Apple File System

The Apple File System (APFS) is a copy-on-write filesystem apparently intended to replace HFS+ on all Apple devices in the near future. This module provides a degree of experimental read-only support on Linux.

This repo is a standalone version of git://github.com/eafer/linux-apfs.git for the purpose of making it easier to build the module out-of-tree. It is 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. If you run into any problem, please send a report to [email protected].

The long-term goal is to support writes as well. To help with testing, a set of userland tools is under development. The git tree can be retrieved from git://github.com/eafer/apfsprogs.git.

Known limitations

This module is the result of reverse engineering. As it is read-only there should be no risk of data corruption, but do not expect everything to be read correctly. Testing in general has been limited so far, so you may experience crashes. Please report any issues that you find.

Apple has released other versions of the filesystem to the public before the current one. I would not expect them to be compatible with this module at all, but I am open to fixing that if requested.

Many features are not yet supported:

o Encryption. o Compression, though the compressed contents of a file can be read from the 'com.apple.decmpfs' and 'com.apple.ResourceFork' xattrs as long as they are under 64k. o Restoring to a snapshot. o Access control lists. This is not a priority.

Build

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

apt-get install linux-headers-$(uname -r)

Now you can just cd to the linux-apfs-oot 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.

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 [email protected], with several contributions from Gabriel Krisman Bertazi [email protected] and Arnaud Ferraris [email protected].

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), http://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