linux-kernel - Re: [PATCH] tracing: add trace console

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Date:	Wed, 16 Nov 2011 19:33:00 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] tracing: add trace console

On Wed, 2011-11-16 at 12:00 -0500, Steven Rostedt wrote:
> On Wed, 2011-11-16 at 17:45 +0100, Johannes Berg wrote:
> 
> > I briefly looked at it just after writing the email, but quickly got
> > lost in printk.c because of the multi-line handling it has. We could
> > instead trace each call to printk(), so the multi-line stuff would end
> > up in multiple events, but all of that code is too much vodoo for me :)
> 
> Here's what can go into printk.c:
> 
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 1455a0d..4b8445a 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -542,6 +542,7 @@ MODULE_PARM_DESC(ignore_loglevel, "ignore loglevel setting, to"
>  static void _call_console_drivers(unsigned start,
>  				unsigned end, int msg_log_level)
>  {
> +	trace_console(&LOG_BUF(start), end - start);
>  	if ((msg_log_level < console_loglevel || ignore_loglevel) &&
>  			console_drivers && start != end) {
>  		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
> 
> 
> And then you can make a TRACE_EVENT(console) that takes a buffer and a
> len, and write that to the ring buffer.

Yes, of course, but if we're going to modify the code then I thought we
should probably trace everything independent of the console printk
level.

johannes

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