|Return to mq_open.3 CVS log||Up to [cvs.NetBSD.org] / src / lib / librt|
|File: [cvs.NetBSD.org] / src / lib / librt / mq_open.3 (download)
Revision 1.6, Thu Mar 15 19:04:47 2012 UTC (7 years, 7 months ago) by njoly
Use Lk macro when dealing with URLs. Another part of PR/29238.
.\" $NetBSD: mq_open.3,v 1.6 2012/03/15 19:04:47 njoly Exp $ .\" .\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved .\" .Dd June 7, 2010 .Dt MQ_OPEN 3 .Os .Sh NAME .Nm mq_open .Nd open a message queue (REALTIME) .Sh LIBRARY .Lb librt .Sh SYNOPSIS .In mqueue.h .Ft mqd_t .Fn mq_open "const char *name" "int oflag" .Ft mqd_t .Fn mq_open "const char *name" "int oflag" "mode_t mode" "struct mq_attr *attr" .Sh DESCRIPTION The .Fn mq_open function establishes the connection between a process and a message queue with a message queue descriptor. It creates 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 .Fa name argument points to a string naming a message queue, which should conform to the construction rules for a pathname. The .Fa name should begin with a slash character. The processes calling .Fn mq_open with the same value of .Fa name will refer to the same message queue object, as long as that name has not been removed. If the .Fa name argument is not the name of an existing message queue and creation is not requested, .Fn mq_open fails and returns an error. .Pp The .Fa oflag argument requests the desired receive and/or send access to the message queue. The requested access permission to receive messages or send messages are granted if the calling process would be granted read or write access, respectively, to an equivalently protected file. .Pp The value of .Fa 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 .Fa oflag : .Bl -tag -width ".Dv O_RDONLY" .It Dv O_RDONLY Open the message queue for receiving messages. The process can use the returned message queue descriptor with .Xr mq_receive 3 , but not .Xr mq_send 3 . .It Dv O_WRONLY Open the queue for sending messages. The process can use the returned message queue descriptor with .Xr mq_send 3 but not .Xr mq_receive 3 . .It Dv O_RDWR Open the queue for both receiving and sending messages. The process can use any of the functions allowed for .Dv O_RDONLY and .Dv O_WRONLY . .El .Pp In all cases, a message queue may be open multiple times in the same or different processes for sending/receiving messages. .Pp Any combination of the remaining flags may be specified in the value of .Fa oflag : .Bl -tag -width ".Dv O_NONBLOCK" .It Dv O_CREAT Create a message queue. It requires two additional arguments: .Fa mode and .Fa attr . If the pathname .Fa name has already been used to create a message queue that still exists, then this flag will have no effect, except as noted under .Dv O_EXCL . Otherwise, a message queue will be created without any messages in it. The user ID of the message queue will be set to the effective user ID of the process, and the group ID of the message queue will be set to the effective group ID of the process. The permission bits of the message queue will be set to the value of the .Fa mode argument, except those set in the file mode creation mask of the process. When bits in .Fa mode other than the file permission bits are specified, the effect is unspecified. If .Fa attr is .Dv NULL , the message queue will be created with implementation-defined default message queue attributes. If .Fa attr is .No non- Ns Dv NULL and the calling process has the appropriate privilege on .Fa name , the message queue .Va mq_maxmsg and .Va mq_msgsize attributes will be set to the values of the corresponding members in the .Vt mq_attr structure referred to by .Fa attr . If .Fa attr is .No non- Ns Dv NULL , but the calling process does not have the appropriate privilege on .Fa name , the .Fn mq_open function will fail and return an error without creating the message queue. .It Dv O_EXCL If .Dv O_EXCL and .Dv O_CREAT are set, .Fn mq_open fails if the message queue .Fa name exists. The check for the existence of the message queue and the creation of the message queue if it does not exist will be atomic with respect to other threads executing .Fn mq_open naming the same .Fa name with .Dv O_EXCL and .Dv O_CREAT set. If .Dv O_EXCL is set and .Dv O_CREAT is not set, the result is undefined. .It Dv O_NONBLOCK Determines whether an .Xr mq_send 3 or .Xr mq_receive 3 waits for resources or messages that are not currently available, or fails with errno set to .Er EAGAIN . .El .Pp The .Fn mq_open function does not add or remove messages from the queue. .Sh IMPLEMENTATION NOTES The .Xr select 2 and .Xr poll 2 system calls to the message queue descriptor are supported by .Nx , however, it is not portable. .Sh RETURN VALUES Upon successful completion, .Fn mq_open returns a message queue descriptor. Otherwise, the function returns .Pq Dv mqd_t \-1 and sets the global variable .Va errno to indicate the error. .Sh ERRORS The .Fn mq_open function fails if: .Bl -tag -width Er .It Bq Er EACCES The message queue exists and the permissions specified by .Fa oflag are denied, or the message queue does not exist and permission to create the message queue is denied. .It Bq Er EEXIST .Dv O_CREAT and .Dv O_EXCL are set and the named message queue already exists. .It Bq Er EINTR The .Fn mq_open function was interrupted by a signal. .It Bq Er EINVAL The .Fn mq_open function is not supported for the given name, or .Dv O_CREAT was specified in .Fa oflag , the value of .Fa attr is not .Dv NULL , and either .Va mq_maxmsg or .Va mq_msgsize was less than or equal to zero. .It Bq Er EMFILE Too many message queue descriptors or file descriptors are currently in use by this process. .It Bq Er ENAMETOOLONG The length of the .Fa name argument exceeds .Brq Dv PATH_MAX or a pathname component is longer than .Brq Dv NAME_MAX . .It Bq Er ENFILE Too many message queues are currently open in the system. .It Bq Er ENOENT .Dv O_CREAT is not set and the named message queue does not exist. .It Bq Er ENOSPC There is insufficient space for the creation of the new message queue. .El .Sh SEE ALSO .Xr mq 3 , .Xr mq_close 3 , .Xr mq_unlink 3 .Sh STANDARDS This function conforms to the .St -p1003.1-2001 standard. .Sh HISTORY This function first appeared in .Nx 5.0 . .Sh 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 .Lk http://www.opengroup.org/unix/online.html .