nixosMod: add vmDisko module

nix/nixos-modules/default.nix

@@ -26,6 +26,7 @@ in
     ./extends
     ./frontend
     ./improvedDefaults
+    ./vmDisko
     # files
     ./allCommon.nix
     ./autoUnfree.nix

nix/nixos-modules/vmDisko/default.nix

@@ -0,0 +1,115 @@
+{
+  config,
+  lib,
+  options,
+  ...
+}:
+let
+  self = options.x-banananetwork.vmDisko;
+  cfg = config.x-banananetwork.vmDisko;
+in
+{
+
+  # TODO upstream that to disko
+
+  options.x-banananetwork.vmDisko = {
+
+    enable = lib.mkEnableOption ''
+      VM disk configuration with disko.
+      Will be automatically enabled when option{x-banananetwork.vmDisko.generation} is manually set.
+    '';
+
+    mainDiskName = lib.mkOption {
+      description = ''
+        Name of the main disk.
+
+        Similar to {option}`system.stateVersion`,
+        **do not change this** unless you know what you are doing.
+      '';
+      type = lib.types.str;
+    };
+
+    generation = lib.mkOption {
+      description = ''
+        Disk generation to use.
+
+        Similar to {option}`system.stateVersion`,
+        **do not change this** unless you know what you are doing.
+
+        See option {option}`x-banananetwork.vmDisko.generations`
+        for a list of all generations available.
+      '';
+      type = with lib.types; nullOr str;
+      default = null;
+      example = self.recommendedGeneration.default;
+    };
+
+    recommendedGeneration = lib.mkOption {
+      description = ''
+        Disk generation recommended to use for new systems.
+      '';
+      default = "ext4-1";
+      readOnly = true;
+    };
+
+    generationsDir = lib.mkOption {
+      description = ''
+        Directories where to search for generations.
+
+        A generation must at least use one disk with the attr name `main`
+        (through its label name can be different)
+        because VMs are expected to have at least one disk as their primary available.
+      '';
+      type = lib.types.path;
+      default = ./.;
+      example = ./.;
+    };
+
+    generationPath = lib.mkOption {
+      description = "Path to selected generation template.";
+      readOnly = true;
+      type = lib.types.path;
+      default =
+        let
+          path = cfg.generationsDir + "/${cfg.generation}";
+        in
+        if builtins.pathExists path then path else path + ".nix";
+      defaultText = lib.literalExpression ''
+        with config.x-banananetwork.vmDisko;
+        generationsDir + ("/''${generation}" or "/''${generation}.nix")
+      '';
+    };
+
+  };
+
+  config = lib.mkMerge [
+    (lib.mkIf (cfg.generation != null) { x-banananetwork.vmDisko.enable = true; })
+    (lib.mkIf cfg.enable {
+
+      assertions = [
+        {
+          assertion = cfg.enable -> cfg.generation != null;
+          message = "x-banananetwork.vmDisko.generation must be set. Currently \"${cfg.recommendedGeneration}\" is recommended.";
+        }
+        {
+          assertion = cfg.generation != null -> builtins.pathExists cfg.generationPath;
+          message = "generation \"${cfg.generation}\" was not found in ${cfg.generationPath}";
+        }
+      ];
+
+      disko.devices = lib.mkMerge [
+        (import cfg.generationPath)
+        {
+          # avoid mixing VM disks
+          # hint: mkOverride required because
+          # - cfg.generations from above is already type-checked, hence priorities are discharged
+          # - assigment from above has default priority of 100
+          #disk.main.name = lib.mkOverride 99 cfg.mainDiskName;
+          disk.main.name = cfg.mainDiskName;
+        }
+      ];
+
+    })
+  ];
+
+}

nix/nixos-modules/vmDisko/ext4-1.nix

@@ -0,0 +1,29 @@
+{
+  disk = {
+    main = {
+      type = "disk";
+      content = {
+        type = "gpt";
+        partitions = {
+          ESP = {
+            type = "EF00";
+            size = "500M";
+            content = {
+              type = "filesystem";
+              format = "vfat";
+              mountpoint = "/boot";
+            };
+          };
+          root = {
+            size = "100%";
+            content = {
+              type = "filesystem";
+              format = "ext4";
+              mountpoint = "/";
+            };
+          };
+        };
+      };
+    };
+  };
+}