Add optional zfsSupport to the nixos grub configuration

nixos/modules/system/boot/loader/grub/grub.nix

@@ -6,7 +6,8 @@ let
 
   cfg = config.boot.loader.grub;
 
-  realGrub = if cfg.version == 1 then pkgs.grub else pkgs.grub2;
+  realGrub = if cfg.version == 1 then pkgs.grub
+    else pkgs.grub2.override { zfsSupport = cfg.zfsSupport };
 
   grub =
     # Don't include GRUB if we're only generating a GRUB menu (e.g.,
@@ -209,6 +210,14 @@ in
         '';
       };
 
+      zfsSupport = mkOption {
+        default = false;
+        type = types.bool;
+        description = ''
+          Whether grub should be build against libzfs.
+        '';
+      };
+
     };
 
   };
@@ -251,6 +260,9 @@ in
           ${pkgs.coreutils}/bin/cp -pf "${v}" "/boot/${n}"
         '') config.boot.loader.grub.extraFiles);
 
+    assertions = [{ assertion = !cfg.zfsSupport || cfg.version == 2;
+                    message = "Only grub version 2 provides zfs support";}];
+
     })
 
   ];

pkgs/top-level/all-packages.nix

@@ -1222,6 +1222,8 @@ let
 
   grub2_efi = grub2.override { EFIsupport = true; };
 
+  grub2_zfs = grub2.override { zfsSupport = true; };
+
   gssdp = callPackage ../development/libraries/gssdp {
     inherit (gnome) libsoup;
   };