Linux kernel: Difference between revisions

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imported>Samueldr
m Adds note about the kernelPatches extraConfig trick.
imported>Samueldr
m Adds link to Choose your kernel on NixOS page
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== Configuring the Linux Kernel ==
== Configuring the Linux Kernel ==
see [https://nixos.org/nixos/manual/index.html#sec-kernel-config NixOS Manual "Linux Kernel"].
See:
 
* [https://nixos.org/nixos/manual/index.html#sec-kernel-config NixOS Manual "Linux Kernel"].
* [[Choose your kernel on NixOS]]


== Developing Kernel Modules ==
== Developing Kernel Modules ==
see [https://nixos.org/nixos/manual/index.html#idm140737316413584 NixOS Manual "Developing kernel modules"]
See also: [https://nixos.org/nixos/manual/index.html#idm140737316413584 NixOS Manual "Developing kernel 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:

Revision as of 22:29, 12 May 2018

Configuring the Linux Kernel

See:

Developing Kernel Modules

See also: 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
              '';
        } ];
}