1.\" $OpenBSD: msync.2,v 1.30 2024/01/21 17:46:03 deraadt Exp $ 2.\" $NetBSD: msync.2,v 1.8 1995/10/12 15:41:09 jtc Exp $ 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)msync.2 8.1 (Berkeley) 6/9/93 32.\" 33.Dd $Mdocdate: January 21 2024 $ 34.Dt MSYNC 2 35.Os 36.Sh NAME 37.Nm msync 38.Nd synchronize a mapped region 39.Sh SYNOPSIS 40.In sys/mman.h 41.Ft int 42.Fn msync "void *addr" "size_t len" "int flags" 43.Sh DESCRIPTION 44The 45.Fn msync 46system call writes all pages with shared modifications 47in the specified region starting from 48.Fa addr 49and continuing for 50.Fa len 51bytes. 52.Fa addr 53should be a multiple of the page size. 54Any required synchronization of memory caches 55will also take place at this time. 56Filesystem operations on a file that is mapped for shared modifications 57are unpredictable except after an 58.Fn msync . 59.Pp 60The 61.Fa flags 62argument is the bitwise OR of zero or more of the following values: 63.Bd -literal -offset indent 64MS_ASYNC Perform asynchronous writes. 65MS_SYNC Perform synchronous writes. 66MS_INVALIDATE Invalidate cached data after writing. 67.Ed 68.Sh RETURN VALUES 69.Rv -std 70.Sh ERRORS 71The following errors may be reported: 72.Bl -tag -width Er 73.It Bq Er EBUSY 74The 75.Dv MS_INVALIDATE 76flag was specified and a portion of the specified region 77was locked with 78.Xr mlock 2 . 79.It Bq Er EINVAL 80The specified 81.Fa flags 82argument was invalid. 83.It Bq Er EINVAL 84The 85.Fa addr 86parameter was not page aligned or 87.Fa addr 88and 89.Fa size 90specify a region that would extend beyond the end of the address space. 91.It Bq Er EPERM 92The 93.Fa addr 94and 95.Fa len 96parameters specify a region which contains at least one page marked immutable. 97.It Bq Er ENOMEM 98Addresses in the specified region are outside the range allowed 99for the address space of the process, or specify one or more pages 100which are unmapped. 101.It Bq Er EIO 102An I/O error occurred while writing. 103.El 104.Sh SEE ALSO 105.Xr madvise 2 , 106.Xr mimmutable 2 , 107.Xr minherit 2 , 108.Xr mprotect 2 , 109.Xr munmap 2 110.Sh HISTORY 111The 112.Fn msync 113function has been available since 114.Bx 4.3 Net/2 . 115It was modified to conform to 116.St -p1003.1b-93 117.Sh BUGS 118Writes are currently done synchronously even if the 119.Dv MS_ASYNC 120flag is specified. 121