Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original documentation from The Open Group can be obtained online at
http://www.opengroup.org/bookstore/.
The Institute of Electrical and Electronics Engineers and The Open
Group, have given us permission to reprint portions of their
documentation.
In the following statement, the phrase ``this text'' refers to portions
of the system documentation.
Portions of this text are reprinted and reproduced in electronic form
in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,
Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6,
Copyright (C) 2001-2004 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy
between these versions 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.
This notice shall appear on any product containing this material.
The contents of this file are subject to the terms of the
Common Development and Distribution License (the "License").
You may not use this file except in compliance with the License.
You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
or http://www.opensolaris.org/os/licensing.
See the License for the specific language governing permissions
and limitations under the License.
When distributing Covered Code, include this CDDL HEADER in each
file and include the License file at usr/src/OPENSOLARIS.LICENSE.
If applicable, add the following below this CDDL HEADER, with the
fields enclosed by brackets "[]" replaced with your own identifying
information: Portions Copyright [yyyy] [name of copyright owner]
Copyright 1989 AT&T
Portions Copyright (c) 1992, X/Open Company Limited All Rights Reserved
Copyright (c) 2008, Sun Microsystems, Inc. All Rights Reserved
#include <mqueue.h> mqd_t mq_open(const char *name, int oflag, /* unsigned long mode, mq_attr attr */ ...);
The mq_open() function establishes the connection between a process and a message queue with a message queue descriptor. It creates a open message queue description that refers to the message queue, and a message queue descriptor that refers to that open message queue description. The message queue descriptor is used by other functions to refer to that message queue.
The name argument points to a string naming a message queue. The name argument must conform to the construction rules for a path-name. If name is not the name of an existing message queue and its creation is not requested, mq_open() fails and returns an error. The first character of name must be a slash (/) character and the remaining characters of name cannot include any slash characters. For maximum portability, name should include no more than 14 characters, but this limit is not enforced.
The oflag argument requests the desired receive and/or send access to the message queue. The requested access permission to receive messages or send messages is granted if the calling process would be granted read or write access, respectively, to a file with the equivalent permissions.
The value of oflag is the bitwise inclusive OR of values from the following list. Applications must specify exactly one of the first three values (access modes) below in the value of oflag: O_RDONLY
Open the message queue for receiving messages. The process can use the returned message queue descriptor with mq_receive(3C), but not mq_send(3C). A message queue may be open multiple times in the same or different processes for receiving messages.
Open the queue for sending messages. The process can use the returned message queue descriptor with mq_send(3C) but not mq_receive(3C). A message queue may be open multiple times in the same or different processes for sending messages.
Open the queue for both receiving and sending messages. The process can use any of the functions allowed for O_RDONLY and O_WRONLY. A message queue may be open multiple times in the same or different processes for sending messages.
Any combination of the remaining flags may additionally be specified in the value of oflag: O_CREAT
This option is used to create a message queue, and it requires two additional arguments: mode, which is of type mode_t, and attr, which is pointer to a mq_attr structure. If the pathname, name, has already been used to create a message queue that still exists, then this flag has no effect, except as noted under O_EXCL (see below). Otherwise, a message queue is created without any messages in it. The user ID of the message queue is set to the effective user ID of process, and the group ID of the message queue is set to the effective group ID of the process. The file permission bits are set to the value of mode, and modified by clearing all bits set in the file mode creation mask of the process (see umask(2)). If attr is non-NULL and the calling process has the appropriate privilege on name, the message queue mq_maxmsg and mq_msgsize attributes are set to the values of the corresponding members in the mq_attr structure referred to by attr. If attr is non-NULL, but the calling process does not have the appropriate privilege on name, the mq_open() function fails and returns an error without creating the message queue.
If both O_EXCL and O_CREAT are set, mq_open() will fail if the message queue name exists. The check for the existence of the message queue and the creation of the message queue if it does not exist are atomic with respect to other processes executing mq_open() naming the same name with both O_EXCL and O_CREAT set. If O_EXCL and O_CREAT are not set, the result is undefined.
The setting of this flag is associated with the open message queue description and determines whether a mq_send(3C) or mq_receive(3C) waits for resources or messages that are not currently available, or fails with errno set to EAGAIN. See mq_send(3C) and mq_receive(3C) for details.
Upon successful completion, mq_open() returns a message queue descriptor; otherwise the function returns (mqd_t)-1 and sets errno to indicate the error condition.
The mq_open() function will fail if: EACCES
The message queue exists and the permissions specified by oflag are denied, or the message queue does not exist and permission to create the message queue is denied.
O_CREAT and O_EXCL are set and the named message queue already exists.
The mq_open() operation was interrupted by a signal.
The mq_open() operation is not supported for the given name, or O_CREAT was specified in oflag, the value of attr is not NULL, and either mq_maxmsg or mq_msgsize was less than or equal to zero.
The number of open message queue descriptors in this process exceeds MQ_OPEN_MAX, of the number of open file descriptors in this process exceeds OPEN_MAX.
The length of the name string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while _POSIX_NO_TRUNC is in effect.
Too many message queues are currently open in the system.
O_CREAT is not set and the named message queue does not exist.
There is insufficient space for the creation of the new message queue.
The mq_open() function is not supported by the system.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| Interface Stability Committed |
| MT-Level MT-Safe |
| Standard See standards(5). |
exec(2), exit(2), umask(2), sysconf(3C), mqueue.h(3HEAD), mq_close(3C), mq_receive(3C), mq_send(3C), mq_setattr(3C), mq_unlink(3C), attributes(5), standards(5)
Due to the manner in which message queues are implemented, they should not be considered secure and should not be used in security-sensitive applications.
Solaris 2.6 was the first release to support the Asynchronous Input and Output option. Prior to this release, this function always returned -1 and set errno to ENOSYS.