1==== 2VFAT 3==== 4 5USING VFAT 6========== 7 8To use the vfat filesystem, use the filesystem type 'vfat'. i.e.:: 9 10 mount -t vfat /dev/fd0 /mnt 11 12 13No special partition formatter is required, 14'mkdosfs' will work fine if you want to format from within Linux. 15 16VFAT MOUNT OPTIONS 17================== 18 19**uid=###** 20 Set the owner of all files on this filesystem. 21 The default is the uid of current process. 22 23**gid=###** 24 Set the group of all files on this filesystem. 25 The default is the gid of current process. 26 27**umask=###** 28 The permission mask (for files and directories, see *umask(1)*). 29 The default is the umask of current process. 30 31**dmask=###** 32 The permission mask for the directory. 33 The default is the umask of current process. 34 35**fmask=###** 36 The permission mask for files. 37 The default is the umask of current process. 38 39**allow_utime=###** 40 This option controls the permission check of mtime/atime. 41 42 **-20**: If current process is in group of file's group ID, 43 you can change timestamp. 44 45 **-2**: Other users can change timestamp. 46 47 The default is set from dmask option. If the directory is 48 writable, utime(2) is also allowed. i.e. ~dmask & 022. 49 50 Normally utime(2) checks current process is owner of 51 the file, or it has CAP_FOWNER capability. But FAT 52 filesystem doesn't have uid/gid on disk, so normal 53 check is too inflexible. With this option you can 54 relax it. 55 56**codepage=###** 57 Sets the codepage number for converting to shortname 58 characters on FAT filesystem. 59 By default, FAT_DEFAULT_CODEPAGE setting is used. 60 61**iocharset=<name>** 62 Character set to use for converting between the 63 encoding is used for user visible filename and 16 bit 64 Unicode characters. Long filenames are stored on disk 65 in Unicode format, but Unix for the most part doesn't 66 know how to deal with Unicode. 67 By default, FAT_DEFAULT_IOCHARSET setting is used. 68 69 There is also an option of doing UTF-8 translations 70 with the utf8 option. 71 72.. note:: ``iocharset=utf8`` is not recommended. If unsure, you should consider 73 the utf8 option instead. 74 75**utf8=<bool>** 76 UTF-8 is the filesystem safe version of Unicode that 77 is used by the console. It can be enabled or disabled 78 for the filesystem with this option. 79 If 'uni_xlate' gets set, UTF-8 gets disabled. 80 By default, FAT_DEFAULT_UTF8 setting is used. 81 82**uni_xlate=<bool>** 83 Translate unhandled Unicode characters to special 84 escaped sequences. This would let you backup and 85 restore filenames that are created with any Unicode 86 characters. Until Linux supports Unicode for real, 87 this gives you an alternative. Without this option, 88 a '?' is used when no translation is possible. The 89 escape character is ':' because it is otherwise 90 illegal on the vfat filesystem. The escape sequence 91 that gets used is ':' and the four digits of hexadecimal 92 unicode. 93 94**nonumtail=<bool>** 95 When creating 8.3 aliases, normally the alias will 96 end in '~1' or tilde followed by some number. If this 97 option is set, then if the filename is 98 "longfilename.txt" and "longfile.txt" does not 99 currently exist in the directory, longfile.txt will 100 be the short alias instead of longfi~1.txt. 101 102**usefree** 103 Use the "free clusters" value stored on FSINFO. It will 104 be used to determine number of free clusters without 105 scanning disk. But it's not used by default, because 106 recent Windows don't update it correctly in some 107 case. If you are sure the "free clusters" on FSINFO is 108 correct, by this option you can avoid scanning disk. 109 110**quiet** 111 Stops printing certain warning messages. 112 113**check=s|r|n** 114 Case sensitivity checking setting. 115 116 **s**: strict, case sensitive 117 118 **r**: relaxed, case insensitive 119 120 **n**: normal, default setting, currently case insensitive 121 122**nocase** 123 This was deprecated for vfat. Use ``shortname=win95`` instead. 124 125**shortname=lower|win95|winnt|mixed** 126 Shortname display/create setting. 127 128 **lower**: convert to lowercase for display, 129 emulate the Windows 95 rule for create. 130 131 **win95**: emulate the Windows 95 rule for display/create. 132 133 **winnt**: emulate the Windows NT rule for display/create. 134 135 **mixed**: emulate the Windows NT rule for display, 136 emulate the Windows 95 rule for create. 137 138 Default setting is `mixed`. 139 140**tz=UTC** 141 Interpret timestamps as UTC rather than local time. 142 This option disables the conversion of timestamps 143 between local time (as used by Windows on FAT) and UTC 144 (which Linux uses internally). This is particularly 145 useful when mounting devices (like digital cameras) 146 that are set to UTC in order to avoid the pitfalls of 147 local time. 148 149**time_offset=minutes** 150 Set offset for conversion of timestamps from local time 151 used by FAT to UTC. I.e. <minutes> minutes will be subtracted 152 from each timestamp to convert it to UTC used internally by 153 Linux. This is useful when time zone set in ``sys_tz`` is 154 not the time zone used by the filesystem. Note that this 155 option still does not provide correct time stamps in all 156 cases in presence of DST - time stamps in a different DST 157 setting will be off by one hour. 158 159**showexec** 160 If set, the execute permission bits of the file will be 161 allowed only if the extension part of the name is .EXE, 162 .COM, or .BAT. Not set by default. 