Tribblix: manual page: t

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

NAME

t_rcv - receive data or expedited data sent over a connection

SYNOPSIS

#include <xti.h>

int t_rcv(int fd, void *buf, unsigned int nbytes, int *flags);

DESCRIPTION

This function 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 function that has the same name as an XTI function,
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 receives either normal or expedited data. The argument
fd identifies the local transport endpoint through which data will
arrive, buf points to a receive buffer where user data will be
placed, and nbytes specifies the size of the receive buffer. The
argument flags may be set on return from t_rcv() and specifies
optional flags as described below.

By default, t_rcv() operates in synchronous mode and will wait for
data to arrive if none is currently available. However, if O_NONBLOCK
is set by means of t_open(3NSL) or fcntl(2), t_rcv() will execute in
asynchronous mode and will fail if no data is available. See TNODATA
below.

On return from the call, if T_MORE is set in flags, this indicates
that there is more data, and the current transport service data unit
(TSDU) or expedited transport service data unit (ETSDU) must be
received in multiple t_rcv() calls. In the asynchronous mode, or
under unusual conditions (for example, the arrival of a signal or
T_EXDATA event), the T_MORE flag may be set on return from the
t_rcv() call even when the number of bytes received is less than the
size of the receive buffer specified. Each t_rcv() with the T_MORE
flag set indicates that another t_rcv() must follow to get more data
for the current TSDU. The end of the TSDU is identified by the return
of a t_rcv() call with the T_MORE flag not set. If the transport
provider does not support the concept of a TSDU as indicated in the
info argument on return from t_open(3NSL) or t_getinfo(3NSL), the
T_MORE flag is not meaningful and should be ignored. If nbytes is
greater than zero on the call to t_rcv(), t_rcv() will return 0 only
if the end of a TSDU is being returned to the user.

On return, the data is expedited if T_EXPEDITED is set in flags. If
T_MORE is also set, it indicates that the number of expedited bytes
exceeded nbytes, a signal has interrupted the call, or that an
entire ETSDU was not available (only for transport protocols that
support fragmentation of ETSDUs). The rest of the ETSDU will be
returned by subsequent calls to t_rcv() which will return with
T_EXPEDITED set in flags. The end of the ETSDU is identified by the
return of a t_rcv() call with T_EXPEDITED set and T_MORE cleared.
If the entire ETSDU is not available it is possible for normal data
fragments to be returned between the initial and final fragments of
an ETSDU.

If a signal arrives, t_rcv() returns, giving the user any data
currently available. If no data is available, t_rcv() returns -1,
sets t_errno to TSYSERR and errno to EINTR. If some data is
available, t_rcv() returns the number of bytes received and T_MORE
is set in flags.

In synchronous mode, the only way for the user to be notified of the
arrival of normal or expedited data is to issue this function or
check for the T_DATA or T_EXDATA events using the t_look(3NSL)
function. Additionally, the process can arrange to be notified by
means of the EM interface.

RETURN VALUES

On successful completion, t_rcv() returns the number of bytes
received. Otherwise, it returns -1 on failure and t_errno is set to
indicate the error.

VALID STATES

T_DATAXFER, T_OUTREL.

ERRORS

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

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

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

TNODATA
O_NONBLOCK was set, but no data is 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 value that can be set by the XTI interface and cannot be
set by the TLI interface is:
TPROTO

ATTRIBUTES