linux/Documentation/filesystems/hpfs.rst
<<
>>
Prefs
   1.. SPDX-License-Identifier: GPL-2.0
   2
   3====================
   4Read/Write HPFS 2.09
   5====================
   6
   71998-2004, Mikulas Patocka
   8
   9:email: mikulas@artax.karlin.mff.cuni.cz
  10:homepage: https://artax.karlin.mff.cuni.cz/~mikulas/vyplody/hpfs/index-e.cgi
  11
  12Credits
  13=======
  14Chris Smith, 1993, original read-only HPFS, some code and hpfs structures file
  15        is taken from it
  16
  17Jacques Gelinas, MSDos mmap, Inspired by fs/nfs/mmap.c (Jon Tombs 15 Aug 1993)
  18
  19Werner Almesberger, 1992, 1993, MSDos option parser & CR/LF conversion
  20
  21Mount options
  22
  23uid=xxx,gid=xxx,umask=xxx (default uid=gid=0 umask=default_system_umask)
  24        Set owner/group/mode for files that do not have it specified in extended
  25        attributes. Mode is inverted umask - for example umask 027 gives owner
  26        all permission, group read permission and anybody else no access. Note
  27        that for files mode is anded with 0666. If you want files to have 'x'
  28        rights, you must use extended attributes.
  29case=lower,asis (default asis)
  30        File name lowercasing in readdir.
  31conv=binary,text,auto (default binary)
  32        CR/LF -> LF conversion, if auto, decision is made according to extension
  33        - there is a list of text extensions (I thing it's better to not convert
  34        text file than to damage binary file). If you want to change that list,
  35        change it in the source. Original readonly HPFS contained some strange
  36        heuristic algorithm that I removed. I thing it's danger to let the
  37        computer decide whether file is text or binary. For example, DJGPP
  38        binaries contain small text message at the beginning and they could be
  39        misidentified and damaged under some circumstances.
  40check=none,normal,strict (default normal)
  41        Check level. Selecting none will cause only little speedup and big
  42        danger. I tried to write it so that it won't crash if check=normal on
  43        corrupted filesystems. check=strict means many superfluous checks -
  44        used for debugging (for example it checks if file is allocated in
  45        bitmaps when accessing it).
  46errors=continue,remount-ro,panic (default remount-ro)
  47        Behaviour when filesystem errors found.
  48chkdsk=no,errors,always (default errors)
  49        When to mark filesystem dirty so that OS/2 checks it.
  50eas=no,ro,rw (default rw)
  51        What to do with extended attributes. 'no' - ignore them and use always
  52        values specified in uid/gid/mode options. 'ro' - read extended
  53        attributes but do not create them. 'rw' - create extended attributes
  54        when you use chmod/chown/chgrp/mknod/ln -s on the filesystem.
  55timeshift=(-)nnn (default 0)
  56        Shifts the time by nnn seconds. For example, if you see under linux
  57        one hour more, than under os/2, use timeshift=-3600.
  58
  59
  60File names
  61==========
  62
  63As in OS/2, filenames are case insensitive. However, shell thinks that names
  64are case sensitive, so for example when you create a file FOO, you can use
  65'cat FOO', 'cat Foo', 'cat foo' or 'cat F*' but not 'cat f*'. Note, that you
  66also won't be able to compile linux kernel (and maybe other things) on HPFS
  67because kernel creates different files with names like bootsect.S and
  68bootsect.s. When searching for file thats name has characters >= 128, codepages
  69are used - see below.
  70OS/2 ignores dots and spaces at the end of file name, so this driver does as
  71well. If you create 'a. ...', the file 'a' will be created, but you can still
  72access it under names 'a.', 'a..', 'a .  . . ' etc.
