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This routine is part of the XTI interfaces which evolved from the TLI interfaces. XTI represents the future evolution of these interfaces. However, TLI interfaces are
supported for compatibility. When using a TLI routine that has the same name as an XTI routine, the tiuser.h header file must be used. Refer to the TLI COMPATIBILITY section for
a description of differences between the two interfaces.
This function receives either normal or expedited data. The argument fd identifies the local transport endpoint through which data will arrive, buf points to a receive buffer where user data will be placed, and nbytes
specifies the size of the receive buffer. The argument flags may be set on return from t_rcv() and specifies optional flags as described below.
By default, t_rcv() operates in synchronous mode and will wait for data to arrive if none is currently available. However, if O_NONBLOCK is set by means of t_open(3NSL) or fcntl(2), t_rcv() 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_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_rcv() call even
when the number of bytes received is less than the size of the receive buffer specified. Each t_rcv() with the T_MORE flag set indicates that another t_rcv() must follow to get more data for the current TSDU. The end of the
TSDU is identified by the return of a t_rcv() 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(3NSL) or t_getinfo(3NSL), the T_MORE flag is not meaningful
and should be ignored. If nbytes is greater than zero on the call to t_rcv(), t_rcv() 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_rcv() which will return with T_EXPEDITED set in flags. The end of the ETSDU is identified
by the return of a t_rcv() 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_rcv() returns, giving the user any data currently available. If no data is available, t_rcv() returns -1, sets t_errno to TSYSERR and errno to EINTR.
If some data is available, t_rcv() 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(3NSL) function. Additionally, the process can arrange to be notified by means of the EM interface.
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