74 lines
3.5 KiB
Perl
74 lines
3.5 KiB
Perl
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.\" Copyright (c) 1983, 1986, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)d.t 8.1 (Berkeley) 6/8/93
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.\"
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.nr H2 1
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.\".ds RH "Out of band data
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.br
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.ne 2i
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.NH
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\s+2Out of band data\s0
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.PP
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Out of band data is a facility peculiar to the stream socket
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abstraction defined. Little agreement appears to exist as
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to what its semantics should be. TCP defines the notion of
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``urgent data'' as in-line, while the NBS protocols [Burruss81]
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and numerous others provide a fully independent logical
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transmission channel along which out of band data is to be
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sent.
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In addition, the amount of the data which may be sent as an out
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of band message varies from protocol to protocol; everything
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from 1 bit to 16 bytes or more.
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.PP
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A stream socket's notion of out of band data has been defined
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as the lowest reasonable common denominator (at least reasonable
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in our minds);
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clearly this is subject to debate. Out of band data is expected
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to be transmitted out of the normal sequencing and flow control
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constraints of the data stream. A minimum of 1 byte of out of
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band data and one outstanding out of band message are expected to
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be supported by the protocol supporting a stream socket.
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It is a protocol's prerogative to support larger-sized messages, or
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more than one outstanding out of band message at a time.
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.PP
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Out of band data is maintained by the protocol and is usually not
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stored in the socket's receive queue.
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A socket-level option, SO_OOBINLINE,
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is provided to force out-of-band data to be placed in the normal
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receive queue when urgent data is received;
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this sometimes amelioriates problems due to loss of data
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when multiple out-of-band
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segments are received before the first has been passed to the user.
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The PRU_SENDOOB and PRU_RCVOOB
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requests to the \fIpr_usrreq\fP routine are used in sending and
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receiving data.
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