diff --git a/pkgs/os-specific/linux/kernel/builder.sh b/pkgs/os-specific/linux/kernel/builder.sh
new file mode 100644
index 0000000000000..44baff1f7dfd3
--- /dev/null
+++ b/pkgs/os-specific/linux/kernel/builder.sh
@@ -0,0 +1,8 @@
+# TODO testing if that's better
+source $stdenv/setup
+
+# that s how cmake replaces
+# if [ -z "$dontUseCmakeConfigure" -a -z "$configurePhase" ]; then
+#     setOutputFlags=
+#     configurePhase=cmakeConfigurePhase
+# fi
diff --git a/pkgs/os-specific/linux/kernel/config.nix b/pkgs/os-specific/linux/kernel/config.nix
new file mode 100644
index 0000000000000..dd7ec4d162323
--- /dev/null
+++ b/pkgs/os-specific/linux/kernel/config.nix
@@ -0,0 +1,155 @@
+{
+  stdenv
+, lib
+# , config
+# , buildRoot
+# , srcRoot
+, ignoreConfigErrors, version
+# , kernelConfig
+, config, configCross ?null
+, kernelPatches
+, runCommand
+, kernel
+, perl, hostPlatform
+, ...
+}:
+
+# with import lib.nix;
+/*
+
+# TODO we should be able to generate standalone config and config on the go
+# => we need functions with module etc
+# espcially we need a bash builder
+# TODO have a standalone
+# etait defini dans generic.nix
+
+There variables are exported to be used by the generate-config.pl script, see the buildPhase
+debug
+autoModules
+preferBuiltin
+ignoreConfigErrors
+kernel_config
+
+kernel-config is a file
+
+TODO doesn t need to be a derviation ?
+can 't we justr override the source or split into two derivations:
+- standalone
+- embedded
+*/
+let
+
+  readConfig = configfile: import (runCommand "config.nix" {} ''
+    echo "{" > "$out"
+    while IFS='=' read key val; do
+      [ "x''${key#CONFIG_}" != "x$key" ] || continue
+      no_firstquote="''${val#\"}";
+      echo '  "'"$key"'" = "'"''${no_firstquote%\"}"'";' >> "$out"
+    done < "${configfile}"
+    echo "}" >> $out
+  '').outPath;
+
+  # RENAME to 'load'
+  convertKernelConfigToJson = readConfig;
+
+  patchKconfig = ''
+        # Patch kconfig to print "###" after every question so that
+        # generate-config.pl from the generic builder can answer them.
+        sed -e '/fflush(stdout);/i\printf("###");' -i scripts/kconfig/conf.c
+  '';
+
+  # generates functor
+  #
+  kernelConfigFun = baseConfig: kernelPatches:
+    let
+      configFromPatches =
+        map ({extraConfig ? "", ...}: extraConfig) kernelPatches;
+    in lib.concatStringsSep "\n" ([baseConfig] ++ configFromPatches);
+in
+stdenv.mkDerivation rec {
+    inherit ignoreConfigErrors;
+    name = "linux-config-${version}";
+
+
+    # Runs generate-config
+    # my $pid = open2(\*IN, \*OUT, "make -C $ENV{SRC} O=$wd config SHELL=bash ARCH=$ENV{ARCH}");
+    generateConfig = ./generate-config.pl;
+
+    # string that will be echoed to kernel-config file
+    # writeFile
+    # echo "$kernelConfig" > kernel-config
+    kernelConfig = kernelConfigFun config kernelPatches;
+
+    nativeBuildInputs = [ perl ];
+
+    platformName = stdenv.platform.name;
+
+    # sthg like "defconfig"
+    kernelBaseConfig = stdenv.platform.kernelBaseConfig;
+
+    # e.g. "bzImage"
+    kernelTarget = stdenv.platform.kernelTarget;
+    # HHHAAAACCKKK
+    autoModules = false; # stdenv.platform.kernelAutoModules;
+    preferBuiltin = stdenv.platform.kernelPreferBuiltin or false;
+    # kernel ARCH
+    arch = stdenv.platform.kernelArch;
+
+    crossAttrs = let
+        cp = hostPlatform.platform;
+      in {
+        arch = cp.kernelArch;
+        platformName = cp.name;
+        kernelBaseConfig = cp.kernelBaseConfig;
+        kernelTarget = cp.kernelTarget;
+        autoModules = cp.kernelAutoModules;
+
+        # Just ignore all options that don't apply (We are lazy).
+        ignoreConfigErrors = true;
+
+        kernelConfig = kernelConfigFun configCross;
+
+        inherit (kernel.crossDrv) src patches preUnpack;
+      };
+
+    patchKconfig = ''
+        # Patch kconfig to print "###" after every question so that
+        # generate-config.pl from the generic builder can answer them.
+        echo "Patching Kconfig"
+        sed -e '/fflush(stdout);/i\printf("###");' -i scripts/kconfig/conf.c
+  '';
+
+    prePatch = kernel.prePatch + patchKconfig;
+    # inherit (kernel) src patches preUnpack;
+    inherit (kernel) src patches preUnpack;
+
+    # TODO replace with config.nix buildPhase
+    # add a cd ?
+    buildPhase =  buildConfigCommands;
+
+    # need to be in srcRoot before launching this !
+    buildConfigCommands = ''
+      set -x
+      echo $PWD
+      cd $buildRoot
+
+      # Get a basic config file for later refinement with $ generateConfig.
+      # make O=$buildRoot $kernelBaseConfig ARCH=$arch
+      # /$sourceRoot
+      make -C .. O=$buildRoot $kernelBaseConfig ARCH=$arch
+
+      # Create the config file.
+      echo "generating kernel configuration..."
+      echo "${kernelConfig}" > $buildRoot/kernel-config
+      echo "Printing kernel config"
+      # TODO SRC ?
+      DEBUG=1 ARCH=$arch KERNEL_CONFIG=$buildRoot/kernel-config \
+        AUTO_MODULES=${builtins.toString autoModules} \
+           ignoreConfigErrors=${builtins.toString ignoreConfigErrors} \
+           PREFER_BUILTIN=$preferBuiltin SRC=. BUILD_FOLDER=$buildRoot perl -w ${generateConfig}
+    '';
+
+    installPhase = "mv $buildRoot/.config $out";
+
+    enableParallelBuilding = true;
+}
diff --git a/pkgs/os-specific/linux/kernel/generate-config.pl b/pkgs/os-specific/linux/kernel/generate-config.pl
index 5bce3af94293a..ba272eefeac1e 100644
--- a/pkgs/os-specific/linux/kernel/generate-config.pl
+++ b/pkgs/os-specific/linux/kernel/generate-config.pl
@@ -13,18 +13,22 @@
 use IPC::Open2;
 use Cwd;
 
