diff --git a/lib/image-builder/default.nix b/lib/image-builder/default.nix
deleted file mode 100644
index cae1f18a..00000000
--- a/lib/image-builder/default.nix
+++ /dev/null
@@ -1,47 +0,0 @@
-{ lib, newScope }:
-
-let
-  inherit (lib) makeScope;
-in
-makeScope newScope (self:
-  let
-    inherit (self) callPackage;
-  in
-  # Note: Prefer using `self.something.deep` rather than making `something` a
-  # recursive set. Otherwise it won't override as expected.
-  {
-    makeFilesystem = callPackage ./makeFilesystem.nix {};
-
-    # All known supported filesystems for image generation.
-    # Use stand-alone (outside of a disk image) is supported.
-    fileSystem = {
-      makeExt4 = callPackage ./makeExt4.nix {};
-      makeBtrfs = callPackage ./makeBtrfs.nix {};
-      makeFAT32 = callPackage ./makeFAT32.nix {};
-      # Specialization of `makeFAT32` with (1) filesystemType showing as ESP,
-      # and (2) the name defaults to ESP.
-      makeESP = args: self.fileSystem.makeFAT32 ({ name = "ESP"; filesystemType = "ESP"; } // args);
-    };
-
-    gap = length: {
-      inherit length;
-      isGap = true;
-    };
-
-    # All supported disk formats for image generation.
-    diskImage = {
-      makeMBR = callPackage ./makeMBR.nix {};
-      makeGPT = callPackage ./makeGPT.nix {};
-    };
-
-    # Don't do maths yourselves, just use the helpers.
-    # Yes, this is the bibytes family of units.
-    # (This is fine as rec; it won't be overriden.)
-    size = rec {
-      TiB = x: 1024 * (GiB x);
-      GiB = x: 1024 * (MiB x);
-      MiB = x: 1024 * (KiB x);
-      KiB = x: 1024 *      x;
-    };
-  }
-)
diff --git a/lib/image-builder/in-depth-tests/README.md b/lib/image-builder/in-depth-tests/README.md
deleted file mode 100644
index 09a6af11..00000000
--- a/lib/image-builder/in-depth-tests/README.md
+++ /dev/null
@@ -1,19 +0,0 @@
-In-depth tests
-==============
-
-Those are rather bulky integration-type tests. They are not ran by default, but
-should be used to better test the image builder infrastructure.
-
-Changes to the infra should be passed through this test suite in addition to the
-slimmer usual tests suite.
-
-> **Tip:**
->
-> From the image-builder infra directory, run the following.
-> 
-> ```
-> nix-build in-depth-tests/[...].nix -I nixpkgs-overlays=$PWD/lib/tests/test-overlay.nix
-> ```
->
-> This allows you to track the bigger builds more easily.
-
diff --git a/lib/image-builder/in-depth-tests/raspi-like.nix b/lib/image-builder/in-depth-tests/raspi-like.nix
deleted file mode 100644
index 429a6272..00000000
--- a/lib/image-builder/in-depth-tests/raspi-like.nix
+++ /dev/null
@@ -1,96 +0,0 @@
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder ubootTools;
-
-  configTxt = pkgs.writeText "config.txt" ''
-    kernel=u-boot-rpi3.bin
-
-    # Boot in 64-bit mode.
-    arm_control=0x200
-
-    # Prevent the firmware from smashing the framebuffer setup done by the mainline kernel
-    # when attempting to show low-voltage or overtemperature warnings.
-    avoid_warnings=1
-  '';
-
-  scrTxt = pkgs.writeText "uboot.scr.txt" ''
-    echo
-    echo
-    echo
-    echo
-
-    echo " **"
-    echo " ** Image Builder sanity checks!"
-    echo " ** This will appear to freeze since the kernel is not built with the VC4 kernel built-in."
-    echo " ** Stay assured, the kernel should be panicking anyway since there is no initrd, no init, and no useful FS."
-    echo " **"
-
-    echo
-
-    load $devtype $devnum:$distro_bootpart $kernel_addr_r boot/kernel
-    booti $kernel_addr_r
-  '';
-
-  scr = pkgs.runCommand "uboot-script" {} ''
-    mkdir -p $out
-    ${ubootTools}/bin/mkimage \
-      -A arm64 \
-      -O linux \
-      -T script \
-      -C none \
-      -n ${scrTxt} -d ${scrTxt} \
-      $out/boot.scr
-  '';
-
-  # Here, we built a fictitious system cloning the AArch64 sd-image setup.
-  # The chosen derivations are known to build fully when cross-compiled.
-  pkgsAArch64 = (if pkgs.stdenv.isAarch64 then pkgs else pkgs.pkgsCross.aarch64-multiplatform);
-
-  # The kernel for the device.
-  kernel = pkgsAArch64.linux_rpi;
-
-  # TODO: for completeness' sake an initrd with the vc4 driver should be built
-  #       to show that this works as a self-contained demo.
-in
-
-with imageBuilder;
-
-/**
- * This disk image is built to be functionally compatible with the usual `sd_image`
- * from NixOS, but *it is not* an actual `sd_image` compatible system.
- *
- * The main thing it aims to do is *minimally* create a bootable system.
- */
-diskImage.makeMBR {
-  name = "diskimage";
-  diskID = "01234567";
-
-  partitions = [
-    (gap (size.MiB 10))
-    (fileSystem.makeFAT32 {
-      # Size-less
-      name = "FIRMWARE";
-      partitionID = "ABADF00D";
-      extraPadding = size.MiB 10;
-      populateCommands = ''
-        (
-        src=${pkgsAArch64.raspberrypifw}/share/raspberrypi/boot
-        cp $src/bootcode.bin $src/fixup*.dat $src/start*.elf ./
-        cp ${pkgsAArch64.ubootRaspberryPi3_64bit}/u-boot.bin ./u-boot-rpi3.bin
-        cp ${configTxt} ./config.txt
-        )
-      '';
-    })
-    (fileSystem.makeExt4 {
-      bootable = true;
-      name = "NIXOS";
-      partitionID = "44444444-4444-4444-8888-888888888888";
-      populateCommands = ''
-        mkdir -p ./boot
-        cp ${kernel}/Image ./boot/kernel
-        cp ${scr}/boot.scr ./boot/boot.scr
-      '';
-    })
-  ];
-}
diff --git a/lib/image-builder/in-depth-tests/size/ext4.nix b/lib/image-builder/in-depth-tests/size/ext4.nix
deleted file mode 100644
index 14906c56..00000000
--- a/lib/image-builder/in-depth-tests/size/ext4.nix
+++ /dev/null
@@ -1,87 +0,0 @@
-# Ensures we can fit stuff in an ext4 image.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  makeNull = size: let
-    filename = "null.img";
-    filesystemType = "FAT32"; # meh, good enough
-  in
-  ''
-    mkdir -p $out
-    dd if=/dev/zero of=./${toString size}.img bs=${toString size} count=1
-  '';
-in
-
-with imageBuilder;
-
-{
-  eight = fileSystem.makeExt4 {
-    name = "eight";
-    partitionID = "44444444-4444-4444-0000-000000000008";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 8)}
-    '';
-  };
-
-  eleven = fileSystem.makeExt4 {
-    name = "eleven";
-    partitionID = "44444444-4444-4444-0000-000000000011";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 11)}
-    '';
-  };
-
-  sixteen = fileSystem.makeExt4 {
-    name = "sixteen";
-    partitionID = "44444444-4444-4444-0000-000000000016";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 16)}
-    '';
-  };
-
-  one_twenty_eight = fileSystem.makeExt4 {
-    name = "one_twenty_eight";
-    partitionID = "44444444-4444-4444-0000-000000000128";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 128)}
-    '';
-  };
-
-  two_fifty_six = fileSystem.makeExt4 {
-    name = "two_fifty_six";
-    partitionID = "44444444-4444-4444-0000-000000000256";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 256)}
-    '';
-  };
-
-  five_twelve = fileSystem.makeExt4 {
-    name = "five_twelve";
-    partitionID = "44444444-4444-4444-0000-000000000512";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 512)}
-    '';
-  };
-
-  with_space = fileSystem.makeExt4 {
-    name = "with_space";
-    partitionID = "44444444-4444-4444-0000-000000000005";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 5)}
-    '';
-    extraPadding = size.MiB 10;
-  };
-
-  # Fills 512 MiB (the downard slump in the high fudge factor) with 512 1MiB
-  # files so we ensure the filesystem overhead is accounted for.
-  multiple-files = fileSystem.makeExt4 {
-    name = "multiple-files";
-    partitionID = "44444444-4444-4444-0000-000000000512";
-    populateCommands = ''
-      for i in {1..512}; do
-        dd if=/dev/zero of=./$i.img bs=${toString (imageBuilder.size.MiB 1)} count=1
-      done
-    '';
-  };
-}
diff --git a/lib/image-builder/lib/overlay.nix b/lib/image-builder/lib/overlay.nix
deleted file mode 100644
index 7fd57631..00000000
--- a/lib/image-builder/lib/overlay.nix
+++ /dev/null
@@ -1,5 +0,0 @@
-[
-  (self: super: { imageBuilder = self.callPackage ../. {}; })
-  # All the software will be upstreamed with NixOS when upstreaming the library.
-  (import ../../../overlay/overlay.nix)
-]
diff --git a/lib/image-builder/lib/tests/test-overlay.nix b/lib/image-builder/lib/tests/test-overlay.nix
deleted file mode 100644
index 9825b09c..00000000
--- a/lib/image-builder/lib/tests/test-overlay.nix
+++ /dev/null
@@ -1,18 +0,0 @@
-# Adds the imageBuilder overlay.
-(import ../overlay.nix) ++
-[
-  # Makes the imageBuilder build impure to force rebuilds to more easily test
-  # reproducibility of outputs.
-  (self: super:
-    let
-      inherit (self.lib.attrsets) mapAttrs;
-    in
-    {
-      imageBuilder = super.imageBuilder.overrideScope'(self: super: {
-        makeFilesystem = args: super.makeFilesystem (args // {
-          REBUILD = "# ${toString builtins.currentTime}";
-        });
-      });
-    }
-  )
-]
diff --git a/lib/image-builder/lib/tests/verify.rb b/lib/image-builder/lib/tests/verify.rb
deleted file mode 100755
index fc110dba..00000000
--- a/lib/image-builder/lib/tests/verify.rb
+++ /dev/null
@@ -1,61 +0,0 @@
-#!/usr/bin/env ruby
-
-require "shellwords"
-require "open3"
-
-# Test harness to validate results of a `nix-build`.
-# This script will `#load()` the given script.
-
-if ARGV.length < 2 then
-  abort "Usage: verify.rb <script> <result>"
-end
-
-$failures = []
-$script = ARGV.shift
-$result = ARGV.shift
-
-module Helpers
-  def compare_output(cmd, expected, message: nil)
-    expected ||= ""
-    message ||= "Command `#{cmd.shelljoin}` has unexpected output:"
-    expected = expected.strip
-    out = `#{cmd.shelljoin}`.strip
-
-    unless out == expected then
-      $failures << "#{message}:\n\tGot:     #{out}\n\tExpected #{expected}"
-    end
-  end
-
-  def sha256sum(filename, expected)
-    filename = File.join($result, filename)
-    compare_output(
-      ["nix-hash", "--flat", "--type", "sha256", filename], expected,
-      message: "File #{filename.shellescape} has unexpected hash",
-    )
-  end
-
-  def file(filename, expected)
-    filename = File.join($result, filename)
-    compare_output(
-      ["file", "--dereference", "--brief", filename], expected,
-      message: "File #{filename.shellescape} has unexpected file type",
-    )
-  end
-end
-
-include Helpers
-
-# Executes the script
-load($script)
-
-at_exit do
-  if $failures.length > 0 then
-    puts "Verification failed:"
-    $failures.each do |failure|
-      puts " → #{failure}"
-    end
-    exit 1
-  end
-
-  exit 0
-end
diff --git a/lib/image-builder/makeBtrfs.nix b/lib/image-builder/makeBtrfs.nix
deleted file mode 100644
index 4f1f22bd..00000000
--- a/lib/image-builder/makeBtrfs.nix
+++ /dev/null
@@ -1,20 +0,0 @@
-{ lib, imageBuilder, libfaketime, btrfs-progs }:
-
-/*  */ let scope = { "fileSystem.makeBtrfs" =
-
-{ partitionID, ... }@args:
-imageBuilder.makeFilesystem (args // {
-  filesystemType = "btrfs";
-  blockSize = 4096; # dummy
-  nativeBuildInputs = [btrfs-progs];
-  copyPhase = ''
-    mkfs.btrfs \
-      -r . \
-      -L "$partName" \
-      -U "$partitionID" \
-      --shrink \
-      "$img"
-  '';
-})
-
-/*  */ ;}; in scope."fileSystem.makeBtrfs"
diff --git a/lib/image-builder/makeExt4.nix b/lib/image-builder/makeExt4.nix
deleted file mode 100644
index 24716bac..00000000
--- a/lib/image-builder/makeExt4.nix
+++ /dev/null
@@ -1,122 +0,0 @@
-{ lib, imageBuilder, libfaketime, e2fsprogs, make_ext4fs }:
-
-/*  */ let scope = { "fileSystem.makeExt4" =
-
-let
-  inherit (lib.strings) splitString;
-  inherit (imageBuilder) makeFilesystem;
-
-  # Bash doesn't do floating point representations. Multiplications and divisions
-  # are handled with enough precision that we can multiply and divide to get a precision.
