Attempt to make ZFS work with custom installer image

hosts/x86_64-linux/installer.nix

@@ -1,12 +1,51 @@
-{ nixpkgs-flake, lib, ... }:
+{
+  config,
+  nixpkgs-flake,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  isUnstable = config.boot.zfs.package == pkgs.zfsUnstable;
+  zfsCompatibleKernelPackages = lib.filterAttrs (
+    name: kernelPackages:
+    (builtins.match "linux_[0-9]+_[0-9]+" name) != null
+    && (builtins.tryEval kernelPackages).success
+    && (
+      (!isUnstable && !kernelPackages.zfs.meta.broken)
+      || (isUnstable && !kernelPackages.zfs_unstable.meta.broken)
+    )
+  ) pkgs.linuxKernel.packages;
+  latestKernelPackage = lib.last (
+    lib.sort (a: b: (lib.versionOlder a.kernel.version b.kernel.version)) (
+      builtins.attrValues zfsCompatibleKernelPackages
+    )
+  );
+  zfs = pkgs.zfsUnstable.override {
+    # this overrides saves 10MB
+    samba = pkgs.coreutils;
+
+    python3 = pkgs.python3Minimal;
+  };
+in
 {
   imports = [
     "${nixpkgs-flake}/nixos/modules/installer/cd-dvd/installation-cd-graphical-combined.nix"
   ];
 
+  # This block copied from https://github.com/nix-community/nixos-images
+  boot.zfs.package = pkgs.zfsUnstable;
+  services.udev.packages = [ zfs ]; # to hook zvol naming, etc.
+  # unsure if need this, but in future udev rules could potentially point to systemd services.
+  systemd.packages = [ zfs ];
+  environment.defaultPackages = lib.mkForce [ zfs ]; # this merges with outer noninteractive module.
+  boot.kernelModules = [ "zfs" ];
+  boot.extraModulePackages = [ config.boot.kernelPackages.zfs_unstable ];
+  boot.kernelPackages = latestKernelPackage;
+
   custom.services.nixCacheClient.enable = true;
-  boot.supportedFilesystems.zfs = lib.mkForce true;
   services.qemuGuest.enable = true;
-  isoImage.squashfsCompression = "gzip -Xcompression-level 1";
+  system.installer.channel.enable = false;
+  isoImage.squashfsCompression = "zstd";
   networking.wireless.enable = false;
 }