===========================
Apple File System for Linux
===========================

The Apple File System (APFS) is the copy-on-write filesystem currently used on
all Apple devices. This module provides a degree of experimental support on
Linux.

It's supposed to work with a range of kernel versions starting at 4.9 or before,
but only a few of those have actually been tested. Also, kernel versions below
4.12 will be slower for some operations. If you run into any problem, please
send a report to <linux-apfs@googlegroups.com> or file a github issue at
https://github.com/eafer/linux-apfs-rw/issues.

To help test write support, a set of userland tools is also under development.
The git tree can be retrieved from https://github.com/eafer/apfsprogs.git.

Known limitations
=================

This module is the result of reverse engineering and testing has been limited.
If you make use of the write support, expect data corruption. Please report any
issues that you find, but I can't promise a quick resolution at this stage.

Many features are not yet implemented, including encryption and most forms of
compression.

Build
=====

In order to build a module out-of-tree, you will first need the Linux kernel
headers. Depending on your distro, you can get them by running (as root)::

	# Debian/Ubuntu
	apt-get install linux-headers-$(uname -r)

	# Arch/Manjaro
	pacman -Sy linux-headers

	# RHEL/Rocky/CentOS/Fedora
	yum install kernel-headers kernel-devel

Now you can just cd to the linux-apfs-rw directory and run::

	make

The resulting module is the apfs.ko file. Before you can use it you must insert
it into the kernel, as well as its dependencies. Again as root::

	modprobe libcrc32c
	insmod apfs.ko

Mount
=====

Like all filesystems, apfs is mounted with::

	mount [-o options] device dir

where ``device`` is the path to your device file or filesystem image, and
``dir`` is the mount point. The following options are accepted:

============   =================================================================
vol=n	       Volume number to mount. The default is volume 0.

uid=n, gid=n   Override on-disk inode ownership data with given uid/gid.

cknodes	       Verify the checksum on all metadata nodes. Right now this has a
	       severe performance cost, so it's not recommended.

readwrite      Enable the experimental write support. This **will** corrupt your
	       container.
============   =================================================================

So for instance, if you want to mount volume number 2, and you want the metadata
to be checked, you should run (as root)::

	mount -o cknodes,vol=2 device dir

To unmount it, run::

	umount dir

Credits
=======

Originally written by Ernesto A. Fernández <ernesto@corellium.com>, with
several contributions from Gabriel Krisman Bertazi <krisman@collabora.com>,
Arnaud Ferraris <arnaud.ferraris@collabora.com> and Stan Skowronek
<skylark@disorder.metrascale.com>. For attribution details see the historical
git tree at https://github.com/eafer/linux-apfs.git.

Work was first based on reverse engineering done by others [1]_ [2]_, and later
on the (very incomplete) official specification [3]_. Some parts of the code
imitate the ext2 module, and to a lesser degree xfs, udf, gfs2 and hfsplus.

.. [1] Hansen, K.H., Toolan, F., Decoding the APFS file system, Digital
   Investigation (2017), https://dx.doi.org/10.1016/j.diin.2017.07.003
.. [2] https://github.com/sgan81/apfs-fuse
.. [3] https://developer.apple.com/support/apple-file-system/Apple-File-System-Reference.pdf
