[ Previous | Next | Table of Contents | Index | Library Home |
Legal |
Search ]
Technical Reference: Communications, Volume 2
Send data or expedited data over
a connection.
X/Open Transport Interface
Library (libxti.a)
#include <xti.h>
int t_snd (
int fd,
void *buf,
unsigned int nbytes,
int *flags)
The t_snd subroutine
is used to send either normal or expedited data. By default, the
t_snd subroutine operates in synchronous mode and may wait if flow
control restrictions prevents the data from being accepted by the local
transport provider at the time the call is made. However, if
O_NONBLOCK is set (via the t_open subroutine or
fcntl), the t_snd subroutine executes in asynchronous
mode, and fails immediately if there are flow control restrictions. The
process can arrange to be informed when the flow control restrictions are
cleared via either the t_look subroutine or the Event Management
interface.
On successful completion, the
t_snd subroutine returns the number of bytes accepted by the
transport provider. Normally this equals the number of bytes specified
in the nbytes parameter. However, if O_NONBLOCK
is set, it is possible that only part of the data is actually accepted by the
transport provider. In this case, the t_snd subroutine
returns a value that is less than the value of the nbytes
parameter. If the value of the nbytes parameter is zero and
sending of zero octets is not supported by the underlying transport service,
the t_snd subroutine returns -1 with t_errno set to
TBADDATA.
fd
| Identifies the local transport endpoint over which data should be
sent.
|
buf
| Points to the user data.
|
nbytes
| Specifies the number of bytes of user data to be sent.
|
flags
| Specifies any optional flags described below:
- T_EXPEDITED
- If set in the flags parameter, the data is sent as expedited
data and is subject to the interpretations of the transport provider.
- T_MORE
- If set in the flags parameter, indicates to the transport
provider that the transport service data unit (TSDU) (or expedited transport
service data unit - ETSDU) is being sent through multiple t_snd
calls. Each t_snd call with the T_MORE flag set
indicates that another t_snd call will follow with more data for
the current TSDU (or ETSDU).
The end of the TSDU (or ETSDU) is
identified by a t_snd call with the T_MORE flag not
set. Use of T_MORE enables a user to break up large logical
data units without losing the boundaries of those units at the other end of
the connection. The flag implies nothing about how the data is packaged
for transfer below the transport interface. If the transport provider
does not support the concept of a TSDU, as indicated in the info
parameter on return from the t_open or t_getinfo
subroutines, the T_MORE flag is not meaningful and is ignored if
set.
The sending of a zero-length
fragment of a TSDU or ETSDU is only permitted where this is used to indicate
the end of a TSDU or ETSDU, for example, when the T_MORE flag is
not set. Some transport providers also forbid zero-length TSDUs and
ETSDUs. See Appendix A, ISO Transport Protocol Information for a fuller
explanation.
|
T_DATAXFER,
T_INREL.
On successful completion, the
t_snd subroutine returns the number of bytes accepted by the
transport provider. Otherwise, -1 is returned on failure and
t_errno is set to indicate the error.
Note, that in asynchronous mode,
if the number of bytes accepted by the transport provider is less than the
number of bytes requested, this may indicate that the transport provider is
blocked due to flow control.
On failure, t_errno is
set to one of the following:
TBADF
| The specified file descriptor does not refer to a transport
endpoint.
|
TBADDATA
| Illegal amount of data:
- A single send was attempted specifying a TSDU (ETSDU)
or fragment TSDU (ETSDU) greater than that specified by the current values of
the TSDU or ETSDU fields in the info argument;
- a send of a zero byte TSDU (ETSDU) or zero byte
fragment of a TSDU (ETSDU) is not supported by the provider (see Appendix A,
ISO Transport Protocol Information)
.
- multiple sends were attempted resulting in a TSDU
(ETSDU) larger than that specified by the current value of the TSDU or ETSDU
fields in the info argument - the ability of an XTI implementation
to detect such an error case is implementation-dependent. See
"Implementation Specifics".
|
TBADFLAG
| An invalid flag was specified.
|
TFLOW
| O_NONBLOCK was set, but the flow control mechanism prevented
the transport provider from accepting any data at this time.
|
TNOTSUPPORT
| This subroutine is not supported by the underlying transport
provider.
|
TLOOK
| An asynchronous event has occurred on this transport endpoint.
|
TOUTSTATE
| The subroutine was issued in the wrong sequence on the transport endpoint
referenced by the fd parameter.
|
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).
|
It is important to remember that
the transport provider treats all users of a transport endpoint as a single
user. Therefore if several processes issue concurrent t_snd
calls then the different data may be intermixed.
Multiple sends which exceed the
maximum TSDU or ETSDU size may not be discovered by the X/Open Transport
Interface. In this case an implementation-dependent error will result
(generated by the transport provider) perhaps on a subsequent XTI call.
This error may take the form of a connection abort, a
TSYSERR. a TBADDATA or a TPROTO
error.
If multiple sends which exceed
the maximum TSDU or ETSDU size are detected by the X/Open Transport Interface,
t_snd fails with TBADDATA.
The t_getinfo subroutine, t_open subroutine, t_rcv subroutine.
[ Previous | Next | Table of Contents | Index |
Library Home |
Legal |
Search ]