Technical Reference: Communications, Volume 2

t_bind Subroutine for X/Open Transport Interface

Purpose

Bind an address to a transport endpoint.

Library

X/Open Transport Interface Library (libxti.a)

Syntax

#include <xti.h>
 
int t_bind (fd, req, ret)
    int fd;
    const struct t_bind *req;
    struct t_bind *ret;

The t_bind subroutine associates a protocol address with the transport endpoint specified by the fd parameter and activates that transport endpoint. In connection mode, the transport provider may begin enqueuing incoming connect indications or servicing a connection request on the transport endpoint. In connectionless mode, the transport user may send or receive data units through the transport endpoint.

The req and ret parameters point to a t_bind structure containing the following members:

struct netbuf addr;
unsigned qlen;

Within this structure, the fields have the following meaning:

addr	Specifies a protocol address.
qlen	Indicates the maximum number of outstanding connect indications.

If the requested address is not available, the t_bind subroutine returns -1 with t_errno set as appropriate. If no address is specified in the req parameter, (that is, the len field of the addr field in the req parameter is zero or the req parameter is NULL), the transport provider assigns an appropriate address to be bound, and returns that address in the addr field of the ret parameter. If the transport provider could not allocate an address, the t_bind subroutine fails with t_errno set to TNOADDR.

The qlen field has meaning only when initializing a connection-mode service. This field specifies the number of outstanding connect indications that the transport provider should support for the given transport endpoint. An outstanding connect indication is one that has been passed to the transport user by the transport provider but which has not been accepted or rejected. A qlen field value of greater than zero is only meaningful when issued by a passive transport user that expects other users to call it. The value of the qlen field is negotiated by the transport provider and may be changed if the transport provider cannot support the specified number of outstanding connect indications. However, this value of the qlen field is never negotiated from a requested value greater than zero to zero. This is a requirement on transport providers. See "Implementation Specifics" for more information. On return, the qlen field in the ret parameter contains the negotiated value.

Parameters

Specifies the transport endpoint. If the fd parameter refers to a connection-mode service, this function allows more than one transport endpoint to be bound to the same protocol address. However, the transport provider must also support this capability and it is not possible to bind more than one protocol address to the same transport endpoint. If a user binds more than one transport endpoint to the same protocol address, only one endpoint can be used to listen for connect indications associated with that protocol address. In other words, only one t_bind for a given protocol address may specify a qlen field value greater than zero. In this way, the transport provider can identify which transport endpoint should be notified of an incoming connect indication. If a user attempts to bind a protocol address to a second transport endpoint with a a qlen field value greater than zero, t_bind will return -1 and set t_errno to TADDRBUSY. When a user accepts a connection on the transport endpoint that is being used as the listening endpoint, the bound protocol address will be found to be busy for the duration of the connection, until a t_unbind or t_close call has been issued. No other transport endpoints may be bound for listening on that same protocol address while that initial listening endpoint is active (in the data transfer phase or in the T_IDLE state). This will prevent more than one transport endpoint bound to the same protocol address from accepting connect indications.

If the fd parameter refers to a connectionless-mode service, only one endpoint may be associated with a protocol address. If a user attempts to bind a second transport endpoint to an already bound protocol address, t_bind will return -1 and set t_errno to TADDRBUSY.

req

Specifies the address to be bound to the given transport endpoint. The req parameter is used to request that an address, represented by the netbuf structure, be bound to the given transport endpoint. The netbuf structure is described in the xti.h file. In the req parameter, the netbuf structure addr fields have the following meanings:

buf: Points to the address buffer.
len: Specifies the number of bytes in the address.
maxlen: Has no meaning for the req parameter.

The req parameter may be a null pointer if the user does not specify an address to be bound. Here, the value of the qlen field is assumed to be zero, and the transport provider assigns an address to the transport endpoint. Similarly, the ret parameter may be a null pointer if the user does not care what address was bound by the provider and is not interested in the negotiated value of the qlen field. It is valid to set the req and ret parameters to the null pointer for the same call, in which case the provider chooses the address to bind to the transport endpoint and does not return that information to the user.

ret

Specifies the maximum size of the address buffer. On return, the ret parameter contains the address that the transport provider actually bound to the transport endpoint; this is the same as the address specified by the user in the req parameter. In the ret parameter, the netbuf structure fields have the following meanings:

buf: Points to the buffer where the address is to be placed. On return, this points to the bound address.
len: Specifies the number of bytes in the bound address on return.
maxlen: Specifies the the maximum size of the address buffer. If the value of the maxlen field is not large enough to hold the returned address, an error will result.

Valid States

T_UNBIND.

Return Values

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:

TACCES	The user does not have permission to use the specified address.
TADDRBUSY	The requested address is in use.
TBADADDR	The specified protocol address was in an incorrect format or contained illegal information.
TBADF	The specified file descriptor does not refer to a transport endpoint.
TBUFOVLW	The number of bytes allowed for an incoming argument (maxlen) is greater than 0 but not sufficient to store the value of that argument. The provider's state will change to T_IDLE and the information to be returned in ret will be discarded.
TNOADDR	The transport provider could not allocate an address.
TOUTSTATE	The function was issued in the wrong sequence.
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).
TSYSERR	A system error has occurred during execution of this function.

Implementation Specifics

The requirement that the value of the qlen field never be negotiated from a requested value greater than zero to zero implies that transport providers, rather than the X/Open Transport Interface implementation itself, accept this restriction.

A transport provider may not allow an explicit binding of more than one transport endpoint to the same protocol address, although it allows more than one connection to be accepted for the same protocol address. To ensure portability, it is, therefore, recommended not to bind transport endpoints that are used as responding endpoints, (those specified in the resfd parameter), in a call to the t_accept subroutine, if the responding address is to be the same as the called address.

Related Information

The t_alloc subroutine, t_close subroutine, t_open subroutine, t_optmgmt subroutine, t_unbind subroutine.