vm-migration: Define the Snapshottable and Transportable traits

A Snapshottable component can snapshot itself and
provide a MigrationSnapshot payload as a result.

A MigrationSnapshot payload is a map of component IDs to a list of
migration sections (MigrationSection). As component can be made of
several Migratable sub-components (e.g. the DeviceManager and its
device objects), a migration snapshot can be made of multiple snapshot
itself.
A snapshot is a list of migration sections, each section being a
component state snapshot. Having multiple sections allows for easier and
backward compatible migration payload extensions.

Once created, a migratable component snapshot may be transported and this
is what the Transportable trait defines, through 2 methods: send and recv.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>

vmm/src/memory_manager.rs

@@ -23,6 +23,7 @@ use vm_memory::{
     GuestMemory, GuestMemoryAtomic, GuestMemoryMmap, GuestMemoryRegion, GuestRegionMmap,
     GuestUsize, MmapRegion,
 };
+use vm_migration::{Migratable, Pausable, Snapshottable, Transportable};
 
 const HOTPLUG_COUNT: usize = 8;
 
@@ -884,3 +885,8 @@ impl Aml for MemoryManager {
         bytes
     }
 }
+
+impl Pausable for MemoryManager {}
+impl Snapshottable for MemoryManager {}
+impl Transportable for MemoryManager {}
+impl Migratable for MemoryManager {}