pci, virtio-devices: Restore proper BAR type

When restoring a VM, the BAR type can be found directly from the
snapshot resources. It is more reliable than the previous method which
was using self.use_64bit_bar from VirtioPciDevice because at the time
the BARs are allocated, the VirtioDevice hasn't been restored yet,
meaning the way to determine the value of use_64bit_bar is wrong for a
device like vDPA. At this time, the device type is not known and relying
on the stored resources is the only reliable way.

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

pci/src/device.rs

@@ -21,6 +21,8 @@ pub enum Error {
     IoRegistrationFailed(u64, configuration::Error),
     /// Expected resource not found.
     MissingResource,
+    /// Invalid resource.
+    InvalidResource(Resource),
 }
 pub type Result<T> = std::result::Result<T, Error>;
 
@@ -37,6 +39,7 @@ impl Display for Error {
                 write!(f, "failed to register an IO BAR, addr={} err={}", addr, e)
             }
             MissingResource => write!(f, "failed to find expected resource"),
+            InvalidResource(r) => write!(f, "invalid resource {:?}", r),
         }
     }
 }