forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
387 lines
14 KiB
387 lines
14 KiB
==== |
|
VFAT |
|
==== |
|
|
|
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 utf8 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 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. |
|
|
|
**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-provisioned 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 <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. |
|
|
|
|
|
|
|
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. |
|
|
|
|
|
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 [email protected] 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:: 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:: 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 either two or four bytes, UTF-16LE encoded.
|
|
|