t_rcvudata - receive a data unit
int t_rcvudata (int fd, struct t_unitdata *unitdata, int *flags);
This function is used in connectionless mode to receive a data unit from
another transport user. fd identifies the local transport endpoint
through which data will be received, unitdata holds information
associated with the received data unit, and flags is set on return to
indicate that the complete data unit was not received. unitdata points
to a t_unitdata structure containing the following members:
struct netbuf addr;
struct netbuf opt;
struct netbuf udata;
The maxlen [see netbuf in intro(3N)] field of addr, opt, and udata must
be set before issuing this function to indicate the maximum size of the
buffer for each.
On return from this call, addr specifies the protocol address of the
sending user, opt identifies protocol-specific options that were
associated with this data unit, and udata specifies the user data that
By default, t_rcvudata operates in synchronous mode and will wait for a
data unit to arrive if none is currently available. However, if O_NDELAY
or O_NONBLOCK is set (via t_open or fcntl), t_rcvudata will execute in
asynchronous mode and will fail if no data units are available.
If the buffer defined in the udata field of unitdata is not large enough
to hold the current data unit, the buffer will be filled and T_MORE will
be set in flags on return to indicate that another t_rcvudata should be
issued to retrieve the rest of the data unit. Subsequent t_rcvudata
call(s) will return zero for the length of the address and options until
the full data unit has been received.
This function resides within both the X/Open compliant libxnet and the
SVR4 compliant libnsl Network Services libraries. Network Services
applications which require X/Open compliance must link-load with -lxnet.
Network Services applications which require SVR4 compliance must linkload
On failure, t_errno may be set to one of the following:
TBADF The specified file descriptor does not refer to a
TNODATA O_NDELAY or O_NONBLOCK was set, but no data units are
currently available from the transport provider.
TBUFOVFLW There are two different conditions in which TBUFOVFLW
will be returned. If _XOPEN_SOURCE is defined and
the number of bytes allocated for incoming data is
greater than zero and is not sufficient to store the
data. If _XOPEN_SOURCE is not defined and the number
of bytes allocated for incoming data is not
sufficient to store the data. The unit data
information to be returned in unitdata will be
TLOOK An asynchronous event has occurred on this transport
endpoint and requires immediate attention.
TNOTSUPPORT This function is not supported by the underlying
TOUTSTATE If _XOPEN_SOURCE is defined and t_rcvudata() is
issued in the wrong sequence on the transport
endpoint referenced by fd, the TOUTSTATE error value
is returned within the variable t_errno.
TSYSERR A system error has occurred during execution of this
intro(3N), fcntl(2), t_alloc(3N), t_open(3N), t_rcvuderr(3N),
t_rcvudata returns 0 on successful completion and -1 on failure and
t_errno is set to indicate the error.
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