Method read

block/src/qcow/raw_file.rs:137–213

(&mut self, buf: &mut [u8])

impl Read for RawFile {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        if self.is_aligned(buf) {
            match self.file.read(buf) {
                Ok(r) => {
                    self.position = self.position.checked_add(r.try_into().unwrap()).unwrap();
                    Ok(r)
                }
                Err(e) => Err(e),
            }
        } else {
            let rounded_pos: u64 = self.round_down(self.position);
            let file_offset: usize = self
                .position
                .checked_sub(rounded_pos)
                .unwrap()
                .try_into()
                .unwrap();
            let buf_len: usize = buf.len();
            let rounded_len: usize = self
                .round_up(
                    file_offset
                        .checked_add(buf_len)
                        .unwrap()
                        .try_into()
                        .unwrap(),
                )
                .try_into()
                .unwrap();

            let layout = Layout::from_size_align(rounded_len, self.alignment).unwrap();
            // SAFETY: layout has non-zero size
            let tmp_ptr = unsafe { alloc_zeroed(layout) };
            if tmp_ptr.is_null() {
                return Err(io::Error::last_os_error());
            }

            // SAFETY: tmp_ptr is valid and at least rounded_len long
            let tmp_buf = unsafe { slice::from_raw_parts_mut(tmp_ptr, rounded_len) };

            // This can eventually replaced with read_at once its interface
            // has been stabilized.
            // SAFETY: FFI call. All parameters are valid.
            let ret = unsafe {
                ::libc::pread64(
                    self.file.as_raw_fd(),
                    tmp_buf.as_mut_ptr().cast(),
                    tmp_buf.len(),
                    rounded_pos.try_into().unwrap(),
                )
            };
            if ret < 0 {
                // SAFETY: tmp_ptr was allocated by alloc_zeroed with layout
                unsafe { dealloc(tmp_ptr, layout) };
                return Err(io::Error::last_os_error());
            }

            let read: usize = ret.try_into().unwrap();
            if read < file_offset {