docs: filesystems: convert hpfs.txt to ReST

- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/581019c3120938118aa55ba28902b62083c3f37a.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 353 insertions, 0 deletions

diff --git a/Documentation/filesystems/hpfs.rst b/Documentation/filesystems/hpfs.rst
new file mode 100644
index 000000000000..0db152278572
--- /dev/null
+++ b/Documentation/filesystems/hpfs.rst
@@ -0,0 +1,353 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+Read/Write HPFS 2.09
+====================
+
+1998-2004, Mikulas Patocka
+
+:email: mikulas@artax.karlin.mff.cuni.cz
+:homepage: http://artax.karlin.mff.cuni.cz/~mikulas/vyplody/hpfs/index-e.cgi
+
+Credits
+=======
+Chris Smith, 1993, original read-only HPFS, some code and hpfs structures file
+	is taken from it
+
+Jacques Gelinas, MSDos mmap, Inspired by fs/nfs/mmap.c (Jon Tombs 15 Aug 1993)
+
+Werner Almesberger, 1992, 1993, MSDos option parser & CR/LF conversion
+
+Mount options
+
+uid=xxx,gid=xxx,umask=xxx (default uid=gid=0 umask=default_system_umask)
+	Set owner/group/mode for files that do not have it specified in extended
+	attributes. Mode is inverted umask - for example umask 027 gives owner
+	all permission, group read permission and anybody else no access. Note
+	that for files mode is anded with 0666. If you want files to have 'x'
+	rights, you must use extended attributes.
+case=lower,asis (default asis)
+	File name lowercasing in readdir.
+conv=binary,text,auto (default binary)
+	CR/LF -> LF conversion, if auto, decision is made according to extension
+	- there is a list of text extensions (I thing it's better to not convert
+	text file than to damage binary file). If you want to change that list,
+	change it in the source. Original readonly HPFS contained some strange
+	heuristic algorithm that I removed. I thing it's danger to let the
+	computer decide whether file is text or binary. For example, DJGPP
+	binaries contain small text message at the beginning and they could be
+	misidentified and damaged under some circumstances.
+check=none,normal,strict (default normal)
+	Check level. Selecting none will cause only little speedup and big
+	danger. I tried to write it so that it won't crash if check=normal on
+	corrupted filesystems. check=strict means many superfluous checks -
+	used for debugging (for example it checks if file is allocated in
+	bitmaps when accessing it).
+errors=continue,remount-ro,panic (default remount-ro)
+	Behaviour when filesystem errors found.
+chkdsk=no,errors,always (default errors)
+	When to mark filesystem dirty so that OS/2 checks it.
+eas=no,ro,rw (default rw)
+	What to do with extended attributes. 'no' - ignore them and use always
+	values specified in uid/gid/mode options. 'ro' - read extended
+	attributes but do not create them. 'rw' - create extended attributes
+	when you use chmod/chown/chgrp/mknod/ln -s on the filesystem.
+timeshift=(-)nnn (default 0)
+	Shifts the time by nnn seconds. For example, if you see under linux
+	one hour more, than under os/2, use timeshift=-3600.
+
+
+File names
+==========
+
+As in OS/2, filenames are case insensitive. However, shell thinks that names
+are case sensitive, so for example when you create a file FOO, you can use
+'cat FOO', 'cat Foo', 'cat foo' or 'cat F*' but not 'cat f*'. Note, that you
+also won't be able to compile linux kernel (and maybe other things) on HPFS
+because kernel creates different files with names like bootsect.S and
+bootsect.s. When searching for file thats name has characters >= 128, codepages
+are used - see below.
+OS/2 ignores dots and spaces at the end of file name, so this driver does as
+well. If you create 'a. ...', the file 'a' will be created, but you can still
+access it under names 'a.', 'a..', 'a .  . . ' etc.
+
+
+Extended attributes
+===================
+
+On HPFS partitions, OS/2 can associate to each file a special information called
+extended attributes. Extended attributes are pairs of (key,value) where key is
+an ascii string identifying that attribute and value is any string of bytes of
+variable length. OS/2 stores window and icon positions and file types there. So
+why not use it for unix-specific info like file owner or access rights? This
+driver can do it. If you chown/chgrp/chmod on a hpfs partition, extended
+attributes with keys "UID", "GID" or "MODE" and 2-byte values are created. Only
+that extended attributes those value differs from defaults specified in mount
+options are created. Once created, the extended attributes are never deleted,
+they're just changed. It means that when your default uid=0 and you type
+something like 'chown luser file; chown root file' the file will contain
+extended attribute UID=0. And when you umount the fs and mount it again with
+uid=luser_uid, the file will be still owned by root! If you chmod file to 444,
+extended attribute "MODE" will not be set, this special case is done by setting
+read-only flag. When you mknod a block or char device, besides "MODE", the
+special 4-byte extended attribute "DEV" will be created containing the device
+number. Currently this driver cannot resize extended attributes - it means
+that if somebody (I don't know who?) has set "UID", "GID", "MODE" or "DEV"
+attributes with different sizes, they won't be rewritten and changing these
+values doesn't work.
