A tool to clone a disk image.

Main features

• Utilises FICLONE to create a copy-on-write clone of the image

• Uses FIFREEZE if the image is mounted in order to ensure consistency of the image

For further details see loclone(1).

loclone doesn't have any dependencies outside of the linux kernel and GNU libc.

loclone uses autotools as it's build system. After downloading the distribution tarball from the github releases,

$ ./configure
$ make

# Optionally to install to /usr/local
$ sudo make install

The original concept was to create a tool to make use of XFS' data CoW features in order to create snapshottable subvolumes which are backed by loopback devices on XFS; Similar to one of the thought experiments laid out by Dave Chinner in their talk, "XFS: Teaching an Old Dog Old Tricks" at LinuxConfAU 2018. (found here https://www.youtube.com/watch?v=wG8FUvSGROw)

However as this concept can be applied to any filesystem that supports FICLONE, I've made the tool more generic. However at the moment this tool only really makes sense to be used on XFS.

The general architecture of the system is as follows:

• Sparse files are created on which a filesystem which supports FIFREEZE (xfs, ext4, btrfs, etc.) can be created in

• The files can then be mounted via a loopback device (generally configured in /etc/fstab) to which ever needs to be snapshotted (e.g. /home)

• CoW copies of the files can then be made using the FICLONE ioctl call; Effectively creating a snapshot of the filesystem at a point in time.

• However if the sparse file is still mounted and being written to during when the copy is made, it can cause data corruption. Hence ideally the filesystem would be unmounted but that's not feasible for some mountpoints (such as /home). Therefore the filesystem is frozen using FIFREEZE for the duration of the copy.

The latter two points are what this tool encompasses.

Contributions (technical or not) are greatly appreciated. If you find any areas for improvement, please feel free to open a pull request.

All contributions are subject to the Gnu Public Licence v3, the full text for which can be found in COPYING.