Documentation/filesystems/adfs.rst

   1 .. SPDX-License-Identifier: GPL-2.0
   2
   3 ===============================
   4 Acorn Disc Filing System - ADFS
   5 ===============================
   6
   7 Filesystems supported by ADFS
   8 -----------------------------
   9
  10 The ADFS module supports the following Filecore formats which have:
  11
  12 - new maps
  13 - new directories or big directories
  14
  15 In terms of the named formats, this means we support:
  16
  17 - E and E+, with or without boot block
  18 - F and F+
  19
  20 We fully support reading files from these filesystems, and writing to
  21 existing files within their existing allocation.  Essentially, we do
  22 not support changing any of the filesystem metadata.
  23
  24 This is intended to support loopback mounted Linux native filesystems
  25 on a RISC OS Filecore filesystem, but will allow the data within files
  26 to be changed.
  27
  28 If write support (ADFS_FS_RW) is configured, we allow rudimentary
  29 directory updates, specifically updating the access mode and timestamp.
  30
  31 Mount options for ADFS
  32 ----------------------
  33
  34   ============  ======================================================
  35   uid=nnn       All files in the partition will be owned by
  36                 user id nnn.  Default 0 (root).
  37   gid=nnn       All files in the partition will be in group
  38                 nnn.  Default 0 (root).
  39   ownmask=nnn   The permission mask for ADFS 'owner' permissions
  40                 will be nnn.  Default 0700.
  41   othmask=nnn   The permission mask for ADFS 'other' permissions
  42                 will be nnn.  Default 0077.
  43   ftsuffix=n    When ftsuffix=0, no file type suffix will be applied.
  44                 When ftsuffix=1, a hexadecimal suffix corresponding to
  45                 the RISC OS file type will be added.  Default 0.
  46   ============  ======================================================
  47
  48 Mapping of ADFS permissions to Linux permissions
  49 ------------------------------------------------
  50
  51   ADFS permissions consist of the following:
  52
  53         - Owner read
  54         - Owner write
  55         - Other read
  56         - Other write
  57
  58   (In older versions, an 'execute' permission did exist, but this
  59   does not hold the same meaning as the Linux 'execute' permission
  60   and is now obsolete).
  61
  62   The mapping is performed as follows::
  63
  64         Owner read                              -> -r--r--r--
  65         Owner write                             -> --w--w---w
  66         Owner read and filetype UnixExec        -> ---x--x--x
  67     These are then masked by ownmask, eg 700    -> -rwx------
  68         Possible owner mode permissions         -> -rwx------
  69
  70         Other read                              -> -r--r--r--
  71         Other write                             -> --w--w--w-
  72         Other read and filetype UnixExec        -> ---x--x--x
  73     These are then masked by othmask, eg 077    -> ----rwxrwx
  74         Possible other mode permissions         -> ----rwxrwx
  75
  76   Hence, with the default masks, if a file is owner read/write, and
  77   not a UnixExec filetype, then the permissions will be::
  78
  79                         -rw-------
  80
  81   However, if the masks were ownmask=0770,othmask=0007, then this would
  82   be modified to::
  83
  84                         -rw-rw----
  85
  86   There is no restriction on what you can do with these masks.  You may
  87   wish that either read bits give read access to the file for all, but
  88   keep the default write protection (ownmask=0755,othmask=0577)::
  89
  90                         -rw-r--r--
  91
  92   You can therefore tailor the permission translation to whatever you
  93   desire the permissions should be under Linux.
  94
  95 RISC OS file type suffix
  96 ------------------------
  97
  98   RISC OS file types are stored in bits 19..8 of the file load address.
  99
 100   To enable non-RISC OS systems to be used to store files without losing
 101   file type information, a file naming convention was devised (initially
 102   for use with NFS) such that a hexadecimal suffix of the form ,xyz
 103   denoted the file type: e.g. BasicFile,ffb is a BASIC (0xffb) file.  This
 104   naming convention is now also used by RISC OS emulators such as RPCEmu.
 105
 106   Mounting an ADFS disc with option ftsuffix=1 will cause appropriate file
 107   type suffixes to be appended to file names read from a directory.  If the
 108   ftsuffix option is zero or omitted, no file type suffixes will be added.