1USING VFAT 2---------------------------------------------------------------------- 3To use the vfat filesystem, use the filesystem type 'vfat'. i.e. 4 mount -t vfat /dev/fd0 /mnt 5 6No special partition formatter is required. mkdosfs will work fine 7if you want to format from within Linux. 8 9VFAT MOUNT OPTIONS 10---------------------------------------------------------------------- 11uid=### -- Set the owner of all files on this filesystem. 12 The default is the uid of current process. 13 14gid=### -- Set the group of all files on this filesystem. 15 The default is the gid of current process. 16 17umask=### -- The permission mask (for files and directories, see umask(1)). 18 The default is the umask of current process. 19 20dmask=### -- The permission mask for the directory. 21 The default is the umask of current process. 22 23fmask=### -- The permission mask for files. 24 The default is the umask of current process. 25 26allow_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 41codepage=### -- Sets the codepage number for converting to shortname 42 characters on FAT filesystem. 43 By default, FAT_DEFAULT_CODEPAGE setting is used. 44 45iocharset=<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 58utf8=<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 63uni_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 74nonumtail=<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 81usefree -- 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 88quiet -- Stops printing certain warning messages. 89 90check=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 95nocase -- This was deprecated for vfat. Use shortname=win95 instead. 96 97shortname=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 107tz=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. 114time_offset=minutes 115 -- Set offset for conversion of timestamps from local time 116 used by FAT to UTC. I.e. <minutes> minutes will be subtracted 117 from each timestamp to convert it to UTC used internally by 118 Linux. This is useful when time zone set in sys_tz is 119 not the time zone used by the filesystem. Note that this 120 option still does not provide correct time stamps in all 121 cases in presence of DST - time stamps in a different DST 122 setting will be off by one hour. 123 124showexec -- If set, the execute permission bits of the file will be 125 allowed only if the extension part of the name is .EXE, 126 .COM, or .BAT. Not set by default. 127 128debug -- Can be set, but unused by the current implementation. 129 130sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as 131 IMMUTABLE flag on Linux. Not set by default. 132 133flush -- If set, the filesystem will try to flush to disk more 134 early than normal. Not set by default. 135 136rodir -- FAT has the ATTR_RO (read-only) attribute. On Windows, 137 the ATTR_RO of the directory will just be ignored, 138 and is used only by applications as a flag (e.g. it's set 139 for the customized folder). 140 141 If you want to use ATTR_RO as read-only flag even for 142 the directory, set this option. 143 144errors=panic|continue|remount-ro 145 -- specify FAT behavior on critical errors: panic, continue 146 without doing anything or remount the partition in 147 read-only mode (default behavior). 148 149discard -- If set, issues discard/TRIM commands to the block 150 device when blocks are freed. This is useful for SSD devices 151 and sparse/thinly-provisoned LUNs. 152 153nfs=stale_rw|nostale_ro 154 Enable this only if you want to export the FAT filesystem 155 over NFS. 156 157 stale_rw: This option maintains an index (cache) of directory 158 inodes by i_logstart which is used by the nfs-related code to 159 improve look-ups. Full file operations (read/write) over NFS is 160 supported but with cache eviction at NFS server, this could 161 result in ESTALE issues. 162 163 nostale_ro: This option bases the inode number and filehandle 164 on the on-disk location of a file in the MS-DOS directory entry. 165 This ensures that ESTALE will not be returned after a file is 166 evicted from the inode cache. However, it means that operations 167 such as rename, create and unlink could cause filehandles that 168 previously pointed at one file to point at a different file, 169 potentially causing data corruption. For this reason, this 170 option also mounts the filesystem readonly. 171 172 To maintain backward compatibility, '-o nfs' is also accepted, 173 defaulting to stale_rw 174 175dos1xfloppy -- If set, use a fallback default BIOS Parameter Block 176 configuration, determined by backing device size. These static 177 parameters match defaults assumed by DOS 1.x for 160 kiB, 178 180 kiB, 320 kiB, and 360 kiB floppies and floppy images. 179 180 181<bool>: 0,1,yes,no,true,false 182 183TODO 184---------------------------------------------------------------------- 185* Need to get rid of the raw scanning stuff. Instead, always use 186 a get next directory entry approach. The only thing left that uses 187 raw scanning is the directory renaming code. 188 189 190POSSIBLE PROBLEMS 191---------------------------------------------------------------------- 192* vfat_valid_longname does not properly checked reserved names. 193* When a volume name is the same as a directory name in the root 194 directory of the filesystem, the directory name sometimes shows 195 up as an empty file. 196* autoconv option does not work correctly. 197 198BUG REPORTS 199---------------------------------------------------------------------- 200If you have trouble with the VFAT filesystem, mail bug reports to 201chaffee@bmrc.cs.berkeley.edu. Please specify the filename 202and the operation that gave you trouble. 203 204TEST SUITE 205---------------------------------------------------------------------- 206If you plan to make any modifications to the vfat filesystem, please 207get the test suite that comes with the vfat distribution at 208 209 http://web.archive.org/web/*/http://bmrc.berkeley.edu/ 210 people/chaffee/vfat.html 211 212This tests quite a few parts of the vfat filesystem and additional 213tests for new features or untested features would be appreciated. 