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/pmem.rs

@@ -299,24 +299,32 @@ impl Pmem {
         iommu: bool,
         seccomp_action: SeccompAction,
         exit_evt: EventFd,
+        state: Option<PmemState>,
     ) -> io::Result<Pmem> {
-        let config = VirtioPmemConfig {
-            start: addr.raw_value().to_le(),
-            size: (_region.size() as u64).to_le(),
+        let (avail_features, acked_features, config) = if let Some(state) = state {
+            info!("Restoring virtio-pmem {}", id);
+            (state.avail_features, state.acked_features, state.config)
+        } else {
+            let config = VirtioPmemConfig {
+                start: addr.raw_value().to_le(),
+                size: (_region.size() as u64).to_le(),
+            };
+
+            let mut avail_features = 1u64 << VIRTIO_F_VERSION_1;
+
+            if iommu {
+                avail_features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
+            }
+            (avail_features, 0, config)
         };
 
-        let mut avail_features = 1u64 << VIRTIO_F_VERSION_1;
-
-        if iommu {
-            avail_features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
-        }
-
         Ok(Pmem {
             common: VirtioCommon {
                 device_type: VirtioDeviceType::Pmem as u32,
                 queue_sizes: QUEUE_SIZES.to_vec(),
                 paused_sync: Some(Arc::new(Barrier::new(2))),
                 avail_features,
+                acked_features,
                 min_queues: 1,
                 ..Default::default()
             },
@@ -338,12 +346,6 @@ impl Pmem {
         }
     }
 
-    fn set_state(&mut self, state: &PmemState) {
-        self.common.avail_features = state.avail_features;
-        self.common.acked_features = state.acked_features;
-        self.config = state.config;
-    }
-
     #[cfg(fuzzing)]
     pub fn wait_for_epoll_threads(&mut self) {
         self.common.wait_for_epoll_threads();
@@ -461,11 +463,6 @@ impl Snapshottable for Pmem {
     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 Pmem {}