++- for aufs5.13 and later
++ Because aufs is not only an ordinary filesystem (callee of VFS), but
++ also a caller of VFS functions for branch filesystems, subclassing of
++ the internal locks for LOCKDEP is necessary. LOCKDEP is a debugging
++ feature of linux kernel. If you enable CONFIG_LOCKDEP, then you will
++ need to customize some LOCKDEP numbers. Here are what I use on my
++ test environment.
++ CONFIG_LOCKDEP_BITS=21
++ CONFIG_LOCKDEP_CHAINS_BITS=21
++ CONFIG_LOCKDEP_STACK_TRACE_BITS=24