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] 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