put(9E)

NAME

     put - receive messages from the preceding queue

SYNOPSIS

     #include <sys/types.h>
     #include <sys/stream.h>
     #include <sys/stropts.h>
     #include <sys/ddi.h>
     #include <sys/sunddi.h>

     int prefixrput(queue_t *q, mblk_t *mp);
     /* read side */

     int prefixwput(queue_t *q, mblk_t *mp);
     /* write side */

INTERFACE LEVEL

     Architecture independent level 1 (DDI/DKI). This entry point
     is required for STREAMS.

ARGUMENTS

     q     Pointer to the queue(9S) structure.

     mp    Pointer to the message block.

DESCRIPTION

     The primary task of the put() routine is to  coordinate  the
     passing  of messages from one queue to the next in a stream.
     The put() routine is called by  the  preceding  stream  com-
     ponent  (stream  module, driver, or stream head). put() rou-
     tines are designated ``write'' or ``read'' depending on  the
     direction of message flow.

     With few exceptions, a streams module or driver must have  a
     put()  routine.  One exception is the read side of a driver,
     which does not need a put() routine because there is no com-
     ponent  downstream  to  call it. The put() routine is always
     called before the component's  corresponding  srv(9E)  (ser-
     vice) routine, and so put() should be used for the immediate
     processing of messages.

     A put() routine must do at least one of the  following  when
     it receives a message:

        o  pass the message to the next component on  the  stream
           by calling the putnext(9F) function;

        o  process  the  message,  if  immediate  processing   is
           required  (for  example,  to handle high priority mes-
           sages); or

        o  enqueue the message (with the putq(9F)  function)  for
           deferred processing by the service srv(9E) routine.

     Typically, a put() routine  will  switch  on  message  type,
     which is contained in the db_type member of the datab struc-
     ture pointed to by mp. The action taken by the put() routine
     depends  on  the  message type. For example, a put() routine
     might process high priority messages,  enqueue  normal  mes-
     sages,  and handle an unrecognized M_IOCTL message by chang-
     ing its type  to  M_IOCNAK  (negative  acknowledgement)  and
     sending  it  back  to  the  stream head using the qreply(9F)
     function.

     The putq(9F) function can be used as a module's  put()  rou-
     tine when no special processing is required and all messages
     are to be enqueued for the srv(9E) routine.

RETURN VALUES

     Ignored.

CONTEXT

     put() routines do not have user context.

SEE ALSO

     srv(9E),     putctl(9F),      putctl1(9F),      putnext(9F),
     putnextctl(9F),   putnextctl1(9F),   putq(9F),   qreply(9F),
     queue(9S), streamtab(9S)

     Writing Device Drivers

     STREAMS Programming Guide