'\"! tbl | mmdoc
'\"macro stdmacro
.if n .pH ddi.rm/d4/gen/queue @(#)queue	43.8 of 11/18/92
.\" Copyright 1992, 1991 UNIX System Laboratories, Inc.
.TH queue D4
.IX "\f4queue\fP(D4)"
.SH NAME
\f4queue\fP \- STREAMS queue structure
.SH SYNOPSIS
.nf
.na
.ft 4
#include <sys/types.h>
#include <sys/stream.h>
#include <sys/ddi.h>
.ft 1
.ad
.fi
.SH DESCRIPTION
A instance of a STREAMS driver or module consists of two
\f4queue\fP structures, one for upstream (read-side) processing
and one for downstream (write-side) processing.
.SH USAGE
This structure is the major building block of a stream.
It contains pointers to the processing procedures, pointers to the
next queue in the stream, flow control parameters, and
a list of messages to be processed.
.SS Structure Definitions
The \f4queue\fP structure is defined as type \f4queue_t\fP
and contains the following members:
.P
.TS
lf4 2 lf4 2 lf4.
struct qinit	*q_qinfo;	/* module or driver entry points */
struct msgb	*q_first;	/* first message in queue */
struct msgb	*q_last;	/* last message in queue */
struct queue	*q_next;	/* next queue in stream */
void	*q_ptr;	/* pointer to private data structure */
ulong_t	q_count;	/* approximate size of message queue */
ulong_t	q_flag;	/* status of queue */
long	q_minpsz;	/* smallest packet accepted by QUEUE */
long	q_maxpsz;	/* largest packet accepted by QUEUE */
ulong_t	q_hiwat;	/* high water mark */
ulong_t	q_lowat;	/* low water mark */
.TE
The \f4q_qinfo\fP field contains a pointer to the \f4qinit\fP(D4)
structure specifying the processing routines and default values for
the queue.
This field should not be changed by drivers or modules.
.P
The \f4q_first\fP field points to the first message on the queue, or
is \f4NULL\fP if the queue is empty.
This field should not be changed
by drivers or modules.
.P
The \f4q_last\fP field points to the last message on the queue, or
is \f4NULL\fP if the queue is empty.
This field should not be changed
by drivers or modules.
.P
The \f4q_next\fP field points to the next queue in the stream.
This
field should not be changed by drivers or modules.
.P
The \f4q_ptr\fP field is a private field for use by drivers and modules.
It provides a way to associate the driver's per-minor data structure with
the queue.
.P
The \f4q_count\fP field contains the number of bytes in messages on the
queue in priority band 0.
This includes normal messages and high priority
messages.
.P
The \f4q_flag\fP field contains a bitmask of flags that indicate
different queue characteristics.
No flags may be set or cleared
by drivers or modules.
However, the following flags may be tested:
.RS 0
.IP \f4QREADR\fP 14n
The queue is the read queue.
Absence of this flag implies
a write queue.
.RE
.P
The \f4q_minpsz\fP field is the minimum packet size for
the queue.
This is an advisory limit specifying
the smallest message that can be accepted by the queue.
It is initially set to the value specified by the \f4mi_minpsz\fP
field in the \f4module_info\fP(D4) structure.
This field
can be changed by drivers or modules.
.P
The \f4q_maxpsz\fP field is the maximum packet size for
the queue.
This is an advisory limit specifying
the largest message that can be accepted by the queue.
It is initially set to the value specified by the \f4mi_maxpsz\fP
field in the \f4module_info\fP structure.
This field
can be changed by drivers or modules.
.P
The \f4q_hiwat\fP field is the high water mark for the
queue.
This specifies the number of bytes of
data contained in messages on the queue such that the queue is
considered full, and hence flow-controlled.
It is initially set to the value specified by the \f4mi_hiwat\fP
field in the \f4module_info\fP structure.
This field
can be changed by drivers or modules.
.P
The \f4q_lowat\fP field is the low water mark for the
queue.
This specifies the number of bytes of
data contained in messages on the queue such that the queue is
no longer flow-controlled.
It is initially set to the value specified by the \f4mi_lowat\fP
field in the \f4module_info\fP structure.
This field
can be changed by drivers or modules.
.SH REFERENCES
.na
\f4getq\fP(D3),
\f4module_info\fP(D4),
\f4msgb\fP(D4),
\f4putq\fP(D3),
\f4qinit\fP(D4),
\f4strqget\fP(D3),
\f4strqset\fP(D3)
.ad