debugfs: function to know if debugfs is initialized

Impact: add new debugfs API

With ftrace, some tracers are registered in early initcalls
and attempt to create files on the debugfs filesystem.
Depending on when they are activated, they can try to create their
file at any time. Some checks can be done on the tracing area
but providing a helper to know if debugfs is registered make it
really more easy.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1237759847-21025-2-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

fs/debugfs/inode.c

@@ -30,6 +30,7 @@
 
 static struct vfsmount *debugfs_mount;
 static int debugfs_mount_count;
+static bool debugfs_registered;
 
 static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t dev)
 {
@@ -496,6 +497,16 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 }
 EXPORT_SYMBOL_GPL(debugfs_rename);
 
+/**
+ * debugfs_initialized - Tells whether debugfs has been registered
+ */
+bool debugfs_initialized(void)
+{
+	return debugfs_registered;
+}
+EXPORT_SYMBOL_GPL(debugfs_initialized);
+
+
 static struct kobject *debug_kobj;
 
 static int __init debugfs_init(void)
@@ -509,11 +520,16 @@ static int __init debugfs_init(void)
 	retval = register_filesystem(&debug_fs_type);
 	if (retval)
 		kobject_put(debug_kobj);
+	else
+		debugfs_registered = true;
+
 	return retval;
 }
 
 static void __exit debugfs_exit(void)
 {
+	debugfs_registered = false;
+
 	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 	unregister_filesystem(&debug_fs_type);
 	kobject_put(debug_kobj);

include/linux/debugfs.h

@@ -71,6 +71,9 @@ struct dentry *debugfs_create_bool(const char *name, mode_t mode,
 struct dentry *debugfs_create_blob(const char *name, mode_t mode,
 				  struct dentry *parent,
 				  struct debugfs_blob_wrapper *blob);
+
+bool debugfs_initialized(void);
+
 #else
 
 #include <linux/err.h>
@@ -183,6 +186,11 @@ static inline struct dentry *debugfs_create_blob(const char *name, mode_t mode,
 	return ERR_PTR(-ENODEV);
 }
 
+static inline bool debugfs_initialized(void)
+{
+	return false;
+}
+
 #endif
 
 #endif