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324 lines
9.1 KiB
Groff
324 lines
9.1 KiB
Groff
.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Portions of this text are reprinted and reproduced in electronic form
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.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
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.\" Portable Operating System Interface (POSIX), The Open Group Base
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.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
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.\" Electrical and Electronics Engineers, Inc and The Open Group. In the
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.\" event of any discrepancy between this version and the original IEEE and
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.\" The Open Group Standard, the original IEEE and The Open Group Standard is
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.\" the referee document. The original Standard can be obtained online at
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.\" http://www.opengroup.org/unix/online.html.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 29, 2005
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.Dt MQ_OPEN 2
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.Os
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.Sh NAME
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.Nm mq_open
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.Nd "open a message queue (REALTIME)"
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.Sh LIBRARY
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.Lb librt
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.Sh SYNOPSIS
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.In mqueue.h
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.Ft mqd_t
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.Fn mq_open "const char *name" "int oflag" "..."
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.Sh DESCRIPTION
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The
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.Fn mq_open
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system call establishes the connection between a process and a message queue
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with a message queue descriptor.
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It creates an open message queue
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description that refers to the message queue, and a message queue descriptor
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that refers to that open message queue description.
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The message queue
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descriptor is used by other functions to refer to that message queue.
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The
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.Fa name
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argument points to a string naming a message queue.
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The
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.Fa name
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argument should conform to the construction rules for a pathname.
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The
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.Fa name
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should begin with a slash character.
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Processes calling
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.Fn mq_open
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with the same value of
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.Fa name
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refers to the same message queue object, as long as that name has not been
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removed.
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If the
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.Fa name
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argument is not the name of an existing message queue and creation is not
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requested,
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.Fn mq_open
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will fail and return an error.
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.Pp
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The
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.Fa oflag
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argument requests the desired receive and/or send access to the message
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queue.
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The requested access permission to receive messages or send messages
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would be granted if the calling process would be granted read or write access,
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respectively, to an equivalently protected file.
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.Pp
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The value of
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.Fa oflag
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is the bitwise-inclusive OR of values from the following list.
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Applications should specify exactly one of the first three values (access
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modes) below in the value of
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.Fa oflag :
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.Bl -tag -width ".Dv O_NONBLOCK"
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.It Dv O_RDONLY
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Open the message queue for receiving messages.
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The process can use the
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returned message queue descriptor with
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.Fn mq_receive ,
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but not
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.Fn mq_send .
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A message queue may be open multiple times in the same or different processes
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for receiving messages.
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.It Dv O_WRONLY
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Open the queue for sending messages.
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The process can use the returned
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message queue descriptor with
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.Fn mq_send
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but not
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.Fn mq_receive .
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A message queue may be open multiple times in the same or different processes
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for sending messages.
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.It Dv O_RDWR
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Open the queue for both receiving and sending messages.
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The process can use
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any of the functions allowed for
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.Dv O_RDONLY
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and
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.Dv O_WRONLY .
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A message queue may be open multiple times in the same or different processes
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for sending messages.
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.El
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.Pp
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Any combination of the remaining flags may be specified in the value of
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.Fa oflag :
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.Bl -tag -width ".Dv O_NONBLOCK"
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.It Dv O_CREAT
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Create a message queue.
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It requires two additional arguments:
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.Fa mode ,
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which is of type
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.Vt mode_t ,
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and
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.Fa attr ,
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which is a pointer to an
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.Vt mq_attr
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structure.
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If the pathname
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.Fa name
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has already been used to create a message queue that still exists, then
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this flag has no effect, except as noted under
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.Dv O_EXCL .
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Otherwise, a message queue will be created without any messages
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in it.
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The user ID of the message queue will be set to the effective user ID
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of the process, and the group ID of the message queue will be set to the
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effective group ID of the process.
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The permission bits of the message queue
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will be set to the value of the
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.Fa mode
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argument, except those set in the file mode creation mask of the process.
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When bits in
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.Fa mode
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other than the file permission bits are specified, the effect is
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unspecified.
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If
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.Fa attr
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is
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.Dv NULL ,
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the message queue is created with implementation-defined default message
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queue attributes.
