Method deallocate_bytes

block/src/qcow/mod.rs:1816–1839

Deallocate the storage for `length` bytes starting at `address`. Any future reads of this range will return all zeroes.

(&mut self, address: u64, length: usize)

    // Deallocate the storage for `length` bytes starting at `address`.
    // Any future reads of this range will return all zeroes.
    fn deallocate_bytes(&mut self, address: u64, length: usize) -> std::io::Result<()> {
        let write_count: usize = self.limit_range_file(address, length);

        let mut nwritten: usize = 0;
        while nwritten < write_count {
            let curr_addr = address + nwritten as u64;
            let count = self.limit_range_cluster(curr_addr, write_count - nwritten);

            if count == self.raw_file.cluster_size() as usize {
                // Full cluster - deallocate the storage.
                self.deallocate_cluster(curr_addr)?;
            } else {
                // Partial cluster - zero out the relevant bytes if it was allocated.
                // Any space in unallocated clusters can be left alone, since
                // unallocated clusters already read back as zeroes.
                let offset = self.file_offset_write(curr_addr)?;
                // Partial cluster - zero it out.
                self.raw_file.file_mut().write_zeroes_at(offset, count)?;
            }

            nwritten += count;
        }
        Ok(())
    }

    // Reads an L2 cluster from the disk, returning an error if the file can't be read or if any
    // cluster is compressed.