When trying to compile/hack the kernel, it would keep asking me to
generate the .config file. That was because I had skipped the
unpackPhase. Also if one exit the nix-shell (voluntarely or because of
	an error) and wants to resume the configure phase, it would fail
because '$buildRoot' is not set; it is set during the unpackPhase.

My tackle on that is that there is a great chance the nix-shell was resumed from the unpacked folder.
Then the configurePhase sets the buildRoot accordingly.
I could have done it via a preConfigure hook but either way the current
situation is not good since one doesn"t know why he is asked to generate
the config. Dying with a message "set $buildRoot" could be an option.

…ell etc wip in pkgs/os-specific/linux/kernel/config.nix

===========
En gros on a linux_mptcp = callPackage generic.nix (linux_mptcp.nix)
generic.nix fait appel a buildLinux qui est defini dans manual-config.nix
generic.nix importe aussi kernelPlatform: import ./common-config.nix

extraConfig (optional) is a string specifying extra options to be concatenated to the kernel configuration file (.config)
===========

kernelPatches is a set of
  bridge_stp_helper =
    { name = "bridge-stp-helper";
      patch = ./bridge-stp-helper.patch;
    };

'make oldconfig' It reads the existing .config file and prompts the user for options in the current kernel source that are not found in the file. This is useful when taking an existing configuration and moving it to a new kernel

configfile est un chemin vers le fichier au format '.config' tandis que 'config'
  pcBase = {
    name = "pc";
    kernelHeadersBaseConfig = "defconfig";
    kernelBaseConfig = "defconfig";
    # Build whatever possible as a module, if not stated in the extra config.
    kernelAutoModules = true;
    kernelTarget = "bzImage";
  };

  pc64 = pcBase // { kernelArch = "x86_64"; };

 kernelTargets

    kernelExtraConfig =
      ''
        # Ubi for the mtd
        MTD_UBI y
        UBIFS_FS y
        UBIFS_FS_XATTR y
        UBIFS_FS_ADVANCED_COMPR y
        UBIFS_FS_LZO y
        UBIFS_FS_ZLIB y
        UBIFS_FS_DEBUG n
      '';

dans la phase de build du noyau
make -C ../$sourceRoot O=$PWD $kernelBaseConfig ARCH=$arch

warning: dumping very large path (> 256 MiB); this may run out of memory

 Using .. as source for kernel

- merge config/kernel and have a stopAtConfig boolean ?
- override src of config ?
- have 2 different configs ? embedded/inplace

fixed perl script. this works in nix-shell but now fails with nix-build,
      aka nixops fails .

…for crossplatform comiplation only

entity