Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Mon, Oct 08, 2012 at 03:07:24PM -0700, Kees Cook wrote:
> On Sun, Oct 7, 2012 at 6:04 PM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > 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?
> 
> I think we should avoid any global configs that disable things. We'll
> just end up in the same place with distros again.

So you believe that we should taint the kernel or splat on boot to
warn distros off of features that might not be ready for 100 million
users?  Or do you have some other approach in mind?

							Thanx, Paul