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kernel.nix
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kernel.nix
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{ config, lib, pkgs, ... }:
with lib;
let
inherit (config.boot) kernelPatches;
inherit (config.boot.kernel) features randstructSeed;
inherit (config.boot.kernelPackages) kernel;
kernelModulesConf = pkgs.writeText "nixos.conf"
''
${concatStringsSep "\n" config.boot.kernelModules}
'';
in
{
###### interface
options = {
boot.kernel.enable = mkEnableOption "the Linux kernel. This is useful for systemd-like containers which do not require a kernel" // {
default = true;
};
boot.kernel.features = mkOption {
default = {};
example = literalExpression "{ debug = true; }";
internal = true;
description = ''
This option allows to enable or disable certain kernel features.
It's not API, because it's about kernel feature sets, that
make sense for specific use cases. Mostly along with programs,
which would have separate nixos options.
`grep features pkgs/os-specific/linux/kernel/common-config.nix`
'';
};
boot.kernelPackages = mkOption {
default = pkgs.linuxPackages;
type = types.raw;
apply = kernelPackages: kernelPackages.extend (self: super: {
kernel = super.kernel.override (originalArgs: {
inherit randstructSeed;
kernelPatches = (originalArgs.kernelPatches or []) ++ kernelPatches;
features = lib.recursiveUpdate super.kernel.features features;
});
});
# We don't want to evaluate all of linuxPackages for the manual
# - some of it might not even evaluate correctly.
defaultText = literalExpression "pkgs.linuxPackages";
example = literalExpression "pkgs.linuxKernel.packages.linux_5_10";
description = ''
This option allows you to override the Linux kernel used by
NixOS. Since things like external kernel module packages are
tied to the kernel you're using, it also overrides those.
This option is a function that takes Nixpkgs as an argument
(as a convenience), and returns an attribute set containing at
the very least an attribute {var}`kernel`.
Additional attributes may be needed depending on your
configuration. For instance, if you use the NVIDIA X driver,
then it also needs to contain an attribute
{var}`nvidia_x11`.
Please note that we strictly support kernel versions that are
maintained by the Linux developers only. More information on the
availability of kernel versions is documented
[in the Linux section of the manual](https://nixos.org/manual/nixos/unstable/index.html#sec-kernel-config).
'';
};
boot.kernelPatches = mkOption {
type = types.listOf types.attrs;
default = [];
example = literalExpression ''
[
{
name = "foo";
patch = ./foo.patch;
extraStructuredConfig.FOO = lib.kernel.yes;
features.foo = true;
}
{
name = "foo-ml-mbox";
patch = (fetchurl {
url = "https://lore.kernel.org/lkml/19700205182810.58382-1-email@domain/t.mbox.gz";
hash = "sha256-...";
});
}
]
'';
description = ''
A list of additional patches to apply to the kernel.
Every item should be an attribute set with the following attributes:
```nix
{
name = "foo"; # descriptive name, required
patch = ./foo.patch; # path or derivation that contains the patch source
# (required, but can be null if only config changes
# are needed)
extraStructuredConfig = { # attrset of extra configuration parameters without the CONFIG_ prefix
FOO = lib.kernel.yes; # (optional)
}; # values should generally be lib.kernel.yes,
# lib.kernel.no or lib.kernel.module
features = { # attrset of extra "features" the kernel is considered to have
foo = true; # (may be checked by other NixOS modules, optional)
};
extraConfig = "FOO y"; # extra configuration options in string form without the CONFIG_ prefix
# (optional, multiple lines allowed to specify multiple options)
# (deprecated, use extraStructuredConfig instead)
}
```
There's a small set of existing kernel patches in Nixpkgs, available as `pkgs.kernelPatches`,
that follow this format and can be used directly.
'';
};
boot.kernel.randstructSeed = mkOption {
type = types.str;
default = "";
example = "my secret seed";
description = ''
Provides a custom seed for the {var}`RANDSTRUCT` security
option of the Linux kernel. Note that {var}`RANDSTRUCT` is
only enabled in NixOS hardened kernels. Using a custom seed requires
building the kernel and dependent packages locally, since this
customization happens at build time.
'';
};
boot.kernelParams = mkOption {
type = types.listOf (types.strMatching ''([^"[:space:]]|"[^"]*")+'' // {
name = "kernelParam";
description = "string, with spaces inside double quotes";
});
default = [ ];
description = "Parameters added to the kernel command line.";
};
boot.consoleLogLevel = mkOption {
type = types.int;
default = 4;
description = ''
The kernel console `loglevel`. All Kernel Messages with a log level smaller
than this setting will be printed to the console.