  73
  74
  75Extended attributes
  76===================
  77
  78On HPFS partitions, OS/2 can associate to each file a special information called
  79extended attributes. Extended attributes are pairs of (key,value) where key is
  80an ascii string identifying that attribute and value is any string of bytes of
  81variable length. OS/2 stores window and icon positions and file types there. So
  82why not use it for unix-specific info like file owner or access rights? This
  83driver can do it. If you chown/chgrp/chmod on a hpfs partition, extended
  84attributes with keys "UID", "GID" or "MODE" and 2-byte values are created. Only
  85that extended attributes those value differs from defaults specified in mount
  86options are created. Once created, the extended attributes are never deleted,
  87they're just changed. It means that when your default uid=0 and you type
  88something like 'chown luser file; chown root file' the file will contain
  89extended attribute UID=0. And when you umount the fs and mount it again with
  90uid=luser_uid, the file will be still owned by root! If you chmod file to 444,
  91extended attribute "MODE" will not be set, this special case is done by setting
  92read-only flag. When you mknod a block or char device, besides "MODE", the
  93special 4-byte extended attribute "DEV" will be created containing the device
  94number. Currently this driver cannot resize extended attributes - it means
  95that if somebody (I don't know who?) has set "UID", "GID", "MODE" or "DEV"
  96attributes with different sizes, they won't be rewritten and changing these
  97values doesn't work.
  98
  99
 100Symlinks
 101========
 102
 103You can do symlinks on HPFS partition, symlinks are achieved by setting extended
 104attribute named "SYMLINK" with symlink value. Like on ext2, you can chown and
 105chgrp symlinks but I don't know what is it good for. chmoding symlink results
 106in chmoding file where symlink points. These symlinks are just for Linux use and
 107incompatible with OS/2. OS/2 PmShell symlinks are not supported because they are
 108stored in very crazy way. They tried to do it so that link changes when file is
 109moved ... sometimes it works. But the link is partly stored in directory
 110extended attributes and partly in OS2SYS.INI. I don't want (and don't know how)
 111to analyze or change OS2SYS.INI.
 112
 113
 114Codepages
 115=========
 116
 117HPFS can contain several uppercasing tables for several codepages and each
 118file has a pointer to codepage its name is in. However OS/2 was created in
 119America where people don't care much about codepages and so multiple codepages
 120support is quite buggy. I have Czech OS/2 working in codepage 852 on my disk.
 121Once I booted English OS/2 working in cp 850 and I created a file on my 852
 122partition. It marked file name codepage as 850 - good. But when I again booted
 123Czech OS/2, the file was completely inaccessible under any name. It seems that
 124OS/2 uppercases the search pattern with its system code page (852) and file
 125name it's comparing to with its code page (850). These could never match. Is it
 126really what IBM developers wanted? But problems continued. When I created in
 127Czech OS/2 another file in that directory, that file was inaccessible too. OS/2
 128probably uses different uppercasing method when searching where to place a file
 129(note, that files in HPFS directory must be sorted) and when searching for
 130a file. Finally when I opened this directory in PmShell, PmShell crashed (the
 131funny thing was that, when rebooted, PmShell tried to reopen this directory
 132again :-). chkdsk happily ignores these errors and only low-level disk
 133modification saved me.  Never mix different language versions of OS/2 on one
 134system although HPFS was designed to allow that.
 135OK, I could implement complex codepage support to this driver but I think it
 136would cause more problems than benefit with such buggy implementation in OS/2.
 137So this driver simply uses first codepage it finds for uppercasing and
 138lowercasing no matter what's file codepage index. Usually all file names are in
 139this codepage - if you don't try to do what I described above :-)
 140
 141
 142Known bugs
 143==========
 144
 145HPFS386 on OS/2 server is not supported. HPFS386 installed on normal OS/2 client
 146should work. If you have OS/2 server, use only read-only mode. I don't know how
 147to handle some HPFS386 structures like access control list or extended perm
 148list, I don't know how to delete them when file is deleted and how to not
 149overwrite them with extended attributes. Send me some info on these structures
 150and I'll make it. However, this driver should detect presence of HPFS386
 151structures, remount read-only and not destroy them (I hope).
