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MSYNC(2)		  FreeBSD System Calls Manual		      MSYNC(2)

NAME
     msync -- synchronize a mapped region

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/mman.h>

     int
     msync(void	*addr, size_t len, int flags);

DESCRIPTION
     The msync() system	call writes all	pages with shared modifications	in the
     specified region of the process's address space back to permanent stor-
     age, and, if requested, invalidates cached	data mapped in the region.  If
     len is 0, all modified pages within the region containing addr will be
     flushed; if len is	non-zero, only modified	pages containing addr and len
     succeeding	locations will be flushed.  Any	required synchronization of
     memory caches will	also take place	at this	time.  Filesystem operations
     on	a file that is mapped for shared modifications are unpredictable
     except after an msync().

     The flags argument	is formed by or'ing the	following values

	   MS_ASYNC	    Perform asynchronous writes.
	   MS_SYNC	    Perform synchronous	writes.
	   MS_INVALIDATE    Invalidate cached data after writing.

ERRORS
     The following errors may be reported:

     [EBUSY]		The MS_INVALIDATE flag was specified and a portion of
			the specified region was locked	with mlock(2).

     [EINVAL]		The specified flags argument was invalid.

     [EINVAL]		The addr parameter was not page	aligned.

     [EINVAL]		The addr parameter did not specify an address part of
			a mapped region.

     [EINVAL]		The len	parameter was negative.

     [EIO]		An I/O error occured while writing to the file system.

     [ENOMEM]		Addresses in the specified region are outside the
			range allowed for the address space of the process, or
			specify	one or more pages which	are unmapped.

SEE ALSO
     mlock(2), mmap(2),	munlock(2)

BUGS
     Writes are	currently done synchronously even if the MS_ASYNC flag is
     specified.

HISTORY
     The msync() function first	appeared in 4.4BSD.  It	was modified to	con-
     form to IEEE Std 1003.1b-1993 (``POSIX.1'') in NetBSD 1.3.

FreeBSD	9.2		       October 10, 1997			   FreeBSD 9.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | ERRORS | SEE ALSO | BUGS | HISTORY

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