35     fn read_at(&self, offset: usize, len: usize, buf: &mut [u8]) -> Result<usize, SystemError>;  in read_at()
42     fn write_at(&self, offset: usize, len: usize, buf: &[u8]) -> Result<usize, SystemError>;  in write_at()
109     fn read_at(&self, offset: usize, len: usize, buf: &mut [u8]) -> Result<usize, SystemError> {  in read_at()
110         if len > buf.len() {  in read_at()
114         let iter = BlockIter::new_multiblock(offset, offset + len, self.blk_size_log2());  in read_at()
141         return Ok(len);  in read_at()
145     fn write_at(&self, offset: usize, len: usize, buf: &[u8]) -> Result<usize, SystemError> {  in write_at()
147         if len > buf.len() {  in write_at()
151         let iter = BlockIter::new_multiblock(offset, offset + len, self.blk_size_log2());  in write_at()
177         return Ok(len);  in write_at()
301     pub fn len(&self) -> usize {  in len()  method
306         return self.len() == (1usize << self.blk_size_log2);  in is_full()
310         return self.len() >= (1usize << self.blk_size_log2)  in is_multi()
311             && (self.len() % (1usize << self.blk_size_log2) == 0);  in is_multi()