Subject: Re: [PATCH, RFC] panic-note: Annotation from user space for panics
From: Artem Bityutskiy <dedekind1@gmail.com>
Reply-To: dedekind1@gmail.com
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Marco Stornelli <marco.stornelli@gmail.com>,
       Simon Kagstrom <simon.kagstrom@netinsight.net>,
       David VomLehn <dvomlehn@cisco.com>, linux-embedded@vger.kernel.org,
       akpm@linux-foundation.org, dwm2@infradead.org,
       linux-kernel@vger.kernel.org, mpm@selenic.com,
       paul.gortmaker@windriver.com
In-Reply-To: <m1pr7hf93s.fsf@fess.ebiederm.org>
References: <20091112021322.GA6166@dvomlehn-lnx2.corp.sa.net>
	 <4AFC4D31.2000101@gmail.com>
	 <20091112215649.GA28349@dvomlehn-lnx2.corp.sa.net>
	 <20091113091031.3f6d4bba@marrow.netinsight.se>
	 <1258112748.21596.1227.camel@localhost> <4AFE6A14.4010507@gmail.com>
	 <1258447997.27437.76.camel@localhost>
	 <2ea1731b0911170445x13225c19w797388d2211de2d9@mail.gmail.com>
	 <1258463404.27437.103.camel@localhost>  <m1pr7hf93s.fsf@fess.ebiederm.org>
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Date: Wed, 18 Nov 2009 10:26:34 +0200
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On Tue, 2009-11-17 at 07:45 -0800, Eric W. Biederman wrote:
> Artem Bityutskiy <dedekind1@gmail.com> writes:
> 
> > On Tue, 2009-11-17 at 13:45 +0100, Marco Stornelli wrote:
> >> 2009/11/17 Artem Bityutskiy <dedekind1@gmail.com>:
> >> > Take a look at my mails where I describe different complications we have
> >> > in our system. We really want to have an OOPS/panic + our environment
> >> > stuff to go together, at once. This makes things so much simpler.
> >> >
> >> > Really, what is the problem providing this trivial panic-note
> >> > capability, where user-space can give the kernel a small buffer, and ask
> >> > the kernel to print this buffer at the oops/panic time. Very simple and
> >> > elegant, and just solves the problem.
> >> >
> >> > Why perversions with time-stamps, separate storages are needed?
> >> >
> >> > IOW, you suggest a complicated approach, and demand explaining why we do
> >> > not go for it. Simply because it is unnecessarily complex.
> >> 
> >> I don't think it's a complicated approach we are talking of a system
> >> log like syslog with a temporal information, nothing more.
> >
> > We need to store this information of NAND flash. Implementing logs on
> > NAND flash is about handling bad blocks, choosing format of records, and
> > may be even handling wear-levelling. This is not that simple.
> >
> > And then I have match oops to the userspace environment prints, using I
> > guess timestamps, which is also about complications in userspace.
> >
> >> > This patch solves the problem gracefully, and I'd rather demand you to point what
> >> > is the technical problem with the patches.
> >> >
> >> 
> >> Simply because I think that we should avoid to include in the kernel
> >> things we can do in a simply way at user space level.
> >
> > If it is much easier to have in the kernel, then this argument does not
> > work, IMHO.
> >
> >>  I think this
> >> patch is well done but it's one of the patches that are solutions "for
> >> embedded only", but it's only my opinion.
> >
> > Also IMHO, but having embedded-only things is not bad at all.
> 
> Why not use the kdump hook?  If you handle a kernel panic that way
> you get enhanced reliability and full user space support.  All in a hook
> that is already present and already works.

For some reasons kdump does not work on ARM out of the box. We need to
investigate this.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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