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printk/tracing: Add console output tracing
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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.

Link: http://lkml.kernel.org/r/1322161388.5366.54.camel@jlt3.sipsolutions.net

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Johannes Berg authored and Steven Rostedt committed Feb 13, 2012
1 parent cdfb0d3 commit 9510035
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41 changes: 41 additions & 0 deletions include/trace/events/printk.h
Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@
#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 + 1)
),

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);
((char *)__get_dynamic_array(msg))[end - start] = 0;
),

TP_printk("%s", __get_str(msg))
);
#endif /* _TRACE_PRINTK_H */

/* This part must be outside protection */
#include <trace/define_trace.h>
5 changes: 5 additions & 0 deletions kernel/printk.c
Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,9 @@

#include <asm/uaccess.h>

#define CREATE_TRACE_POINTS
#include <trace/events/printk.h>

/*
* Architectures can override it:
*/
Expand Down Expand Up @@ -542,6 +545,8 @@ 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(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)) {
Expand Down

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