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Technical Reference: Base Operating System and Extensions , Volume 2

t_rcvvudata Subroutine


Receive a data unit into one or more noncontiguous buffers.


Standard library (libxti.a)


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


This function is used in connectionless mode to receive a data unit from another transport user. The argument fd identifies the local transport endpoint through which data will be received, unitdata holds information associated with the received data unit, iovcount contains the number of non-contiguous udata buffers which is limited to T_IOV_MAX (an implementation-defined value of at least 16), and flags is set on return to indicate that the complete data unit was not received. If the limit on iovcount is exceeded, the function fails with [TBADDATA]. The argument unitdata points to a t_unitdata structure containing the following members:

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

The maxlen field of addr and opt must be set before calling this function to indicate the maximum size of the buffer for each. The udata field of t_unitdata is not used. The iov_len and iov_base fields of iov[0] through iov[iovcount-1] must be set before calling t_rcvvudata to define the buffer where the userdata will be placed. If the maxlen field of addr or opt is set to zero then no information is returned in the buf field for this parameter.

On return from this call, addr specifies the protocol address of the sending user, opt identifies options that were associated with this data unit, and iov[0].iov_base through iov[iovcount-1]. iov_base contains the user data that was received. The return value of t_rcvvudata is the number of bytes of user data given to the user.

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.

By default, t_rcvvudata operates in synchronous mode and waits for a data unit to arrive if none is currently available. However, if O_NONBLOCK is set (via t_open or fcntl ), t_rcvvudata executes in asynchronous mode and fails if no data units are available. If the buffers defined in the iov[] array are not large enough to hold the current data unit, the buffers will be filled and T_MORE will be set in flags on return to indicate that another t_rcvvudata should be called to retrieve the rest of the data unit. Subsequent calls to t_rcvvudata will return zero for the length of the address and options, until the full data unit has been received.

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

Return Values

On successful completion, t_rcvvudata 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.
TBUFOVFLW The number of bytes allocated for the incoming protocol address or options (maxlen) is greater than 0 but not sufficient to store the information. The unit data information to be returned in unitdata will be discarded.
TLOOK An asynchronous event has occurred on this transport endpoint and requires immediate attention.
TNODATA O_NONBLOCK was set, but no data units are 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_alloc subroutine, t_open subroutine, t_rcvudata subroutine, t_rcvuderr subroutine, t_sndudata subroutine, t_sndvudata (t_sndvudata Subroutine) subroutine.

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