-my $wd = getcwd;
+# my $wd = getcwd;
 
+# exported via nix
 my $debug = $ENV{'DEBUG'};
 my $autoModules = $ENV{'AUTO_MODULES'};
 my $preferBuiltin = $ENV{'PREFER_BUILTIN'};
-    
+my $ignoreConfigErrors = $ENV{'ignoreConfigErrors'};
+my $buildFolder=$ENV{'BUILD_FOLDER'};
+my $finalConfig="$buildFolder/.config";
+
 $SIG{PIPE} = 'IGNORE';
 
 # Read the answers.
 my %answers;
 my %requiredAnswers;
-open ANSWERS, "<$ENV{KERNEL_CONFIG}" or die;
+open ANSWERS, "<$ENV{KERNEL_CONFIG}" or die "Could not open answer file";
 while (<ANSWERS>) {
     chomp;
     s/#.*//;
@@ -40,7 +44,7 @@
 sub runConfig {
 
     # Run `make config'.
-    my $pid = open2(\*IN, \*OUT, "make -C $ENV{SRC} O=$wd config SHELL=bash ARCH=$ENV{ARCH}");
+    my $pid = open2(\*IN, \*OUT, "make -C $ENV{SRC} O=$buildFolder config SHELL=bash ARCH=$ENV{ARCH}");
 
     # Parse the output, look for questions and then send an
     # appropriate answer.
@@ -122,7 +126,7 @@ sub runConfig {
 # there.  `make config' often overrides answers if later questions
 # cause options to be selected.
 my %config;
-open CONFIG, "<.config" or die;
+open CONFIG, "<$finalConfig" or die "Could not read .config";
 while (<CONFIG>) {
     chomp;
     if (/^CONFIG_([A-Za-z0-9_]+)="(.*)"$/) {
@@ -137,7 +141,7 @@ sub runConfig {
 close CONFIG;
 
 foreach my $name (sort (keys %answers)) {
-    my $f = $requiredAnswers{$name} && $ENV{'ignoreConfigErrors'} ne "1"
+    my $f = $requiredAnswers{$name} && $ignoreConfigErrors ne "1"
         ? sub { die "error: " . $_[0]; } : sub { warn "warning: " . $_[0]; };
     &$f("unused option: $name\n") unless defined $config{$name};
     &$f("option not set correctly: $name (wanted '$answers{$name}', got '$config{$name}')\n")
diff --git a/pkgs/os-specific/linux/kernel/generic.nix b/pkgs/os-specific/linux/kernel/generic.nix
index c2f4e6843f591..05672caf96d18 100644
--- a/pkgs/os-specific/linux/kernel/generic.nix
+++ b/pkgs/os-specific/linux/kernel/generic.nix
@@ -6,7 +6,11 @@
 , # The kernel version.
   version
 
-, # Overrides to the kernel config.
+, # path to a .config file (or its content ?)
+  # if it s null we generate it
+  configfilename ? null
+
+, # Appended verbatim to kernel .config
   extraConfig ? ""
 
 , # The version number used for the module directory
@@ -26,8 +30,10 @@
 , ignoreConfigErrors ? stdenv.platform.name != "pc"
 , extraMeta ? {}
 , hostPlatform
+, callPackage
+# , pkgs
 , ...
-}:
+} @ args:
 
 assert stdenv.isLinux;
 
@@ -51,79 +57,38 @@ let
   config = configWithPlatform stdenv.platform;
   configCross = configWithPlatform hostPlatform.platform;
 
-  kernelConfigFun = baseConfig:
-    let
-      configFromPatches =
-        map ({extraConfig ? "", ...}: extraConfig) kernelPatches;
-    in lib.concatStringsSep "\n" ([baseConfig] ++ configFromPatches);
-
-  configfile = stdenv.mkDerivation {
+    configDrv = callPackage ./config.nix {
     inherit ignoreConfigErrors;
-    name = "linux-config-${version}";
-
-    generateConfig = ./generate-config.pl;
-
-    kernelConfig = kernelConfigFun config;
-
-    nativeBuildInputs = [ perl ];
-
-    platformName = stdenv.platform.name;
-    kernelBaseConfig = stdenv.platform.kernelBaseConfig;
-    kernelTarget = stdenv.platform.kernelTarget;
-    autoModules = stdenv.platform.kernelAutoModules;
-    preferBuiltin = stdenv.platform.kernelPreferBuiltin or false;
-    arch = stdenv.platform.kernelArch;
-
-    crossAttrs = let
-        cp = hostPlatform.platform;
-      in {
-        arch = cp.kernelArch;
-        platformName = cp.name;
-        kernelBaseConfig = cp.kernelBaseConfig;
-        kernelTarget = cp.kernelTarget;
-        autoModules = cp.kernelAutoModules;
-
-        # Just ignore all options that don't apply (We are lazy).
-        ignoreConfigErrors = true;
-
-        kernelConfig = kernelConfigFun configCross;
 
-        inherit (kernel.crossDrv) src patches preUnpack;
-      };
+    inherit version src kernelPatches stdenv config;
+    # modDirVersion
+    inherit kernel;
+    };
 
-    prePatch = kernel.prePatch + ''
-      # Patch kconfig to print "###" after every question so that
-      # generate-config.pl from the generic builder can answer them.
-      sed -e '/fflush(stdout);/i\printf("###");' -i scripts/kconfig/conf.c
-    '';
-
-    inherit (kernel) src patches preUnpack;
-
-    buildPhase = ''
-      cd $buildRoot
-
-      # Get a basic config file for later refinement with $generateConfig.
-      make -C ../$sourceRoot O=$PWD $kernelBaseConfig ARCH=$arch
-
-      # Create the config file.
-      echo "generating kernel configuration..."
-      echo "$kernelConfig" > kernel-config
-      DEBUG=1 ARCH=$arch KERNEL_CONFIG=kernel-config AUTO_MODULES=$autoModules \
-           PREFER_BUILTIN=$preferBuiltin SRC=../$sourceRoot perl -w $generateConfig
-    '';
-
-    installPhase = "mv .config $out";
-
-    enableParallelBuilding = true;
-  };
+  # TODO moved it
+  # callPackage ./config.nix {};
+  # configfile = stdenv.mkDerivation {
+  # configfile = (import ./config.nix);
 
+    # TODO le transformer plutot en
   kernel = buildLinux {
+    # TODO args
     inherit version modDirVersion src kernelPatches stdenv;
+    # inherit ignoreConfigErrors;
+    inherit configDrv;
+
+    # configfile = configfile.nativeDrv or configfile;
+    # configfile = configfile.nativeDrv or configfile;
+
+    # this is really configfilename
+    # configfile = if configfilename then configfilename else (callPackage ./config.nix {});
+    configfile = null;
 
-    configfile = configfile.nativeDrv or configfile;
 
-    crossConfigfile = configfile.crossDrv or configfile;
+    # TODO fix later
+    # crossConfigfile = configfile.crossDrv or configfile;
 
+    # erase parent config ???!
     config = { CONFIG_MODULES = "y"; CONFIG_FW_LOADER = "m"; };
 
     crossConfig = { CONFIG_MODULES = "y"; CONFIG_FW_LOADER = "m"; };
diff --git a/pkgs/os-specific/linux/kernel/lib.nix b/pkgs/os-specific/linux/kernel/lib.nix
new file mode 100644
index 0000000000000..23918a47f47ce
--- /dev/null
+++ b/pkgs/os-specific/linux/kernel/lib.nix
@@ -0,0 +1,63 @@
+# this should be
+#
+{
+  stdenv
+, lib
+# , buildRoot
+# , srcRoot
+# , ignoreConfigErrors: version, kernelConfig, runCommand
+, version
+, runCommand
+}:
+rec {
+  # runCommand = name: env: buildCommand:
+  /* generate a file config.nix with {
+      key=val;
+    }
+    from a kernel .config file passed as "configfile"
+    key#CONFIG_ removes "CONFIG_" prefix
+    */
+  readConfig = configfile: import (runCommand "config.nix" {} ''
+    echo "{" > "$out"
+    while IFS='=' read key val; do
+      [ "x''${key#CONFIG_}" != "x$key" ] || continue
+      no_firstquote="''${val#\"}";
+      echo '  "'"$key"'" = "'"''${no_firstquote%\"}"'";' >> "$out"
+    done < "${configfile}"
+    echo "}" >> $out
+  '').outPath;
+
+  # RENAME to 'load'
+  convertKernelConfigToJson = readConfig;
+
+  patchKconfig = ''
+        # Patch kconfig to print "###" after every question so that
+        # generate-config.pl from the generic builder can answer them.
+        sed -e '/fflush(stdout);/i\printf("###");' -i scripts/kconfig/conf.c
+  '';
+
+  # generates functor
+  #
+  kernelConfigFun = baseConfig: kernelPatches:
+    let
+      configFromPatches =
+        map ({extraConfig ? "", ...}: extraConfig) kernelPatches;
+    in lib.concatStringsSep "\n" ([baseConfig] ++ configFromPatches);
+
+  # TODO check bash variables exist -u
+  buildKernelConfig = arch: autoModules: ''
+      # cd $buildRoot
+
+      # Get a basic config file for later refinement with $generateConfig.
+      # make -C ../$sourceRoot O=$PWD $kernelBaseConfig ARCH=$arch
+      make -C .. O=$PWD $kernelBaseConfig ARCH=$arch
+
+      # Create the config file.
+      echo "generating kernel configuration..."
+      echo "$kernelConfig" > kernel-config
+      DEBUG=1 ARCH=$arch KERNEL_CONFIG=kernel-config AUTO_MODULES=$autoModules \
+           PREFER_BUILTIN=$preferBuiltin SRC=../$sourceRoot perl -w $generateConfig
+    '';
+}
+
+
diff --git a/pkgs/os-specific/linux/kernel/linux-4.9.nix b/pkgs/os-specific/linux/kernel/linux-4.9.nix
index 3e3626cb39d4b..15d64ad0db1b1 100644
--- a/pkgs/os-specific/linux/kernel/linux-4.9.nix
+++ b/pkgs/os-specific/linux/kernel/linux-4.9.nix
@@ -1,9 +1,17 @@
-{ stdenv, hostPlatform, fetchurl, perl, buildLinux, ... } @ args:
+{ stdenv, hostPlatform, ignoreConfigErrors ? true, fetchurl, perl, buildLinux, callPackage, ... } @ args:
 
