STREAMS-UX Programmer's Guide (February 2007)

Modules and Drivers

Data Structures

Chapter 4

Data Structures

A STREAMS module or driver must define and initialize three data structures — module_info, qinit, and

streamtab. An optional module_stat structure can also be defined and initialized. In addition to these data

structures, HP-UX requires all modules and drivers to define streams_info_t. Drivers must define

drv_info_t and drv_ops_t.

DLKM modules require additional data structures to be defined. These are described in the “DLKM

STREAMS” section.

The module_info Structure

The module_info structure provides the information about a module or driver. The information in this

structure is shared between both the read and write queues:

unsigned short mi_idnum; /* module ID number */

char * mi_idname; /* module name */

long mi_minpsz; /* min packet size use */

long mi_maxpsz; /* max packet size use */

ulong mi_hiwat; /* high water mark, for flow control */

ulong mi_lowat; /* low water mark, for flow control */

mi_idnum

Represents a number used to identify the module or driver. When this field is set to zero,

STREAMS assigns a unique number. If it is set by the driver or module, case, STREAMS

cannot ensure a unique number. The mi_idnum can be used by user processes and the

STREAMS driver or modules in tracing events and logging errors as specified in strlog (7).

See Appendix B, “STREAMS Utilities Supported by HP-UX.”

mi_idname

Is a pointer to an array of characters representing a unique name. The name identifies the

module or driver. This parameter is set by the module or driver developer. STREAMS

truncates the extra characters if the name exceeds FMNAMESZ.

mi_minpsz and mi_maxpsz

The minimum and maximum packet size of an M_DATA message that are accepted by a

module or driver. These values are copied onto q_minpsz and q_maxpsz during open (), for a

driver or the push () for a module.

These limits are used by the stream head when sending messages downstream. The stream

head uses q_maxpsz of the top most module to fragment the data, if required, for large

writes. These are advisory limits between modules and drivers.

mi_hiwat and mi_lowat

The values represent the flow control parameters for a queue. These values represent the

maximum and minimum number of bytes that can be put onto the message queues. They

are copied onto q_hiwat and q_lowat, respectively.