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librt/mq_getfd_np.3: Initial manual page

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The mq_getfd_np function appeared in FreeBSD 11 with no documentation.
This function dereferences the mqd_t as a pointer to an int.

Relnotes:		yes
MFC after:		3 days
Reviewed by:		kib (previous), markj, ziaee
Differential Revision:	https://reviews.freebsd.org/D43947
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Rick Parrish 2025-12-18 17:12:32 -05:00 • committed by Alexander Ziaee
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2
lib/librt/Makefile
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@ -24,4 +24,6 @@ SYMBOL_MAPS=${.CURDIR}/Symbol.map
HAS_TESTS=
SUBDIR.${MK_TESTS}+= tests
MAN= mq_getfd_np.3
.include <bsd.lib.mk>

57
lib/librt/mq_getfd_np.3 Normal file
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@ -0,0 +1,57 @@
.\"
.\" Copyright (c) 2024 Rick Parrish <unitrunker@unitrunker.net>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd December 18, 2025
.Dt MQ_GETFD_NP 3
.Os
.Sh NAME
.Nm mq_getfd_np
.Nd get a file descriptor for an open message queue descriptor
.Sh SYNOPSIS
.Lb librt
.In mqueue.h
.Ft int
.Fn mq_getfd_np "mqd_t mqd"
.Sh DESCRIPTION
The
.Nm
function retrieves the underlying file descriptor
from the given message queue descriptor returned from
.Xr mq_open 2 .
The file descriptor is used by other functions
to refer to that message queue.
The
.Fa mqd
argument must be an open message queue descriptor.
.Sh IMPLEMENTATION NOTES
.Fx
implements retrieval or alteration of message queue attributes
based on the file descriptor.
The open file descriptor is copied into a child after
.Xr fork 2 .
The
.Xr fstat 2 ,
.Xr fchmod 2 ,
and
.Xr fchown 2
system calls are supported for the file descriptor.
.Pp
The file descriptor is safe to use so long as
the message queue descriptor remains open.
.Sh RETURN VALUES
Upon successful completion, the function returns a file descriptor.
.Sh ERRORS
The
.Nm
function does not return any errors.
.Sh SEE ALSO
.Xr mq_close 2 ,
.Xr mq_open 2 ,
.Xr mqueuefs 4
.Sh HISTORY
Support for the
.Nm
function first appeared in
.Fx 11.0 .