freebsd-dev/lib/libc/sys/mq_getattr.2

.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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.\" Portions of this text are reprinted and reproduced in electronic form
.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
.\" Portable Operating System Interface (POSIX), The Open Group Base
.\" Specifications Issue 6, Copyright (C) 2001-2004 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.
.\"
.\" $FreeBSD$
.\"
.Dd February 21, 2014
.Dt MQ_GETATTR 2
.Os
.Sh NAME
.Nm mq_getattr
.Nd "get message queue attributes (REALTIME)"
.Sh LIBRARY
.Lb librt
.Sh SYNOPSIS
.In mqueue.h
.Ft int
.Fn mq_getattr "mqd_t mqdes" "struct mq_attr *mqstat"
.Sh DESCRIPTION
The
.Fn mq_getattr
system call obtains status information and attributes of the message queue and
the open message queue description associated with the message queue
descriptor.
.Pp
The
.Fa mqdes
argument specifies a message queue descriptor.
.Pp
The results are returned in the
.Vt mq_attr
structure referenced by the
.Fa mqstat
argument.
.Pp
Upon return, the following members will have the values associated with the
open message queue description as set when the message queue was opened and
as modified by subsequent
.Fn mq_setattr
calls:
.Va mq_flags .
.Pp
The following attributes of the message queue will be returned as set at
message queue creation:
.Va mq_maxmsg , mq_msgsize .
.Pp
Upon return, the following members within the
.Vt mq_attr
structure referenced by the
.Fa mqstat
argument will be set to the current state
of the message queue:
.Bl -tag -width ".Va mq_curmsgs"
.It Va mq_curmsgs
The number of messages currently on the queue.
.El
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn mq_getattr
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa mqdes
argument is not a valid message queue descriptor.
.El
.Sh SEE ALSO
.Xr mq_open 2 ,
.Xr mq_send 2 ,
.Xr mq_setattr 2 ,
.Xr mq_timedsend 2
.Sh STANDARDS
The
.Fn mq_getattr
system call conforms to
.St -p1003.1-2004 .
.Sh HISTORY
Support for
.Tn POSIX
message queues first appeared in
.Fx 7.0 .
.Sh COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2004 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.