msync.3p (5773B)
- '\" et
- .TH MSYNC "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- msync
- \(em synchronize memory with physical storage
- .SH SYNOPSIS
- .LP
- .nf
- #include <sys/mman.h>
- .P
- int msync(void *\fIaddr\fP, size_t \fIlen\fP, int \fIflags\fP);
- .fi
- .SH DESCRIPTION
- The
- \fImsync\fR()
- 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
- .IR addr
- and continuing for
- .IR len
- bytes. If no such storage exists,
- \fImsync\fR()
- need not have any effect. If requested, the
- \fImsync\fR()
- function shall then invalidate cached copies of data.
- .P
- The implementation may require that
- .IR addr
- be a multiple of the page size as returned by
- \fIsysconf\fR().
- .P
- For mappings to files, the
- \fImsync\fR()
- 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\fR()
- 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\fR()
- 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\fR().
- .P
- The
- .IR flags
- argument is constructed from the bitwise-inclusive OR of one or more of
- the following flags defined in the
- .IR <sys/mman.h>
- header:
- .TS
- center box tab(!);
- cB | cB
- lw(1.5i) | lw(2i).
- Symbolic Constant!Description
- _
- MS_ASYNC!Perform asynchronous writes.
- MS_SYNC!Perform synchronous writes.
- MS_INVALIDATE!Invalidate cached data.
- .TE
- .P
- When MS_ASYNC is specified,
- \fImsync\fR()
- shall return immediately once all the write operations are initiated or
- queued for servicing; when MS_SYNC is specified,
- \fImsync\fR()
- shall not return until all write operations are completed as defined for
- synchronized I/O data integrity completion. Either MS_ASYNC or MS_SYNC
- shall be specified, but not both.
- .P
- When MS_INVALIDATE is specified,
- \fImsync\fR()
- 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\fR()
- and the first subsequent memory reference to the data.
- .P
- If
- \fImsync\fR()
- causes any write to a file, the file's last data modification and
- last file status change timestamps shall be marked for update.
- .SH "RETURN VALUE"
- Upon successful completion,
- \fImsync\fR()
- shall return 0; otherwise, it shall return \-1 and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- The
- \fImsync\fR()
- function shall fail if:
- .TP
- .BR EBUSY
- Some or all of the addresses in the range starting at
- .IR addr
- and continuing for
- .IR len
- bytes are locked, and MS_INVALIDATE is specified.
- .TP
- .BR EINVAL
- The value of
- .IR flags
- is invalid.
- .TP
- .BR ENOMEM
- The addresses in the range starting at
- .IR addr
- and continuing for
- .IR len
- bytes are outside the range allowed for the address space of a process
- or specify one or more pages that are not mapped.
- .P
- The
- \fImsync\fR()
- function may fail if:
- .TP
- .BR EINVAL
- The value of
- .IR addr
- is not a multiple of the page size as returned by
- \fIsysconf\fR().
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- The
- \fImsync\fR()
- function is only supported if the Synchronized Input and Output
- option is supported, and thus need not be available on all implementations.
- .P
- The
- \fImsync\fR()
- function should be used by programs that require a memory object to be
- in a known state; for example, in building transaction facilities.
- .P
- Normal system activity can cause pages to be written to disk.
- Therefore, there are no guarantees that
- \fImsync\fR()
- is the only control over when pages are or are not written to disk.
- .SH RATIONALE
- The
- \fImsync\fR()
- function writes out data in a mapped region to the permanent
- storage for the underlying object. The call to
- \fImsync\fR()
- ensures data integrity of the file.
- .P
- 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"
- None.
- .SH "SEE ALSO"
- .IR "\fImmap\fR\^(\|)",
- .IR "\fIsysconf\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<sys_mman.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 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 .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .