(wip) Setup btrfs impermanence

hosts/nixos-testbed/configuration.nix

@@ -6,6 +6,7 @@
   ];
 
   sydnix = {
+    filesystemType = "btrfs";
     impermanence = {
       enable = false;
       directories = [
@@ -13,10 +14,12 @@
         # This means all users/groups without specified uids/gids will have them
         # reassigned on reboot."
         "/var/lib/nixos"
+        # We don't want to have different ssh keys on reboot, because ssh keys
+        # are expected to consistently identify machines... I think.  I mostly
+        # just think it's annoying to edit ~/.ssh/known_hosts all the time.
         "/etc/ssh"
       ];
-      rollbackTo = "blank";
+      device = "placeholderrrr";
-      dataset = "rpool/local/home";
       archiveLimit = 3;
     };
     users.users = [

modules/nixos/filesystemType.nix

@@ -0,0 +1,13 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  options = {
+    sydnix.filesystemType = mkOption {
+      type = types.nullOr (types.enum [ "btrfs" ]);
+      description = "The name of the filesystem to be used.";
+      default = null;
+    };
+  };
+}

modules/nixos/impermanence.nix

@@ -32,30 +32,29 @@ in {
         default = [];
       };
 
-      rollbackTo = mkOption {
+      device = mkOption {
-        type = types.str;
+        description = "Device to be wiped";
-      };
-      archiveTo = mkOption {
-        type = types.str;
-        default = "/persist/previous/home";
-      };
-      dataset = mkOption {
         type = types.str;
       };
+
       archiveLimit = mkOption {
         type = types.ints.positive;
+        description = "The number of previous roots to preserve.";
         default = 3;
       };
     };
   };
 
   config = mkIf cfg.enable {
+    # Create a group called `cfg.persistGroupName`
     users.groups.${cfg.persistGroupName} = {
       name = cfg.persistGroupName;
     };
 
     systemd.tmpfiles.settings = {
       "10-persist" = {
+        # Permit members of `cfg.persistGroupName` to read, write, and execute
+        # /persist.
         "/persist" = {
           z = {
             group = cfg.persistGroupName;
@@ -65,68 +64,100 @@ in {
       };
     };
 
-    boot.initrd.systemd.initrdBin = with pkgs; [
-      zfs
-    ];
-
     # TODO: Move this somewhere else.
     programs.fuse.userAllowOther = true;
 
+    # sudo mount -o ro -t virtiofs mount-dots /persist/dots
+    boot.initrd.systemd = {
+      # `pkgs.babashka` calls `pkgs.babashka-unwrapped`, and will explode if it
+      # cannot find it.
+      storePaths = [ pkgs.babashka-unwrapped ];
+
+      initrdBin = with pkgs; [
+        babashka
+        util-linux
+      ];
+    };
+
     boot.initrd.systemd.services.erase-darlings =
       let service = {
             description = "Rollback filesystem to a blank state on boot";
             wantedBy = [
               "initrd.target"
             ];
-            after = [
-              # "zfs-import.service"
-              "zfs-import-rpool.service"
-            ];
             before = [
               "sysroot.mount"
             ];
-            path = [ pkgs.zfs ];
+            path = with pkgs; [ util-linux babashka ];
             unitConfig.DefaultDependencies = "no";
             serviceConfig = {
               Type = "oneshot";
               RemainAfterExit = true;
             };
-            script = /* bash */ ''
+            script =
-              zfs rollback -r rpool/local/root@blank \
+              let bb-script = "/sysroot" + ./impermanence/erase-darlings.clj;
-                && echo ">> >> rollback complete << <<"
+              in ''${pkgs.babashka}/bin/bb "${bb-script}" -n "${toString cfg.archiveLimit}" --device "${cfg.device}"'';
-            '';
           };
       in if config.boot.initrd.systemd.enable
          then service
          else throw "sydnix.impermanence currently requires config.boot.initrd.systemd.enable'!";
 
