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Add a minimal membarrier man page that documents the available cmd values and errors that can be returned. We can add more information and iterate on it in the tree. Reviewed by: kib Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D46967 (cherry picked from commit 1fc766e3b41d0cdbd166ef95258434069a90ca52) (cherry picked from commit 92cd5abb64dd70c305535c9504c6a2b73552147f) (cherry picked from commit 8b41e693fc3956385d5771d60ee93e18001a5a0d)
151 lines
4.4 KiB
Groff
151 lines
4.4 KiB
Groff
.\" SPDX-License-Identifier: BSD-2-Clause
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.\"
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.\" Copyright (c) 2024 The FreeBSD Foundation
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.\"
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.\" This documentation was written by Ed Maste <emaste@FreeBSD.org>
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.\" under sponsorship from the FreeBSD Foundation.
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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 October 6, 2024
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.Dt MEMBARRIER 2
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.Os
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.Sh NAME
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.Nm membarrier
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.Nd memory barrier
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/membarrier.h
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.Ft int
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.Fn membarrier "int cmd" "unsigned flags" "int cpu_id"
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.Sh DESCRIPTION
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The
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.Nm
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system call provides a memory barrier, ensuring ordering between memory
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accesses performed by different threads or processes within the same address
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space.
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.Pp
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The following values for
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.Fa cmd
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may be specified:
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.Bl -tag -width Dv
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.It Dv MEMBARRIER_CMD_QUERY
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Query supported commands.
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A bitmask of commands supported by the kernel is returned.
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.It Dv MEMBARRIER_CMD_GLOBAL
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Issue a memory barrier for all threads from all processes.
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.It Dv MEMBARRIER_CMD_SHARED
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This is an alias for
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.Dv MEMBARRIER_CMD_GLOBAL .
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.It Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED
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Execute a memory barrier on all running threads of all processes registered
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with
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.Dv MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED .
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.It Dv MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED
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Register the process to receive
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.Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED
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memory barriers.
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.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED
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Execute a memory barrier on each running thread belonging to the same process
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as the thread calling
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.Nm .
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.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED
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Register the process to receive
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.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED
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memory barriers.
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.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE
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In addition to the guarantees provided by
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.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED
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it also executes machine-specific serialization instructions, which
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ensures that all possible speculative and out-of-order activities on the target
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CPU are fenced.
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.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE
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Register the process to receive
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.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE
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memory barriers.
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.El
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.Pp
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The following
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.Fa cmd
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values are defined for source compatibility but are not yet supported:
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.Pp
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.Bl -tag -width Dv -compact
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.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ
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.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ
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.El
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.Pp
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The
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.Fa flags
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argument must be 0.
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The
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.Fa cpu_id
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argument is ignored.
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.Sh RETURN VALUES
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If the
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.Fa cmd
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is
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.Dv MEMBARRIER_CMD_QUERY
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a bitmask of supported commands is returned.
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Otherwise, on success,
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.Nm
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returns 0.
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On error, -1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Nm
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may fail with the following errors:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa cmd
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does not specify a valid command.
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.It Bq Er EINVAL
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.Fa flags
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is not 0.
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.It Bq Er EPERM
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An attempt was made to use
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.Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED ,
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.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED ,
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or
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.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE
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by a process that did not previously register use with the corresponding
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.Dv MEMBARRIER_CMD_REGISTER_*
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.Fa cmd .
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.El
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.\" .Sh SEE ALSO
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.Sh STANDARDS
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The
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.Nm
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system call originated in Linux.
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This implementation aims to be source-compatible with the Linux implementation.
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Certain
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.Fa cmd
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and
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.Fa flags
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values are currently not supported by
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.Fx .
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.Sh HISTORY
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The
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.Nm
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function was introduced in
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.Fx 14.1 .
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