'';
};
boot.vesa = mkOption {
type = types.bool;
default = false;
description = ''
(Deprecated) This option, if set, activates the VESA 800x600 video
mode on boot and disables kernel modesetting. It is equivalent to
specifying `[ "vga=0x317" "nomodeset" ]` in the
{option}`boot.kernelParams` option. This option is
deprecated as of 2020: Xorg now works better with modesetting, and
you might want a different VESA vga setting, anyway.
'';
};
boot.extraModulePackages = mkOption {
type = types.listOf types.package;
default = [];
example = literalExpression "[ config.boot.kernelPackages.nvidia_x11 ]";
description = "A list of additional packages supplying kernel modules.";
};
boot.kernelModules = mkOption {
type = types.listOf types.str;
default = [];
description = ''
The set of kernel modules to be loaded in the second stage of
the boot process. Note that modules that are needed to
mount the root file system should be added to
{option}`boot.initrd.availableKernelModules` or
{option}`boot.initrd.kernelModules`.
'';
};
boot.initrd.availableKernelModules = mkOption {
type = types.listOf types.str;
default = [];
example = [ "sata_nv" "ext3" ];
description = ''
The set of kernel modules in the initial ramdisk used during the
boot process. This set must include all modules necessary for
mounting the root device. That is, it should include modules
for the physical device (e.g., SCSI drivers) and for the file
system (e.g., ext3). The set specified here is automatically
closed under the module dependency relation, i.e., all
dependencies of the modules list here are included
automatically. The modules listed here are available in the
initrd, but are only loaded on demand (e.g., the ext3 module is
loaded automatically when an ext3 filesystem is mounted, and
modules for PCI devices are loaded when they match the PCI ID
of a device in your system). To force a module to be loaded,
include it in {option}`boot.initrd.kernelModules`.
'';
};
boot.initrd.kernelModules = mkOption {
type = types.listOf types.str;
default = [];
description = "List of modules that are always loaded by the initrd.";
};
boot.initrd.includeDefaultModules = mkOption {
type = types.bool;
default = true;
description = ''
This option, if set, adds a collection of default kernel modules
to {option}`boot.initrd.availableKernelModules` and
{option}`boot.initrd.kernelModules`.
'';
};
system.modulesTree = mkOption {
type = types.listOf types.path;
internal = true;
default = [];
description = ''
Tree of kernel modules. This includes the kernel, plus modules
built outside of the kernel. Combine these into a single tree of
symlinks because modprobe only supports one directory.
'';
# Convert the list of path to only one path.
apply = let
kernel-name = config.boot.kernelPackages.kernel.name or "kernel";
in modules: (pkgs.aggregateModules modules).override { name = kernel-name + "-modules"; };
};
system.requiredKernelConfig = mkOption {
default = [];
example = literalExpression ''
with config.lib.kernelConfig; [
(isYes "MODULES")
(isEnabled "FB_CON_DECOR")
(isEnabled "BLK_DEV_INITRD")
]
'';
internal = true;
type = types.listOf types.attrs;
description = ''
This option allows modules to specify the kernel config options that
must be set (or unset) for the module to work. Please use the
lib.kernelConfig functions to build list elements.
'';
};
};
###### implementation
config = mkMerge
[ (mkIf config.boot.initrd.enable {
boot.initrd.availableKernelModules =
optionals config.boot.initrd.includeDefaultModules ([
# Note: most of these (especially the SATA/PATA modules)
# shouldn't be included by default since nixos-generate-config
# detects them, but I'm keeping them for now for backwards
# compatibility.
# Some SATA/PATA stuff.
"ahci"
"sata_nv"
"sata_via"
"sata_sis"
"sata_uli"
"ata_piix"
"pata_marvell"
# NVMe
"nvme"
# Standard SCSI stuff.
"sd_mod"
"sr_mod"
# SD cards and internal eMMC drives.
"mmc_block"
# Support USB keyboards, in case the boot fails and we only have
# a USB keyboard, or for LUKS passphrase prompt.
"uhci_hcd"
"ehci_hcd"
"ehci_pci"
"ohci_hcd"
"ohci_pci"
"xhci_hcd"
"xhci_pci"
"usbhid"
"hid_generic" "hid_lenovo" "hid_apple" "hid_roccat"
"hid_logitech_hidpp" "hid_logitech_dj" "hid_microsoft" "hid_cherry"
"hid_corsair"
