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Linux kernel: Difference between revisions

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→Custom configuration: emphasise structuredExtraConfig and note what actually causes the "unused option" errors
 
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<syntaxhighlight lang=nix>
<syntaxhighlight lang=nix>
{
{
      boot.kernelPatches = [ {
  boot.kernelPatches = [ {
        name = "crashdump-config";
    name = "crashdump-config";
        patch = null;
    patch = null;
        extraConfig = ''
    structuredExtraConfig = {
                CRASH_DUMP y
      CRASH_DUMP = lib.kernel.yes;
                DEBUG_INFO y
      DEBUG_INFO = lib.kernel.yes;
                PROC_VMCORE y
      PROC_VMCORE = lib.kernel.yes;
                LOCKUP_DETECTOR y
      LOCKUP_DETECTOR = lib.kernel.yes;
                HARDLOCKUP_DETECTOR y
      HARDLOCKUP_DETECTOR = lib.kernel.yes;
              '';
    };
        } ];
  } ];
}
}
</syntaxhighlight>
</syntaxhighlight>


Another way is to create a overlay to configure either {{ic|extraConfig}} or {{ic|structuredExtraConfig}}. This allows for more flexibility, since you can basically override any available kernel option<ref>[https://github.com/NixOS/nixpkgs/blob/e6db435973160591fe7348876a5567c729495175/pkgs/os-specific/linux/kernel/generic.nix#L11-L56<tt>pkgs/os-specific/linux/kernel/generic.nix#L11-L56</tt>]</ref>. Using {{ic|structuredExtraConfig}} is recommended as it checks if the configured option are correct. You may also want to set {{ic|ignoreConfigErrors}} to avoid {{ic|error: unused option}} during builds.
Alternatively, you can pass a string as <code>extraConfig</code>, with option names and answers formatted like so:
 
<pre>
CRASH_DUMP y
DEBUG_INFO y
PROC_VMCORE y
LOCKUP_DETECTOR y
HARDLOCKUP_DETECTOR y
</pre>
 
Another way is to create an overlay to configure either {{ic|extraConfig}} or {{ic|structuredExtraConfig}}. This allows for more flexibility, since you can basically override any available kernel option<ref>[https://github.com/NixOS/nixpkgs/blob/e6db435973160591fe7348876a5567c729495175/pkgs/os-specific/linux/kernel/generic.nix#L11-L56<tt>pkgs/os-specific/linux/kernel/generic.nix#L11-L56</tt>]</ref>. Using {{ic|structuredExtraConfig}} is recommended as it checks if the configured option are correct.


{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{{file|/etc/nixos/configuration.nix|nix|<nowiki>
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     overlays = [
     overlays = [
       (self: super: {
       (self: super: {
         linuxZenWMuQSS = pkgs.linuxPackagesFor (pkgs.linux_zen.kernel.override {
         linuxZenWMuQSS = pkgs.linuxPackagesFor (pkgs.linuxKernel.kernels.linux_zen.override {
           structuredExtraConfig = with lib.kernel; {
           structuredExtraConfig = with lib.kernel; {
             SCHED_MUQSS = yes;
             SCHED_MUQSS = yes;
           };
           };
           ignoreConfigErrors = true;
           ignoreConfigErrors = true; # not necessarily a good idea
         });
         });
       })
       })
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}
}
</nowiki>}}
</nowiki>}}
If the kernel config fails to build with messages like <code>error: unused option: DRM_I915_GVT</code>, try setting e.g. <code>DRM_I915_GVT = lib.kernel.unset</code>. Setting {{ic|ignoreConfigErrors}} will also silence these errors, at the cost of ignoring potential problems. ([https://github.com/NixOS/nixpkgs/blob/3ab9a9d12ba76f6a544c207e1364da5b3087b77c/pkgs/os-specific/linux/kernel/generate-config.pl generate-config.pl] is responsible for these; they are often produced when [https://github.com/NixOS/nixpkgs/blob/3ab9a9d12ba76f6a544c207e1364da5b3087b77c/pkgs/os-specific/linux/kernel/common-config.nix the default config] doesn't use <code>lib.kernel.option</code> for an option that is implicitly disabled by whatever change you made.)


=== Pinning a kernel version ===
=== Pinning a kernel version ===
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{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{
{
   boot.kernelPackages = pkgs.linuxPackagesFor (pkgs.linux_4_19.override {
   boot.kernelPackages = pkgs.linuxPackagesFor (pkgs.linuxKernel.kernels.linux_4_19.override {
     argsOverride = rec {
     argsOverride = rec {
       src = pkgs.fetchurl {
       src = pkgs.fetchurl {
             url = "mirror://kernel/linux/kernel/v4.x/linux-${version}.tar.xz";
             url = "mirror://kernel/linux/kernel/v${lib.versions.major version}.x/linux-${version}.tar.xz";
             sha256 = "0ibayrvrnw2lw7si78vdqnr20mm1d3z0g6a0ykndvgn5vdax5x9a";
             sha256 = "0ibayrvrnw2lw7si78vdqnr20mm1d3z0g6a0ykndvgn5vdax5x9a";
       };
       };
       version = "4.19.60";
       version = "4.19.60";
       modDirVersion = "4.19.60";
       modDirVersion = "4.19.60";
      };
    };
   });
   });
}
}
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   targetPkgs = pkgs: (with pkgs;
   targetPkgs = pkgs: (with pkgs;
     [
     [
       pkgconfig
       pkg-config
       ncurses
       ncurses
       qt5.qtbase
       qt5.qtbase
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== make menuconfig ==
== make menuconfig ==
It is (currently) not possible to run <code>make menuconfig</code> in the checked out linux kernel sources. This is because <code>ncurses</code> is not part of your working environment when you start it with <code>nix-shell '<nixpkgs>' -A linuxPackages.kernel</code>.
It is not possible to run <code>make menuconfig</code> in the standard kernel shell. This is because <code>ncurses</code> is not part of your working environment when you start it with <code>nix-shell '<nixpkgs>' -A linuxPackages.kernel</code>.


