Linux kernel: Difference between revisions

From NixOS Wiki
imported>Mic92
out-of-tree kernel modules
imported>Samueldr
m Adds note about the kernelPatches extraConfig trick.
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[nix-shell] $ make menuconfig
[nix-shell] $ make menuconfig
</syntaxHighlight> (thanks to sphalerite)
</syntaxHighlight> (thanks to sphalerite)
== Adding <code>extraConfig</code> ==
It is sometimes desirable to change the configuration of your kernel, while keeping the kernel version itself managed through nixpkgs. To do so, you can add the configuration to a dummy {{nixos:option|boot.kernelPatches}}<ref>[https://logs.nix.samueldr.com/nixos/2018-05-09#1525898458-1525898534; #nixos 2018-05-09]</ref><ref>[https://github.com/NixOS/nixpkgs/blob/03d4694e6110fa9c16e88ee74085ea2068c27494/nixos/modules/misc/crashdump.nix#L63-L73 <tt>nixos/modules/misc/crashdump.nix#L63-L73</tt>]</ref>, which will then be merged and applied to the current kernel. As with kernel configuration with NixOS, drop the <tt>CONFIG_</tt> from the kernel configuration names.
This example is from the {{nixos:option|boot.crashDump.enable}} option:
<syntaxhighlight lang=nix>
{
      boot.kernelPatches = [ {
        name = "crashdump-config";
        patch = null;
        extraConfig = ''
                CRASH_DUMP y
                DEBUG_INFO y
                PROC_VMCORE y
                LOCKUP_DETECTOR y
                HARDLOCKUP_DETECTOR y
              '';
        } ];
}
</syntaxhighlight>

Revision as of 22:26, 12 May 2018

Configuring the Linux Kernel

see NixOS Manual "Linux Kernel".

Developing Kernel Modules

see NixOS Manual "Developing kernel modules"

If you work on an out-of-tree kernel module the workflow could look as follow:

#include <linux/module.h>
#define MODULE_NAME "hello"
static int __init hello_init(void)
{
    printk(KERN_INFO "hello world!");
    return 0;
}
static void __exit hello_cleanup(void) {}
module_init(hello_init);
module_exit(hello_cleanup);
$ nix-shell '<nixpkgs>' -A linux.dev
$ make -C $(nix-build -E '(import <nixpkgs> {}).linux.dev' --no-out-link)/lib/modules/*/build M=$(pwd) modules
$ insmod ./hello.ko
$ dmesg | grep hello
[   82.027229] hello world!

make menuconfig

It is (currently) not possible to run make menuconfig in the checked out linux kernel sources. This is because ncurses is not part of your working environment when you start it with nix-shell '<nixpkgs>' -A linuxPackages.kernel.

This nix-shell hack adds ncurses as a build dependency to the kernel:

$ nix-shell -E 'with import <nixpkgs> {}; linux.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkgconfig ncurses ];})'
[nix-shell] $ unpackPhase && cd linux-*
[nix-shell] $ make menuconfig

(thanks to sphalerite)

Adding extraConfig

It is sometimes desirable to change the configuration of your kernel, while keeping the kernel version itself managed through nixpkgs. To do so, you can add the configuration to a dummy boot.kernelPatches[1][2], which will then be merged and applied to the current kernel. As with kernel configuration with NixOS, drop the CONFIG_ from the kernel configuration names.

This example is from the boot.crashDump.enable option:

{
      boot.kernelPatches = [ {
        name = "crashdump-config";
        patch = null;
        extraConfig = ''
                CRASH_DUMP y
                DEBUG_INFO y
                PROC_VMCORE y
                LOCKUP_DETECTOR y
                HARDLOCKUP_DETECTOR y
              '';
        } ];
}