| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | BUGS | SEE ALSO | COLOPHON | The Linux Programming Interface |
MQ_OPEN(3) Linux Programmer's Manual MQ_OPEN(3)
mq_open - open a message queue
#include <fcntl.h> /* For O_* constants */
#include <sys/stat.h> /* For mode constants */
#include <mqueue.h>
mqd_t mq_open(const char *name, int oflag);
mqd_t mq_open(const char *name, int oflag, mode_t mode,
struct mq_attr *attr);
Link with -lrt.
mq_open() creates a new POSIX message queue or opens an existing queue. The
queue is identified by name. For details of the construction of name, see
mq_overview(7).
The oflag argument specifies flags that control the operation of the call.
(Definitions of the flags values can be obtained by including <fcntl.h>.)
Exactly one of the following must be specified in oflag:
O_RDONLY
Open the queue to receive messages only.
O_WRONLY
Open the queue to send messages only.
O_RDWR Open the queue to both send and receive messages.
Zero or more of the following flags can additionally be ORed in oflag:
O_NONBLOCK
Open the queue in nonblocking mode. In circumstances where
mq_receive(3) and mq_send(3) would normally block, these functions
instead fail with the error EAGAIN.
O_CREAT
Create the message queue if it does not exist. The owner (user ID) of
the message queue is set to the effective user ID of the calling
process. The group ownership (group ID) is set to the effective group
ID of the calling process.
O_EXCL If O_CREAT was specified in oflag, and a queue with the given name
already exists, then fail with the error EEXIST.
If O_CREAT is specified in oflag, then two additional arguments must be
supplied. The mode argument specifies the permissions to be placed on the new
queue, as for open(2). (Symbolic definitions for the permissions bits can be
obtained by including <sys/stat.h>.) The permissions settings are masked
against the process umask. The attr argument specifies attributes for the
queue. See mq_getattr(3) for details. If attr is NULL, then the queue is
created with implementation-defined default attributes.
On success, mq_open() returns a message queue descriptor for use by other
message queue functions. On error, mq_open() returns (mqd_t) -1, with errno
set to indicate the error.
EACCES The queue exists, but the caller does not have permission to open it in
the specified mode.
EACCES name contained more than one slash.
EEXIST Both O_CREAT and O_EXCL were specified in oflag, but a queue with this
name already exists.
EINVAL O_CREAT was specified in oflag, and attr was not NULL, but
attr->mq_maxmsg or attr->mq_msqsize was invalid. Both of these fields
must be greater than zero. In a process that is unprivileged (does not
have the CAP_SYS_RESOURCE capability), attr->mq_maxmsg must be less
than or equal to the msg_max limit, and attr->mq_msgsize must be less
than or equal to the msgsize_max limit. In addition, even in a
privileged process, attr->mq_maxmsg cannot exceed the HARD_MAX limit.
(See mq_overview(7) for details of these limits.)
EMFILE The process already has the maximum number of files and message queues
open.
ENAMETOOLONG
name was too long.
ENFILE The system limit on the total number of open files and message queues
has been reached.
ENOENT The O_CREAT flag was not specified in oflag, and no queue with this
name exists.
ENOENT name was just "/" followed by no other characters.
ENOMEM Insufficient memory.
ENOSPC Insufficient space for the creation of a new message queue. This
probably occurred because the queues_max limit was encountered; see
mq_overview(7).
POSIX.1-2001.
In kernels before 2.6.14, the process umask was not applied to the permissions
specified in mode.
mq_close(3), mq_getattr(3), mq_notify(3), mq_receive(3), mq_send(3),
mq_unlink(3), mq_overview(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2009-02-20 MQ_OPEN(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface