Re: [RFC] CONFIG_FORCE_MINIMALLY_SANE_CONFIG=y (was: Re: [RFC PATCH] x86/kconfig: Sanity-check config file during oldconfig)

Ingo Molnar
2016-01-19T08:54:19Z

* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:

> On 2016.01.19 at 09:20 +0100, Ingo Molnar wrote:
> >
> > ( I've Cc:-ed Linus, Greg and Andrew, to see whether doing something like what I
> > suggest below in the x86 architecture would be acceptable. )
> >
> > * Borislav Petkov <bp@suse.de> wrote:
> >
> > > From: Borislav Petkov <bp@suse.de>
> > >
> > > Thomas Voegtle reported that doing oldconfig with a .config which has
> > > CONFIG_MICROCODE enabled but BLK_DEV_INITRD disabled prevents the
> > > microcode loading mechanism from being built.
> > >
> > > Add a short script which hooks into the "make oldconfig" handling and
> > > sanity-checks the config file for that discrepancy. It issues a message
> > > which should hopefully sensitize the user to that issue and point her
> > > into the right direction.
> >
> > So it would be much better to just do such things automatically, and only allow
> > 'safe' combination of options - without the user having to do anything.
> >
> > The guiding principle is: kernel configuration is (still...) our worst barrier of
> > entry for new users/developers, and kernel configuration still sucks very much
> > from a UI point of view.
> >
> > In fact our kernel configuration UI and workflow is still so bad that it's an
> > effort to stay current even with a standalone and working .config, even for
> > experienced kernel developers...
> >
> > Adding a (somewhat hacky) post processing script and forcing users to read
> > something 99% of them does not have a clue about is a step in the wrong direction,
> > IMHO.
> >
> > So can we do something more intelligent instead, such as modifying the Kconfigs in
> > a way that it's not possible to have CONFIG_MICROCODE enabled while BLK_DEV_INITRD
> > is disabled?
> >
> > I'd be fine with a 'select BLK_DEV_INITRD' for example. If people doing super
> > specialized setups disagree because they really need that nonsensical combination
> > of config options, they can complain and provide a better solution.
> >
> > In fact on x86 I'd suggest we go farther than that and add a core set of selects
> > that can be disabled only through a sufficiently scary "I really know I'm doing
> > something utmost weird" (and default disabled) config option.
>
> This is essential. Because, believe it or not, there are still users out
> there that don't use systemd. And to force enable totally superfluous
> config options for them would be bad.

Well, I think the argument I raised later on is important:

> > [...] from a usability POV it's _much_ better to have a few more options
> > enabled in a .config of thousands of entries, than to accidentally have the
> > one option not enabled that your user-space somehow critically depends on ...

I.e. the costs of quirks are _massively_ assymetric: having an extra system call
or compat option quirk enabled is essentially unmeasurable for those who don't
technically need them, while it can be a big and hard to debug show-stopper for
others.

'default y' was supposed to cover such cases, but arguably it's too opaque, I
think we need a separate, more obvious layer - such as the
CONFIG_FORCE_MINIMALLY_SANE_CONFIG=y option I suggested.

> So, as long as this "systemd config" could be easily disabled, your approach
> looks fine and would definitely be helpful to many mainstream distro users.

It sure can be easily disabled, that's a given.

The key point is that I'd like "naively configured" kernels to work on just about
any Linux distro that allow kernel testing - so the superset of all quirks should
be included - as long as enabling a quirk does not break things (and none of the
ones I listed do as far as I've tested).

Thanks,

Ingo