linux-kernel - Re: [PATCH v2] printk: add console output tracing

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Message-ID: <20111118184401.GA24787@somewhere.redhat.com>
Date:	Fri, 18 Nov 2011 19:44:06 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2] printk: add console output tracing

On Thu, Nov 17, 2011 at 04:21:08PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> Add a printk.console trace point to record any printk
> messages into the trace, regardless of the current
> console loglevel. This can help correlate (existing)
> printk debugging with other tracing.
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> ---
> v2: remove extra file
> 
>  include/trace/events/printk.h |   44 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/printk.c               |    5 ++++
>  2 files changed, 49 insertions(+)
> 
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ b/include/trace/events/printk.h	2011-11-16 23:18:35.000000000 +0100
> @@ -0,0 +1,44 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM printk
> +
> +#if !defined(_TRACE_PRINTK_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_PRINTK_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT_CONDITION(console,
> +	TP_PROTO(const char *log_buf, unsigned start, unsigned end,
> +		 unsigned log_buf_len),
> +
> +	TP_ARGS(log_buf, start, end, log_buf_len),
> +
> +	TP_CONDITION(start != end),
> +
> +	TP_STRUCT__entry(
> +		__dynamic_array(char, msg,
> +				((end - start + log_buf_len) &
> +				 (log_buf_len - 1)) + 1)

Is all that care about log_buf_len necessary? It seems that
printk ensures that log_end - con_start never exceeds log_buf_len,
looking at emit_log_char()

Thanks.

> +	),
> +
> +	TP_fast_assign(
> +		if ((start & (log_buf_len - 1)) > (end & (log_buf_len - 1))) {
> +			memcpy(__get_dynamic_array(msg),
> +			       log_buf + (start & (log_buf_len - 1)),
> +			       log_buf_len - (start & (log_buf_len - 1)));
> +			memcpy((char *)__get_dynamic_array(msg) +
> +			       log_buf_len - (start & (log_buf_len - 1)),
> +			       log_buf, end & (log_buf_len - 1));
> +		} else
> +			memcpy(__get_dynamic_array(msg),
> +			       log_buf + (start & (log_buf_len - 1)),
> +			       (end - start + log_buf_len) & (log_buf_len - 1));
> +		((char *)__get_dynamic_array(msg))[(end - start + log_buf_len) &
> +						   (log_buf_len - 1)] = 0;
> +	),
> +
> +	TP_printk("%s", __get_str(msg))
> +);
> +#endif /* _TRACE_PRINTK_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> --- a/kernel/printk.c	2011-11-16 22:25:43.000000000 +0100
> +++ b/kernel/printk.c	2011-11-17 16:19:19.000000000 +0100
> @@ -44,6 +44,9 @@
>  
>  #include <asm/uaccess.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/printk.h>
> +
>  /*
>   * Architectures can override it:
>   */
> @@ -542,6 +545,8 @@ MODULE_PARM_DESC(ignore_loglevel, "ignor
>  static void _call_console_drivers(unsigned start,
>  				unsigned end, int msg_log_level)
>  {
> +	trace_console(&LOG_BUF(0), start, end, log_buf_len);
> +
>  	if ((msg_log_level < console_loglevel || ignore_loglevel) &&
>  			console_drivers && start != end) {
>  		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
> 
> 
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