f14fb60209
* Updating common/lib * Updating lib/csu * Updating lib/libc * Updating libexec/ld.elf_so * Corrected test on __minix in featuretest to actually follow the meaning of the comment. * Cleaned up _REENTRANT-related defintions. * Disabled -D_REENTRANT for libfetch * Removing some unneeded __NBSD_LIBC defines and tests Change-Id: Ic1394baef74d11b9f86b312f5ff4bbc3cbf72ce2
278 lines
7.4 KiB
Groff
278 lines
7.4 KiB
Groff
.\" $NetBSD: send.2,v 1.30 2012/06/22 22:54:26 wiz Exp $
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.\"
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.\" 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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.\" @(#)send.2 8.2 (Berkeley) 2/21/94
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.\"
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.Dd June 22, 2012
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.Dt SEND 2
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.Os
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.Sh NAME
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.Nm send ,
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.Nm sendto ,
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.Nm sendmsg ,
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.Nm sendmmsg
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.Nd send a message from a 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/socket.h
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.Ft ssize_t
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.Fn send "int s" "const void *msg" "size_t len" "int flags"
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.Ft ssize_t
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.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen"
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.Ft ssize_t
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.Fn sendmsg "int s" "const struct msghdr *msg" "int flags"
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.Ft int
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.Fn sendmmsg "int s" "struct mmsghdr *mmsg" "unsigned int vlen" "unsigned int flags"
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.Sh DESCRIPTION
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.Fn send ,
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.Fn sendto ,
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.Fn sendmsg ,
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and
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.Fn sendmmsg
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are used to transmit a message to another socket.
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.Fn send
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may be used only when the socket is in a
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.Em connected
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state, while
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.Fn sendto ,
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.Fn sendmsg
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and
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.Fn sendmmsg
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may be used at any time.
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.Pp
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The
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.Fn sendmmsg
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call be used to send multiple messages in the same call using an array of
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.Fa mmsghdr
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elements with the following form, as defined in
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.Ao Pa sys/socket.h Ac :
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.Pp
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.Bd -literal
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struct mmsghdr {
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struct msghdr msg_hdr; /* the message to be sent */
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unsigned int msg_len; /* number of bytes transmitted */
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};
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.Ed
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.Pp
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The
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.Fa msg_len
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member contains the number of bytes sent for each
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.Fa msg_hdr
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member.
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The array has
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.Fa vlen
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elements, which is limited to
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.Dv 1024 .
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If there is an error, a number fewer than
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.Fa vlen
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may be returned, and the error may be retrieved using
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.Xr getsockopt 2
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with
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.Dv SO_ERROR .
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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 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, the error
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.Er EMSGSIZE
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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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.Fn send .
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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 messages space is available at the socket to hold
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the message to be transmitted, then
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.Fn send
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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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or
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.Xr poll 2
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call may be used to determine when it is possible to
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send more data.
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Unfortunately this does not work when the interface queue which is used to
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send the message is full, and the call returns
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.Er ENOBUFS .
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.Pp
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The
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.Fa flags
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parameter may include one or more of the following:
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.Bd -literal
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#define MSG_OOB 0x0001 /* process out-of-band data */
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#define MSG_PEEK 0x0002 /* peek at incoming message */
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#define MSG_DONTROUTE 0x0004 /* bypass routing, use direct interface */
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#define MSG_EOR 0x0008 /* data completes record */
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#define MSG_NOSIGNAL 0x0400 /* do not generate SIGPIPE on EOF */
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.Ed
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.Pp
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The flag
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.Dv MSG_OOB
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is used to send
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.Dq out-of-band
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data on sockets that support this notion (e.g.
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.Dv SOCK_STREAM ) ;
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the underlying protocol must also support
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.Dq out-of-band
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data.
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.Dv MSG_EOR
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is used to indicate a record mark for protocols which support the
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concept.
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.\" .Dv MSG_EOF
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.\" requests that the sender side of a socket be shut down, and that an
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.\" appropriate indication be sent at the end of the specified data;
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.\" this flag is only implemented for
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.\" .Dv SOCK_STREAM
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.\" sockets in the
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.\" .Dv PF_INET
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.\" protocol family, and is used to implement Transaction
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.\" .Tn TCP
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.\" (see
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.\" .Xr ttcp 4 ) .
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.Dv MSG_DONTROUTE
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is usually used only by diagnostic or routing programs.
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.Pp
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See
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.Xr recv 2
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for a description of the
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.Fa msghdr
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structure.
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.Dv MSG_NOSIGNAL
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is used to prevent
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.Dv SIGPIPE
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generation when writing a socket that
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may be closed.
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.Sh RETURN VALUES
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The
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.Fn send ,
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.Fn sendto ,
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and
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.Fn sendmsg
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calls return the number of characters sent, or \-1
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if an error occurred.
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The
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.Fn sendmmsg
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call returns the number of messages sent, or \-1
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if an error occured.
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.Sh ERRORS
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.Fn send ,
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.Fn sendto ,
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.Fn sendmsg ,
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and
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.Fn sendmmsg
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fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The SO_BROADCAST option is not set on the socket, and a broadcast address
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was given as the destination.
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.It Bq Er EAFNOSUPPORT
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Addresses in the specified address family cannot be used with this socket.
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.It Bq Er EAGAIN|EWOULDBLOCK
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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 EBADF
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An invalid descriptor was specified.
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.It Bq Er EDSTADDRREQ
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In a non-connected socket a destination address has not been specified.
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.It Bq Er EFAULT
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An invalid user space address was specified for a parameter.
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.It Bq Er EHOSTDOWN
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The destination is a host on the local subnet and does not respond to
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.Xr arp 4 .
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.It Bq Er EHOSTUNREACH
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The destination for the message is unreachable.
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.It Bq Er EINVAL
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The total length of the I/O is more than can be expressed by the ssize_t
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return value.
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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 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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.Pp
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An alternative reason: 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 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 EPIPE
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In a connected socket the connection has been broken.
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.El
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.Pp
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.Fn sendto
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will also fail if:
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.Bl -tag -width Er
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.It Bq Er EISCONN
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A destination address was specified and the socket is already connected.
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.El
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.Pp
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.Fn sendmsg
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and
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.Fn sendmmsg
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will also fail if:
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.Bl -tag -width Er
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.It Bq Er EMSGSIZE
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The
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.Fa msg_iovlen
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member of the
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.Fa msg
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structure is less than or equal to 0
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or is greater than
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.Dv {IOV_MAX} .
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.El
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.Sh SEE ALSO
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.Xr fcntl 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 socket 2 ,
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.Xr write 2
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.Sh HISTORY
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The
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.Fn send
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function call appeared in
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.Bx 4.2 .
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The
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.Fn sendmmsg
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function call appeared in
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.Tn Linux 3.0
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and
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.Nx 7.0 .
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