STREAMS/UX for the HP 9000 Reference Manual

Differences Between STREAMS/UX and System V Release 4 STREAMS

STREAMS/UX Uniprocessor Synchronization

than those listed above. A put or service routine can only pass its own queue's

q_next field or the q_next field of the other queue in its queue pair. These

requirements apply to bcanput, canput, put, putctl, putctl1, putctl2, and

streams_put. These utilities are not restricted when they are passed a parameter

of the form q, except that the queue must still be allocated.

2 Some STREAMS/UX utilities cannot be called from user functions passed to

timeout and bufcall or from non-STREAMS/UX code in the kernel. Also, this

software cannot share data structures with STREAMS/UX modules and drivers,

unless it raises the spl level to protect against interrupts. The utilities which

cannot be called are backq, bcanputnext, canputnext, ﬂushband, ﬂushq, freezestr,

getq, insq, putbq, putnext, putnextctl, putnextctl1, putnextctl2, qreply, qsize,

rmvq, SAMESTR, strqget, strqset, and unfreezestr. The user functions and

non-STREAMS/UX code cannot call bcanput, canput, put, putctl1, putctl2, or

streams_put if they pass the utility a parameter of the form q->q_next. They can

call these utilities if they pass a parameter of the form q (q must be a valid,

allocated queue). User functions and non-STREAMS/UX code can only call

putq if they pass it a driver's read queue or a lower mux's write queue. User

functions and non-STREAMS/UX code can use the new streams_put utility

documented in this chapter to get around these restrictions.

3 Some STREAMS/UX utilities cannot be called from free routines passed to

esballoc. A free routine can call the same utilities as the module or driver entry

point that called freeb.

4 If a multiplexor can execute on the ICS, take care when using putnext to pass

messages across the multiplexor. If the upper mux passes messages downward

by passing the lower mux's write queue to putnext, the upper mux must ensure

that the driver stays linked under the mux until after the putnext completes.

Likewise, if the lower mux passes messages upward by passing the upper mux's

read queue to putnext, the lower mux must guarantee that the driver stays linked

under the mux, the mux stays open, and modules are not pushed or popped until

after the putnext finishes.

5 A protect_q parameter can be passed to the weldq utility. The protect_q

parameter specifies which queue the func parameter can access safely. The func

function can use the same STREAMS/UX utilities as the protect_q put and

service routines.

6 The put and service routines cannot be called directly. They must be executed by

calling STREAMS/UX utilities such as putnext, putq or qenable. They cannot be

called using the function pointer stored in the q_qinfo structure.