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t_sndv(3)
NAME
t_sndv - Receive data or expedited data sent over a connection and put the
data into one or more non-contiguous buffers
SYNOPSIS
#include <xti.h>
int t_sndv(
int fd,
const struct t_iovec *iov,
unsigned int iovcount,
int *flags );
LIBRARY
XTI Library (libxti.a)
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
t_sndv(): XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
The following table summarizes the relevance of input and output parameters
before and after t_sndv() is called:
__________________________________________________
Parameters Before Call After Call
__________________________________________________
fd y n
iov y n
iovcount y n
iov[0].iov_base y(y) e(e)
iov[0].iov_len y e
...
y(y) e(e)
iov[iovcount-
1].iov_base
iov[iovcount-1].iov_len y e
flags y n
__________________________________________________
Notes to Table:
y This is a meaningful parameter.
(y) The content of the object pointed to by y is meaningful.
o This is a meaningful but optional parameter.
(o) The content of the object pointed to by o is meaningful.
e The parameter value after the call is the same as before the call.
(e) The content of the object pointed to by e after the call is the same as
before the call.
n This is not a meaningful parameter.
fd Identifies the local transport endpoint over which to send data.
iov Points to an array of buffer address/buffer size pairs (iov_base,
iov_len).
iovcount
Specifies the number of buffers, which is limited to T_IOV_MAX (an
implementation-defined value of at least 16). If the limit is
exceeded, the function will fail with [TBADDATA].
flags
Specifies on of the following flags options:
T_EXPEDITED
If set, the data will be sent as expedited data and will be subject
to the interpretations of the transport provider.
T_MORE
If set, 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.
DESCRIPTION
The t_sndv() function sends data either normal or expedited data. The data
is contained in buffers iov[0], iov[1], through iov[iovcount-1].
Note
The limit on the total number of bytes available in all buffers passed
(that is, iov(0).iov_len + ... + iov(iovcount-1).iov_len) 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.
Each t_sndv() with the T_MORE flag set indicates that another t_sndv() (or
t_snd()) 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 the T_MORE flag 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()
or t_getinfo(), 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 flags (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.
Note
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 (via t_open() or fcntl()), 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() or the EM interface.
On successful completion, t_sndv() returns the number of bytes accepted by
the transport provider. Normally this equals the total number of bytes to
be sent, according to the following formula:
iov[0].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 previous note) 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().
The [TLOOK] error is returned for asynchronous events. It is required only
for an incoming disconnect event, but may be returned for other events.
NOTES
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()
calls, the different data may be intermixed.
Multiple sends that 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 that exceed the maximum TSDU or ETSDU size are detected
by XTI, t_sndv() fails with [TBADDATA].
ERRORS
If the t_sndv() function fails, t_errno may be set to one of the following
values:
[TBADDATA]
Illegal amount of data. Possible reasons include:
· An attempt to send once, 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.
· An attempt to send zero-byte TSDU (ETSDU) or zero-byte fragment of
a TSDU (ETSDU) is not supported by the provider.
· An attempt to send multiple times, 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.
· The iovcount parameter is greater than T_IOV_MAX.
[TBADF]
File descriptor (fd) is not a valid transport endpoint.
[TBADFLAG]
An invalid option was specified.
[TFLOW]
O_NONBLOCK was set, but the flow control mechanism prevented the
transport provider from accepting the function.
[TLOOK]
An asynchronous event occurred on this transport endpoint and requires
immediate attention.
[TNOTSUPPORT]
This function is not supported by the underlying transport provider.
[TOUTSTATE]
The communications endpoint referenced by fd is not in a valid state in
which a call to this function.
[TPROTO]
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 occurred during execution of this function.
VALID STATES
The t_sndv() function can be called in either the T_DATAXFER or T_INREL
transport provider states.
RETURN VALUE
Upon successful completion, t_sndv() returns a value of 0 (zero).
Otherwise, it returns a value of -1 and sets t_errno to indicate the error.
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.
SEE ALSO
Functions: t_getinfo(3), t_open(3), t_rcv(3), t_rcvv(3), t_snd(3).
Standards: standards(5)
Network Programmer's Guide
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