Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 478409dd authored by Chunyan Zhang's avatar Chunyan Zhang Committed by Steven Rostedt
Browse files

tracing: Add hook to function tracing for other subsystems to use 

Currently Function traces can be only exported to the ring buffer. This
adds a trace_export concept which can process traces and export
them to a registered destination as an addition to the current
one that outputs to Ftrace - i.e. ring buffer.

In this way, if we want function traces to be sent to other destinations
rather than only to the ring buffer, we just need to register a new
trace_export and implement its own .write() function for writing traces to
storage.

With this patch, only function tracing (trace type is TRACE_FN)
is supported.

Link: http://lkml.kernel.org/r/1479715043-6534-2-git-send-email-zhang.chunyan@linaro.org



Signed-off-by: default avatarChunyan Zhang <zhang.chunyan@linaro.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 153aae5f

include/linux/trace.h

0 → 100644
+28 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_TRACE_H

#define _LINUX_TRACE_H



#ifdef CONFIG_TRACING

/*

 * The trace export - an export of Ftrace output. The trace_export

 * can process traces and export them to a registered destination as

 * an addition to the current only output of Ftrace - i.e. ring buffer.

 *

 * If you want traces to be sent to some other place rather than ring

 * buffer only, just need to register a new trace_export and implement

 * its own .write() function for writing traces to the storage.

 *

 * next		- pointer to the next trace_export

 * write	- copy traces which have been delt with ->commit() to

 *		  the destination

 */

struct trace_export {

	struct trace_export __rcu	*next;

	void (*write)(const void *, unsigned int);

};



int register_ftrace_export(struct trace_export *export);

int unregister_ftrace_export(struct trace_export *export);



#endif	/* CONFIG_TRACING */



#endif	/* _LINUX_TRACE_H */

kernel/trace/trace.c

+128 −1
Original line number Diff line number Diff line
@@ -40,6 +40,7 @@ 
#include <linux/poll.h>

#include <linux/nmi.h>

#include <linux/fs.h>

#include <linux/trace.h>

#include <linux/sched/rt.h>



#include "trace.h"
@@ -2128,6 +2129,129 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr, 
	ftrace_trace_userstack(buffer, flags, pc);

}



static void

trace_process_export(struct trace_export *export,

	       struct ring_buffer_event *event)

{

	struct trace_entry *entry;

	unsigned int size = 0;



	entry = ring_buffer_event_data(event);

	size = ring_buffer_event_length(event);

	export->write(entry, size);

}



static DEFINE_MUTEX(ftrace_export_lock);



static struct trace_export __rcu *ftrace_exports_list __read_mostly;



static DEFINE_STATIC_KEY_FALSE(ftrace_exports_enabled);



static inline void ftrace_exports_enable(void)

{

	static_branch_enable(&ftrace_exports_enabled);

}



static inline void ftrace_exports_disable(void)

{

	static_branch_disable(&ftrace_exports_enabled);

}



void ftrace_exports(struct ring_buffer_event *event)

{

	struct trace_export *export;



	preempt_disable_notrace();



	export = rcu_dereference_raw_notrace(ftrace_exports_list);

	while (export) {

		trace_process_export(export, event);

		export = rcu_dereference_raw_notrace(export->next);

	}



	preempt_enable_notrace();

}



static inline void

add_trace_export(struct trace_export **list, struct trace_export *export)

{

	rcu_assign_pointer(export->next, *list);

	/*

	 * We are entering export into the list but another

	 * CPU might be walking that list. We need to make sure

	 * the export->next pointer is valid before another CPU sees

	 * the export pointer included into the list.

	 */

	rcu_assign_pointer(*list, export);

}



static inline int

rm_trace_export(struct trace_export **list, struct trace_export *export)

{

	struct trace_export **p;



	for (p = list; *p != NULL; p = &(*p)->next)

		if (*p == export)

			break;



	if (*p != export)

		return -1;



	rcu_assign_pointer(*p, (*p)->next);



	return 0;

}



static inline void

add_ftrace_export(struct trace_export **list, struct trace_export *export)

{

	if (*list == NULL)

		ftrace_exports_enable();



	add_trace_export(list, export);

}



static inline int

rm_ftrace_export(struct trace_export **list, struct trace_export *export)

{

	int ret;



	ret = rm_trace_export(list, export);

	if (*list == NULL)

		ftrace_exports_disable();



	return ret;

}



int register_ftrace_export(struct trace_export *export)

{

	if (WARN_ON_ONCE(!export->write))

		return -1;



	mutex_lock(&ftrace_export_lock);



	add_ftrace_export(&ftrace_exports_list, export);



	mutex_unlock(&ftrace_export_lock);



	return 0;

}

EXPORT_SYMBOL_GPL(register_ftrace_export);



int unregister_ftrace_export(struct trace_export *export)

{

	int ret;



	mutex_lock(&ftrace_export_lock);



	ret = rm_ftrace_export(&ftrace_exports_list, export);



	mutex_unlock(&ftrace_export_lock);



	return ret;

}

EXPORT_SYMBOL_GPL(unregister_ftrace_export);



void

trace_function(struct trace_array *tr,

	       unsigned long ip, unsigned long parent_ip, unsigned long flags,
@@ -2146,9 +2270,12 @@ trace_function(struct trace_array *tr, 
	entry->ip			= ip;

	entry->parent_ip		= parent_ip;



	if (!call_filter_check_discard(call, entry, buffer, event))

	if (!call_filter_check_discard(call, entry, buffer, event)) {

		if (static_branch_unlikely(&ftrace_exports_enabled))

			ftrace_exports(event);

		__buffer_unlock_commit(buffer, event);

	}

}



#ifdef CONFIG_STACKTRACE