8.3 short names. |
189 | |
190 | Here is the description of the traditional FAT entry in the current |
191 | Windows 95 filesystem: |
192 | |
193 | struct directory { // Short 8.3 names |
194 | unsigned char name[8]; // file name |
195 | unsigned char ext[3]; // file extension |
196 | unsigned char attr; // attribute byte |
197 | unsigned char lcase; // Case for base and extension |
198 | unsigned char ctime_ms; // Creation time, milliseconds |
199 | unsigned char ctime[2]; // Creation time |
200 | unsigned char cdate[2]; // Creation date |
201 | unsigned char adate[2]; // Last access date |
202 | unsigned char reserved[2]; // reserved values (ignored) |
203 | unsigned char time[2]; // time stamp |
204 | unsigned char date[2]; // date stamp |
205 | unsigned char start[2]; // starting cluster number |
206 | unsigned char size[4]; // size of the file |
207 | }; |
208 | |
209 | The lcase field specifies if the base and/or the extension of an 8.3 |
210 | name should be capitalized. This field does not seem to be used by |
211 | Windows 95 but it is used by Windows NT. The case of filenames is not |
212 | completely compatible from Windows NT to Windows 95. It is not completely |
213 | compatible in the reverse direction, however. Filenames that fit in |
214 | the 8.3 namespace and are written on Windows NT to be lowercase will |
215 | show up as uppercase on Windows 95. |
216 | |
217 | Note that the "start" and "size" values are actually little |
218 | endian integer values. The descriptions of the fields in this |
219 | structure are public knowledge and can be found elsewhere. |
220 | |
221 | With the extended FAT system, Microsoft has inserted extra |
222 | directory entries for any files with extended names. (Any name which |
223 | legally fits within the old 8.3 encoding scheme does not have extra |
224 | entries.) I call these extra entries slots. Basically, a slot is a |
225 | specially formatted directory entry which holds up to 13 characters of |
226 | a file's extended name. Think of slots as additional labeling for the |
227 | directory entry of the file to which they correspond. Microsoft |
228 | prefers to refer to the 8.3 entry for a file as its alias and the |
229 | extended slot directory entries as the file name. |
230 | |
231 | The C structure for a slot directory entry follows: |
232 | |
233 | struct slot { // Up to 13 characters of a long name |
234 | unsigned char id; // sequence number for slot |
235 | unsigned char name0_4[10]; // first 5 characters in name |
236 | unsigned char attr; // attribute byte |
237 | unsigned char reserved; // always 0 |
238 | unsigned char alias_checksum; // checksum for 8.3 alias |
239 | unsigned char name5_10[12]; // 6 more characters in name |
240 | unsigned char start[2]; // starting cluster number |
241 | unsigned char name11_12[4]; // last 2 characters in name |
242 | }; |
243 | |
244 | If the layout of the slots looks a little odd, it's only |
245 | because of Microsoft's efforts to maintain compatibility with old |
246 | software. The slots must be disguised to prevent old software from |
247 | panicking. To this end, a number of measures are taken: |
248 | |
249 | 1) The attribute byte for a slot directory entry is always set |
250 | to 0x0f. This corresponds to an old directory entry with |
251 | attributes of "hidden", "system", "read-only", and "volume |
252 | label". Most old software will ignore any directory |
253 | entries with the "volume label" bit set. Real volume label |
254 | entries don't have the other three bits set. |
255 | |
256 | 2) The starting cluster is always set to 0, an impossible |
257 | value for a DOS file. |
258 | |
259 | Because the extended FAT system is backward compatible, it is |
260 | possible for old software to modify directory entries. Measures must |
261 | be taken to ensure the validity of slots. An extended FAT system can |
262 | verify that a slot does in fact belong to an 8.3 directory entry by |
263 | the following: |
264 | |
265 | 1) Positioning. Slots for a file always immediately proceed |
266 | their corresponding 8.3 directory entry. In addition, each |
267 | slot has an id which marks its order in the extended file |
268 | name. Here is a very abbreviated view of an 8.3 directory |
269 | entry and its corresponding long name slots for the file |
270 | "My Big File.Extension which is long": |
271 | |
272 | <proceeding files...> |
273 | <slot #3, id = 0x43, characters = "h is long"> |
274 | <slot #2, id = 0x02, characters = "xtension whic"> |
275 | <slot #1, id = 0x01, characters = "My Big File.E"> |
276 | <directory entry, name = "MYBIGFIL.EXT"> |
277 | |
278 | Note that the slots are stored from last to first. Slots |
279 | are numbered from 1 to N. The Nth slot is or'ed with 0x40 |
280 | to mark it as the last one. |
281 | |
282 | 2) Checksum. Each slot has an "alias_checksum" value. The |
283 | checksum is calculated from the 8.3 name using the |
284 | following algorithm: |
285 | |
286 | for (sum = i = 0; i < 11; i++) { |
287 | sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i] |
288 | } |
289 | |
290 | 3) If there is free space in the final slot, a Unicode NULL (0x0000) |
291 | is stored after the final character. After that, all unused |
292 | characters in the final slot are set to Unicode 0xFFFF. |
293 | |
294 | Finally, note that the extended name is stored in Unicode. Each Unicode |
295 | character takes two bytes. |
296 |
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