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

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Date:   Mon, 4 May 2020 15:17:40 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Kees Cook <keescook@...omium.org>
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 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.

Thank you,
Pasha

>
> --
> Kees Cook