vm-virtio: Add the ability to serialize a Queue

This commit relies on serde to serialize and deserialize the content of
a Queue structure. This will be useful information to store when
implementing snapshot/restore feature for virtio devices.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>

vm-virtio/src/queue.rs

@@ -383,11 +383,15 @@ impl<'a, 'b> Iterator for AvailIter<'a, 'b> {
     }
 }
 
-#[derive(Clone)]
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "GuestAddress")]
+struct GuestAddressDef(pub u64);
+
+#[derive(Clone, Serialize, Deserialize)]
 /// A virtio queue's parameters.
 pub struct Queue {
     /// The maximal size in elements offered by the device
-    max_size: u16,
+    pub max_size: u16,
 
     /// The queue size in elements the driver selected
     pub size: u16,
@@ -398,18 +402,22 @@ pub struct Queue {
     /// Interrupt vector index of the queue
     pub vector: u16,
 
+    #[serde(with = "GuestAddressDef")]
     /// Guest physical address of the descriptor table
     pub desc_table: GuestAddress,
 
+    #[serde(with = "GuestAddressDef")]
     /// Guest physical address of the available ring
     pub avail_ring: GuestAddress,
 
+    #[serde(with = "GuestAddressDef")]
     /// Guest physical address of the used ring
     pub used_ring: GuestAddress,
 
     pub next_avail: Wrapping<u16>,
     pub next_used: Wrapping<u16>,
 
+    #[serde(skip)]
     pub iommu_mapping_cb: Option<Arc<VirtioIommuRemapping>>,
 }