linux-kernel - Re: [RFC][Patch] Adding kmsg_dump() to reboot/halt/poweroff/emergency

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Message-Id: <20101027163505.c88095da.akpm@linux-foundation.org>
Date:	Wed, 27 Oct 2010 16:35:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Artem.Bityutskiy@...ia.com
Cc:	ext KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Seiji Aguchi <seiji.aguchi@....com>,
	"simon.kagstrom@...insight.net" <simon.kagstrom@...insight.net>,
	"David.Woodhouse@...el.com" <David.Woodhouse@...el.com>,
	"anders.grafstrom@...insight.net" <anders.grafstrom@...insight.net>,
	"jason.wessel@...driver.com" <jason.wessel@...driver.com>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"eparis@...hat.com" <eparis@...hat.com>, "hch@....de" <hch@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: Re: [RFC][Patch] Adding kmsg_dump() to
 reboot/halt/poweroff/emergency_restart path

On Tue, 19 Oct 2010 11:51:12 +0300
Artem Bityutskiy <Artem.Bityutskiy@...ia.com> wrote:

> On Tue, 2010-10-19 at 10:52 +0200, ext KOSAKI Motohiro wrote:
> > > Hi,
> > > 
> > > Final messages from reboot, halt and poweroff aren't output to disk because klogd/syslogd 
> > > has been killed and root file system has been turned read-only.
> > > 
> > > Final messages from emergency_restart aren't output to disk as well because system may
> > > reboot before klogd/syslogd outputs messages to disk.
> > > 
> > > Therefore, it is better to put kmsg_dumper in reboot/halt/poweroff/emergency_restart path.
> > > Any comments/advices are welcome.
> > 
> > I think mtdoops user don't want to dump logs if a system reboot/poweroff
> > safely because mtd device have write count limitation. and they are main
> > user of kmsg_dump().

mtdoops was the only user until ramoops came along.

> Right, at least this is how we use mtdoops - we log crashes.

Fair enough.  So I suppose the existing clients (mtdoops_do_dump and
ramoops_do_dump) should be altered to inspect the `reason' argument,
and return if it isn't KMSG_DUMP_OOPS, KMSG_DUMP_PANIC or
KMSG_DUMP_KEXEC (I assume?)

If that sounds suitable then I'd ask Seiji to update and resend the
patch, along with a complete changelog as earlier dicussed.

I'd suggest doing it as two patches, the first of which alters mtdoops
and ramoops to perform their actions only for the appropriate `reason'
values.

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