[PATCH 3/3] tracing: Add 2 new funcs. for kernel access to Ftrace instances.

[Divya Indi]

Adding 2 new functions -
1) trace_array_lookup : Look up and return a trace array, given its
name.
2) trace_array_set_clr_event : Enable/disable event recording to the
given trace array.

Newly added functions trace_array_lookup and trace_array_create also
need to increment the reference counter associated with the trace array
they return. This is to ensure the trace array does not get freed
while in use by the newly introduced APIs.
The reference ctr is decremented in the trace_array_destroy.

Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
---
 include/linux/trace_events.h |  3 +++
 kernel/trace/trace.c         | 30 +++++++++++++++++++++++++++++-
 kernel/trace/trace_events.c  | 22 ++++++++++++++++++++++
 3 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index d7b7d85..0cc99a8 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -545,7 +545,10 @@ int trace_array_printk(struct trace_array *tr, unsigned long ip,
 struct trace_array *trace_array_create(const char *name);
 int trace_array_destroy(struct trace_array *tr);
 int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set);
+struct trace_array *trace_array_lookup(const char *name);
 int trace_set_clr_event(const char *system, const char *event, int set);
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+		const char *event, int set);
 
 /*
  * The double __builtin_constant_p is because gcc will give us an error
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a60dc13..fb70ccc 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8364,6 +8364,8 @@ struct trace_array *trace_array_create(const char *name)
 
 	list_add(&tr->list, &ftrace_trace_arrays);
 
+	tr->ref++;
+
 	mutex_unlock(&trace_types_lock);
 	mutex_unlock(&event_mutex);
 
@@ -8385,7 +8387,14 @@ struct trace_array *trace_array_create(const char *name)
 
 static int instance_mkdir(const char *name)
 {
-	return PTR_ERR_OR_ZERO(trace_array_create(name));
+	struct trace_array *tr;
+
+	tr = trace_array_create(name);
+	if (IS_ERR(tr))
+		return PTR_ERR(tr);
+	trace_array_put(tr);
+
+	return 0;
 }
 
 static int __remove_instance(struct trace_array *tr)
@@ -8434,6 +8443,7 @@ int trace_array_destroy(struct trace_array *tr)
 	mutex_lock(&event_mutex);
 	mutex_lock(&trace_types_lock);
 
+	tr->ref--;
 	ret = __remove_instance(tr);
 
 	mutex_unlock(&trace_types_lock);
@@ -8465,6 +8475,24 @@ static int instance_rmdir(const char *name)
 	return ret;
 }
 
+struct trace_array *trace_array_lookup(const char *name)
+{
+	struct trace_array *tr;
+
+	mutex_lock(&trace_types_lock);
+
+	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+		if (tr->name && strcmp(tr->name, name) == 0) {
+			tr->ref++;
+			mutex_unlock(&trace_types_lock);
+			return tr;
+		}
+	}
+	mutex_unlock(&trace_types_lock);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(trace_array_lookup);
+
 static __init void create_trace_instances(struct dentry *d_tracer)
 {
 	trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 445b059..c126d2c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -859,6 +859,28 @@ int trace_set_clr_event(const char *system, const char *event, int set)
 }
 EXPORT_SYMBOL_GPL(trace_set_clr_event);
 
+/**
+ * trace_array_set_clr_event - enable or disable an event for a trace array
+ * @system: system name to match (NULL for any system)
+ * @event: event name to match (NULL for all events, within system)
+ * @set: 1 to enable, 0 to disable
+ *
+ * This is a way for other parts of the kernel to enable or disable
+ * event recording to instances.
+ *
+ * Returns 0 on success, -EINVAL if the parameters do not match any
+ * registered events.
+ */
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+		const char *event, int set)
+{
+	if (!tr)
+		return -ENODEV;
+
+	return __ftrace_set_clr_event(tr, NULL, system, event, set);
+}
+EXPORT_SYMBOL_GPL(trace_array_set_clr_event);
+
 /* 128 should be much more than enough */
 #define EVENT_BUF_SIZE		127
 
-- 
1.8.3.1