nixos: Add ZFS auto-snapshotting module

nixos/modules/tasks/filesystems/zfs.nix

@@ -11,10 +11,22 @@ with pkgs.lib;
 let
 
   cfgSpl = config.boot.spl;
+  cfgSnapshots = config.services.zfs.autoSnapshot;
+
   inInitrd = any (fs: fs == "zfs") config.boot.initrd.supportedFilesystems;
   inSystem = any (fs: fs == "zfs") config.boot.supportedFilesystems;
+
+  enableAutoSnapshots = cfgSnapshots.enable;
+  enableZfs = inInitrd || inSystem || enableAutoSnapshots;
+
   kernel = config.boot.kernelPackages;
 
+  autosnapPkg = pkgs.zfstools.override {
+    zfs = config.boot.kernelPackages.zfs;
+  };
+
+  zfsAutoSnap = "${autosnapPkg}/bin/zfs-auto-snapshot";
+
 in
 
 {
@@ -34,12 +46,69 @@ in
         manually import pools.
       '';
     };
+
+    services.zfs.autoSnapshot = {
+      enable = mkOption {
+        default = false;
+        type = types.bool;
+        description = ''
+          Enable the (OpenSolaris-compatible) ZFS auto-snapshotting service.
+          Note that you must set the <literal>com.sun:auto-snapshot</literal>
+          property to <literal>true</literal> on all datasets which you wish
+          to auto-snapshot.
+
+          You can override a child dataset to use, or not use auto-snapshotting
+          by setting its flag with the given interval:
+          <literal>zfs set com.sun:auto-snapshot:weekly=false DATASET</literal>
+        '';
+      };
+
+      frequent = mkOption {
+        default = 4;
+        type = types.int;
+        description = ''
+          Number of frequent (15-minute) auto-snapshots that you wish to keep.
+        '';
+      };
+
+      hourly = mkOption {
+        default = 24;
+        type = types.int;
+        description = ''
+          Number of hourly auto-snapshots that you wish to keep.
+        '';
+      };
+
+      daily = mkOption {
+        default = 7;
+        type = types.int;
+        description = ''
+          Number of daily auto-snapshots that you wish to keep.
+        '';
+      };
+
+      weekly = mkOption {
+        default = 4;
+        type = types.int;
+        description = ''
+          Number of weekly auto-snapshots that you wish to keep.
+        '';
+      };
+
+      monthly = mkOption {
+        default = 12;
+        type = types.int;
+        description = ''
+          Number of monthly auto-snapshots that you wish to keep.
+        '';
+      };
+    };
   };
 
   ###### implementation
 
-  config = mkIf ( inInitrd || inSystem ) {
+  config = mkMerge [
-
+    (mkIf enableZfs {
       boot = {
         kernelModules = [ "spl" "zfs" ] ;
         extraModulePackages = [ kernel.zfs kernel.spl ];
@@ -70,9 +139,9 @@ in
         serviceConfig = {
           Type = "oneshot";
           RemainAfterExit = true;
-        restartIfChanged = false;
           ExecStart = "${kernel.zfs}/sbin/zpool import -f -a";
         };
+        restartIfChanged = false;
       };
 
       systemd.services."zfs-mount" = {
@@ -82,14 +151,72 @@ in
         serviceConfig = {
           Type = "oneshot";
           RemainAfterExit = true;
-        restartIfChanged = false;
           ExecStart = "${kernel.zfs}/sbin/zfs mount -a";
           ExecStop = "${kernel.zfs}/sbin/zfs umount -a";
         };
+        restartIfChanged = false;
       };
 
       system.fsPackages = [ kernel.zfs ];                  # XXX: needed? zfs doesn't have (need) a fsck
       environment.systemPackages = [ kernel.zfs ];
       services.udev.packages = [ kernel.zfs ];             # to hook zvol naming, etc.
+    })
+
+    (mkIf enableAutoSnapshots {
+      systemd.services."zfs-snapshot-frequent" = {
+        description = "ZFS auto-snapshotting every 15 mins";
+        after = [ "zpool-import.service" ];
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${zfsAutoSnap} frequent ${toString cfgSnapshots.frequent}";
         };
+        restartIfChanged = false;
+        startAt = "*:15,30,45";
+      };
+
+      systemd.services."zfs-snapshot-hourly" = {
+        description = "ZFS auto-snapshotting every hour";
+        after = [ "zpool-import.service" ];
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${zfsAutoSnap} hourly ${toString cfgSnapshots.hourly}";
+        };
+        restartIfChanged = false;
+        startAt = "hourly";
+      };
+
+      systemd.services."zfs-snapshot-daily" = {
+        description = "ZFS auto-snapshotting every day";
+        after = [ "zpool-import.service" ];
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${zfsAutoSnap} daily ${toString cfgSnapshots.daily}";
+        };
+        restartIfChanged = false;
+        startAt = "daily";
+      };
+
+      systemd.services."zfs-snapshot-weekly" = {
+        description = "ZFS auto-snapshotting every week";
+        after = [ "zpool-import.service" ];
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${zfsAutoSnap} weekly ${toString cfgSnapshots.weekly}";
+        };
+        restartIfChanged = false;
+        startAt = "weekly";
+      };
+
+      systemd.services."zfs-snapshot-monthly" = {
+        description = "ZFS auto-snapshotting every month";
+        after = [ "zpool-import.service" ];
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${zfsAutoSnap} monthly ${toString cfgSnapshots.monthly}";
+        };
+        restartIfChanged = false;
+        startAt = "monthly";
+      };
+    })
+  ];
 }