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>

vm-virtio/src/iommu.rs

@@ -21,11 +21,12 @@ use std::result;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, RwLock};
 use std::thread;
-use vm_device::{ExternalDmaMapping, Migratable, MigratableError, Pausable, Snapshotable};
+use vm_device::ExternalDmaMapping;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
     GuestMemoryError, GuestMemoryMmap,
 };
+use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;
 
 /// Queues sizes
@@ -1038,5 +1039,6 @@ impl VirtioDevice for Iommu {
 }
 
 virtio_pausable!(Iommu);
-impl Snapshotable for Iommu {}
+impl Snapshottable for Iommu {}
+impl Transportable for Iommu {}
 impl Migratable for Iommu {}