] ++ optionals pkgs.stdenv.hostPlatform.isx86 [
# Misc. x86 keyboard stuff.
"pcips2" "atkbd" "i8042"
# x86 RTC needed by the stage 2 init script.
"rtc_cmos"
]);
boot.initrd.kernelModules =
optionals config.boot.initrd.includeDefaultModules [
# For LVM.
"dm_mod"
];
})
(mkIf config.boot.kernel.enable {
system.build = { inherit kernel; };
system.modulesTree = [ kernel ] ++ config.boot.extraModulePackages;
# Not required for, e.g., containers as they don't have their own kernel or initrd.
# They boot directly into stage 2.
system.systemBuilderArgs.kernelParams = config.boot.kernelParams;
system.systemBuilderCommands =
let
kernelPath = "${config.boot.kernelPackages.kernel}/" +
"${config.system.boot.loader.kernelFile}";
initrdPath = "${config.system.build.initialRamdisk}/" +
"${config.system.boot.loader.initrdFile}";
in
''
if [ ! -f ${kernelPath} ]; then
echo "The bootloader cannot find the proper kernel image."
echo "(Expecting ${kernelPath})"
false
fi
ln -s ${kernelPath} $out/kernel
ln -s ${config.system.modulesTree} $out/kernel-modules
${optionalString (config.hardware.deviceTree.package != null) ''
ln -s ${config.hardware.deviceTree.package} $out/dtbs
''}
echo -n "$kernelParams" > $out/kernel-params
ln -s ${initrdPath} $out/initrd
ln -s ${config.system.build.initialRamdiskSecretAppender}/bin/append-initrd-secrets $out
ln -s ${config.hardware.firmware}/lib/firmware $out/firmware
'';
# Implement consoleLogLevel both in early boot and using sysctl
# (so you don't need to reboot to have changes take effect).
boot.kernelParams =
[ "loglevel=${toString config.boot.consoleLogLevel}" ] ++
optionals config.boot.vesa [ "vga=0x317" "nomodeset" ];
boot.kernel.sysctl."kernel.printk" = mkDefault config.boot.consoleLogLevel;
boot.kernelModules = [ "loop" "atkbd" ];
# Create /etc/modules-load.d/nixos.conf, which is read by
# systemd-modules-load.service to load required kernel modules.
environment.etc =
{ "modules-load.d/nixos.conf".source = kernelModulesConf;
};
systemd.services.systemd-modules-load =
{ wantedBy = [ "multi-user.target" ];
restartTriggers = [ kernelModulesConf ];
serviceConfig =
{ # Ignore failed module loads. Typically some of the
# modules in ‘boot.kernelModules’ are "nice to have but
# not required" (e.g. acpi-cpufreq), so we don't want to
# barf on those.
SuccessExitStatus = "0 1";
};
};
lib.kernelConfig = {
isYes = option: {
assertion = config: config.isYes option;
message = "CONFIG_${option} is not yes!";
configLine = "CONFIG_${option}=y";
};
isNo = option: {
assertion = config: config.isNo option;
message = "CONFIG_${option} is not no!";
configLine = "CONFIG_${option}=n";
};
isModule = option: {
assertion = config: config.isModule option;
message = "CONFIG_${option} is not built as a module!";
configLine = "CONFIG_${option}=m";
};
### Usually you will just want to use these two
# True if yes or module
isEnabled = option: {
assertion = config: config.isEnabled option;
message = "CONFIG_${option} is not enabled!";
configLine = "CONFIG_${option}=y";
};
# True if no or omitted
isDisabled = option: {
assertion = config: config.isDisabled option;
message = "CONFIG_${option} is not disabled!";
configLine = "CONFIG_${option}=n";
};
};
# The config options that all modules can depend upon
system.requiredKernelConfig = with config.lib.kernelConfig;
[
# !!! Should this really be needed?
(isYes "MODULES")
(isYes "BINFMT_ELF")
] ++ (optional (randstructSeed != "") (isYes "GCC_PLUGIN_RANDSTRUCT"));
# nixpkgs kernels are assumed to have all required features
assertions = if config.boot.kernelPackages.kernel ? features then [] else
let cfg = config.boot.kernelPackages.kernel.config; in map (attrs:
{ assertion = attrs.assertion cfg; inherit (attrs) message; }
) config.system.requiredKernelConfig;
})
];
}