disk usage in perl without modules or /bin/df

I have a very minimal system where I can't use df because I want an extended output df can't do, and I can't install CPAN modules (there isn't Filesys::Df, Filesys::Statfs, etc) I want it to take args of a given file/directory. stat()'s first returned arg is st_dev. What's a system call that can return current usage and total size of a dev? stracing df shows it does a stat then a statfs, but I can't seem to access the statfs system call from perl without Filesys::Statfs. Sigh, embedded (very large) systems. -- Tim Connors