-    systemd.services =
+    # TODO: Remove this.
-      let erase-home-darlings = {
+    # boot.initrd.systemd.services.erase-darlings-old =
-            description = "Rollback home to a blank state on boot";
+    #   let service = {
-            wantedBy = [
+    #         description = "Rollback filesystem to a blank state on boot";
-              "local-fs-pre.target"
+    #         wantedBy = [
-              "zfs-mount.service"
+    #           "initrd.target"
-            ];
+    #         ];
-            before = [
+    #         after = [
-              "local-fs.target"
+    #           # "zfs-import.service"
-              "local-fs-pre.target"
+    #           "zfs-import-rpool.service"
-              "zfs-mount.service"
+    #         ];
-            ];
+    #         before = [
-            path = [ pkgs.zfs pkgs.babashka pkgs.util-linux ];
+    #           "sysroot.mount"
-            unitConfig.DefaultDependencies = "no";
+    #         ];
-            serviceConfig = {
+    #         path = [ pkgs.zfs ];
-              Type = "oneshot";
+    #         unitConfig.DefaultDependencies = "no";
-              RemainAfterExit = true;
+    #         serviceConfig = {
-              ExecStart =
+    #           Type = "oneshot";
-                let script = ./erase-home-darlings.clj;
+    #           RemainAfterExit = true;
-                in ''${pkgs.babashka}/bin/bb "${script}" -n "${toString cfg.archiveLimit}" --dataset "${cfg.dataset}" --rollback-to "${cfg.rollbackTo}"'';
+    #         };
-            };
+    #         script = /* bash */ ''
-            stopIfChanged = false;
+    #           zfs rollback -r rpool/local/root@blank \
-            restartIfChanged = false;
+    #             && echo ">> >> rollback complete << <<"
-          };
+    #         '';
-      in {
+    #       };
-        # inherit erase-home-darlings;
+    #   in if config.boot.initrd.systemd.enable
-      };
+    #      then service
+    #      else throw "sydnix.impermanence currently requires config.boot.initrd.systemd.enable'!";
+
+    # systemd.services =
+    #   let erase-home-darlings = {
+    #         description = "Rollback home to a blank state on boot";
+    #         wantedBy = [
+    #           "local-fs-pre.target"
+    #           "zfs-mount.service"
+    #         ];
+    #         before = [
+    #           "local-fs.target"
+    #           "local-fs-pre.target"
+    #           "zfs-mount.service"
+    #         ];
+    #         path = [ pkgs.zfs pkgs.babashka pkgs.util-linux ];
+    #         unitConfig.DefaultDependencies = "no";
+    #         serviceConfig = {
+    #           Type = "oneshot";
+    #           RemainAfterExit = true;
+    #           ExecStart =
+    #             let script = ./erase-home-darlings.clj;
+    #             in ''${pkgs.babashka}/bin/bb "${script}" -n "${toString cfg.archiveLimit}" --dataset "${cfg.dataset}" --rollback-to "${cfg.rollbackTo}"'';
+    #         };
+    #         stopIfChanged = false;
+    #         restartIfChanged = false;
+    #       };
+    #   in {
+    #     # inherit erase-home-darlings;
+    #   };
 
     environment.persistence."/persist/root" = {
       directories = cfg.directories;

modules/nixos/impermanence/erase-darlings.clj

@@ -0,0 +1,43 @@
+#!/usr/bin/env bb
+
+(require '[clojure.core.match :refer [match]]
+         '[babashka.cli :as cli]
+         '[clojure.pprint :as pp]
+         '[clojure.tools.logging :as l]
+         '[babashka.process :refer [shell check process] :as p])
+
+(def cli-spec
+  {:spec
+   {:archive-limit {:coerce :int
+                    :alias :n
+                    :validate #(pos? %)
+                    :default 3
+                    :desc "Number of archives to save at a time."}
+    :device {:coerce :string
+             ;; :validate fs/exists?
+             :require true
+             :desc "Dataset to be archived and rolled back."}
+    :previous-roots
+    {:coerce :string
+     :default "/persist/previous"
+     :desc "The path under which previous roots will be stored."}
+    :error-fn
+    (fn [{:keys [spec type cause msg option] :as data}]
+      (when (= :org.babashka/cli type)
+        (case cause
+          :require
+          (println
+           (format "Missing required argument: %s\n" option))))
+      (System/exit 1))}})
+
+(defmacro with-echoed-shell-commands [& body]
+  (let [print-cmd #(println (str "+ " (str/join (:cmd %))))]
+    `(binding [p/*defaults* {:pre-start-fn ~print-cmd}]
+             ~@body)))
+
+(defn -main [opts]
+  (pp/pprint opts)
+  (with-echoed-shell-commands
+    (shell "mount")))
+
+(-main (cli/parse-opts *command-line-args* cli-spec))