+
+
+Symlinks
+========
+
+You can do symlinks on HPFS partition, symlinks are achieved by setting extended
+attribute named "SYMLINK" with symlink value. Like on ext2, you can chown and
+chgrp symlinks but I don't know what is it good for. chmoding symlink results
+in chmoding file where symlink points. These symlinks are just for Linux use and
+incompatible with OS/2. OS/2 PmShell symlinks are not supported because they are
+stored in very crazy way. They tried to do it so that link changes when file is
+moved ... sometimes it works. But the link is partly stored in directory
+extended attributes and partly in OS2SYS.INI. I don't want (and don't know how)
+to analyze or change OS2SYS.INI.
+
+
+Codepages
+=========
+
+HPFS can contain several uppercasing tables for several codepages and each
+file has a pointer to codepage its name is in. However OS/2 was created in
+America where people don't care much about codepages and so multiple codepages
+support is quite buggy. I have Czech OS/2 working in codepage 852 on my disk.
+Once I booted English OS/2 working in cp 850 and I created a file on my 852
+partition. It marked file name codepage as 850 - good. But when I again booted
+Czech OS/2, the file was completely inaccessible under any name. It seems that
+OS/2 uppercases the search pattern with its system code page (852) and file
+name it's comparing to with its code page (850). These could never match. Is it
+really what IBM developers wanted? But problems continued. When I created in
+Czech OS/2 another file in that directory, that file was inaccessible too. OS/2
+probably uses different uppercasing method when searching where to place a file
+(note, that files in HPFS directory must be sorted) and when searching for
+a file. Finally when I opened this directory in PmShell, PmShell crashed (the
+funny thing was that, when rebooted, PmShell tried to reopen this directory
+again :-). chkdsk happily ignores these errors and only low-level disk
+modification saved me.  Never mix different language versions of OS/2 on one
+system although HPFS was designed to allow that.
+OK, I could implement complex codepage support to this driver but I think it
+would cause more problems than benefit with such buggy implementation in OS/2.
+So this driver simply uses first codepage it finds for uppercasing and
+lowercasing no matter what's file codepage index. Usually all file names are in
+this codepage - if you don't try to do what I described above :-)
+
+
+Known bugs
+==========
+
+HPFS386 on OS/2 server is not supported. HPFS386 installed on normal OS/2 client
+should work. If you have OS/2 server, use only read-only mode. I don't know how
+to handle some HPFS386 structures like access control list or extended perm
+list, I don't know how to delete them when file is deleted and how to not
+overwrite them with extended attributes. Send me some info on these structures
+and I'll make it. However, this driver should detect presence of HPFS386
+structures, remount read-only and not destroy them (I hope).
+
+When there's not enough space for extended attributes, they will be truncated
+and no error is returned.
+
+OS/2 can't access files if the path is longer than about 256 chars but this
+driver allows you to do it. chkdsk ignores such errors.
+
+Sometimes you won't be able to delete some files on a very full filesystem
+(returning error ENOSPC). That's because file in non-leaf node in directory tree
+(one directory, if it's large, has dirents in tree on HPFS) must be replaced
+with another node when deleted. And that new file might have larger name than
+the old one so the new name doesn't fit in directory node (dnode). And that
+would result in directory tree splitting, that takes disk space. Workaround is
+to delete other files that are leaf (probability that the file is non-leaf is
+about 1/50) or to truncate file first to make some space.
+You encounter this problem only if you have many directories so that
+preallocated directory band is full i.e.::
+
+	number_of_directories / size_of_filesystem_in_mb > 4.
+
+You can't delete open directories.
+
+You can't rename over directories (what is it good for?).
+
+Renaming files so that only case changes doesn't work. This driver supports it
+but vfs doesn't. Something like 'mv file FILE' won't work.
+
+All atimes and directory mtimes are not updated. That's because of performance
+reasons. If you extremely wish to update them, let me know, I'll write it (but
+it will be slow).
+
+When the system is out of memory and swap, it may slightly corrupt filesystem
+(lost files, unbalanced directories). (I guess all filesystem may do it).
+
+When compiled, you get warning: function declaration isn't a prototype. Does
+anybody know what does it mean?
+
+
+What does "unbalanced tree" message mean?
+=========================================
+
+Old versions of this driver created sometimes unbalanced dnode trees. OS/2
+chkdsk doesn't scream if the tree is unbalanced (and sometimes creates
+unbalanced trees too :-) but both HPFS and HPFS386 contain bug that it rarely
+crashes when the tree is not balanced. This driver handles unbalanced trees
+correctly and writes warning if it finds them. If you see this message, this is
+probably because of directories created with old version of this driver.
+Workaround is to move all files from that directory to another and then back
+again. Do it in Linux, not OS/2! If you see this message in directory that is
+whole created by this driver, it is BUG - let me know about it.
+
+
+Bugs in OS/2
+============
+
+When you have two (or more) lost directories pointing each to other, chkdsk
+locks up when repairing filesystem.
