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 examined.  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 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.

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 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.