Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 347 insertions, 0 deletions

diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
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+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 either two or four bytes, UTF-16LE encoded.