What:		/sys/fs/aufs/si_<id>/
Date:		March 2009
Contact:	J. R. Okajima <hooanon05g@gmail.com>
Description:
		Under /sys/fs/aufs, a directory named si_<id> is created
		per aufs mount, where <id> is a unique id generated
		internally.

What:		/sys/fs/aufs/si_<id>/br<idx>
Date:		March 2009
Contact:	J. R. Okajima <hooanon05g@gmail.com>
Description:
		It shows the abolute path of a member directory (which
		is called branch) in aufs, and its permission.

What:		/sys/fs/aufs/si_<id>/brid<idx>
Date:		July 2013
Contact:	J. R. Okajima <hooanon05g@gmail.com>
Description:
		It shows the id of a member directory (which is called
		branch) in aufs.

What:		/sys/fs/aufs/si_<id>/xi_path
Date:		March 2009
Contact:	J. R. Okajima <hooanon05g@gmail.com>
Description:
		It shows the abolute path of XINO (External Inode Number
		Bitmap, Translation Table and Generation Table) file
		even if it is the default path.
		When the aufs mount option 'noxino' is specified, it
		will be empty. About XINO files, see the aufs manual.