def store_atomically(path, data):
    tmppath = path +".tmp"
    output = open(tmppath,"wb")
    output.write(data)

    output.flush()
    os.fsync(output.fileno())  # The needed fsync().
    output.close()
    os.rename(tmppath, path)

When mounting an ext4 filesystem, the following option are accepted:
(*) == default

auto_da_alloc(*)    Many broken applications don't use fsync() when
noauto_da_alloc     replacing existing files via patterns such as
                    fd = open("foo.new")/write(fd,..)/close(fd)/
                    rename("foo.new","foo"), or worse yet,
                    fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).
                    If auto_da_alloc is enabled, ext4 will detect
                    the replace-via-rename and replace-via-truncate
                    patterns and force that any delayed allocation
                    blocks are allocated such that at the next
                    journal commit, in the default data=ordered
                    mode, the data blocks of the new file are forced
                    to disk before the rename() operation is
                    committed.  This provides roughly the same level
                    of guarantees as ext3, and avoids the
                   "zero-length" problem that can happen when a
                    system crashes before the delayed allocation
                    blocks are forced to disk.