-  precision = 1000;
-
-  first = list: lib.lists.last (lib.lists.reverseList list);
-  chopDecimal = f: first (splitString "." (toString f));
-  makeFudge = f: toString (chopDecimal (f * precision));
-
-  # This applies only to 256MiB and greater.
-  # For smaller than 256MiB images the overhead from the FS is much greater.
-  # This will also let *some* slack space at the end at greater sizes.
-  # This is the value at 512MiB where it goes slightly down compared to 256MiB.
-  fudgeFactor = makeFudge 0.05208587646484375;
-
-  # This table was built using a script that built an image with `make_ext4fs`
-  # for the given size in MiB, and recorded the available size according to `df`.
-  smallFudgeLookup = lib.strings.concatStringsSep "\n" (lib.lists.reverseList(
-    lib.attrsets.mapAttrsToList (size: factor: ''
-      elif (( size > ${toString size} )); then
-        fudgeFactor=${toString factor}
-    '') {
-    "${toString (imageBuilder.size.MiB   5)}" = makeFudge 0.84609375;
-    "${toString (imageBuilder.size.MiB   8)}" = makeFudge 0.5419921875;
-    "${toString (imageBuilder.size.MiB  16)}" = makeFudge 0.288818359375;
-    "${toString (imageBuilder.size.MiB  32)}" = makeFudge 0.1622314453125;
-    "${toString (imageBuilder.size.MiB  64)}" = makeFudge 0.09893798828125;
-    "${toString (imageBuilder.size.MiB 128)}" = makeFudge 0.067291259765625;
-    "${toString (imageBuilder.size.MiB 256)}" = makeFudge 0.0518646240234375;
-  }
-  ));
-
-  minimumSize = imageBuilder.size.MiB 5;
-in
-{ partitionID
-, blockSize ? imageBuilder.size.KiB 4
-, ... } @ args:
-makeFilesystem (args // {
-  filesystemType = "ext4";
-
-  inherit blockSize minimumSize;
-
-  nativeBuildInputs = [
-    e2fsprogs
-    make_ext4fs
-    libfaketime
-  ];
-
-  filesystemPhase = ''
-    :
-  '';
-
-  computeMinimalSize = ''
-    # `local size` is in bytes.
-
-    # We don't have a static reserved factor figured out. It is rather hard with
-    # ext4fs as there are multiple factors increasing the overhead.
-    local reservedSize=0
-    local fudgeFactor=${toString fudgeFactor}
-    
-    # Instead we rely on a lookup table. See how it is built in the derivation file.
-    if (( size < ${toString (imageBuilder.size.MiB 256)} )); then
-      echo "$size is smaller than 256MiB; using the lookup table." 1>&2
-      
-      # A bit of a hack, though allows us to build the lookup table using only
-      # elifs.
-      if false; then
-        :
-      ${smallFudgeLookup}
-      else
-        # The data is smaller than 5MiB... The filesystem image size will likely
-        # not be able to accomodate... here we handle it in another way.
-        fudgeFactor=0
-        echo "Fudge factor skipped for extra small partition. Instead increasing by a fixed amount." 1>&2
-        size=$(( size + ${toString minimumSize}))
-      fi
-    fi
-
-    local reservedSize=$(( size * $fudgeFactor / ${toString precision} ))
-
-    echo "Fudge factor: $fudgeFactor / ${toString precision}" 1>&2
-    echo -n "Adding reservedSize: $size + $reservedSize = " 1>&2
-    size=$((size + reservedSize))
-    echo "$size" 1>&2
-  '';
-
-  copyPhase = ''
-
-    echo "Computing inode count..."
-    inodes=$(find . ! -type d -print0 | du --files0-from=- --inodes | cut -f1 | sum-lines)
-    echo "    Min inodes: $inodes" 1>&2
-    inodes=$(( inodes * 2 ))
-    echo "    Inodes reserved: $inodes" 1>&2
-    echo ""
-
-    faketime -f "1970-01-01 00:00:01" \
-      make_ext4fs \
-      -i $inodes \
-      -b $blockSize \
-      -L $partName \
-      -l $size \
-      -U $partitionID \
-      "$img" \
-      .
-  '';
-
-  checkPhase = ''
-  '';
-    # FIXME:
-    # Padding at end of inode bitmap is not set. Fix? no
-    # exit code
-    #EXT2FS_NO_MTAB_OK=yes fsck.ext4 -n -f $img
-})
-
-/*  */ ;}; in scope."fileSystem.makeExt4"
diff --git a/lib/image-builder/makeFAT32.nix b/lib/image-builder/makeFAT32.nix
deleted file mode 100644
index 68bf3e75..00000000
--- a/lib/image-builder/makeFAT32.nix
+++ /dev/null
@@ -1,107 +0,0 @@
-{ lib, imageBuilder, dosfstools, mtools, libfaketime}:
-
-/*  */ let scope = { "fileSystem.makeFAT32" =
-
-let
-  inherit (lib.strings) splitString;
-  inherit (imageBuilder) makeFilesystem;
-  # The default from `mkfs.fat`.
-  reservedSectors = 32;
-  # The default from `mkfs.fat`.
-  hiddenSectors = 0;
-
-  # The default from `mkfs.fat`.
-  numberOfFats = 2;
-  # Extra padding per FAT, a constant in code
-  fatPadding = 4;
-
-  # I have not been able to validate that it could be different from 1 for FAT32.
-  # It seems the different values (e.g. 4) are for FAT12 and FAT16.
-  # This is the only "bad" assumption here.
-  clusterSize = 1;
-
-  # Bash doesn't do floating point representations. Multiplications and divisions
-  # are handled with enough precision that we can multiply and divide to get a precision.
-  precision = 1000;
-
-  first = list: lib.lists.last (lib.lists.reverseList list);
-  chopDecimal = f: first (splitString "." (toString f));
-in
-{ partitionID
-# These defaults are assuming small~ish FAT32 filesystems are generated.
-, blockSize ? 512
-, sectorSize ? 512
-, ... } @ args:
-makeFilesystem (args // {
-  # FAT32 can be used for ESP. Let's make this obvious.
-  filesystemType = if args ? filesystemType then args.filesystemType else "FAT32";
-
-  inherit blockSize sectorSize;
-  minimumSize = imageBuilder.size.KiB 500;
-
-  nativeBuildInputs = [
-    libfaketime
-    dosfstools
-    mtools
-  ];
-
-  computeMinimalSize = ''
-    # `local size` is in bytes.
-
-    # This amount is a static amount of reserved space.
-    local static_reserved=${toString ( (reservedSectors + hiddenSectors) * sectorSize )}
-
-    # This is a constant representing the relative reserved space ratio.
-    local relative_reserved=${
-      chopDecimal (
-        precision - (
-          1.0 * sectorSize / ((clusterSize * sectorSize) + (numberOfFats * fatPadding))
-          # ^ forces floating point
-        ) * precision
-      )
-    }
-    # Rounds up the likely truncated result. At worst it's a bit more space.
-    (( relative_reserved++ ))
-
-    echo "static_reserved=$static_reserved" 1>&2
-    echo "relative_reserved=$relative_reserved" 1>&2
-
-    local reservedSize=$(( (static_reserved + size) * relative_reserved / ${toString precision} + static_reserved ))
-
-    echo -n "Adding reservedSize: $size + $reservedSize = " 1>&2
-    size=$((size + reservedSize))
-    echo "$size" 1>&2
-  '';
-
-  filesystemPhase = ''
-    fatSize=16
-    if (( size > 1024*1024*32 )); then
-      fatSize=32
-    fi
-    faketime -f "1970-01-01 00:00:01" mkfs.vfat \
-      -F $fatSize \
-      -R ${toString reservedSectors} \
-      -h ${toString hiddenSectors} \
-      -s ${toString (blockSize / sectorSize)} \
-      -S ${toString sectorSize} \
-      -i $partitionID \
-      -n $partName \
-      "$img"
-  '';
-
-  copyPhase = ''
-    for f in ./* ./.*; do
-      if [[ "$f" != "./." && "$f" != "./.." ]]; then
-        faketime -f "1970-01-01 00:00:01" \
-          mcopy -psv -i "$img" "$f" ::
-      fi
-    done
-  '';
-
-  checkPhase = ''
-    # Always verify FS
-    fsck.vfat -vn "$img"
-  '';
-})
-
-/*  */ ;}; in scope."fileSystem.makeFAT32"
diff --git a/lib/image-builder/makeFilesystem.nix b/lib/image-builder/makeFilesystem.nix
deleted file mode 100644
index 52d5cc11..00000000
--- a/lib/image-builder/makeFilesystem.nix
+++ /dev/null
@@ -1,156 +0,0 @@
-{ stdenvNoCC, lib, writeText }:
-
-/*  */ let scope = { "fileSystem.makeFilesystem" =
-
-let
-  inherit (lib) optionals optionalString assertMsg;
-in
-
-{
-  name
-  # Size (in bytes) the filesystem image will be given.
-  # When size is not given, it is assumed that `populateCommands` will populate
-  # the filesystem, and the size will be derived (see computeMinimalSize).
-  , size ? null
-
-  # The populate commands are executed in a subshell. The CWD at the star is the
-  # public API to know where to add files that will be added to the image.
-  , populateCommands ? null
-
-  # Used with the assumption that files are rounded up to blockSize increments.
-  , blockSize
-
-  # Additional commands to compute a required increase in size to fit files.
-  , computeMinimalSize ? null
-
-  # When automatic sizing is used, additional amount of bytes to pad the image by.
-  , extraPadding ? 0
-  , ...
-} @ args:
-
-assert lib.asserts.assertMsg
-  (size !=null || populateCommands != null)
-  "Either a size or populateCommands needs to be given to build a filesystem.";
-
-let
-  partName = name;
-in
-stdenvNoCC.mkDerivation (args // rec {
-  # Do not inherit `size`; we don't want to accidentally use it. The `size` can
-  # be dynamic depending on the contents.
-  inherit partName blockSize;
-
-  name = "partition-${partName}";
-  filename = "${partName}.img";
-  img = "${placeholder "out"}/${filename}";
-
-  nativeBuildInputs = [
-  ] ++ optionals (args ? nativeBuildInputs) args.nativeBuildInputs;
-
-  buildCommand = ''
-    adjust-minimal-size() {
-      size="$1"
-
-      echo "$size"
-    }
-
-    compute-minimal-size() {
-      local size=0
-      (
-      cd files
-      # Size rounded in blocks. This assumes all files are to be rounded to a
-      # multiple of blockSize.
-      # Use of `--apparent-size` is to ensure we don't get the block size of the underlying FS.
-      # Use of `--block-size` is to get *our* block size.
-      size=$(find . ! -type d -print0 | du --files0-from=- --apparent-size --block-size "$blockSize" | cut -f1 | sum-lines)
-      echo "Reserving $size sectors for files..." 1>&2
-
-      # Adds one blockSize per directory, they do take some place, in the end.
-      # FIXME: write test to confirm this assumption
-      local directories=$(find . -type d | wc -l)
-      echo "Reserving $directories sectors for directories..." 1>&2
-
-      size=$(( directories + size ))
-
-      size=$((size * blockSize))
-
-      ${if computeMinimalSize == null then "" else computeMinimalSize}
-
-      size=$(( size + ${toString extraPadding} ))
-
-      echo "$size"
-      )
-    }
-
-    sum-lines() {
-      local acc=0
-      while read -r number; do
-          acc=$((acc+number))
-      done
-
-      echo "$acc"
-    }
-
-
-    # The default stdenv/generic clashes with `runHook`.
-    # It doesn't override as expected.
-    unset -f checkPhase
-
-    mkdir -p $out
-    mkdir -p files
-
-    ${optionalString (populateCommands != null) ''
-    echo
-    echo "Populating disk image"
-    echo
-    (
-      cd files
-      ${populateCommands}
-    )
-    ''}
-    ${optionalString (size == null) ''
-      size=$(compute-minimal-size)
-    ''}
-
-    if (( size < minimumSize )); then
-      size=$minimumSize
-      echo "WARNING: the '$partName' partition was too small, size increased to $minimumSize bytes."
