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To: Linus Torvalds <torvalds@transmeta.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Werner Almesberger <wa@almesberger.net>,
       Suparna Bhattacharya <suparna@in.ibm.com>,
       Jeff Garzik <jgarzik@pobox.com>,
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       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Mike Galbraith <efault@gmx.de>,
       "Martin J. Bligh" <Martin.Bligh@us.ibm.com>
Subject: Re: [lkcd-devel] Re: What's left over.
References: <Pine.LNX.4.44.0211091901240.2336-100000@home.transmeta.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: 11 Nov 2002 11:03:43 -0700
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Linus Torvalds <torvalds@transmeta.com> writes:

> On 9 Nov 2002, Eric W. Biederman wrote:
> > 
> > And despite my utter puzzlement on why you want the syscall cut in two.
> 
> I'm amazed about your puzzlement, since everybody else seem to get my 
> arguments, but as long as you play along I don't much care.

I think this comes from being the guy down in the trenches implementing
the code.   And it is sometimes hard to look up, far enough to have design
discussions.

I totally agree that having a load/exec split is the right
approach now that I can imagine an implementation where the code will
actually work for the panic case.  Before it felt like lying.  Doing
the  split-up, promising that kexec on panic will work eventually,
when I could not even see it as a possibility was at the core of my
objections.

What brought me around is that I can add a flag field to kexec_load.
With that flag field I can tell the kernel please step extra carefully
this code will be used to handle kexec on panic.  Without that I may
be up a creek without a paddle for figuring out how to debug that code.

To be able to support this at all I have had to be very creative in
inventing debugging code.  Which is why I have the serial console
program kexec_test.  It provides visibility into what is happening
when nothing else will.  That and memtest86 which will occasionally
catch DMA's that have not been stopped, (memory errors on good ram) I
at least have a place to start rather than a blank screen when
guessing why the new kernel did not start up.

Eric
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