vmm: extract a helper to send the VM state

On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>

vmm/src/lib.rs

@@ -1453,15 +1453,7 @@ impl Vmm {
 
         // Capture snapshot and send it
         let vm_snapshot = vm.snapshot()?;
-        let snapshot_data = serde_json::to_vec(&vm_snapshot).unwrap();
+        migration_transport::send_state(&mut socket, &vm_snapshot)?;
-        Request::state(snapshot_data.len() as u64).write_to(&mut socket)?;
-        socket
-            .write_all(&snapshot_data)
-            .map_err(MigratableError::MigrateSocket)?;
-        migration_transport::expect_ok_response(
-            &mut socket,
-            MigratableError::MigrateSend(anyhow!("Error during state migration")),
-        )?;
         // Complete the migration
         // At this step, the receiving VMM will acquire disk locks again.
         migration_transport::send_request_expect_ok(

vmm/src/migration_transport.rs

@@ -12,8 +12,8 @@ use std::result::Result;
 use anyhow::{Context, anyhow};
 use log::info;
 use serde_json;
-use vm_migration::MigratableError;
 use vm_migration::protocol::{Request, Response};
+use vm_migration::{MigratableError, Snapshot};
 
 use crate::{SocketStream, VmMigrationConfig};
 
@@ -117,3 +117,21 @@ pub(crate) fn send_config(
         MigratableError::MigrateSend(anyhow!("Error during config migration")),
     )
 }
+
+/// Serialize and send the VM snapshot payload.
+pub(crate) fn send_state(
+    socket: &mut SocketStream,
+    snapshot: &Snapshot,
+) -> Result<(), MigratableError> {
+    let snapshot_data = serde_json::to_vec(snapshot)
+        .context("Error serializing VM snapshot")
+        .map_err(MigratableError::MigrateSend)?;
+    Request::state(snapshot_data.len() as u64).write_to(socket)?;
+    socket
+        .write_all(&snapshot_data)
+        .map_err(MigratableError::MigrateSocket)?;
+    expect_ok_response(
+        socket,
+        MigratableError::MigrateSend(anyhow!("Error during state migration")),
+    )
+}