Adding host device renaming for snapshot restore

Author: andrewla

src/firecracker/src/api_server/request/snapshot.rs

@@ -105,6 +105,7 @@ fn parse_put_snapshot_load(body: &Body) -> Result<ParsedRequest, RequestError> {
         mem_backend,
         enable_diff_snapshots: snapshot_config.enable_diff_snapshots,
         resume_vm: snapshot_config.resume_vm,
+        network_overrides: snapshot_config.network_overrides,
     };
 
     // Construct the `ParsedRequest` object.

src/firecracker/swagger/firecracker.yaml

@@ -1203,6 +1203,24 @@ definitions:
           Type of snapshot to create. It is optional and by default, a full
           snapshot is created.
 
+  NetworkOverride:
+    type: object
+    description:
+      Allows for changing the mapping between tap devices and host devices
+      during snapshot restore
+    required:
+      - iface_id
+      - host_dev_name
+    properties:
+      iface_id:
+        type: string
+        description:
+          The name of the interface to modify
+      host_dev_name:
+        type: string
+        description:
+          The new host device of the interface
+
   SnapshotLoadParams:
     type: object
     description:
@@ -1234,6 +1252,12 @@ definitions:
         type: boolean
         description:
           When set to true, the vm is also resumed if the snapshot load is successful.
+      network_overrides:
+        type: array
+        description: Network host device names to override
+        items:
+          $ref: "#/definitions/NetworkOverride"
+
 
   TokenBucket:
     type: object

src/vmm/src/builder.rs

@@ -443,6 +443,8 @@ pub enum BuildMicrovmFromSnapshotError {
     ACPIDeviManager(#[from] ACPIDeviceManagerRestoreError),
     /// VMGenID update failed: {0}
     VMGenIDUpdate(std::io::Error),
+    /// Unknown Network Device.
+    UnknownNetworkDevice,
 }
 
 /// Builds and starts a microVM based on the provided MicrovmState.

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

@@ -35,8 +35,8 @@ pub struct NetConfigSpaceState {
 /// at snapshot.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct NetState {
-    id: String,
-    tap_if_name: String,
+    pub id: String,
+    pub tap_if_name: String,
     rx_rate_limiter_state: RateLimiterState,
     tx_rate_limiter_state: RateLimiterState,
     /// The associated MMDS network stack.

src/vmm/src/persist.rs

@@ -398,7 +398,16 @@ pub fn restore_from_snapshot(
     params: &LoadSnapshotParams,
     vm_resources: &mut VmResources,
 ) -> Result<Arc<Mutex<Vmm>>, RestoreFromSnapshotError> {
-    let microvm_state = snapshot_state_from_file(&params.snapshot_path)?;
+    let mut microvm_state = snapshot_state_from_file(&params.snapshot_path)?;
+    for entry in &params.network_overrides {
+        let net_devices = &mut microvm_state.device_states.net_devices;
+        if let Some(idx) = net_devices.iter().position(|x| x.device_state.id == entry.iface_id) {
+
+            net_devices.get_mut(idx).unwrap().device_state.tap_if_name = entry.host_dev_name.clone();
+        } else {
+            return Err(BuildMicrovmFromSnapshotError::UnknownNetworkDevice.into());
+        }
+    }
     let track_dirty_pages = params.enable_diff_snapshots;
 
     let vcpu_count = microvm_state

src/vmm/src/vmm_config/snapshot.rs

@@ -47,6 +47,16 @@ pub struct CreateSnapshotParams {
     pub mem_file_path: PathBuf,
 }
 
+/// Allows for changing the mapping between tap devices and host devices
+/// during snapshot restore
+#[derive(Debug, PartialEq, Eq, Deserialize)]
+pub struct NetworkOverride {
+    /// The index of the interface to modify
+    pub iface_id: String,
+    /// The new name of the interface to be assigned
+    pub host_dev_name: String,
+}
+
 /// Stores the configuration that will be used for loading a snapshot.
 #[derive(Debug, PartialEq, Eq)]
 pub struct LoadSnapshotParams {
@@ -60,6 +70,8 @@ pub struct LoadSnapshotParams {
     /// When set to true, the vm is also resumed if the snapshot load
     /// is successful.
     pub resume_vm: bool,
+    /// The network devices to override on load.
+    pub network_overrides: Vec<NetworkOverride>,
 }
 
 /// Stores the configuration for loading a snapshot that is provided by the user.
@@ -82,6 +94,9 @@ pub struct LoadSnapshotConfig {
     /// Whether or not to resume the vm post snapshot load.
     #[serde(default)]
     pub resume_vm: bool,
+    /// The network devices to override on load.
+    #[serde(default)]
+    pub network_overrides: Vec<NetworkOverride>,
 }
 
 /// Stores the configuration used for managing snapshot memory.