linux-kernel - Re: [PATCH -v5 5/5] Make reboot

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Message-ID: <516F40C5.40409@zytor.com>
Date:	Wed, 17 Apr 2013 17:39:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Robin Holt <holt@....com>
CC:	Ingo Molnar <mingo@...nel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Russ Anderson <rja@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH -v5 5/5] Make reboot_cpuid a kernel parameter.

On 04/17/2013 05:17 PM, Robin Holt wrote:
> 
> There are 4 items being parsed out of reboot= for x86:
>  - reboot_mode		w[arm] | c[old]
>  - reboot_cpu		s[mp]####
>  - reboot_type		b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]
>  - reboot_force		f[orce]
> 
> This seems like a lot to push into the generic kernel just to make it
> appear consistent when there will be no real cross arch consistency.
> 
> Contrast that with:
> 1) New kernel parameter (reboot_cpu) which is clear and concise, uses standard
>    parsing methods.
> 2) Backwards compatibility in that a user with an existing (broken) reboot=s32
>    on the command line will set reboot_cpu unless both were specified, in which
>    case reboot_cpu takes precedence.
> 
> What is so fundamentally wrong with that?  It accomplishes exactly what
> you had asked for in that existing users are not broken.  We are introducing
> a new functionality in the general kernel.  Why not introduce a new parameter
> associated with that functionality.
> 

You are confusing implementation with interface.  That is what is so
fundamentally wrong with that.  You really, really don't want to change
interface unless the world will end if you don't.

As far as why centralize -- the main concern I have is that someone
might try to introduce an arch-specific reboot= which is *syntactically*
different, which is yet again really awful from a user perspective.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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