virtio: Enable qcow support for virtio-block

With this enabled, one can pass a QCOW format disk
image with '--disk' switch.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>

qcow/src/qcow.rs

@@ -315,7 +315,7 @@ fn max_refcount_clusters(refcount_order: u32, cluster_size: u32, num_clusters: u
 /// #   Ok(())
 /// # }
 /// ```
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct QcowFile {
     raw_file: QcowRawFile,
     header: QcowHeader,

qcow/src/qcow_raw_file.rs

@@ -134,3 +134,13 @@ impl QcowRawFile {
         address & self.cluster_mask
     }
 }
+
+impl Clone for QcowRawFile {
+    fn clone(&self) -> Self {
+        QcowRawFile {
+            file: self.file.try_clone().expect("QcowRawFile cloning failed"),
+            cluster_size: self.cluster_size,
+            cluster_mask: self.cluster_mask,
+        }
+    }
+}

qcow/src/refcount.rs

@@ -48,7 +48,7 @@ impl Display for Error {
 }
 
 /// Represents the refcount entries for an open qcow file.
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct RefCount {
     ref_table: VecCache<u64>,
     refcount_table_offset: u64,

qcow/src/vec_cache.rs

@@ -15,7 +15,7 @@ pub trait Cacheable {
     fn dirty(&self) -> bool;
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 /// Represents a vector that implements the `Cacheable` trait so it can be held in a cache.
 pub struct VecCache<T: 'static + Copy + Default> {
     vec: Box<[T]>,
@@ -83,7 +83,7 @@ impl<T: 'static + Copy + Default> IndexMut<usize> for VecCache<T> {
     }
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct CacheMap<T: Cacheable> {
     capacity: usize,
     map: HashMap<usize, T>,