putnextctl(9F)

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).

DESCRIPTION

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

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