structure are macros, because not all OS have F_FAVAIL and it seems tidier to
have macros for F_BAVAIL and F_FILES as well. Some kinds of file system do not
have inodes, and they return -1 for the number available.
Later: It turns out that some file systems that do not have the concept of
inodes return 0 rather than -1. Such systems should also return 0 for the total
structure are macros, because not all OS have F_FAVAIL and it seems tidier to
have macros for F_BAVAIL and F_FILES as well. Some kinds of file system do not
have inodes, and they return -1 for the number available.
Later: It turns out that some file systems that do not have the concept of
inodes return 0 rather than -1. Such systems should also return 0 for the total