.\"	$NetBSD: msync.2,v 1.8 1995/10/12 15:41:09 jtc Exp $
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.\"	@(#)msync.2	8.1 (Berkeley) 6/9/93
.\"
.Dd June 9, 1993
.Dt MSYNC 2
.Os
.Sh NAME
.Nm msync
.Nd synchronize a mapped region
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Ft int
.Fn msync "caddr_t addr" "size_t len"
.Sh DESCRIPTION
The
.Fn msync
system call
writes any modified pages back to the filesystem and updates
the file modification time.
If
.Fa len
is 0, all modified pages within the region containing
.Fa addr
will be flushed;
if
.Fa len
is non-zero, only the pages containing
.Fa addr
and
.Fa len
succeeding locations will be examined.
Any required synchronization of memory caches
will also take place at this time.
Filesystem operations on a file that is mapped for shared modifications
are unpredictable except after an
.Fn msync .
.Sh RETURN VALUES
Upon successful completion,
a value of 0 is returned.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The following errors may be reported:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa addr
parameter was not page aligned.
.It Bq Er EINVAL
The
.Fa addr
parameter did not specify an address part of a mapped region.
.It Bq Er EINVAL
The
.Fa len
parameter was negative.
.It Bq Er EIO
An I/O error occured while writing to the file system.
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr minherit 2 ,
.Xr munmap 2 ,
.Xr mprotect 2 ,
.Xr mincore 2
.Sh HISTORY
The
.Fn msync
function first appeared in 4.4BSD.