vmm: migration: emit lifecycle events

Emit migration lifecycle events via the event monitor.

This aligns migration with other VM lifecycle operations such as boot,
pause, and resume, allowing external management software to observe
migration progress consistently.

Events emitted:
  src:
    vm.migration-started
    vm.migration-finished
    vm.migration-failed
  dst:
    vm.migration-receive-started
    vm.migration-receive-finished
    vm.migration-receive-failed

Please note that these features are independent of an upcoming new
endpoint to fetch migration statistics.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

vmm/src/lib.rs

@@ -2305,6 +2305,8 @@ impl RequestHandler for Vmm {
         // Accept the connection and get the socket
         let mut socket = Vmm::receive_migration_socket(&receive_data_migration.receiver_url)?;
 
+        event!("vm", "migration-receive-started");
+
         let mut state = ReceiveMigrationState::Established;
 
         while !state.finished() {
@@ -2334,8 +2336,11 @@ impl RequestHandler for Vmm {
         }
 
         if let ReceiveMigrationState::Aborted = state {
+            event!("vm", "migration-receive-failed");
             self.vm = None;
             self.vm_config = None;
+        } else {
+            event!("vm", "migration-receive-finished");
         }
 
         Ok(())
@@ -2379,6 +2384,7 @@ impl RequestHandler for Vmm {
             )));
         }
 
+        event!("vm", "migration-started");
         Self::send_migration(
             vm,
             #[cfg(all(feature = "kvm", target_arch = "x86_64"))]
@@ -2387,6 +2393,7 @@ impl RequestHandler for Vmm {
         )
         .map_err(|migration_err| {
             error!("Migration failed: {migration_err:?}");
+            event!("vm", "migration-failed");
 
             // Stop logging dirty pages only for non-local migrations
             if !send_data_migration.local
@@ -2404,6 +2411,8 @@ impl RequestHandler for Vmm {
             migration_err
         })?;
 
+        event!("vm", "migration-finished");
+
         // Shutdown the VM after the migration succeeded
         self.exit_evt.write(1).map_err(|e| {
             MigratableError::MigrateSend(anyhow!(