linux-kernel - Re: [PATCH] kconfig: remove EXPERT from CHECKPOINT

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Message-Id: <20180713135541.7ada72437862c32f4563a9a8@linux-foundation.org>
Date:   Fri, 13 Jul 2018 13:55:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     ebiederm@...ssion.com (Eric W. Biederman)
Cc:     Adrian Reber <adrian@...as.de>, linux-kernel@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Andrei Vagin <avagin@...tuozzo.com>,
        Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] kconfig: remove EXPERT from CHECKPOINT_RESTORE

On Thu, 12 Jul 2018 11:33:33 -0500 ebiederm@...ssion.com (Eric W. Biederman) wrote:

> 
> Adrian Reber <adrian@...as.de> writes:
> 
> > The CHECKPOINT_RESTORE configuration option was introduced in 2012 and
> > combined with EXPERT. CHECKPOINT_RESTORE is already enabled in many
> > distribution kernels and also part of the defconfigs of various
> > architectures.
> >
> > To make it easier for distributions to enable CHECKPOINT_RESTORE this
> > removes EXPERT and moves the configuration option out of the EXPERT
> > block.
> 
> I think we should change the help text at the same time, to match
> our improve understanding of the situation.
> 
> Does anyone remember why this option was added at all?

Because at the time it was quite unclear that the overall project would
produce a viable result.  But the code is splattered over so many
places that getting it all going out-of-tree was impractical.  So the
#ifdef CONFIG_CHECKPOINT_RESTORE markers were initially there to a)
identify places where we should go if we decide to rip the whole thing
out and to b) ensure that the kernel would still compile and work OK
after that removal.

This caution eventually proved to be unnecessary.

> Why this option was placed under expert?

Dunno.

> What is the value of disabling this functionality ever?
> 
> Is there any reason why we don't just delete CONFIG_CHECKPOINT_RESTORE
> entirely?

For the vast number of Linux machines which aren't servers?  Check out
some defconfigs - only one of arm's 119 defconfigs selects it.