1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)msync.2 8.2 (Berkeley) 6/21/94 29.\" $FreeBSD$ 30.\" 31.Dd March 18, 2012 32.Dt MSYNC 2 33.Os 34.Sh NAME 35.Nm msync 36.Nd synchronize a mapped region 37.Sh LIBRARY 38.Lb libc 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 47writes any modified pages back to the file system and updates 48the file modification time. 49If 50.Fa len 51is 0, all modified pages within the region containing 52.Fa addr 53will be flushed; 54if 55.Fa len 56is non-zero, only those pages containing 57.Fa addr 58and 59.Fa len-1 60succeeding locations will be examined. 61The 62.Fa flags 63argument may be specified as follows: 64.Pp 65.Bl -tag -width ".Dv MS_INVALIDATE" -compact 66.It Dv MS_ASYNC 67Return immediately 68.It Dv MS_SYNC 69Perform synchronous writes 70.It Dv MS_INVALIDATE 71Invalidate all cached data 72.El 73.Sh RETURN VALUES 74.Rv -std msync 75.Sh ERRORS 76The 77.Fn msync 78system call 79will fail if: 80.Bl -tag -width Er 81.It Bq Er EBUSY 82Some or all of the pages in the specified region are locked and 83.Dv MS_INVALIDATE 84is specified. 85.It Bq Er EINVAL 86The 87.Fa addr 88argument 89is not a multiple of the hardware page size. 90.It Bq Er ENOMEM 91The addresses in the range starting at 92.Fa addr 93and continuing for 94.Fa len 95bytes are outside the range allowed for the address space of a 96process or specify one or more pages that are not mapped. 97.It Bq Er EINVAL 98The 99.Fa flags 100argument 101was both MS_ASYNC and MS_INVALIDATE. 102Only one of these flags is allowed. 103.It Bq Er EIO 104An error occurred while writing at least one of the pages in 105the specified region. 106.El 107.Sh SEE ALSO 108.Xr madvise 2 , 109.Xr mincore 2 , 110.Xr mlock 2 , 111.Xr mprotect 2 , 112.Xr munmap 2 113.Sh HISTORY 114The 115.Fn msync 116system call first appeared in 117.Bx 4.4 . 118.Sh BUGS 119The 120.Fn msync 121system call is usually not needed since 122.Bx 123implements a coherent file system buffer cache. 124However, it may be used to associate dirty VM pages with file system 125buffers and thus cause them to be flushed to physical media sooner 126rather than later. 127