1 files changed, 89 insertions, 0 deletions
diff --git a/nixpkgs/nixos/tests/filesystems-overlayfs.nix b/nixpkgs/nixos/tests/filesystems-overlayfs.nix
new file mode 100644
index 000000000000..d7cbf640abe4
--- /dev/null
+++ b/nixpkgs/nixos/tests/filesystems-overlayfs.nix
@@ -0,0 +1,89 @@
+{ lib, pkgs, ... }:
+
+let
+  initrdLowerdir = pkgs.runCommand "initrd-lowerdir" { } ''
+    mkdir -p $out
+    echo "initrd" > $out/initrd.txt
+  '';
+  initrdLowerdir2 = pkgs.runCommand "initrd-lowerdir-2" { } ''
+    mkdir -p $out
+    echo "initrd2" > $out/initrd2.txt
+  '';
+  userspaceLowerdir = pkgs.runCommand "userspace-lowerdir" { } ''
+    mkdir -p $out
+    echo "userspace" > $out/userspace.txt
+  '';
+  userspaceLowerdir2 = pkgs.runCommand "userspace-lowerdir-2" { } ''
+    mkdir -p $out
+    echo "userspace2" > $out/userspace2.txt
+  '';
+in
+{
+
+  name = "writable-overlays";
+
+  meta.maintainers = with lib.maintainers; [ nikstur ];
+
+  nodes.machine = { config, pkgs, ... }: {
+    boot.initrd.systemd.enable = true;
+    boot.initrd.availableKernelModules = [ "overlay" ];
+
+    virtualisation.fileSystems = {
+      "/initrd-overlay" = {
+        overlay = {
+          lowerdir = [ initrdLowerdir ];
+          upperdir = "/.rw-initrd-overlay/upper";
+          workdir = "/.rw-initrd-overlay/work";
+        };
+        neededForBoot = true;
+      };
+      "/userspace-overlay" = {
+        overlay = {
+          lowerdir = [ userspaceLowerdir ];
+          upperdir = "/.rw-userspace-overlay/upper";
+          workdir = "/.rw-userspace-overlay/work";
+        };
+      };
+      "/ro-initrd-overlay" = {
+        overlay.lowerdir = [
+          initrdLowerdir
+          initrdLowerdir2
+        ];
+        neededForBoot = true;
+      };
+      "/ro-userspace-overlay" = {
+        overlay.lowerdir = [
+          userspaceLowerdir
+          userspaceLowerdir2
+        ];
+      };
+    };
+  };
+
+  testScript = ''
+    machine.wait_for_unit("default.target")
+
+    with subtest("Initrd overlay"):
+      machine.wait_for_file("/initrd-overlay/initrd.txt", 5)
+      machine.succeed("touch /initrd-overlay/writable.txt")
+      machine.succeed("findmnt --kernel --types overlay /initrd-overlay")
+
+    with subtest("Userspace overlay"):
+      machine.wait_for_file("/userspace-overlay/userspace.txt", 5)
+      machine.succeed("touch /userspace-overlay/writable.txt")
+      machine.succeed("findmnt --kernel --types overlay /userspace-overlay")
+
+    with subtest("Read only initrd overlay"):
+      machine.wait_for_file("/ro-initrd-overlay/initrd.txt", 5)
+      machine.wait_for_file("/ro-initrd-overlay/initrd2.txt", 5)
+      machine.fail("touch /ro-initrd-overlay/not-writable.txt")
+      machine.succeed("findmnt --kernel --types overlay /ro-initrd-overlay")
+
+    with subtest("Read only userspace overlay"):
+      machine.wait_for_file("/ro-userspace-overlay/userspace.txt", 5)
+      machine.wait_for_file("/ro-userspace-overlay/userspace2.txt", 5)
+      machine.fail("touch /ro-userspace-overlay/not-writable.txt")
+      machine.succeed("findmnt --kernel --types overlay /ro-userspace-overlay")
+  '';
+
+}