075dc1b3fb
While FreeBSD's implementation of these expect an int inside of libc, that's an implementation detail that we can hide from the user as it's the natural promotion of the current mode_t type and before it is used in the kernel, it's converted back to the narrower type that's the current definition of mode_t. As such, documenting int is at best confusing and at worst misleading. Instead add a note that these args are variadic and as such calling conventions may differ from non-variadic arguments.
337 lines
9.4 KiB
Groff
337 lines
9.4 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 September 28, 2019
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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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.Pp
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Please see the
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.Xr mqueuefs 5
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man page for instructions on loading the module or compiling the service into
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the kernel.
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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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.Xr mqueuefs 5
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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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.Pp
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The
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.Fa mode
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and
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.Fa attr
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arguments are variadic and may result in different calling conventions
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than might otherwise be expected.
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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
|
|
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.
|