-    fi
-
-    echo
-    echo "Building partition ${partName}"
-    echo "With ${if size == null
-      then "automatic size ($size bytes)"
-      else "$size bytes"
-    }"
-    echo
-
-    echo " -> Allocating space"
-    truncate -s $size "$img"
-
-    echo " -> Making filesystem"
-    runHook filesystemPhase
-
-    echo " -> Copying files"
-    (
-      cd files
-      runHook copyPhase
-    )
-
-    echo " -> Checking filesystem"
-    echo "$checkPhase"
-    runHook checkPhase
-
-    if [ -n "$postProcess" ]; then
-      echo "-> Running post-processing"
-      runHook postProcess
-    fi
-  '';
-
-})
-    # mkdir -p $out/nix-support
-    # cat ${writeText "${name}-metadata" (builtins.toJSON {
-    #   inherit size;
-    # })} > $out/nix-support/partition-metadata.json
-
-/*  */ ;}; in scope."fileSystem.makeFilesystem"
diff --git a/lib/image-builder/makeGPT.nix b/lib/image-builder/makeGPT.nix
deleted file mode 100644
index 554da2aa..00000000
--- a/lib/image-builder/makeGPT.nix
+++ /dev/null
@@ -1,190 +0,0 @@
-{ stdenvNoCC, lib
-, imageBuilder
-, vboot_reference
-}:
-
-/*  */ let scope = { "diskImage.makeGPT" =
-
-let
-  inherit (lib) concatMapStringsSep optionalString;
-
-  # List of known mappings of GPT partition types to filesystems.
-  # This is not exhaustive, only used as a default.
-  # See also: https://sourceforge.net/p/gptfdisk/code/ci/master/tree/parttypes.cc
-  types = {
-    "FAT32" = "EBD0A0A2-B9E5-4433-87C0-68B6B72699C7";
-    "ESP"   = "C12A7328-F81F-11D2-BA4B-00A0C93EC93B";
-    "LUKS"  = "CA7D7CCB-63ED-4C53-861C-1742536059CC";
-    "ext2"  = "0FC63DAF-8483-4772-8E79-3D69D8477DE4";
-    "ext3"  = "0FC63DAF-8483-4772-8E79-3D69D8477DE4";
-    "ext4"  = "0FC63DAF-8483-4772-8E79-3D69D8477DE4";
-    "btrfs" = "0FC63DAF-8483-4772-8E79-3D69D8477DE4";
-  };
-in
-{
-  name
-  , partitions
-  , diskID
-  , headerHole ? 0 # in bytes
-  , postProcess ? null
-}:
-
-let
-  _name = name;
-
-  eachPart = partitions: fn: (
-    concatMapStringsSep "\n" (partition:
-      fn partition
-  ) partitions);
-
-  # Default alignment.
-  alignment = toString (imageBuilder.size.MiB 1);
-
-  image = partition: 
-    if lib.isDerivation partition then
-      "${partition}/${partition.filename}"
-    else
-      partition.filename
-  ;
-in
-stdenvNoCC.mkDerivation rec {
-  name = "disk-image-${_name}";
-  filename = "${_name}.img";
-  img = "${placeholder "out"}/${filename}";
-
-  inherit
-    postProcess
-  ;
-
-  nativeBuildInputs = [
-    vboot_reference
-  ];
-
-  buildCommand = let
-    # This fragment is used to compute the (aligned) size of the partition.
-    # It is used *only* to track the tally of the space used, thus the starting
-    # offset of the next partition. The filesystem sizes are untouched.
-    sizeFragment = partition: ''
-      start=$totalSize
-      ${
-        if partition ? length then
-        ''size=$((${toString partition.length}))''
-        else
-        ''size=$(($(du --apparent-size -B 512 "$input_img" | awk '{ print $1 }') * 512))''
-      }
-      size=$(( $(if (($size % ${alignment})); then echo 1; else echo 0; fi ) + size / ${alignment} ))
-      size=$(( size * ${alignment} ))
-      totalSize=$(( totalSize + size ))
-      echo "Partition: start $start | size $size | totalSize $totalSize"
-    '';
-
-    # This fragment is used to add the desired gap to `totalSize`.
-    # We're setting `start` and `size` only to mirror the information shown
-    # for partitions.
-    # Do note that gaps are always aligned, so two gaps sized half the alignment
-    # would create 2× the space expected.
-    # What may *instead* be done at one point is always align `start` for partitions.
-    gapFragment = partition: ''
-      start=$totalSize
-      size=${toString partition.length}
-      size=$(( $(if (($size % ${alignment})); then echo 1; else echo 0; fi ) + size / ${alignment} ))
-      totalSize=$(( totalSize + size ))
-      echo "Gap: start $start | size $size | totalSize $totalSize"
-    '';
-  in ''
-    mkdir -p $out
-
-    # 34 is the base GPT header size, as added to -p by cgpt.
-    gptSize=$((${toString headerHole} + 34*512))
-
-    touch commands.sh
-
-    cat <<EOF > commands.sh
-    # Zeroes the GPT
-    cgpt create -z $img
-
-    # Create the GPT with space if desired
-    cgpt create -p ${toString (headerHole / 512)} $img
-
-    # Add the PMBR
-    cgpt boot -p $img
-
-    EOF
-
-    totalSize=$((gptSize))
-    echo
-    echo "Gathering information about partitions."
-    ${eachPart partitions (partition:
-      if partition ? isGap && partition.isGap then
-        (gapFragment partition)
-      else
-        ''
-          input_img="${image partition}"
-          ${sizeFragment partition}
-          echo " -> ${partition.name}: $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
-
-
-          (
-          printf "cgpt add"
-          printf " -b %s" "$((start/512))"
-          printf " -s %s" "$((size/512))"
-          printf " -t %s" '${
-            if partition ? partitionType then
-              partition.partitionType
-            else
-              types.${partition.filesystemType}
-          }'
-          ${optionalString (partition ? partitionUUID)
-              "printf ' -u %s' '${partition.partitionUUID}'"}
-          ${optionalString (partition ? bootable && partition.bootable)
-              "printf ' -B 1'"}
-          ${optionalString (partition ? partitionLabel)
-              "printf ' -l \"%s\"' '${partition.partitionLabel}'"}
-          printf " $img\n"
-          ) >> commands.sh
-        ''
-    )}
-
-    # Allow space for secondary partition table / header.
-    totalSize=$(( totalSize + 34*512 ))
-
-    echo "--- script ----"
-    cat commands.sh
-    echo "--- script ----"
-
-    echo
-    echo "Making image, $totalSize bytes..."
-    truncate -s $((totalSize)) $img
-
-    PS4=" > " sh -x commands.sh
-
-    totalSize=$((gptSize))
-    echo
-    echo "Writing partitions into image"
-    ${eachPart partitions (partition: 
-      if partition ? isGap && partition.isGap then
-        (gapFragment partition)
-      else
-        ''
-          input_img="${image partition}"
-          ${sizeFragment partition}
-          echo " -> ${partition.name}: $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
-
-          echo "$start / $size"
-          dd conv=notrunc if=$input_img of=$img seek=$((start/512)) count=$((size/512)) bs=512
-        ''
-    )}
-
-    echo
-    echo "Information about the image:"
-    ls -lh $img
-    cgpt show $img
-
-    if [ -n "$postProcess" ]; then
-      echo "-> Running post-processing"
-      runHook postProcess
-    fi
-  '';
-}
-
-/*  */ ;}; in scope."diskImage.makeGPT"
diff --git a/lib/image-builder/makeMBR.nix b/lib/image-builder/makeMBR.nix
deleted file mode 100644
index 325b0398..00000000
--- a/lib/image-builder/makeMBR.nix
+++ /dev/null
@@ -1,140 +0,0 @@
-{ stdenvNoCC, lib
-, imageBuilder
-, util-linux
-}:
-
-/*  */ let scope = { "diskImage.makeMBR" =
-
-let
-  inherit (lib) concatMapStringsSep optionalString;
-
-  # List of known mappings of MBR partition types to filesystems.
-  types = {
-    "FAT32" =  "b";
-    "ESP"   = "ef";
-    "ext2"  = "83";
-    "ext3"  = "83";
-    "ext4"  = "83";
-  };
-in
-{
-  name
-  , partitions
-  # Without the prefixed `0x`
-  , diskID
-}:
-
-let
-  _name = name;
-
-  eachPart = partitions: fn: (
-    concatMapStringsSep "\n" (partition:
-      fn partition
-  ) partitions);
-
-  # Default alignment.
-  alignment = toString (imageBuilder.size.MiB 1);
-in
-stdenvNoCC.mkDerivation rec {
-  name = "disk-image-${_name}";
-  filename = "${_name}.img";
-  img = "${placeholder "out"}/${filename}";
-
-  nativeBuildInputs = [
-    util-linux
-  ];
-
-  buildCommand = let
-    # This fragment is used to compute the (aligned) size of the partition.
-    # It is used *only* to track the tally of the space used, thus the starting
-    # offset of the next partition. The filesystem sizes are untouched.
-    sizeFragment = ''
-      start=$totalSize
-      size=$(($(du --apparent-size -B 512 "$input_img" | awk '{ print $1 }') * 512))
-      size=$(( $(if (($size % ${alignment})); then echo 1; else echo 0; fi ) + size / ${alignment} ))
-      size=$(( size * ${alignment} ))
-      totalSize=$(( totalSize + size ))
-      echo "Partition: start $start | size $size | totalSize $totalSize"
-    '';
-
-    # This fragment is used to add the desired gap to `totalSize`.
-    # We're setting `start` and `size` only to mirror the information shown
-    # for partitions.
-    # Do note that gaps are always aligned, so two gaps sized half the alignment
-    # would create 2× the space expected.
-    # What may *instead* be done at one point is always align `start` for partitions.
-    gapFragment = partition: ''
-      start=$totalSize
-      size=${toString partition.length}
-      size=$(( $(if (($size % ${alignment})); then echo 1; else echo 0; fi ) + size / ${alignment} ))
-      size=$(( size * ${alignment} ))
-      totalSize=$(( totalSize + size ))
-      echo "Gap: start $start | size $size | totalSize $totalSize"
-    '';
-  in ''
-    mkdir -p $out
-
-    cat <<EOF > script.sfdisk
-    label: dos
-    grain: 1024
-    label-id: 0x${diskID}
-    EOF
-
-    totalSize=${alignment}
-    echo
-    echo "Gathering information about partitions."
-    ${eachPart partitions (partition:
-      if partition ? isGap && partition.isGap then
-        (gapFragment partition)
-      else
-        ''
-          input_img="${partition}/${partition.filename}"
-          ${sizeFragment}
-          echo " -> ${partition.name}: $size / ${partition.filesystemType}"
-
-          (
-          # The size is /1024; otherwise it's in sectors.
-          echo -n 'start='"$((start/1024))"'KiB'
-          echo -n ', size='"$((size/1024))"'KiB'
-          echo -n ', type=${types."${partition.filesystemType}"}'
-          ${optionalString (partition ? bootable && partition.bootable)
-              "echo -n ', bootable'"}
-          echo "" # Finishes the command
-          ) >> script.sfdisk
-        ''
-    )}
-
-    echo "--- script ----"
-    cat script.sfdisk
-    echo "--- script ----"
-
-    echo
-    echo "Making image, $totalSize bytes..."
-    truncate -s $((totalSize)) $img
-    sfdisk $img < script.sfdisk
-
-    totalSize=${alignment}
-    echo
-    echo "Writing partitions into image"
-    ${eachPart partitions (partition: 
-      if partition ? isGap && partition.isGap then
-        (gapFragment partition)
-      else
-        ''
-          input_img="${partition}/${partition.filename}"
-          ${sizeFragment}
-          echo " -> ${partition.name}: $size / ${partition.filesystemType}"
-
-          echo "$start / $size"
-          dd conv=notrunc if=$input_img of=$img seek=$((start/512)) count=$((size/512)) bs=512
-        ''
-    )}
-
-    echo
-    echo "Information about the image:"
-    ls -lh $img
-    sfdisk -V --list $img
-  '';
-}
-
-/*  */ ;}; in scope."diskImage.makeMBR"
diff --git a/lib/image-builder/test.rb b/lib/image-builder/test.rb
deleted file mode 100755
index 295a3cbe..00000000
--- a/lib/image-builder/test.rb
+++ /dev/null
@@ -1,144 +0,0 @@
-#!/usr/bin/env nix-shell
-# All dependencies `verify` will need too.
-#!nix-shell --pure -p nix -p ruby -p file -i ruby
-
-require "tmpdir"
-require "open3"
-require "json"
-# require "fileutils"
-
-prefix = File.join(__dir__, "tests")
-NIX_PATH = "nixpkgs-overlays=#{__dir__}/lib/tests/test-overlay.nix:nixpkgs=channel:nixos-19.03"
-
-# Default directives for the test.
-DEFAULT_DIRECTIVES = {
-  # Default is to succeed.
-  status: 0,
-
-  # Nothing to grep for in particular.
-  # (Caution! Successes are likely not to have logs!)
-  grep: nil,
-}
-
-Env = {
-  "NIX_PATH" => NIX_PATH,
-}
-
-tests =
-  if ARGV.count > 0 then
-    ARGV
-  else
-    # Assumes all nix files in `./tests` are tests to `nix-build`.
-    Dir.glob(File.join(prefix, "**/*.nix"))
-  end
-
-tests.sort!
-
-$exit = 0
-$failed_tests = []
-
-puts ""
-puts "Tests"
-puts "====="
-puts ""
-
-tests.each_with_index do |file, index|
-  short_name = file.sub("#{prefix}/", "")
-  print "Running test #{(index+1).to_s.rjust(tests.length.to_s.length)}/#{tests.length} '#{short_name}' "
-
-  failures = []
-
-  # Reads the first line of the file. It may hold a json snippet
-  # configuring the expected test results.
