t_getinfo Subroutine for X/Open Transport Interface

Purpose

Get protocol-specific service information.

Library

X/Open Transport Interface Library (libxti.a)

Syntax

#include <xti.h>
int t_getinfo (fd, info)
int fd;
struct t_info *info;

Description

The t_getinfo subroutine returns the current characteristics of the underlying transport protocol and/or transport connection associated with the file descriptor specified by the fd parameter. The pointer specified by the info parameter returns the same information returned by the t_open subroutine, although not necessarily precisely the same values. This subroutine enables a transport user to access this information during any phase of communication.

Parameters

Item Description
fd Specifies the file descriptor.
info Points to a t_info structure which contains the following members: 
long addr;     /* max size of the transport protocol       */
               /* address                                  */
long options;  /* max number of bytes of protocol-specific */
               /* options                                  */
long tsdu;     /* max size of a transport service data     */
               /* unit (TSDU)                              */
long etsdu;    /* max size of an expedited transport       */
               /* service data unit (ETSDU)                */
long connect;  /* max amount of data allowed on connection */
               /* establishment functions                  */
long discon;   /* max amount of data allowed on t_snddis   */
               /* and t_rcvdis functions                   */
long servtype; /* service type supported by the transport  */
               /* provider                                 */
long flags;    /* other info about the transport provider  */

The values of the fields have the following meanings:

Field Description
addr A value greater than zero indicates the maximum size of a transport protocol address and a value of -2 specifies that the transport provider does not provide user access to transport protocol addresses.
options A value greater than zero indicates the maximum number of bytes of protocol-specific options supported by the provider, and a value of -2 specifies that the transport provider does not support options set by users.
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 datastream 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.
etsdu 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. Note that the semantics of expedited data may be quite different for different transport providers (see Appendix A, ISO Transport Protocol Information and Appendix B, Internet Protocol-specific Information) .
connect A value greater than zero specifies the maximum amount of data that may be associated with connection establishment functions 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 zero specifies the maximum amount of data that may be associated with the t_snddis and t_rcvdis subroutines 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 on return. The possible values are:
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 will return -2 for etsdu, connect and discon.
flags This is a bit field used to specify other information about the transport provider. If the T_SENDZERO bit is set in flags, this indicates that the underlying transport provider supports the sending of zero-length TSDUs. See Appendix A, ISO Transport Protocol Information for a discussion of the separate issue of zero-length fragments within a TSDU.

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 subroutine may be used to allocate these buffers. An error results if a transport user exceeds the allowed data size on any subroutine. The value of each field may change as a result of protocol option negotiation during connection establishment (the t_optmgmt call has no affect on the values returned by the t_getinfo subroutine). These values will only change from the values presented to the t_open subroutine after the endpoint enters the T_DATAXFER state.

Valid States

ALL - apart from T_UNINIT.

Return Values

Item Description
0 Successful completion.
-1 t_errno is set to indicate an error.

Error Codes

On failure, t_errno is set to one of the following:

Value Description
TBADF The specified file descriptor does not refer to a transport endpoint.
TSYSERR A system error has occurred during execution of this subroutine.
TPROTO This error indicates that a communication problem has been detected between the X/Open Transport Interface and the transport provider for which there is no other suitable X/Open Transport Interface (t_errno).