nix: Build kernel module

crane-build.nix

@@ -74,6 +74,15 @@ let
     // {
       inherit cargoArtifacts;
 
+      outputs = [
+        "out"
+        "dkms"
+      ];
+
+      makeFlags = args.makeFlags ++ [
+        "DKMSDIR=${placeholder "dkms"}"
+      ];
+
       enableParallelBuilding = true;
       buildPhaseCargoCommand = ''
         make ''${enableParallelBuilding:+-j''${NIX_BUILD_CORES}} $makeFlags
@@ -81,13 +90,15 @@ let
       doNotPostBuildInstallCargoBinaries = true;
       enableParallelInstalling = true;
       installPhaseCommand = ''
-        make ''${enableParallelInstalling:+-j''${NIX_BUILD_CORES}} $makeFlags install
+        make ''${enableParallelInstalling:+-j''${NIX_BUILD_CORES}} $makeFlags install install_dkms
       '';
 
       doInstallCheck = true;
       nativeInstallCheckInputs = [ versionCheckHook ];
       versionCheckProgramArg = "version";
 
+      passthru.kernelModule = import ./module-build.nix package;
+
       meta = {
         description = "Userspace tools for bcachefs";
         license = lib.licenses.gpl2Only;

flake.nix

@@ -93,6 +93,12 @@
                   crossPackages = {
                     "bcachefs-tools" = craneBuild.package;
                     "bcachefs-tools-fuse" = craneBuild.packageFuse;
+                    "bcachefs-module-linux-latest" =
+                      pkgs'.linuxPackages_latest.callPackage craneBuild.package.kernelModule
+                        { };
+                    "bcachefs-module-linux-testing" =
+                      pkgs'.linuxPackages_testing.callPackage craneBuild.package.kernelModule
+                        { };
                   };
                 in
                 (withCrossName crossPackages) // lib.optionalAttrs (crossSystem == localSystem) crossPackages;
@@ -109,6 +115,8 @@
               bcachefs-tools-aarch64-linux
               bcachefs-tools-fuse
               bcachefs-tools-fuse-i686-linux
+              bcachefs-module-linux-latest
+              bcachefs-module-linux-testing
               ;
             inherit (pkgs.callPackage ./crane-build.nix { inherit crane version; })
               # cargo-clippy

module-build.nix

@@ -0,0 +1,67 @@
+/*
+  Copyright (c) 2003-2025 Eelco Dolstra and the Nixpkgs/NixOS contributors
+
+  Permission is hereby granted, free of charge, to any person obtaining
+  a copy of this software and associated documentation files (the
+  "Software"), to deal in the Software without restriction, including
+  without limitation the rights to use, copy, modify, merge, publish,
+  distribute, sublicense, and/or sell copies of the Software, and to
+  permit persons to whom the Software is furnished to do so, subject to
+  the following conditions:
+
+  The above copyright notice and this permission notice shall be
+  included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+bcachefs-tools:
+{
+  lib,
+  stdenv,
+  kernelModuleMakeFlags,
+  kernel,
+}:
+
+stdenv.mkDerivation {
+  pname = "bcachefs";
+  version = "${kernel.version}-${bcachefs-tools.version}";
+
+  __structuredAttrs = true;
+
+  src = bcachefs-tools.dkms;
+
+  nativeBuildInputs = kernel.moduleBuildDependencies;
+
+  enableParallelBuilding = true;
+
+  makeFlags = kernelModuleMakeFlags ++ [
+    "KDIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"
+    "INSTALL_MOD_PATH=${placeholder "out"}"
+  ];
+
+  installPhase = ''
+    runHook preInstall
+    make -C ${kernel.dev}/lib/modules/${kernel.modDirVersion}/build M=$(pwd) modules_install "''${makeFlags[@]}" "''${installFlags[@]}"
+    runHook postInstall
+  '';
+
+  passthru = {
+    inherit (bcachefs-tools.passthru) tests;
+  };
+
+  meta = {
+    description = "out-of-tree bcachefs kernel module";
+
+    inherit (bcachefs-tools.meta)
+      license
+      maintainers
+      ;
+  };
+}