solaris Man Page: putnextctl(9f)

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putnextctl(9F) manual page Table of Contents

Name

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).

Arguments

q: Queue to which the message is to be sent.
type: Message type (must be control, not data type).

putnextctl() 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.

putnextctl() 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

putnextctl() can be called from user or interrupt context.

Example

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, u_char type, u_char 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  }