Manpage of WR

Description: Manual Page

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WR

Section: Linux Fast-STREAMS DDI/DKI (9)
Updated: 2008-10-31
Index Return to Main Contents

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NAME

WR - return the write queue of a STREAMS queue pair

SYNOPSIS

#include <sys/stream.h>

queue_t *WR(q);

ARGUMENTS

q

a pointer to either the read or write queue of a queue pair.

INTERFACE

STREAMS.

DESCRIPTION

WR() returns the write queue associated with the queue pair indicated by the queue pointer q, regardless of whether q points to the write queue or the write queue of the queue pair.

USAGE

WR() is typically and often used to find the write queue from a pointer to one of the queues in a queue pair.

See also RD(9) for finding the read queue in the pair, and OTHERQ(9) for finding the other queue in the pair.

RETURN

WR() returns a pointer to the write queue of the queue pair referenced by q.

ERRORS

WR() always succeeds.

CONTEXT

WR() can be called from any context, including user context, module procedures, callouts, callbacks, soft interrupts (tasklets and bottom halves), and interrupt service routines.

MP-STREAMS

WR() is MP-safe; however, the caller is responsible for the validity of the reference q. References to q from a procedure, call-out or callback predicated on the queue pair to which q belongs are guaranteed valid. The caller must guarantee validity from call-outs, callbacks, soft interrupts and interrupt service routines not predicated on the queue pair to which q belongs.

IMPLEMENTATION

queue(9) structures are always allocated in pairs as an array of two queue(9) structure elements. The first structure in the array is always the read queue and has QREADR set in q_flag; the second, the write queue, with QREADR clear. Because of this relationship between queues in a pair, WR() is easily implemented as a macro as follows:

#define WR(q) ((q->q_flag & QREADR) ? (q+1) : (q))

NOTICES

If q is invalid, the result is undefined.

If q is NULL, a kernel panic may occur.

If q points to a write queue, q will be returned.

SEE ALSO

WR(9), OTHERQ(9), SAMESTR(9).

BUGS

WR() has no known bugs.

COMPATIBILITY

WR() is compatible with SVR 4.2 MP DDI/DKI[1], and systems based on SVR 4, with the following portability considerations:

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SUPER-UX®[2], UnixWare®[3], LiS[4], permit both a read or write queue pointer to be passed as the q argument to WR(). If a write queue pointer is passed to WR(), then the passed in write queue pointer is returned.

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AIX®[5], OSF/1®[6], Solaris®[7], UXP/V®[8], permit only a read queue to be passed as the q argument to WR(). Passing a write queue to WR() on these implementations can cause a kernel panic. On these systems WR() is often defined as:

#define WR(__q) ((__q)+1)

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WR() is implemented on Linux Fast-STREAMS as both an extern inline function as well as a macro. It accepts either read or write queue pointer and returns the passed in write queue pointer when called with a write queue. WR(q) == WR(WR(q)) and WR(RD(q)) == (RD(q) + 1) are invariantly true.

#undef WR
#define WR(__q) ((__q)+1)

is a valid alternative implementation if the STREAMS programmer wishes the more restrictive WR() behavior.

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Portable STREAMS drivers and modules should not call WR() with a queue other than the read queue; nor rely upon WR() being defined as a macro or a function.

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Because the size and members of the queue(9) structure vary from implementation to implementation, binary compatibility is not guaranteed.

See STREAMS(9) for additional compatibility information.

CONFORMANCE

SVR 4.2 MP DDI/DKI[1]

HISTORY

WR() appears as part of SVR 4.0 STREAMS[9].

WR() first appeared in SVR 3[10], where it was defined as a macro.

REFERENCES

[1]

USL DDI/DKI, Device Driver Interface/Driver-Kernel Interface (DDI/DKI) Reference Manual for Intel Processors, 1992, (Englewood Cliffs, New Jersey), AT&T UNIX System Laboratories, Inc., Prentice Hall.

[2]

SUPER-UX® Release 9.2, SUPER-UX STREAMS Programmers Guide, 1999, NEC Corporation, NEC.

[3]

UnixWare® 7.1.3, UnixWare® 7 STREAMS Programmer's Guide, 2002, (Lindon, Utah), Caldera International, Inc., Caldera. <http://uw713doc.sco.com/>

[4]

LIS 2.18, Linux STREAMS (LiS) 2.18.6 Source Code, Brian Bidulock, ed., OpenSS7 Corporation. <http://www.openss7.org/>

[5]

AIX® 5L Version 5.1, AIX STREAMS Programmers Guide, 2001, (Boulder, Colorado), Internatonal Business Machines Corp., IBM. <http://publibn.boulder.ibm.com/>

[6]

Digital® UNIX (OSF/1.2), Digital UNIX: Network Programmers Guide, 1996, (Palo Alto, California), Digital Equipment Corporation, Hewlett-Packard Company. <http://www.true64unix.compaq.com/docs/>

[7]

Solaris® 8, STREAMS Programming Guide, August 1999, (Palo Alto, California), Sun Microsystems, Inc., Sun. [Part No: 805-7478-05] <http://docs-pdf.sun.com/>

[8]

UXP/V® V10L10, UXP/V Programmer's Guide: STREAMS V10, 1997, Fujitsu Limited, Fujitsu.

[9]

SVR 4, UNIX® System V Release 4 STREAMS Programmer's Guide, 1990, (Englewood Cliffs, New Jersey), AT&T UNIX System Laboratories, Inc., Prentice Hall.

[10]

SVR 3, UNIX® System V Release 3 STREAMS Programmer's Guide, (Englewood Cliffs, New Jersey), AT&T UNIX System Laboratories, Inc., Prentice Hall.

TRADEMARKS

OpenSS7tm

is a trademark of OpenSS7 Corporation.

Linux®

is a registered trademark of Linus Torvalds.

UNIX®

is a registered trademark of The Open Group.

Solaris®

is a registered trademark of Sun Microsystems.

Other trademarks are the property of their respective owners.

IDENTIFICATION

Linux Fast-STREAMS: Package streams version 0.9.2.4 released 2008-10-31.

Copyright©1997-2008OpenSS7 Corp. All Rights Reserved.
(See roff source for permission notice.)

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Index

NAME

SYNOPSIS

ARGUMENTS

INTERFACE

DESCRIPTION

USAGE

RETURN

ERRORS

CONTEXT

MP-STREAMS

IMPLEMENTATION

NOTICES

SEE ALSO

BUGS

COMPATIBILITY

CONFORMANCE

HISTORY

REFERENCES

TRADEMARKS

IDENTIFICATION

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