Method write_refblocks

block/src/qcow/mod.rs:1202–1249

Write the updated reference count blocks and reftable.

(
            refcounts: &[u64],
            mut header: QcowHeader,
            ref_table: &[u64],
            raw_file: &mut QcowRawFile,
            refcount_block_entries: u64,
        )

        // Write the updated reference count blocks and reftable.
        fn write_refblocks(
            refcounts: &[u64],
            mut header: QcowHeader,
            ref_table: &[u64],
            raw_file: &mut QcowRawFile,
            refcount_block_entries: u64,
        ) -> Result<()> {
            // Rewrite the header with lazy refcounts enabled while we are rebuilding the tables.
            header.compatible_features |= COMPATIBLE_FEATURES_LAZY_REFCOUNTS;
            raw_file.file_mut().rewind().map_err(Error::SeekingFile)?;
            header.write_to(raw_file.file_mut())?;

            for (i, refblock_addr) in ref_table.iter().enumerate() {
                // Write a block of refcounts to the location indicated by refblock_addr.
                let refblock_start = i * (refcount_block_entries as usize);
                let refblock_end = min(
                    refcounts.len(),
                    refblock_start + refcount_block_entries as usize,
                );
                let refblock = &refcounts[refblock_start..refblock_end];
                raw_file
                    .write_refcount_block(*refblock_addr, refblock)
                    .map_err(Error::WritingHeader)?;

                // If this is the last (partial) cluster, pad it out to a full refblock cluster.
                if refblock.len() < refcount_block_entries as usize {
                    let refblock_padding =
                        vec![0u64; refcount_block_entries as usize - refblock.len()];
                    let byte_offset =
                        refblock.len() as u64 * raw_file.cluster_size() / refcount_block_entries;
                    raw_file
                        .write_refcount_block(*refblock_addr + byte_offset, &refblock_padding)
                        .map_err(Error::WritingHeader)?;
                }
            }

            // Rewrite the top-level refcount table.
            raw_file
                .write_pointer_table_direct(header.refcount_table_offset, ref_table.iter())
                .map_err(Error::WritingHeader)?;

            // Rewrite the header again, now with lazy refcounts disabled.
            header.compatible_features &= !COMPATIBLE_FEATURES_LAZY_REFCOUNTS;
            raw_file.file_mut().rewind().map_err(Error::SeekingFile)?;
            header.write_to(raw_file.file_mut())?;

            Ok(())
        }

        let cluster_size = raw_file.cluster_size();