295 lines
8.4 KiB
Groff
295 lines
8.4 KiB
Groff
.\" Copyright (c) 1983, 1991, 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. 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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.\" $FreeBSD$
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.\"
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.Dd April 23, 2015
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.Dt SCTP_RECVMSG 3
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.Os
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.Sh NAME
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.Nm sctp_recvmsg
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.Nd receive a message from an SCTP socket
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netinet/sctp.h
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.Ft ssize_t
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.Fo sctp_recvmsg
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.Fa "int s" "void *msg" "size_t len" "struct sockaddr * restrict from"
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.Fa "socklen_t * restrict fromlen" "struct sctp_sndrcvinfo *sinfo" "int *flags"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn sctp_recvmsg
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system call
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is used to receive a message from another SCTP endpoint.
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The
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.Fn sctp_recvmsg
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call is used by one-to-one (SOCK_STREAM) type sockets after a
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successful
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.Fn connect
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call or after the application has performed a
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.Fn listen
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followed by a successful
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.Fn accept .
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For a one-to-many (SOCK_SEQPACKET) type socket, an endpoint may call
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.Fn sctp_recvmsg
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after having implicitly started an association via one
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of the send calls including
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.Fn sctp_sendmsg ,
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.Fn sendto
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and
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.Fn sendmsg .
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Or, an application may also receive a message after having
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called
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.Fn listen
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with a positive backlog to enable the reception of new associations.
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.Pp
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The address of the sender is held in the
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.Fa from
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argument with
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.Fa fromlen
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specifying its size.
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At the completion of a successful
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.Fn sctp_recvmsg
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call
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.Fa from
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will hold the address of the peer and
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.Fa fromlen
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will hold the length of that address.
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Note that
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the address is bounded by the initial value of
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.Fa fromlen
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which is used as an in/out variable.
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.Pp
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The length of the message
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.Fa msg
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to be received is bounded by
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.Fa len .
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If the message is too long to fit in the users
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receive buffer, then the
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.Fa flags
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argument will
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.Em not
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have the
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.Dv MSG_EOR
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flag applied.
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If the message is a complete message then
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the
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.Fa flags
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argument will have
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.Dv MSG_EOR
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set.
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Locally detected errors are
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indicated by a return value of -1 with
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.Va errno
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set accordingly.
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The
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.Fa flags
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argument may also hold the value
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.Dv MSG_NOTIFICATION .
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When this
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occurs it indicates that the message received is
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.Em not
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from
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the peer endpoint, but instead is a notification from the
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SCTP stack (see
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.Xr sctp 4
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for more details).
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Note that no notifications are ever
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given unless the user subscribes to such notifications using
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the
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.Dv SCTP_EVENTS
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socket option.
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.Pp
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If no messages are available at the socket then
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.Fn sctp_recvmsg
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normally blocks on the reception of a message or NOTIFICATION, unless the
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socket has been placed in non-blocking I/O mode.
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The
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.Xr select 2
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system call may be used to determine when it is possible to
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receive a message.
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.Pp
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The
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.Fa sinfo
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argument is defined as follows.
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.Bd -literal
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struct sctp_sndrcvinfo {
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uint16_t sinfo_stream; /* Stream arriving on */
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uint16_t sinfo_ssn; /* Stream Sequence Number */
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uint16_t sinfo_flags; /* Flags on the incoming message */
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uint32_t sinfo_ppid; /* The ppid field */
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uint32_t sinfo_context; /* context field */
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uint32_t sinfo_timetolive; /* not used by sctp_recvmsg */
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uint32_t sinfo_tsn; /* The transport sequence number */
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uint32_t sinfo_cumtsn; /* The cumulative acknowledgment point */
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sctp_assoc_t sinfo_assoc_id; /* The association id of the peer */
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};
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.Ed
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.Pp
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The
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.Fa sinfo->sinfo_ppid
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field is an opaque 32 bit value that is passed transparently
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through the stack from the peer endpoint.
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Note that the stack passes this value without regard to byte
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order.
