vmm: virtio-devices: Restore every VirtioDevice upon creation

Following the new design proposal to improve the restore codepath when
migrating a VM, all virtio devices are supplied with an optional state
they can use to restore from. The restore() implementation every device
was providing has been removed in order to prevent from going through
the restoration twice.

Here is the list of devices now following the new restore design:

- Block (virtio-block)
- Net (virtio-net)
- Rng (virtio-rng)
- Fs (vhost-user-fs)
- Blk (vhost-user-block)
- Net (vhost-user-net)
- Pmem (virtio-pmem)
- Vsock (virtio-vsock)
- Mem (virtio-mem)
- Balloon (virtio-balloon)
- Watchdog (virtio-watchdog)
- Vdpa (vDPA)
- Console (virtio-console)
- Iommu (virtio-iommu)

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

virtio-devices/src/rng.rs

@@ -174,13 +174,22 @@ impl Rng {
         iommu: bool,
         seccomp_action: SeccompAction,
         exit_evt: EventFd,
+        state: Option<RngState>,
     ) -> io::Result<Rng> {
         let random_file = File::open(path)?;
-        let mut avail_features = 1u64 << VIRTIO_F_VERSION_1;
 
-        if iommu {
-            avail_features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
-        }
+        let (avail_features, acked_features) = if let Some(state) = state {
+            info!("Restoring virtio-rng {}", id);
+            (state.avail_features, state.acked_features)
+        } else {
+            let mut avail_features = 1u64 << VIRTIO_F_VERSION_1;
+
+            if iommu {
+                avail_features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
+            }
+
+            (avail_features, 0)
+        };
 
         Ok(Rng {
             common: VirtioCommon {
@@ -188,6 +197,7 @@ impl Rng {
                 queue_sizes: QUEUE_SIZES.to_vec(),
                 paused_sync: Some(Arc::new(Barrier::new(2))),
                 avail_features,
+                acked_features,
                 min_queues: 1,
                 ..Default::default()
             },
@@ -205,11 +215,6 @@ impl Rng {
         }
     }
 
-    fn set_state(&mut self, state: &RngState) {
-        self.common.avail_features = state.avail_features;
-        self.common.acked_features = state.acked_features;
-    }
-
     #[cfg(fuzzing)]
     pub fn wait_for_epoll_threads(&mut self) {
         self.common.wait_for_epoll_threads();
@@ -319,11 +324,6 @@ impl Snapshottable for Rng {
     fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
         Snapshot::new_from_versioned_state(&self.id, &self.state())
     }
-
-    fn restore(&mut self, snapshot: Snapshot) -> std::result::Result<(), MigratableError> {
-        self.set_state(&snapshot.to_versioned_state(&self.id)?);
-        Ok(())
-    }
 }
 
 impl Transportable for Rng {}