mq_open(3RT)															      mq_open(3RT)

NAME

       mq_open - open a message queue

SYNOPSIS

       cc [ flag... ] file... -lrt [ library... ]
       #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  descrip-
       tion. 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  char-
       acter  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  mes-
       sages 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(3RT), but not mq_send(3RT). A message queue may be open multiple times in the same or  different  processes  for
		       receiving messages.

       O_WRONLY        Open  the  queue  for sending messages. The process can use the returned message queue descriptor with mq_send(3RT) but not
		       mq_receive(3RT). A message queue may be open multiple times in the same or different processes for sending messages.

       O_RDWR	       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_msg-
		       size 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.

       O_EXCL	       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.

       O_NONBLOCK      The setting of this flag is associated with the open message queue description and determines  whether  a  mq_send(3RT)	or
		       mq_receive(3RT)	waits  for resources or messages that are not currently available, or fails with errno set to EAGAIN.  See
		       mq_send(3RT) and mq_receive(3RT) for details.

       Upon successful completion, mq_open() returns a message queue descriptor; otherwise the function returns (mqd_t)-1 and sets errno to  indi-
       cate 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.

       EEXIST		       O_CREAT and O_EXCL are set and the named message queue already exists.

       EINTR		       The mq_open() operation was interrupted by a signal.

       EINVAL		       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.

       EMFILE		       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.

       ENAMETOOLONG	       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.

       ENFILE		       Too many message queues are currently open in the system.

       ENOENT		       O_CREAT is not set and the named message queue does not exist.

       ENOSPC		       There is insufficient space for the creation of the new message queue.

       ENOSYS		       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	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       exec(2),  exit(2),  umask(2),  sysconf(3C), mqueue.h(3HEAD), mq_close(3RT), mq_receive(3RT), mq_send(3RT), mq_setattr(3RT), mq_unlink(3RT),
       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-sensi-
       tive 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.

								    28 Jun 2002 						      mq_open(3RT)