msync man page on FreeBSD

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MSYNC(2)		    BSD System Calls Manual		      MSYNC(2)

     msync — synchronize a mapped region

     Standard C Library (libc, -lc)

     #include <sys/mman.h>

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

     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
     examined.	The flags argument may be specified as follows:

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

     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

     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.

     [EINVAL]		The len argument is too large or negative.

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

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

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

     The msync() system call is obsolete since BSD implements a coherent file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.

BSD				 June 21, 1994				   BSD

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