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0112f8c4a8
Reviewed by: kib, paumma MFC after: 1 week Differential revision: https://reviews.freebsd.org/D43845
181 lines
5.6 KiB
Groff
181 lines
5.6 KiB
Groff
.\"-
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.\" SPDX-License-Identifier: BSD-2-Clause
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.\"
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.\" Copyright (c) 2024 Rick Parrish <unitrunker@unitrunker.net>.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd February 19, 2024
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.Dt POSIXMQCONTROL 1
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.Os
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.Sh NAME
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.Nm posixmqcontrol
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.Nd Control POSIX mqueuefs message queues
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.Sh SYNOPSIS
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.Nm
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.Ar create
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.Fl q Ar queue
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.Fl s Ar size
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.Fl d Ar depth
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.Op Fl m Ar mode
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.Op Fl g Ar group
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.Op Fl u Ar user
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.Nm
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.Ar info
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.Fl q Ar queue
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.Nm
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.Ar recv
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.Fl q Ar queue
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.Nm
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.Ar rm
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.Fl q Ar queue
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.Nm
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.Ar send
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.Fl q Ar queue
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.Fl c Ar content
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.Op Fl p Ar priority
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.Sh DESCRIPTION
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The
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.Nm
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command allows separating POSIX message queue administration from application
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stack.
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Defining and adjusting queue attributes can be done without touching
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application code.
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It allows creating queues, inspecting queue metadata, altering group and user
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access to queues, dumping queue contents, and unlinking queues.
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.Pp
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Unlinking removes the name from the system and frees underlying memory.
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.Pp
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The maximum message size, maximum queue size, and current queue size are
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displayed by the
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.Ic info
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subcommand. This output is similar to running
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.Ic cat
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on a mqueuefs queue mounted under a mount point.
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This utility requires the
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.Ic mqueuefs
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kernel module to be loaded but does not require
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.Ic mqueuefs
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to be mounted as a file system.
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.Pp
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The following subcommands are provided:
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.Bl -tag -width truncate
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.It Ic create
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Create the named queues, if they do not already exist.
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More than one queue name may be created. The same maximum queue depth and
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maximum message size are used to create all queues.
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If a queue exists, then depth and size are optional.
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.Pp
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The required
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.Ar size
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and
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.Ar depth
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arguments specify the maximum message size (bytes per message) and maximum queue
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size (depth or number of messages in the queue).
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The optional numerical
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.Ar mode
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argument specifies the initial access mode.
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If the queue exists but does not match the requested size and depth, this
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utility will attempt to recreate the queue by first unlinking and then creating
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it.
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This will fail if the queue is not empty or is opened by other processes.
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.It Ic rm
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Unlink the queues specified - one attempt per queue.
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Failure to unlink one queue does not stop this sub-command from attempting to
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unlink the others.
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.It Ic info
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For each named queue, dispay the maximum message size, maximum queue size,
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current queue depth, user owner id, group owner id, and mode permission bits.
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.It Ic recv
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Wait for a message from a single named queue and display the message to
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standard output.
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.It Ic send
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Send messages to one or more named queues.
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If multiple messages and multiple queues are specified, the utility attempts to
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send all messages to all queues.
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The optional -p priority, if omitted, defaults to MQ_PRIO_MAX / 2 or medium
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priority.
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.El
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.Sh NOTES
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A change of queue geometry (maximum message size and/or maximum number of
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messages) requires destroying and re-creating the queue.
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As a safety feature,
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the create subcommand refuses to destroy a non-empty queue.
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If you use the rm subcommand to destroy a queue, any queued messages are lost.
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To avoid down-time when altering queue attributes, consider creating a new
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queue and configure reading applications to drain both new and old queues.
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Retire the old queue once all writers have been updated to write to the new
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queue.
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.Sh EXIT STATUS
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.Ex -std
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.Bl -bullet
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.It
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EX_NOTAVAILABLE usually means the mqueuefs kernel module is not loaded.
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.It
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EX_USAGE reports one or more incorrect parameters.
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.El
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.Sh EXAMPLES
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.Bl -bullet
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.It
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To retrieve the current message from a named queue,
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.Pa /1 ,
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use the command
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.Dl "posixmqcontrol recv -q /1"
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.It
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To create a queue with the name
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.Pa /2
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with maximum message size 100 and maximum queue depth 10,
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use the command
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.Dl "posixmqcontrol create -q /2 -s 100 -d 10"
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.It
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To send a message to a queue with the name
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.Pa /3
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use the command
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.Dl "posixmqcontrol send -q /3 -c 'some choice words.'"
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.It
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To examine attributes of a queue named
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.Pa /4
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use the command
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.Dl "posixmqcontrol info -q /4"
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.El
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.Sh SEE ALSO
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.Xr mq_open 2 ,
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.Xr mq_getattr 2 ,
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.Xr mq_receive 2 ,
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.Xr mq_send 2 ,
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.Xr mq_setattr 2 ,
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.Xr mq_unlink 2 ,
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.Xr mqueuefs 5
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.Sh BUGS
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mq_timedsend and mq_timedrecv are not implemented.
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info reports a worst-case estimate for QSIZE.
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Fx 15.0 .
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.Sh AUTHORS
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The
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.Nm
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command and this manual page were written by
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.An Rick Parrish Aq Mt unitrunker@unitrunker.net.
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