In non-canonical mode input is available immediately (without the  user
       having  to  type  a line-delimiter character), and line editing is dis-
       abled.  The settings of MIN (c_cc[VMIN]) and TIME (c_cc[VTIME])  deter-
       mine  the  circumstances  in  which a read(2) completes; there are four
       distinct cases:

       * MIN == 0; TIME == 0: If data is available,  read(2)  returns  immedi-
         ately,  with the lesser of the number of bytes available, or the num-
         ber of bytes requested.  If no data is available, read(2) returns 0.

       * MIN > 0; TIME == 0: read(2) blocks until the lesser of MIN  bytes  or
         the  number  of bytes requested are available, and returns the lesser
         of these two values.

       * MIN == 0; TIME > 0: TIME specifies the limit for a timer in tenths of
         a  second.   The  timer  is  started when read(2) is called.  read(2)
         returns either when at least one byte of data is available,  or  when
         the  timer  expires.  If the timer expires without any input becoming
         available, read(2) returns 0.

       * MIN > 0; TIME > 0: TIME specifies the limit for a timer in tenths  of
         a second.  Once an initial byte of input becomes available, the timer
         is restarted after each further byte is  received.   read(2)  returns
         either  when  the lesser of the number of bytes requested or MIN byte
         have been read, or when the inter-byte timeout expires.  Because  the
         timer  is  only  started after the initial byte becomes available, at
         least one byte will be read.