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.\"	@(#)msync.2	8.2 (Berkeley) 6/21/94
.\" $FreeBSD: src/lib/libc/sys/msync.2,v 1.17 2000/04/21 09:41:53 phantom Exp $
.\"
.Dd June 21, 1994
.Dt MSYNC 2
.Os
.Sh NAME
.Nm msync
.Nd synchronize a mapped region
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include <sys/mman.h>
.Ft int
.Fo msync
.Fa "void *addr"
.Fa "size_t len"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
The
.Fn msync
system call writes modified whole pages back to the filesystem
and updates the file modification time.
Only those pages containing 
.Fa addr
and
.Fa len-1
succeeding locations will be examined.
.Pp
The
.Fa flags
argument may be specified as follows:
.Bd -literal
MS_ASYNC	Return immediately
MS_SYNC		Perform synchronous writes
MS_INVALIDATE	Invalidate all cached data
.Ed
.Pp
The
.Fa MS_ASYNC
flag is not permitted to be combined with other flags.
.Sh RETURN VALUES
If any errors occur, -1 is returned and errno is set to indicate the
error.
Otherwise, a 0 value is returned.
.Sh ERRORS
.Fn msync
will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EBUSY
Some of the specified addresses are locked
and MS_INVALIDATE is specified.
.\" ===========
.It Bq Er EINVAL
.Fa addr
is not a multiple of the hardware page size.
.\" ===========
.It Bq Er EINVAL
.Fa len
is too large, or less than 1.
.\" ===========
.It Bq Er EINVAL
.Fa flags
is invalid
(e.g., it combines MS_ASYNC with another flag,
which is not permitted).
.\" ===========
.It Bq Er EIO
An I/O error occurs while writing to the file system.
.\" ===========
.It Bq Er ENOMEM
The specified address range is outside of the address range
of the process or includes an unmapped page.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Pp
The include file
.In sys/types.h
is necessary.
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr mprotect 2 ,
.Xr munmap 2 ,
.Xr compat 5
.Sh HISTORY
The
.Fn msync
function first appeared in
.Bx 4.4 .