man-pages/man2/msync.2

.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (C) 1996 Andries Brouwer (aeb@cwi.nl)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH MSYNC 2 2003-08-21 "Linux" "Linux Programmer's Manual"
.SH NAME
msync \- synchronize a file with a memory map
.SH SYNOPSIS
.B #include <sys/mman.h>
.sp
.BI "int msync(void *" start ", size_t " length ", int " flags );
.SH DESCRIPTION
.BR msync ()
flushes changes made to the in-core copy of a file that was mapped
into memory using
.BR mmap (2)
back to disk.
Without use of this call
there is no guarantee that changes are written back before
.BR munmap (2)
is called.
To be more precise, the part of the file that
corresponds to the memory area starting at
.I start
and having length
.I length
is updated.

The
.I flags
argument may have the bits
.BR MS_ASYNC ,
.BR MS_SYNC ,
and
.B MS_INVALIDATE
set, but not both
.B MS_ASYNC
and
.BR MS_SYNC .
.B MS_ASYNC
specifies that an update be scheduled, but the call
returns immediately.
.B MS_SYNC
asks for an update and waits for it to complete.
.B MS_INVALIDATE
asks to invalidate other mappings of the same file
(so that they can be updated with the fresh values just written).
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.BR EBUSY
MS_INVALIDATE was specified in
.IR flags ,
and a memory lock exists for the specified address range.
.TP
.BR EINVAL
.I start
is not a multiple of PAGESIZE; or any bit other than
.BR MS_ASYNC " | " MS_INVALIDATE " | " MS_SYNC
is set in
.IR flags ;
or both
.B MS_SYNC
and
.B MS_ASYNC
are set in
.IR flags .
.TP
.B ENOMEM
The indicated memory (or part of it) was not mapped.
.SH "CONFORMING TO"
POSIX.1-2001.

This call was introduced in Linux 1.3.21, and then used
.B EFAULT
instead of
.BR ENOMEM .
In Linux 2.4.19 this was changed to the POSIX value
.BR ENOMEM .
.SH AVAILABILITY
On POSIX systems on which
.BR msync ()
is available, both
.B _POSIX_MAPPED_FILES
and
.B _POSIX_SYNCHRONIZED_IO
are defined in \fI<unistd.h>\fP to a value greater than 0.
(See also
.BR sysconf (3).)
.\" POSIX.1-2001: It shall be defined to -1 or 0 or 200112L.
.\" -1: unavailable, 0: ask using sysconf().
.\" glibc defines them to 1.
.SH "SEE ALSO"
.BR mmap (2)
.br
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.