 152
 153When there's not enough space for extended attributes, they will be truncated
 154and no error is returned.
 155
 156OS/2 can't access files if the path is longer than about 256 chars but this
 157driver allows you to do it. chkdsk ignores such errors.
 158
 159Sometimes you won't be able to delete some files on a very full filesystem
 160(returning error ENOSPC). That's because file in non-leaf node in directory tree
 161(one directory, if it's large, has dirents in tree on HPFS) must be replaced
 162with another node when deleted. And that new file might have larger name than
 163the old one so the new name doesn't fit in directory node (dnode). And that
 164would result in directory tree splitting, that takes disk space. Workaround is
 165to delete other files that are leaf (probability that the file is non-leaf is
 166about 1/50) or to truncate file first to make some space.
 167You encounter this problem only if you have many directories so that
 168preallocated directory band is full i.e.::
 169
 170        number_of_directories / size_of_filesystem_in_mb > 4.
 171
 172You can't delete open directories.
 173
 174You can't rename over directories (what is it good for?).
 175
 176Renaming files so that only case changes doesn't work. This driver supports it
 177but vfs doesn't. Something like 'mv file FILE' won't work.
 178
 179All atimes and directory mtimes are not updated. That's because of performance
 180reasons. If you extremely wish to update them, let me know, I'll write it (but
 181it will be slow).
 182
 183When the system is out of memory and swap, it may slightly corrupt filesystem
 184(lost files, unbalanced directories). (I guess all filesystem may do it).
 185
 186When compiled, you get warning: function declaration isn't a prototype. Does
 187anybody know what does it mean?
 188
 189
 190What does "unbalanced tree" message mean?
 191=========================================
 192
 193Old versions of this driver created sometimes unbalanced dnode trees. OS/2
 194chkdsk doesn't scream if the tree is unbalanced (and sometimes creates
 195unbalanced trees too :-) but both HPFS and HPFS386 contain bug that it rarely
 196crashes when the tree is not balanced. This driver handles unbalanced trees
 197correctly and writes warning if it finds them. If you see this message, this is
 198probably because of directories created with old version of this driver.
 199Workaround is to move all files from that directory to another and then back
 200again. Do it in Linux, not OS/2! If you see this message in directory that is
 201whole created by this driver, it is BUG - let me know about it.
 202
 203
 204Bugs in OS/2
 205============
 206
 207When you have two (or more) lost directories pointing each to other, chkdsk
 208locks up when repairing filesystem.
 209
 210Sometimes (I think it's random) when you create a file with one-char name under
 211OS/2, OS/2 marks it as 'long'. chkdsk then removes this flag saying "Minor fs
 212error corrected".
 213
 214File names like "a .b" are marked as 'long' by OS/2 but chkdsk "corrects" it and
 215marks them as short (and writes "minor fs error corrected"). This bug is not in
 216HPFS386.
 217
 218Codepage bugs described above
 219=============================
 220
 221If you don't install fixpacks, there are many, many more...
 222
 223
 224History
 225=======
 226
 227====== =========================================================================
 2280.90   First public release
 2290.91   Fixed bug that caused shooting to memory when write_inode was called on
 230       open inode (rarely happened)
 2310.92   Fixed a little memory leak in freeing directory inodes
 2320.93   Fixed bug that locked up the machine when there were too many filenames
 233       with first 15 characters same
 234       Fixed write_file to zero file when writing behind file end
 2350.94   Fixed a little memory leak when trying to delete busy file or directory
 2360.95   Fixed a bug that i_hpfs_parent_dir was not updated when moving files
 2371.90   First version for 2.1.1xx kernels
 2381.91   Fixed a bug that chk_sectors failed when sectors were at the end of disk
 239       Fixed a race-condition when write_inode is called while deleting file
 240       Fixed a bug that could possibly happen (with very low probability) when
 241       using 0xff in filenames.
