nixos: generalize copy-paste from stage-1 and zfs to utils

nixos/lib/utils.nix

@@ -2,6 +2,10 @@ pkgs: with pkgs.lib;
 
 rec {
 
+  # Check whenever fileSystem is needed for boot
+  fsNeededForBoot = fs: fs.neededForBoot
+                     || elem fs.mountPoint [ "/" "/nix" "/nix/store" "/var" "/var/log" "/var/lib" "/etc" ];
+
   # Check whenever `b` depends on `a` as a fileSystem
   # FIXME: it's incorrect to simply use hasPrefix here: "/dev/a" is not a parent of "/dev/ab"
   fsBefore = a: b: ((any (x: elem x [ "bind" "move" ]) b.options) && (a.mountPoint == b.device))

nixos/modules/system/boot/stage-1.nix

@@ -26,9 +26,7 @@ let
   # The initrd only has to mount `/` or any FS marked as necessary for
   # booting (such as the FS containing `/nix/store`, or an FS needed for
   # mounting `/`, like `/` on a loopback).
-  fileSystems = filter
-    (fs: fs.neededForBoot || elem fs.mountPoint [ "/" "/nix" "/nix/store" "/var" "/var/log" "/var/lib" "/etc" ])
-    config.system.build.fileSystems;
+  fileSystems = filter utils.fsNeededForBoot config.system.build.fileSystems;
 
 
   # Some additional utilities needed in stage 1, like mount, lvm, fsck

nixos/modules/tasks/filesystems/zfs.nix

@@ -38,11 +38,9 @@ let
 
   zfsFilesystems = filter (x: x.fsType == "zfs") config.system.build.fileSystems;
 
-  isRoot = fs: fs.neededForBoot || elem fs.mountPoint [ "/" "/nix" "/nix/store" "/var" "/var/log" "/var/lib" "/etc" ];
-
   allPools = unique ((map fsToPool zfsFilesystems) ++ cfgZfs.extraPools);
 
-  rootPools = unique (map fsToPool (filter isRoot zfsFilesystems));
+  rootPools = unique (map fsToPool (filter fsNeededForBoot zfsFilesystems));
 
   dataPools = unique (filter (pool: !(elem pool rootPools)) allPools);