Instead of running meson install and hoping for the best, let's build
distribution packages from the downstream packaging specs. This gets
us the following:
- Vastly simplified mkosi scripts since we don't need a separate initrd
image anymore but can just reuse the default mkosi initrd.
- Almost everything can move to the base image as its not the basis
anymore for the initrd and as such we don't need to care about the
size anymore.
- The systemd packages that get pulled in as dependencies of other
packages get properly uninstalled and replaced with our packages that
we built instead of just installing on top of an existing systemd
installation with no guarantee that everything from that previous
installation was removed.
- Much better testing coverage as what we're testing is much closer
to what will actually be deployed in distributions.
- Immediate feedback if something we change breaks distribution packaging
- We get integration with the distribution for free as we'll automatically
use the proper directories and such instead of having to hack this
into a mkosi build script.
- ...
Configuration now takes priority over CLI options so we have to
configure the defaults for settings that we want to allow overriding
from the CLI. We also explicitly set some other settings so that they
can't be overridden from the CLI anymore. For example the base and
initrd image should never be made bootable so we set Bootable=no
explicitly for both.
Instead of building the initrds for the mkosi images with dracut,
let's switch to using mkosi presets to build the initrd with mkosi
as well.
This commit splits up our single image build into three separate
mkosi presets:
1. The "base" preset. This image contains systemd and all its runtime
dependencies. The sole purpose of this image is to serve as a base image
for the initrd and the final image. It's also responsible for building
systemd from source with the build script. The results are installed into
the base image. Note that we install the systemd and udev packages into this
image as well to prevent package managers from overriding the systemd we built
from source with the distro packaged systemd if it's pulled in as a dependency
by another package from the initrd or final profiles.
2. The "initrd" preset. This image provides the initrd. It's trivial and does
nothing more than packaging the base image up as a zstd compressed initramfs and
adds /init and /etc/initrd-release symlinks to the image.
3. The "final" preset. This image builds on top of the base image and adds
a kernel and extra packages that are useful for testing and debugging.
We also split out the optional kernel build into a separate set of config files
that are only included if a kernel to build is actually provided.
Note that this commit doesn't really change anything about how mkosi is used.
The commands remain the same, except that mkosi will now build all the presets
in order. "mkosi summary" will show the summary of all the presets. "mkosi qemu,
boot, shell" will always boot the final preset. With "-f", all presets will be
built and the final one is booted. "-i" makes a cache of each preset.
The only thing to keep in mind is that specifying config via the mkosi CLI will
apply to each of the presets. e.g. any extra packages added with "-p" will be
installed in both the initrd and the final image. To apply local configuration
to a single preset, create a file 00-local.conf in
mkosi.presets/<profile>/mkosi.conf.d and put all the preset specific configuration
in there.
