Unverified Commit d7ef2def authored by WilliButz's avatar WilliButz
Browse files

nixos/repart-image: refactor to use mkDerivation 

As a follow-up to https://github.com/NixOS/nixpkgs/pull/294096 this
should further improve the flexibility around building OS images with
systemd-repart:

* Previously the attribute set `compression` needed to be fully
  populated, including `algorithm` and `level` because
  `compression.enable` was evaluated by bash, after being interpolated
  as strings into the `buildCommand`. Now it's sufficient to pass
  `compression.enable = false` to the builder, e.g. in `overrideAttrs`,
  to disable the compression.
* Using mkDerivation allows for much more customization than the
  previously used `runCommand`, making use of phases and pre/post hooks.
  This is especially helpful for building multiple images from the same
  system configuration, e.g. to build an image `Y` based on a partially
  built raw image `X`,  by injecting a UKI that depends on `X` into a
  defered ESP.
* Before this change it was non-trivial to conduct further manipulations
  on the amended repart definitions. Now, the definitions that
  systemd-repart uses to build the image can be easily manipulated in
  `postPatch` or `preBuild`.

Aside from this, the build is now executed in the build directory, rather
than `$out`. This allows references to relative paths in the build
environment to be used, especially for `--definitions`, which previously
required an absolute path.
parent 1357b820

nixos/modules/image/repart-image.nix

+59 −26
Original line number Diff line number Diff line
@@ -2,8 +2,8 @@ 
# NixOS module that can be imported.



{ lib

, stdenvNoCC

, runCommand

, runCommandLocal

, python3

, black

, ruff
@@ -26,15 +26,18 @@ 
, xz



  # arguments

, name

, version

, imageFileBasename

, compression

, fileSystems

, partitions

, partitionsJSON

, split

, seed

, definitionsDirectory

, sectorSize

, mkfsEnv ? {}

, createEmpty ? true

}:



let
@@ -52,11 +55,6 @@ let 
    mypy --strict $out

  '';



  amendedRepartDefinitions = runCommandLocal "amended-repart.d" {} ''

    definitions=$(${amendRepartDefinitions} ${partitions} ${definitionsDirectory})

    cp -r $definitions $out

  '';



  fileSystemToolMapping = {

    "vfat" = [ dosfstools mtools ];

    "ext4" = [ e2fsprogs.bin ];
@@ -78,38 +76,56 @@ let 
    "xz" = "xz --keep --verbose --threads=0 -${toString compression.level}";

  }."${compression.algorithm}";

in



runCommand imageFileBasename

{

  stdenvNoCC.mkDerivation (finalAttrs:

  (if (version != null)

  then { pname = name; inherit version; }

  else { inherit name;  }

  ) // {

  __structuredAttrs = true;



  nativeBuildInputs = [

    systemd

    fakeroot

    util-linux

  ] ++ lib.optionals (compression.enable) [

    compressionPkg

  ] ++ fileSystemTools;



  env = mkfsEnv;



  inherit partitionsJSON definitionsDirectory;



  # relative path to the repart definitions that are read by systemd-repart

  finalRepartDefinitions = "repart.d";



  systemdRepartFlags = [

    "--dry-run=no"

    "--empty=create"

    "--size=auto"

    "--seed=${seed}"

    "--definitions=${amendedRepartDefinitions}"

    "--definitions=${finalAttrs.finalRepartDefinitions}"

    "--split=${lib.boolToString split}"

    "--json=pretty"

  ] ++ lib.optionals createEmpty [

    "--empty=create"

  ] ++ lib.optionals (sectorSize != null) [

    "--sector-size=${toString sectorSize}"

  ];



  passthru = {

    inherit amendRepartDefinitions amendedRepartDefinitions;

  };

} ''

  mkdir -p $out

  cd $out

  dontUnpack = true;

  dontConfigure = true;

  doCheck = false;



  patchPhase = ''

    runHook prePatch



    amendedRepartDefinitionsDir=$(${amendRepartDefinitions} $partitionsJSON $definitionsDirectory)

    ln -vs $amendedRepartDefinitionsDir $finalRepartDefinitions



    runHook postPatch

  '';



  buildPhase = ''

    runHook preBuild



    echo "Building image with systemd-repart..."

    unshare --map-root-user fakeroot systemd-repart \
@@ -117,14 +133,31 @@ runCommand imageFileBasename 
      ${imageFileBasename}.raw \

      | tee repart-output.json



    runHook postBuild

  '';



  installPhase = ''

    runHook preInstall



    mkdir -p $out

  ''

  # Compression is implemented in the same derivation as opposed to in a

  # separate derivation to allow users to save disk space. Disk images are

  # already very space intensive so we want to allow users to mitigate this.

  if ${lib.boolToString compression.enable}; then

  + lib.optionalString compression.enable

  ''

    for f in ${imageFileBasename}*; do

      echo "Compressing $f with ${compression.algorithm}..."

      # Keep the original file when compressing and only delete it afterwards

      ${compressionCommand} $f && rm $f

    done

  fi

''
 
  '' + ''

    mv -v repart-output.json ${imageFileBasename}* $out



    runHook postInstall

  '';



  passthru = {

    inherit amendRepartDefinitions;

  };

})

nixos/modules/image/repart.nix

+3 −3
Original line number Diff line number Diff line
@@ -266,14 +266,14 @@ in 
          format

          (lib.mapAttrs (_n: v: { Partition = v.repartConfig; }) finalPartitions);



        partitions = pkgs.writeText "partitions.json" (builtins.toJSON finalPartitions);

        partitionsJSON = pkgs.writeText "partitions.json" (builtins.toJSON finalPartitions);



        mkfsEnv = mkfsOptionsToEnv cfg.mkfsOptions;

      in

      pkgs.callPackage ./repart-image.nix {

        systemd = cfg.package;

        inherit (cfg) imageFileBasename compression split seed sectorSize;

        inherit fileSystems definitionsDirectory partitions mkfsEnv;

        inherit (cfg) name version imageFileBasename compression split seed sectorSize;

        inherit fileSystems definitionsDirectory partitionsJSON mkfsEnv;

      };



    meta.maintainers = with lib.maintainers; [ nikstur ];