man pages section 3: Networking Library Functions

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Updated: July 2014



t_sndudata - send a data unit


#include <xti.h> 

int t_sndudata(int fd, const struct t_unitdata *unitdata);


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 send a data unit to another transport user. The argument fd identifies the local transport endpoint through which data will be sent, and unitdata points to a t_unitdata structure containing the following members:

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

In unitdata, addr specifies the protocol address of the destination user, opt identifies options that the user wants associated with this request, and udata specifies the user data to be sent. The user may choose not to specify what protocol options are associated with the transfer by setting the len field of opt to zero. In this case, the provider uses the option values currently set for the communications endpoint.

If the len field of udata is zero, and sending of zero octets is not supported by the underlying transport service, the t_sndudata() will return –1 with t_errno set to TBADDATA.

By default, t_sndudata() operates in synchronous mode and may wait if flow control restrictions prevent the data from being accepted by the local transport provider at the time the call is made. However, if O_NONBLOCK is set by means of t_open(3NSL) or fcntl(2), t_sndudata() will execute in asynchronous mode and will fail under such conditions. The process can arrange to be notified of the clearance of a flow control restriction by means of either t_look(3NSL) or the EM interface.

If the amount of data specified in udata exceeds the TSDU size as returned in the tsdu field of the info argument of t_open(3NSL) or t_getinfo(3NSL), a TBADDATA error will be generated. If t_sndudata() is called before the destination user has activated its transport endpoint (see t_bind(3NSL)), the data unit may be discarded.

If it is not possible for the transport provider to immediately detect the conditions that cause the errors TBADDADDR and TBADOPT, these errors will alternatively be returned by t_rcvuderr. Therefore, an application must be prepared to receive these errors in both of these ways.

If the call is interrupted, t_sndudata() will return EINTR and the datagram will not be sent.

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.





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


The specified protocol address was in an incorrect format or contained illegal information.


Illegal amount of data. A single send was attempted specifying a TSDU greater than that specified in the info argument, or a send of a zero byte TSDU is not supported by the provider.


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


The specified options were in an incorrect format or contained illegal information.


O_NONBLOCK was set, but the flow control mechanism prevented the transport provider from accepting any data at this time.


An asynchronous event has occurred on this transport endpoint.


This function is not supported by the underlying transport provider.


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


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 function.



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:



Whenever this function fails with t_error set to TFLOW, O_NONBLOCK must have been set.

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

See also

fcntl(2), t_alloc(3NSL), t_bind(3NSL), t_error(3NSL), t_getinfo(3NSL), t_look(3NSL), t_open(3NSL), t_rcvudata(3NSL), t_rcvuderr(3NSL), attributes(5)