xfs: add xlog sysfs kobject and attribute handlers

Embed a kobject into the xfs log data structure (xlog). This creates a
'log' subdirectory for every XFS mount instance in sysfs. The lifecycle
of the log kobject is tied to the lifecycle of the log.

Also define a set of generic attribute handlers associated with the log
kobject in preparation for the addition of attributes.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_sysfs.h b/fs/xfs/xfs_sysfs.h
index 4bd5fff..54a2091 100644
--- a/fs/xfs/xfs_sysfs.h
+++ b/fs/xfs/xfs_sysfs.h
@@ -20,6 +20,7 @@
 #define __XFS_SYSFS_H__
 
 extern struct kobj_type xfs_mp_ktype;	/* xfs_mount */
+extern struct kobj_type xfs_log_ktype;	/* xlog */
 
 static inline struct xfs_kobj *
 to_kobj(struct kobject *kobject)