MQ_OPEN(3) | Library Functions Manual | MQ_OPEN(3) |
mq_open
—
#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);
mq_open
() function establishes the connection
between a process and a message queue with a message queue descriptor. It
creates an 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, which should conform to the construction rules
for a pathname. The name should begin with a slash
character. The processes calling mq_open
() with the
same value of name will refer to the same message queue
object, as long as that name has not been removed. If the
name argument is not the name of an existing message
queue and creation is not requested, mq_open
() fails
and returns an error.
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 are granted if the calling process would be granted read or write access, respectively, to an equivalently protected file.
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
O_WRONLY
O_RDWR
O_RDONLY
and
O_WRONLY
.In all cases, a message queue may be open multiple times in the same or different processes for sending/receiving messages.
Any combination of the remaining flags may be specified in the value of oflag:
O_CREAT
O_EXCL
. Otherwise, a message queue will be
created without any messages in it. The user ID of the message queue will
be set to the effective user ID of the process, and the group ID of the
message queue will be set to the effective group ID of the process. The
permission bits of the message queue will be set to the value of the
mode argument, except those set in the file mode
creation mask of the process. When bits in mode
other than the file permission bits are specified, the effect is
unspecified. If attr is
NULL
, the message queue will be created with
implementation-defined default message queue attributes. If
attr is
non-NULL
and the calling
process has the appropriate privilege on name, the
message queue mq_maxmsg and
mq_msgsize attributes will be 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
will fail and return an error without creating the message queue.O_EXCL
O_EXCL
and O_CREAT
are
set, mq_open
() fails 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
will be atomic with respect to other threads executing
mq_open
() naming the same
name with O_EXCL
and
O_CREAT
set. If O_EXCL
is
set and O_CREAT
is not set, the result is
undefined.O_NONBLOCK
EAGAIN
.The mq_open
() function does not add or
remove messages from the queue.
mq_open
() returns a message
queue descriptor. Otherwise, the function returns
(mqd_t
) -1 and sets the global variable
errno to indicate the error.
mq_open
() function fails if:
EACCES
]EEXIST
]O_CREAT
and O_EXCL
are set and the named message queue
already exists.EINTR
]mq_open
() function was interrupted by a
signal.EINVAL
]mq_open
() function 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.EMFILE
]ENAMETOOLONG
]PATH_MAX
} or a pathname component is longer than
{NAME_MAX
}.ENFILE
]ENOENT
]O_CREAT
is not set and the named message queue does not exist.ENOSPC
]June 7, 2010 | NetBSD 9.2 |