Re: [BLOG] custom kernel config

[Marius Bakke <mbakke@fastmail.com>]

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Hi Efraim,

Efraim Flashner <efraim@flashner.co.il> writes:

> I've cleaned up the blog post a bit and run it through a spell checker.
> I'm unsure about Linux-Libre vs linux-libre, regarding talking about the
> kernel and the package. I think I glossed over it well enough that I
> didn't actually get a custom kernel up and running on my laptop, but for
> the purpose of the blog post I don't think it's actually necessary.
>
> -- 
> Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
> GPG key = A28B F40C 3E55 1372 662D  14F7 41AA E7DC CA3D 8351
> Confidentiality cannot be guaranteed on emails sent or received unencrypted
> title: Creating and using a custom Linux kernel on Guix System
> date: 2019-05-20 00:00
> author: Efraim Flashner
> tags: kernel, customization
> ---
>
> Guix is, at its core, a source based distribution with substitutes, and
> as such building packages from their source code is an expected part of
> regular package installations and upgrades.  Given this starting point,
> it makes sense that efforts are made to reduce the amount of time spent
> compiling packages, and recent changes and upgrades to the building and
> distribution of substitutes continues to be a topic of discussion within
> Guix.  One of the packages which I prefer to not build myself is the
> Linux-Libre kernel.  The kernel, while not requiring an overabundance of
> RAM to build, does take a very long time on my build machine (which my
> children argue is actually their Kodi computer), and I will often delay
> reconfiguring my laptop while I want for a substitute to be prepared by
> the official build farm.  The official kernel configuration, as is the
> case with many GNU/Linux distributions, errs on the side of
> inclusiveness, and this is really what causes the build to take such a
> long time when I build the package for myself.
>
> The Linux kernel, however, can also just be described as a package
> installed on my machine, and as such can be customized just like any
> other package.  The procedure is a little bit different, although this
> is primarily due to the nature of how the package definition is written.
>
> The linux-libre kernel package definition is actually a procedure which
> creates a package.
>
> ```scheme
> (define* (make-linux-libre version hash supported-systems
>                            #:key
>                            ;; A function that takes an arch and a variant.
>                            ;; See kernel-config for an example.
>                            (extra-version #f)
>                            (configuration-file #f)
>                            (defconfig "defconfig")
>                            (extra-options %default-extra-linux-options)
>                            (patches (list %boot-logo-patch)))
>   ...)
> ```
>
> The current linux-libre package is for the 5.1.x series, and is
> declared like this:
>
> ```scheme
> (define-public linux-libre
>   (make-linux-libre %linux-libre-version
>                     %linux-libre-hash
>                     '("x86_64-linux" "i686-linux" "armhf-linux" "aarch64-linux")
>                     #:patches %linux-libre-5.1-patches
>                     #:configuration-file kernel-config))
> ```
>
> Any keys which are not assigned values inherit their default value from
> the make-linux-libre definition.  When comparing the two snippets above,
> you may notice that the code comment in the first doesn't actually refer
> to the extra-version keyword; it is actually for configuration-file.
> Because of this, it is not actually easy to include a custom kernel
> configuration from the definition, but don't worry, there are other ways
> to work with what we do have.

Thank you for writing this!  I'm sure many would-be power users are
stymied by the weird Scheme interfaces :-)

I just want to point out an (IMO) easier way to provide a custom kernel
configuration, that does not involve the "make-linux-libre" procedure:

--8<---------------cut here---------------start------------->8---
(define-public linux-libre/custom
  (package
    (inherit linux-libre)
    (native-inputs
     `(("kconfig" ,(local-file "kernel.config"))
       ,@(alist-delete "kconfig"
                       (package-native-inputs linux-libre))))))
--8<---------------cut here---------------end--------------->8---

At the end of the day, Linux-Libre is just a regular package that can be
inherited and overridden like any other :-)

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