man/man9e/put.9e

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 PUT 9E "Mar 21, 2019"
 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 component (stream module, driver, or stream
head). put() routines 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 component downstream to call it. The
put() routine is always called before the component's corresponding
srv(9E) (service) 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:


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


process the message, if immediate processing is required (for example, to
handle high priority messages); or


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 structure 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 messages, and handle an unrecognized M_IOCTL message by
changing 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() routine 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