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MSYNC(2)                  FreeBSD 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.

     [ENOMEM]           The addresses in the range starting at addr and
                        continuing 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.

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

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

     The msync() system call is usually not needed 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.

FreeBSD 11.1-RELEASE-p4         March 18, 2012         FreeBSD 11.1-RELEASE-p4
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