[arch-general] Kernel PKGBUILD proposition: Ease custom kernel compilation.

[Nicolas Bigaouette]

Hi all!

Since a couple of years of using Arch, I often wanted to compile a custom
kernel, as many others did. There is many, many, many! forum threads about
that, a couple of wiki pages too, with questions and howtos.

Many efforts has been put to create new PKGBUILDs[1-2] to ease the effort of
this. Unfortunately, these PKGBUILDs suffer from some drawback:
1) They are placed on a wiki which can be edited by everybody. This mean it
is not a trusted place to store a PKGBUILD, specifically one as vital as the
kernel's.
2) They tend to be forgotten and not updated anymore. This can lead to an
unbootable kernel, rendering all this useless.
3) They do not take advantage of the devs' work: They are the best one to
trust for a quality PKGBUILD. They also have all the feedback from Arch
users, bug reports, etc. They know what has changed in the kernel and what
needs to be adapted for the installation, for example new "provides=()". A
PKGBUILD from a wiki page or a forum post might be good at the time of post,
but be outdated just days latter...
4) They build a kernel which is way different then the stock one, for
example because they don't have the same patchset.

Users most often wants to build a custom kernel just to try it, change some
configurations, add one or two patch, optimize for their own machines, etc.
Maily, they just want to take the existing one, change a couple of things,
and be ready. One also wants to install this kernel side by side with the
stock one, at least until his own kernel is stabilized and running as
wanted. Actually, Arch's stock kernel does not allow that.

What I propose is some simple modifications to the PKGBUILD so users can try
to compile their own kernel based on the original, trusted, working and
approved one. With theese modifications, one only needs to add a "kernel
name" to the pkgname: "pkgname=kernel26-mykernel" for example. Nothing else
is needed to compile a custom kernel. The created package would sit without
problem side by side with the stock kernel. Also, if the pkgname is kept to
"kernel26", then the stock -ARCH kernel will be built.

This approach has many advatanges:
1) The patch is relativelly small: not much is changed in the original
PKGBUILD.
1) Nothing changes for the devs. They continue to provide a quality kernel
to Arch users.
2) Users who wants to compile a custom kernel can just sync abs, change the
pkgname and install a new kernel, in the KISS philosophy. They know that if
they just change the name, they will have the same package so they can
easily test whatever feature/patch/bug solution/optimization they want.
3) Because one only needs to change the pkgname, they use the devs' high
quality, tried and truth PKGBUILD. When a new kernel is out, they can sync
the devs' modifications easily.
4) Bugs affecting the kernel can be easily tested for solutions. Affected
users just need to compile a "-testing" kernel where a patch is applied,
install it and see if it works, without having to risk breaking his system
by replacing -ARCH kernel with an unbootable one.
5) Better feedback to the devs since the users would be using (almost) the
same PKGBUILD as the original one.
6) Simplify a lot all these "custom kernels" threads and wiki posts.

I did "maintained" such a patch for myself because I wanted to keep in sync
with the original PKGBUILD. After posting it on the forum[3], I got some
positive feedback. People reporting back said they liked the simplicity and
the effectiveness of the method. They also positively tested it with
different configuration. The patch should be applied to revision 19747 for
i686 or 19749 for x86_64. It modifies the PKGBUILD and also slightly the
kernel26.install and kernel26.preset file.

I am thus reporting this to be include in the official file. I think it
would be a great addition to an already great distro. I am open to
discussion on the subject. I hope I am posting this on the right mailing
list and that it can be included! :)

Sincerely,

big_gie

[1] http://wiki.archlinux.org/index.php/Kernel_Compilation_with_ABS
[2] http://wiki.archlinux.org/index.php/Custom_Kernel_Compilation_with_ABS
[3] http://bbs.archlinux.org/viewtopic.php?id=37579
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