nixos/repart: add option for configuring sector size

This option is helpful for situations when the target host disk's sector
size differs from that of the build host.

nixos/modules/image/repart-image.nix

@@ -32,6 +32,7 @@
 , split
 , seed
 , definitionsDirectory
+, sectorSize
 }:
 
 let
@@ -94,6 +95,7 @@ runCommand imageFileBasename
     --definitions="$amendedRepartDefinitions" \
     --split="${lib.boolToString split}" \
     --json=pretty \
+    ${lib.optionalString (sectorSize != null) "--sector-size=${toString sectorSize}"} \
     ${imageFileBasename}.raw \
     | tee repart-output.json
 

nixos/modules/image/repart.nix

@@ -135,6 +135,16 @@ in
       '';
     };
 
+    sectorSize = lib.mkOption {
+      type = with lib.types; nullOr int;
+      default = 512;
+      example = lib.literalExpression "4096";
+      description = lib.mdDoc ''
+        The sector size of the disk image produced by systemd-repart. This
+        value must be a power of 2 between 512 and 4096.
+      '';
+    };
+
     package = lib.mkPackageOption pkgs "systemd-repart" {
       # We use buildPackages so that repart images are built with the build
       # platform's systemd, allowing for cross-compiled systems to work.
@@ -232,7 +242,7 @@ in
       in
       pkgs.callPackage ./repart-image.nix {
         systemd = cfg.package;
-        inherit (cfg) imageFileBasename compression split seed;
+        inherit (cfg) imageFileBasename compression split seed sectorSize;
         inherit fileSystems definitionsDirectory partitions;
       };