linux-kernel - Re: [Xen-devel] [PATCH] xen: remove unused Kconfig parameter

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Date:	Thu, 11 Jul 2013 10:57:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Paul Bolle <pebolle@...cali.nl>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Borislav Petkov <bp@...en8.de>, Matt Wilson <msw@...zon.com>,
	Michael Opdenacker <michael.opdenacker@...e-electrons.com>,
	jeremy@...p.org, xen-devel@...ts.xensource.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de
Subject: Re: [Xen-devel] [PATCH] xen: remove unused Kconfig parameter

On 07/11/2013 03:08 AM, Paul Bolle wrote:
> On Mon, 2013-07-08 at 20:26 -0400, Konrad Rzeszutek Wilk wrote:
>> Could you explain to me please why the check in the scripts is
>> superfluous?
> 
> The discussion has since moved on a bit, but I haven't answered this
> question yet.
> 
> The check grub2 currently performs in one of its configuration scripts
> is (reformatted):
>     if (grep -qx "CONFIG_XEN_DOM0=y" "${config}" 2> /dev/null ||
>         grep -qx "CONFIG_XEN_PRIVILEGED_GUEST=y" "${config}" 2> /dev/null);
>     then echo -n "$i " ;
>     fi
> 

If only grep supported looking for more than one string at a time.
Maybe we could construct some kind of pattern expression syntax for it,
perhaps based on the theory of regular languages?

> But the Kconfig entry for XEN_PRIVILEGED_GUEST reads: 
>     # Dummy symbol since people have come to rely on the PRIVILEGED_GUEST
>     # name in tools.
>     config XEN_PRIVILEGED_GUEST
>             def_bool XEN_DOM0
> 
> In other words: CONFIG_XEN_PRIVILEGED_GUEST should always be equal to
> CONFIG_XEN_DOM0. So the two grep commands should always both evaluate to
> true or both evaluate to false. One of these two commands can safely be
> dropped.

Not necessarily true across kernel versions.

> Another consequence is that dropping XEN_PRIVILEGED_GUEST doesn't break
> this configuration script. It will still behave as it does now.
> 
> (Whether that script should grep for Kconfig macros in the first place
> is another discussion.)

"Hell no".

	-hpa

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