-  directives = File.read(file).split("\n").first || ""
-  directives = DEFAULT_DIRECTIVES.merge(
-    if directives.match(/^\s*#\s*expect:/i) then
-      # Parse...
-      JSON.parse(
-        # Everything after the first colon as json
-        directives.split(":", 2).last,
-        symbolize_names: true,
-    )
-  else
-    {}
-  end
-  )
-
-  # The result symlink is in a temp directory...
-  Dir.mktmpdir("image-builder-test") do |dir|
-    result = File.join(dir, "result")
-
-    # TODO : figure out how to keep stdout/stderr synced but logged separately.
-    log, status = Open3.capture2e(Env, "nix-build", "--show-trace", "--out-link", result, file)
-
-    unless status.exitstatus == directives[:status]
-      failures << "Build exited with status #{status.exitstatus} expected #{directives[:status]}."
-    end
-
-    if directives[:grep] then
-      unless log.match(directives[:grep])
-        failures << "Output log did not match `#{directives[:grep]}`."
-      end
-    end
-
-    # Do we test further with the test scripts?
-    if failures.length == 0 and status.success? then
-      script = file.sub(/\.nix$/, ".rb")
-      if File.exists?(script) then
-        log, status = Open3.capture2e(Env, File.join(__dir__, "lib/tests/verify.rb"), script, result)
-      end
-
-      unless status.exitstatus == 0
-        failures << "Verification exited with status #{status.exitstatus} expected 0."
-      end
-
-      store_path = File.readlink(result)
-    end
-
-    if failures.length == 0 then
-      puts "[Success] (#{store_path || "no output"})  "
-    else
-      $exit = 1
-      $failed_tests << file
-      puts "[Failed] (#{store_path || "no output"})  "
-      puts ""
-      puts "Failures:"
-      failures.each do |failure|
-        puts " - #{failure}"
-      end
-      puts ""
-      puts "Directives:"
-      puts ""
-      puts "```"
-      puts "#{directives.inspect}"
-      puts "```"
-
-      puts ""
-      puts "Output from the test:"
-      puts ""
-      puts "````"
-      puts "#{log}"
-      puts "````"
-    end
-  end
-end
-
-puts ""
-puts "* * *"
-puts ""
-puts "Test summary"
-puts "============"
-puts ""
-
-puts "#{tests.length - $failed_tests.length}/#{tests.length} tests successful."
-
-if $failed_tests.length > 0 then
-puts ""
-puts "Failed tests:\n"
-$failed_tests.each do |filename|
-  puts " - #{filename.sub(/^#{__dir__}/, ".")}"
-end
-puts ""
-end
-
-exit $exit
diff --git a/lib/image-builder/tests/alignment/aligned.nix b/lib/image-builder/tests/alignment/aligned.nix
deleted file mode 100644
index aad766bd..00000000
--- a/lib/image-builder/tests/alignment/aligned.nix
+++ /dev/null
@@ -1,50 +0,0 @@
-# Verifies that filesystems sized to be aligned works.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  makeNull = size: pkgs.runCommand "filesystems-test" {
-    filename = "null.img";
-    filesystemType = "FAT32"; # meh, good enough
-  } ''
-    mkdir -p $out
-    dd if=/dev/zero of=$out/$filename bs=${toString size} count=1
-  '';
-in
-
-with imageBuilder;
-
-{
-  one = diskImage.makeMBR {
-    name = "diskimage";
-    diskID = "012345678";
-    partitions = [
-      (makeNull (size.MiB 1))
-      (makeNull (size.MiB 1))
-    ];
-  };
-  nine = diskImage.makeMBR {
-    name = "diskimage";
-    diskID = "012345678";
-    partitions = [
-      (makeNull (size.MiB 9))
-      (makeNull (size.MiB 9))
-    ];
-  };
-  ten = diskImage.makeMBR {
-    name = "diskimage";
-    diskID = "012345678";
-    partitions = [
-      (makeNull (size.MiB 10))
-      (makeNull (size.MiB 10))
-    ];
-  };
-  eleven = diskImage.makeMBR {
-    name = "diskimage";
-    diskID = "012345678";
-    partitions = [
-      (makeNull (size.MiB 11))
-      (makeNull (size.MiB 11))
-    ];
-  };
-}
diff --git a/lib/image-builder/tests/alignment/unaligned.nix b/lib/image-builder/tests/alignment/unaligned.nix
deleted file mode 100644
index 8eed6c1e..00000000
--- a/lib/image-builder/tests/alignment/unaligned.nix
+++ /dev/null
@@ -1,42 +0,0 @@
-# Verifies that filesystems sized to be unaligned will work.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  makeNull = size: pkgs.runCommand "filesystems-test" {
-    filename = "null.img";
-    filesystemType = "FAT32"; # meh, good enough
-  } ''
-    mkdir -p $out
-    dd if=/dev/zero of=$out/$filename bs=${toString size} count=1
-  '';
-in
-
-with imageBuilder;
-
-# Through empirical testing, it was found out that the defaults from `sfdisk`
-# are not as documented.
-# First of all, on small disks no alignment will be made.
-# Starting with 3MiB (empirically derived) alignment will be made.
-# The alignment is documented as being based on the I/O limits. It seems like
-# for files it ends up causing alignments at the 2MiB boundaries.
-# Such, `grain: 1024` has to be set to configure sfdisk for the sane default
-# documented in its manpage
-#
-# > grain  Specify minimal size in bytes used to calculate partitions alignment.
-# >        The default is 1MiB and it's strongly recommended to use the default.
-# >        Do not modify this variable if you're not sure.
-#
-# The default is *not* 1MiB and will break the generation of images if it tries
-# to align a small partition at the very end of the disk, when the disk is sized
-# just right to fit.
-#
-# This is what this test validates.
-diskImage.makeMBR {
-  name = "diskimage";
-  diskID = "012345678";
-  partitions = [
-    (makeNull (size.MiB 3))
-    (makeNull (size.MiB 1))
-  ];
-}
diff --git a/lib/image-builder/tests/failures/filesystem-without_size_without_commands.nix b/lib/image-builder/tests/failures/filesystem-without_size_without_commands.nix
deleted file mode 100644
index 222078b2..00000000
--- a/lib/image-builder/tests/failures/filesystem-without_size_without_commands.nix
+++ /dev/null
@@ -1,13 +0,0 @@
-# Expect: { "status": 1, "grep": "Either a size or populateCommands needs to be given to build a filesystem." }
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-in
-
-with imageBuilder;
-
-fileSystem.makeFAT32 {
-  name = "whatever";
-  partitionID = "0123456789ABCDEF";
-}
diff --git a/lib/image-builder/tests/filesystems/default.nix b/lib/image-builder/tests/filesystems/default.nix
deleted file mode 100644
index 2b09e722..00000000
--- a/lib/image-builder/tests/filesystems/default.nix
+++ /dev/null
@@ -1,35 +0,0 @@
-# Tests all known filesystems as empty, with defaults.
-# This test helps ensure the basic interface stays stable, and works.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  inherit (pkgs.lib.attrsets) mapAttrsToList;
-  inherit (pkgs.lib.strings) concatStringsSep removePrefix;
-  IDs = {
-    FAT32 = "0123456789ABCDEF";
-    ESP = "0123456789ABCDEF";
-    Ext4 = "44444444-4444-4444-1324-123456789098";
-  };
-in
-
-with imageBuilder;
-
-let
-  cmds =
-    mapAttrsToList (fn_name: fn:
-    let
-      fs = fn rec {
-        name = removePrefix "make" fn_name;
-        size = imageBuilder.size.MiB 10;
-        partitionID = IDs."${name}";
-      };
-    in
-    ''
-      ln -s ${fs}/${fs.filename} $out/
-    '') fileSystem;
-in
-  pkgs.runCommand "filesystems-test" {} ''
-    mkdir -p $out/
-    ${concatStringsSep "\n" cmds}
-  ''
diff --git a/lib/image-builder/tests/filesystems/default.rb b/lib/image-builder/tests/filesystems/default.rb
deleted file mode 100644
index e63cae2e..00000000
--- a/lib/image-builder/tests/filesystems/default.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-hashes = {
-  "ESP.img"   => "f9b39d98bfb797b050467ca5214671b5b427b7896cae44d27d2fc8dbceaccd88",
-  "FAT32.img" => "79028d8af97ae4400ea2ab36d34e2a80684c9f8d31ea75e3f54d908c75adc3a4",
-  "Ext4.img"  => "8182df3038f43cdf2aba6f3980d9fa794affab0f040f9c07450ebbf0d3d8c2ad",
-}
-
-filetypes = {
-  "ESP.img"   => 'DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", reserved sectors 32, root entries 512, sectors 20480 (volumes <=32 MB), Media descriptor 0xf8, sectors/FAT 80, sectors/track 32, heads 64, serial number 0x89abcdef, label: "ESP        ", FAT (16 bit)',
-  "FAT32.img" => 'DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", reserved sectors 32, root entries 512, sectors 20480 (volumes <=32 MB), Media descriptor 0xf8, sectors/FAT 80, sectors/track 32, heads 64, serial number 0x89abcdef, label: "FAT32      ", FAT (16 bit)',
-  "Ext4.img"  => 'Linux rev 1.0 ext4 filesystem data, UUID=44444444-4444-4444-1324-123456789098, volume name "Ext4" (extents) (large files)'
-}
-
-# By globbing on the output, we can validate all built images are verified.
-# The builder should have built everything under `fileSystems`.
-Dir.glob(File.join($result, "**/*")) do |file|
-  name = File.basename(file)
-  sha256sum(name, hashes[name])
-  file(name, filetypes[name])
-end
diff --git a/lib/image-builder/tests/filesystems/default_with_files.nix b/lib/image-builder/tests/filesystems/default_with_files.nix
deleted file mode 100644
index dd0cfced..00000000
--- a/lib/image-builder/tests/filesystems/default_with_files.nix
+++ /dev/null
@@ -1,39 +0,0 @@
-# Tests all known filesystems with files.
-# This test helps ensure the basic interface stays stable, and works.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  inherit (pkgs.lib.attrsets) mapAttrsToList;
-  inherit (pkgs.lib.strings) concatStringsSep removePrefix;
-  IDs = {
-    FAT32 = "0123456789ABCDEF";
-    ESP = "0123456789ABCDEF";
-    Ext4 = "44444444-4444-4444-1324-123456789098";
-  };
-in
-
-with imageBuilder;
-
-let
-  cmds =
-    mapAttrsToList (fn_name: fn:
-    let
-      fs = fn rec {
-        name = removePrefix "make" fn_name;
-        partitionID = IDs."${name}";
-        populateCommands = ''
-          echo "I am ${name}." > file
-          ls -lA
-        '';
-      };
-    in
-    ''
-      ln -s ${fs}/${fs.filename} $out/
-    '') fileSystem;
-in
-  pkgs.runCommand "filesystems-test" {} ''
-    mkdir -p $out/
-    ${concatStringsSep "\n" cmds}
-  ''
-
diff --git a/lib/image-builder/tests/filesystems/default_with_files.rb b/lib/image-builder/tests/filesystems/default_with_files.rb
deleted file mode 100644
index e9e504c1..00000000
--- a/lib/image-builder/tests/filesystems/default_with_files.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-hashes = {
-  "ESP.img"   => "d70b24594f0615b83fddb8608b4819432380359bc5c6763d7c318e0c3233ea64",
-  "FAT32.img" => "73ab1acd845fd0f7f5ddd30edea074f0b14bf4f2b4137f904a90939f1cb2ac8d",
-  "Ext4.img"  => "56181a43406c4ba731ed14b3ed32ed6c169b1c2abfe385eef989faef55e3cd07",
-}
-
-filetypes = {
-  "ESP.img"   => 'DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", reserved sectors 32, root entries 512, sectors 1000 (volumes <=32 MB), Media descriptor 0xf8, sectors/FAT 3, sectors/track 32, heads 64, serial number 0x89abcdef, label: "ESP        ", FAT (12 bit)',
-  "FAT32.img" => 'DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", reserved sectors 32, root entries 512, sectors 1000 (volumes <=32 MB), Media descriptor 0xf8, sectors/FAT 3, sectors/track 32, heads 64, serial number 0x89abcdef, label: "FAT32      ", FAT (12 bit)',
-  "Ext4.img"  => 'Linux rev 1.0 ext4 filesystem data, UUID=44444444-4444-4444-1324-123456789098, volume name "Ext4" (extents) (large files)'
-}
-
-# By globbing on the output, we can validate all built images are verified.
-# The builder should have built everything under `fileSystems`.
-Dir.glob(File.join($result, "**/*")) do |file|
-  name = File.basename(file)
-  sha256sum(name, hashes[name])
-  file(name, filetypes[name])
-end
diff --git a/lib/image-builder/tests/size/ext4.nix b/lib/image-builder/tests/size/ext4.nix
deleted file mode 100644
index b4105270..00000000
--- a/lib/image-builder/tests/size/ext4.nix
+++ /dev/null
@@ -1,70 +0,0 @@
-# Ensures we can fit stuff in an ext4 image.
