This lets you implement filesystems in perl, through the FUSE (Filesystem in USErspace) kernel/lib interface. FUSE expects you to implement callbacks for the various functions. In the following definitions, "errno" can be 0 (for a success), -EINVAL, -ENOENT, -EONFIRE, any integer less than 1 really. You can import standard error constants by saying something like "use POSIX qw(EDOTDOT ENOANO);". Every constant you need (file types, open() flags, error values, etc) can be imported either from POSIX or from Fcntl, often both. See their respective documentations, for more information. WWW: http://search.cpan.org/dist/Fuse/