linux-kernel - Re: [PATCHSET] printk, netconsole: implement reliable netconsole

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Date:	Fri, 17 Apr 2015 14:07:32 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	davem@...emloft.net, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCHSET] printk, netconsole: implement reliable netconsole

On Sat, Apr 18, 2015 at 03:03:46AM +0900, Tetsuo Handa wrote:
> If you tolerate loss of kernel messages, adding sequence number to each UDP

Well, there's a difference between accepting loss when log buffer
overflows and when any packets get lost.

> packet will be sufficient for finding out whether the packets were lost and/or
> reordered in flight.
> 
>   printk("Hello");
>    => netconsole sends "00000000 Hello" using UDP
>   printk("netconsole");
>    => netconsole sends "00000001 netconsole" using UDP
>   printk("world\n");
>    => netconsole sends "00000002 world\n" using UDP
> 
> It might be nice to allow administrator to prefix a sequence number
> to netconsole messages for those who are using special receiver
> program (e.g. ncrx) which checks that sequence number.

That said, this is pretty much what the first 12 patches do (except
for the last printk patch, which can be taken out).  We already have
sequencing and established format to expose them to userland - try cat
/dev/kmsg, which btw is what local loggers on modern systems use
anyway.  Why introduce netconsole's own version of metadata?

Thanks.

-- 
tejun
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