mq_open(3C)						   Standard C Library Functions 					       mq_open(3C)

NAME

       mq_open - open a message queue

SYNOPSIS

       #include <mqueue.h>

       mqd_t mq_open(const char *name, int oflag,
	    /* unsigned long mode, mq_attr attr */  ...);

DESCRIPTION

       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(3C),
		    but not mq_send(3C). 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(3C)  but  not
		    mq_receive(3C). 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 execut-
		      ing 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 unde-
		      fined.

       O_NONBLOCK     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.

RETURN VALUES

       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.

ERRORS

       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  per-
			mission 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.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |ATTRIBUTE TYPE		     |ATTRIBUTE VALUE		   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       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)

NOTES

       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.

SunOS 5.11							    5 Feb 2008							       mq_open(3C)