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
218 lines
5.6 KiB
Groff
218 lines
5.6 KiB
Groff
.\" $NetBSD: msgrcv.2,v 1.19 2009/01/28 08:57:02 wiz Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd January 26, 2009
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.Dt MSGRCV 2
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.Os
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.Sh NAME
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.Nm msgrcv
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.Nd receive a message from a message queue
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/msg.h
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.Ft ssize_t
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.Fn msgrcv "int msqid" "void *msgp" "size_t msgsz" "long msgtyp" "int msgflg"
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.Sh DESCRIPTION
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The
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.Fn msgrcv
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function receives a message from the message queue specified in
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.Fa msqid ,
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and places it into the user-defined structure pointed to by
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.Fa msgp .
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This structure must contain a first field of type
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.Sy long
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that will indicate the user-defined type of the message.
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The remaining fields will contain the contents of the message.
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The following is an example of what this user-defined structure might
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look like:
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.Bd -literal
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struct mymsg {
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long mtype; /* message type */
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char mtext[1]; /* body of message */
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};
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.Ed
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.Pp
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.Va mtype
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is an integer greater than 0 that can be used to select messages.
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.Va mtext
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is an array of bytes, with size up to the system limit
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.Dv MSGMAX .
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.Pp
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The value of
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.Fa msgtyp
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has one of the following meanings:
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.Bl -bullet
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.It
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.Fa msgtyp
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is greater than 0.
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The first message of type
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.Fa msgtyp
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will be received.
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.It
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.Fa msgtyp
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is equal to 0.
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The first message on the queue will be received.
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.It
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.Fa msgtyp
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is less than 0.
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The first message of the lowest message type that is
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less than or equal to the absolute value of
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.Fa msgtyp
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will be received.
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.El
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.Pp
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.Fa msgsz
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specifies the maximum length of the requested message.
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If the received message has a length greater than
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.Fa msgsz
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it will be silently truncated if the
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.Dv MSG_NOERROR
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flag is set in
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.Fa msgflg ,
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otherwise an error will be returned.
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.Pp
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If no matching message is present on the message queue specified by
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.Fa msqid ,
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the behaviour of
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.Fn msgrcv
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depends on whether the
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.Dv IPC_NOWAIT
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flag is set in
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.Fa msgflg
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or not.
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If
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.Dv IPC_NOWAIT
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is set, then
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.Fn msgrcv
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will immediately return a value of \-1 and set
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.Va errno
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to
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.Er EAGAIN .
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If
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.Dv IPC_NOWAIT
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is not set, the calling process will block until:
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.Bl -bullet
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.It
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A message of the requested type becomes available on the message queue.
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.It
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The message queue is removed, in which case \-1 will be returned and
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.Va errno
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set to
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.Er EIDRM .
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.It
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A signal is received and caught.
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\-1 is returned and
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.Va errno
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is set to
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.Er EINTR .
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.El
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.Pp
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If a message is successfully received, the data structure associated with
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.Fa msqid
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is updated as follows:
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.Bl -bullet
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.It
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.Va msg_lrpid
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is set to the pid of the caller.
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.It
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.Va msg_lrtime
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is set to the current time.
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.It
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.Va msg_qnum
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is decremented by 1.
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.El
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn msgrcv
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returns the number of bytes received into the
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.Va mtext
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field of the structure pointed to by
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.Fa msgp .
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Otherwise, \-1 is returned, and
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.Va errno
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set to indicate the error.
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.Sh ERRORS
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.Fn msgrcv
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will fail if:
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.Bl -tag -width Er
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.It Bq Er E2BIG
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A matching message was received, but its size was greater than
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.Fa msgsz
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and the
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.Dv MSG_NOERROR
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flag was not set in
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.Fa msgflg .
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.It Bq Er EACCES
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The calling process does not have read access to the message queue.
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.It Bq Er EAGAIN
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There is no message of the requested type available on the message queue,
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and
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.Dv IPC_NOWAIT
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is set in
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.Fa msgflg .
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.It Bq Er EFAULT
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.Fa msgp
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points to an invalid address.
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.It Bq Er EIDRM
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The message queue identifier
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.Fa msqid
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is removed from the system.
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.It Bq Er EINTR
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The system call was interrupted by the delivery of a signal.
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.It Bq Er EINVAL
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.Fa msqid
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is not a valid message queue identifier
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.Pp
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The message queue was removed while
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.Fn msgrcv
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was waiting for a message of the requested type to become available in it.
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.Pp
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.Fa msgsz
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is greater than
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.Dv SSIZE_MAX .
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.It Bq Er ENOMSG
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The queue does not contain a message of the desired type and
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.Dv IPC_NOWAIT
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is set.
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.El
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.Sh SEE ALSO
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.Xr msgctl 2 ,
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.Xr msgget 2 ,
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.Xr msgsnd 2
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Message queues appeared in the first release of
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.At V .
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