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MSYNC(2)		       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 any modified pages back to the file system
     and updates the file modification time.  If len is 0,  all  modified  pages
     within the region containing addr will be flushed; if len is non-zero, only
     those  pages  containing  addr and len-1 succeeding locations will be exam-
     ined.  The flags argument may be specified as follows:

     MS_ASYNC	    Return immediately
     MS_SYNC	    Perform synchronous writes
     MS_INVALIDATE  Invalidate all cached data

RETURN VALUES
     The msync() function returns the  value  0  if  successful;  otherwise  the
     value  -1	is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The msync() system call will fail if:

     [EBUSY]		Some or all of the pages in  the  specified  region  are
			locked and MS_INVALIDATE is specified.

     [EINVAL]		The addr argument is not a multiple of the hardware page
			size.

     [ENOMEM]		The addresses in the range starting at addr and continu-
			ing  for len bytes are outside the range allowed for the
			address space of a process or specify one or more  pages
			that are not mapped.

     [EINVAL]		The  flags argument was both MS_ASYNC and MS_INVALIDATE.
			Only one of these flags is allowed.

     [EIO]		An error occurred while writing  at  least  one  of  the
			pages in the specified region.

SEE ALSO
     madvise(2), mincore(2), mlock(2), mprotect(2), munmap(2)

HISTORY
     The msync() system call first appeared in 4.4BSD.

BUGS
     The msync() system call is usually not needed since BSD implements a coher-
     ent  file	system buffer cache.  However, it may be used to associate dirty
     VM pages with file system buffers and thus cause  them  to  be  flushed  to
     physical media sooner rather than later.

FreeBSD ports 15.quarterly	 March 18, 2012 			MSYNC(2)

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