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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 ---------------------------------------------------------------------- codepage=### -- Sets the codepage for converting to shortname characters on FAT and VFAT filesystems. By default, codepage 437 is used. This is the default for the U.S. and some European countries. iocharset=name-- Character set to use for converting between 8 bit characters 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. There is also an option of doing UTF8 translations with the utf8 option. utf8 -- UTF8 is the filesystem safe version of Unicode that is used by the console. It can be be enabled for the filesystem with this option. If 'uni_xlate' gets set, UTF8 gets disabled. uni_xlate -- 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, where u is the unicode character, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12), posix -- Allow names of same letters, different case such as 'LongFileName' and 'longfilename' to coexist. This has some problems currently because 8.3 conflicts are not handled correctly for Posix filesystem compliance. nonumtail -- 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'. quiet -- Stops printing certain warning messages. Explanation of Native Language Support in the VFAT Filesystem ---------------------------------------------------------------------- There are two different character sets are needed by the vfat filesystem. The first is the codepage character set. The codepage is the character set that is used to store short filenames on disk. Its mount option is 'codepage=437' which 437 is the codepage number. Long filenames are stored in Unicode, but since the Linux filesystem doesn't deal with 16 bit characters, we need some way of converting characters. There are a couple options of how to do this. One is to use the 'utf8' mount option and I will cover that a bit later. The other is to use the 'iocharset=iso8859-1' mount option where the iso8859-1 tells the filesystem which character set is used for input and output. If you are in Russia, you might specify koi8-r here. If a Unicode character on disk cannot be mapped to anything in the iocharset, it is replaced with a '?'. The iocharset is used to convert long filenames to and from Unicode. It is currently implemented. The codepage is used to convert short filenames to and from the iocharset. This translation is not currently implemented. If no iocharset is specified and the default is unable to be loaded, the mount will succeed while falling back to doing no conversions at all. If a charset is explicity specified and the charset cannot be loaded, the mount will fail. For the codepage, the default mount option is 'codepage=437'. If a codepage is explicitly asked for and the load of the character set fails, the mount will fail. Is no codepage is explicitly asked for and the load of the character set fails, the load will still succeed. UTF8 is an 8 bit, filesystem safe representation of Unicode. It does not lose any information in the conversion. However, you need to have a terminal or a program that knows how to deal with UTF8. The Linux console can be put into a mode where it will correctly display UTF8 characters. I don't know if there is a similar mode for xterms, but I don't believe there is. More information about UTF8 can be found at http://www.unicode.com TODO ---------------------------------------------------------------------- * When only shortnames exist, translate them from the codepage character set to the iocharset. Currently, translations only occur when longnames exist. To translate, first convert from codepage to Unicode and then to the output character set. * Need to add dcache_lookup code msdos filesystem. This means the directories need to be versioned like the vfat filesystem. * 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. * Fix the Posix filesystem support to work in 8.3 space. This involves renaming aliases if a conflict occurs between a new filename and an old alias. This is quite a mess. 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 empty an empty file. * autoconv option does not work correctly. BUG REPORTS ---------------------------------------------------------------------- If you have trouble with the VFAT filesystem, mail bug reports to chaffee@bugs-bunny.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://www-plateau.cs.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. Theses 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 files 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 panicing. 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 insure 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 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 two bytes.