t_snd(3N) t_snd(3N)
NAME
tsnd - send data or expedited data over a connection
SYNOPSIS
#include <sys/tiuser.h>
int tsnd(int fd, char *buf, unsigned nbytes, int flags);
DESCRIPTION
This function is used to send either normal or expedited data. 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, and flags specifies any optional flags
described below.
By default, tsnd 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 ONDELAY
or ONONBLOCK is set (via topen or fcntl), tsnd will execute in
asynchronous mode, and will fail immediately if there are flow control
restrictions.
Even when there are no flow control restrictions, tsnd will wait if
STREAMS internal resources are not available, regardless of the state
of ONDELAY or ONONBLOCK.
On successful completion, tsnd returns the number of bytes accepted
by the transport provider. Normally this will equal the number of
bytes specified in nbytes. However, if ONDELAY or ONONBLOCK is set,
it is possible that only part of the data will be accepted by the
transport provider. In this case, tsnd will set TMORE for the data
that was sent (see below) and will return a value less than nbytes. If
nbytes is zero and sending of zero bytes is not supported by the
underlying transport provider, tsnd() will return -1 with terrno set
to TBADDATA. A return value of zero indicates that the request to send
a zero-length data message was sent to the provider.
If TEXPEDITED is set in flags, the data will be sent as expedited
data, and will be subject to the interpretations of the transport pro-
vider.
If TMORE is set in flags, or is set as described above, an indication
is sent to the transport provider that the transport service data unit
(TSDU) or expedited transport service data unit (ETSDU) is being sent
through multiple tsnd calls. Each tsnd with the TMORE flag set
indicates that another tsnd will follow with more data for the
current TSDU. The end of the TSDU (or ETSDU) is identified by a tsnd
call with the TMORE flag not set. Use of TMORE 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 noth-
ing about how the data is packaged for transfer below the transport
interface. If the transport provider does not support the concept of a
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t_snd(3N) t_snd(3N)
TSDU as indicated in the info argument on return from topen or
tgetinfo, the TMORE flag is not meaningful and should be ignored.
The size of each TSDU or ETSDU must not exceed the limits of the
transport provider as returned by topen or tgetinfo. If the size is
exceeded, a TSYSERR with system error EPROTO will occur. However, the
tsnd may not fail because EPROTO errors may not be reported immedi-
ately. In this case, a subsequent call that accesses the transport
endpoint will fail with the associated TSYSERR.
If tsnd is issued from the TIDLE state, the provider may silently
discard the data. If tsnd is issued from any state other than
TDATAXFER, TINREL or TIDLE, the provider will generate a TSYSERR
with system error EPROTO (which may be reported in the manner
described above).
ERRORS
On failure, terrno may be set to one of the following:
TBADF The specified file descriptor does not refer to a
transport endpoint.
TFLOW ONDELAY or ONONBLOCK was set, but the flow control
mechanism prevented the transport provider from
accepting data at this time.
TNOTSUPPORT This function is not supported by the underlying
transport provider.
TSYSERR A system error has been detected during execution of
this function.
TBADDATA nbytes is zero and sending zero bytes is not supported
by the transport provider.
DIAGNOSTICS
On successful completion, tsnd returns the number of bytes accepted
by the transport provider, and it returns -1 on failure and terrno is
set to indicate the error.
SEE ALSO
topen(3N), trcv(3N).
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