nixos/zfs: expose zfs package as readonly attribute

nixos/modules/tasks/filesystems/zfs.nix

@@ -19,18 +19,8 @@ let
 
   enableZfs = inInitrd || inSystem;
 
-  kernel = config.boot.kernelPackages;
-
-  packages = if config.boot.zfs.enableUnstable then {
-    zfs = kernel.zfsUnstable;
-    zfsUser = pkgs.zfsUnstable;
-  } else {
-    zfs = kernel.zfs;
-    zfsUser = pkgs.zfs;
-  };
-
   autosnapPkg = pkgs.zfstools.override {
-    zfs = packages.zfsUser;
+    zfs = cfgZfs.package;
   };
 
   zfsAutoSnap = "${autosnapPkg}/bin/zfs-auto-snapshot";
@@ -111,6 +101,12 @@ in
 
   options = {
     boot.zfs = {
+      package = mkOption {
+        readOnly = true;
+        type = types.package;
+        default = if config.boot.zfs.enableUnstable then pkgs.zfsUnstable else pkgs.zfs;
+        description = "Configured ZFS userland tools package.";
+      };
       enableUnstable = mkOption {
         type = types.bool;
         default = false;
@@ -370,16 +366,22 @@ in
 
       boot = {
         kernelModules = [ "zfs" ];
-        extraModulePackages = with packages; [ zfs ];
+
+        extraModulePackages = [
+          (if config.boot.zfs.enableUnstable then
+            config.boot.kernelPackages.zfsUnstable
+           else
+            config.boot.kernelPackages.zfs)
+        ];
       };
 
       boot.initrd = mkIf inInitrd {
         kernelModules = [ "zfs" ] ++ optional (!cfgZfs.enableUnstable) "spl";
         extraUtilsCommands =
           ''
-            copy_bin_and_libs ${packages.zfsUser}/sbin/zfs
-            copy_bin_and_libs ${packages.zfsUser}/sbin/zdb
-            copy_bin_and_libs ${packages.zfsUser}/sbin/zpool
+            copy_bin_and_libs ${cfgZfs.package}/sbin/zfs
+            copy_bin_and_libs ${cfgZfs.package}/sbin/zdb
+            copy_bin_and_libs ${cfgZfs.package}/sbin/zpool
           '';
         extraUtilsCommandsTest = mkIf inInitrd
           ''
@@ -433,7 +435,7 @@ in
       services.zfs.zed.settings = {
         ZED_EMAIL_PROG = mkDefault "${pkgs.mailutils}/bin/mail";
         PATH = lib.makeBinPath [
-          packages.zfsUser
+          cfgZfs.package
           pkgs.coreutils
           pkgs.curl
           pkgs.gawk
@@ -461,18 +463,18 @@ in
             "vdev_clear-led.sh"
           ]
         )
-        (file: { source = "${packages.zfsUser}/etc/${file}"; })
+        (file: { source = "${cfgZfs.package}/etc/${file}"; })
       // {
         "zfs/zed.d/zed.rc".text = zedConf;
-        "zfs/zpool.d".source = "${packages.zfsUser}/etc/zfs/zpool.d/";
+        "zfs/zpool.d".source = "${cfgZfs.package}/etc/zfs/zpool.d/";
       };
 
-      system.fsPackages = [ packages.zfsUser ]; # XXX: needed? zfs doesn't have (need) a fsck
-      environment.systemPackages = [ packages.zfsUser ]
+      system.fsPackages = [ cfgZfs.package ]; # XXX: needed? zfs doesn't have (need) a fsck
+      environment.systemPackages = [ cfgZfs.package ]
         ++ optional cfgSnapshots.enable autosnapPkg; # so the user can run the command to see flags
 
-      services.udev.packages = [ packages.zfsUser ]; # to hook zvol naming, etc.
-      systemd.packages = [ packages.zfsUser ];
+      services.udev.packages = [ cfgZfs.package ]; # to hook zvol naming, etc.
+      systemd.packages = [ cfgZfs.package ];
 
       systemd.services = let
         getPoolFilesystems = pool:
@@ -506,8 +508,8 @@ in
             environment.ZFS_FORCE = optionalString cfgZfs.forceImportAll "-f";
             script = (importLib {
               # See comments at importLib definition.
-              zpoolCmd="${packages.zfsUser}/sbin/zpool";
-              awkCmd="${pkgs.gawk}/bin/awk";
+              zpoolCmd = "${cfgZfs.package}/sbin/zpool";
+              zfsCmd = "${cfgZfs.package}/sbin/zfs";
               inherit cfgZfs;
             }) + ''
               poolImported "${pool}" && exit
@@ -561,7 +563,7 @@ in
               RemainAfterExit = true;
             };
             script = ''
-              ${packages.zfsUser}/sbin/zfs set nixos:shutdown-time="$(date)" "${pool}"
+              ${cfgZfs.package}/sbin/zfs set nixos:shutdown-time="$(date)" "${pool}"
             '';
           };
         createZfsService = serv:
@@ -633,11 +635,11 @@ in
           Type = "oneshot";
         };
         script = ''
-          ${packages.zfsUser}/bin/zpool scrub ${
+          ${cfgZfs.package}/bin/zpool scrub ${
             if cfgScrub.pools != [] then
               (concatStringsSep " " cfgScrub.pools)
             else
-              "$(${packages.zfsUser}/bin/zpool list -H -o name)"
+              "$(${cfgZfs.package}/bin/zpool list -H -o name)"
             }
         '';
       };
@@ -656,7 +658,7 @@ in
       systemd.services.zpool-trim = {
         description = "ZFS pools trim";
         after = [ "zfs-import.target" ];
-        path = [ packages.zfsUser ];
+        path = [ cfgZfs.package ];
         startAt = cfgTrim.interval;
         # By default we ignore errors returned by the trim command, in case:
         # - HDDs are mixed with SSDs