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.\" 30.Dd March 18, 2012 31.Dt MSYNC 2 32.Os 33.Sh NAME 34.Nm msync 35.Nd synchronize a mapped region 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In sys/mman.h 40.Ft int 41.Fn msync "void *addr" "size_t len" "int flags" 42.Sh DESCRIPTION 43The 44.Fn msync 45system call 46writes any modified pages back to the file system and updates 47the file modification time. 48If 49.Fa len 50is 0, all modified pages within the region containing 51.Fa addr 52will be flushed; 53if 54.Fa len 55is non-zero, only those pages containing 56.Fa addr 57and 58.Fa len-1 59succeeding locations will be examined. 60The 61.Fa flags 62argument may be specified as follows: 63.Pp 64.Bl -tag -width ".Dv MS_INVALIDATE" -compact 65.It Dv MS_ASYNC 66Return immediately 67.It Dv MS_SYNC 68Perform synchronous writes 69.It Dv MS_INVALIDATE 70Invalidate all cached data 71.El 72.Sh RETURN VALUES 73.Rv -std msync 74.Sh ERRORS 75The 76.Fn msync 77system call 78will fail if: 79.Bl -tag -width Er 80.It Bq Er EBUSY 81Some or all of the pages in the specified region are locked and 82.Dv MS_INVALIDATE 83is specified. 84.It Bq Er EINVAL 85The 86.Fa addr 87argument 88is not a multiple of the hardware page size. 89.It Bq Er ENOMEM 90The addresses in the range starting at 91.Fa addr 92and continuing for 93.Fa len 94bytes are outside the range allowed for the address space of a 95process or specify one or more pages that are not mapped. 96.It Bq Er EINVAL 97The 98.Fa flags 99argument 100was both MS_ASYNC and MS_INVALIDATE. 101Only one of these flags is allowed. 102.It Bq Er EIO 103An error occurred while writing at least one of the pages in 104the specified region. 105.El 106.Sh SEE ALSO 107.Xr madvise 2 , 108.Xr mincore 2 , 109.Xr mlock 2 , 110.Xr mprotect 2 , 111.Xr munmap 2 112.Sh HISTORY 113The 114.Fn msync 115system call first appeared in 116.Bx 4.4 . 117.Sh BUGS 118The 119.Fn msync 120system call is usually not needed since 121.Bx 122implements a coherent file system buffer cache. 123However, it may be used to associate dirty VM pages with file system 124buffers and thus cause them to be flushed to physical media sooner 125rather than later. 126