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Technical Reference: Base Operating System and Extensions , Volume 2

t_sndvudata Subroutine


Send a data unit from one or more noncontiguous buffers.



#include <xti.h>
int t_sndvudata(
    int fd,
    struct t_unitdata *unitdata,
    struct t_iovec *iov,
    unsigned int iovcount)


This function is used in connectionless mode to send a data unit to another transport user. The argument fd identifies the local transport endpoint through which data will be sent, iovcount contains the number of non-contiguous udata buffers and is limited to an implementation-defined value given by T_IOV_MAX, which is at least 16, and unitdata points to a t_unitdata structure containing the following members:

struct netbuf addr;
struct netbuf opt;
struct netbuf udata;

If the limit on iovcount is exceeded, the function fails with [TBADDATA].

In unitdata, addr specifies the protocol address of the destination user, and opt identifies options that the user wants associated with this request. The udata field is not used. The user may choose not to specify what protocol options are associated with the transfer by setting the len field of opt to zero. In this case, the provider may use default options.

The data to be sent is identified by iov[0] through iov[iovcount-1].

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.

By default, t_sndvudata 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_sndvudata executes in asynchronous mode and will fail under such conditions. The process can arrange to be notified of the clearance of a flow control restriction via either t_look or the EM interface.

If the amount of data specified in iov[0] through iov[iovcount-1] exceeds the TSDU size as returned in the tsdu field of the info argument of t_open or t_getinfo, or is zero and sending of zero octets is not supported by the underlying transport service, a [TBADDATA] error is generated. If t_sndvudata is called before the destination user has activated its transport endpoint (see t_bind), the data unit may be discarded.

If it is not possible for the transport provider to immediately detect the conditions that cause the errors [TBADDADDR] and [TBADOPT], these errors will alternatively be returned by t_rcvuderr. An application must therefore be prepared to receive these errors in both of these ways.

Parameters Before call After call
fd x /
unitdata-> addr.maxlen /
unitdata-> addr.len x
unitdata-> addr.buf x(x)
unitdata-> opt.maxlen /
unitdata-> opt.len x
unitdata-> opt.buf ?(?)
unitdata-> udata.maxlen /
unitdata-> udata.len /
unitdata-> udata.buf /
iov[0].iov_base x(x) =(=)
left>iov[0].iov_len x =
. . . .    
iov[iovcount-1].iov_base x(x) =(=)
iov[iovcount-1].iov_len x =
iovcount x /

Valid States


Error Codes

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

[TBADADDR] The specified protocol address was in an incorrect format or contained illegal information.
[TBADDATA] Illegal amount of data.
  • A single send was attempted specifying a TSDU greater than that specified in the info argument, or a send of a zero byte TSDU is not supported by the provider.
  • iovcount is greater than T_IOV_MAX.
[TBADF] The specified file descriptor does not refer to a transport endpoint.
[TBADOPT] The specified options were in an incorrect format or contained illegal information.
[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.

Return Values

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and t_errno is set to indicate an error.

Related Information

The fcntl, t_alloc, t_open, t_rcvudata, t_rcvvudata (t_rcvvudata Subroutine), t_rcvuderr, t_sndudata subroutines.

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