synchronize a mapped region
Standard C Library (libc, -lc)
*addr, size_t len,
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:
- Return immediately
- Perform synchronous writes
- Invalidate all cached data
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.
msync() system call will fail if:
- Some or all of the pages in the specified region are locked and
MS_INVALIDATE is specified.
- The addr argument is not a multiple of the hardware
- 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.
- The flags argument was both MS_ASYNC and
MS_INVALIDATE. Only one of these flags is allowed.
- An error occurred while writing at least one of the pages in the specified
msync() system call first appeared in
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.