t_open Subroutine for Transport Layer Interface

Communications Technical Reference, Volume 2

t_open Subroutine for Transport Layer Interface

Purpose

Establishes a transport end point.

Library

Transport Layer Interface Library (libtli.a)

Syntax

#include <tiuser.h>

int t_open(path, oflag, info)
char *path;
int oflag;
struct t_info *info;

Description

The t_open subroutine must be called as the first step in the initialization of a transport end point. This subroutine establishes a transport end point, first, by opening a UNIX system file that identifies a particular transport provider (that is, transport protocol) and then returning a file descriptor that identifies that end point. For example, opening the /dev/dlpi/tr file identifies an 802.5 data link provider.

Parameters

path

Points to the path name of the file to open.

oflag

Specifies the open routine flags.

info

Points to a t_info structure.

The info parameter points to a t_info structure that contains the following elements:

long addr;
long options;
long tsdu;
long etsdu;
long connect;
long discon;
long servtype;

The values of the elements have the following meanings:

`addr`	A value greater than or equal to 0 indicates the maximum size of a transport protocol address; a value of -1 specifies that there is no limit on the address size; and a value of -2 specifies that the transport provider does not provide user access to transport protocol addresses.
`options`	A value greater than or equal to 0 indicates the maximum number of bytes of protocol-specific options supported by the provider; a value of -1 specifies that there is no limit on the option size; and a value of -2 specifies that the transport provider does not support user-settable options.
`tsdu`	A value greater than 0 specifies the maximum size of a transport service data unit (TSDU); a value of 0 specifies that the transport provider does not support the concept of TSDU, although it does support the sending of a data stream having no logical boundaries preserved across a connection; a value of -1 specifies that there is no limit on the size of a TSDU; and a value of -2 specifies that the transfer of normal data is not supported by the transport provider.
`etsdu`	A value greater than 0 specifies the maximum size of a expedited transport service data unit (ETSDU); a value of 0 specifies that the transport provider does not support the concept of ETSDU, although it does support the sending of an expedited data stream having no logical boundaries preserved across a connection; a value of -1 specifies that there is no limit on the size of an ETSDU; and a value of -2 specifies that the transfer of expedited data is not supported by the transport provider.
`connect`	A value greater than or equal to 0 specifies the maximum amount of data that may be associated with connection establishment functions; a value of -1 specifies that there is no limit on the amount of data sent during connection establishment; and a value of -2 specifies that the transport provider does not allow data to be sent with connection establishment functions.
`discon`	A value greater than or equal to 0 specifies the maximum amount of data that may be associated with the t_snddis and t_rcvdis functions; a value of -1 specifies that there is no limit on the amount of data sent with these abortive release functions; and a value of -2 specifies that the transport provider does not allow data to be sent with the abortive release functions.
`servtype`	This field specifies the service type supported by the transport provider, as described in the Return Values section.

If a transport user is concerned with protocol independence, these sizes may be accessed to determine how large the buffers must be to hold each piece of information. Alternatively, the t_alloc subroutine can be used to allocate these buffers. An error results if a transport user exceeds the allowed data size on any function.

Return Values

On successful completion, the t_open subroutine returns a valid file descriptor. Otherwise, it returns a value of -1, and the t_errno variable is set to indicate the error.

The servtype field of the info parameter can specify one of the following values on return:

T_COTS	The transport provider supports a connection-mode service but does not support the optional orderly release facility.
T_COTS_ORD	The transport provider supports a connection-mode service with the optional orderly release facility.
T_CLTS	The transport provider supports a connectionless-mode service. For this service type, the t_open subroutine returns -2 for the values in the `etsdu`, `connect`, and `discon` fields.

A single transport end point can support only one of the above services at one time.

If the info parameter is set to null by the transport user, no protocol information is returned by the t_open subroutine.

Error Codes

If unsuccessful, the t_errno variable is set to the following:

TSYSERR

A system error has occurred during the startup of this function.

Implementation Specifics

This subroutine is part of Base Operating System (BOS) Runtime.

Related Information

The open subroutine, t_close subroutine.

List of Streams Programming References and STREAMS Overview in AIX Version 4.3 Communications Programming Concepts.