348 lines
16 KiB
Plaintext
348 lines
16 KiB
Plaintext
|
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 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
|
||
|
|
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
|
||
|
|
|
||
|
|
dos1xfloppy -- 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
|
||
|
|
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
|
||
|
|
the inode from the memory. As a result, for any dependency on
|
||
|
|
the fallocated region, user should make sure to recheck fallocate
|
||
|
|
after reopening the file.
|
||
|
|
|
||
|
|
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.
|