zaphyra's git: nixfiles

config/nixos/modules/filesystem: add `impermanence` (still untested)

diff --git a/config/nixos/modules/filesystem/impermanence.nix b/config/nixos/modules/filesystem/impermanence.nix
@@ -0,0 +1,121 @@
+{
+  pov,
+  povSelf,
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  inherit (lib) types;
+  cfgFilesystem = lib.getAttrFromPath pov config;
+  cfg = lib.getAttrFromPath povSelf config;
+  perms = {
+    user = lib.mkOption {
+      type = with types; nullOr str;
+      default = null;
+    };
+    group = lib.mkOption {
+      type = with types; nullOr str;
+      default = null;
+    };
+    mode = lib.mkOption {
+      type = with types; nullOr str;
+      default = null;
+    };
+  };
+
+in
+{
+
+  options = {
+    home.enable = {
+      type = types.bool;
+      default = false;
+    };
+    system = {
+      enable = {
+        type = types.bool;
+        default = false;
+      };
+      dirs = {
+        default = [ ];
+        type =
+          with types;
+          listOf (oneOf [
+            str
+            (submodule {
+              options = {
+                directory = lib.mkOption { type = types.str; };
+              } // perms;
+            })
+          ]);
+      };
+      files = {
+        default = [ ];
+        type =
+          with types;
+          listOf (oneOf [
+            str
+            (submodule {
+              options = {
+                file = lib.mkOption { type = types.str; };
+                parentDirectory = lib.mkOption {
+                  type = with types; nullOr (submodule perms);
+                  default = null;
+                };
+              } // perms;
+            })
+          ]);
+      };
+
+    };
+  };
+
+  config = lib.mkMerge [
+    (lib.mkIf (cfg.system.enable && (cfgFilesystem.rootDisk.type == "zfs")) {
+      boot.initrd.systemd.services = {
+        defenestrate = {
+          description = "Defenestrate old root";
+          wantedBy = [ "initrd.target" ];
+          after = [ "zfs-import.target" ];
+          before = [ "sysroot.mount" ];
+          onFailure = [ "emergency.target" ];
+          unitConfig.DefaultDependencies = "no";
+          serviceConfig.Type = "oneshot";
+          script =
+            let
+              prefix = "${config.networking.hostName}/os/nixos/root-";
+            in
+            ''
+              # We keep root from the previous last 3 boots
+              # Any command except create can fail in case the system has not
+              # booted that often yet
+              zfs destroy -r ${prefix}4 || true
+              zfs rename ${prefix}3 ${prefix}4 || true
+              zfs rename ${prefix}2 ${prefix}3 || true
+              zfs rename ${prefix}1 ${prefix}2 || true
+              zfs create -o devices=off -o exec=off -o mountpoint=legacy -o setuid=off ${prefix}1
+            '';
+        };
+      };
+      environment.persistence."/nix/persist/system" = {
+        enable = true;
+        hideMounts = true;
+        directories = [
+          "/etc/nixos"
+          "/etc/zfs"
+          "/var/log"
+          "/var/db/sudo/lectured" # "We trust you have received the usual lecture from the local System Administrator."
+          "/var/lib/nixos"
+          "/var/lib/systemd/coredump"
+        ] ++ cfg.system.dirs;
+        files = [
+          "/etc/machine-id"
+        ] ++ cfg.system.files;
+      };
+    })
+  ];
+
+}