linux-kernel - [PATCH] tracing: Kernel access to ftrace instances

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Date:   Fri, 15 Mar 2019 16:35:25 -0700
From:   Divya Indi <divya.indi@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Divya Indi <divya.indi@...cle.com>
Subject: [PATCH] tracing: Kernel access to ftrace instances

Ftrace provides the feature “instances” that provides the capability to
create multiple Ftrace ring buffers. However, currently these buffers
are created/accessed via userspace only. The kernel APIs providing these
features are not exported, hence cannot be used by other kernel
components.

This patch aims to extend this infrastructure to provide the
flexibility to create/log/remove/ enable-disable existing trace events
to these buffers from within the kernel.

Signed-off-by: Divya Indi <divya.indi@...cle.com>
---
 kernel/trace/trace.c        | 72 +++++++++++++++++++++++++++++----------------
 kernel/trace/trace_events.c |  1 +
 2 files changed, 48 insertions(+), 25 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c4238b4..a5e7e51 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2878,6 +2878,7 @@ void trace_printk_init_buffers(void)
 	if (global_trace.trace_buffer.buffer)
 		tracing_start_cmdline_record();
 }
+EXPORT_SYMBOL_GPL(trace_printk_init_buffers);
 
 void trace_printk_start_comm(void)
 {
@@ -3038,6 +3039,7 @@ int trace_array_printk(struct trace_array *tr,
 	va_end(ap);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(trace_array_printk);
 
 __printf(3, 4)
 int trace_array_printk_buf(struct ring_buffer *buffer,
@@ -7832,7 +7834,7 @@ static void update_tracer_options(struct trace_array *tr)
 	mutex_unlock(&trace_types_lock);
 }
 
-static int instance_mkdir(const char *name)
+struct trace_array *trace_array_create(const char *name)
 {
 	struct trace_array *tr;
 	int ret;
@@ -7896,7 +7898,7 @@ static int instance_mkdir(const char *name)
 	mutex_unlock(&trace_types_lock);
 	mutex_unlock(&event_mutex);
 
-	return 0;
+	return tr;
 
  out_free_tr:
 	free_trace_buffers(tr);
@@ -7908,33 +7910,21 @@ static int instance_mkdir(const char *name)
 	mutex_unlock(&trace_types_lock);
 	mutex_unlock(&event_mutex);
 
-	return ret;
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(trace_array_create);
 
+static int instance_mkdir(const char *name)
+{
+	return PTR_ERR_OR_ZERO(trace_array_create(name));
 }
 
-static int instance_rmdir(const char *name)
+static int __remove_instance(struct trace_array *tr)
 {
-	struct trace_array *tr;
-	int found = 0;
-	int ret;
 	int i;
-
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
-
-	ret = -ENODEV;
-	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
-		if (tr->name && strcmp(tr->name, name) == 0) {
-			found = 1;
-			break;
-		}
-	}
-	if (!found)
-		goto out_unlock;
-
-	ret = -EBUSY;
+	
 	if (tr->ref || (tr->current_trace && tr->current_trace->ref))
-		goto out_unlock;
+		return -EBUSY;
 
 	list_del(&tr->list);
 
@@ -7961,9 +7951,41 @@ static int instance_rmdir(const char *name)
 	kfree(tr->name);
 	kfree(tr);
 
-	ret = 0;
+	return 0;
+}
 
- out_unlock:
+int trace_array_destroy(struct trace_array *tr)
+{
+	int ret;
+
+	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
+
+	ret = __remove_instance(tr);
+
+	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(trace_array_destroy);
+	
+static int instance_rmdir(const char *name)
+{
+	struct trace_array *tr;
+	int ret;
+
+	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
+
+	ret = -ENODEV;
+	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+		if (tr->name && strcmp(tr->name, name) == 0) {
+			ret = __remove_instance(tr);
+			break;
+		}
+	}
+	
 	mutex_unlock(&trace_types_lock);
 	mutex_unlock(&event_mutex);
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 5b3b0c3..81c038e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -832,6 +832,7 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(ftrace_set_clr_event);
 
 /**
  * trace_set_clr_event - enable or disable an event
-- 
1.8.3.1