+
+Sometimes (I think it's random) when you create a file with one-char name under
+OS/2, OS/2 marks it as 'long'. chkdsk then removes this flag saying "Minor fs
+error corrected".
+
+File names like "a .b" are marked as 'long' by OS/2 but chkdsk "corrects" it and
+marks them as short (and writes "minor fs error corrected"). This bug is not in
+HPFS386.
+
+Codepage bugs described above
+=============================
+
+If you don't install fixpacks, there are many, many more...
+
+
+History
+=======
+
+====== =========================================================================
+0.90   First public release
+0.91   Fixed bug that caused shooting to memory when write_inode was called on
+       open inode (rarely happened)
+0.92   Fixed a little memory leak in freeing directory inodes
+0.93   Fixed bug that locked up the machine when there were too many filenames
+       with first 15 characters same
+       Fixed write_file to zero file when writing behind file end
+0.94   Fixed a little memory leak when trying to delete busy file or directory
+0.95   Fixed a bug that i_hpfs_parent_dir was not updated when moving files
+1.90   First version for 2.1.1xx kernels
+1.91   Fixed a bug that chk_sectors failed when sectors were at the end of disk
+       Fixed a race-condition when write_inode is called while deleting file
+       Fixed a bug that could possibly happen (with very low probability) when
+       using 0xff in filenames.
+
+       Rewritten locking to avoid race-conditions
+
+       Mount option 'eas' now works
+
+       Fsync no longer returns error
+
+       Files beginning with '.' are marked hidden
+
+       Remount support added
+
+       Alloc is not so slow when filesystem becomes full
+
+       Atimes are no more updated because it slows down operation
+
+       Code cleanup (removed all commented debug prints)
+1.92   Corrected a bug when sync was called just before closing file
+1.93   Modified, so that it works with kernels >= 2.1.131, I don't know if it
+       works with previous versions
+
+       Fixed a possible problem with disks > 64G (but I don't have one, so I can't
+       test it)
+
+       Fixed a file overflow at 2G
+
+       Added new option 'timeshift'
+
+       Changed behaviour on HPFS386: It is now possible to operate on HPFS386 in
+       read-only mode
+
+       Fixed a bug that slowed down alloc and prevented allocating 100% space
+       (this bug was not destructive)
+1.94   Added workaround for one bug in Linux
+
+       Fixed one buffer leak
+
+       Fixed some incompatibilities with large extended attributes (but it's still
+       not 100% ok, I have no info on it and OS/2 doesn't want to create them)
+
+       Rewritten allocation
+
+       Fixed a bug with i_blocks (du sometimes didn't display correct values)
+
+       Directories have no longer archive attribute set (some programs don't like
+       it)
+
+       Fixed a bug that it set badly one flag in large anode tree (it was not
+       destructive)
+1.95   Fixed one buffer leak, that could happen on corrupted filesystem
+
+       Fixed one bug in allocation in 1.94
+1.96   Added workaround for one bug in OS/2 (HPFS locked up, HPFS386 reported
+       error sometimes when opening directories in PMSHELL)
+
+       Fixed a possible bitmap race
+
+       Fixed possible problem on large disks
+
+       You can now delete open files
+
+       Fixed a nondestructive race in rename
+1.97   Support for HPFS v3 (on large partitions)
+
+       ZFixed a bug that it didn't allow creation of files > 128M
+       (it should be 2G)
+1.97.1 Changed names of global symbols
+
+       Fixed a bug when chmoding or chowning root directory
+1.98   Fixed a deadlock when using old_readdir
+       Better directory handling; workaround for "unbalanced tree" bug in OS/2
+1.99   Corrected a possible problem when there's not enough space while deleting
+       file
+
+       Now it tries to truncate the file if there's not enough space when
+       deleting
+
+       Removed a lot of redundant code
+2.00   Fixed a bug in rename (it was there since 1.96)
+       Better anti-fragmentation strategy
+2.01   Fixed problem with directory listing over NFS
+
+       Directory lseek now checks for proper parameters
+
+       Fixed race-condition in buffer code - it is in all filesystems in Linux;
+       when reading device (cat /dev/hda) while creating files on it, files
+       could be damaged
+2.02   Workaround for bug in breada in Linux. breada could cause accesses beyond
+       end of partition
+2.03   Char, block devices and pipes are correctly created
+
+       Fixed non-crashing race in unlink (Alexander Viro)
+
+       Now it works with Japanese version of OS/2
+2.04   Fixed error when ftruncate used to extend file
+2.05   Fixed crash when got mount parameters without =
+
+       Fixed crash when allocation of anode failed due to full disk
+
+       Fixed some crashes when block io or inode allocation failed
+2.06   Fixed some crash on corrupted disk structures
+
+       Better allocation strategy
+
+       Reschedule points added so that it doesn't lock CPU long time
+
+       It should work in read-only mode on Warp Server
+2.07   More fixes for Warp Server. Now it really works
+2.08   Creating new files is not so slow on large disks
+
+       An attempt to sync deleted file does not generate filesystem error
+2.09   Fixed error on extremely fragmented files
+====== =========================================================================