 242
 243       Rewritten locking to avoid race-conditions
 244
 245       Mount option 'eas' now works
 246
 247       Fsync no longer returns error
 248
 249       Files beginning with '.' are marked hidden
 250
 251       Remount support added
 252
 253       Alloc is not so slow when filesystem becomes full
 254
 255       Atimes are no more updated because it slows down operation
 256
 257       Code cleanup (removed all commented debug prints)
 2581.92   Corrected a bug when sync was called just before closing file
 2591.93   Modified, so that it works with kernels >= 2.1.131, I don't know if it
 260       works with previous versions
 261
 262       Fixed a possible problem with disks > 64G (but I don't have one, so I can't
 263       test it)
 264
 265       Fixed a file overflow at 2G
 266
 267       Added new option 'timeshift'
 268
 269       Changed behaviour on HPFS386: It is now possible to operate on HPFS386 in
 270       read-only mode
 271
 272       Fixed a bug that slowed down alloc and prevented allocating 100% space
 273       (this bug was not destructive)
 2741.94   Added workaround for one bug in Linux
 275
 276       Fixed one buffer leak
 277
 278       Fixed some incompatibilities with large extended attributes (but it's still
 279       not 100% ok, I have no info on it and OS/2 doesn't want to create them)
 280
 281       Rewritten allocation
 282
 283       Fixed a bug with i_blocks (du sometimes didn't display correct values)
 284
 285       Directories have no longer archive attribute set (some programs don't like
 286       it)
 287
 288       Fixed a bug that it set badly one flag in large anode tree (it was not
 289       destructive)
 2901.95   Fixed one buffer leak, that could happen on corrupted filesystem
 291
 292       Fixed one bug in allocation in 1.94
 2931.96   Added workaround for one bug in OS/2 (HPFS locked up, HPFS386 reported
 294       error sometimes when opening directories in PMSHELL)
 295
 296       Fixed a possible bitmap race
 297
 298       Fixed possible problem on large disks
 299
 300       You can now delete open files
 301
 302       Fixed a nondestructive race in rename
 3031.97   Support for HPFS v3 (on large partitions)
 304
 305       ZFixed a bug that it didn't allow creation of files > 128M
 306       (it should be 2G)
 3071.97.1 Changed names of global symbols
 308
 309       Fixed a bug when chmoding or chowning root directory
 3101.98   Fixed a deadlock when using old_readdir
 311       Better directory handling; workaround for "unbalanced tree" bug in OS/2
 3121.99   Corrected a possible problem when there's not enough space while deleting
 313       file
 314
 315       Now it tries to truncate the file if there's not enough space when
 316       deleting
 317
 318       Removed a lot of redundant code
 3192.00   Fixed a bug in rename (it was there since 1.96)
 320       Better anti-fragmentation strategy
 3212.01   Fixed problem with directory listing over NFS
 322
 323       Directory lseek now checks for proper parameters
 324
 325       Fixed race-condition in buffer code - it is in all filesystems in Linux;
 326       when reading device (cat /dev/hda) while creating files on it, files
 327       could be damaged
 3282.02   Workaround for bug in breada in Linux. breada could cause accesses beyond
 329       end of partition
 3302.03   Char, block devices and pipes are correctly created
 331
 332       Fixed non-crashing race in unlink (Alexander Viro)
 333
 334       Now it works with Japanese version of OS/2
 3352.04   Fixed error when ftruncate used to extend file
 3362.05   Fixed crash when got mount parameters without =
 337
 338       Fixed crash when allocation of anode failed due to full disk
 339
 340       Fixed some crashes when block io or inode allocation failed
 3412.06   Fixed some crash on corrupted disk structures
 342
 343       Better allocation strategy
 344
 345       Reschedule points added so that it doesn't lock CPU long time
 346
 347       It should work in read-only mode on Warp Server
 3482.07   More fixes for Warp Server. Now it really works
 3492.08   Creating new files is not so slow on large disks
 350
 351       An attempt to sync deleted file does not generate filesystem error
 3522.09   Fixed error on extremely fragmented files
 353====== =========================================================================
 354