This nix-shell hack adds ncurses as a build dependency to the kernel:
Use <code>linuxPackages.kernel.configEnv</code> instead, which adds ncurses as a build dependency to the kernel:
<syntaxHighlight lang=console>
<syntaxHighlight lang=console>
$ nix-shell -E 'with import <nixpkgs> {}; linux.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkg-config ncurses ];})'
$ nix-shell '<nixpkgs>' -A linuxPackages.kernel.configEnv
[nix-shell] $ unpackPhase && cd linux-*
[nix-shell] $ unpackPhase && cd linux-*
[nix-shell] $ patchPhase
[nix-shell] $ patchPhase
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=== Packaging out-of-tree kernel modules ===
=== Packaging out-of-tree kernel modules ===
There are a couple of steps that you will most likely need to do a couple of things. Here is an annotated example:
There are a couple of steps that you will most likely need to do a couple of things. Here is an annotated example:
<syntaxHighlight lang=nix>
<syntaxhighlight lang="nix">
{ stdenv, lib, fetchFromGitHub, kernel, kmod }:
{ stdenv, lib, fetchFromGitHub, kernel, kernelModuleMakeFlags, kmod }:


stdenv.mkDerivation rec {
stdenv.mkDerivation rec {
   name = "v4l2loopback-dc-${version}-${kernel.version}";
   pname = "v4l2loopback-dc";
   version = "1.6";
   version = "1.6";


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   nativeBuildInputs = kernel.moduleBuildDependencies;                      # 2
   nativeBuildInputs = kernel.moduleBuildDependencies;                      # 2


   makeFlags = [
   makeFlags = kernelModuleMakeFlags ++ [
     "KERNELRELEASE=${kernel.modDirVersion}"                                # 3
     "KERNELRELEASE=${kernel.modDirVersion}"                                # 3
     "KERNEL_DIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"    # 4
     "KERNEL_DIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"    # 4
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   };
   };
}
}
</syntaxHighlight>
</syntaxhighlight>


1. For kernel modules it is necessary to disable <code>pic</code> in compiler hardenings as the kernel need different compiler flags.
1. For kernel modules it is necessary to disable <code>pic</code> in compiler hardenings as the kernel need different compiler flags.
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=== Developing out-of-tree kernel modules ===
=== Developing out-of-tree kernel modules ===
See also:  {{manual:nixos|sec=#sec-linux-config-developing-modules|chapter=12.2. Developing kernel modules}}
See also:  {{Nixpkgs Manual|name=Nixpkgs Manual, Developing kernel modules|anchor=#sec-linux-kernel-developing-modules}}


If you work on an out-of-tree kernel module the workflow could look as follow:
If you work on an out-of-tree kernel module the workflow could look as follow:
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and the module will be automatically loaded after a reboot. If you want instead to load it at stage 1 (before the root is even mounted), you need to add it to <code>boot.initrd.availableKernelModules</code> and <code>boot.initrd.kernelModules</code>.
and the module will be automatically loaded after a reboot. If you want instead to load it at stage 1 (before the root is even mounted), you need to add it to <code>boot.initrd.availableKernelModules</code> and <code>boot.initrd.kernelModules</code>.


Note that if you don't reboot, you can still load manually the module using <code>modprobe yourmodulename></code>, and to automatically enable a module during configuration switch/reboot, you can put <code>modprobe yourmodulename || true</code> inside the script of a systemctl service (it is for example what does wireguard).
Note that if you don't reboot, you can still load manually the module using <code>modprobe <yourmodulename></code>, and to automatically enable a module during configuration switch/reboot, you can put <code>modprobe yourmodulename || true</code> inside the script of a systemctl service (it is for example what does wireguard).


Finally, if you want to define some options by default (used when you load manually a module using <code>modprobe</code>, or when the system boots), you can specify them in:
Finally, if you want to define some options by default (used when you load manually a module using <code>modprobe</code>, or when the system boots), you can specify them in:
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     }))
     }))
   ];
   ];
}
</syntaxhighlight>
== Sysctls ==
Example of configuring kernel sysctls:
<syntaxhighlight lang="nix">
{
  boot.kernel.sysctl."net.ipv4.tcp_ecn" = 1;
}
</syntaxhighlight>
== Sysfs ==
Example of configuring kernel sysfs:
<syntaxhighlight lang="nix">
{
  boot.kernel.sysfs = {
    kernel.mm.transparent_hugepage = {
      enabled = "always";
      defrag = "defer";
      shmem_enabled = "within_size";
    };
  };
}
}
</syntaxhighlight>
</syntaxhighlight>
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=== Build fails ===
=== Build fails ===
==== Too high ram usage ====
==== Too high ram usage ====
turn off `DEBUG_INFO_BTF`
turn off <code>DEBUG_INFO_BTF</code>


== See also ==
== See also ==
Retrieved from "https://wiki.nixos.org/wiki/Linux_kernel"