-{ pkgs ? import <nixpkgs> {} }:
-
-let
-  inherit (pkgs) imageBuilder;
-  makeNull = size: let
-    filename = "null.img";
-    filesystemType = "FAT32"; # meh, good enough
-  in
-  ''
-    mkdir -p $out
-    dd if=/dev/zero of=./${toString size}.img bs=${toString size} count=1
-  '';
-in
-
-with imageBuilder;
-
-{
-  one = fileSystem.makeExt4 {
-    name = "one";
-    partitionID = "44444444-4444-4444-0000-000000000001";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 1)}
-    '';
-  };
-  two = fileSystem.makeExt4 {
-    name = "two";
-    partitionID = "44444444-4444-4444-0000-000000000002";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 2)}
-    '';
-  };
-  three = fileSystem.makeExt4 {
-    name = "three";
-    partitionID = "44444444-4444-4444-0000-000000000003";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 3)}
-    '';
-  };
-  four = fileSystem.makeExt4 {
-    name = "four";
-    partitionID = "44444444-4444-4444-0000-000000000004";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 4)}
-    '';
-  };
-  five = fileSystem.makeExt4 {
-    name = "five";
-    partitionID = "44444444-4444-4444-0000-000000000005";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 5)}
-    '';
-  };
-  # This is the boundary where otherwise it would begin to fail.
-  five_plus_one = fileSystem.makeExt4 {
-    name = "five_plus_one";
-    partitionID = "44444444-4444-4444-0001-000000000005";
-    populateCommands = ''
-      ${makeNull ((imageBuilder.size.MiB 5) + 1)}
-    '';
-  };
-  six = fileSystem.makeExt4 {
-    name = "six";
-    partitionID = "44444444-4444-4444-0000-000000000006";
-    populateCommands = ''
-      ${makeNull (imageBuilder.size.MiB 6)}
-    '';
-  };
-  # For bigger tests, see in-depth-tests
-}
diff --git a/overlay/image-builder/default.nix b/overlay/image-builder/default.nix
new file mode 100644
index 00000000..9521fb09
--- /dev/null
+++ b/overlay/image-builder/default.nix
@@ -0,0 +1,10 @@
+{ pkgs, lib }:
+
+{
+  evaluateFilesystemImage = { config ? {}, modules ? [] }: import ./filesystem-image/eval-config.nix {
+    inherit pkgs config modules;
+  };
+  evaluateDiskImage = { config ? {}, modules ? [] }: import ./disk-image/eval-config.nix {
+    inherit pkgs config modules;
+  };
+}
diff --git a/overlay/image-builder/disk-image/basic.nix b/overlay/image-builder/disk-image/basic.nix
new file mode 100644
index 00000000..adf4f6c9
--- /dev/null
+++ b/overlay/image-builder/disk-image/basic.nix
@@ -0,0 +1,73 @@
+{ config, lib, ... }:
+
+let
+  inherit (lib)
+    mkOption
+    types
+  ;
+in
+{
+  options = {
+    name = mkOption {
+      type = types.str;
+      default = "disk-image";
+      description = "Base name of the output";
+    };
+
+    alignment = mkOption {
+      type = types.int;
+      default = config.helpers.size.MiB 1;
+      description = lib.mdDoc ''
+        Partitions alignment.
+
+        Automatically computed partition start position will be aligned to
+        multiples of this value.
+
+        The default value is most likely appropriate.
+      '';
+    };
+
+    sectorSize = mkOption {
+      type = types.int;
+      default = 512;
+      internal = true;
+      description = lib.mdDoc ''
+        Sector size. This is used mainly internally. Changing this should have
+        no effects on the actual disk image produced.
+
+        The default value is most likely appropriate.
+      '';
+    };
+
+    output = mkOption {
+      type = types.package;
+      internal = true;
+      description = lib.mdDoc ''
+        The build output for the disk image.
+      '';
+    };
+
+    additionalCommands = mkOption {
+      type = types.str;
+      default = "";
+      description = lib.mdDoc ''
+        Additional commands to run during the disk image build.
+      '';
+    };
+
+    # TODO: implement this:
+    # mergeDerivationScripts = mkOption {
+    #   type = types.bool;
+    #   default = false;
+    #   internal = true;
+    #   description = lib.mdDoc ''
+    #     Whether to produce discrete derivations for each steps, or to produce
+    #     a single derivation that builds the image from A to Z.
+    #
+    #     Setting this to true may be helpful with some CI/CD environments where
+    #     limitations in output sizes makes it impossible to produce discrete
+    #     derivations for every steps along the way.
+    #   '';
+    # };
+  };
+}
diff --git a/overlay/image-builder/disk-image/eval-config.nix b/overlay/image-builder/disk-image/eval-config.nix
new file mode 100644
index 00000000..89c15cbd
--- /dev/null
+++ b/overlay/image-builder/disk-image/eval-config.nix
@@ -0,0 +1,18 @@
+/**
+ * Evaluates the configuration for a disk image build.
+ */
+{ pkgs
+, modules ? []
+, config ? {}
+}:
+let config' = config; in
+rec {
+  module = { imports = import ./module-list.nix; };
+  config = (pkgs.lib.evalModules {
+    modules = [
+      { _module.args.pkgs = pkgs; }
+      module
+      config'
+    ] ++ modules;
+  }).config;
+}
diff --git a/overlay/image-builder/disk-image/module-list.nix b/overlay/image-builder/disk-image/module-list.nix
new file mode 100644
index 00000000..cb12f435
--- /dev/null
+++ b/overlay/image-builder/disk-image/module-list.nix
@@ -0,0 +1,8 @@
+# Note: No `filesystem` modules are to be added here. Filesystems are used as
+#       submodules in the partitions options.
+[
+  ../helpers.nix
+  ./basic.nix
+  ./partitioning-scheme
+  ./partitions.nix
+]
diff --git a/overlay/image-builder/disk-image/partitioning-scheme/default.nix b/overlay/image-builder/disk-image/partitioning-scheme/default.nix
new file mode 100644
index 00000000..dfc02c71
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitioning-scheme/default.nix
@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+
+let
+  inherit (lib)
+    mkOption
+    types
+  ;
+in
+{
+  imports = [
+    ./gpt
+    ./mbr
+  ];
+
+  options = {
+    availablePartitioningSchemes = mkOption {
+      type = with types; listOf str;
+      internal = true;
+    };
+    partitioningScheme = mkOption {
+      type = types.enum config.availablePartitioningSchemes;
+      description = lib.mdDoc ''
+        Partitioning scheme for the disk image output.
+      '';
+    };
+  };
+}
diff --git a/overlay/image-builder/disk-image/partitioning-scheme/gpt/builder.nix b/overlay/image-builder/disk-image/partitioning-scheme/gpt/builder.nix
new file mode 100644
index 00000000..fb2e7cf6
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitioning-scheme/gpt/builder.nix
@@ -0,0 +1,197 @@
+{ stdenvNoCC
+, lib
+, fetchpatch
+, gptfdisk
+, buildPackages
+, utillinux
+, config
+}:
+
+let
+  inherit (lib)
+    concatMapStringsSep
+    concatStringsSep
+    optionalString
+  ;
+  inherit (config.helpers)
+    each
+  ;
+  inherit (config)
+    partitions
+  ;
+  inherit (config.gpt)
+    hybridMBR
+  ;
+in
+stdenvNoCC.mkDerivation rec {
+  inherit (config)
+    name
+    alignment
+    sectorSize
+    additionalCommands
+  ;
+  inherit (config.gpt)
+    diskID
+    partitionEntriesCount
+  ;
+
+  img = placeholder "out";
+
+  nativeBuildInputs = [
+    gptfdisk
+    utillinux
+  ];
+
+  buildCommand = let
+    # This fragment is used to compute the (aligned) size of the partition.
+    # It is used *only* to track the tally of the space used, thus the starting
+    # offset of the next partition. The filesystem sizes are untouched.
+    sizeFragment = partition: ''
+      ${if (partition ? offset && partition.offset != null) then ''
+        # If a partition asks to start at a specific offset, restart tally at
+        # that location.
+        offset=$((${toString partition.offset}))
+
+        if (( offset < totalSize )); then
+          echo "Partition '${partition.name}' wanted to start at $offset while we were already at $totalSize"
+          echo "As of right now, partitions need to be in order."
+          exit 1
+        else
+          totalSize=$offset
+        fi
+        start=$totalSize
+        # *by design* we're not aligning the start of the partition here if an
+        # offset was given.
+      '' else ''
+        # Assume we start where we left off...
+        start=$totalSize
+        # Align to the nearest alignment
+        if (( start % alignment )); then
+          start=$(( start + (alignment - start % alignment) ))
+        fi
+      ''}
+      ${
+        if (partition ? length && partition.length != null) then
+        ''size=$((${toString partition.length}))''
+        else
+        ''size=$(($(du --apparent-size -B 512 "$input_img" | awk '{ print $1 }') * 512))''
+      }
+      size=$(( $(if ((size % alignment)); then echo 1; else echo 0; fi ) + size / alignment ))
+      size=$(( size * alignment ))
+      totalSize=$(( totalSize + size ))
+      # Align the end too
+      if (( totalSize % alignment )); then
+        totalSize=$(( totalSize + (alignment - totalSize % alignment) ))
+      fi
+      echo "Partition: start $start | size $size | totalSize $totalSize"
+    '';
+
+    # This fragment is used to add the desired gap to `totalSize`.
+    # We're setting `start` and `size` only to mirror the information shown
+    # for partitions.
+    gapFragment = partition: ''
+      start=$totalSize
+      size=${toString partition.length}
+      totalSize=$(( totalSize + size ))
+      echo "Gap: start $start | size $size | totalSize $totalSize"
+    '';
+  in ''
+    set -u
+
+    # LBA0 and LBA1 contains the PMBR and GPT.
+    #
+    #  2 is LBA2, where the header hole starts.
+    # One partition entry is 128 bytes long.
+    gptSize=$((2*512 + partitionEntriesCount*128))
+
+    cat <<EOF > script.sfdisk
+    label: gpt
+    unit: sectors
+    first-lba: $(( gptSize % sectorSize ? gptSize / sectorSize + 1 : gptSize / sectorSize ))
+    sector-size: $sectorSize
+    table-length: $partitionEntriesCount
+    grain: $alignment
+    ${optionalString (diskID != null) ''
+    label-id: ${diskID}
+    ''}
+    EOF
+
+    totalSize=$((gptSize))
+    echo
+    echo "Gathering information about partitions."
+    ${each partitions (partition:
+      if partition ? isGap && partition.isGap then
+        (gapFragment partition)
+      else
+        ''
+          input_img="${if partition.raw != null then partition.raw else ""}"
+          ${sizeFragment partition}
+          echo ' -> '${lib.escapeShellArg partition.name}": $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
+
+          (
+          echo -n 'start='"$((start/sectorSize))"
+          echo -n ', size='"$((size/sectorSize))"
+          echo -n ', type=${partition.partitionType}'
+          ${optionalString (partition.partitionUUID != null)
+              "echo -n ', uuid=${partition.partitionUUID}'"}
+          ${optionalString (partition ? bootable && partition.bootable)
+              ''echo -n ', attrs="LegacyBIOSBootable"' ''}
+          ${optionalString (partition ? requiredPartition && partition.requiredPartition)
+              ''echo -n ', attrs="RequiredPartition"' ''}
+          ${optionalString (partition ? partitionLabel)
+              ''echo -n ', name="${partition.partitionLabel}"' ''}
+          echo "" # Finishes the command
+          ) >> script.sfdisk
+        ''
+    )}
+
+    # Allow space for secondary partition table / header.
+    totalSize=$(( totalSize + gptSize ))
+
+    echo "--- script ----"
+    cat script.sfdisk
+    echo "--- script ----"
+
+    echo
+    echo "Making image, $totalSize bytes..."
+    truncate -s $((totalSize)) $img
+
+    sfdisk $img < script.sfdisk
+
+    totalSize=$((gptSize))
+    echo
+    echo "Writing partitions into image"
+    ${each partitions (partition: 
+      if !(partition ? raw && partition.raw != null) && partition ? isGap && partition.isGap then
+        (gapFragment partition)
+      else
+        ''
+          input_img="${if partition.raw != null then partition.raw else ""}"
+          if [[ "$input_img" == "" ]]; then
+            input_img="/dev/zero"
+          fi
+          ${sizeFragment partition}
+          echo ' -> '${lib.escapeShellArg partition.name}": $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
+
+          echo "$start / $size"
+          dd conv=notrunc if=$input_img of=$img seek=$((start/512)) count=$((size/512)) bs=512
+        ''
+    )}
+
+    ${optionalString (hybridMBR != []) ''
+      echo
+      echo "Making Hybrid MBR"
+      echo
+      sgdisk --hybrid=${concatStringsSep ":" hybridMBR} "$img"
+    ''}
+
+    echo
+    echo "Information about the image:"
+    ls -lh $img
+    sfdisk -V --list $img
+
+    runHook additionalCommands
+
+    set +u
+  '';
+}
diff --git a/overlay/image-builder/disk-image/partitioning-scheme/gpt/default.nix b/overlay/image-builder/disk-image/partitioning-scheme/gpt/default.nix
new file mode 100644
index 00000000..91d28c8b
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitioning-scheme/gpt/default.nix
@@ -0,0 +1,56 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.partitioningScheme == "gpt";
+  inherit (lib)
+    mkIf
+    mkMerge
+    mkOption
+    types
+  ;
+in
+{
+  options.gpt = {
+    diskID = mkOption {
+      type = types.nullOr config.helpers.types.uuid;
+      default = null;
+      description = lib.mdDoc ''
+        Identifier for the disk.
