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 for the
  		 filesystem with this option. If 'uni_xlate' gets set,
  		 UTF-8 gets disabled.
  
  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
  
  
  <bool>: 0,1,yes,no,true,false
  
  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 two bytes.