linux-kernel - Re: CONFIG_HOTPLUG

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Date:	Thu, 30 Aug 2007 13:40:25 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
cc:	Sam Ravnborg <sam@...nborg.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	linux-kernel@...r.kernel.org, kbuild-devel@...ts.sourceforge.net
Subject: Re: CONFIG_HOTPLUG_CPU: kconfig bug?

On Thu, 30 Aug 2007, Roman Zippel wrote:
> 
> > > > > I've noticed an oddity with CONFIG_HOTPLUG_CPU in 2.6.23-rc:
> > > > > make oldconfig seems to turn it on even when nothing wants it,
> > > > > increasing kernel size by about 10k; but if you then edit the
> > > > > line out of .config and make oldconfig again, it correctly
> > > > > offers the choice and lets it be turned off after all.
> 
> It's somewhat a side effect of using select and defaults, the order of the 
> config symbols becomes significant for oldconfig, if you look at the 
> output you'll find:
> 
> Support for suspend on SMP and hot-pluggable CPUs (EXPERIMENTAL) (HOTPLUG_CPU) [Y/?] y
> 
> this sets it to 'y'. In this case one isn't asked about it, because there 
> is only one choice. The patch below avoids the setting of the value here.

Thanks for working that out: your patch certainly works for me,
and would be good to see in 2.6.23, to prevent lots of users getting
an unnecessary CONFIG_HOTPLUG_CPU forever after.  I wonder what config
options this might have forced in the past.

> 
> Avoid setting the value if the symbol doesn't need to be changed or can't 
> be changed. Later choices may change the dependencies and thus the 
> possible input range.
> 
> Signed-off-by: Roman Zippel <zippel@...ux-m68k.org>

But please add a sentence to your patch description, something like:

make oldconfig from a 2.6.22 .config with CONFIG_HOTPLUG_CPU not set
was in some configurations setting CONFIG_HOTPLUG_CPU=y without asking,
even when there was no actual requirement for CONFIG_HOTPLUG_CPU.

Thanks,
Hugh
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