Documentation: filesystems: convert vfat.txt to RST

   autofs

   virtiofs

   vfat

====

VFAT

====

USING VFAT

----------------------------------------------------------------------

To use the vfat filesystem, use the filesystem type 'vfat'.  i.e.

==========

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.

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.

==================

**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.

**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)).

**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.

**dmask=###**

	The permission mask for the directory.

	The default is the umask of current process.

fmask=###     -- The permission mask for files.

**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.

**allow_utime=###**

	This option controls the permission check of mtime/atime.

                  20 - If current process is in group of file's group ID,

		**-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)

		**-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

	check is too unflexible. With this option you can

	relax it.

codepage=###  -- Sets the codepage number for converting to shortname

**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

**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

	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.

.. note:: ``iocharset=utf8`` is not recommended. If unsure, you should consider

	  the utf8 option instead.

utf8=<bool>   -- UTF-8 is the filesystem safe version of Unicode that

**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

**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,

	that gets used is ':' and the four digits of hexadecimal

	unicode.

nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will

**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'. 

	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

**usefree**

	Use the "free clusters" value stored on FSINFO. It will

	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.

**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

**check=s|r|n**

	Case sensitivity checking setting.

nocase        -- This was deprecated for vfat. Use shortname=win95 instead.

	**s**: strict, case sensitive

shortname=lower|win95|winnt|mixed

	      -- Shortname display/create setting.

		 lower: convert to lowercase for display,

	**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,

	**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.

	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

**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

	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

**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.

**debug**

	Can be set, but unused by the current implementation.

sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as

**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

**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,

**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

**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

**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

**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

		**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

		**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

		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

	To maintain backward compatibility, ``'-o nfs'`` is also accepted,

	defaulting to "stale_rw".

dos1xfloppy  -- If set, use a fallback default BIOS Parameter Block

**dos1xfloppy  <bool>: 0,1,yes,no,true,false**

	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

==========

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

after reopening the file.

TODO

----------------------------------------------------------------------

* Need to get rid of the raw scanning stuff.  Instead, always use

====

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

=================

- 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.

- 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

`<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 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

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

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:

Windows 95 filesystem::

        struct directory { // Short 8.3 names

                unsigned char name[8];          // file name

                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

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

.. note:: 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.

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:

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 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

           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":

           "My Big File.Extension which is long"::

                <proceeding files...>

                <slot #3, id = 0x43, characters = "h is long">

                <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

           .. note:: 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:

           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) 

	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.

VFAT/FAT/MSDOS FILESYSTEM

M:	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

S:	Maintained

F:	Documentation/filesystems/vfat.txt

F:	Documentation/filesystems/vfat.rst

F:	fs/fat/

VFIO DRIVER