msgb(D4) msgb(D4)
NAME
msgb - STREAMS message block structure
SYNOPSIS
#include <sys/types.h>
#include <sys/stream.h>
#include <sys/ddi.h>
DESCRIPTION
A STREAMS message is made up of one or more message blocks,
referenced by a pointer to a msgb structure. When a message
is on a queue, all fields are read-only to drivers and
modules.
USAGE
Structure Definitions
The msgb structure is defined as type mblk_t and contains the
following members:
struct msgb *b_next; /* next message on queue */
struct msgb *b_prev; /* previous message on queue */
struct msgb *b_cont; /* next block in message */
uchar_t *b_rptr; /* 1st unread data byte of buffer */
uchar_t *b_wptr; /* 1st unwritten data byte of buffer */
struct datab *b_datap; /* pointer to data block */
uchar_t b_band; /* message priority */
ushort_t b_flag; /* used by stream head */
The b_next and b_prev pointers are used to link messages
together on a queue(D4). These fields can be used by drivers
and modules to create linked lists of messages.
The b_cont pointer links message blocks together when a
message is composed of more than one block. Drivers and
modules can use this field to create complex messages from
single message blocks.
The b_rptr and b_wptr pointers describe the valid data region
in the associated data buffer. The b_rptr field points to the
first unread byte in the buffer and the b_wptr field points to
the next byte to be written in the buffer.
The b_datap field points to the data block [see datab(D4)]
associated with the message block. This field should never be
changed by modules or drivers.
Copyright 1994 Novell, Inc. Page 1
msgb(D4) msgb(D4)
The b_band field contains the priority band associated with
the message. Normal priority messages and high priority
messages have b_band set to zero. High priority messages are
high priority by virtue of their message type. This field can
be used to alter the queuing priority of the message. The
higher the priority band, the closer to the head of the queue
the message is placed.
The b_flag field contains a bitmask of flags that can be set
to alter the way the stream head will process the message.
Valid flags are:
MSGMARK The last byte in the message is ``marked.''
This condition is testable from user level via
the I_ATMARK ioctl(2).
REFERENCES
allocb(D3), datab(D4), esballoc(D3), freeb(D3), free_rtn(D4),
messages(D5)
NOTICES
Portability
All processors
Copyright 1994 Novell, Inc. Page 2