Tribblix: manual page: t

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

NAME

t_sndv - send data or expedited data, from one or more non-contiguous
buffers, on a connection

SYNOPSIS

#include <xti.h>

int t_sndv(int fd, const struct t_iovec *iov, unsigned int iovcount, int flags);

DESCRIPTION

This function is used to send either normal or expedited data. The
argument fd identifies the local transport endpoint over which data
should be sent, iov points to an array of buffer address/buffer
length pairs. t_sndv() sends data contained in buffers iov0 , iov1
, through iov [iovcount-1]. iovcount contains the number of non-
contiguous data buffers which is limited to T_IOV_MAX, an
implementation-defined value of at least 16. If the limit is
exceeded, the function fails with TBADDATA.

iov(0).iov_len + . . + iov(iovcount-1).iov_len)

Note that the limit on the total number of bytes available in all
buffers passed:

may be constrained by implementation limits. If no other constraint
applies, it will be limited by INT_MAX. In practice, the availability
of memory to an application is likely to impose a lower limit on the
amount of data that can be sent or received using scatter/gather
functions.

The argument flags specifies any optional flags described below:

T_EXPEDITED
If set in flags, the data will be sent as expedited
data and will be subject to the interpretations of
the transport provider.

T_MORE
If set in flags, this 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_sndv() calls. Each
t_sndv() with the T_MORE flag set indicates that
another t_sndv() or t_snd(3NSL) will follow with
more data for the current TSDU (or ETSDU).

The end of the TSDU (or ETSDU) is identified by a t_sndv() 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 argument on return from t_open(3NSL) or
t_getinfo(3NSL), the T_MORE flag is not meaningful and will be
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,
that is, when the T_MORE flag is not set. Some transport providers
also forbid zero-length TSDUs and ETSDUs.

If set in flags, requests that the provider transmit all data that it
has accumulated but not sent. The request is a local action on the
provider and does not affect any similarly named protocol flag (for
example, the TCP PUSH flag). This effect of setting this flag is
protocol-dependent, and it may be ignored entirely by transport
providers which do not support the use of this feature.

The communications provider is free to collect data in a send buffer
until it accumulates a sufficient amount for transmission.

By default, t_sndv() 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_sndv()
executes in asynchronous mode, and will fail immediately if there are
flow control restrictions. The process can arrange to be informed
when the flow control restrictions are cleared via either
t_look(3NSL) or the EM interface.

On successful completion, t_sndv() returns the number of bytes
accepted by the transport provider. Normally this will equal the
total number of bytes to be sent, that is,

(iov0.iov_len + .. + iov[iovcount-1].iov_len)

However, the interface is constrained to send at most INT_MAX bytes
in a single send. When t_sndv() has submitted INT_MAX (or lower
constrained value, see the note above) bytes to the provider for a
single call, this value is returned to the user. However, if
O_NONBLOCK is set or the function is interrupted by a signal, it is
possible that only part of the data has actually been accepted by the
communications provider. In this case, t_sndv() returns a value that
is less than the value of nbytes. If t_sndv() is interrupted by a
signal before it could transfer data to the communications provider,
it returns -1 with t_errno set to TSYSERR and errno set to EINTR.

If the number of bytes of data in the iov array is zero and sending
of zero octets is not supported by the underlying transport service,
t_sndv() returns -1 with t_errno set to TBADDATA.

The size of each TSDU or ETSDU must not exceed the limits of the
transport provider as specified by the current values in the TSDU or
ETSDU fields in the info argument returned by t_getinfo(3NSL).

The error TLOOK is returned for asynchronous events. It is required
only for an incoming disconnect event but may be returned for other
events.

RETURN VALUES

On successful completion, t_sndv() 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 synchronous mode, if more than INT_MAX bytes of data
are passed in the iov array, only the first INT_MAX bytes will be
passed to the provider.

If the number of bytes accepted by the communications provider is
less than the number of bytes requested, this may either indicate
that O_NONBLOCK is set and the communications provider is blocked
due to flow control, or that O_NONBLOCK is clear and the function was
interrupted by a signal.

VALID STATES

T_DATAXFER, T_INREL.

ERRORS

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

TBADDATA
Illegal amount of data:

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

o 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.

o A send of a zero byte TSDU (ETSDU) or zero
byte fragment of a TSDU (ETSDU) is not
supported by the provider.

o 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
WARNINGS, below.

o iovcount is greater than T_IOV_MAX.

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.

TLOOK
An asynchronous event has occurred on this transport
endpoint.

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

In the TLI interface definition, no counterpart of this routine was
defined.

ATTRIBUTES

WARNINGS

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_sndv() or t_snd(3NSL) calls, then the
different data may be intermixed.

Multiple sends which exceed the maximum TSDU or ETSDU size may not be
discovered by XTI. 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 XTI, t_sndv() fails with TBADDATA.

August 23, 2001 T_SNDV(3NSL)