Add a role for mounting the nix store over 9pfs.

This is useful for virtual machines since we can have a persistent /nix/store on the host machine.

nix/configuration/roles/9pfs_nix_store/default.nix

@@ -0,0 +1,77 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+{
+  imports = [ ];
+
+  options.me = {
+    _9pfs_nix_store.enable = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether we want to mount /nix/store over 9pfs (useful in virtual machines to share a directory from the host as a persistent nix store.";
+    };
+
+    _9pfs_nix_store.is_iso = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether this build is for an ISO. It changes how we mount the nix store.";
+    };
+  };
+
+  config = lib.mkIf config.me._9pfs_nix_store.enable (
+    lib.mkMerge [
+      (lib.mkIf config.me._9pfs_nix_store.is_iso {
+        # fileSystems = {
+        #   "/nix/store" = lib.mkForce {
+        #     fsType = "overlay";
+        #     device = "overlay";
+        #     options = [
+        #       "lowerdir=/nix/.ro-store"
+        #       "upperdir=/store"
+        #       "workdir=/work"
+        #     ];
+        #     depends = [
+        #       "/nix/.ro-store"
+        #       "/store"
+        #       "/work"
+        #     ];
+        #   };
+
+        #   "/store" = lib.mkForce {
+        #     fsType = "9p";
+        #     device = "nixstore";
+        #     options = [
+        #       "trans=virtio"
+        #       "version=9p2000.L"
+        #       "x-systemd.requires=modprobe@9pnet_virtio.service"
+        #       "msize=16384" # Maximum packet size. Increasing this should improve performance at the cost of increased memory usage.
+        #       "cache=loose"
+        #     ];
+        #   };
+        # };
+      })
+      (lib.mkIf (!config.me._9pfs_nix_store.is_iso) {
+        fileSystems = {
+          "/nix/store" = lib.mkForce {
+            fsType = "9p";
+            device = "nixstore";
+            neededForBoot = true;
+            options = [
+              "trans=virtio"
+              "version=9p2000.L"
+              "x-systemd.requires=modprobe@9pnet_virtio.service"
+              "msize=16384" # Maximum packet size. Increasing this should improve performance at the cost of increased memory usage.
+              "cache=loose"
+            ];
+          };
+        };
+      })
+    ]
+  );
+}

nix/configuration/roles/network/default.nix

@@ -18,8 +18,8 @@
 {
   imports = [ ];
 
-  networking.dhcpcd.enable = false;
-  networking.useDHCP = false;
+  networking.dhcpcd.enable = lib.mkDefault false;
+  networking.useDHCP = lib.mkDefault false;
   networking.nameservers = [
     "194.242.2.2#doh.mullvad.net"
     "2a07:e340::2#doh.mullvad.net"

nix/configuration/roles/wasm/default.nix

@@ -24,7 +24,15 @@
         environment.systemPackages = with pkgs; [
           wabt
           wasm-bindgen-cli
-          pkgs-unoptimized.binaryen # for wasm-opt
+          binaryen # for wasm-opt
+        ];
+
+        nixpkgs.overlays = [
+          (final: prev: {
+            inherit (pkgs-unoptimized)
+              binaryen
+              ;
+          })
         ];
       }
     ]