putctl

- send a control message to a queue

Synopsis

#include <sys/stream.h>

int putctl(queue_t *q, int type);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

q

Queue to which the message is to be sent.

type

Message type (must be control, not data type).

Description

The putctl() function tests the type argument to make sure a data type has not been specified, and then attempts to allocate a message block. putctl() fails if type is M_DATA, M_PROTO, or M_PCPROTO, or if a message block cannot be allocated. If successful, putctl() calls the put(9E) routine of the queue pointed to by q with the newly allocated and initialized messages.

Return Values

On success, 1 is returned. If type is a data type, or if a message block cannot be allocated, 0 is returned.

Context

The putctl() function can be called from user, interrupt, or kernel context.

Examples

Example 1 Using putctl()

The send_ctl() routine is used to pass control messages downstream. M_BREAK messages are handled with putctl() (line 11). putctl1(9F) (line 16) is used for M_DELAY messages, so that parm can be used to specify the length of the delay. In either case, if a message block cannot be allocated a variable recording the number of allocation failures is incremented (lines 12, 17). If an invalid message type is detected, cmn_err(9F) panics the system (line 21).

1  void
 2  send_ctl(wrq, type, parm)
 3      queue_t *wrq;
 4      uchar_t type;
 5      uchar_t parm;
 6  {
 7          extern int num_alloc_fail;
 8
 9       switch (type) {
10          case M_BREAK:
11             if (!putctl(wrq->q_next, M_BREAK))
12                      num_alloc_fail++;
13                break;
14
15       case M_DELAY:
16             if (!putctl1(wrq->q_next, M_DELAY, parm))
17                      num_alloc_fail++;
18             break;
19
20       default:
21             cmn_err(CE_PANIC, "send_ctl: bad message type passed");
22                break;
23          }
24  }

See Also

put(9E), cmn_err(9F), datamsg(9F), putctl1(9F), putnextctl(9F)

Writing Device Drivers

STREAMS Programming Guide