t_rcvudata.3xti

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3XTI 代码 · 共 134 行

.TH t_rcvudata 3xti
.SH Name
t_rcvudata \- receive a data unit
.SH Syntax
.B #include <xti.h>
.br
.sp 1
.B int t_rcvudata(\fIfd, unitdata, flags\fB)
.br
.B int \fIfd\fR;
.br
.B struct t_unitdata \fI*unitdata\fB;
.br
.B int \fI*flags\fR:
.SH Arguments
.IP \fIfd\fR 10
Identifies the local transport endpoint through which data is received.
.IP \fIunitdata\fR 10
Holds information associated with the received data unit. The
\fIunitdata\fR argument points to a \fBt_unitdata\fR structure
containing the following members:
.EX
struct netbuf \fIaddr\fP;
struct netbuf \fIopt\fP;
struct netbuf \fIudata\fP
.EE
.IP
On return from this call, the members have the following meanings:
.RS 10
.IP \fIaddr\fP 12
Specifies the protocol address of the sending unit.
.IP \fIopt\fP
Identifies protocol-specific options that were associated with this data unit.
.IP \fIudata\fP
Specifies the user data that was received.
.IP \fIflags\fR 
Set on return to indicate that the complete data unit was not received.
.RE
.SH Description
This function is used in connectionless mode to receive a data unit from
another transport user.
.NXR "t_rcvudata system call"
.NXR "connectionless mode" "receiving data"
.PP
By default, 
.PN t_rcvudata()
operates in synchronous mode waits
for a data unit to arrive if none is currently available. However, if
O_NONBLOCK is set by means of 
.PN t_open() 
or
.PN fcntl()\fR,\fR 
\fIudata\fR executes in asynchronous mode and fails if no data units are available.
.PP
The \fImaxlen\fR field of \fIaddr\fR, \fIopt\fR, and \fIudata\fR must be
set before issuing this function to indicate the maximum size of the
buffer for each.
.PP
If the buffer defined in the \fIudata\fR field of \fIunitdata\fR is not
large enough to hold the current data unit, the buffer fills
and T_MORE sets in \fIflags\fR on return to indicate that
another 
.PN t_rcvudata() 
should be issued to retrieve the rest of the
data unit. Subsequent 
.PN t_rcvudata() 
calls return zero for the length of the address and options until the full data unit 
has been received.
.PP
.TS
tab(@);
lfHB lfHB lfHB
lfR  lfR  lfR .
_
.sp 6p
Parameters@Before Call@After Call
.sp 6p
_
.sp 6p
fd@x@/
unitdata->addr.maxlen@x@/
unitdata->addr.len@/@x
unitdata->addr.buf@x@(x)
unitdata->opt.maxlen@x@/
unitdata->opt.len@/@x
unitdata->opt.buf@x@(x)
unitdata->udata.maxlen@x@/
unitdata->udata.len@/@x
unitdata->udata.buf@x@(x)
flags@/@x
.sp 6p
_
.TE
.PP
.sp 12p
.SH Return Values
Upon successful completion, a value of 0 is returned. On failure,  a
value of \-1 is returned, and \fBt_errno\fR is set to indicate the
error.
.SH Diagnostics
On failure, \fBt_errno\fR is set to one of the following:
.TP 20
[TBADF]
The specified file descriptor does not refer to a transport endpoint.
.TP 20 
[TOUTSTATE]
The function was issued in the wrong sequence on the transport endpoint
referenced by \fIfd\fR.
.TP 20
[TNODATA]
O_NONBLOCK was set, but no data units are currently available from
the transport provider.
.TP 20
[TBUFOVFLW]
The number of bytes allocated for the incoming protocol address or
options is not sufficient to store the information. The unit data
information to be returned in \fIunitdata\fR is discarded.
.TP 20
[TLOOK]
An asynchronous event has occurred on the transport endpoint and requires 
immediate attention.
.TP 20
[TNOTSUPPORT]
This function is not supported by the underlying transport provider. 
.TP 20
[TSYSERR]
A system error has occurred during execution of this function.
.SH See Also
fcntl(2), 
t_alloc(3xti), 
t_open(3xti),
t_rcvuderr(3xti), 
t_sndudata(3xti)