-APUE-:
fig15.31, print where various types of data are stored.
fig15.33, IPC between parent and child using memory mapped
          I/O of /dev/zero.
(mod)fig15.33, use MAP_ANON with mmap.
-APUE-:
ex15.3, what happens if popen runs a nonexist program.
ex15.5, use standard library function in pipe_add2.
ex15.7, how select() handles pipes.
ex15.10, a FIFO for both reading and writing.
ex15.12, testing message queue.