1====
2VFAT
3====
4
5USING VFAT
6==========
7
8To use the vfat filesystem, use the filesystem type 'vfat'.  i.e.::
9
10  mount -t vfat /dev/fd0 /mnt
11
12
13No special partition formatter is required,
14'mkdosfs' will work fine if you want to format from within Linux.
15
16VFAT MOUNT OPTIONS
17==================
18
19**uid=###**
20	Set the owner of all files on this filesystem.
21	The default is the uid of current process.
22
23**gid=###**
24	Set the group of all files on this filesystem.
25	The default is the gid of current process.
26
27**umask=###**
28	The permission mask (for files and directories, see *umask(1)*).
29	The default is the umask of current process.
30
31**dmask=###**
32	The permission mask for the directory.
33	The default is the umask of current process.
34
35**fmask=###**
36	The permission mask for files.
37	The default is the umask of current process.
38
39**allow_utime=###**
40	This option controls the permission check of mtime/atime.
41
42		**-20**: If current process is in group of file's group ID,
43                you can change timestamp.
44
45		**-2**: Other users can change timestamp.
46
47	The default is set from dmask option. If the directory is
48	writable, utime(2) is also allowed. i.e. ~dmask & 022.
49
50	Normally utime(2) checks current process is owner of
51	the file, or it has CAP_FOWNER capability. But FAT
52	filesystem doesn't have uid/gid on disk, so normal
53	check is too unflexible. With this option you can
54	relax it.
55
56**codepage=###**
57	Sets the codepage number for converting to shortname
58	characters on FAT filesystem.
59	By default, FAT_DEFAULT_CODEPAGE setting is used.
60
61**iocharset=<name>**
62	Character set to use for converting between the
63	encoding is used for user visible filename and 16 bit
64	Unicode characters. Long filenames are stored on disk
65	in Unicode format, but Unix for the most part doesn't
66	know how to deal with Unicode.
67	By default, FAT_DEFAULT_IOCHARSET setting is used.
68
69	There is also an option of doing UTF-8 translations
70	with the utf8 option.
71
72.. note:: ``iocharset=utf8`` is not recommended. If unsure, you should consider
73	  the utf8 option instead.
74
75**utf8=<bool>**
76	UTF-8 is the filesystem safe version of Unicode that
77	is used by the console. It can be enabled or disabled
78	for the filesystem with this option.
79	If 'uni_xlate' gets set, UTF-8 gets disabled.
80	By default, FAT_DEFAULT_UTF8 setting is used.
81
82**uni_xlate=<bool>**
83	Translate unhandled Unicode characters to special
84	escaped sequences.  This would let you backup and
85	restore filenames that are created with any Unicode
86	characters.  Until Linux supports Unicode for real,
87	this gives you an alternative.  Without this option,
88	a '?' is used when no translation is possible.  The
89	escape character is ':' because it is otherwise
90	illegal on the vfat filesystem.  The escape sequence
91	that gets used is ':' and the four digits of hexadecimal
92	unicode.
93
94**nonumtail=<bool>**
95	When creating 8.3 aliases, normally the alias will
96	end in '~1' or tilde followed by some number.  If this
97	option is set, then if the filename is
98	"longfilename.txt" and "longfile.txt" does not
99	currently exist in the directory, longfile.txt will
100	be the short alias instead of longfi~1.txt.
101
102**usefree**
103	Use the "free clusters" value stored on FSINFO. It will
104	be used to determine number of free clusters without
105	scanning disk. But it's not used by default, because
106	recent Windows don't update it correctly in some
107	case. If you are sure the "free clusters" on FSINFO is
108	correct, by this option you can avoid scanning disk.
109
110**quiet**
111	Stops printing certain warning messages.
112
113**check=s|r|n**
114	Case sensitivity checking setting.
115
116	**s**: strict, case sensitive
117
118	**r**: relaxed, case insensitive
119
120	**n**: normal, default setting, currently case insensitive
121
122**nocase**
123	This was deprecated for vfat. Use ``shortname=win95`` instead.
124
125**shortname=lower|win95|winnt|mixed**
126	Shortname display/create setting.
127
128	**lower**: convert to lowercase for display,
129	emulate the Windows 95 rule for create.
130
131	**win95**: emulate the Windows 95 rule for display/create.
132
133	**winnt**: emulate the Windows NT rule for display/create.
134
135	**mixed**: emulate the Windows NT rule for display,
136	emulate the Windows 95 rule for create.
137
138	Default setting is `mixed`.
139
140**tz=UTC**
141	Interpret timestamps as UTC rather than local time.
142	This option disables the conversion of timestamps
143	between local time (as used by Windows on FAT) and UTC
144	(which Linux uses internally).  This is particularly
145	useful when mounting devices (like digital cameras)
146	that are set to UTC in order to avoid the pitfalls of
147	local time.
