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Based on kernel version 4.8. Page generated on 2016-10-06 23:16 EST.

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