linux-kernel - Re: printk feature for syzbot?

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Message-ID: <20180510121122.GA29136@jagdpanzerIV>
Date:   Thu, 10 May 2018 21:11:22 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: printk feature for syzbot?

On (05/10/18 13:30), Petr Mladek wrote:
[..]
> I guess that you are talking about the patchset adding possibility
> to use different time-stamps[1]. It changed the semantic of the
> timestamp. All the tools needed an update to show the timestamp
> correctly.
> 
> The patchset was rejected by Linus because it would broke some
> userspace tool, e.g. systemd, that depend on the format and semantic
> provided by /dev/kmsg[2].

Right, but I think I was talking about this email
 https://lkml.kernel.org/r/20171123124648.s4oigunxjfzvhtqh@pathway.suse.cz

But yeah, it's not really related to the extension of struct printk_log,
so I think we should be fine.

> By other words, we must not change /dev/kmsg format. But it should
> be acceptable to change/extend the internal format and eventually
> extend the format used on consoles.

Sure.

> Anyway, we need to be careful and test makedumpfile and crash tools
> and eventually provide patches for them.

Agreed. I'd prefer it to be hidden somewhere under kernel hacking config,
so only syzkaller folks would enable it. I think Steven also mentioned
a config option.

> Reference:
> [0] https://lkml.kernel.org/r/20160419085613.GJ6862@pathway.suse.cz
> [1] https://lkml.kernel.org/r/CA+55aFzLH9crdMtUFkD-PtNGuxu_fsG5GH2ACni69ug9iM=09g@mail.gmail.com

Thanks.

	-ss