feat: make network device snapshots backwards compatible

TODO

Signed-off-by: Babis Chalios <babis.chalios@e2b.dev>

Author: bchalios

src/vmm/src/devices/virtio/net/persist.rs

@@ -30,6 +30,16 @@ pub struct NetConfigSpaceState {
     guest_mac: Option<MacAddr>,
 }
 
+#[derive(Debug, Default, Clone, Serialize, Deserialize)]
+pub struct RxBufferState {
+    // Number of iovecs we have parsed from the guest
+    parsed_descriptor_chains_nr: u16,
+    // Number of used descriptors
+    used_descriptors: u16,
+    // Number of used bytes
+    used_bytes: u32,
+}
+
 /// Information about the network device that are saved
 /// at snapshot.
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -42,6 +52,7 @@ pub struct NetState {
     pub mmds_ns: Option<MmdsNetworkStackState>,
     config_space: NetConfigSpaceState,
     pub virtio_state: VirtioDeviceState,
+    rx_buffers_state: RxBufferState,
 }
 
 /// Auxiliary structure for creating a device when resuming from a snapshot.
@@ -84,6 +95,7 @@ impl Persist<'_> for Net {
                 guest_mac: self.guest_mac,
             },
             virtio_state: VirtioDeviceState::from_device(self),
+            rx_buffers_state: RxBufferState::default(),
         }
     }
 
@@ -128,6 +140,10 @@ impl Persist<'_> for Net {
         net.avail_features = state.virtio_state.avail_features;
         net.acked_features = state.virtio_state.acked_features;
 
+        if state.virtio_state.activated {
+            net.queues[RX_INDEX].next_avail -= state.rx_buffers_state.parsed_descriptor_chains_nr;
+        }
+
         Ok(net)
     }
 }