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.Dd March 18, 2012 29.Dt MSYNC 2 30.Os 31.Sh NAME 32.Nm msync 33.Nd synchronize a mapped region 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/mman.h 38.Ft int 39.Fn msync "void *addr" "size_t len" "int flags" 40.Sh DESCRIPTION 41The 42.Fn msync 43system call 44writes any modified pages back to the file system and updates 45the file modification time. 46If 47.Fa len 48is 0, all modified pages within the region containing 49.Fa addr 50will be flushed; 51if 52.Fa len 53is non-zero, only those pages containing 54.Fa addr 55and 56.Fa len-1 57succeeding locations will be examined. 58The 59.Fa flags 60argument may be specified as follows: 61.Pp 62.Bl -tag -width ".Dv MS_INVALIDATE" -compact 63.It Dv MS_ASYNC 64Return immediately 65.It Dv MS_SYNC 66Perform synchronous writes 67.It Dv MS_INVALIDATE 68Invalidate all cached data 69.El 70.Sh RETURN VALUES 71.Rv -std msync 72.Sh ERRORS 73The 74.Fn msync 75system call 76will fail if: 77.Bl -tag -width Er 78.It Bq Er EBUSY 79Some or all of the pages in the specified region are locked and 80.Dv MS_INVALIDATE 81is specified. 82.It Bq Er EINVAL 83The 84.Fa addr 85argument 86is not a multiple of the hardware page size. 87.It Bq Er ENOMEM 88The addresses in the range starting at 89.Fa addr 90and continuing for 91.Fa len 92bytes are outside the range allowed for the address space of a 93process or specify one or more pages that are not mapped. 94.It Bq Er EINVAL 95The 96.Fa flags 97argument 98was both MS_ASYNC and MS_INVALIDATE. 99Only one of these flags is allowed. 100.It Bq Er EIO 101An error occurred while writing at least one of the pages in 102the specified region. 103.El 104.Sh SEE ALSO 105.Xr madvise 2 , 106.Xr mincore 2 , 107.Xr mlock 2 , 108.Xr mprotect 2 , 109.Xr munmap 2 110.Sh HISTORY 111The 112.Fn msync 113system call first appeared in 114.Bx 4.4 . 115.Sh BUGS 116The 117.Fn msync 118system call is usually not needed since 119.Bx 120implements a coherent file system buffer cache. 121However, it may be used to associate dirty VM pages with file system 122buffers and thus cause them to be flushed to physical media sooner 123rather than later. 124