Проект OpenNet: MAN putnextctl (9) Ядро (FreeBSD и Linux)

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putnextctl (9)

>> putnextctl (9) ( Solaris man: Ядро )

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).

PARAMETERS

: 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  }