109 lines
3.7 KiB
ReStructuredText
109 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===============================
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Acorn Disc Filing System - ADFS
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===============================
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Filesystems supported by ADFS
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-----------------------------
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The ADFS module supports the following Filecore formats which have:
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- new maps
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- new directories or big directories
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In terms of the named formats, this means we support:
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- E and E+, with or without boot block
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- F and F+
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We fully support reading files from these filesystems, and writing to
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existing files within their existing allocation. Essentially, we do
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not support changing any of the filesystem metadata.
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This is intended to support loopback mounted Linux native filesystems
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on a RISC OS Filecore filesystem, but will allow the data within files
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to be changed.
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If write support (ADFS_FS_RW) is configured, we allow rudimentary
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directory updates, specifically updating the access mode and timestamp.
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Mount options for ADFS
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----------------------
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============ ======================================================
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uid=nnn All files in the partition will be owned by
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user id nnn. Default 0 (root).
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gid=nnn All files in the partition will be in group
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nnn. Default 0 (root).
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ownmask=nnn The permission mask for ADFS 'owner' permissions
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will be nnn. Default 0700.
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othmask=nnn The permission mask for ADFS 'other' permissions
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will be nnn. Default 0077.
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ftsuffix=n When ftsuffix=0, no file type suffix will be applied.
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When ftsuffix=1, a hexadecimal suffix corresponding to
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the RISC OS file type will be added. Default 0.
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============ ======================================================
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Mapping of ADFS permissions to Linux permissions
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------------------------------------------------
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ADFS permissions consist of the following:
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- Owner read
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- Owner write
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- Other read
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- Other write
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(In older versions, an 'execute' permission did exist, but this
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does not hold the same meaning as the Linux 'execute' permission
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and is now obsolete).
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The mapping is performed as follows::
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Owner read -> -r--r--r--
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Owner write -> --w--w---w
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Owner read and filetype UnixExec -> ---x--x--x
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These are then masked by ownmask, eg 700 -> -rwx------
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Possible owner mode permissions -> -rwx------
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Other read -> -r--r--r--
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Other write -> --w--w--w-
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Other read and filetype UnixExec -> ---x--x--x
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These are then masked by othmask, eg 077 -> ----rwxrwx
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Possible other mode permissions -> ----rwxrwx
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Hence, with the default masks, if a file is owner read/write, and
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not a UnixExec filetype, then the permissions will be::
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-rw-------
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However, if the masks were ownmask=0770,othmask=0007, then this would
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be modified to::
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-rw-rw----
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There is no restriction on what you can do with these masks. You may
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wish that either read bits give read access to the file for all, but
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keep the default write protection (ownmask=0755,othmask=0577)::
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-rw-r--r--
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You can therefore tailor the permission translation to whatever you
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desire the permissions should be under Linux.
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RISC OS file type suffix
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------------------------
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RISC OS file types are stored in bits 19..8 of the file load address.
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To enable non-RISC OS systems to be used to store files without losing
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file type information, a file naming convention was devised (initially
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for use with NFS) such that a hexadecimal suffix of the form ,xyz
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denoted the file type: e.g. BasicFile,ffb is a BASIC (0xffb) file. This
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naming convention is now also used by RISC OS emulators such as RPCEmu.
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Mounting an ADFS disc with option ftsuffix=1 will cause appropriate file
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type suffixes to be appended to file names read from a directory. If the
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ftsuffix option is zero or omitted, no file type suffixes will be added.
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