The files fsusage.c and fsusage.h have been stolen from the GNU
Coreutils package (version 5.0) and are the actual implementation of
the fsusage function.

The only changes that have been made to these files is that some code
for SVR2 has been ripped out since it depended on some more code (SVR3
was released in 1986 and introduced shared libraries), and the
functions have been prefixed with glibtop_private to avoid name
clashes with user code.