putnextctl

- send a control message to a queue

Synopsis

#include <sys/stream.h>

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

A call to putnextctl(q,type) is an atomic equivalent of putctl(q->q_next,type). The STREAMS framework provides whatever mutual exclusion is necessary to insure that dereferencing q through its q_next field and then invoking putctl(9F) proceeds without interference from other threads.

The putnextctl() function should always be used in preference to putctl(9F)

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 putnextctl() function can be user, interrupt, or kernel context.

Examples

The send_ctl routine is used to pass control messages downstream. M_BREAK messages are handled with putnextctl( ) (line 8). putnextctl1(9F) (line 13) 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 9, 14). If an invalid message type is detected, cmn_err(9F) panics the system (line 18).

1 void
 2 send_ctl(queue_t *wrq, uchar_t type, uchar_t parm)
 3 {
 4            extern int num_alloc_fail;
 5
 6            switch (type) {
 7         case M_BREAK:
 8                if (!putnextctl(wrq, M_BREAK))
 9                            num_alloc_fail++;
10                   break;
11
12            case M_DELAY:
13                if (!putnextctl1(wrq, M_DELAY, parm))
14                            num_alloc_fail++;
15                break;
16
17         default:
18                cmn_err(CE_PANIC, "send_ctl: bad message type passed");
19                   break;
20            }
21  }

See Also

put(9E), cmn_err(9F), datamsg(9F), putctl(9F), putnextctl1(9F)

Writing Device Drivers

STREAMS Programming Guide