mq_open — open a message queue
#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
() 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.
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
OR
ed in oflag
:
O_NONBLOCK
Open the queue in non-blocking 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). The permissions
settings are masked against the process umask. The attr
argument specifies
attributes for the queue. See mq_getattr(2) 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.
The queue exists, but the caller does not have permission to open it in the specified mode.
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.)
Both O_CREAT
and
O_EXCL
were specified in
oflag
, but a
queue with this name
already exists.
The process already has the maximum number of files and message queues open.
name
was too
long.
The system limit on the total number of open files and message queues has been reached.
The O_CREAT
flag was
not specified in oflag
, and no queue with
this name
exists.
Insufficient memory.
Insufficient space for the creation of a new message
queue. This probably occurred because the queues_max
limit was
encountered; see mq_overview(7).
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)
|