Loopback

In case you don't have a spare disk or partition but would like to play around with eg btrfs this tool creates a loopback device from a file which you can mount whereever you want.

Use cases:

• systemd machinectl
• conair (https://github.com/teemow/conair)

Prerequisites

Getting Loopback

Download the latest release from here: https://github.com/teemow/loopback/releases/latest

Clone the latest git repository version from here: https://github.com/teemow/loopback.git

How to build

Build Dependencies

• make
• docker

Building the standard way

make && sudo make install

Usage

You can create a mounted loopback device with 15G size like this:

loopback create --fs=ext4 --name=loopback-test size=15

Whenever you are done with working in the device you can unmount it like this:

loopback umount --name=loopback-test

When you don't need the device and image anymore you can destroy it like this:

loopback destroy --name=loopback-test

Using with Docker containers

You can also use loopback in Docker containers:

docker run \
    --rm \
    -it \
    --privileged \
    -v /:/host:shared \
    teemow/loopback \
    create --fs=ext4 --image-path=/host/var/lib/loopback --name=loopback-test

If you are not yet using Docker 1.10 you can use nsenter which is shipped with the image:

docker run \
    --rm \
    -it \
    --privileged \
    -v /:/host \
    --entrypoint=/bin/bash \
    teemow/loopback \
    -c "/opt/loopback attach --fs=ext4 --image-path=/host/var/lib/loopback --name=loopback-test --create-missing-image && /opt/loopback list --no-headings | grep loopback-test.img | awk '{print \$1}' | xargs -I{} nsenter --mount=/host/proc/1/ns/mnt -- mount {} /mnt"

Dependencies

• dd
• losetup
• mkfs (eg for btrfs)
• mount

Create a btrfs fs for machined

sudo loopback create --name=machined --size=10 --mount-path=/var/lib/machines

Remove the loopbacks

sudo loopback destroy --name=machined

Further Steps

Check more detailed documentation: docs

Check code documentation: godoc

Contact

• Mailing list: giantswarm
• IRC: #giantswarm on freenode.org
• Bugs: issues

Contributing & Reporting Bugs

See CONTRIBUTING for details on submitting patches, the contribution workflow as well as reporting bugs.

License

Loopback is under the Apache 2.0 license. See the LICENSE file for details.