163 164**debug** 165 Can be set, but unused by the current implementation. 166 167**sys_immutable** 168 If set, ATTR_SYS attribute on FAT is handled as 169 IMMUTABLE flag on Linux. Not set by default. 170 171**flush** 172 If set, the filesystem will try to flush to disk more 173 early than normal. Not set by default. 174 175**rodir** 176 FAT has the ATTR_RO (read-only) attribute. On Windows, 177 the ATTR_RO of the directory will just be ignored, 178 and is used only by applications as a flag (e.g. it's set 179 for the customized folder). 180 181 If you want to use ATTR_RO as read-only flag even for 182 the directory, set this option. 183 184**errors=panic|continue|remount-ro** 185 specify FAT behavior on critical errors: panic, continue 186 without doing anything or remount the partition in 187 read-only mode (default behavior). 188 189**discard** 190 If set, issues discard/TRIM commands to the block 191 device when blocks are freed. This is useful for SSD devices 192 and sparse/thinly-provisioned LUNs. 193 194**nfs=stale_rw|nostale_ro** 195 Enable this only if you want to export the FAT filesystem 196 over NFS. 197 198 **stale_rw**: This option maintains an index (cache) of directory 199 *inodes* by *i_logstart* which is used by the nfs-related code to 200 improve look-ups. Full file operations (read/write) over NFS is 201 supported but with cache eviction at NFS server, this could 202 result in ESTALE issues. 203 204 **nostale_ro**: This option bases the *inode* number and filehandle 205 on the on-disk location of a file in the MS-DOS directory entry. 206 This ensures that ESTALE will not be returned after a file is 207 evicted from the inode cache. However, it means that operations 208 such as rename, create and unlink could cause filehandles that 209 previously pointed at one file to point at a different file, 210 potentially causing data corruption. For this reason, this 211 option also mounts the filesystem readonly. 212 213 To maintain backward compatibility, ``'-o nfs'`` is also accepted, 214 defaulting to "stale_rw". 215 216**dos1xfloppy <bool>: 0,1,yes,no,true,false** 217 If set, use a fallback default BIOS Parameter Block 218 configuration, determined by backing device size. These static 219 parameters match defaults assumed by DOS 1.x for 160 kiB, 220 180 kiB, 320 kiB, and 360 kiB floppies and floppy images. 221 222 223 224LIMITATION 225========== 226 227The fallocated region of file is discarded at umount/evict time 228when using fallocate with FALLOC_FL_KEEP_SIZE. 229So, User should assume that fallocated region can be discarded at 230last close if there is memory pressure resulting in eviction of 231the inode from the memory. As a result, for any dependency on 232the fallocated region, user should make sure to recheck fallocate 233after reopening the file. 234 235TODO 236==== 237Need to get rid of the raw scanning stuff. Instead, always use 238a get next directory entry approach. The only thing left that uses 239raw scanning is the directory renaming code. 240 241 242POSSIBLE PROBLEMS 243================= 244 245- vfat_valid_longname does not properly checked reserved names. 246- When a volume name is the same as a directory name in the root 247 directory of the filesystem, the directory name sometimes shows 248 up as an empty file. 249- autoconv option does not work correctly. 250 251 252TEST SUITE 253========== 254If you plan to make any modifications to the vfat filesystem, please 255get the test suite that comes with the vfat distribution at 256 257`<http://web.archive.org/web/*/http://bmrc.berkeley.edu/people/chaffee/vfat.html>`_ 258 259This tests quite a few parts of the vfat filesystem and additional 260tests for new features or untested features would be appreciated. 261 262NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM 263============================================= 264This documentation was provided by Galen C. Hunt gchunt@cs.rochester.edu and 265lightly annotated by Gordon Chaffee. 266 267This document presents a very rough, technical overview of my 268knowledge of the extended FAT file system used in Windows NT 3.5 and 269Windows 95. I don't guarantee that any of the following is correct, 270but it appears to be so. 271 272The extended FAT file system is almost identical to the FAT 273file system used in DOS versions up to and including *6.223410239847* 274:-). The significant change has been the addition of long file names. 275These names support up to 255 characters including spaces and lower 276case characters as opposed to the traditional 8.3 short names. 