+      '';
+    };
+
+    partitionEntriesCount = mkOption {
+      type = types.int;
+      default = 128;
+      description = lib.mdDoc ''
+        Number of partitions in the partition table.
+
+        The default value is likely appropriate.
+      '';
+    };
+
+    hybridMBR = mkOption {
+      type = with types; listOf str;
+      default = [];
+      example = [ "1" "3" "6" "EE" ];
+      description = lib.mdDoc ''
+        Creates an hybrid MBR with the given (string) partition numbers.
+
+        Up to three partitions can be present in the hybrid MBR, an additional
+        special partition can be placed last, named `EE`. When `EE` is present
+        last the protective partition for the GPT will be placed last.
+
+        See `man sgdisk`
+      '';
+    };
+  };
+
+  config = mkMerge [
+    { availablePartitioningSchemes = [ "gpt" ]; }
+    (mkIf enabled {
+      output = pkgs.callPackage ./builder.nix {
+        inherit config;
+      };
+    })
+  ];
+}
diff --git a/overlay/image-builder/disk-image/partitioning-scheme/mbr/builder.nix b/overlay/image-builder/disk-image/partitioning-scheme/mbr/builder.nix
new file mode 100644
index 00000000..4e4406d9
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitioning-scheme/mbr/builder.nix
@@ -0,0 +1,174 @@
+{ stdenvNoCC
+, lib
+, fetchpatch
+, buildPackages
+, utillinux
+, config
+}:
+
+let
+  inherit (lib)
+    concatMapStringsSep
+    concatStringsSep
+    optionalString
+  ;
+  inherit (config.helpers)
+    each
+  ;
+  inherit (config)
+    partitions
+  ;
+in
+stdenvNoCC.mkDerivation rec {
+  inherit (config)
+    name
+    alignment
+    sectorSize
+    additionalCommands
+  ;
+  inherit (config.mbr)
+    diskID
+  ;
+
+  img = placeholder "out";
+
+  nativeBuildInputs = [
+    utillinux
+  ];
+
+  buildCommand = let
+    # This fragment is used to compute the (aligned) size of the partition.
+    # It is used *only* to track the tally of the space used, thus the starting
+    # offset of the next partition. The filesystem sizes are untouched.
+    sizeFragment = partition: ''
+      ${if (partition ? offset && partition.offset != null) then ''
+        # If a partition asks to start at a specific offset, restart tally at
+        # that location.
+        offset=$((${toString partition.offset}))
+
+        if (( offset < totalSize )); then
+          echo "Partition '${partition.name}' wanted to start at $offset while we were already at $totalSize"
+          echo "As of right now, partitions need to be in order."
+          exit 1
+        else
+          totalSize=$offset
+        fi
+        start=$totalSize
+        # *by design* we're not aligning the start of the partition here if an
+        # offset was given.
+      '' else ''
+        # Assume we start where we left off...
+        start=$totalSize
+        # Align to the nearest alignment
+        if (( start % alignment )); then
+          start=$(( start + (alignment - start % alignment) ))
+        fi
+      ''}
+      ${
+        if (partition ? length && partition.length != null) then
+        ''size=$((${toString partition.length}))''
+        else
+        ''size=$(($(du --apparent-size -B 512 "$input_img" | awk '{ print $1 }') * 512))''
+      }
+      size=$(( $(if ((size % alignment)); then echo 1; else echo 0; fi ) + size / alignment ))
+      size=$(( size * alignment ))
+      totalSize=$(( totalSize + size ))
+      # Align the end too
+      if (( totalSize % alignment )); then
+        totalSize=$(( totalSize + (alignment - totalSize % alignment) ))
+      fi
+      echo "Partition: start $start | size $size | totalSize $totalSize"
+    '';
+
+    # This fragment is used to add the desired gap to `totalSize`.
+    # We're setting `start` and `size` only to mirror the information shown
+    # for partitions.
+    gapFragment = partition: ''
+      start=$totalSize
+      size=${toString partition.length}
+      totalSize=$(( totalSize + size ))
+      echo "Gap: start $start | size $size | totalSize $totalSize"
+    '';
+  in ''
+    set -u
+
+    # LBA0 contains the MBR.
+    mbrSize=$((1*512))
+
+    cat <<EOF > script.sfdisk
+    label: dos
+    unit: sectors
+    first-lba: $(( mbrSize % sectorSize ? mbrSize / sectorSize + 1 : mbrSize / sectorSize ))
+    sector-size: $sectorSize
+    grain: $alignment
+    ${optionalString (diskID != null) ''
+    label-id: ${diskID}
+    ''}
+    EOF
+
+    totalSize=$((mbrSize))
+    echo
+    echo "Gathering information about partitions."
+    ${each partitions (partition:
+      if partition ? isGap && partition.isGap then
+        (gapFragment partition)
+      else
+        ''
+          input_img="${if partition.raw != null then partition.raw else ""}"
+          ${sizeFragment partition}
+          echo ' -> '${lib.escapeShellArg partition.name}": $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
+
+          (
+          echo -n 'start='"$((start/sectorSize))"
+          echo -n ', size='"$((size/sectorSize))"
+          echo -n ', type=${partition.partitionType}'
+          ${optionalString (partition ? bootable && partition.bootable)
+              ''echo -n ', bootable' ''}
+          echo "" # Finishes the command
+          ) >> script.sfdisk
+        ''
+    )}
+
+    # Allow space for secondary partition table / header.
+    totalSize=$(( totalSize + mbrSize ))
+
+    echo "--- script ----"
+    cat script.sfdisk
+    echo "--- script ----"
+
+    echo
+    echo "Making image, $totalSize bytes..."
+    truncate -s $((totalSize)) $img
+
+    sfdisk $img < script.sfdisk
+
+    totalSize=$((mbrSize))
+    echo
+    echo "Writing partitions into image"
+    ${each partitions (partition: 
+      if !(partition ? raw && partition.raw != null) && partition ? isGap && partition.isGap then
+        (gapFragment partition)
+      else
+        ''
+          input_img="${if partition.raw != null then partition.raw else ""}"
+          if [[ "$input_img" == "" ]]; then
+            input_img="/dev/zero"
+          fi
+          ${sizeFragment partition}
+          echo ' -> '${lib.escapeShellArg partition.name}": $size / ${if partition ? filesystemType then partition.filesystemType else ""}"
+
+          echo "$start / $size"
+          dd conv=notrunc if=$input_img of=$img seek=$((start/512)) count=$((size/512)) bs=512
+        ''
+    )}
+
+    echo
+    echo "Information about the image:"
+    ls -lh $img
+    sfdisk -V --list $img
+
+    runHook additionalCommands
+
+    set +u
+  '';
+}
diff --git a/overlay/image-builder/disk-image/partitioning-scheme/mbr/default.nix b/overlay/image-builder/disk-image/partitioning-scheme/mbr/default.nix
new file mode 100644
index 00000000..e84887ce
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitioning-scheme/mbr/default.nix
@@ -0,0 +1,34 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.partitioningScheme == "mbr";
+  inherit (lib)
+    mkIf
+    mkMerge
+    mkOption
+    types
+  ;
+in
+{
+  options.mbr = {
+    diskID = mkOption {
+      type = types.strMatching (
+        let hex = "[0-9a-fA-F]"; in
+          "${hex}{8}"
+      );
+      default = null;
+      description = lib.mdDoc ''
+        Identifier for the disk.
+      '';
+    };
+  };
+
+  config = mkMerge [
+    { availablePartitioningSchemes = [ "mbr" ]; }
+    (mkIf enabled {
+      output = pkgs.callPackage ./builder.nix {
+        inherit config;
+      };
+    })
+  ];
+}
diff --git a/overlay/image-builder/disk-image/partitions.nix b/overlay/image-builder/disk-image/partitions.nix
new file mode 100644
index 00000000..1f40a355
--- /dev/null
+++ b/overlay/image-builder/disk-image/partitions.nix
@@ -0,0 +1,153 @@
+{ config, lib, pkgs, ... }:
+
+let
+  inherit (lib)
+    mkIf
+    mkMerge
+    mkOption
+    types
+  ;
+  listEntrySubmodule = {
+    options = {
+    };
+  };
+
+  inherit (config) helpers;
+
+  partitionSubmodule = { name, config, ... }: {
+    options = {
+      name = mkOption {
+        type = types.str;
+        description = lib.mdDoc ''
+          Identifier for the partition.
+        '';
+      };
+
+      partitionLabel = mkOption {
+        type = types.str;
+        default = config.name;
+        defaultText = lib.literalExpression "config.name";
+        description = lib.mdDoc ''
+          Partition label on supported partition schemes. Defaults to ''${name}.
+
+          Not to be confused with _filesystem_ label.
+        '';
+      };
+
+      partitionUUID = mkOption {
+        type = types.nullOr helpers.types.uuid;
+        default = null;
+        description = lib.mdDoc ''
+          Partition UUID, for supported partition schemes.
+
+          Not to be confused with _filesystem_ UUID.
+
+          Not to be confused with _partitionType_.
+        '';
+      };
+
+      length = mkOption {
+        type = types.nullOr types.int;
+        default = null;
+        description = lib.mdDoc ''
+          Size in bytes for the partition.
+
+          Defaults to the filesystem image length (computed at runtime).
+        '';
+      };
+
+      offset = mkOption {
+        type = types.nullOr types.int;
+        default = null;
+        description = lib.mdDoc ''
+          Offset (in bytes) the partition starts at.
+
+          Defaults to the next aligned location on disk.
+        '';
+      };
+
+      partitionType = mkOption {
+        type = types.oneOf [
+          helpers.types.uuid
+          (types.strMatching "[0-9a-fA-F]{2}")
+        ];
+        default = "0FC63DAF-8483-4772-8E79-3D69D8477DE4";
+        defaultText = "Linux filesystem data (0FC63DAF-8483-4772-8E79-3D69D8477DE4)";
+        description = lib.mdDoc ''
+          Partition type UUID.
+
+          Not to be confused with _partitionUUID_.
+
+          See: https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs
+        '';
+      };
+
+      bootable = mkOption {
+        type = types.bool;
+        default = false;
+        description = lib.mdDoc ''
+          Sets the "legacy bios bootable flag" on the partition.
+        '';
+      };
+
+      requiredPartition = mkOption {
+        type = types.bool;
+        default = false;
+        description = lib.mdDoc ''
+          For GPT, sets the Required Partition attribute on the partition.
+        '';
+      };
+
+      filesystem = mkOption {
+        type = types.nullOr (types.submodule ({
+          imports = import (../filesystem-image/module-list.nix);
+          _module.args.pkgs = pkgs;
+        }));
+        default = null;
+        description = lib.mdDoc ''
+          A filesystem image configuration.
+
+          The filesystem image produced by this configuration is the default
+          value for the `raw` submodule option, unless overriden.
+        '';
+      };
+
+      isGap = mkOption {
+        type = types.bool;
+        default = false;
+        description = lib.mdDoc ''
+          When set to true, only the length attribute is used, and describes
+          an unpartitioned span in the disk image.
+        '';
+      };
+
+      raw = mkOption {
+        type = with types; nullOr (oneOf [ package path ]);
+        defaultText = "[contents of the filesystem attribute]";
+        default = null;
+        description = lib.mdDoc ''
+          Raw image to be used as the partition content.
+
+          By default uses the output of the `filesystem` submodule.
+        '';
+      };
+    };
+
+    config = mkMerge [
+      (mkIf (!config.isGap && config.filesystem != null) {
+        raw = lib.mkDefault config.filesystem.output;
+      })
+    ];
+  };
+
+in
+{
+  options = {
+    partitions = mkOption {
+      type = with types; listOf (submodule partitionSubmodule);
+      description = lib.mdDoc ''
+        List of partitions to include in the disk image.
+      '';
+    };
+  };
+}
diff --git a/overlay/image-builder/filesystem-image/basic.nix b/overlay/image-builder/filesystem-image/basic.nix
new file mode 100644
index 00000000..dcff67d5
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/basic.nix
@@ -0,0 +1,262 @@
+{ config, lib, pkgs, ... }:
+
+let
+  inherit (lib)
+    mkOption
+    optionalString
+    types
+  ;
+
+  inherit (config)
+    computeMinimalSize
+    extraPadding
+    size
+  ;
+in
+{
+  options = {
+    name = mkOption {
+      type = types.str;
+      default = "filesystem-image";
+      description = "Base name of the output";
+    };
+
+    label = mkOption {
+      type = with types; nullOr str;
+      default = null;
+      description = lib.mdDoc ''
+        Filesystem label
+
+        Not to be confused with either the output name, or the partition label.
