modules/virtualisation: add hyperv-image

This module implements builder for hyper-v images.

nixos/modules/virtualisation/hyperv-image.nix

@@ -0,0 +1,69 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.hyperv;
+
+in {
+  options = {
+    hyperv = {
+      baseImageSize = mkOption {
+        type = types.int;
+        default = 2048;
+        description = ''
+          The size of the hyper-v base image in MiB.
+        '';
+      };
+      vmDerivationName = mkOption {
+        type = types.str;
+        default = "nixos-hyperv-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}";
+        description = ''
+          The name of the derivation for the hyper-v appliance.
+        '';
+      };
+      vmFileName = mkOption {
+        type = types.str;
+        default = "nixos-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}.vhdx";
+        description = ''
+          The file name of the hyper-v appliance.
+        '';
+      };
+    };
+  };
+
+  config = {
+    system.build.hypervImage = import ../../lib/make-disk-image.nix {
+      name = cfg.vmDerivationName;
+      postVM = ''
+        ${pkgs.vmTools.qemu}/bin/qemu-img convert -f raw -o subformat=dynamic -O vhdx $diskImage $out/${cfg.vmFileName}
+      '';
+      format = "raw";
+      diskSize = cfg.baseImageSize;
+      partitionTableType = "efi";
+      inherit config lib pkgs;
+    };
+
+    fileSystems."/" = {
+      device = "/dev/disk/by-label/nixos";
+      autoResize = true;
+      fsType = "ext4";
+    };
+
+    fileSystems."/boot" = {
+      device = "/dev/disk/by-label/ESP";
+      fsType = "vfat";
+    };
+
+    boot.growPartition = true;
+
+    boot.loader.grub = {
+      version = 2;
+      device = "nodev";
+      efiSupport = true;
+      efiInstallAsRemovable = true;
+    };
+
+    virtualisation.hypervGuest.enable = true;
+  };
+}