take it or drop it

At CERN controls installations, devices of the same class are
enumerated by a statically defined number known as LUN (logical
unit number), that maps into geographical information via
database entries. These are mapped through userspace programs
and stored as tags in device node names.

This patch adds a function to exploit this numbering

Under CERN CO current standard compiler
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-52)
a long, 64 bit division is generated even if the divisor is
a power of 2 (sigh). So we need yet another div_u64_rem.