Re: [RFC][Patch] Adding kmsg_dump() to reboot/halt/poweroff/emergency_restart path

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 19 Oct 2010 11:51:12 +0300
Artem Bityutskiy <Artem.Bityutskiy@nokia.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.