ext4: Add sysfs support

Add basic sysfs support so that information about the mounted
filesystem and various tuning parameters can be accessed via
/sys/fs/ext4/<dev>/*.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 50ab116..57b71fe 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -64,6 +64,8 @@
 	struct percpu_counter s_dirtyblocks_counter;
 	struct blockgroup_lock *s_blockgroup_lock;
 	struct proc_dir_entry *s_proc;
+	struct kobject s_kobj;
+	struct completion s_kobj_unregister;
 
 	/* Journaling */
 	struct inode *s_journal_inode;