mq_open man page on Mageia

Man page or keyword search:  
man Server   17783 pages
apropos Keyword Search (all sections)
Output format
Mageia logo
[printable version]

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

PROLOG
       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.

NAME
       mq_open - open a message queue (REALTIME)

SYNOPSIS
       #include <mqueue.h>

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

DESCRIPTION
       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 shall conform to the  construction	 rules
       for a pathname. 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 implementa‐
       tion-defined.   The  interpretation  of slash characters other than the
       leading slash character in name is implementation-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 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 be specified in the value of
       oflag:

       O_CREAT
	      Create a message queue. It requires  two	additional  arguments:
	      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 message queue shall be set to
	      the  effective  user  ID of the process, and the group ID of the
	      message queue shall be set to the	 effective  group  ID  of  the
	      process.	The  file permission bits shall be set to the value of
	      mode. When bits in mode other than file permission bits are set,
	      the  effect is implementation-defined. If attr is NULL, the mes‐
	      sage queue shall 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 shall 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()	 func‐
	      tion 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  mes‐
	      sage  queue name exists. The check for the existence of the mes‐
	      sage 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.

RETURN VALUE
       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.

ERRORS
       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
	      exists.

       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
	      zero.

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

       ENAMETOOLONG
	      The length of the name argument exceeds {PATH_MAX} or a pathname
	      component is longer than {NAME_MAX}.

       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.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       mq_close(),  mq_getattr(),   mq_receive(),   mq_send(),	 mq_setattr(),
       mq_timedreceive(),  mq_timedsend(),  mq_unlink(),  msgctl(),  msgget(),
       msgrcv(),    msgsnd(),	 the	Base	 Definitions	 volume	    of
       IEEE Std 1003.1-2001, <mqueue.h>

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	by  the	 Institute  of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			   MQ_OPEN(3P)
[top]

List of man pages available for Mageia

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]
Tweet
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