datab(D4)datab(D4)NAMEdatab - STREAMS data block structure
SYNOPSIS
#include <sys/types.h>
#include <sys/stream.h>
#include <sys/ddi.h>
DESCRIPTION
The datab structure describes the data of a STREAMS message.
USAGE
The actual data contained in a STREAMS message is stored in a data buffer
pointed to by this structure. A message block structure [msgb(D4)]
includes a field that points to a datab structure.
A data block can have more than one message block pointing to it at one
time, so the db_ref member keeps track of a data block's references,
preventing it from being deallocated until all message blocks are
finished with it.
Structure Definitions
The datab structure is defined as type dblk_t and contains the following
members:
uchar_t *db_base; /* first byte of buffer */
uchar_t *db_lim; /* last byte (+1) of buffer */
uchar_t db_ref; /* # of message pointers to this data */
uchar_t db_type; /* message type */
The db_base field points to the beginning of the data buffer. Drivers
and modules should not change this field.
The db_lim field points to one byte past the end of the data buffer.
Drivers and modules should not change this field.
The db_ref field contains a count of the number of message blocks sharing
the data buffer. If it is greater than 1, drivers and modules should not
change the contents of the data buffer. Drivers and modules should not
change this field.
The db_type field contains the message type associated with the data
buffer. This field can be changed by the driver. However, if the db_ref
field is greater than 1, this field should not be changed.
REFERENCESfree_rtn(D4), messages(D5), msgb(D4)
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