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