Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

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

On Wed, Oct 03, 2012 at 03:23:27PM -0700, Eric W. Biederman wrote:
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:
> 
> > On Wed, Oct 03, 2012 at 11:43:32AM -0700, Kees Cook wrote:
> >> On Wed, Oct 3, 2012 at 9:47 AM, Paul E. McKenney
> >> <paulmck@linux.vnet.ibm.com> wrote:
> >> > On Wed, Oct 03, 2012 at 09:17:02AM -0700, Greg Kroah-Hartman wrote:
> >> >> On Wed, Oct 03, 2012 at 06:25:38AM -0700, Paul E. McKenney wrote:
> >> >> > On Tue, Oct 02, 2012 at 12:50:42PM -0700, Kees Cook wrote:
> >> >> > > This config item has not carried much meaning for a while now and is
> >> >> > > almost always enabled by default. As agreed during the Linux kernel
> >> >> > > summit, it should be removed. As a first step, remove it from being
> >> >> > > listed, and default it to on. Once it has been removed from all
> >> >> > > subsystem Kconfigs, it will be dropped entirely.
> >> >> > >
> >> >> > > CC: Greg KH <gregkh@linuxfoundation.org>
> >> >> > > CC: "Eric W. Biederman" <ebiederm@xmission.com>
> >> >> > > CC: Serge Hallyn <serge.hallyn@canonical.com>
> >> >> > > CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >> >> > > CC: Andrew Morton <akpm@linux-foundation.org>
> >> >> > > CC: Frederic Weisbecker <fweisbec@gmail.com>
> >> >> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >> >> > > ---
> >> >> > >
> >> >> > > This is the first of a series of 202 patches removing EXPERIMENTAL from
> >> >> > > all the Kconfigs in the tree. Should I send them all to lkml (with all
> >> >> > > the associated CCs), or do people want to cherry-pick changes from my
> >> >> > > tree? I don't want to needlessly flood the list.
> >> >> > >
> >> >> > > http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/experimental
> >> >> > >
> >> >> > > I figure this patch can stand alone to at least make EXPERIMENTAL go
> >> >> > > away from the menus, and give us a taste of what the removal would do
> >> >> > > to builds.
> >> >> >
> >> >> > OK, I will bite...  How should I flag an option that is initially only
> >> >> > intended for those willing to take some level of risk?
> >> >>
> >> >> In the text say "You really don't want to enable this option, use at
> >> >> your own risk!"  Or something like that :)
> >> >
> >> > OK, so the only real hope for experimental features is to refrain from
> >> > creating a config option for them, so that people wishing to use them
> >> > must modify the code?  Or is the philosophy that we keep things out of
> >> > tree until we are comfortable with distros turning them on?
> >> 
> >> I would expect a simple addition of "this is dangerous/buggy" to the
> >> description and "default n" is likely the way to go for that kind of
> >> thing. I think the history of CONFIG_EXPERIMENTAL has proven there
> >> isn't a sensible way to create a global flag for this kind of thing.
> >> To paraphrase Serge: my experimental options are not your experimental
> >> options.
> >
> > That has not proven sufficient for me in the past, RCU_FAST_NO_HZ
> > being a case in point.
> 
> One option that does work is to add a negative Kconfig dependency such
> as "depends on EXT4 = n".  Where what you depend on is something that
> distros want.
> 
> Where I had a legitimate reason to do that with the user namespace
> (aka the code that had not been converted did not compile and was not
> safe to use) it worked very well in keeping distros from getting ahead
> of them selves, and likewise it works very well for ensuring it got
> itself removed as ultimately you want to the two kconfig options to work
> together.

Cute!  ;-)

> >> For example, some of the things that already had the experimental
> >> config removed, they left the "(EXPERIMENTAL)" in their config title.
> >
> > Or I could just make it splat at boot time.  ;-)
> 
> Yes.  Treating a truly experimental feature like a deprecated feature
> and complaining to the world also seems reasonable, and it seems like
> something that would ultimatley get removed as well.

Either removed or fixed, as the case may be.

							Thanx, Paul