bcanputnext.9

7号信令功能代码,为开源代码

'\" tr
.\" -*- nroff -*-
.\"
.\" @(#) bcanputnext.9,v 1.1.4.1 2004/01/12 23:32:58 brian Exp
.\"
.\" =========================================================================
.\"
.\" Copyright (C) 2001-2004  OpenSS7 Corp. <www.openss7.com>
.\"
.\" All Rights Reserved.
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one
.\" 
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\" 
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" =========================================================================
.\"
.\" Modified 2004/01/12 23:32:58 by brian
.\"
.\" =========================================================================
.so lis.macros
.R1
bracket-label "\fR[\fB" "\fR]" "\fR, \fB"
no-default-database
database lis.refs
accumulate
move-punctuation
abbreviate A
join-authors ", " ", " " and "
et-al " et al" 2 3
abbreviate-label-ranges ".."
sort-adjacent-labels
.R2
.\"
.\"
.TH BCANPUTNEXT 9 "2004/01/12 23:32:58" "LiS-2_16_18-8" "Linux STREAMS DDI/DKI"
.SH NAME
.B bcanputnext
\- test flow control on a \fISTREAMS\fR message queue
.SH SYNOPSIS
.PP
.B #include <sys/stream.h>
.HP 8
.BI "int " retval " = bcanputnext(queue_t *" q ", int " band );
.SH DESCRIPTION
.PP
It is the responsibility of a
.IR STREAMS (4)
module putting a banded non-priority
message to a subsequent queue to check for flow control on that queue using
.BR bcanputnext ()
for the band associated with the message before placing a message on that
queue with
.BR putnext (9).
.PP
.BR bcanputnext ()
checks whether the stream is flow controlled starting at the specified queue,
.IR q ,
and for the specified
.IR band .
Starting at the
.I q
specified and for the
.I band
specified,
.BR bcanputnext ()
looks for the next forward queue which has a service routine or which has no
further forward queue.
.PP
If this forward queue has the
.B QB_FULL
flag clear indicating that it is not full for the specified
.IR band ,
.BR bcanputnext ()
will return true (1).
.PP
If this forward queue has the
.B QB_FULL
flag set indicating that it is full for the specified
.IR band ,
.BR bcanputnext ()
will return fails (0).
.PP
When
.BR bcanputnext ()
return false (0), it also sets the
.B QB_WANTW
flag for the specified
.IR band ,
indicating that the
.IR STREAMS (4)
executive should backenable service procedures
backwards up the queues when the flow controlled
.I band
is no longer full.
.SH "RETURN VALUES"
.PP
.BR bcanputnext ()
will return false (0) when the specified
.IR STREAMS (4)
message queue is flow
controlled for the specified band, and return true (1) when the specified
.IR STREAMS (4)
message queue is not flow controlled for the specified band.
.SH ERRORS
.PP
.BR bcanputnext ()
always succeed.
.SH CAVEATS
.PP
In the
.B LiS
.[
LiS
.]
implementation, if
.BR bcanputnext ()
suffers an internal error, it will return false (0).
.PP
.B LiS
.[
LiS
.]
implements
\fB\)canput(\fI\)q\fB\))\fR\),
\fB\)canputnext(\fI\)q\fB\))\fR\) and
\fB\)bcanputnext(\fI\)q\fB\), \fI\)band\fB\))\fR\)
with a macros that call
\fB\)bcanput(\fI\)q\fB\), \fI\)band\fB\))\fR\).
This does not protect the
.I q->q_next
dereference and can cause problems when modules are being pushed onto or
popped from running streams.
.SH "NOTES"
.PP
.B LfS
.[
LfS
.]
implements
.BR bcanputnext ()
directly and protects the
.I q->q_next
dereference.
.SH "SEE ALSO"
.PP
.BR putnext (9),
.BR canput (9),
.BR canputnext (9),
.BR bcanput (9),
.BR noenable "(9), and "
.BR enableok (9).
.SH BUGS
.PP
Because
.B LiS
calls
.BR bcanput (9)
with
.IR q->q_next ,
without locking the stream against module pushes, pops and other changes to
the
.I q->q_next
pointer, it is not MP-safe, largely defeating the purpose of the function.
.SH HISTORY
.PP
.BR bcanputnext ()
first appeared in SVR 4 MP.
.[
svr4
.]
.SH VERSIONS
.PP
This manpage was written for
.B LiS\c
.
.[
LiS
.]
.\"
.\"
.XX
.[
magic
.]
.[
svr42
.]
.[
svr4
.]
.\"
.\"
.[
$LIST$
.]
.TA