nix: interactive nixos vm

This is useful for quickly spinning up an ephemeral hakurei environment for testing changes or reproducing vm test failures.

Signed-off-by: Ophestra <cat@gensokyo.uk>

test/interactive/vm.nix

@@ -0,0 +1,55 @@
+{
+  virtualisation.vmVariant.virtualisation = {
+    memorySize = 4096;
+    qemu.options = [
+      "-vga none -device virtio-gpu-pci"
+      "-smp 8"
+    ];
+
+    mountHostNixStore = true;
+    writableStore = true;
+    writableStoreUseTmpfs = false;
+
+    sharedDirectories = {
+      cwd = {
+        target = "/mnt/.ro-cwd";
+        source = ''"$OLDPWD"'';
+        securityModel = "none";
+      };
+    };
+
+    fileSystems = {
+      "/mnt/.ro-cwd".options = [
+        "ro"
+        "noatime"
+      ];
+      "/mnt/cwd".overlay = {
+        lowerdir = [ "/mnt/.ro-cwd" ];
+        upperdir = "/tmp/.cwd/upper";
+        workdir = "/tmp/.cwd/work";
+      };
+
+      "/mnt/src".overlay = {
+        lowerdir = [ ../.. ];
+        upperdir = "/tmp/.src/upper";
+        workdir = "/tmp/.src/work";
+      };
+    };
+  };
+
+  systemd.services = {
+    logrotate-checkconf.enable = false;
+    hakurei-src-fix-ownership = {
+      wantedBy = [ "multi-user.target" ];
+      wants = [ "mnt-src.mount" ];
+      after = [ "mnt-src.mount" ];
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = true;
+      };
+      script = ''
+        chown -R alice:users /mnt/src/
+      '';
+    };
+  };
+}