148
149**time_offset=minutes**
150	Set offset for conversion of timestamps from local time
151	used by FAT to UTC. I.e. <minutes> minutes will be subtracted
152	from each timestamp to convert it to UTC used internally by
153	Linux. This is useful when time zone set in ``sys_tz`` is
154	not the time zone used by the filesystem. Note that this
155	option still does not provide correct time stamps in all
156	cases in presence of DST - time stamps in a different DST
157	setting will be off by one hour.
158
159**showexec**
160	If set, the execute permission bits of the file will be
161	allowed only if the extension part of the name is .EXE,
162	.COM, or .BAT. Not set by default.
163
164**debug**
165	Can be set, but unused by the current implementation.
166
167**sys_immutable**
168	If set, ATTR_SYS attribute on FAT is handled as
169	IMMUTABLE flag on Linux. Not set by default.
170
171**flush**
172	If set, the filesystem will try to flush to disk more
173	early than normal. Not set by default.
174
175**rodir**
176	FAT has the ATTR_RO (read-only) attribute. On Windows,
177	the ATTR_RO of the directory will just be ignored,
178	and is used only by applications as a flag (e.g. it's set
179	for the customized folder).
180
181	If you want to use ATTR_RO as read-only flag even for
182	the directory, set this option.
183
184**errors=panic|continue|remount-ro**
185	specify FAT behavior on critical errors: panic, continue
186	without doing anything or remount the partition in
187	read-only mode (default behavior).
188
189**discard**
190	If set, issues discard/TRIM commands to the block
191	device when blocks are freed. This is useful for SSD devices
192	and sparse/thinly-provisioned LUNs.
193
194**nfs=stale_rw|nostale_ro**
195	Enable this only if you want to export the FAT filesystem
196	over NFS.
197
198		**stale_rw**: This option maintains an index (cache) of directory
199		*inodes* by *i_logstart* which is used by the nfs-related code to
200		improve look-ups. Full file operations (read/write) over NFS is
201		supported but with cache eviction at NFS server, this could
202		result in ESTALE issues.
203
204		**nostale_ro**: This option bases the *inode* number and filehandle
205		on the on-disk location of a file in the MS-DOS directory entry.
206		This ensures that ESTALE will not be returned after a file is
207		evicted from the inode cache. However, it means that operations
208		such as rename, create and unlink could cause filehandles that
209		previously pointed at one file to point at a different file,
210		potentially causing data corruption. For this reason, this
211		option also mounts the filesystem readonly.
212
213	To maintain backward compatibility, ``'-o nfs'`` is also accepted,
214	defaulting to "stale_rw".
215
216**dos1xfloppy  <bool>: 0,1,yes,no,true,false**
217	If set, use a fallback default BIOS Parameter Block
218	configuration, determined by backing device size. These static
219	parameters match defaults assumed by DOS 1.x for 160 kiB,
220	180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
221
222
223
224LIMITATION
225==========
226
227The fallocated region of file is discarded at umount/evict time
228when using fallocate with FALLOC_FL_KEEP_SIZE.
229So, User should assume that fallocated region can be discarded at
230last close if there is memory pressure resulting in eviction of
231the inode from the memory. As a result, for any dependency on
232the fallocated region, user should make sure to recheck fallocate
233after reopening the file.
234
235TODO
236====
237Need to get rid of the raw scanning stuff.  Instead, always use
238a get next directory entry approach.  The only thing left that uses
239raw scanning is the directory renaming code.
240
241
242POSSIBLE PROBLEMS
243=================
244
245- vfat_valid_longname does not properly checked reserved names.
246- When a volume name is the same as a directory name in the root
247  directory of the filesystem, the directory name sometimes shows
248  up as an empty file.
249- autoconv option does not work correctly.
250
251
252TEST SUITE
253==========
254If you plan to make any modifications to the vfat filesystem, please
255get the test suite that comes with the vfat distribution at
256
257`<http://web.archive.org/web/*/http://bmrc.berkeley.edu/people/chaffee/vfat.html>`_
258
259This tests quite a few parts of the vfat filesystem and additional
260tests for new features or untested features would be appreciated.
261
262NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
263=============================================
264This documentation was provided by Galen C. Hunt gchunt@cs.rochester.edu and
265lightly annotated by Gordon Chaffee.
266
267This document presents a very rough, technical overview of my
268knowledge of the extended FAT file system used in Windows NT 3.5 and
269Windows 95.  I don't guarantee that any of the following is correct,
270but it appears to be so.
271
272The extended FAT file system is almost identical to the FAT
273file system used in DOS versions up to and including *6.223410239847*
274:-).  The significant change has been the addition of long file names.
275These names support up to 255 characters including spaces and lower
276case characters as opposed to the traditional 8.3 short names.
