Architecture independent level 1 (DDI/DKI).

cq

The pointer to the current queue. queue_t is an alias for the queue(9S) structure.

backq() returns a pointer to the queue preceding cq (the current queue). If cq is a read queue, backq() returns a pointer to the queue downstream from cq, unless it is the stream end. If cq is a write queue, backq() returns a pointer to the next queue upstream from cq, unless it is the stream head.

If successful, backq() returns a pointer to the queue preceding the current queue. Otherwise, it returns NULL.

backq() can be called from user or interrupt context.

queue(9S)

Writing Device Drivers

STREAMS Programming Guide