install_docker-btrfs

#!/bin/bash

build() {
    add_module btrfs
    add_binary btrfs
    add_binary btrfsck
    add_binary get-docker-cache-id
    add_file /etc/docker-btrfs.json
    add_runscript
}

help() {
    cat <<HELPEOF
This hook provides support for using docker image as root. Only btrfs
is supported. This hook creates an rwlayer as a snapshot of the subvolume
in docker cache of the specified image and use this rwlayer as root.
The rwlayer is not automatically saved and will be emptied the next time
during boot.

To setup this hook:

In /etc/docker-btrfs.sh, the user specify the image and tag that would
be used as root. During installation, this file will be copied to the
initramfs generated and read by the runtime hook during booting.

While booting, the kernel option "root" should be the drive that contains
the docker directory (the directory that will become /var/lib/docker after
boot). The "docker_path" is used to specify the relative path of docker
directory with respect to "root". The "rootflags" should at least have a
"subvol=******"; this subvolume will become the rwlayer, and all existing
data will be emptied. The "toplayer" is the drive that stores top layer
data which will be applied to rwlayer after rwlayer is mounted. The
"toplayerfstype", "toplayerflags" playes the same role to top layer as
"rootfstype", "rootflags" plays to root. The "toplayer_path" is the relative
path of the directory of the top layer with respect to "toplayer".

HELPEOF
}