T_RCVUDATA(3NSL) Networking Services Library Functions T_RCVUDATA(3NSL)


t_rcvudata - receive a data unit


#include <xti.h>

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


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

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(3NSL) or fcntl(2), t_rcvudata()
will execute in asynchronous mode and will fail if no data units are

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.


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.




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

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

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.

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

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

This function is not supported by the underlying transport

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

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).

A system error has occurred during execution of this


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:

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

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.


See attributes(5) for descriptions of the following attributes:

|MT Level | Safe |


fcntl(2), t_alloc(3NSL), t_open(3NSL), t_rcvuderr(3NSL),
t_sndudata(3NSL), attributes(5)

October 22, 2014 T_RCVUDATA(3NSL)