Function create_qcow_tempfile

performance-metrics/src/util.rs:38–51

Create a QCOW2 image with `num_clusters` allocated clusters and return the tempfile handle. Each cluster is default QCOW2 cluster size of 64 KiB. The image is created via `QcowFile::new` then populated with writes so that the clusters are actually allocated in the L2 / refcount tables.

(num_clusters: usize)

/// created via `QcowFile::new` then populated with writes so that the
/// clusters are actually allocated in the L2 / refcount tables.
fn create_qcow_tempfile(num_clusters: usize) -> TempFile {
    let tmp = TempFile::new().expect("failed to create tempfile");
    let virtual_size = QCOW_CLUSTER_SIZE * num_clusters as u64;
    let raw = RawFile::new(tmp.as_file().try_clone().unwrap(), false);
    let mut qcow = QcowFile::new(raw, 3, virtual_size, true).expect("failed to create QCOW2 file");
    let buf = vec![0xA5u8; QCOW_CLUSTER_SIZE as usize];
    for i in 0..num_clusters {
        qcow.seek(SeekFrom::Start(i as u64 * QCOW_CLUSTER_SIZE))
            .expect("seek failed");
        qcow.write_all(&buf).expect("write failed");
    }
    qcow.flush().expect("flush failed");
    tmp
}

/// Create a QCOW2 image with `num_clusters` allocated clusters opened
/// via QcowDisk with synchronous backend.