From 0d896304de6875b630ff6426cd82781ae9149ad6 Mon Sep 17 00:00:00 2001
From: "Jan B." <git@keksgesicht.de>
Date: Tue, 9 Sep 2025 10:38:01 +0200
Subject: [PATCH 1/2] nixos/installer: add option to change fileystem during
 sd-image creation

enables the usage of different filesystems besides EXT4 for the root partition on the sd-card (e.g. BTRFS, XFS, ...)
---
 nixos/modules/installer/sd-card/sd-image.nix | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/installer/sd-card/sd-image.nix b/nixos/modules/installer/sd-card/sd-image.nix
index 7a2e271c4dde..c43f1642cdec 100644
--- a/nixos/modules/installer/sd-card/sd-image.nix
+++ b/nixos/modules/installer/sd-card/sd-image.nix
@@ -21,7 +21,7 @@
 with lib;
 
 let
-  rootfsImage = pkgs.callPackage ../../../lib/make-ext4-fs.nix (
+  rootfsImage = pkgs.callPackage config.sdImage.rootFilesystemCreator (
     {
       inherit (config.sdImage) storePaths;
       compressImage = config.sdImage.compressImage;
@@ -128,6 +128,20 @@ in
       '';
     };
 
+    rootFilesystemCreator = mkOption {
+      type = types.oneOf [
+        types.package
+        types.path
+      ];
+      default = ../../../lib/make-ext4-fs.nix;
+      example = ''
+        nixpkgs/nixos/lib/make-btrfs-fs.nix
+      '';
+      description = ''
+        The filesystem creator used for the root partition.
+      '';
+    };
+
     firmwareSize = mkOption {
       type = types.int;
       # As of 2019-08-18 the Raspberry pi firmware + u-boot takes ~18MiB

From f5ae72b1c1049ab6e112b78a04e4b198201745c4 Mon Sep 17 00:00:00 2001
From: "Jan B." <git@keksgesicht.de>
Date: Fri, 12 Sep 2025 14:01:46 +0200
Subject: [PATCH 2/2] nixos/installer: add option to override the root
 filesystem image creator itself

allows overriding the process how the filesystem image is created which the resulting sd-card image will use.
---
 nixos/modules/installer/sd-card/sd-image.nix | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/nixos/modules/installer/sd-card/sd-image.nix b/nixos/modules/installer/sd-card/sd-image.nix
index c43f1642cdec..b3251f9c6e1d 100644
--- a/nixos/modules/installer/sd-card/sd-image.nix
+++ b/nixos/modules/installer/sd-card/sd-image.nix
@@ -142,6 +142,15 @@ in
       '';
     };
 
+    rootFilesystemImage = mkOption {
+      type = types.package;
+      default = rootfsImage;
+      description = ''
+        The finished root partition image with all custom fileystem modifications.
+        Used to override the filesystem creator itself.
+      '';
+    };
+
     firmwareSize = mkOption {
       type = types.int;
       # As of 2019-08-18 the Raspberry pi firmware + u-boot takes ~18MiB
@@ -268,11 +277,11 @@ in
             echo "file sd-image $img" >> $out/nix-support/hydra-build-products
           fi
 
-          root_fs=${rootfsImage}
+          root_fs=${config.sdImage.rootFilesystemImage}
           ${lib.optionalString config.sdImage.compressImage ''
             root_fs=./root-fs.img
             echo "Decompressing rootfs image"
-            zstd -d --no-progress "${rootfsImage}" -o $root_fs
+            zstd -d --no-progress "${config.sdImage.rootFilesystemImage}" -o $root_fs
           ''}
 
           # Gap in front of the first partition, in MiB