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.Pp
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The
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.Fa sinfo->sinfo_flags
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field may include the following:
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.Bd -literal
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#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */
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.Ed
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.Pp
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The
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.Dv SCTP_UNORDERED
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flag is used to specify that the message arrived with no
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specific order and was delivered to the peer application
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as soon as possible.
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When this flag is absent the message
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was delivered in order within the stream it was received.
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.Pp
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The
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.Fa sinfo->sinfo_stream
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field is the SCTP stream that the message was received on.
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Streams in SCTP are reliable (or partially reliable) flows of ordered
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messages.
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.Pp
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The
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.Fa sinfo->sinfo_context
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field is used only if the local application set an association level
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context with the
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.Dv SCTP_CONTEXT
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socket option.
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Optionally a user process can use this value to index some application
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specific data structure for all data coming from a specific
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association.
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.Pp
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The
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.Fa sinfo->sinfo_ssn
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field will hold the stream sequence number assigned
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by the peer endpoint if the message is
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.Em not
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unordered.
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For unordered messages this field holds an undefined value.
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.Pp
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The
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.Fa sinfo->sinfo_tsn
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field holds a transport sequence number (TSN) that was assigned
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to this message by the peer endpoint.
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For messages that fit in or less
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than the path MTU this will be the only TSN assigned.
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Note that for messages that span multiple TSNs this
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value will be one of the TSNs that was used on the
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message.
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.Pp
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The
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.Fa sinfo->sinfo_cumtsn
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field holds the current cumulative acknowledgment point of
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the transport association.
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Note that this may be larger
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or smaller than the TSN assigned to the message itself.
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.Pp
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The
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.Fa sinfo->sinfo_assoc_id
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is the unique association identification that was assigned
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to the association.
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For one-to-many (SOCK_SEQPACKET) type
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sockets this value can be used to send data to the peer without
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the use of an address field.
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It is also quite useful in
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setting various socket options on the specific association
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(see
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.Xr sctp 4 ) .
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.Pp
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The
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.Fa sinfo->info_timetolive
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field is not used by
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.Fn sctp_recvmsg .
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.Sh RETURN VALUES
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The call returns the number of bytes received, or -1
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if an error occurred.
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.Sh ERRORS
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The
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.Fn sctp_recvmsg
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system call
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fails if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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An invalid descriptor was specified.
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.It Bq Er ENOTSOCK
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The argument
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.Fa s
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is not a socket.
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.It Bq Er EFAULT
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An invalid user space address was specified for an argument.
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.It Bq Er EMSGSIZE
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The socket requires that message be sent atomically,
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and the size of the message to be sent made this impossible.
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.It Bq Er EAGAIN
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The socket is marked non-blocking and the requested operation
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would block.
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.It Bq Er ENOBUFS
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The system was unable to allocate an internal buffer.
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The operation may succeed when buffers become available.
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.It Bq Er ENOBUFS
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The output queue for a network interface was full.
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This generally indicates that the interface has stopped sending,
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but may be caused by transient congestion.
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.It Bq Er EHOSTUNREACH
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The remote host was unreachable.
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.It Bq Er ENOTCONN
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On a one-to-one style socket no association exists.
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.It Bq Er ECONNRESET
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An abort was received by the stack while the user was
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attempting to send data to the peer.
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.It Bq Er ENOENT
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On a one to many style socket no address is specified
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so that the association cannot be located or the
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SCTP_ABORT flag was specified on a non-existing association.
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.It Bq Er EPIPE
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The socket is unable to send anymore data
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.Dv ( SBS_CANTSENDMORE
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has been set on the socket).
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This typically means that the socket
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is not connected and is a one-to-one style socket.
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.El
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.Sh SEE ALSO
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.Xr getsockopt 2 ,
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.Xr recv 2 ,
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.Xr select 2 ,
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.Xr sendmsg 2 ,
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.Xr setsockopt 2 ,
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.Xr socket 2 ,
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.Xr write 2 ,
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.Xr sctp_send 3 ,
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.Xr sctp_sendmsg 3 ,
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.Xr sctp 4
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