SVR5 and SCO OpenServer 5

bcanput(D3str)

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);

Description

Like the canput(D3str) 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.

Arguments

q: Pointer to the message queue.
pri: Message priority. If pri is 0, the bcanput call is equivalent to a call to canput.

Return values (DDI)

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.

Return values (ODDI)

bcanput( ) returns 1 if there is room for the given priority message in the queue, or 0 if the queue has no more room for messages of the given priority.

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 DDI 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). bcanputnext(q) is provided as a multiprocessor-safe equivalent to the common call bcanput(q->q_next), which is no longer allowed (see canputnext(D3str)).

Context

Base or Interrupt.

Synchronization constraints

Does not block.

Driver-defined basic locks, read/write locks, and sleep locks may be held across calls to this function.

For DDI drivers, the caller cannot have the stream frozen (see freezestr(D3str)) when calling this function.

Hardware applicability

All

Version applicability

ddi: 1, 2, 3, 4, 5, 5mp, 6, 6mp, 7, 7mp, 7.1, 7.1mp, 8, 8mp
oddi: 1, 2, 2mp, 3, 3mp, 4, 4mp, 5, 5mp, 6, 6mp

SCO OpenServer 5 ODDI compatibility

References

bcanputnext(D3str), canput(D3str), canputnext(D3str), putbq(D3str), putnext(D3str)

``Uniplexor (UNI multiplexor)'' in HDK Technical Reference