linux-kernel - Re: [RFC][PATCH] printk: add console_msg

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Date:   Thu, 7 Dec 2017 23:01:04 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Kevin Hilman <khilman@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCH] printk: add console_msg_format command line option

Hi,

On (12/07/17 14:48), Petr Mladek wrote:
[..]
> > This patch introduces a `console_msg_format=' command line option,
> > to switch between different message formatting on serial consoles.
> > For the time being we have just one option - syslog. This option
> > makes serial console messages to appear in syslog format, matching
> > the `dmesg --raw' and `cat /proc/kmsg' output formats:
> 
> I have realized that 'cat /proc/kmsg' did not work. It can be done using:

hm, it does work on my system. what do you mean by 'did not work'?


> Also the format is more comlicated here, see printk.c:
> 
>  * /dev/kmsg exports the structured data in the following line format:
>  *   "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"

that's /dev/kmsg. /dev/kmsg != /proc/kmsg. I never mentioned /dev/kmsg
in my commit. /dev/kmsg prints the extended stuff, /proc/kmsg does not.


> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 28467638488d..2dd91c5073f9 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -643,6 +643,16 @@
> >  			console=brl,ttyS0
> >  		For now, only VisioBraille is supported.
> >  
> > +	console_msg_format=
> > +			[KNL] Control message format
> > +			By default we print messages in "[time stamp] text\n"
> > +			format (time stamp may not be printed, depending on
> > +			CONFIG_PRINTK_TIME or `printk_time' param).
> > +		syslog
> > +			Switch to syslog format (similar to "dmesg --raw" or
> > +			reading from /proc/kmsg): "<%u>[time stamp] text\n"
> 
> To be precise, it exactly the same as "dmesg -S --raw". Also it is the
> format used by SYSLOG_ACTION_READ* actions of the syslog syscall.

hmm... `dmesg -S --raw' doesn't show anything on my system. `dmesg --raw'
matches the console_msg_format=syslog.


> > +static int __init console_msg_format_setup(char *str)
> > +{
> > +	if (!strncmp(str, "syslog", 6))
> > +		console_msg_format = MSG_FORMAT_SYSLOG;
> 
> It might make sense to accept also the "default" format.
> 
> > +	return 1;
> > +}
> > +__setup("console_msg_format=", console_msg_format_setup);
> 
> I would use early_param() so that it takes effect as soon as possible.

ok. can take a look.

	-ss