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man pages section 3: Basic Library Functions

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Updated: Thursday, June 13, 2019
 
 

t_rcvudata(3C)

Name

t_rcvudata - receive a data unit

Synopsis

#include <xti.h>

int t_rcvudata(int fd, struct t_unitdata *unitdata, int *flags);

Description

This routine is part of the XTI interfaces which evolved from the TLI interfaces. XTI represents the future evolution of these interfaces. However, TLI interfaces are supported for compatibility. When using a TLI routine that has the same name as an XTI routine, the tiuser.h header file must be used. Refer to the TLI COMPATIBILITY section for a description of differences between the two interfaces.

This function is used in connectionless-mode to receive a data unit from another transport user. The argument fd identifies the local transport endpoint through which data will be received, unitdata holds information associated with the received data unit, and flags is set on return to indicate that the complete data unit was not received. The argument unitdata points to a t_unitdata structure containing the following members:

struct netbuf addr;
struct netbuf opt;
struct netbuf udata;

The maxlen field of addr, opt and udata must be set before calling this function to indicate the maximum size of the buffer for each. If the maxlen field of addr or opt is set to zero, no information is returned in the buf field of this parameter.

On return from this call, addr specifies the protocol address of the sending user, opt identifies options that were associated with this data unit, and udata specifies the user data that was received.

By default, t_rcvudata() operates in synchronous mode and will wait for a data unit to arrive if none is currently available. However, if O_NONBLOCK is set by means of t_open(3C) or fcntl(2), t_rcvudata() will execute in asynchronous mode and will fail if no data units are available.

If the buffer defined in the udata field of unitdata is not large enough to hold the current data unit, the buffer will be filled and T_MORE will be set in flags on return to indicate that another t_rcvudata() should be called to retrieve the rest of the data unit. Subsequent calls to t_rcvudata() will return zero for the length of the address and options until the full data unit has been received.

If the call is interrupted, t_rcvudata() will return EINTR and no datagrams will have been removed from the endpoint.

Return Values

Upon successful completion, a value of 0 is returned. Otherwise, a value of −1 is returned and t_errno is set to indicate an error.

VALID STATES

T_IDLE.

Errors

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

TBADF

The specified file descriptor does not refer to a transport endpoint.

TBUFOVFLW

The number of bytes allocated for the incoming protocol address or options (maxlen) is greater than 0 but not sufficient to store the information. The unit data information to be returned in unitdata will be discarded.

TLOOK

An asynchronous event has occurred on this transport endpoint and requires immediate attention.

TNODATA

O_NONBLOCK was set, but no data units are currently available from the transport provider.

TNOTSUPPORT

This function is not supported by the underlying transport provider.

TOUTSTATE

The communications endpoint referenced by fd is not in one of the states in which a call to this function is valid.

TPROTO

This error indicates that a communication problem has been detected between XTI and the transport provider for which there is no other suitable XTI error (t_errno).

TSYSERR

A system error has occurred during execution of this function.

TLI COMPATIBILITY

The XTI and TLI interface definitions have common names but use different header files. This, and other semantic differences between the two interfaces are described in the subsections below.

Interface Header

The XTI interfaces use the header file, xti.h. TLI interfaces should not use this header. They should use the header:

  • #include <tiuser.h>

Error Description Values

The t_errno values that can be set by the XTI interface and cannot be set by the TLI interface are:

  • TPROTO
  • TOUTSTATE

A t_errno value that this routine can return under different circumstances than its XTI counterpart is TBUFOVFLW. It can be returned even when the maxlen field of the corresponding buffer has been set to zero.

Option Buffers

The format of the options in an opt buffer is dictated by the transport provider. Unlike the XTI interface, the TLI interface does not fix the buffer format.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT Level
Safe

See Also

fcntl(2), t_alloc(3C), t_open(3C), t_rcvuderr(3C), t_sndudata(3C), attributes(7)