One of my goals for Consfigurator is to make it capable of installing Debian to my laptop, so that I can stop booting to GRML and manually partitioning and debootstrapping a basic system, only to then turn to configuration management to set everything else up. My configuration management should be able to handle the partitioning and debootstrapping, too.

The first stage was to make Consfigurator capable of debootstrapping a basic system, chrooting into it, and applying other arbitrary configuration, such as installing packages. That’s been in place for some weeks now. It’s sophisticated enough to avoid starting up newly installed services, but I still need to add some bind mounting.

Another significant piece is teaching Consfigurator how to partition block devices. That’s quite tricky to do in a sufficiently general way – I want to cleanly support various combinations of LUKS, LVM and regular partitions, including populating /etc/crypttab and /etc/fstab. I have some ideas about how to do it, but it’ll probably take a few tries to get the abstractions right.

Let’s imagine that code is all in place, such that Consfigurator can be pointed at a block device and it will install a bootable Debian system to it. Then to install Debian to my laptop I’d just need to take my laptop’s disk drive out and plug it into another system, and run Consfigurator on that system, as root, pointed at the block device representing my laptop’s disk drive. For virtual machines, it would be easy to write code which loop-mounts an empty disk image, and then Consfigurator could be pointed at the loop-mounted block device, thereby making the disk image file bootable.

This is adequate for virtual machines, or small single-board computers with tiny storage devices (not that I actually use any of those, but I want Consfigurator to be able to make disk images for them!). But it’s not much good for my laptop. I casually referred to taking out my laptop’s disk drive and connecting it to another computer, but this would void my laptop’s warranty. And Consfigurator would not be able to update my laptop’s NVRAM, as is needed on UEFI systems.

What’s wanted here is a live system which can run Consfigurator directly on the laptop, pointed at the block device representing its physical disk drive. Ideally this live system comes with a chroot with the root filesystem for the new Debian install already built, so that network access is not required, and all Consfigurator has to do is partition the drive and copy in the contents of the chroot. The live system could be set up to automatically start doing that upon boot, but another option is to just make Consfigurator itself available to be used interactively. The user boots the live system, starts up Emacs, starts up Lisp, and executes a Consfigurator deployment, supplying the block device representing the laptop’s disk drive as an argument to the deployment. Consfigurator goes off and partitions that drive, copies in the contents of the chroot, and executes grub-install to make the laptop bootable. This is also much easier to debug than a live system which tries to start partitioning upon boot. It would look something like this:

    ;; melete.silentflame.com is a Consfigurator host object representing the
    ;; laptop, including information about the partitions it should have
    (deploy-these :local ...
      (chroot:partitioned-and-installed
        melete.silentflame.com "/srv/chroot/melete" "/dev/nvme0n1"))

Now, building live systems is a fair bit more involved than installing Debian to a disk drive and making it bootable, it turns out. While I want Consfigurator to be able to completely replace the Debian Installer, I decided that it is not worth trying to reimplement the relevant parts of the Debian Live tool suite, because I do not need to make arbitrary customisations to any live systems. I just need to have some packages installed and some files in place. Nevertheless, it is worth teaching Consfigurator how to invoke Debian Live, so that the customisation of the chroot which isn’t just a matter of passing options to lb_config(1) can be done with Consfigurator. This is what I’ve ended up with – in Consfigurator’s source code:

(defpropspec image-built :lisp (config dir properties)
  "Build an image under DIR using live-build(7), where the resulting live
system has PROPERTIES, which should contain, at a minimum, a property from
CONSFIGURATOR.PROPERTY.OS setting the Debian suite and architecture.  CONFIG
is a list of arguments to pass to lb_config(1), not including the '-a' and
'-d' options, which Consfigurator will supply based on PROPERTIES.

This property runs the lb_config(1), lb_bootstrap(1), lb_chroot(1) and
lb_binary(1) commands to build or rebuild the image.  Rebuilding occurs only
when changes to CONFIG or PROPERTIES mean that the image is potentially
out-of-date; e.g. if you just add some new items to PROPERTIES then in most
cases only lb_chroot(1) and lb_binary(1) will be re-run.

Note that lb_chroot(1) and lb_binary(1) both run after applying PROPERTIES,
and might undo some of their effects.  For example, to configure
/etc/apt/sources.list, you will need to use CONFIG not PROPERTIES."
  (:desc (declare (ignore config properties))
         #?"Debian Live image built in ${dir}")
  (let* (...)
    ;; ...
    `(eseqprops
      ;; ...
      (on-change
          (eseqprops
           (on-change
               (file:has-content ,auto/config ,(auto/config config) :mode #o755)
             (file:does-not-exist ,@clean)
             (%lbconfig ,dir)
             (%lbbootstrap t ,dir))
           (%lbbootstrap nil ,dir)
           (deploys ((:chroot :into ,chroot)) ,host))
        (%lbchroot ,dir)
        (%lbbinary ,dir)))))

Here, %lbconfig is a property running lb_config(1), %lbbootstrap one which runs lb_bootstrap(1), etc. Those properties all just change directory to the right place and run the command, essentially, with a little extra code to handle failed debootstraps and the like.

The ON-CHANGE and ESEQPROPS combinators work together to sequence the interaction of the Debian Live suite and Consfigurator.

  • In the innermost ON-CHANGE expression: create the file auto/config and populate it with the call to lb_config(1) that we need to make, as described in the Debian Live manual, chapter 6.

    • If doing so resulted in a change to the auto/config file – e.g. the user added some more options – ensure that lb_config(1) and lb_bootstrap(1) both get rerun.
  • Now in the inner ESEQPROPS expression, use DEPLOYS to configure the chroot, essentially by forking into the chroot and recursively reinvoking Consfigurator.

  • Finally, if any of the above resulted in a change being made, call lb_chroot(1) and lb_binary(1).

This way, we only rebuild the chroot if the configuration changed, and we only rebuild the image if the chroot changed.

Now over in my personal consfig:

(try-register-data-source
 :git-snapshot :name "consfig" :repo #P"src/cl/consfig/" ...)

(defproplist hybrid-live-iso-built :lisp ()
  "Build a Debian Live system in /srv/live/spw.

Typically this property is not applied in a DEFHOST form, but rather run as
needed at the REPL.  The reason for this is that otherwise the whole image will
get rebuilt each time a commit is made to my dotfiles repo or to my consfig."
  (:desc "Sean's Debian Live system image built")
  (live-build:image-built.
      '("--archive-areas" "main contrib non-free" ...)
      "/srv/live/spw"
    (os:debian-stable "buster" :amd64)
    (basic-props)
    (apt:installed "whatever" "you" "want")

    (git:snapshot-extracted "/etc/skel/src" "dotfiles")
    (file:is-copy-of "/etc/skel/.bashrc" "/etc/skel/src/dotfiles/.bashrc")

    (git:snapshot-extracted "/root/src/cl" "consfig")))

The first argument to LIVE-BUILD:IMAGE-BUILT. is additional arguments to lb_config(1). The third argument onwards are the properties for the live system. The cool thing is GIT:SNAPSHOT-EXTRACTED – the calls to this ensure that a copy of my Emacs configuration and my consfig end up in the live image, ready to be used interactively to install Debian, as described above. I’ll need to add something like (chroot:host-chroot-bootstrapped melete.silentflame.com "/srv/chroot/melete") too.

As with everything Consfigurator-related, Joey Hess’s Propellor is the giant upon whose shoulders I’m standing.

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