vmm: device_manager: Implement the Pausable trait

Since the Snapshotable placeholder and Migratable traits are provided as
well, the DeviceManager object and all its objects are now Migratable.

All Migratable devices are tracked as Arc<Mutex<dyn Migratable>>
references.

Keeping track of all migratable devices allows for implementing the
Migratable trait for the DeviceManager structure, making the whole
device model potentially migratable.

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

vmm/src/vm.rs

@@ -43,6 +43,7 @@ use std::os::unix::io::FromRawFd;
 use std::sync::{Arc, Mutex, RwLock};
 use std::{result, str, thread};
 use vm_allocator::{GsiApic, SystemAllocator};
+use vm_device::{MigratableError, Pausable};
 use vm_memory::guest_memory::FileOffset;
 use vm_memory::{
     Address, Bytes, Error as MmapError, GuestAddress, GuestMemory, GuestMemoryMmap,
@@ -145,6 +146,12 @@ pub enum Error {
 
     /// Capability missing
     CapabilityMissing(Cap),
+
+    /// Cannot pause devices
+    PauseDevices(MigratableError),
+
+    /// Cannot resume devices
+    ResumeDevices(MigratableError),
 }
 pub type Result<T> = result::Result<T, Error>;
 
@@ -627,6 +634,7 @@ impl Vm {
             .unwrap()
             .pause()
             .map_err(Error::CpuManager)?;
+        self.devices.pause().map_err(Error::PauseDevices)?;
 
         *state = new_state;
 
@@ -639,6 +647,7 @@ impl Vm {
 
         state.valid_transition(new_state)?;
 
+        self.devices.resume().map_err(Error::ResumeDevices)?;
         self.cpu_manager
             .lock()
             .unwrap()