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

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Date:	Wed, 16 Nov 2011 12:00:56 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Johannes Berg <johannes@...solutions.net>
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 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.

-- Steve


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