[linux-yocto] Fwd: [RFC] Simplifying kernel configuration for distro issues

[Bruce Ashfield]

Something to watch/participate in. While not a replacement for
fragments, it would be something reasonable to generate / wrap
where appropriate.

Cheers,

Bruce

---------- Forwarded message ----------
From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Fri, Jul 13, 2012 at 4:37 PM
Subject: [RFC] Simplifying kernel configuration for distro issues
To: Dave Jones <davej at redhat.com>, Greg Kroah-Hartman
<greg at kroah.com>, Ubuntu Kernel Team <kernel-team at lists.ubuntu.com>,
Debian Kernel Team <debian-kernel at lists.debian.org>, OpenSUSE Kernel
Team <opensuse-kernel at opensuse.org>
Cc: Linux Kernel Mailing List <linux-kernel at vger.kernel.org>


So this has long been one of my pet configuration peeves: as a user I
am perfectly happy answering the questions about what kinds of
hardware I want the kernel to support (I kind of know that), but many
of the "support infrastructure" questions are very opaque, and I have
no idea which of the them any particular distribution actually depends
on.

And it tends to change over time. For example, F14 (iirc) started
using TMPFS and TMPFS_POSIX_ACL/XATTR for /dev. And starting in F16,
the initrd setup requires DEVTMPFS and DEVTMPFS_MOUNT. There's been
several times when I started with my old minimal config, and the
resulting kernel would boot, but something wouldn't quite work right,
and it can be very subtle indeed.

Similarly, the distro ends up having very particular requirements for
exactly *which* security models it uses and needs, and they tend to
change over time. And now with systemd, CGROUPS suddenly aren't just
esoteric things that no normal person would want to use, but are used
for basic infrastructure. And I remember being surprised by OpenSUSE
suddenly needing the RAW table support for netfilter, because it had a
NOTRACK rule or something.

The point I'm slowly getting to is that I would actually love to have
*distro* Kconfig-files, where the distribution would be able to say
"These are the minimums I *require* to work". So we'd have a "Distro"
submenu, where you could pick the distro(s) you use, and then pick
which release, and we'd have something like

  - distro/Kconfig:

     config DISTRO_REQUIREMENTS
         bool "Pick minimal distribution requirements"

     choice DISTRO
         prompt "Distribution"
         depends on DISTRO_REQUIREMENTS

     config FEDORA
     config OPENSUSE
     config UBUNTU
     ...

     endchoice

and then depending on the DISTRO config, we'd include one of the
distro-specific ones with lists of supported distro versions and then
the random config settings for that version:

  - distro/Kconfig.suse:

     config OPENSUSE_121
         select OPENSUSE_11
         select IP_NF_RAW  # ..

  - distro/Kconfig.Fedora:

     config FEDORA_16
         select FEDORA_15
         select DEVTMPFS               # F16 initrd needs this
         select DEVTMPFS_MOUNT  # .. and expects the kernel to mount
DEVTMPFS automatically
         ...

     config FEDORA_17
         select FEDORA_16
         select CGROUP_xyzzy
         ...

and the point would be that it would make it much easier for a normal
user (and quite frankly, I want to put myself in that group too) to
make a kernel config that "just works".

Sure, you can copy the config file that came with the distro, but it
has tons of stuff that really isn't required. Not just in hardware,
but all the debug choices etc that are really a user choice. And it's
really hard to figure out - even for somebody like me - what a minimal
usable kernel is.

And yes, I know about "make localmodconfig". That's missing the point
for the same reason the distro config is missing the point.

Comments? It doesn't have to start out perfect, but I think it would
*really* help make the kernel configuration much easier for people.

In addition to the "minimal distro settings", we might also have a few
"common platform" settings, so that you could basically do a "hey, I
have a modern PC laptop, make it pick the obvious stuff that a normal
person needs, like USB storage, FAT/VFAT support, the core power
management etc". The silly stuff that you need, and that
"localyesconfig" actually misses because if you haven't inserted a USB
thumb drive, you won't necessarily have the FAT module loaded, but we
all know you do want it in real life. But that's really independent
issue, so let's keep it to just distro core things at first, ok?

Would something like this make sense to people? I really think that
"How do I generate a kernel config file" is one of those things that
keeps normal people from compiling their own kernel. And we *want*
people to compile their own kernel so that they can help with things
like bisecting etc. The more, the merrier.

                     Linus
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