linux-kernel - Re: [RFC 1/4] CONFIG

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Message-ID: <46A0A186.4030908@redhat.com>
Date:	Fri, 20 Jul 2007 07:50:30 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Satyam Sharma <satyam.sharma@...il.com>
CC:	"clameter@....com" <clameter@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC 1/4] CONFIG_STABLE: Define it

Satyam Sharma wrote:
> On 7/20/07, Chris Snook <csnook@...hat.com> wrote:
>> Satyam Sharma wrote:
>> > On 7/20/07, Chris Snook <csnook@...hat.com> wrote:
>> >> Satyam Sharma wrote:
>> >> > [ Just cleaning up my inbox, and stumbled across this thread ... ]
>> >> >
>> >> >
>> >> > On 5/31/07, clameter@....com <clameter@....com> wrote:
>> >> >> Introduce CONFIG_STABLE to control checks only useful for 
>> development.
>> >> >>
>> >> >> Signed-off-by: Christoph Lameter <clameter@....com>
>> >> >> [...]
>> >> >>  menu "General setup"
>> >> >>
>> >> >> +config STABLE
>> >> >> +       bool "Stable kernel"
>> >> >> +       help
>> >> >> +         If the kernel is configured to be a stable kernel then
>> >> various
>> >> >> +         checks that are only of interest to kernel development
>> >> will be
>> >> >> +         omitted.
>> >> >> +
>> >> >
>> >> >
>> >> > "A programmer who uses assertions during testing and turns them off
>> >> > during production is like a sailor who wears a life vest while 
>> drilling
>> >> > on shore and takes it off at sea."
>> >> >                                                - Tony Hoare
>> >> >
>> >> >
>> >> > Probably you meant to turn off debug _output_ (and not _checks_)
>> >> > with this config option? But we already have CONFIG_FOO_DEBUG_BAR
>> >> > for those situations ...
>> >>
>> >> There are plenty of validation and debugging features in the kernel
>> >> that go WAY
>> >> beyond mere assertions, often imposing significant overhead
>> >> (particularly when
>> >> you scale up) or creating interfaces you'd never use unless you were
>> >> doing
>> >> kernel development work.  You really do want these features completely
>> >> removed
>> >> from production kernels.
>> >
>> > As for entire such "development/debugging-related features", most (all,
>> > really)
>> > should anyway have their own config options.
>>
>> They do.  With kconfig dependencies, we can ensure that those config 
>> options are
>> off when CONFIG_STABLE is set.  That way you only have to set one 
>> option to
>> ensure that all these expensive checks are disabled.
> 
> Oh, so you mean use this (the negation of this, actually) as a universal
> kconfig dependency of all other such development/debugging related stuff?
> Hmm, the name is quite misleading in that case.

There are many different ways you can use it.  If I'm writing a configurable 
feature, I could make it depend on !CONFIG_STABLE, or I could ifdef my code out 
if CONFIG_STABLE is set, unless a more granular option is also set.  The 
maintainer of the code that uses the config option has a lot of flexibility, at 
least until we start enforcing standards.

	-- Chris
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