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diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt deleted file mode 100644 index 91031298beb1..000000000000 --- a/Documentation/filesystems/vfat.txt +++ /dev/null @@ -1,347 +0,0 @@ -USING VFAT ----------------------------------------------------------------------- -To use the vfat filesystem, use the filesystem type 'vfat'. i.e. - mount -t vfat /dev/fd0 /mnt - -No special partition formatter is required. mkdosfs will work fine -if you want to format from within Linux. - -VFAT MOUNT OPTIONS ----------------------------------------------------------------------- -uid=### -- Set the owner of all files on this filesystem. - The default is the uid of current process. - -gid=### -- Set the group of all files on this filesystem. - The default is the gid of current process. - -umask=### -- The permission mask (for files and directories, see umask(1)). - The default is the umask of current process. - -dmask=### -- The permission mask for the directory. - The default is the umask of current process. - -fmask=### -- The permission mask for files. - The default is the umask of current process. - -allow_utime=### -- This option controls the permission check of mtime/atime. - - 20 - If current process is in group of file's group ID, - you can change timestamp. - 2 - Other users can change timestamp. - - The default is set from `dmask' option. (If the directory is - writable, utime(2) is also allowed. I.e. ~dmask & 022) - - Normally utime(2) checks current process is owner of - the file, or it has CAP_FOWNER capability. But FAT - filesystem doesn't have uid/gid on disk, so normal - check is too unflexible. With this option you can - relax it. - -codepage=### -- Sets the codepage number for converting to shortname - characters on FAT filesystem. - By default, FAT_DEFAULT_CODEPAGE setting is used. - -iocharset=<name> -- Character set to use for converting between the - encoding is used for user visible filename and 16 bit - Unicode characters. Long filenames are stored on disk - in Unicode format, but Unix for the most part doesn't - know how to deal with Unicode. - By default, FAT_DEFAULT_IOCHARSET setting is used. - - There is also an option of doing UTF-8 translations - with the utf8 option. - - NOTE: "iocharset=utf8" is not recommended. If unsure, - you should consider the following option instead. - -utf8=<bool> -- UTF-8 is the filesystem safe version of Unicode that - is used by the console. It can be enabled or disabled - for the filesystem with this option. - If 'uni_xlate' gets set, UTF-8 gets disabled. - By default, FAT_DEFAULT_UTF8 setting is used. - -uni_xlate=<bool> -- Translate unhandled Unicode characters to special - escaped sequences. This would let you backup and - restore filenames that are created with any Unicode - characters. Until Linux supports Unicode for real, - this gives you an alternative. Without this option, - a '?' is used when no translation is possible. The - escape character is ':' because it is otherwise - illegal on the vfat filesystem. The escape sequence - that gets used is ':' and the four digits of hexadecimal - unicode. - -nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will - end in '~1' or tilde followed by some number. If this - option is set, then if the filename is - "longfilename.txt" and "longfile.txt" does not - currently exist in the directory, 'longfile.txt' will - be the short alias instead of 'longfi~1.txt'. - -usefree -- Use the "free clusters" value stored on FSINFO. It'll - be used to determine number of free clusters without - scanning disk. But it's not used by default, because - recent Windows don't update it correctly in some - case. If you are sure the "free clusters" on FSINFO is - correct, by this option you can avoid scanning disk. - -quiet -- Stops printing certain warning messages. - -check=s|r|n -- Case sensitivity checking setting. - s: strict, case sensitive - r: relaxed, case insensitive - n: normal, default setting, currently case insensitive - -nocase -- This was deprecated for vfat. Use shortname=win95 instead. - -shortname=lower|win95|winnt|mixed - -- Shortname display/create setting. - lower: convert to lowercase for display, - emulate the Windows 95 rule for create. - win95: emulate the Windows 95 rule for display/create. - winnt: emulate the Windows NT rule for display/create. - mixed: emulate the Windows NT rule for display, - emulate the Windows 95 rule for create. - Default setting is `mixed'. - -tz=UTC -- Interpret timestamps as UTC rather than local time. - This option disables the conversion of timestamps - between local time (as used by Windows on FAT) and UTC - (which Linux uses internally). This is particularly - useful when mounting devices (like digital cameras) - that are set to UTC in order to avoid the pitfalls of - local time. -time_offset=minutes - -- Set offset for conversion of timestamps from local time - used by FAT to UTC. I.e. <minutes> minutes will be subtracted - from each timestamp to