[PATCH] printk: add console output tracing

[Johannes Berg <johannes@sipsolutions.net>]

From: Johannes Berg <johannes.berg@intel.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@intel.com>
---
 include/trace/events/printk.h |   44 ++++++++++++++++++++++++++++++++++++++++++
 kernel/printk.c               |    3 ++
 kernel/trace/Makefile         |    1 
 kernel/trace/printk-trace.c   |   14 +++++++++++++
 4 files changed, 62 insertions(+)

--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ b/include/trace/events/printk.h	2011-11-16 22:06:43.000000000 +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)
+	),
+
+	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 16:37:20.000000000 +0100
+++ b/kernel/printk.c	2011-11-16 21:47:20.000000000 +0100
@@ -41,6 +41,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/rculist.h>
+#include <trace/events/printk.h>
 
 #include <asm/uaccess.h>
 
@@ -542,6 +543,8 @@ 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)) {
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ b/kernel/trace/printk-trace.c	2011-11-16 21:22:20.000000000 +0100
@@ -0,0 +1,14 @@
+/*
+ * printk trace points
+ *
+ * Copyright (C) 2011 Johannes Berg <johannes.berg@intel.com>
+ */
+
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/printk.h>
--- a/kernel/trace/Makefile	2011-11-16 16:37:20.000000000 +0100
+++ b/kernel/trace/Makefile	2011-11-16 21:38:49.000000000 +0100
@@ -55,6 +55,7 @@ endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
 obj-$(CONFIG_TRACEPOINTS) += power-traces.o
+obj-$(CONFIG_TRACEPOINTS) += printk-trace.o
 ifeq ($(CONFIG_PM_RUNTIME),y)
 obj-$(CONFIG_TRACEPOINTS) += rpm-traces.o
 endif