 import ./generic.nix (args // rec {
   version = "4.9.65";
   extraMeta.branch = "4.9";
 
+  extraConfig=''
+    VIRTIO_PCI y
+    VIRTIO_PCI_LEGACY y
+    VIRTIO_BALLOON m
+    VIRTIO_INPUT m
+    VIRTIO_MMIO m
+    '';
+
   src = fetchurl {
     url = "mirror://kernel/linux/kernel/v4.x/linux-${version}.tar.xz";
     sha256 = "15a8a7p6i2dgiglps22cwsy5gsfkc39fy4jzvhjwz8s9fn3p1fi4";
diff --git a/pkgs/os-specific/linux/kernel/linux-mptcp.nix b/pkgs/os-specific/linux/kernel/linux-mptcp.nix
index 92b202100a63d..d5d7d59748dc3 100644
--- a/pkgs/os-specific/linux/kernel/linux-mptcp.nix
+++ b/pkgs/os-specific/linux/kernel/linux-mptcp.nix
@@ -1,5 +1,6 @@
-{ stdenv, hostPlatform, fetchFromGitHub, perl, buildLinux, ... } @ args:
+{ stdenv, callPackage, hostPlatform, fetchFromGitHub, perl, buildLinux, ... } @ args:
 
+# ~ linux_mptcp = callPackage generic.nix (linux_mptcp.nix)
 import ./generic.nix (rec {
   mptcpVersion = "0.93";
   modDirVersion = "4.9.60";
@@ -43,4 +44,4 @@ import ./generic.nix (rec {
     TCP_CONG_BALIA m
 
   '' + (args.extraConfig or "");
-} // args // (args.argsOverride or {}))
+} // removeAttrs args ["extraConfig"])
diff --git a/pkgs/os-specific/linux/kernel/manual-config.nix b/pkgs/os-specific/linux/kernel/manual-config.nix
index b4ee23079d930..3cbc554b52299 100644
--- a/pkgs/os-specific/linux/kernel/manual-config.nix
+++ b/pkgs/os-specific/linux/kernel/manual-config.nix
@@ -1,20 +1,28 @@
-{ runCommand, nettools, bc, perl, gmp, libmpc, mpfr, kmod, openssl
+# defines buildLinux, aka returns a function
+{ runCommand, stdenv, nettools, bc, perl, gmp, libmpc, mpfr, kmod, openssl
 , libelf ? null
 , utillinux ? null
 , writeTextFile, ubootTools
+# , callPackage
+
+# in fact this refers to a system (see lib/systems/examples.nix) and not a "platform"
+# since this sometimes call
+# should be a set like https://github.com/NixOS/nixpkgs/issues/24388
 , hostPlatform
 }:
 
