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pckt(7)


NAME

  pckt - STREAMS module for constructing message packets on a pty


DESCRIPTION

  The pckt module is a STREAMS module that can be used with a pseudoterminal
  to transfer messages in packet mode. The packet mode feature of pty devices
  allows the user process on the master side of the device to be informed of
  state changes.

  For packet mode to be enabled in the pty device, the user process must push
  the pckt module onto the master side of the pty with a call to the STREAMS
  I_PUSH ioctl() function.

  When the user process writes data, the pckt module passes the message on to
  the next module or driver unchanged. When the user process reads data or
  when the pckt module receives certain STREAMS message types, it constructs
  a packet out of the message for forwarding upstream.

  To construct a message packet, the module creates an M_PROTO message. This
  M_PROTO message contains the original message type in the first data block
  and the original message in as many data blocks as needed. The user process
  can then retrieve the M_PROTO message with a call to the getmsg() function.

  The STREAMS message types that the pckt module places in packets, are the
  following:

       M_DATA
       M_IOCTL
       M_PROTO
       M_PCPROTO
       M_FLUSH
       M_START
       M_STOP
       M_STARTI
       M_STOPI
       M_READ

  All other messages are passed unchanged upstream.

  If the message is an M_FLUSH message, the pckt module looks at the flag and
  takes the following actions:

    ·  If the flag is FLUSHW, the module changes it to FLUSHR before creating
       the M_PROTO message, and passes the message upstream. The module also
       sends an M_FLUSH message with the FLUSHW flag set.

    ·  If the flag is FLUSHR, the module changes it to FLUSHW before creating
       the M_PROTO message, and passes the message upstream.

    ·  If the flag is FLUSHRW, the module changes it to FLUSHW before
       creating the M_PROTO message, and passes the message upstream. The
       module also sends an M_FLUSH message with the FLUSHW flag set.


SEE ALSO

  Functions: getmsg(2), ioctl(2)

  Interfaces: ldterm(7), ptem(7), streamio(7)

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