330 lines
10 KiB
Groff
330 lines
10 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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.\" From: @(#)send.2 8.2 (Berkeley) 2/21/94
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.\" $FreeBSD$
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.\"
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.Dd December 15, 2006
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.Dt SCTP_SENDMSG 3
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.Os
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.Sh NAME
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.Nm sctp_sendmsg ,
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.Nm sctp_sendmsgx
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.Nd send 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_sendmsg
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.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to"
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.Fa "socklen_t tolen" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no"
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.Fa "uint32_t timetolive" "uint32_t context"
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.Fc
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.Ft ssize_t
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.Fo sctp_sendmsgx
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.Fa "int s" "const void *msg" "size_t len" "const struct sockaddr *to"
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.Fa "int addrcnt" "uint32_t ppid" "uint32_t flags" "uint16_t stream_no"
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.Fa "uint32_t timetolive" "uint32_t context"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn sctp_sendmsg
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system call
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is used to transmit a message to another SCTP endpoint.
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The
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.Fn sctp_sendmsg
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may be used at any time.
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If the socket is a one-to-many type (SOCK_SEQPACKET)
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socket then an attempt to send to an address that no association exists to will
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implicitly create a new association.
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Data sent in such an instance will result in
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the data being sent on the third leg of the SCTP four-way handshake.
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Note that if
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the socket is a one-to-one type (SOCK_STREAM) socket then an association must
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be in existence (by use of the
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.Xr connect 2
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system call).
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Calling
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.Fn sctp_sendmsg
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or
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.Fn sctp_sendmsgx
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on a non-connected one-to-one socket will result in
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.Va errno
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being set to
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.Er ENOTCONN ,
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-1 being returned, and the message not being transmitted.
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.Pp
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The address of the target is given by
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.Fa to
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with
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.Fa tolen
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specifying its size.
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The length of the message
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.Fa msg
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is given by
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.Fa len .
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If the message is too long to pass atomically through the
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underlying protocol,
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.Va errno
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is set to
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.Er EMSGSIZE ,
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-1 is returned, and
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the message is not transmitted.
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.Pp
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No indication of failure to deliver is implicit in a
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.Xr sctp_sendmsg 3
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call.
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Locally detected errors are indicated by a return value of -1.
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.Pp
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If no space is available at the socket to hold
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the message to be transmitted, then
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.Xr sctp_sendmsg 3
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normally blocks, unless the socket has been placed in
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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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send more data on one-to-one type (SOCK_STREAM) sockets.
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.Pp
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The
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.Fa ppid
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argument is an opaque 32 bit value that is passed transparently
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through the stack to the peer endpoint.
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It will be available on
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reception of a message (see
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.Xr sctp_recvmsg 3 ) .
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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 flags
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argument may include one or more of the following:
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.Bd -literal
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#define SCTP_EOF 0x0100 /* Start a shutdown procedures */
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#define SCTP_ABORT 0x0200 /* Send an ABORT to peer */
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#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */
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#define SCTP_ADDR_OVER 0x0800 /* Override the primary-address */
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#define SCTP_SENDALL 0x1000 /* Send this on all associations */
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/* for the endpoint */
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/* The lower byte is an enumeration of PR-SCTP policies */
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#define SCTP_PR_SCTP_TTL 0x0001 /* Time based PR-SCTP */
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#define SCTP_PR_SCTP_BUF 0x0002 /* Buffer based PR-SCTP */
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#define SCTP_PR_SCTP_RTX 0x0003 /* Number of retransmissions based PR-SCTP */
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.Ed
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.Pp
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The flag
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.Dv SCTP_EOF
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is used to instruct the SCTP stack to queue this message
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and then start a graceful shutdown of the association.
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All
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remaining data in queue will be sent after which the association
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will be shut down.
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.Pp
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.Dv SCTP_ABORT
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is used to immediately terminate an association.
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An abort
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is sent to the peer and the local TCB is destroyed.
