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

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Date:	Wed, 17 Apr 2013 19:17:26 -0500
From:	Robin Holt <holt@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Robin Holt <holt@....com>, 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 Wed, Apr 17, 2013 at 03:15:33PM -0500, Robin Holt wrote:
> On Wed, Apr 17, 2013 at 12:59:57PM -0700, H. Peter Anvin wrote:
> > It is also worth noting that the documentation says reboot=s[mp]#
> > whereas in fact only reboot=s# parse correctly.  I consider this to be a
> > bug.
> > 
> > If we centralized the parser, we could take a string like
> > 
> > "reboot=bios,smp32,warm"
> > 
> > and parse it into:
> > 
> > reboot_cpu = 32
> > reboot_mode = "bw"
> > 
> > ... and pass the information in that form to the arch layer.  I don't
> > think we can do more parsing at that in the main kernel.
> 
> OK.  I will go back to the drawing board again.

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.

Thanks,
Robin
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