277 278Here is the description of the traditional FAT entry in the current 279Windows 95 filesystem:: 280 281 struct directory { // Short 8.3 names 282 unsigned char name[8]; // file name 283 unsigned char ext[3]; // file extension 284 unsigned char attr; // attribute byte 285 unsigned char lcase; // Case for base and extension 286 unsigned char ctime_ms; // Creation time, milliseconds 287 unsigned char ctime[2]; // Creation time 288 unsigned char cdate[2]; // Creation date 289 unsigned char adate[2]; // Last access date 290 unsigned char reserved[2]; // reserved values (ignored) 291 unsigned char time[2]; // time stamp 292 unsigned char date[2]; // date stamp 293 unsigned char start[2]; // starting cluster number 294 unsigned char size[4]; // size of the file 295 }; 296 297 298The lcase field specifies if the base and/or the extension of an 8.3 299name should be capitalized. This field does not seem to be used by 300Windows 95 but it is used by Windows NT. The case of filenames is not 301completely compatible from Windows NT to Windows 95. It is not completely 302compatible in the reverse direction, however. Filenames that fit in 303the 8.3 namespace and are written on Windows NT to be lowercase will 304show up as uppercase on Windows 95. 305 306.. note:: Note that the ``start`` and ``size`` values are actually little 307 endian integer values. The descriptions of the fields in this 308 structure are public knowledge and can be found elsewhere. 309 310With the extended FAT system, Microsoft has inserted extra 311directory entries for any files with extended names. (Any name which 312legally fits within the old 8.3 encoding scheme does not have extra 313entries.) I call these extra entries slots. Basically, a slot is a 314specially formatted directory entry which holds up to 13 characters of 315a file's extended name. Think of slots as additional labeling for the 316directory entry of the file to which they correspond. Microsoft 317prefers to refer to the 8.3 entry for a file as its alias and the 318extended slot directory entries as the file name. 319 320The C structure for a slot directory entry follows:: 321 322 struct slot { // Up to 13 characters of a long name 323 unsigned char id; // sequence number for slot 324 unsigned char name0_4[10]; // first 5 characters in name 325 unsigned char attr; // attribute byte 326 unsigned char reserved; // always 0 327 unsigned char alias_checksum; // checksum for 8.3 alias 328 unsigned char name5_10[12]; // 6 more characters in name 329 unsigned char start[2]; // starting cluster number 330 unsigned char name11_12[4]; // last 2 characters in name 331 }; 332 333 334If the layout of the slots looks a little odd, it's only 335because of Microsoft's efforts to maintain compatibility with old 336software. The slots must be disguised to prevent old software from 337panicking. To this end, a number of measures are taken: 338 339 1) The attribute byte for a slot directory entry is always set 340 to 0x0f. This corresponds to an old directory entry with 341 attributes of "hidden", "system", "read-only", and "volume 342 label". Most old software will ignore any directory 343 entries with the "volume label" bit set. Real volume label 344 entries don't have the other three bits set. 345 346 2) The starting cluster is always set to 0, an impossible 347 value for a DOS file. 348 349Because the extended FAT system is backward compatible, it is 350possible for old software to modify directory entries. Measures must 351be taken to ensure the validity of slots. An extended FAT system can 352verify that a slot does in fact belong to an 8.3 directory entry by 353the following: 354 355 1) Positioning. Slots for a file always immediately proceed 356 their corresponding 8.3 directory entry. In addition, each 357 slot has an id which marks its order in the extended file 358 name. Here is a very abbreviated view of an 8.3 directory 359 entry and its corresponding long name slots for the file 360 "My Big File.Extension which is long":: 361 362 <proceeding files...> 363 <slot #3, id = 0x43, characters = "h is long"> 364 <slot #2, id = 0x02, characters = "xtension whic"> 365 <slot #1, id = 0x01, characters = "My Big File.E"> 366 <directory entry, name = "MYBIGFIL.EXT"> 367 368 369 .. note:: Note that the slots are stored from last to first. Slots 370 are numbered from 1 to N. The Nth slot is ``or'ed`` with 371 0x40 to mark it as the last one. 372 373 2) Checksum. Each slot has an alias_checksum value. The 374 checksum is calculated from the 8.3 name using the 375 following algorithm:: 376 377 for (sum = i = 0; i < 11; i++) { 378 sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i] 379 } 380 381 382 3) If there is free space in the final slot, a Unicode ``NULL (0x0000)`` 383 is stored after the final character. After that, all unused 384 characters in the final slot are set to Unicode 0xFFFF. 385 386Finally, note that the extended name is stored in Unicode. Each Unicode 387character takes either two or four bytes, UTF-16LE encoded. 388