use iso image for nixos qemu test

.github/workflows/nix-portable.yml

@@ -58,7 +58,6 @@ jobs:
         install_url: https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20201221_9fab14a/install
         extra_nix_config: |
           experimental-features = nix-command flakes
-          system-features = benchmark big-parallel kvm nixos-test recursive-nix
 
     - uses: cachix/cachix-action@v8
       with:

flake.nix

@@ -40,10 +40,11 @@
           excludeRuntimes = [ "bwrap" ];
         };
         nixos = {
+          # use iso image for nixos because building a qcow2 would require KVM
           img = (toString (nixosSystem {
             system = "x86_64-linux";
-            modules = [(import ./testing/nixos-qcow2.nix)];
-          }).config.system.build.qcow) + "/nixos.qcow2";
+            modules = [(import ./testing/nixos-iso.nix)];
+          }).config.system.build.isoImage) + "/iso/nixos.iso";
         };
         ubuntu = {
           url = "https://cloud-images.ubuntu.com/focal/20210415/focal-server-cloudimg-amd64.img";

testing/nixos-iso.nix

@@ -0,0 +1,29 @@
+{ config, lib, pkgs, modulesPath, ... }:
+with builtins;
+with lib;
+{
+  imports = [
+    "${toString modulesPath}/installer/cd-dvd/iso-image.nix"
+  ];
+
+  boot.loader.timeout = mkForce 0;
+
+  fileSystems."/" = {
+    fsType = "tmpfs";
+    options = [ "mode=0755" "size=2G" ];
+  };
+
+  # EFI booting
+  isoImage.makeEfiBootable = true;
+
+  # USB booting
+  isoImage.makeUsbBootable = true;
+
+  isoImage.squashfsCompression = "zstd -Xcompression-level 5";
+
+  users.users.test.isNormalUser = true;
+  users.users.test.openssh.authorizedKeys.keys = [ (readFile ./id_ed25519.pub) ];
+  users.users.root.openssh.authorizedKeys.keys = config.users.users.test.openssh.authorizedKeys.keys;
+  services.openssh.enable = true;
+
+}