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| Kernel Functions for Drivers | putnextctl(9F) |
| | putnextctl - send a control message to a queue |
SYNOPSIS
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#include <sys/stream.h>
int putnextctl(queue_t *q, int type); |
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Architecture independent level 1 (DDI/DKI).
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q
- Queue to which the message is to be sent.
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type
- Message type (must be control, not data type).
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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)
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On success, 1 is returned. If type is a data type, or if a message block cannot be allocated, 0 is returned.
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putnextctl() can be called from user or interrupt context.
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| | Example 1.
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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).
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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 }
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