+      '';
+    };
+
+    sectorSize = mkOption {
+      type = types.int;
+      internal = true;
+      description = lib.mdDoc ''
+        Default value should probably not be changed. Used internally for some
+        automatic size maths.
+      '';
+    };
+
+    blockSize = mkOption {
+      type = types.int;
+      internal = true;
+      description = lib.mdDoc ''
+        Used with the assumption that files are rounded up to blockSize increments.
+      '';
+    };
+
+    size = mkOption {
+      type = with types; nullOr int;
+      default = null;
+      defaultText = "[automatically computed]";
+      description = lib.mdDoc ''
+        When null, size is computed automatically.
+
+        Otherwise sets the size of the filesystem image.
+
+        Note that the usable space in the disk image will most likely be
+        smaller than the size given here!
+      '';
+    };
+
+    computeMinimalSize = mkOption {
+      internal = true;
+      type = types.str;
+      description = lib.mdDoc ''
+        Filesystem-specific snippet to adapt the size of the filesystem image
+        so the content can fit.
+      '';
+    };
+
+    extraPadding = mkOption {
+      type = types.int;
+      default = 0;
+      description = lib.mdDoc ''
+        When size is computed automatically, how many bytes to add to the
+        filesystem total size.
+      '';
+    };
+
+    minimumSize = mkOption {
+      type = types.int;
+      internal = true;
+      default = 0;
+      description = lib.mdDoc ''
+        Minimum usable size the filesystem must have. "Usable" here may not
+        actually be useful.
+      '';
+    };
+
+    builderFunctions = mkOption {
+      type = types.lines;
+      internal = true;
+      default = "";
+      description = lib.mdDoc ''
+        Bash functions required by the builder.
+      '';
+    };
+
+    buildPhases = mkOption {
+      type = with types; lazyAttrsOf str;
+      internal = true;
+      description = lib.mdDoc ''
+        Implementation of build phases for the filesystem image.
+      '';
+    };
+
+    buildPhasesOrder = mkOption {
+      type = with types; listOf str;
+      internal = true;
+      description = lib.mdDoc ''
+        Order of the filesystem image build phase. Adding to this is likely to
+        cause issues. Use this sparingly, and as a last resort.
+      '';
+    };
+
+    populateCommands = lib.mkOption {
+      type = types.lines;                  
+      default = "";
+      description = lib.mdDoc ''
+        Commands used to fill the filesystem.
+
+        `$PWD` is the root of the filesystem.
+      '';
+    };                                       
+
+    buildInputs = mkOption {
+      type = with types; listOf package;
+      internal = true;
+      description = lib.mdDoc ''
+        Allows adding to the builder buildInputs.
+      '';
+    };
+
+    nativeBuildInputs = mkOption {
+      type = with types; listOf package;
+      internal = true;
+      description = lib.mdDoc ''
+        Allows adding to the builder nativeBuildInputs.
+
+        As this list is built without *splicing*, use `pkgs.buildPackages` as
+        a source for packages.
+      '';
+    };
+
+    output = mkOption {
+      type = types.package;
+      internal = true;
+      description = lib.mdDoc ''
+        The build output for the filesystem image.
+      '';
+    };
+  };
+
+  config = {
+    buildInputs = [
+    ];
+    nativeBuildInputs = with pkgs.buildPackages; [
+      libfaketime
+    ];
+    buildPhasesOrder = [
+      # Copy the files to be copied into the target filesystem image first in
+      # the `pwd` during this phase.
+      "populatePhase"
+
+      # Default phase should be fine, pre-allocate the disk image file.
+      "allocationPhase"
+
+      # Phase in which the `mkfs` command is called on the disk image file.
+      "filesystemPhase"
+
+      # Commands to copy the files into the disk image (if the creation command
+      # does not intrinsically do it).
+      # The prep/unprep phases change the CWD to the directory containing the
+      # files to copy into the filesystem image, and back into the build dir.
+      "_prepCopyPhase"
+      "copyPhase"
+      "_unprepCopyPhase"
+
+      # Commands where a filesystem check should be ran.
+      "checkPhase"
+
+      # Any other extra business to run, normally left to the consumer.
+      "additionalCommandsPhase"
+    ];
+
+    buildPhases = {
+      "allocationPhase" = lib.mkDefault ''
+        ${optionalString (size == null) ''
+          size=$(compute-minimal-size)
+        ''}
+
+        if (( size < minimumSize )); then
+          size=$minimumSize
+          echo "WARNING: the '${"\${label:-(unlabeled)}"}' partition was too small, size increased to $minimumSize bytes."
+        fi
+
+        truncate -s $size "$img"
+      '';
+
+      "populatePhase" = lib.mkDefault ''
+        (
+          cd "$files"
+          ${config.populateCommands}
+        )
+      '';
+
+      "_prepCopyPhase" = ''
+        cd "$files"
+      '';
+
+      "_unprepCopyPhase" = ''
+        cd "$NIX_BUILD_TOP"
+      '';
+
+      "additionalCommandsPhase" = ''
+      '';
+    };
+
+    builderFunctions = ''
+      compute-minimal-size() {
+        local size=0
+        (
+        cd files
+        # Size rounded in blocks. This assumes all files are to be rounded to a
+        # multiple of blockSize.
+        # Use of `--apparent-size` is to ensure we don't get the block size of the underlying FS.
+        # Use of `--block-size` is to get *our* block size.
+        size=$(find . ! -type d -print0 | du --files0-from=- --apparent-size --block-size "$blockSize" | cut -f1 | sum-lines)
+        echo "Reserving $size sectors for files..." 1>&2
+
+        # Adds one blockSize per directory, they do take some place, in the end.
+        local directories=$(find . -type d | wc -l)
+        echo "Reserving $directories sectors for directories..." 1>&2
+
+        size=$(( directories + size ))
+
+        size=$((size * blockSize))
+
+        ${computeMinimalSize}
+
+        size=$(( size + ${toString extraPadding} ))
+
+        echo "$size"
+        )
+      }
+
+      sum-lines() {
+        local acc=0
+        while read -r number; do
+            acc=$((acc+number))
+        done
+
+        echo "$acc"
+      }
+    '';
+
+    output = pkgs.callPackage ./builder.nix { inherit config; };
+  };
+}
diff --git a/overlay/image-builder/filesystem-image/builder.nix b/overlay/image-builder/filesystem-image/builder.nix
new file mode 100644
index 00000000..825a232f
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/builder.nix
@@ -0,0 +1,68 @@
+{ stdenvNoCC, config, ncdu, tree }:
+
+# This builder is heavily influenced by the configuration.
+stdenvNoCC.mkDerivation (config.buildPhases // {
+  inherit (config)
+    name
+    buildInputs
+    filesystem
+    label
+    size
+    minimumSize
+    blockSize
+    sectorSize
+  ;
+
+  nativeBuildInputs = config.nativeBuildInputs ++ [
+    ncdu
+    tree
+  ];
+
+  phases = config.buildPhasesOrder;
+
+  img = placeholder "out";
+
+  outputs = [ "out" "metadata" ];
+
+  buildCommand = ''
+    PS4=" $ "
+    set -u
+
+    header() {
+      printf "\n:: %s\n\n" "$1"
+    }
+
+    ${config.builderFunctions}
+
+    # The default stdenv/generic clashes with `runHook`.
+    # It doesn't override as expected.
+    unset -f checkPhase
+
+    # Location where extra metadata about the filesystem can be stored.
+    # Use for extra useful debugging data.
+    mkdir -p $metadata
+
+    # Location where the filesystem content will be copied to.
+    mkdir -p files
+    files="$(cd files; pwd)"
+
+    for phase in ''${phases[@]}; do
+      if [[ "$phase" != _* ]]; then
+        header "Running $phase"
+      fi
+      runHook "$phase"
+    done
+
+    (
+      cd "$files"
+      faketime -f "1970-01-01 00:00:01" tree -a | xz > $metadata/tree.xz
+      faketime -f "1970-01-01 00:00:01" ncdu -0x -o - | xz > $metadata/ncdu.xz
+    )
+
+    set +u
+  '';
+
+  passthru = {
+    inherit (config) filesystem;
+  };
+})
diff --git a/overlay/image-builder/filesystem-image/eval-config.nix b/overlay/image-builder/filesystem-image/eval-config.nix
new file mode 100644
index 00000000..90e6cad2
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/eval-config.nix
@@ -0,0 +1,18 @@
+/**
+ * Evaluates the configuration for a single filesystem image build.
+ */
+{ pkgs
+, modules ? []
+, config ? {}
+}:
+let config' = config; in
+rec {
+  module = { imports = import ./module-list.nix; };
+  config = (pkgs.lib.evalModules {
+    modules = [
+      { _module.args.pkgs = pkgs; }
+      module
+      config'
+    ] ++ modules;
+  }).config;
+}
diff --git a/overlay/image-builder/filesystem-image/filesystem/btrfs.nix b/overlay/image-builder/filesystem-image/filesystem/btrfs.nix
new file mode 100644
index 00000000..dd51b461
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/filesystem/btrfs.nix
@@ -0,0 +1,62 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.filesystem == "btrfs";
+  inherit (lib)
+    escapeShellArg
+    mkIf
+    mkMerge
+    mkOption
+    optionalString
+    types
+  ;
+
+  inherit (config) label sectorSize blockSize;
+  inherit (config.btrfs) partitionID;
+in
+{
+  options.btrfs = {
+    partitionID = mkOption {
+      type = types.nullOr config.helpers.types.uuid;
+      example = "45454545-4545-4545-4545-454545454545";
+      default = null;
+      description = lib.mdDoc ''
+        Volume ID of the filesystem.
+      '';
+    };
+  };
+
+  config = mkMerge [
+    { availableFilesystems = [ "btrfs" ]; }
+    (mkIf enabled {
+      nativeBuildInputs = with pkgs.buildPackages; [
+        btrfs-progs
+      ];
+
+      blockSize = config.helpers.size.KiB 4;
+      sectorSize = lib.mkDefault 512;
+
+      # Generated an empty filesystem, it was 114294784 bytes long.
+      # Rounded up to 110MiB.
+      minimumSize = config.helpers.size.MiB 110;
+
+      computeMinimalSize = ''
+      '';
+
+      buildPhases = {
+        copyPhase = ''
+          mkfs.btrfs \
+            -r . \
+            ${optionalString (partitionID != null) "-U ${partitionID}"} \
+            ${optionalString (label != null) "-L ${escapeShellArg label}"} \
+            ${optionalString (config.size == null) "--shrink"} \
+            "$img"
+        '';
+
+        checkPhase = ''
+          faketime -f "1970-01-01 00:00:01" btrfs check "$img"
+        '';
+      };
+    })
+  ];
+}
diff --git a/overlay/image-builder/filesystem-image/filesystem/default.nix b/overlay/image-builder/filesystem-image/filesystem/default.nix
new file mode 100644
index 00000000..047260de
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/filesystem/default.nix
@@ -0,0 +1,29 @@
+{ config, lib, ... }:
+
+let
+  inherit (lib)
+    mkOption
+    types
+  ;
+in
+{
+  imports = [
+    ./btrfs.nix
+    ./ext4.nix
+    ./fat32.nix
+    ./squashfs.nix
+  ];
+
+  options = {
+    availableFilesystems = mkOption {
+      type = with types; listOf str;
+      internal = true;
+    };
+    filesystem = mkOption {
+      type = types.enum config.availableFilesystems;
+      description = lib.mdDoc ''
+        Filesystem used in this filesystem image.
+      '';
+    };
+  };
+}
diff --git a/overlay/image-builder/filesystem-image/filesystem/ext4.nix b/overlay/image-builder/filesystem-image/filesystem/ext4.nix
new file mode 100644
index 00000000..41a7a077
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/filesystem/ext4.nix
@@ -0,0 +1,128 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.filesystem == "ext4";
+  inherit (lib)
+    escapeShellArg
+    mkIf
+    mkMerge
+    mkOption
+    optionalString
+    types
+  ;
+  inherit (config.helpers)
+    chopDecimal
+  ;
+
+  inherit (config) label sectorSize blockSize;
+  inherit (config.ext4) partitionID;
+
+  # Bash doesn't do floating point representations. Multiplications and divisions
+  # are handled with enough precision that we can multiply and divide to get a precision.
+  precision = 1000;
+
+  makeFudge = f: toString (chopDecimal (f * precision));
+
+  # This applies only to 256MiB and greater.
+  # For smaller than 256MiB images the overhead from the FS is much greater.
+  # This will also let *some* slack space at the end at greater sizes.
+  # This is the value at 512MiB where it goes slightly down compared to 256MiB.
+  fudgeFactor = makeFudge 0.05208587646484375;
+
+  # This table was built using a script that built an image with `make_ext4fs`
+  # for the given size in MiB, and recorded the available size according to `df`.
