Need efficient way to read file in reverse

[Guy Harris]

 >Alas, neither stat->st_blksize nor setbuffer() are universally
 >available, not even in a **IX environment.  You may need to use
 >setvbuf() instead, which itself isn't universally available.
 >
 >Modifying the meaning of "portable" still further, perhaps we could
 >settle for it to mean "works under 4.3BSD and System V Release 4".  Now
 >you're talking!

How about "works under 4.4BSD (which, if they offer the promised ANSI
C compatibility, will have 'setvbuf', as well as having 'st_blksize' in
the 'stat' structure) and System V Release 4 (which has 'st_blksize' in
the 'stat' structure, as well as having 'setvbuf')"?