17 const PIPE_BUFF_SIZE: usize = 1024;
77         _offset: usize,  in read_at()  argument
78         len: usize,  in read_at()  argument
81     ) -> Result<usize, crate::syscall::SystemError> {  in read_at()  argument
104         let mut num = inode.valid_cnt as usize;  in read_at()
106         let start = inode.read_pos as usize;  in read_at()
108         let mut end = (inode.valid_cnt as usize + inode.read_pos as usize) % PIPE_BUFF_SIZE;  in read_at()
110         if len < inode.valid_cnt as usize {  in read_at()
111             end = (len + inode.read_pos as usize) % PIPE_BUFF_SIZE;  in read_at()
156         _offset: usize,  in write_at()  argument
157         len: usize,  in write_at()  argument
160     ) -> Result<usize, crate::syscall::SystemError> {  in write_at()  argument
170         while len + inode.valid_cnt as usize > PIPE_BUFF_SIZE {  in write_at()
185         let start = inode.write_pos as usize;  in write_at()
186         let end = (inode.write_pos as usize + len) % PIPE_BUFF_SIZE;  in write_at()