+ *
+ * Note: The parent process must be careful to avoid deadlock.
+ * 1) If you write more than PIPE_MAX bytes or, more generally, if you write
+ * more bytes than the subprocess can handle at once, the subprocess
+ * may write its data and wait on you to read it, but you are currently
+ * busy writing.
+ * 2) When you don't know ahead of time how many bytes the subprocess
+ * will produce, the usual technique of calling read (fd, buf, BUFSIZ)
+ * with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause
+ * the read() call to block until *all* of the buffer has been filled.
+ * But the subprocess cannot produce more data until you gave it more
+ * input. But you are currently busy reading from it.