1 files changed, 29 insertions, 0 deletions
diff --git a/nixpkgs/nixos/tests/common/auto-format-root-device.nix b/nixpkgs/nixos/tests/common/auto-format-root-device.nix
new file mode 100644
index 000000000000..fef8c7004991
--- /dev/null
+++ b/nixpkgs/nixos/tests/common/auto-format-root-device.nix
@@ -0,0 +1,29 @@
+# This is a test utility that automatically formats
+# `config.virtualisation.rootDevice` in the initrd.
+# Note that when you are using
+# `boot.initrd.systemd.enable = true`, you can use
+# `virtualisation.fileSystems."/".autoFormat = true;`
+# instead.
+
+{ lib, config, pkgs, ... }:
+
+let
+  rootDevice = config.virtualisation.rootDevice;
+in
+{
+
+  boot.initrd.extraUtilsCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
+    # We need mke2fs in the initrd.
+    copy_bin_and_libs ${pkgs.e2fsprogs}/bin/mke2fs
+  '';
+
+  boot.initrd.postDeviceCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
+    # If the disk image appears to be empty, run mke2fs to
+    # initialise.
+    FSTYPE=$(blkid -o value -s TYPE ${rootDevice} || true)
+    PARTTYPE=$(blkid -o value -s PTTYPE ${rootDevice} || true)
+    if test -z "$FSTYPE" -a -z "$PARTTYPE"; then
+        mke2fs -t ext4 ${rootDevice}
+    fi
+  '';
+}