nixos: Switch to systemd initrd

nixos/modules/common.nix

@@ -94,6 +94,7 @@ in
             "net.ipv6.route.max_size" = mkDefault 16384;
           };
         };
+
         loader = {
           efi = {
             efiSysMountPoint = mkDefault "/boot";
@@ -111,6 +112,14 @@ in
             memtest86.enable = mkDefault true;
           };
         };
+
+        initrd = {
+          systemd = {
+            enable = mkDefault true;
+            emergencyAccess = mkDefault true;
+          };
+          services.lvm.enable = mkDefault true;
+        };
       };
 
       environment.systemPackages = with pkgs; mkMerge [

nixos/modules/containers.nix

@@ -208,7 +208,13 @@ in
 
             mkdir -p -m 0755 "$root"/sbin "$root"/etc
             touch "$root"/etc/os-release
-            ln -sf "${containerSystem}"/init "$root"/sbin/init
+
+            if [ -e "${containerSystem}"/prepare-root ]; then
+              initSource="${containerSystem}"/prepare-root
+            else
+              initSource="${containerSystem}"/init
+            fi
+            ln -sf "$initSource" "$root"/sbin/init
           '';
           postStop =
           ''

nixos/modules/tmproot.nix

@@ -224,8 +224,9 @@ in
 
         # Catch non-existent source directories that are needed for boot (see `pathsNeededForBoot` in
         # nixos/lib/util.nix). We do this by monkey-patching the `waitDevice` function that would otherwise hang.
-        boot.initrd.postDeviceCommands =
-          ''
+        # Seems like systemd initrd doesn't care because it uses the systemd.mount units
+        # ("If this mount is a bind mount and the specified path does not exist yet it is created as directory.")
+        boot.initrd.postDeviceCommands = mkIf (!config.boot.initrd.systemd.enable) ''
             ensurePersistSource() {
               [ -e "/mnt-root$1" ] && return
               echo "Persistent source directory $1 does not exist, creating..."