linux-kernel - Re: [PATCH 3/9] printk: add CON

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Message-ID: <x49fw0f2m5r.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 01 Mar 2013 10:08:00 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Joern Engel <joern@...fs.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/9] printk: add CON_ALLDATA console flag

Borislav Petkov <bp@...en8.de> writes:

> On Fri, Mar 01, 2013 at 09:52:27AM -0500, Jeff Moyer wrote:
>> > For consoles like netconsole and blockconsole the loglevel filtering
>> > really doesn't make any sense.  If a line gets printed at all, please
>> > send it down to that console, no questions asked.
>> 
>> Could you please explain this a bit further?  Why wouldn't you want to
>> allow the admin to filter log messages to the block or network console?
>> This doesn't make a whole lot of sense to me, and in fact could cause
>> problems for netconsole now that you're potentially sending a ton more
>> traffic over the wire.
>
> Let's reverse the question: why would the admin ever want to filter
> messages to debugging consoles like netconsole or blockconsole?
>
> When running a debugging session, you generally want to see *all*
> messages.

People don't just use this for "debugging sessions."  They use it in
production, and I already gave you one reason why you might not want to
do this with netconsole (udp is unreliable, and I've definitely seem
cases where netconsole suffered due to dropped packets; this won't make
that better, especially when you multiply the extra bytes times the
number of servers on the subnet).

Cheers,
Jeff
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