t_sndv(3)t_sndv(3)NAMEt_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 stan‐
dards 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 param‐
eters 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
...
iov[iov‐ y(y)e(e)
count-1].iov_base
iov[iovcount-1].iov_len y e
flags y n
───────────────────────────────────────────────────
Notes to Table: This is a meaningful parameter. The content of the
object pointed to by y is meaningful. This is a meaningful but
optional parameter. The content of the object pointed to by o is mean‐
ingful. The parameter value after the call is the same as before the
call. The content of the object pointed to by e after the call is the
same as before the call. This is not a meaningful parameter. Identi‐
fies the local transport endpoint over which to send data. Points to
an array of buffer address/buffer size pairs (iov_base, iov_len).
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]. Specifies on of the
following flags options: If set, the data will be sent as expedited
data and will be subject to the interpretations of the transport
provider. 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 con‐
strained 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 trans‐
port 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 pro‐
tocol-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_NON‐
BLOCK is set (via t_open() or fcntl()), t_sndv() executes in asynchro‐
nous mode, and will fail immediately if there are flow control restric‐
tions. 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 con‐
strained value, see the previous note) bytes to the provider for a sin‐
gle 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 trans‐
port 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 subse‐
quent 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 fol‐
lowing values: 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-depen‐
dent. The iovcount parameter is greater than T_IOV_MAX. File descrip‐
tor (fd) is not a valid transport endpoint. An invalid option was
specified. O_NONBLOCK was set, but the flow control mechanism pre‐
vented the transport provider from accepting the function. An asyn‐
chronous event occurred on this transport endpoint and requires immedi‐
ate attention. This function is not supported by the underlying trans‐
port provider. The communications endpoint referenced by fd is not in
a valid state in which a call to this function. A communication prob‐
lem has been detected between XTI and the transport provider for which
there is no other suitable XTI error (t_errno). 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). Oth‐
erwise, 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 inter‐
rupted 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
t_sndv(3)
