feat: add microvm module to simplify setup

modules/microvms.nix

@@ -0,0 +1,78 @@
+{
+  inputs,
+  config,
+  lib,
+  nodeName,
+  nodePath,
+  microvm,
+  pkgs,
+  ...
+}: let
+  inherit
+    (lib)
+    mapAttrs
+    mdDoc
+    mkDefault
+    mkForce
+    mkIf
+    mkOption
+    types
+    ;
+
+  cfg = config.extra.microvms;
+
+  defineMicrovm = vmName: vmCfg: let
+    node =
+      (import ../nix/generate-node.nix inputs)
+      "${nodeName}-microvm-${vmName}" {
+        inherit (vmCfg) system;
+        config = nodePath + "/microvms/${vmName}";
+      };
+  in {
+    inherit (node) pkgs specialArgs;
+    config = {
+      imports = [microvm.microvm] ++ node.imports;
+
+      microvm = {
+        hypervisor = mkDefault "cloud-hypervisor";
+
+        # Share the nix-store of the host
+        shares = [
+          {
+            source = "/nix/store";
+            mountPoint = "/nix/.ro-store";
+            tag = "ro-store";
+            proto = "virtiofs";
+          }
+        ];
+      };
+
+      # TODO change once microvms are compatible with stage-1 systemd
+      boot.initrd.systemd.enable = mkForce false;
+    };
+  };
+in {
+  imports = [microvm.host];
+
+  options.extra.microvms = mkOption {
+    default = {};
+    description = "Provides a base configuration for MicroVMs.";
+    type = types.attrsOf (types.submodule {
+      options = {
+        system = mkOption {
+          type = types.str;
+          description = mdDoc "The system that this microvm should use";
+        };
+      };
+    });
+  };
+
+  config = {
+    microvm = {
+      host.enable = cfg != {};
+      declarativeUpdates = true;
+      restartIfChanged = true;
+      vms = mkIf (cfg != {}) (mapAttrs defineMicrovm cfg);
+    };
+  };
+}