vmm: memory_manager: Make the snapshot source directory an Option

This allows the code to be reused when creating the VM from a snapshot
when doing VM migration.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/lib.rs

@@ -397,7 +397,7 @@ impl Vmm {
             &snapshot,
             exit_evt,
             reset_evt,
-            source_url,
+            Some(source_url),
             restore_cfg.prefault,
             &self.seccomp_action,
             self.hypervisor.clone(),

vmm/src/memory_manager.rs

@@ -760,10 +760,13 @@ impl MemoryManager {
         snapshot: &Snapshot,
         vm: Arc<dyn hypervisor::Vm>,
         config: &MemoryConfig,
-        source_url: &str,
+        source_url: Option<&str>,
         prefault: bool,
         phys_bits: u8,
     ) -> Result<Arc<Mutex<MemoryManager>>, Error> {
+        let mm = MemoryManager::new(vm, config, prefault, phys_bits)?;
+
+        if let Some(source_url) = source_url {
             let url = Url::parse(source_url).unwrap();
             /* url must be valid dir which is verified in recv_vm_snapshot() */
             let vm_snapshot_path = url.to_file_path().unwrap();
@@ -800,8 +803,8 @@ impl MemoryManager {
                     }
                 }
 
-            let mm = MemoryManager::new(vm, config, prefault, phys_bits)?;
                 mm.lock().unwrap().fill_saved_regions(saved_regions)?;
+
                 Ok(mm)
             } else {
                 Err(Error::Restore(MigratableError::Restore(anyhow!(
@@ -809,6 +812,9 @@ impl MemoryManager {
                     MEMORY_MANAGER_SNAPSHOT_ID
                 ))))
             }
+        } else {
+            Ok(mm)
+        }
     }
 
     fn memfd_create(name: &ffi::CStr, flags: u32) -> Result<RawFd, io::Error> {

vmm/src/vm.rs

@@ -680,7 +680,7 @@ impl Vm {
         snapshot: &Snapshot,
         exit_evt: EventFd,
         reset_evt: EventFd,
-        source_url: &str,
+        source_url: Option<&str>,
         prefault: bool,
         seccomp_action: &SeccompAction,
         hypervisor: Arc<dyn hypervisor::Hypervisor>,