[PATCH 2/2] tracing/filter: remove empty subsystem and it's directory

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

Remove empty subsystem and it's directory when module unload.

Before patch:
 # rmmod trace-events-sample.ko
 # ls sample
 enable  filter

After patch:
 # rmmod trace-events-sample.ko
 # ls sample
 ls: cannot access sample: No such file or directory

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
 kernel/trace/trace.h        |    1 +
 kernel/trace/trace_events.c |   32 +++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 61b4e94..0e7de4b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -780,6 +780,7 @@ struct event_subsystem {
 	const char		*name;
 	struct dentry		*entry;
 	void			*filter;
+	int			nr_events;
 };
 
 struct filter_pred;
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index fecac13..90cf936 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -851,8 +851,10 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 
 	/* First see if we did not already create this dir */
 	list_for_each_entry(system, &event_subsystems, list) {
-		if (strcmp(system->name, name) == 0)
+		if (strcmp(system->name, name) == 0) {
+			system->nr_events++;
 			return system->entry;
+		}
 	}
 
 	/* need to create new entry */
@@ -871,6 +873,7 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 		return d_events;
 	}
 
+	system->nr_events = 1;
 	system->name = kstrdup(name, GFP_KERNEL);
 	if (!system->name) {
 		debugfs_remove(system->entry);
@@ -905,6 +908,32 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 	return system->entry;
 }
 
+static void remove_subsystem_dir(const char *name)
+{
+	struct event_subsystem *system;
+
+	if (strcmp(name, TRACE_SYSTEM) == 0)
+		return;
+
+	list_for_each_entry(system, &event_subsystems, list) {
+		if (strcmp(system->name, name) == 0) {
+			if (!--system->nr_events) {
+				struct event_filter *filter = system->filter;
+
+				debugfs_remove_recursive(system->entry);
+				list_del(&system->list);
+				if (filter) {
+					kfree(filter->filter_string);
+					kfree(filter);
+				}
+				kfree(system->name);
+				kfree(system);
+			}
+			break;
+		}
+	}
+}
+
 static int
 event_create_dir(struct ftrace_event_call *call, struct dentry *d_events,
 		 const struct file_operations *id,
@@ -1079,6 +1108,7 @@ static void trace_module_remove_events(struct module *mod)
 			list_del(&call->list);
 			trace_destroy_fields(call);
 			destroy_preds(call);
+			remove_subsystem_dir(call->system);
 		}
 	}
 
-- 
1.6.1.2