1b7e43471f
At this point kernel.features is more of an implementation detail and normal users should not come into contact with it.
113 lines
5.2 KiB
Markdown
113 lines
5.2 KiB
Markdown
# Linux kernel {#sec-linux-kernel}
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The Nix expressions to build the Linux kernel are in [`pkgs/os-specific/linux/kernel`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/linux/kernel).
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The function [`pkgs.buildLinux`](https://github.com/NixOS/nixpkgs/blob/d77bda728d5041c1294a68fb25c79e2d161f62b9/pkgs/os-specific/linux/kernel/generic.nix) builds a kernel with [common configuration values](https://github.com/NixOS/nixpkgs/blob/d77bda728d5041c1294a68fb25c79e2d161f62b9/pkgs/os-specific/linux/kernel/common-config.nix).
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This is the preferred option unless you have a very specific use case.
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Most kernels packaged in Nixpkgs are built that way, and it will also generate kernels suitable for NixOS.
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[`pkgs.linuxManualConfig`](https://github.com/NixOS/nixpkgs/blob/d77bda728d5041c1294a68fb25c79e2d161f62b9/pkgs/os-specific/linux/kernel/manual-config.nix) requires a complete configuration to be passed.
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It has fewer additional features than `pkgs.buildLinux`, which provides common configuration values and exposes the `features` attribute, as explained below.
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Both functions have an argument `kernelPatches` which should be a list of `{name, patch, extraConfig}` attribute sets, where `name` is the name of the patch (which is included in the kernel’s `meta.description` attribute), `patch` is the patch itself (possibly compressed), and `extraConfig` (optional) is a string specifying extra options to be concatenated to the kernel configuration file (`.config`).
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The kernel derivation created with `pkgs.buildLinux` exports an attribute `features` specifying whether optional functionality is or isn’t enabled. This is used in NixOS to implement kernel-specific behaviour.
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If you are using a kernel packaged in Nixpkgs, you can customize it by overriding its arguments. For details on how each argument affects the generated kernel, refer to [the `pkgs.buildLinux` source code](https://github.com/NixOS/nixpkgs/blob/d77bda728d5041c1294a68fb25c79e2d161f62b9/pkgs/os-specific/linux/kernel/generic.nix).
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:::{.example #ex-overriding-kernel-derivation}
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# Overriding the kernel derivation
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Assuming you are using the kernel from `pkgs.linux_latest`:
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```nix
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pkgs.linux_latest.override {
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ignoreConfigErrors = true;
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autoModules = false;
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kernelPreferBuiltin = true;
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extraStructuredConfig = with lib.kernel; {
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DEBUG_KERNEL = yes;
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FRAME_POINTER = yes;
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KGDB = yes;
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KGDB_SERIAL_CONSOLE = yes;
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DEBUG_INFO = yes;
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};
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}
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```
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:::
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## Manual kernel configuration {#sec-manual-kernel-configuration}
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Sometimes it may not be desirable to use kernels built with `pkgs.buildLinux`, especially if most of the common configuration has to be altered or disabled to achieve a kernel as expected by the target use case.
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An example of this is building a kernel for use in a VM or micro VM. You can use `pkgs.linuxManualConfig` in these cases. It requires the `src`, `version`, and `configfile` attributes to be specified.
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:::{.example #ex-using-linux-manual-config}
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# Using `pkgs.linuxManualConfig` with a specific source, version, and config file
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```nix
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{ pkgs, ... }: {
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version = "6.1.55";
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src = pkgs.fetchurl {
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url = "https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-${version}.tar.xz";
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hash = "sha256:1h0mzx52q9pvdv7rhnvb8g68i7bnlc9rf8gy9qn4alsxq4g28zm8";
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};
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configfile = ./path_to_config_file;
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linux = pkgs.linuxManualConfig {
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inherit version src configfile;
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allowImportFromDerivation = true;
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};
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}
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```
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If necessary, the version string can be slightly modified to explicitly mark it as a custom version. If you do so, ensure the `modDirVersion` attribute matches the source's version, otherwise the build will fail.
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```nix
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{ pkgs, ... }: {
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version = "6.1.55-custom";
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modDirVersion = "6.1.55";
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src = pkgs.fetchurl {
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url = "https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-${modDirVersion}.tar.xz";
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hash = "sha256:1h0mzx52q9pvdv7rhnvb8g68i7bnlc9rf8gy9qn4alsxq4g28zm8";
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};
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configfile = ./path_to_config_file;
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linux = pkgs.linuxManualConfig {
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inherit version modDirVersion src configfile;
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allowImportFromDerivation = true;
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};
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}
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```
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:::
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Additional attributes can be used with `linuxManualConfig` for further customisation. You're encouraged to read [the `pkgs.linuxManualConfig` source code](https://github.com/NixOS/nixpkgs/blob/d77bda728d5041c1294a68fb25c79e2d161f62b9/pkgs/os-specific/linux/kernel/manual-config.nix) to understand how to use them.
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To edit the `.config` file for Linux X.Y from within Nix, proceed as follows:
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```ShellSession
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$ nix-shell '<nixpkgs>' -A linuxKernel.kernels.linux_X_Y.configEnv
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$ unpackPhase
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$ cd linux-*
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$ make nconfig
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```
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## Developing kernel modules {#sec-linux-kernel-developing-modules}
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When developing kernel modules it's often convenient to run the edit-compile-run loop as quickly as possible.
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See the snippet below as an example.
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:::{.example #ex-edit-compile-run-kernel-modules}
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# Edit-compile-run loop when developing `mellanox` drivers
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```ShellSession
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$ nix-build '<nixpkgs>' -A linuxPackages.kernel.dev
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$ nix-shell '<nixpkgs>' -A linuxPackages.kernel
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$ unpackPhase
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$ cd linux-*
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$ make -C $dev/lib/modules/*/build M=$(pwd)/drivers/net/ethernet/mellanox modules
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# insmod ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko
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```
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:::
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