diff --git a/lib/libsys/membarrier.2 b/lib/libsys/membarrier.2 new file mode 100644 --- /dev/null +++ b/lib/libsys/membarrier.2 @@ -0,0 +1,150 @@ +.\" SPDX-License-Identifier: BSD-2-Clause +.\" +.\" Copyright (c) 2024 The FreeBSD Foundation +.\" +.\" This documentation was written by Ed Maste +.\" under sponsorship from the FreeBSD Foundation. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.Dd October 6, 2024 +.Dt MEMBARRIER 2 +.Os +.Sh NAME +.Nm membarrier +.Nd memory barrier +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In sys/membarrier.h +.Ft int +.Fn membarrier "int cmd" "unsigned flags" "int cpu_id" +.Sh DESCRIPTION +The +.Nm +system call provides a memory barrier, ensuring ordering between memory +accesses performed by different threads or processes within the same address +space. +.Pp +The following values for +.Fa cmd +may be specified: +.Bl -tag -width Dv +.It Dv MEMBARRIER_CMD_QUERY +Query supported commands. +A bitmask of commands supported by the kernel is returned. +.It Dv MEMBARRIER_CMD_GLOBAL +Issue a memory barrier for all threads from all processes. +.It Dv MEMBARRIER_CMD_SHARED +This is an alias for +.Dv MEMBARRIER_CMD_GLOBAL . +.It Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED +Execute a memory barrier on all running threads of all processes registered +with +.Dv MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED +.It Dv MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED +Register the process to receive +.Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED +memory barriers. +.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED +Execute a memory barrier on each running thread belonging to the same process +as the thread calling +.Nm . +.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED +Register the process to receive +.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED +memory barriers. +.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE +In addition to the guarantees provided by +.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED +it also executes machine-specific serialization instructions, which +ensures that all possible speculative and out-of-order activities on the target +CPU are fenced. +.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE +Register the process to receive +.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE +memory barriers. +.El +.Pp +The following +.Fa cmd +values are defined for source compatibility but are not yet supported: +.Pp +.Bl -tag -width Dv -compact +.It Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ +.It Dv MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ +.El +.Pp +The +.Fa flags +argument must be 0. +The +.Fa cpu_id +argument is ignored. +.Sh RETURN VALUES +If the +.Dv cmd +is MEMBARRIER_CMD_QUERY +a bitmask of supported commands is returned. +Otherwise, on success, +.Nm +returns 0. +On error, -1 is returned and +.Va errno +is set to indicate the error. +.Sh ERRORS +.Nm +may fail with the following errors: +.Bl -tag -width Er +.It Bq Er EINVAL +.Fa cmd +does not specify a valid command. +.It Bq Er EINVAL +.Fa flags +is not 0. +.It Bq Er EPERM +An attempt was made to use +.Dv MEMBARRIER_CMD_GLOBAL_EXPEDITED , +.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED , +or +.Dv MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE +by a process that did not previously register use with the corresponding +.Dv MEMBARRIER_CMD_REGISTER_* +.Fa cmd . +.El +.\" .Sh SEE ALSO +.Sh STANDARDS +The +.Nm +system call originated in Linux. +This implementation aims to be source-compatible with the Linux implementation. +Certain +.Fa cmd +and +.Fa flags +values are currently not supported by +.Fx . +.Sh HISTORY +The +.Nm +function was introduced in +.Fx 14.1 .