t_rcv.3xti

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3XTI 代码 · 共 143 行

.TH t_rcv 3xti
.SH Name
t_rcv \- receive data or expedited data sent over a connection 
.SH Syntax
.B #include <xti.h>
.br
.sp 1
.B int t_rcv(\fIfd, buf, nbytes, flags\fB)
.br
.B int \fIfd\fB;
.br
.B char \fI*buf\fB;
.br
.B unsigned \fInbytes\fB;
.br
.B int \fI*flags\fR;
.SH Arguments
.IP \fIfd\fR 10
Identifies the local transport endpoint through which data arrives.
.IP \fIbuf\fR 10
Points to a receive buffer where user data is placed.
.IP \fInbytes\fR 10
Specifies the size of the receive buffer.
.IP \fIflags\fR 10
Specifies optional flags. Can be set on return from
.PN t_rcv().
.SH Description
This function receives either normal or expedited data.
.NXR "t_rcv system call"
.NXR "connection" "receiving normal data"
.NXR "connection" "receiving expedited data"
.PP
By default, 
.PN t_rcv()
operates in synchronous mode and waits for
data to arrive if none is currently available. However, if
O_NONBLOCK is set (by means of 
.PN t_open()
or
.PN fcntl()\fR,\fR 
.PN t_rcv()
executes in asynchronous mode and fails if no data is available.
.PP
On return from the call, if T_MORE is set in \fIflags\fR this
indicates that there is more data and the current transport service
data unit (TSDU) or expedited transport service data (ETSDU) must be
received in multiple 
.PN t_rcv() 
calls. Each 
.PN t_rcv()
with the T_MORE flag set indicates that another 
.PN t_rcv()
must follow immediately to get more data from the current TSDU. The end
of the TSDU is identified by the return of a 
.PN 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 \fIinfo\fR argument
on return from 
.PN t_open() 
or 
.PN t_getinfo()\fR,\fR 
the
T_MORE flag is not meaningful and should be ignored.
.PP 
On return, the data returned is expedited data if T_EXPEDITED is
set in \fIflags\fR. If the number of bytes of expedited data exceeds
\fInbytes\fR, 
.PN t_rcv() 
sets T_EXPEDITED and T_MORE
on return from the initial call. Subsequent calls to retrieve the
remaining ETSDU have T_EXPEDITED set on return. The end of
the ETSDU is identified by the return of a 
.PN t_rcv
call with the
T_MORE flag not set.
.PP
If expedited data arrives after part of a TSDU has been retrieved,
receipt of the remainder of the TSDU is suspended until the ETSDU
has been processed. Only after the full ETSDU has been retrieved
(T_MORE not set) will the remainder of the TSDU be available to
the user.
.PP
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
.PN t_look() 
function. 
.PP
.TS
tab(@);
lfHB lfHB lfHB
lfR  lfR  lfR .
_
.sp 6p
Parameters@Before Call@After Call
.sp 6p
_
.sp 6p
fd@x@/
buf@x@(x)
nbytes@x@/
flags@/@x
.sp 6p
_
.TE
.PP
.sp 12p
.SH Return Values
Upon successful completion, 
.PN t_rcv()
returns the number of
bytes received. 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 is currently available from the
transport provider.
.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_getinfo(3xti), 
t_look(3xti), 
t_open(3xti),
t_snd(3xti)