243 lines
4.8 KiB
HTML
243 lines
4.8 KiB
HTML
|
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<HTML><HEAD><TITLE>Man page of MSYNC</TITLE>
|
|
</HEAD><BODY>
|
|
<H1>MSYNC</H1>
|
|
Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
|
|
<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
|
|
|
|
<A NAME="lbAB"> </A>
|
|
<H2>NAME</H2>
|
|
|
|
msync - synchronize a file with a memory map
|
|
<A NAME="lbAC"> </A>
|
|
<H2>SYNOPSIS</H2>
|
|
|
|
<B>#include <<A HREF="file:///usr/include/sys/mman.h">sys/mman.h</A>></B>
|
|
|
|
<P>
|
|
|
|
<B>int msync(void *</B><I>addr</I><B>, size_t </B><I>length</I><B>, int </B><I>flags</I><B>);</B>
|
|
|
|
<A NAME="lbAD"> </A>
|
|
<H2>DESCRIPTION</H2>
|
|
|
|
<B>msync</B>()
|
|
|
|
flushes changes made to the in-core copy of a file that was mapped
|
|
into memory using
|
|
<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
|
|
|
|
back to the filesystem.
|
|
Without use of this call,
|
|
there is no guarantee that changes are written back before
|
|
<B><A HREF="/cgi-bin/man/man2html?2+munmap">munmap</A></B>(2)
|
|
|
|
is called.
|
|
To be more precise, the part of the file that
|
|
corresponds to the memory area starting at
|
|
<I>addr</I>
|
|
|
|
and having length
|
|
<I>length</I>
|
|
|
|
is updated.
|
|
<P>
|
|
|
|
The
|
|
<I>flags</I>
|
|
|
|
argument should specify exactly one of
|
|
<B>MS_ASYNC</B>
|
|
|
|
and
|
|
<B>MS_SYNC</B>,
|
|
|
|
and may additionally include the
|
|
<B>MS_INVALIDATE</B>
|
|
|
|
bit.
|
|
These bits have the following meanings:
|
|
<DL COMPACT>
|
|
<DT id="1"><B>MS_ASYNC</B>
|
|
|
|
<DD>
|
|
Specifies that an update be scheduled, but the call returns immediately.
|
|
<DT id="2"><B>MS_SYNC</B>
|
|
|
|
<DD>
|
|
Requests an update and waits for it to complete.
|
|
<DT id="3"><B>MS_INVALIDATE</B>
|
|
|
|
<DD>
|
|
|
|
|
|
Asks to invalidate other mappings of the same file
|
|
(so that they can be updated with the fresh values just written).
|
|
</DL>
|
|
<A NAME="lbAE"> </A>
|
|
<H2>RETURN VALUE</H2>
|
|
|
|
On success, zero is returned.
|
|
On error, -1 is returned, and
|
|
<I>errno</I>
|
|
|
|
is set appropriately.
|
|
<A NAME="lbAF"> </A>
|
|
<H2>ERRORS</H2>
|
|
|
|
<DL COMPACT>
|
|
<DT id="4"><B>EBUSY</B>
|
|
|
|
<DD>
|
|
<B>MS_INVALIDATE</B>
|
|
|
|
was specified in
|
|
<I>flags</I>,
|
|
|
|
and a memory lock exists for the specified address range.
|
|
<DT id="5"><B>EINVAL</B>
|
|
|
|
<DD>
|
|
<I>addr</I>
|
|
|
|
is not a multiple of PAGESIZE; or any bit other than
|
|
<B>MS_ASYNC</B> | <B>MS_INVALIDATE</B> | <B>MS_SYNC</B>
|
|
|
|
is set in
|
|
<I>flags</I>;
|
|
|
|
or both
|
|
<B>MS_SYNC</B>
|
|
|
|
and
|
|
<B>MS_ASYNC</B>
|
|
|
|
are set in
|
|
<I>flags</I>.
|
|
|
|
<DT id="6"><B>ENOMEM</B>
|
|
|
|
<DD>
|
|
The indicated memory (or part of it) was not mapped.
|
|
</DL>
|
|
<A NAME="lbAG"> </A>
|
|
<H2>CONFORMING TO</H2>
|
|
|
|
POSIX.1-2001, POSIX.1-2008.
