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Technical Reference: Base Operating System and Extensions , Volume 2

t_rcvv Subroutine


Receive data or expedited data sent over a connection and put the data into one or more non-contiguous buffers.




#include <xti.h>

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


This function receives either normal or expedited data. The argument fd identifies the local transport endpoint through which data will arrive, iov points to an array of buffer address/buffer size pairs (iov_base, iov_len). The t_rcvv function receives data into the buffers specified by iov[0].iov_base, iov[1].iov_base, through iov[iovcount-1].iov_base, always filling one buffer before proceding to the next.

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.

The argument iovcount contains 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].

The argument flags may be set on return from t_rcvv and specifies optional flags as described below.

By default, t_rcvv operates in synchronous mode and will wait for data to arrive if none is currently available. However, if O_NONBLOCK is set (via t_open or fcntl, t_rcvv will execute in asynchronous mode and will fail if no data is available (see [TNODATA] below).

On return from the call, if T_MORE is set in flags, this indicates that there is more data, and the current transport service data unit (TSDU) or expedited transport service data unit (ETSDU) must be received in multiple t_rcvv or t_rcv calls. In the asynchronous mode, or under unusual conditions (for example, the arrival of a signal or T_EXDATA event), the T_MORE flag may be set on return from the t_rcvv call even when the number of bytes received is less than the total size of all the receive buffers. Each t_rcvv with the T_MORE flag set indicates that another t_rcvv must follow to get more data for the current TSDU. The end of the TSDU is identified by the return of a t_rcvv call with the T_MORE flag not set. If the transport provider does not support the concept of a TSDU as indicated in the info argument on return from t_open ort_getinfo , the T_MORE flag is not meaningful and should be ignored. If the amount of buffer space passed in iov is greater than zero on the call to t_rcvv, then t_rcvv will return 0 only if the end of a TSDU is being returned to the user.

On return, the data is expedited if T_EXPEDITED is set in flags. If T_MORE is also set, it indicates that the number of expedited bytes exceeded nbytes, a signal has interrupted the call, or that an entire ETSDU was not available (only for transport protocols that support fragmentation of ETSDUs). The rest of the ETSDU will be returned by subsequent calls to t_rcvv which will return with T_EXPEDITED set in flags. The end of the ETSDU is identified by the return of a t_rcvv call with T_EXPEDITED set and T_MORE cleared. If the entire ETSDU is not available it is possible for normal data fragments to be returned between the initial and final fragments of an ETSDU.

If a signal arrives, t_rcvv returns, giving the user any data currently available. If no data is available, t_rcvv returns -1, sets t_errno to [TSYSERR] and errno to [EINTR]. If some data is available, t_rcvv returns the number of bytes received and T_MORE is set in flags.

In synchronous mode, the only way for the user to be notified of the arrival of normal or expedited data is to issue this function or check for the T_DATA or T_EXDATA events using the t_look function. Additionally, the process can arrange to be notified via the EM interface.

Parameters Before call After call
fd X /
iov X/  
iovcount X /
iov[0].iov_base X(/) =(X)
iov[0].iov_len X =
. . . .    
iov[iovcount-1].iov_base X(/) =(X)
iov[iovcount-1].iov_len X =

Return Values

On successful completion, t_rcvv returns the number of bytes received. Otherwise, it returns -1 on failure and t_errno is set to indicate the error.

Error Codes

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

TBADDATA iovcount is greater than T_IOV_MAX.
TBADF The specified file descriptor does not refer to a transport endpoint.
TLOOK An asynchronous event has occurred on this transport endpoint and requires immediate attention.
TNODATA O_NONBLOCK was set, but no data is currently available from the transport provider.
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.

Implementation Specifics

This subroutine is part of Base Operating System (BOS) subroutine.

Related Information

The fcntl subroutine, t_getinfo subroutine, t_look subroutine, t_open subroutine, t_rcv subroutine, t_snd subroutine, and t_sndv (t_sndv Subroutine) subroutine.

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