linux-kernel - Re: [PATCH] printk: add per console loglevel

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Message-ID: <20141223162013.GB19144@fifo99.com>
Date:	Tue, 23 Dec 2014 16:20:13 +0000
From:	dwalker@...o99.com
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: add per console loglevel

On Sun, Dec 21, 2014 at 07:47:53PM +0100, Bruno Prémont wrote:
> On Sat, 20 December 2014 dwalker@...o99.com wrote:
> > This adds to to the console= command line options allowing the
> > addition of a per console log level setting.
> > 
> > examples,
> > 
> > 	console=ttyS0,ll4
> > 	console=tty0,ll6
> > 
> > This can be used on systems which have multiple serial consoles, but
> > it's desired for logging to be light on one and heavy on another.
> 
> Looks useful to me.
> What would be the best way to make these per-console loglevels
> configurable at runtime? `dmesg -n $LEVEL` only affects the global
> limit.
> 
> One drawback to letting global loglevel have precedence is that
> all consoles that should not get detailed log messages need to have
> their loglevel explicitly lowered and it's not possible to have
> one console forced to show more than the global loglevel.

Right, reason for the patch.
 
> 
> An approach I would prefer is to have all consoles follow global
> loglevel except when something different had been explicitly requested
> for them.

This patch is mostly like this. It breaks down when you set the "llX"
parameter to something above KERN_NOTICE, and the global one is also
set above that.

> This way a single console can be added later on (e.g. netconsole)
> and set to pass through debug messages without affecting anyone else.

Not following the "added later" part.

Daniel
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