|
|
<P>
|
|
|
|
This call was introduced in Linux 1.3.21, and then used
|
|
<B>EFAULT</B>
|
|
|
|
instead of
|
|
<B>ENOMEM</B>.
|
|
|
|
In Linux 2.4.19, this was changed to the POSIX value
|
|
<B>ENOMEM</B>.
|
|
|
|
<A NAME="lbAH"> </A>
|
|
<H2>AVAILABILITY</H2>
|
|
|
|
On POSIX systems on which
|
|
<B>msync</B>()
|
|
|
|
is available, both
|
|
<B>_POSIX_MAPPED_FILES</B>
|
|
|
|
and
|
|
<B>_POSIX_SYNCHRONIZED_IO</B>
|
|
|
|
are defined in
|
|
<I><<A HREF="file:///usr/include/unistd.h">unistd.h</A>></I>
|
|
|
|
to a value greater than 0.
|
|
(See also
|
|
<B><A HREF="/cgi-bin/man/man2html?3+sysconf">sysconf</A></B>(3).)
|
|
|
|
|
|
|
|
|
|
<A NAME="lbAI"> </A>
|
|
<H2>NOTES</H2>
|
|
|
|
According to POSIX, either
|
|
<B>MS_SYNC</B>
|
|
|
|
or
|
|
<B>MS_ASYNC</B>
|
|
|
|
must be specified in
|
|
<I>flags</I>,
|
|
|
|
and indeed failure to include one of these flags will cause
|
|
<B>msync</B>()
|
|
|
|
to fail on some systems.
|
|
However, Linux permits a call to
|
|
<B>msync</B>()
|
|
|
|
that specifies neither of these flags,
|
|
with semantics that are (currently) equivalent to specifying
|
|
<B>MS_ASYNC</B>.
|
|
|
|
(Since Linux 2.6.19,
|
|
|
|
<B>MS_ASYNC</B>
|
|
|
|
is in fact a no-op, since the kernel properly tracks dirty
|
|
pages and flushes them to storage as necessary.)
|
|
Notwithstanding the Linux behavior,
|
|
portable, future-proof applications should ensure that they specify either
|
|
<B>MS_SYNC</B>
|
|
|
|
or
|
|
<B>MS_ASYNC</B>
|
|
|
|
in
|
|
<I>flags</I>.
|
|
|
|
<A NAME="lbAJ"> </A>
|
|
<H2>SEE ALSO</H2>
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
|
|
|
|
<P>
|
|
|
|
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
|
|
<A NAME="lbAK"> </A>
|
|
<H2>COLOPHON</H2>
|
|
|
|
This page is part of release 5.05 of the Linux
|
|
<I>man-pages</I>
|
|
|
|
project.
|
|
A description of the project,
|
|
information about reporting bugs,
|
|
and the latest version of this page,
|
|
can be found at
|
|
<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
|
|
<P>
|
|
|
|
<HR>
|
|
<A NAME="index"> </A><H2>Index</H2>
|
|
<DL>
|
|
<DT id="7"><A HREF="#lbAB">NAME</A><DD>
|
|
<DT id="8"><A HREF="#lbAC">SYNOPSIS</A><DD>
|
|
<DT id="9"><A HREF="#lbAD">DESCRIPTION</A><DD>
|
|
<DT id="10"><A HREF="#lbAE">RETURN VALUE</A><DD>
|
|
<DT id="11"><A HREF="#lbAF">ERRORS</A><DD>
|
|
<DT id="12"><A HREF="#lbAG">CONFORMING TO</A><DD>
|
|
<DT id="13"><A HREF="#lbAH">AVAILABILITY</A><DD>
|
|
<DT id="14"><A HREF="#lbAI">NOTES</A><DD>
|
|
<DT id="15"><A HREF="#lbAJ">SEE ALSO</A><DD>
|
|
<DT id="16"><A HREF="#lbAK">COLOPHON</A><DD>
|
|
</DL>
|
|
<HR>
|
|
This document was created by
|
|
<A HREF="/cgi-bin/man/man2html">man2html</A>,
|
|
using the manual pages.<BR>
|
|
Time: 00:05:33 GMT, March 31, 2021
|
|
</BODY>
|
|
</HTML>
|