Documentation/filesystems/adfs.rst

Source file repositories/reference/linux-study-clean/Documentation/filesystems/adfs.rst

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Documentation/filesystems/adfs.rst
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Support Tooling And Documentation
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Documentation
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Support Tooling And Documentation: documentation
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

===============================
Acorn Disc Filing System - ADFS
===============================

Filesystems supported by ADFS
-----------------------------

The ADFS module supports the following Filecore formats which have:

- new maps
- new directories or big directories

In terms of the named formats, this means we support:

- E and E+, with or without boot block
- F and F+

We fully support reading files from these filesystems, and writing to
existing files within their existing allocation.  Essentially, we do
not support changing any of the filesystem metadata.

This is intended to support loopback mounted Linux native filesystems
on a RISC OS Filecore filesystem, but will allow the data within files
to be changed.

If write support (ADFS_FS_RW) is configured, we allow rudimentary
directory updates, specifically updating the access mode and timestamp.

Mount options for ADFS
----------------------

  ============  ======================================================
  uid=nnn	All files in the partition will be owned by
		user id nnn.  Default 0 (root).
  gid=nnn	All files in the partition will be in group
		nnn.  Default 0 (root).
  ownmask=nnn	The permission mask for ADFS 'owner' permissions
		will be nnn.  Default 0700.
  othmask=nnn	The permission mask for ADFS 'other' permissions
		will be nnn.  Default 0077.
  ftsuffix=n	When ftsuffix=0, no file type suffix will be applied.
		When ftsuffix=1, a hexadecimal suffix corresponding to
		the RISC OS file type will be added.  Default 0.
  ============  ======================================================

Mapping of ADFS permissions to Linux permissions
------------------------------------------------

  ADFS permissions consist of the following:

	- Owner read
	- Owner write
	- Other read
	- Other write

  (In older versions, an 'execute' permission did exist, but this
  does not hold the same meaning as the Linux 'execute' permission
  and is now obsolete).

  The mapping is performed as follows::

	Owner read				-> -r--r--r--
	Owner write				-> --w--w---w
	Owner read and filetype UnixExec	-> ---x--x--x
    These are then masked by ownmask, eg 700	-> -rwx------
	Possible owner mode permissions		-> -rwx------

	Other read				-> -r--r--r--

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Implementation Notes