pci, vmm: Extend PciDevice trait to support BAR relocation

By adding a new method id() to the PciDevice trait, we allow the caller
to retrieve a unique identifier. This is used in the context of BAR
relocation to identify the device being relocated, so that we can update
the DeviceTree resources for all PCI devices (and not only
VirtioPciDevice).

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

pci/src/device.rs

@@ -110,6 +110,9 @@ pub trait PciDevice: BusDevice {
     /// Provides a mutable reference to the Any trait. This is useful to let
     /// the caller have access to the underlying type behind the trait.
     fn as_any(&mut self) -> &mut dyn Any;
+
+    /// Optionally returns a unique identifier.
+    fn id(&self) -> Option<String>;
 }
 
 /// This trait defines a set of functions which can be triggered whenever a