pub unsafe extern "C" fn ext2fs_set_block_alloc_stats_callback(
fs: ext2_filsys,
func: Option<unsafe extern "C" fn(fs: ext2_filsys, blk: blk64_t, inuse: c_int)>,
old: *mut Option<unsafe extern "C" fn(fs: ext2_filsys, blk: blk64_t, inuse: c_int)>
)