vmm: Provide a restoring state to the DeviceManager

In anticipation for creating vhost-user devices in a different way when
being restored compared to a fresh start, this commit introduces a new
boolean created by the Vm depending on the use case, and passed down to
the DeviceManager. In the future, the DeviceManager will use this flag
to assess how vhost-user devices should be created.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/device_manager.rs

@@ -941,6 +941,9 @@ pub struct DeviceManager {
 
     // Flag to force setting the iommu on virtio devices
     force_iommu: bool,
+
+    // Helps identify if the VM is currently being restored
+    restoring: bool,
 }
 
 impl DeviceManager {
@@ -955,6 +958,7 @@ impl DeviceManager {
         #[cfg(feature = "acpi")] numa_nodes: NumaNodes,
         activate_evt: &EventFd,
         force_iommu: bool,
+        restoring: bool,
     ) -> DeviceManagerResult<Arc<Mutex<Self>>> {
         let device_tree = Arc::new(Mutex::new(DeviceTree::new()));
 
@@ -1028,6 +1032,7 @@ impl DeviceManager {
             #[cfg(target_arch = "aarch64")]
             gpio_device: None,
             force_iommu,
+            restoring,
         };
 
         let device_manager = Arc::new(Mutex::new(device_manager));
@@ -3637,6 +3642,10 @@ impl DeviceManager {
             }
         }
 
+        // The devices have been fully restored, we can now update the
+        // restoring state of the DeviceManager.
+        self.restoring = false;
+
         Ok(())
     }