modules/outputs/zyxel-nwa-fit: init

Zyxel "firmware" format is just… a FIT with some metadata on the models.

This FIT is like this:

--------------------------
    uImage FIT header
--------------------------
    Linux kernel
--------------------------
    FDT DTB
--------------------------
    Padding so that
    this makes
    8192kb [1]
--------------------------
    UBI volume
    as a root filesystem
--------------------------

We just reproduce this in a very brutal and naive way.
In the future, this seems worth to generalize and modularize this idea
so that zyxel-nwa-fit is just an instance of a more general output.

[1]: https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/ramips/image/mt7621.mk;h=ab1b829ba0086cb9fc9ca8cbbf3cbc14735034d6;hb=refs/heads/main#l3097

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>

modules/outputs/zyxel-nwa-fit.nix

@@ -0,0 +1,71 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+  inherit (lib) mkIf mkEnableOption mkOption types concatStringsSep;
+  models = "6b e1 6f e1 ff ff ff ff ff ff";
+in {
+  options.system.outputs = {
+    zyxel-nwa-fit = mkOption {
+      type = types.package;
+      description = ''
+zyxel-nwa-fit
+*************
+
+This output provides a FIT image for Zyxel NWA series
+containing a kernel image and an UBIFS rootfs.
+
+It can usually be used as a factory image to install Liminix
+on a system with pre-existing firmware and OS.
+      '';
+    };
+  };
+
+  imports = [
+    ./ubivolume.nix
+  ];
+
+  config = mkIf (config.rootfsType == "ubifs") {
+
+    system.outputs.zyxel-nwa-fit =
+      let 
+        o = config.system.outputs;
+        # 8129kb padding.
+        paddedKernel = pkgs.runCommand "padded-kernel" {} ''
+          cp --no-preserve=mode ${o.uimage} $out
+          dd if=/dev/zero of=$out bs=1 count=1 seek=8388607
+        '';
+        firmwareImage = pkgs.runCommand "firmware-image" {} ''
+          cat ${paddedKernel} ${o.rootfs} > $out
+        '';
+        dts = pkgs.writeText "image.its" ''
+        /dts-v1/;
+
+        / {
+          description = "Zyxel FIT (Flattened Image Tree)";
+          compat-models = [${models}];
+          #address-cells = <1>;
+
+          images {
+            firmware {
+              data = /incbin/("${firmwareImage}");
+              type = "firmware";
+              compression = "none";
+              hash@1 {
+                algo = "sha1";
+              };
+            };
+          };
+        };
+      '';
+      in
+      pkgs.runCommand "zyxel-nwa-fit" {
+        nativeBuildInputs = [ pkgs.pkgsBuildBuild.ubootTools pkgs.pkgsBuildBuild.dtc ];
+      } ''
+        mkimage -f ${dts} $out
+      '';
+  };
+}