Generalize and split up more files

modules/system/boot/default.nix

@@ -0,0 +1,7 @@
+{ ... }:
+{
+  imports = [
+    ./firmware
+    ./systemd
+  ];
+}

modules/system/boot/firmware/default.nix

@@ -0,0 +1,4 @@
+{ ... }:
+{
+  hardware.enableRedistributableFirmware = true;
+}

modules/system/boot/systemd/default.nix

@@ -0,0 +1,6 @@
+{ ... }:
+{
+  imports = [ ./root-reset ];
+
+  boot.initrd.systemd.enable = true;
+}

modules/system/boot/systemd/root-reset/default.nix

@@ -0,0 +1,30 @@
+{ config, ... }:
+{
+  boot.initrd.systemd.services.root-reset = {
+    description = "Reset root and snapshot last boot";
+    wantedBy = [ "initrd.target" ];
+    before = [ "sysroot.mount" ];
+    after = [ "dev-${config.networking.hostName}-root.device" ];
+    unitConfig.DefaultDependencies = "no";
+    serviceConfig.Type = "oneshot";
+    script = ''
+      mkdir -p /mnt
+      mount /dev/${config.networking.hostName}/root /mnt
+
+      if [[ -e /mnt/prev ]]; then
+        btrfs subvolume delete /mnt/prev
+      fi
+
+      btrfs subvolume snapshot /mnt/root /mnt/prev
+
+      btrfs subvolume list -o /mnt/root | cut -f9 -d' ' | while read subvolume; do
+        btrfs subvolume delete "/mnt/$subvolume"
+      done
+
+      btrfs subvolume delete /mnt/root
+      btrfs subvolume create /mnt/root
+
+      umount /mnt
+    '';
+  };
+}