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t_rcvudata - Receives a data unit


XTI Library (libxti.a)


#include <xti.h> int t_rcvudata( int fd, struct t_unitdata *unitdata, int *flags) ;


Interfaces documented on this reference page conform to industry standards as follows: t_rcvudata: XPG4-UNIX Refer to the standards(5) reference page for more information about industry standards and associated tags.


The following table summarizes the relevance of input and output parameter data before and after t_rcvudata() is called: Parameters Before Call After Call _________________________________________________ fd y n unitdata->addr.maxlen y n unitdata->addr.len n y unitdata->addr.buf o (o) unitdata->opt.maxlen y n unitdata->opt.len n y unitdata->opt.buf o (o) unitdata->udata.maxlen y n unitdata->udata.len n y unitdata->udata.buf o (o) flags n y Notes to Table: y This is a meaningful parameter. n This is not a meaningful parameter. (y) The content of the object pointed to by y is meaningful. fd Specifies a file descriptor returned by the t_open() function that identifies the transport endpoint. unitdata Points to a type t_unitdata structure used to specify information required by the transport provider user to receive a data unit through the transport endpoint specified by the fd parameter. The t_unitdata structure has the following members: struct netbuf addr References a buffer for protocol address information required from the transport endpoint specified by the fd parameter. The type netbuf structure referenced by this member is defined in the xti.h include file and has the following members: unsigned int maxlen Specifies the maximum byte length of the data buffer. unsigned int len Specifies the actual byte length of the data written to the buffer. char *buf Points to the buffer location. struct netbuf opt Specifies a buffer for protocol-specific parameters associated with the data unit. struct netbuf udata Specifies parameters for any user data unit that may be returned to the caller. Before the t_rcvudata() function is called the unitdata->addr.maxlen, unitdata->opt.maxlen, and unitdata->udata.maxlen parameters must be set to specify the maximum byte length of the protocol address buffer, the protocol options buffer, and the user data buffer, respectively. flags Points to a flag integer that indicates that the complete data unit was not received. Corresponding values and symbolic names for flags are defined in the xti.h include file (see the t_optmgmt() and t_rcv() functions). The flag specified by this function is: T_MORE. When the data buffer specified by the unitdata->udata.buf parameter is not large enough to hold the current user data unit, the buffer is filled and this bit is set to indicate that another t_rcvudata() function should be called to retrieve the rest of the data unit. The set state of this bit notifies the local transport user that the received data unit is a fragment and that another data unit is available. When this bit is set on return of this function, another data unit must also be fetched with another t_rcvudata() call. Each time this flag is set on return, another t_rcvudata() call must immediately be made to receive additional current data units. When the final data unit is received, this flag bit has a value of 0 (zero) on return. Subsequent calls to the t_rcvudata() function return 0 (zero) as the length of the address specified by the unitdata->addr.len and unitdata->opt.len parameters until the full data unit has been received.


The t_rcvudata() function can only be called in the T_IDLE transport provider state.


The t_rcvudata() function is an XTI connectionless service function that is used to receive a data unit from a remote transport provider user. By default, t_rcvudata() executes in the synchronous operating mode. The t_rcvudata() function waits for data to arrive at the transport endpoint specified by fd before returning control to the transport user who called this function. However, when the transport endpoint, specified by the fd parameter, has been previously opened with the O_NONBLOCK flag set in the t_open() or fcntl() function, the t_rcvudata() function executes in asynchronous mode. In asynchronous mode, when a data unit is unavailable, control is immediately returned to the caller.


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


If the t_rcvudata() function fails, t_errno may be set to one of the following values: [TBADF] The specified file descriptor does not refer to a transport endpoint. [TNODATA] Asynchronous mode is indicated because O_NONBLOCK was set, but no data is currently available from the transport provider. [TBUFOVFLW] The number of bytes allocated for the incoming protocol address or protocol options is not sufficient to store the information. The unit data information normally returned to the unitdata parameter is discarded. [TLOOK] An asynchronous event that requires immediate attention has occurred at the transport endpoint specified by the fd parameter. [TOUTSTATE] The t_rcvudata() function was issued in the wrong sequence at the transport endpoint referenced by the fd parameter. [TSYSERR] A system error occurred during execution of this function. [TNOTSUPPORT] This function is not supported by the underlying transport provider. [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(t_errno).


Functions: fcntl(2), t_alloc(3), t_open(3), t_optmgmt(3), t_rcv(3), t_rcvuderr(3), t_sndudata(3)