mq_open man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

MQ_OPEN(3P)		   POSIX Programmer's Manual		   MQ_OPEN(3P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       mq_open — open a message queue (REALTIME)

       #include <mqueue.h>

       mqd_t mq_open(const char *name, int oflag, ...);

       The mq_open() function shall establish the connection between a process
       and a message queue with a message queue descriptor. It shall create 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 nam‐
       ing a message queue. It is unspecified whether the name appears in  the
       file  system  and  is visible to other functions that take pathnames as
       arguments. The name argument conforms to the construction rules	for  a
       pathname,  except  that	the interpretation of <slash> characters other
       than the leading <slash> character in name  is  implementation-defined,
       and  that  the  length limits for the name argument are implementation-
       defined and need not be the same as the pathname limits {PATH_MAX}  and
       {NAME_MAX}.   If name begins with the <slash> character, then processes
       calling mq_open() with the same value of name shall refer to  the  same
       message	queue  object,	as  long as that name has not been removed. If
       name does not begin with the <slash> character, the effect is implemen‐
       tation-defined.	If  the	 name  argument is not the name of an existing
       message queue and creation is not requested, mq_open() shall  fail  and
       return an error.

       A  message queue descriptor may be implemented using a file descriptor,
       in which case applications can open up to at least {OPEN_MAX} file  and
       message queues.

       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  shall  be  granted  if the calling process would be
       granted read or write access, respectively,  to	an  equivalently  pro‐
       tected file.

       The  value of oflag is the bitwise-inclusive OR of values from the fol‐
       lowing list.  Applications shall 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(),  but  not  mq_send().	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()  but
		   not	mq_receive().	A  message  queue may be open multiple
		   times in the same or different processes for	 sending  mes‐

       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 be specified in the value of

       O_CREAT	   Create  a  message  queue. It requires two additional argu‐
		   ments: mode, which shall be of type mode_t, and attr, which
		   shall be a pointer to an mq_attr structure. If the pathname
		   name has already been used to create a message  queue  that
		   still  exists,  then this flag shall have no effect, except
		   as noted under O_EXCL.  Otherwise, a message queue shall be
		   created without any messages in it. The user ID of the mes‐
		   sage queue shall be set to the effective  user  ID  of  the
		   process.  The group ID of the message queue shall be set to
		   the effective group ID of the process; however, if the name
		   argument is visible in the file system, the group ID may be
		   set to the group ID of the containing directory. When  bits
		   in  mode other than the file permission bits are specified,
		   the effect is unspecified. If attr  is  NULL,  the  message
		   queue  shall be created with implementation-defined default
		   message queue attributes. If attr is non-NULL and the call‐
		   ing process has appropriate privileges on name, the message
		   queue mq_maxmsg and mq_msgsize attributes shall be  set  to
		   the	values	of  the	 corresponding	members in the mq_attr
		   structure referred to by attr.  The values of the  mq_flags
		   and	mq_curmsgs  members  of the mq_attr structure shall be
		   ignored. If attr is non-NULL, but the calling process  does
		   not	have  appropriate  privileges  on  name, the mq_open()
		   function shall fail and return an  error  without  creating
		   the message queue.

       O_EXCL	   If  O_EXCL and O_CREAT are set, mq_open() shall 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 shall 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  Determines  whether	an mq_send() or mq_receive() waits for
		   resources or messages that are not currently available,  or
		   fails  with	errno  set  to	[EAGAIN];  see	mq_send()  and
		   mq_receive() for details.

       The mq_open() function does not add or remove messages from the queue.

       Upon successful completion, the function shall return a	message	 queue
       descriptor;  otherwise,	the  function  shall  return (mqd_t)−1 and set
       errno to indicate the error.

       The mq_open() function shall 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

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

       EINVAL The mq_open() function is not supported for the given name.

       EINVAL 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

       EMFILE Too  many message queue descriptors or file descriptors are cur‐
	      rently in use by this process.

       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

       If  any	of  the following conditions occur, the mq_open() function may
       return (mqd_t)−1 and set errno to the corresponding value.

	      The length of the name  argument	exceeds	 {_POSIX_PATH_MAX}  on
	      systems	that   do  not	support	 the  XSI  option  or  exceeds
	      {_XOPEN_PATH_MAX} on XSI systems, or has	a  pathname  component
	      that  is	longer	than  {_POSIX_NAME_MAX} on systems that do not
	      support the XSI option or longer than {_XOPEN_NAME_MAX}  on  XSI

       The following sections are informative.




       A  future version might require the mq_open() and mq_unlink() functions
       to have semantics similar to normal file system operations.

       mq_close(),  mq_getattr(),   mq_receive(),   mq_send(),	 mq_setattr(),
       mq_unlink(), msgctl(), msgget(), msgrcv(), msgsnd()

       The Base Definitions volume of POSIX.1‐2008, <mqueue.h>

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐ .

IEEE/The Open Group		     2013			   MQ_OPEN(3P)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net