vm-migration: Extend Migratable trait

Add new methods to the Migratable trait so that each device implementing
this trait can be notified when the migration starts/stops, as well as
when a dirty bitmap must be returned.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-migration/src/lib.rs

@@ -6,6 +6,7 @@
 #[macro_use]
 extern crate serde_derive;
 
+use crate::protocol::MemoryRangeTable;
 use anyhow::anyhow;
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
@@ -46,6 +47,15 @@ pub enum MigratableError {
 
     #[error("Socket error: {0}")]
     MigrateSocket(#[source] std::io::Error),
+
+    #[error("Failed to start migration for migratable component: {0}")]
+    MigrateStart(#[source] anyhow::Error),
+
+    #[error("Failed to stop migration for migratable component: {0}")]
+    MigrateStop(#[source] anyhow::Error),
+
+    #[error("Failed to retrieve dirty ranges for migratable component: {0}")]
+    MigrateDirtyRanges(#[source] anyhow::Error),
 }
 
 /// A Pausable component can be paused and resumed.
@@ -279,4 +289,16 @@ pub trait Transportable: Pausable + Snapshottable {
 /// and Snapshottable.
 /// Moreover a migratable component can be transported to a remote or local
 /// destination and thus must be Transportable.
-pub trait Migratable: Send + Pausable + Snapshottable + Transportable {}
+pub trait Migratable: Send + Pausable + Snapshottable + Transportable {
+    fn start_dirty_log(&mut self) -> std::result::Result<(), MigratableError> {
+        Ok(())
+    }
+
+    fn stop_dirty_log(&mut self) -> std::result::Result<(), MigratableError> {
+        Ok(())
+    }
+
+    fn dirty_log(&mut self) -> std::result::Result<MemoryRangeTable, MigratableError> {
+        Ok(MemoryRangeTable::default())
+    }
+}