uturn is a continuous integration system.  While primitive in some
ways, it uses advanced features of modern Linux to manage build roots
efficiently and cleanly.  Build roots are maintained as btrfs
subvolumes and projects are built and tested in a btrfs snapshot of a
pristine build root.  To ensure maximum isolation from the host
system, the build roots are activated using systemd-nspawn, which also
brings up enough of the system that many tests can run inside the
container.

The main build script is uturn-builder.sh, which typically runs in a
daemon mode, rebuilding projects when a new upstream version is
committed.  This mode relies of notification over ssh and the git repo
must be configured to run the uturn-post-receive hook.  If
uturn-bot.sh is running, uturn-builder.sh will use it to log the build
status to IRC.  If a build config file specifies an upstream, the
builder will try to push into the upstream repo if the build was
successful.


The core build system is independent of any package manager, but the
uturn repo has a couple of helper scripts for creating build roots
using yum and Fedora:

	cache-rpms.sh		This script downloads and caches
				RPMs needed to create a given install root.

	create-container.sh	This creates a build root from the local
				cached RPMs.

both tools source a simple config file that defines the build root.
The config file is just a few variable assignments:

	name		Name of the build root
	rpms		The RPMs that should be available in the build root
	release		Fedora release version 

The create repo script configures the build root and installs the
systemd uturn target which systemd-nspawn will boot into to build the
project.