2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
289 lines
8.1 KiB
Groff
289 lines
8.1 KiB
Groff
.\" $NetBSD: recv.2,v 1.27 2006/04/23 19:06:59 wiz Exp $
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.\"
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.\" Copyright (c) 1983, 1990, 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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.\" @(#)recv.2 8.3 (Berkeley) 2/21/94
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.\"
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.Dd April 23, 2006
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.Dt RECV 2
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.Os
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.Sh NAME
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.Nm recv ,
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.Nm recvfrom ,
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.Nm recvmsg
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.Nd receive 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 recv "int s" "void *buf" "size_t len" "int flags"
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.Ft ssize_t
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.Fn recvfrom "int s" "void * restrict buf" "size_t len" "int flags" "struct sockaddr * restrict from" "socklen_t * restrict fromlen"
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.Ft ssize_t
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.Fn recvmsg "int s" "struct msghdr *msg" "int flags"
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.Sh DESCRIPTION
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.Fn recvfrom
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and
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.Fn recvmsg
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are used to receive messages from a socket,
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and may be used to receive data on a socket whether or not
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it is connection-oriented.
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.Pp
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If
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.Fa from
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is non-nil, and the socket is not connection-oriented,
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the source address of the message is filled in.
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.Fa fromlen
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is a value-result parameter, initialized to the size of
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the buffer associated with
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.Fa from ,
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and modified on return to indicate the actual size of the
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address stored there.
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.Pp
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The
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.Fn recv
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call is normally used only on a
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.Em connected
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socket (see
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.Xr connect 2 )
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and is identical to
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.Fn recvfrom
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with a nil
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.Fa from
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parameter.
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As it is redundant, it may not be supported in future releases.
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.Pp
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All three routines return the length of the message on successful
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completion.
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If a message is too long to fit in the supplied buffer,
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excess bytes may be discarded depending on the type of socket
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the message is received from (see
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.Xr socket 2 ) .
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.Pp
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If no messages are available at the socket, the
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receive call waits for a message to arrive, unless
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the socket is nonblocking (see
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.Xr fcntl 2 )
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in which case the value
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\-1 is returned and the external variable
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.Va errno
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set to
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.Er EAGAIN .
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The receive calls normally return any data available,
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up to the requested amount,
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rather than waiting for receipt of the full amount requested;
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this behavior is affected by the socket-level options
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.Dv SO_RCVLOWAT
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and
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.Dv SO_RCVTIMEO
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described in
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.Xr getsockopt 2 .
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.Pp
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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 more data arrive.
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.Pp
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The
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.Fa flags
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argument to a recv call is formed by
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.Em or Ap ing
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one or more of the values:
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.Bl -column MSG_WAITALL -offset indent
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.It Dv MSG_OOB Ta process out-of-band data
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.It Dv MSG_PEEK Ta peek at incoming message
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.It Dv MSG_WAITALL Ta wait for full request or error
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.El
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The
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.Dv MSG_OOB
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flag requests receipt of out-of-band data
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that would not be received in the normal data stream.
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Some protocols place expedited data at the head of the normal
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data queue, and thus this flag cannot be used with such protocols.
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The
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.Dv MSG_PEEK
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flag causes the receive operation to return data
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from the beginning of the receive queue without removing that
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data from the queue.
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Thus, a subsequent receive call will return the same data.
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The
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.Dv MSG_WAITALL
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flag requests that the operation block until
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the full request is satisfied.
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However, the call may still return less data than requested
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if a signal is caught, an error or disconnect occurs,
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or the next data to be received is of a different type than that returned.
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.Pp
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The
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.Fn recvmsg
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call uses a
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.Fa msghdr
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structure to minimize the number of directly supplied parameters.
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This structure has 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 msghdr {
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void *msg_name; /* optional address */
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socklen_t msg_namelen; /* size of address */
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struct iovec *msg_iov; /* scatter/gather array */
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int msg_iovlen; /* # elements in msg_iov */
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void *msg_control; /* ancillary data, see below */
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socklen_t msg_controllen; /* ancillary data buffer len */
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int msg_flags; /* flags on received message */
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};
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.Ed
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.Pp
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Here
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.Fa msg_name
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and
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.Fa msg_namelen
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specify the source address if the socket is unconnected;
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.Fa msg_name
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may be given as a null pointer if no names are desired or required.
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If the socket is connected,
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.Fa msg_name
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and
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.Fa msg_namelen
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are ignored.
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.Fa msg_iov
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and
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.Fa msg_iovlen
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describe scatter gather locations, as discussed in
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.Xr read 2 .
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.Fa msg_control ,
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which has length
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.Fa msg_controllen ,
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points to a buffer for other protocol control related messages
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or other miscellaneous ancillary data.
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The messages are of the form:
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.Bd -literal
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struct cmsghdr {
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socklen_t cmsg_len; /* data byte count, including hdr */
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int cmsg_level; /* originating protocol */
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int cmsg_type; /* protocol-specific type */
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/* followed by
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u_char cmsg_data[]; */
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};
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.Ed
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As an example, one could use this to learn of changes in the data-stream
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in XNS/SPP, or in ISO, to obtain user-connection-request data by requesting
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a recvmsg with no data buffer provided immediately after an
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.Fn accept
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call.
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.Pp
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Open file descriptors are now passed as ancillary data for
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.Dv AF_LOCAL
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domain sockets, with
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.Fa cmsg_level
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set to
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.Dv SOL_SOCKET
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and
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.Fa cmsg_type
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set to
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.Dv SCM_RIGHTS .
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.Pp
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The
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.Fa msg_flags
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field is set on return according to the message received.
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.Dv MSG_EOR
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indicates end-of-record;
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the data returned completed a record (generally used with sockets of type
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.Dv SOCK_SEQPACKET ) .
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.Dv MSG_TRUNC
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indicates that
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the trailing portion of a datagram was discarded because the datagram
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was larger than the buffer supplied.
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.Dv MSG_CTRUNC
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indicates that some
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control data were discarded due to lack of space in the buffer
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for ancillary data.
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.Dv MSG_OOB
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is returned to indicate that expedited or out-of-band data were received.
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.Sh RETURN VALUES
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These calls return 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 calls fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The argument
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.Fa s
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is an invalid descriptor.
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.It Bq Er ENOTCONN
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The socket is associated with a connection-oriented protocol
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and has not been connected (see
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.Xr connect 2
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and
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.Xr accept 2 ) .
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.It Bq Er ENOTSOCK
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The argument
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.Fa s
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does not refer to a socket.
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.It Bq Er EAGAIN
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The socket is marked non-blocking, and the receive operation
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would block, or
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a receive timeout had been set,
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and the timeout expired before data were received.
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.It Bq Er EINTR
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The receive was interrupted by delivery of a signal before
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any data were available.
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.It Bq Er EFAULT
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The receive buffer pointer(s) point outside the process's
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address space.
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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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.El
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.Pp
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.Fn recvmsg
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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 poll 2 ,
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.Xr read 2 ,
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.Xr select 2 ,
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.Xr socket 2
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.Sh HISTORY
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The
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.Fn recv
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function call appeared in
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.Bx 4.2 .
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