vm-virtio: Implement the Pausable trait for all virtio devices

Due to the amount of code currently duplicated across virtio devices,
the stats for this commit is on the large side but it's mostly more
duplicated code, unfortunately.

Migratable and Snapshotable placeholder implementations are provided as
well, making all virtio devices Migratable.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vm-virtio/src/transport/mmio.rs

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+use std::result;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex, RwLock};
 
@@ -15,6 +16,7 @@ use crate::{
     INTERRUPT_STATUS_CONFIG_CHANGED, INTERRUPT_STATUS_USED_RING,
 };
 use devices::{BusDevice, Interrupt};
+use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
 use vm_memory::{GuestAddress, GuestMemoryMmap};
 use vmm_sys_util::{errno::Result, eventfd::EventFd};
 
@@ -275,3 +277,16 @@ impl BusDevice for MmioDevice {
         }
     }
 }
+
+impl Pausable for MmioDevice {
+    fn pause(&mut self) -> result::Result<(), MigratableError> {
+        Ok(())
+    }
+
+    fn resume(&mut self) -> result::Result<(), MigratableError> {
+        Ok(())
+    }
+}
+
+impl Snapshotable for MmioDevice {}
+impl Migratable for MmioDevice {}

vm-virtio/src/transport/pci_device.rs

@@ -15,6 +15,7 @@ extern crate vmm_sys_util;
 
 use libc::EFD_NONBLOCK;
 use std::any::Any;
+use std::result;
 use std::sync::atomic::{AtomicU16, AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex, RwLock};
 
@@ -26,6 +27,7 @@ use pci::{
     PciMassStorageSubclass, PciNetworkControllerSubclass, PciSubclass,
 };
 use vm_allocator::SystemAllocator;
+use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
 use vm_memory::{Address, ByteValued, GuestAddress, GuestMemoryMmap, GuestUsize, Le32};
 use vmm_sys_util::{errno::Result, eventfd::EventFd};
 
@@ -762,3 +764,16 @@ impl BusDevice for VirtioPciDevice {
         self.write_bar(base, offset, data)
     }
 }
+
+impl Pausable for VirtioPciDevice {
+    fn pause(&mut self) -> result::Result<(), MigratableError> {
+        Ok(())
+    }
+
+    fn resume(&mut self) -> result::Result<(), MigratableError> {
+        Ok(())
+    }
+}
+
+impl Snapshotable for VirtioPciDevice {}
+impl Migratable for VirtioPciDevice {}