Merge pull request #294096 from WilliButz/repart-image/overridability

systemd-repart: improve overridability of image builder

nixos/modules/image/repart-image.nix

@@ -3,6 +3,7 @@
 
 { lib
 , runCommand
+, runCommandLocal
 , python3
 , black
 , ruff
@@ -33,6 +34,7 @@
 , seed
 , definitionsDirectory
 , sectorSize
+, mkfsEnv ? {}
 }:
 
 let
@@ -50,6 +52,11 @@ let
     mypy --strict $out
   '';
 
+  amendedRepartDefinitions = runCommandLocal "amended-repart.d" {} ''
+    definitions=$(${amendRepartDefinitions} ${partitions} ${definitionsDirectory})
+    cp -r $definitions $out
+  '';
+
   fileSystemToolMapping = {
     "vfat" = [ dosfstools mtools ];
     "ext4" = [ e2fsprogs.bin ];
@@ -74,28 +81,39 @@ in
 
 runCommand imageFileBasename
 {
+  __structuredAttrs = true;
+
   nativeBuildInputs = [
     systemd
     fakeroot
     util-linux
     compressionPkg
   ] ++ fileSystemTools;
-} ''
-  amendedRepartDefinitions=$(${amendRepartDefinitions} ${partitions} ${definitionsDirectory})
 
+  env = mkfsEnv;
+
+  systemdRepartFlags = [
+    "--dry-run=no"
+    "--empty=create"
+    "--size=auto"
+    "--seed=${seed}"
+    "--definitions=${amendedRepartDefinitions}"
+    "--split=${lib.boolToString split}"
+    "--json=pretty"
+  ] ++ lib.optionals (sectorSize != null) [
+    "--sector-size=${toString sectorSize}"
+  ];
+
+  passthru = {
+    inherit amendRepartDefinitions amendedRepartDefinitions;
+  };
+} ''
   mkdir -p $out
   cd $out
 
   echo "Building image with systemd-repart..."
   unshare --map-root-user fakeroot systemd-repart \
-    --dry-run=no \
-    --empty=create \
-    --size=auto \
-    --seed="${seed}" \
-    --definitions="$amendedRepartDefinitions" \
-    --split="${lib.boolToString split}" \
-    --json=pretty \
-    ${lib.optionalString (sectorSize != null) "--sector-size=${toString sectorSize}"} \
+    ''${systemdRepartFlags[@]} \
     ${imageFileBasename}.raw \
     | tee repart-output.json
 

nixos/modules/image/repart.nix

@@ -60,6 +60,11 @@ let
       };
     };
   };
+
+  mkfsOptionsToEnv = opts: lib.mapAttrs' (fsType: options: {
+    name = "SYSTEMD_REPART_MKFS_OPTIONS_${lib.toUpper fsType}";
+    value = builtins.concatStringsSep " " options;
+  }) opts;
 in
 {
   options.image.repart = {
@@ -183,6 +188,29 @@ in
       '';
     };
 
+    mkfsOptions = lib.mkOption {
+      type = with lib.types; attrsOf (listOf str);
+      default = {};
+      example = lib.literalExpression ''
+        {
+          vfat = [ "-S 512" "-c" ];
+        }
+      '';
+      description = lib.mdDoc ''
+        Specify extra options for created file systems. The specified options
+        are converted to individual environment variables of the format
+        `SYSTEMD_REPART_MKFS_OPTIONS_<FSTYPE>`.
+
+        See [upstream systemd documentation](https://github.com/systemd/systemd/blob/v255/docs/ENVIRONMENT.md?plain=1#L575-L577)
+        for information about the usage of these environment variables.
+
+        The example would produce the following environment variable:
+        ```
+        SYSTEMD_REPART_MKFS_OPTIONS_VFAT="-S 512 -c"
+        ```
+      '';
+    };
+
   };
 
   config = {
@@ -239,11 +267,13 @@ in
           (lib.mapAttrs (_n: v: { Partition = v.repartConfig; }) finalPartitions);
 
         partitions = 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;
+        inherit fileSystems definitionsDirectory partitions mkfsEnv;
       };
 
     meta.maintainers = with lib.maintainers; [ nikstur ];