convert it to UTC used internally by - Linux. This is useful when time zone set in sys_tz is - not the time zone used by the filesystem. Note that this - option still does not provide correct time stamps in all - cases in presence of DST - time stamps in a different DST - setting will be off by one hour. - -showexec -- If set, the execute permission bits of the file will be - allowed only if the extension part of the name is .EXE, - .COM, or .BAT. Not set by default. - -debug -- Can be set, but unused by the current implementation. - -sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as - IMMUTABLE flag on Linux. Not set by default. - -flush -- If set, the filesystem will try to flush to disk more - early than normal. Not set by default. - -rodir -- FAT has the ATTR_RO (read-only) attribute. On Windows, - the ATTR_RO of the directory will just be ignored, - and is used only by applications as a flag (e.g. it's set - for the customized folder). - - If you want to use ATTR_RO as read-only flag even for - the directory, set this option. - -errors=panic|continue|remount-ro - -- specify FAT behavior on critical errors: panic, continue - without doing anything or remount the partition in - read-only mode (default behavior). - -discard -- If set, issues discard/TRIM commands to the block - device when blocks are freed. This is useful for SSD devices - and sparse/thinly-provisoned LUNs. - -nfs=stale_rw|nostale_ro - Enable this only if you want to export the FAT filesystem - over NFS. - - stale_rw: This option maintains an index (cache) of directory - inodes by i_logstart which is used by the nfs-related code to - improve look-ups. Full file operations (read/write) over NFS is - supported but with cache eviction at NFS server, this could - result in ESTALE issues. - - nostale_ro: This option bases the inode number and filehandle - on the on-disk location of a file in the MS-DOS directory entry. - This ensures that ESTALE will not be returned after a file is - evicted from the inode cache. However, it means that operations - such as rename, create and unlink could cause filehandles that - previously pointed at one file to point at a different file, - potentially causing data corruption. For this reason, this - option also mounts the filesystem readonly. - - To maintain backward compatibility, '-o nfs' is also accepted, - defaulting to stale_rw - -dos1xfloppy -- If set, use a fallback default BIOS Parameter Block - configuration, determined by backing device size. These static - parameters match defaults assumed by DOS 1.x for 160 kiB, - 180 kiB, 320 kiB, and 360 kiB floppies and floppy images. - - -<bool>: 0,1,yes,no,true,false - -LIMITATION ---------------------------------------------------------------------- -* The fallocated region of file is discarded at umount/evict time - when using fallocate with FALLOC_FL_KEEP_SIZE. - So, User should assume that fallocated region can be discarded at - last close if there is memory pressure resulting in eviction of - the inode from the memory. As a result, for any dependency on - the fallocated region, user should make sure to recheck fallocate - after reopening the file. - -TODO ----------------------------------------------------------------------- -* Need to get rid of the raw scanning stuff. Instead, always use - a get next directory entry approach. The only thing left that uses - raw scanning is the directory renaming code. - - -POSSIBLE PROBLEMS ----------------------------------------------------------------------- -* vfat_valid_longname does not properly checked reserved names. -* When a volume name is the same as a directory name in the root - directory of the filesystem, the directory name sometimes shows - up as an empty file. -* autoconv option does not work correctly. - -BUG REPORTS ----------------------------------------------------------------------- -If you have trouble with the VFAT filesystem, mail bug reports to -chaffee@bmrc.cs.berkeley.edu. Please specify the filename -and the operation that gave you trouble. - -TEST SUITE ----------------------------------------------------------------------- -If you plan to make any modifications to the vfat filesystem, please -get the test suite that comes with the vfat distribution at - - http://web.archive.org/web/*/http://bmrc.berkeley.edu/ - people/chaffee/vfat.html - -This tests quite a few parts of the vfat filesystem and additional -tests for new features or untested features would be appreciated. - -NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM ----------------------------------------------------------------------- -(This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu> - and lightly annotated by Gordon Chaffee). - -This document presents a very rough, technical overview of my -knowledge of the extended FAT file system used in Windows NT 3.5 and -Windows 95. I don't guarantee that any of the following is correct, -but it appears to be so. - -The extended FAT file system is almost identical to the FAT -file system used in