linux-kernel - Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

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Message-ID: <20121008010410.GL2485@linux.vnet.ibm.com>
Date:	Sun, 7 Oct 2012 18:04:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Jones <davej@...hat.com>, Dave Airlie <airlied@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Kees Cook <keescook@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

On Sun, Oct 07, 2012 at 04:18:54PM -0400, Dave Jones wrote:
> On Sun, Oct 07, 2012 at 09:30:29AM -0700, Paul E. McKenney wrote:
> 
>  > > I think Kconfig is mostly what distro would like to use the thing is
>  > > the Kconfig text needs to be there upfront when its merged, not two
>  > > months later, since then it too late for a distro to notice.
>  > > 
>  > > I'd bet most distros would read the warnings, but in a lot of cases
>  > > the warning don't exist until its too late.
>  > 
>  > In the case of CONFIG_RCU_USER_QS you are quite right, the warning
>  > should have been there from the beginning and was not.  I suppose you
>  > could argue that the warning was not sufficiently harsh in the case of
>  > CONFIG_RCU_FAST_NO_HZ, but either way it did get ignored:
> 
> Maybe if we had a universally agreed upon tag for kconfig, like
> "distro recommendation: N" that would make things obvious, and also allow
> those of us unfortunate enough to maintain distro kernels to have something
> to easily grep for.  This would also catch the case when you eventually (hopefully)
> flip from an N to a Y.
> 
> There will likely still be some distros that will decide they know better
> (and I'm pretty sure eventually I'll find reason to do so myself), but it at least
> gives the feature maintainer the "I told you so" clause.
> 
> Something we do quite often for our in-development kernels is enable something
> that's shiny, new and unproven, and then when we branch for a release, we turn
> it back off.  It would be great if a lot of this kind of thing could be more automated.

One approach would be to have CONFIG_DISTRO, so that experimental
features could use "depends on !DISTRO", but also to have multiple
"BLEEDING" symbols.  For example, given a CONFIG_DISTRO_BLEEDING_HPC
and CONFIG_DISTRO_BLEEDING_RT, CONFIG_RCU_USER_QS might eventually
use the following clause:

	depends on !DISTRO || DISTRO_BLEEDING_HPC || DISTRO_BLEEDING_RT

A normal distro would define DISTRO, a distro looking to provide bleeding-edge
HPC or real-time features would also define DISTRO_BLEEDING_HPC or
DISTRO_BLEEDING_RT, respectively.

Does that make sense, or am I being overly naive?

							Thanx, Paul

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