 let
-  readConfig = configfile: import (runCommand "config.nix" {} ''
-    echo "{" > "$out"
-    while IFS='=' read key val; do
-      [ "x''${key#CONFIG_}" != "x$key" ] || continue
-      no_firstquote="''${val#\"}";
-      echo '  "'"$key"'" = "'"''${no_firstquote%\"}"'";' >> "$out"
-    done < "${configfile}"
-    echo "}" >> $out
-  '').outPath;
+  # TODO import from config
+  # readConfig = configfile: import (runCommand "config.nix" {} ''
+  #   echo "{" > "$out"
+  #   while IFS='=' read key val; do
+  #     [ "x''${key#CONFIG_}" != "x$key" ] || continue
+  #     no_firstquote="''${val#\"}";
+  #     echo '  "'"$key"'" = "'"''${no_firstquote%\"}"'";' >> "$out"
+  #   done < "${configfile}"
+  #   echo "}" >> $out
+  # '').outPath;
+  confHelpers = stdenv.lib.callPackage ./config.nix {};
 in {
   # Allow overriding stdenv on each buildLinux call
   stdenv,
@@ -30,15 +38,20 @@ in {
   nativeKernelPatches ? [],
   # Patches for cross compiling only
   crossKernelPatches ? [],
+  # ignoreConfigErrors,
+  # NEW pass a set with config inside
+  configDrv,
   # The native kernel .config file
+  # TODO if null, generate it from  readFile configDrv
   configfile,
   # The cross kernel .config file
   crossConfigfile ? configfile,
   # Manually specified nixexpr representing the config
   # If unspecified, this will be autodetected from the .config
-  config ? stdenv.lib.optionalAttrs allowImportFromDerivation (readConfig configfile),
+  config ? stdenv.lib.optionalAttrs allowImportFromDerivation (confHelpers.readConfig configfile),
+  # config ? null,
   # Cross-compiling config
-  crossConfig ? if allowImportFromDerivation then (readConfig crossConfigfile) else config,
+  crossConfig ? if allowImportFromDerivation then (confHelpers.readConfig crossConfigfile) else config,
   # Whether to utilize the controversial import-from-derivation feature to parse the config
   allowImportFromDerivation ? false
 }:
@@ -47,6 +60,8 @@ let
   inherit (stdenv.lib)
     hasAttr getAttr optional optionalString optionalAttrs maintainers platforms;
 
+  platform = stdenv.platform;
+
   installkernel = writeTextFile { name = "installkernel"; executable=true; text = ''
     #!${stdenv.shell} -e
     mkdir -p $4
@@ -54,10 +69,12 @@ let
     cp -av $3 $4
   ''; };
 
+  # flags common to the cross-compiled and native builds
   commonMakeFlags = [
     "O=$(buildRoot)"
+
   ] ++ stdenv.lib.optionals (stdenv.platform ? kernelMakeFlags)
-    stdenv.platform.kernelMakeFlags;
+    platform.kernelMakeFlags;
 
   drvAttrs = config_: platform: kernelPatches: configfile:
     let
@@ -81,17 +98,25 @@ let
 
       installsFirmware = (config.isEnabled "FW_LOADER") &&
         (isModular || (config.isDisabled "FIRMWARE_IN_KERNEL"));
-    in (optionalAttrs isModular { outputs = [ "out" "dev" ]; }) // {
+    in (optionalAttrs isModular { outputs = [ "out" "dev" ]; }) // rec {
       passthru = {
-        inherit version modDirVersion config kernelPatches configfile;
+        inherit version modDirVersion  kernelPatches configfile;
+        # inherit config;
       };
 
       inherit src;
 
+      # to help debug
+      # inherit config crossConfig;
+
+      # why this
       preUnpack = ''
-        mkdir build
-        export buildRoot="$(pwd)/build"
       '';
+      # HAAAACCKKKKK
+      autoModules = platform.kernelAutoModules;
+      preferBuiltin = platform.kernelPreferBuiltin or false;
+      arch = platform.kernelArch;
+      kernelBaseConfig = platform.kernelBaseConfig;
 
       patches = map (p: p.patch) kernelPatches;
 
