T_OPEN(3N)

NAME
t_open - establish a transport endpoint

SYNOPSIS

#include <tiuser.h>

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

DESCRIPTION

t_open() must be called as the first step in the initialization of a transport endpoint. It establishes a transport endpoint by opening a file that identifies a particular transport provider (such as a transport protocol) and returning a file descriptor that identifies that endpoint. For example, opening the file /dev/tcp identifies an OSI connection-oriented transport layer protocol as the transport provider. Currently, /dev/tcp is the only transport protocol available to t_open().

path points to the pathname of the file to open, and oflag identifies any open flags (as in open(2V)). t_open() returns a file descriptor that will be used by all subsequent functions to identify the particular local transport endpoint.

This function also returns various default characteristics of the underlying transport protocol by setting fields in the t_info structure pointed to by info. t_info is defined in <nettli/tiuser.h> as:

    struct t_info {
    	long addr;	/* size of protocol address */
    	long options;	/* size of protocol options */
    	long tsdu;	/* size of max transport service data unit */
    	long etsdu;	/* size of max expedited tsdu */
    	long connect;	/* max data for connection primitives */
    	long discon;	/* max data for disconnect primitives */
    	long servtype;	/* provider service type */
    };

The fields of this structure have the following values:

addr
    A value greater than or equal to zero 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 zero 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 zero specifies the maximum size of a transport service data unit (TSDU); a value of zero specifies that the transport provider does not support the concept of TSDU, although it does support the sending of a data stream with 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.

etdsu
    A value greater than zero specifies the maximum size of an expedited transport service data unit (ETSDU); a value of zero specifies that the transport provider does not support the concept of ETSDU, although it does support the sending of an expedited data stream with 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 zero 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 zero specifies the maximum amount of data that may be associated with the t_snddis(3N) and t_rcvdis(3N) 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.

The servtype field of info may 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, t_open() will return -2 for etsdu, connect, and discon.

A single transport endpoint may support only one of the above services at one time.

If info is set to NULL by the transport user, no protocol information is returned by t_open().

If a transport user is concerned with protocol independence, the above sizes may be accessed to determine how large the buffers must be to hold each piece of information. Alternatively, the t_alloc(3N) function may be used to allocate these buffers. An error will result if a transport user exceeds the allowed data size on any function.

RETURN VALUES

t_open() returns a non-negative file descriptor on success. On failure, it returns -1 and sets t_errno to indicate the error.

ERRORS

TSYSERR
    The function failed due to a system error and set errno to indicate the error.

SEE ALSO
open(2V), tcp(4P)