bcanput(D3) bcanput(D3)
NAME
bcanput - test for flow control in a specified priority band
SYNOPSIS
#include <sys/types.h>
#include <sys/stream.h>
#include <sys/ddi.h>
int bcanput(queue_t *q, uchar_t pri);
Arguments
q Pointer to the message queue.
pri Message priority.
DESCRIPTION
Like the canput(D3) function, bcanput searches through the
stream (starting at q) until it finds a queue containing a
service routine, or until it reaches the end of the stream.
If found, the queue containing the service routine is tested
to see if a message of priority pri can be enqueued. If the
band is full, bcanput marks the queue to automatically back-
enable the caller's service routine when the amount of data in
messages on the queue has reached its low water mark.
Return Values
bcanput returns 1 if a message of priority pri can be sent in
the stream, or 0 if the priority band is flow-controlled. If
bcanput reaches the end of the stream without finding a queue
with a service routine, then it returns 1.
USAGE
The driver is responsible for both testing a queue with
bcanput and refraining from placing a message on the queue if
bcanput fails.
It is possible because of race conditions to test for room
using bcanput and get an indication that there is room for a
message, and then have the queue fill up before subsequently
enqueuing the message, causing a violation of flow control.
This is not a problem, since the violation of flow control in
this case is bounded.
In multithreaded drivers, the q argument may not reference
q_next (for example, an argument of q->q_next is erroneous in
a multithreaded driver and is disallowed by the DDI/DKI).
bcanputnext(q) is provided as a multiprocessor-safe equivalent
Copyright 1994 Novell, Inc. Page 1
bcanput(D3) bcanput(D3)
to the common call bcanput(q->q_next), which is no longer
allowed [see canputnext(D3)].
If pri is 0, the bcanput call is equivalent to a call to
canput.
Level
Base or Interrupt.
Synchronization Constraints
Does not sleep.
Driver-defined basic locks, read/write locks, and sleep locks
may be held across calls to this function.
The caller cannot have the stream frozen [see freezestr(D3)]
when calling this function.
REFERENCES
bcanputnext(D3), canput(D3), canputnext(D3), putbq(D3),
putnext(D3)
NOTICES
Portability
All processors
Applicability
ddi: 1, 2, 3, 4, 5, 5mp, 6, 6mp, 7, 7mp
Copyright 1994 Novell, Inc. Page 2