214 215NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM 216---------------------------------------------------------------------- 217(This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu> 218 and lightly annotated by Gordon Chaffee). 219 220This document presents a very rough, technical overview of my 221knowledge of the extended FAT file system used in Windows NT 3.5 and 222Windows 95. I don't guarantee that any of the following is correct, 223but it appears to be so. 224 225The extended FAT file system is almost identical to the FAT 226file system used in DOS versions up to and including 6.223410239847 227:-). The significant change has been the addition of long file names. 228These names support up to 255 characters including spaces and lower 229case characters as opposed to the traditional 8.3 short names. 230 231Here is the description of the traditional FAT entry in the current 232Windows 95 filesystem: 233 234 struct directory { // Short 8.3 names 235 unsigned char name[8]; // file name 236 unsigned char ext[3]; // file extension 237 unsigned char attr; // attribute byte 238 unsigned char lcase; // Case for base and extension 239 unsigned char ctime_ms; // Creation time, milliseconds 240 unsigned char ctime[2]; // Creation time 241 unsigned char cdate[2]; // Creation date 242 unsigned char adate[2]; // Last access date 243 unsigned char reserved[2]; // reserved values (ignored) 244 unsigned char time[2]; // time stamp 245 unsigned char date[2]; // date stamp 246 unsigned char start[2]; // starting cluster number 247 unsigned char size[4]; // size of the file 248 }; 249 250The lcase field specifies if the base and/or the extension of an 8.3 251name should be capitalized. This field does not seem to be used by 252Windows 95 but it is used by Windows NT. The case of filenames is not 253completely compatible from Windows NT to Windows 95. It is not completely 254compatible in the reverse direction, however. Filenames that fit in 255the 8.3 namespace and are written on Windows NT to be lowercase will 256show up as uppercase on Windows 95. 257 258Note that the "start" and "size" values are actually little 259endian integer values. The descriptions of the fields in this 260structure are public knowledge and can be found elsewhere. 261 262With the extended FAT system, Microsoft has inserted extra 263directory entries for any files with extended names. (Any name which 264legally fits within the old 8.3 encoding scheme does not have extra 265entries.) I call these extra entries slots. Basically, a slot is a 266specially formatted directory entry which holds up to 13 characters of 267a file's extended name. Think of slots as additional labeling for the 268directory entry of the file to which they correspond. Microsoft 269prefers to refer to the 8.3 entry for a file as its alias and the 270extended slot directory entries as the file name. 271 272The C structure for a slot directory entry follows: 273 274 struct slot { // Up to 13 characters of a long name 275 unsigned char id; // sequence number for slot 276 unsigned char name0_4[10]; // first 5 characters in name 277 unsigned char attr; // attribute byte 278 unsigned char reserved; // always 0 279 unsigned char alias_checksum; // checksum for 8.3 alias 280 unsigned char name5_10[12]; // 6 more characters in name 281 unsigned char start[2]; // starting cluster number 282 unsigned char name11_12[4]; // last 2 characters in name 283 }; 284 285If the layout of the slots looks a little odd, it's only 286because of Microsoft's efforts to maintain compatibility with old 287software. The slots must be disguised to prevent old software from 288panicking. To this end, a number of measures are taken: 289 290 1) The attribute byte for a slot directory entry is always set 291 to 0x0f. This corresponds to an old directory entry with 292 attributes of "hidden", "system", "read-only", and "volume 293 label". Most old software will ignore any directory 294 entries with the "volume label" bit set. Real volume label 295 entries don't have the other three bits set. 296 297 2) The starting cluster is always set to 0, an impossible 298 value for a DOS file. 299 300Because the extended FAT system is backward compatible, it is 301possible for old software to modify directory entries. Measures must 302be taken to ensure the validity of slots. An extended FAT system can 303verify that a slot does in fact belong to an 8.3 directory entry by 304the following: 305 306 1) Positioning. Slots for a file always immediately proceed 307 their corresponding 8.3 directory entry. In addition, each 308 slot has an id which marks its order in the extended file 309 name. Here is a very abbreviated view of an 8.3 directory 310 entry and its corresponding long name slots for the file 311 "My Big File.Extension which is long": 312 313 <proceeding files...> 314 <slot #3, id = 0x43, characters = "h is long"> 315 <slot #2, id = 0x02, characters = "xtension whic"> 316 <slot #1, id = 0x01, characters = "My Big File.E"> 317 <directory entry, name = "MYBIGFIL.EXT"> 318 319 Note that the slots are stored from last to first. Slots 320 are numbered from 1 to N. The Nth slot is or'ed with 0x40 321 to mark it as the last one. 322 323 2) Checksum. Each slot has an "alias_checksum" value. The 324 checksum is calculated from the 8.3 name using the 325 following algorithm: 326 327 for (sum = i = 0; i < 11; i++) { 328 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i] 329 } 330 331 3) If there is free space in the final slot, a Unicode NULL (0x0000) 332 is stored after the final character. After that, all unused 333 characters in the final slot are set to Unicode 0xFFFF. 334 335Finally, note that the extended name is stored in Unicode. Each Unicode 336character takes two bytes. 337