Method modify

easy-fs/src/block_cache.rs:59–61

(&mut self, offset: usize, f: impl FnOnce(&mut T) -> V)

    }

    pub fn modify<T, V>(&mut self, offset: usize, f: impl FnOnce(&mut T) -> V) -> V {
        f(self.get_mut(offset))
    }

    pub fn sync(&mut self) {
        if self.modified {