@@ -101,11 +126,52 @@ let
             sed -i "$mf" -e 's|/usr/bin/||g ; s|/bin/||g ; s|/sbin/||g'
         done
         sed -i Makefile -e 's|= depmod|= ${kmod}/bin/depmod|'
-      '';
-
-      configurePhase = ''
+      ''
+      # if no configfile set then it means we have to generate it on the go
+      # configfile == null
+      # configfile.patchKconfig
+      # + stdenv.lib.optionalString (true) confHelpers.patchKconfig;
+      + stdenv.lib.optionalString (true) configDrv.patchKconfig;
+
+      # imported from generic.nix
+
+    # preConfigure = buildConfigPhase;
+
+
+    # we are in $sourceRoot
+    configurePhase = let
+
+        # if configfile is valid file
+        linkConfig = if (configfile != null) then ''
+          ln -sv ${configfile} $buildRoot/.config
+        '' else
+        # TODO la le kernel config n est pas genere
+        configDrv.buildConfigCommands
+        # ''
+        #   # TODO generate CONFIG !!!
+        #   ''
+          ;
+
+      in ''
+        # if [ -z "$buildRoot" ]; then
+
+          # we should be in $sourceRoot
+          # assume we are in the $sourceRoot folder
+          # echo "buildRoot is not set"
+          mkdir build
+          export buildRoot="$PWD/build"
+          echo "buildRoot was not set, now is $buildRoot"
+        # fi
         runHook preConfigure
-        ln -sv ${configfile} $buildRoot/.config
+        ''
+        +
+        linkConfig
+        +
+        ''
+
+
+        # reads the existing .config file and prompts the user for options in
+        # the current kernel source that are not found in the file.
         make $makeFlags "''${makeFlagsArray[@]}" oldconfig
         runHook postConfigure
 
@@ -154,7 +220,7 @@ let
         unlink $out/lib/modules/${modDirVersion}/source
 
         mkdir -p $dev/lib/modules/${modDirVersion}/build
-        cp -dpR ../$sourceRoot $dev/lib/modules/${modDirVersion}/source
+        cp -dpR .. $dev/lib/modules/${modDirVersion}/source
         cd $dev/lib/modules/${modDirVersion}/source
 
         cp $buildRoot/{.config,Module.symvers} $dev/lib/modules/${modDirVersion}/build
@@ -211,6 +277,8 @@ let
         make firmware_install $makeFlags "''${makeFlagsArray[@]}" \
           $installFlags "''${installFlagsArray[@]}"
       '');
+      # TODO add it as an output
+    # installPhase = "mv .config $out";
 
       requiredSystemFeatures = [ "big-parallel" ];
 
@@ -234,24 +302,35 @@ in
 
 assert stdenv.lib.versionAtLeast version "4.15" -> libelf != null;
 assert stdenv.lib.versionAtLeast version "4.15" -> utillinux != null;
-stdenv.mkDerivation ((drvAttrs config stdenv.platform (kernelPatches ++ nativeKernelPatches) configfile) // {
+stdenv.mkDerivation ((drvAttrs config platform (kernelPatches ++ nativeKernelPatches) configfile) // {
+# config ? stdenv.lib.optionalAttrs allowImportFromDerivation (readConfig configfile),
+# stdenv.mkDerivation ((drvAttrs config stdenv.platform (kernelPatches ++ nativeKernelPatches) configfile) // rec {
   name = "linux-${version}";
 
   enableParallelBuilding = true;
 
   nativeBuildInputs = [ perl bc nettools openssl gmp libmpc mpfr ]
-      ++ optional (stdenv.platform.kernelTarget == "uImage") ubootTools
+      ++ optional (platform.kernelTarget == "uImage") ubootTools
       ++ optional (stdenv.lib.versionAtLeast version "4.15") libelf
       ++ optional (stdenv.lib.versionAtLeast version "4.15") utillinux
       ;
 
   hardeningDisable = [ "bindnow" "format" "fortify" "stackprotector" "pic" ];
 
-  makeFlags = commonMakeFlags ++ [
-    "ARCH=${stdenv.platform.kernelArch}"
-  ];
+  # concatenated from drvAttrs
+  # configurePhase = ''
+  #   '';
+  # TODO add an output for the config ?
 
-  karch = stdenv.platform.kernelArch;
+  makeFlags = commonMakeFlags ++ [
+    "ARCH=${platform.kernelArch}"
+  ]
+  # {cfg.buildCores}
+  # ++ stdenv.lib.optional enableParallelBuilding "-j4"
+    # cfg.buildCores # TODO set
+    ;
+
+  karch = platform.kernelArch;
 
   crossAttrs = let cp = hostPlatform.platform; in
     (drvAttrs crossConfig cp (kernelPatches ++ crossKernelPatches) crossConfigfile) // {