277
278Here is the description of the traditional FAT entry in the current
279Windows 95 filesystem::
280
281        struct directory { // Short 8.3 names
282                unsigned char name[8];          // file name
283                unsigned char ext[3];           // file extension
284                unsigned char attr;             // attribute byte
285		unsigned char lcase;		// Case for base and extension
286		unsigned char ctime_ms;		// Creation time, milliseconds
287		unsigned char ctime[2];		// Creation time
288		unsigned char cdate[2];		// Creation date
289		unsigned char adate[2];		// Last access date
290		unsigned char reserved[2];	// reserved values (ignored)
291                unsigned char time[2];          // time stamp
292                unsigned char date[2];          // date stamp
293                unsigned char start[2];         // starting cluster number
294                unsigned char size[4];          // size of the file
295        };
296
297
298The lcase field specifies if the base and/or the extension of an 8.3
299name should be capitalized.  This field does not seem to be used by
300Windows 95 but it is used by Windows NT.  The case of filenames is not
301completely compatible from Windows NT to Windows 95.  It is not completely
302compatible in the reverse direction, however.  Filenames that fit in
303the 8.3 namespace and are written on Windows NT to be lowercase will
304show up as uppercase on Windows 95.
305
306.. note:: Note that the ``start`` and ``size`` values are actually little
307          endian integer values.  The descriptions of the fields in this
308          structure are public knowledge and can be found elsewhere.
309
310With the extended FAT system, Microsoft has inserted extra
311directory entries for any files with extended names.  (Any name which
312legally fits within the old 8.3 encoding scheme does not have extra
313entries.)  I call these extra entries slots.  Basically, a slot is a
314specially formatted directory entry which holds up to 13 characters of
315a file's extended name.  Think of slots as additional labeling for the
316directory entry of the file to which they correspond.  Microsoft
317prefers to refer to the 8.3 entry for a file as its alias and the
318extended slot directory entries as the file name.
319
320The C structure for a slot directory entry follows::
321
322        struct slot { // Up to 13 characters of a long name
323                unsigned char id;               // sequence number for slot
324                unsigned char name0_4[10];      // first 5 characters in name
325                unsigned char attr;             // attribute byte
326                unsigned char reserved;         // always 0
327                unsigned char alias_checksum;   // checksum for 8.3 alias
328                unsigned char name5_10[12];     // 6 more characters in name
329                unsigned char start[2];         // starting cluster number
330                unsigned char name11_12[4];     // last 2 characters in name
331        };
332
333
334If the layout of the slots looks a little odd, it's only
335because of Microsoft's efforts to maintain compatibility with old
336software.  The slots must be disguised to prevent old software from
337panicking.  To this end, a number of measures are taken:
338
339        1) The attribute byte for a slot directory entry is always set
340           to 0x0f.  This corresponds to an old directory entry with
341           attributes of "hidden", "system", "read-only", and "volume
342           label".  Most old software will ignore any directory
343           entries with the "volume label" bit set.  Real volume label
344           entries don't have the other three bits set.
345
346        2) The starting cluster is always set to 0, an impossible
347           value for a DOS file.
348
349Because the extended FAT system is backward compatible, it is
350possible for old software to modify directory entries.  Measures must
351be taken to ensure the validity of slots.  An extended FAT system can
352verify that a slot does in fact belong to an 8.3 directory entry by
353the following:
354
355        1) Positioning.  Slots for a file always immediately proceed
356           their corresponding 8.3 directory entry.  In addition, each
357           slot has an id which marks its order in the extended file
358           name.  Here is a very abbreviated view of an 8.3 directory
359           entry and its corresponding long name slots for the file
360           "My Big File.Extension which is long"::
361
362                <proceeding files...>
363                <slot #3, id = 0x43, characters = "h is long">
364                <slot #2, id = 0x02, characters = "xtension whic">
365                <slot #1, id = 0x01, characters = "My Big File.E">
366                <directory entry, name = "MYBIGFIL.EXT">
367
368
369           .. note:: Note that the slots are stored from last to first.  Slots
370		     are numbered from 1 to N.  The Nth slot is ``or'ed`` with
371		     0x40 to mark it as the last one.
372
373        2) Checksum.  Each slot has an alias_checksum value.  The
374           checksum is calculated from the 8.3 name using the
375           following algorithm::
376
377                for (sum = i = 0; i < 11; i++) {
378                        sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
379                }
380
381
382	3) If there is free space in the final slot, a Unicode ``NULL (0x0000)``
383	   is stored after the final character.  After that, all unused
384	   characters in the final slot are set to Unicode 0xFFFF.
385
386Finally, note that the extended name is stored in Unicode.  Each Unicode
387character takes either two or four bytes, UTF-16LE encoded.
388