+  smallFudgeLookup = lib.strings.concatStringsSep "\n" (lib.lists.reverseList(
+    lib.attrsets.mapAttrsToList (size: factor: ''
+      elif (( size > ${toString size} )); then
+        fudgeFactor=${toString factor}
+    '') {
+    "${toString (config.helpers.size.MiB   5)}" = makeFudge 0.84609375;
+    "${toString (config.helpers.size.MiB   8)}" = makeFudge 0.5419921875;
+    "${toString (config.helpers.size.MiB  16)}" = makeFudge 0.288818359375;
+    "${toString (config.helpers.size.MiB  32)}" = makeFudge 0.1622314453125;
+    "${toString (config.helpers.size.MiB  64)}" = makeFudge 0.09893798828125;
+    "${toString (config.helpers.size.MiB 128)}" = makeFudge 0.067291259765625;
+    "${toString (config.helpers.size.MiB 256)}" = makeFudge 0.0518646240234375;
+  }
+  ));
+
+  minimumSize = config.helpers.size.MiB 5;
+in
+{
+  options.ext4 = {
+    partitionID = mkOption {
+      type = types.nullOr config.helpers.types.uuid;
+      example = "45454545-4545-4545-4545-454545454545";
+      default = null;
+      description = lib.mdDoc ''
+        Volume ID of the filesystem.
+      '';
+    };
+  };
+
+  config = mkMerge [
+    { availableFilesystems = [ "ext4" ]; }
+    (mkIf enabled {
+      nativeBuildInputs = with pkgs.buildPackages; [
+        e2fsprogs
+        make_ext4fs
+      ];
+
+      blockSize = config.helpers.size.KiB 4;
+      sectorSize = lib.mkDefault 512;
+
+      inherit minimumSize;
+
+      computeMinimalSize = ''
+        # `local size` is in bytes.
+
+        # We don't have a static reserved factor figured out. It is rather hard with
+        # ext4fs as there are multiple factors increasing the overhead.
+        local reservedSize=0
+        local fudgeFactor=${toString fudgeFactor}
+        
+        # Instead we rely on a lookup table. See how it is built in the derivation file.
+        if (( size < ${toString (config.helpers.size.MiB 256)} )); then
+          echo "$size is smaller than 256MiB; using the lookup table." 1>&2
+          
+          # A bit of a hack, though allows us to build the lookup table using only elifs.
+          if false; then
+            :
+          ${smallFudgeLookup}
+          else
+            # The data is smaller than 5MiB... The filesystem image size will likely
+            # not be able to accomodate... here we handle it in another way.
+            fudgeFactor=0
+            echo "Fudge factor skipped for extra small partition. Instead increasing by a fixed amount." 1>&2
+            size=$(( size + ${toString minimumSize}))
+          fi
+        fi
+
+        local reservedSize=$(( size * $fudgeFactor / ${toString precision} ))
+
+        echo "Fudge factor: $fudgeFactor / ${toString precision}" 1>&2
+        echo -n "Adding reservedSize: $size + $reservedSize = " 1>&2
+        size=$((size + reservedSize))
+        echo "$size" 1>&2
+      '';
+
+      buildPhases = {
+        copyPhase = ''
+          faketime -f "1970-01-01 00:00:01" \
+            make_ext4fs \
+            -b $blockSize \
+            -l $size \
+            ${optionalString (partitionID != null) "-U ${partitionID}"} \
+            ${optionalString (label != null) "-L ${escapeShellArg label}"} \
+            "$img" \
+            .
+        '';
+
+        checkPhase = ''
+          EXT2FS_NO_MTAB_OK=yes faketime -f "1970-01-01 00:00:01" fsck.ext4 -y -f "$img" || :
+          EXT2FS_NO_MTAB_OK=yes faketime -f "1970-01-01 00:00:01" fsck.ext4 -n -f "$img"
+        '';
+      };
+    })
+  ];
+}
diff --git a/overlay/image-builder/filesystem-image/filesystem/fat32.nix b/overlay/image-builder/filesystem-image/filesystem/fat32.nix
new file mode 100644
index 00000000..f1f1dadb
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/filesystem/fat32.nix
@@ -0,0 +1,136 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.filesystem == "fat32";
+  inherit (lib)
+    escapeShellArg
+    mkIf
+    mkMerge
+    mkOption
+    optionalString
+    types
+  ;
+  inherit (config.helpers)
+    chopDecimal
+  ;
+  type32bitHex = types.strMatching "[0-9a-fA-F]{1,8}";
+
+  inherit (config) label sectorSize blockSize;
+  inherit (config.fat32) partitionID;
+
+  # Should these be configurable?
+  # The default from `mkfs.fat`.
+  reservedSectors = 32;
+
+  # The default from `mkfs.fat`.
+  hiddenSectors = 0;
+
+  # The default from `mkfs.fat`.
+  numberOfFats = 2;
+
+  # Extra padding per FAT, a constant in code
+  fatPadding = 4;
+
+  # I have not been able to validate that it could be different from 1 for FAT32.
+  # It seems the different values (e.g. 4) are for FAT12 and FAT16.
+  # This is the only "bad" assumption here.
+  clusterSize = 1;
+
+  # Bash doesn't do floating point representations. Multiplications and divisions
+  # are handled with enough precision that we can multiply and divide to get a precision.
+  precision = 1000;
+in
+{
+  options.fat32 = {
+    partitionID = mkOption {
+      type = types.nullOr type32bitHex;
+      example = "2e24ec82";
+      default = null;
+      defaultText = "[Depends on the file system creation time]";
+      description = lib.mdDoc ''
+        Volume ID of the filesystem.
+
+        The default is a number which depends on the file system creation time.
+      '';
+    };
+  };
+
+  config = mkMerge [
+    { availableFilesystems = [ "fat32" ]; }
+    (mkIf enabled {
+      nativeBuildInputs = with pkgs.buildPackages; [
+        dosfstools
+        mtools
+      ];
+
+      blockSize = lib.mkDefault 512;
+      sectorSize = lib.mkDefault 512;
+
+      minimumSize = config.helpers.size.KiB 500;
+
+      buildPhases = {
+        checkPhase = ''
+          # Always check and verify FS
+          fsck.vfat -a "$img" || :
+          fsck.vfat -vn "$img"
+        '';
+
+        filesystemPhase = ''
+          fatSize=16
+          if (( size > 1024*1024*32 )); then
+            fatSize=32
+          fi
+          faketime -f "1970-01-01 00:00:01" mkfs.vfat \
+            -F $fatSize \
+            -R ${toString reservedSectors} \
+            -h ${toString hiddenSectors} \
+            -s ${toString (blockSize / sectorSize)} \
+            -S ${toString sectorSize} \
+            ${optionalString (partitionID != null) "-i ${partitionID}"} \
+            ${optionalString (label != null) "-n ${escapeShellArg label}"} \
+            "$img"
+        '';
+
+        copyPhase = ''
+          (
+          for f in ./* ./.*; do
+            if [[ "$f" != "./." && "$f" != "./.." ]]; then
+              faketime -f "1970-01-01 00:00:01" \
+                mcopy -psv -i "$img" "$f" ::
+            fi
+          done
+          )
+        '';
+      };
+
+      computeMinimalSize = ''
+        # `local size` is in bytes.
+
+        # This amount is a static amount of reserved space.
+        local static_reserved=${toString ( (reservedSectors + hiddenSectors) * sectorSize )}
+
+        # This is a constant representing the relative reserved space ratio.
+        local relative_reserved=${
+          chopDecimal (
+            precision - (
+              1.0 * sectorSize / ((clusterSize * sectorSize) + (numberOfFats * fatPadding))
+              # ^ forces floating point
+            ) * precision
+          )
+        }
+        # Rounds up the likely truncated result. At worst it's a bit more space.
+        (( relative_reserved++ ))
+
+        echo "static_reserved=$static_reserved" 1>&2
+        echo "relative_reserved=$relative_reserved" 1>&2
+
+        local reservedSize=$(( (static_reserved + size) * relative_reserved / ${toString precision} + static_reserved ))
+
+        echo -n "Adding reservedSize: $size + $reservedSize = " 1>&2
+        size=$((size + reservedSize))
+        echo "$size" 1>&2
+      '';
+
+    })
+  ];
+}
diff --git a/overlay/image-builder/filesystem-image/filesystem/squashfs.nix b/overlay/image-builder/filesystem-image/filesystem/squashfs.nix
new file mode 100644
index 00000000..cc90b435
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/filesystem/squashfs.nix
@@ -0,0 +1,86 @@
+{ config, lib, pkgs, ... }:
+
+let
+  enabled = config.filesystem == "squashfs";
+  inherit (lib)
+    escapeShellArg
+    mkIf
+    mkMerge
+    mkOption
+    optionalString
+    types
+  ;
+
+  inherit (config) label sectorSize blockSize;
+  inherit (config.squashfs)
+    compression
+    compressionParams
+  ;
+in
+{
+  options.squashfs = {
+    compression = mkOption {
+      type = types.enum [
+        # Uses the name used in the -comp param
+        "gzip"
+        "xz"
+        "zstd"
+      ];
+      default = "xz";
+      description = lib.mdDoc ''
+        Volume ID of the filesystem.
+      '';
+    };
+    compressionParams = mkOption {
+      type = types.str;
+      internal = true;
+    };
+  };
+
+  config = mkMerge [
+    { availableFilesystems = [ "squashfs" ]; }
+    (mkIf enabled {
+      squashfs.compressionParams = mkMerge [
+        (mkIf (compression == "xz") "-Xdict-size 100%")
+        (mkIf (compression == "zstd") "-Xcompression-level 6")
+      ];
+
+      nativeBuildInputs = with pkgs.buildPackages; [
+        squashfsTools
+      ];
+
+      # NixOS's make-squashfs uses 1MiB
+      # mksquashfs's help says its default is 128KiB
+      blockSize = config.helpers.size.MiB 1;
+      # This is actually unused (and irrelevant)
+      sectorSize = lib.mkDefault 512;
+      minimumSize = 0;
+
+      computeMinimalSize = "";
+
+      buildPhases = {
+        copyPhase = ''
+          # The empty pre-allocated file will confuse mksquashfs
+          rm "$img"
+
+          (
+          # This also activates dotglob automatically.
+          # Using this means hidden files will be added too.
+          GLOBIGNORE=".:.."
+
+          # Using `.` as the input will put the PWD, including its name
+          # in the root of the filesystem.
+          mksquashfs \
+            * \
+            "$img" \
+            -info \
+            -b "$blockSize" \
+            -no-hardlinks -keep-as-directory -all-root \
+            -comp "${compression}" ${compressionParams} \
+            -processors $NIX_BUILD_CORES                                         
+          )
+        '';
+      };
+    })
+  ];
+}
diff --git a/overlay/image-builder/filesystem-image/module-list.nix b/overlay/image-builder/filesystem-image/module-list.nix
new file mode 100644
index 00000000..be0df334
--- /dev/null
+++ b/overlay/image-builder/filesystem-image/module-list.nix
@@ -0,0 +1,5 @@
+[
+  ../helpers.nix
+  ./basic.nix
+  ./filesystem
+]
diff --git a/overlay/image-builder/helpers.nix b/overlay/image-builder/helpers.nix
new file mode 100644
index 00000000..0b5c305c
--- /dev/null
+++ b/overlay/image-builder/helpers.nix
@@ -0,0 +1,70 @@
+{ lib, ... }:
+
+let
+  inherit (lib)
+    concatMapStringsSep
+    mkOption
+    splitString
+    types
+  ;
+in
+{
+  options.helpers = mkOption {
+    # Unspecified on purpose
+    type = types.attrs;
+    internal = true;
+  };
+
+  config.helpers = rec {
+    /**
+     * Silly alias to concat/map script segments for a given list.
+     */
+    each = els: fn: (
+      concatMapStringsSep "\n" (el:
+      fn el
+    ) els);
+
+    /**
+     * Provides user-friendly aliases for defining sizes.
+     */
+    size = rec {
+      TiB = x: 1024 * (GiB x);
+      GiB = x: 1024 * (MiB x);
+      MiB = x: 1024 * (KiB x);
+      KiB = x: 1024 *      x;
+    };
+
+    /**
+     * Drops the decimal portion of a floating point number.
+     */
+    chopDecimal = f: first (splitString "." (toString f));
+
+    /**
+     * Like `last`, but for the first element of a list.
+     */
+    first = list: lib.lists.last (lib.lists.reverseList list);
+
+    types = {
+      uuid = lib.types.strMatching (
+        let hex = "[0-9a-fA-F]"; in
+        "${hex}{8}-${hex}{4}-${hex}{4}-${hex}{4}-${hex}{12}"
+      );
+    };
+
+    makeGap = length: {
+      isGap = true;
+      inherit length;
+    };
+    makeESP = args: lib.recursiveUpdate {
+      name = "ESP-filesystem";
+      partitionLabel = "$ESP";
+      partitionType = "C12A7328-F81F-11D2-BA4B-00A0C93EC93B";
+      partitionUUID = "63E19453-EF00-4BD9-9AAF-000000000000";
+      filesystem = {
+        filesystem = "fat32";
+        label = "$ESP";
+        fat32.partitionID = "ef00ef00";
+      };
+    } args;
+  };
+}