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.Pp
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.Dv SCTP_UNORDERED
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is used to specify that the message being sent has no
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specific order and should be delivered to the peer application
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as soon as possible.
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When this flag is absent messages
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are delivered in order within the stream they are sent, but without
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respect to order to peer streams.
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.Pp
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The flag
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.Dv SCTP_ADDR_OVER
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is used to specify that an specific address should be used.
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Normally
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SCTP will use only one of a multi-homed peers addresses as the primary
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address to send to.
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By default, no matter what the
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.Fa to
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argument is, this primary address is used to send data.
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By specifying
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this flag, the user is asking the stack to ignore the primary address
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and instead use the specified address not only as a lookup mechanism
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to find the association but also as the actual address to send to.
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.Pp
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For a one-to-many type (SOCK_SEQPACKET) socket the flag
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.Dv SCTP_SENDALL
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can be used as a convenient way to make one send call and have
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all associations that are under the socket get a copy of the message.
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Note that this mechanism is quite efficient and makes only one actual
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copy of the data which is shared by all the associations for sending.
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.Pp
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The remaining flags are used for the partial reliability extension (RFC3758)
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and will only be effective if the peer endpoint supports this extension.
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This option specifies what local policy the local endpoint should use
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in skipping data.
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If none of these options are set, then data is
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never skipped over.
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.Pp
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.Dv SCTP_PR_SCTP_TTL
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is used to indicate that a time based lifetime is being applied
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to the data.
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The
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.Fa timetolive
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argument is then a number of milliseconds for which the data is
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attempted to be transmitted.
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If that many milliseconds elapse
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and the peer has not acknowledged the data, the data will be
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skipped and no longer transmitted.
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Note that this policy does
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not even assure that the data will ever be sent.
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In times of a congestion
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with large amounts of data being queued, the
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.Fa timetolive
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may expire before the first transmission is ever made.
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.Pp
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The
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.Dv SCTP_PR_SCTP_BUF
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based policy transforms the
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.Fa timetolive
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field into a total number of bytes allowed on the outbound
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send queue.
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If that number or more bytes are in queue, then
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other buffer based sends are looked to be removed and
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skipped.
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Note that this policy may also result in the data
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never being sent if no buffer based sends are in queue and
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the maximum specified by
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.Fa timetolive
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bytes is in queue.
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.Pp
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The
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.Dv SCTP_PR_SCTP_RTX
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policy transforms the
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.Fa timetolive
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into a number of retransmissions to allow.
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This policy
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always assures that at a minimum one send attempt is
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made of the data.
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After which no more than
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.Fa timetolive
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retransmissions will be made before the data is skipped.
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.Pp
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.Fa stream_no
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is the SCTP stream that you wish to send the
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message 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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The
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.Fa context
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field is used only in the event the message cannot be sent.
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This is an opaque
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value that the stack retains and will give to the user when a failed send
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is given if that notification is enabled (see
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.Xr sctp 4 ) .
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Normally a user process can use this value to index some application
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specific data structure when a send cannot be fulfilled.
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.Fn sctp_sendmsgx
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is identical to
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.Fn sctp_sendmsg
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with the exception that it takes an array of sockaddr structures in the
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argument
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.Fa to
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and adds the additional argument
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.Fa addrcnt
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which specifies how many addresses are in the array.
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This allows a
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caller to implicitly set up an association passing multiple addresses
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as if
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.Fn sctp_connectx
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had been called to set up the association.
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.Sh RETURN VALUES
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The call returns the number of characters sent, 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_sendmsg
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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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.Dv SCTP_ABORT
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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 connect 2 ,
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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 socket 2 ,
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.Xr write 2 ,
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.Xr sctp_connectx 3 ,
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.Xr sctp 4
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.Sh BUGS
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Because in the one-to-many style socket
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.Fn sctp_sendmsg
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or
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.Fn sctp_sendmsgx
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may have multiple associations under one endpoint, a
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select on write will only work for a one-to-one style
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socket.
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