linux-kernel - Re: [PATCH v1 0/3] allow ramoops to collect all kmesg

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Message-ID: <202005041230.806B1581D@keescook>
Date:   Mon, 4 May 2020 12:30:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>, anton@...msg.org,
        ccross@...roid.com, Tony Luck <tony.luck@...el.com>,
        robh+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 0/3] allow ramoops to collect all kmesg_dump events

On Mon, May 04, 2020 at 03:17:40PM -0400, Pavel Tatashin wrote:
> On Mon, May 4, 2020 at 3:12 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, May 04, 2020 at 02:47:45PM -0400, Pavel Tatashin wrote:
> > > > > # reboot -f
> > > > >
> > > > > After VM is back:
> > > > >
> > > > > # mount -t pstore pstore /mnt
> > > > > # head /mnt/dmesg-ramoops-0
> > > > > Restart#1 Part1
> > > >
> > > > Is there a reason that using ramoops.console_size isn't sufficient for
> > > > this?
> > >
> > > Unfortunately, the console option is not working for us (Microsoft),
> > > we have an embedded device with a serial console, and the baud rate
> > > reduces the reboot performance, so we must keep the console quiet. We
> > > also want to be able collect full shutdown logs from the field that
> > > are collected during kexec based updates.
> >
> > I meant collecting console via pstore (i.e. /mnt/console-ramoops-0). Are
> > you saying that's still too large for your situation?
> 
> pstore /mnt/console-ramoops-0 outputs only messages below the console
> loglevel, and our console loglevel is set to 3 due to slowness of
> serial console. Which means only errors and worse types of messages
> are recorded. AFAIK, there is no way to have different log levels for
> different consoles.

Ah-ha! Okay, thanks. Please include this rationale in the v2 changelog.
That makes perfect sense; I just didn't see it and maybe others will
need the same clarity too. Thanks!

-Kees

-- 
Kees Cook