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If attr is
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.Pf non- Dv NULL
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and the calling process has the
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appropriate privilege on name, the message queue
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.Va mq_maxmsg
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and
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.Va mq_msgsize
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attributes will be set to the values of the corresponding members in the
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.Vt mq_attr
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structure referred to by
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.Fa attr .
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If
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.Fa attr
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is
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.Pf non- Dv NULL ,
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but the calling process does not have the appropriate privilege
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on name, the
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.Fn mq_open
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function will fail and return an error without creating the message queue.
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.It Dv O_EXCL
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If
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.Dv O_EXCL
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and
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.Dv O_CREAT
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are set,
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.Fn mq_open
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will fail if the message queue name exists.
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.It Dv O_NONBLOCK
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Determines whether an
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.Fn mq_send
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or
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.Fn mq_receive
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waits for resources or messages that are not currently available, or fails
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with
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.Va errno
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set to
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.Er EAGAIN ;
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see
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.Xr mq_send 2
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and
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.Xr mq_receive 2
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for details.
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.El
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.Pp
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The
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.Fn mq_open
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system call does not add or remove messages from the queue.
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.Sh NOTES
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.Fx
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implements message queue based on file descriptor.
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The descriptor
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is inherited by child after
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.Xr fork 2 .
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The descriptor is closed in a new image after
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.Xr exec 3 .
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The
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.Xr select 2
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and
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.Xr kevent 2
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system calls are supported for message queue descriptor.
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.Sh RETURN VALUES
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Upon successful completion, the function returns a message queue
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descriptor; otherwise, the function returns
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.Po Vt mqd_t Pc Ns \-1
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and sets the global variable
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.Va errno
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to indicate the error.
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.Sh ERRORS
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The
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.Fn mq_open
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The message queue exists and the permissions specified by
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.Fa oflag
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are denied, or the message queue does not exist and permission to create the
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message queue is denied.
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.It Bq Er EEXIST
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.Dv O_CREAT
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and
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.Dv O_EXCL
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are set and the named message queue already exists.
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.It Bq Er EINTR
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The
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.Fn mq_open
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function was interrupted by a signal.
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.It Bq Er EINVAL
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The
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.Fn mq_open
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function is not supported for the given name.
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.It Bq Er EINVAL
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.Dv O_CREAT
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was specified in
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.Fa oflag ,
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the value of
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.Fa attr
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is not
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.Dv NULL ,
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and either
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.Va mq_maxmsg
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or
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.Va mq_msgsize
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was less than or equal to zero.
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.It Bq Er EMFILE
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Too many message queue descriptors or file descriptors are currently in use
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by this process.
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.It Bq Er ENAMETOOLONG
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The length of the
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.Fa name
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argument exceeds
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.Brq Dv PATH_MAX
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or a pathname component
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is longer than
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.Brq Dv NAME_MAX .
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.It Bq Er ENFILE
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Too many message queues are currently open in the system.
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.It Bq Er ENOENT
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.Dv O_CREAT
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is not set and the named message queue does not exist.
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.It Bq Er ENOSPC
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There is insufficient space for the creation of the new message queue.
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.El
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.Sh SEE ALSO
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.Xr mq_close 2 ,
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.Xr mq_getattr 2 ,
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.Xr mq_receive 2 ,
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.Xr mq_send 2 ,
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.Xr mq_setattr 2 ,
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.Xr mq_timedreceive 3 ,
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.Xr mq_timedsend 3 ,
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.Xr mq_unlink 3
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.Sh STANDARDS
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The
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.Fn mq_open
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system call conforms to
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.St -p1003.1-2004 .
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.Sh HISTORY
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Support for
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.Tn POSIX
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message queues first appeared in
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.Fx 7.0 .
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.Sh BUGS
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This implementation places strict requirements on the value of
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.Fa name :
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it must begin with a slash
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.Pq Ql /
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and contain no other slash characters.
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.Sh COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
|
|
from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
|
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Portable Operating System Interface (POSIX), The Open Group Base
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|
Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
|
|
event of any discrepancy between this version and the original IEEE and
|
|
The Open Group Standard, the original IEEE and The Open Group Standard is
|
|
the referee document. The original Standard can be obtained online at
|
|
http://www.opengroup.org/unix/online.html.
|