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: Chunyan Zhang <zhang.chunyan@linaro.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Chunyan Zhang 2016-11-21 15:57:18 +08:00 committed by Steven Rostedt
parent 153aae5f99
commit 478409dd68
2 changed files with 156 additions and 1 deletions

28
include/linux/trace.h Normal file
View file

@ -0,0 +1,28 @@
#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 */

View file

@ -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,
@ -2146,8 +2270,11 @@ 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