DOS versions up to and including 6.223410239847 -:-). The significant change has been the addition of long file names. -These names support up to 255 characters including spaces and lower -case characters as opposed to the traditional 8.3 short names. - -Here is the description of the traditional FAT entry in the current -Windows 95 filesystem: - - struct directory { // Short 8.3 names - unsigned char name[8]; // file name - unsigned char ext[3]; // file extension - unsigned char attr; // attribute byte - unsigned char lcase; // Case for base and extension - unsigned char ctime_ms; // Creation time, milliseconds - unsigned char ctime[2]; // Creation time - unsigned char cdate[2]; // Creation date - unsigned char adate[2]; // Last access date - unsigned char reserved[2]; // reserved values (ignored) - unsigned char time[2]; // time stamp - unsigned char date[2]; // date stamp - unsigned char start[2]; // starting cluster number - unsigned char size[4]; // size of the file - }; - -The lcase field specifies if the base and/or the extension of an 8.3 -name should be capitalized. This field does not seem to be used by -Windows 95 but it is used by Windows NT. The case of filenames is not -completely compatible from Windows NT to Windows 95. It is not completely -compatible in the reverse direction, however. Filenames that fit in -the 8.3 namespace and are written on Windows NT to be lowercase will -show up as uppercase on Windows 95. - -Note that the "start" and "size" values are actually little -endian integer values. The descriptions of the fields in this -structure are public knowledge and can be found elsewhere. - -With the extended FAT system, Microsoft has inserted extra -directory entries for any files with extended names. (Any name which -legally fits within the old 8.3 encoding scheme does not have extra -entries.) I call these extra entries slots. Basically, a slot is a -specially formatted directory entry which holds up to 13 characters of -a file's extended name. Think of slots as additional labeling for the -directory entry of the file to which they correspond. Microsoft -prefers to refer to the 8.3 entry for a file as its alias and the -extended slot directory entries as the file name. - -The C structure for a slot directory entry follows: - - struct slot { // Up to 13 characters of a long name - unsigned char id; // sequence number for slot - unsigned char name0_4[10]; // first 5 characters in name - unsigned char attr; // attribute byte - unsigned char reserved; // always 0 - unsigned char alias_checksum; // checksum for 8.3 alias - unsigned char name5_10[12]; // 6 more characters in name - unsigned char start[2]; // starting cluster number - unsigned char name11_12[4]; // last 2 characters in name - }; - -If the layout of the slots looks a little odd, it's only -because of Microsoft's efforts to maintain compatibility with old -software. The slots must be disguised to prevent old software from -panicking. To this end, a number of measures are taken: - - 1) The attribute byte for a slot directory entry is always set - to 0x0f. This corresponds to an old directory entry with - attributes of "hidden", "system", "read-only", and "volume - label". Most old software will ignore any directory - entries with the "volume label" bit set. Real volume label - entries don't have the other three bits set. - - 2) The starting cluster is always set to 0, an impossible - value for a DOS file. - -Because the extended FAT system is backward compatible, it is -possible for old software to modify directory entries. Measures must -be taken to ensure the validity of slots. An extended FAT system can -verify that a slot does in fact belong to an 8.3 directory entry by -the following: - - 1) Positioning. Slots for a file always immediately proceed - their corresponding 8.3 directory entry. In addition, each - slot has an id which marks its order in the extended file - name. Here is a very abbreviated view of an 8.3 directory - entry and its corresponding long name slots for the file - "My Big File.Extension which is long": - - <proceeding files...> - <slot #3, id = 0x43, characters = "h is long"> - <slot #2, id = 0x02, characters = "xtension whic"> - <slot #1, id = 0x01, characters = "My Big File.E"> - <directory entry, name = "MYBIGFIL.EXT"> - - Note that the slots are stored from last to first. Slots - are numbered from 1 to N. The Nth slot is or'ed with 0x40 - to mark it as the last one. - - 2) Checksum. Each slot has an "alias_checksum" value. The - checksum is calculated from the 8.3 name using the - following algorithm: - - for (sum = i = 0; i < 11; i++) { - sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i] - } - - 3) If there is free space in the final slot, a Unicode NULL (0x0000) - is stored after the final character. After that, all unused - characters in the final slot are set to Unicode 0xFFFF. - -Finally, note that the extended name is stored in Unicode. Each Unicode -character takes either two or four bytes, UTF-16LE encoded. |