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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "MSYNC" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" msync 

.SH NAME

msync \- synchronize memory with physical storage

.SH SYNOPSIS

.LP

\fB#include <sys/mman.h>

.br

.sp

int msync(void *\fP\fIaddr\fP\fB, size_t\fP \fIlen\fP\fB, int\fP \fIflags\fP\fB);

\fP

\fB

.br

\fP

.SH DESCRIPTION

.LP

The \fImsync\fP() function shall write all modified data to permanent

storage locations, if any, in those whole pages

containing any part of the address space of the process starting at

address \fIaddr\fP and continuing for \fIlen\fP bytes. If no

such storage exists, \fImsync\fP() need not have any effect. If requested,

the \fImsync\fP() function shall then invalidate

cached copies of data.

.LP

The implementation shall require that \fIaddr\fP be a multiple of

the page size as returned by \fIsysconf\fP().

.LP

For mappings to files, the \fImsync\fP() function shall ensure that

all write operations are completed as defined for

synchronized I/O data integrity completion. It is unspecified whether

the implementation also writes out other file attributes.

When the \fImsync\fP() function is called on MAP_PRIVATE mappings,

any modified data shall not be written to the underlying object

and shall not cause such data to be made visible to other processes.

It is unspecified whether data in MAP_PRIVATE mappings has any

permanent storage locations.   \ The effect of \fImsync\fP() on a

shared memory object or a typed memory object is unspecified.

The behavior of this function is unspecified if the mapping was not

established by a call to \fImmap\fP().

.LP

The \fIflags\fP argument is constructed from the bitwise-inclusive

OR of one or more of the following flags defined in the \fI<sys/mman.h>\fP

header:

.TS C

center; l2 l.

\fBSymbolic Constant\fP	\fBDescription\fP

MS_ASYNC	Perform asynchronous writes.

MS_SYNC	Perform synchronous writes.

MS_INVALIDATE	Invalidate cached data.

.TE

.LP

When MS_ASYNC is specified, \fImsync\fP() shall return immediately

once all the write operations are initiated or queued for

servicing; when MS_SYNC is specified, \fImsync\fP() shall not return

until all write operations are completed as defined for

synchronized I/O data integrity completion. Either MS_ASYNC or MS_SYNC

is specified, but not both.

.LP

When MS_INVALIDATE is specified, \fImsync\fP() shall invalidate all

cached copies of mapped data that are inconsistent with the

permanent storage locations such that subsequent references shall

obtain data that was consistent with the permanent storage

locations sometime between the call to \fImsync\fP() and the first

subsequent memory reference to the data.

.LP

If \fImsync\fP() causes any write to a file, the file's \fIst_ctime\fP

and \fIst_mtime\fP fields shall be marked for

update.

.SH RETURN VALUE

.LP

Upon successful completion, \fImsync\fP() shall return 0; otherwise,

it shall return -1 and set \fIerrno\fP to indicate the

error.

.SH ERRORS

.LP

The \fImsync\fP() function shall fail if:

.TP 7

.B EBUSY

Some or all of the addresses in the range starting at \fIaddr\fP and

continuing for \fIlen\fP bytes are locked, and

MS_INVALIDATE is specified.

.TP 7

.B EINVAL

The value of \fIflags\fP is invalid.

.TP 7

.B EINVAL

The value of \fIaddr\fP is not a multiple of the page size {PAGESIZE}.

.TP 7

.B ENOMEM

The addresses in the range starting at \fIaddr\fP and continuing for

\fIlen\fP bytes are outside the range allowed for the

address space of a process or specify one or more pages that are not

mapped.

.sp

.LP

\fIThe following sections are informative.\fP

.SH EXAMPLES

.LP

None.

.SH APPLICATION USAGE

.LP

The \fImsync\fP() function is only supported if the Memory Mapped

Files option and the Synchronized Input and Output option are

supported, and thus need not be available on all implementations.

.LP

The \fImsync\fP() function should be used by programs that require

a memory object to be in a known state; for example, in

building transaction facilities.

.LP

Normal system activity can cause pages to be written to disk. Therefore,

there are no guarantees that \fImsync\fP() is the only

control over when pages are or are not written to disk.

.SH RATIONALE

.LP

The \fImsync\fP() function writes out data in a mapped region to the

permanent storage for the underlying object. The call to

\fImsync\fP() ensures data integrity of the file.

.LP

After the data is written out, any cached data may be invalidated

if the MS_INVALIDATE flag was specified. This is useful on

systems that do not support read/write consistency.

.SH FUTURE DIRECTIONS

.LP

None.

.SH SEE ALSO

.LP

\fImmap\fP() , \fIsysconf\fP() , the Base Definitions volume of

IEEE\ Std\ 1003.1-2001, \fI<sys/mman.h>\fP

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group. In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.opengroup.org/unix/online.html .