refactor: Remove function pointer from MMIODevManagerConstructorArgs

The function pointer is called for every device being restored, however
all use-sites of it pointed to the same function
(VmResources::update_from_restored_device), so the
indirection/abstraction is not needed. Removing this function point
removes restrictions on the signature of the function, and thus makes
adding error handling easier (for example, we can now update
update_from_restored_device to validate whether the devices read from
the snapshot are actually consistent with the rest of the vm
configuration).

The entire `SharedDeviceType` enum can probably be removed too, but lets
keep the changes minimal in this commit, as its for the 1.7 release
branch.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/vmm/src/builder.rs

@@ -470,7 +470,6 @@ pub fn build_microvm_from_snapshot(
         mem: guest_memory,
         vm: vmm.vm.fd(),
         event_manager,
-        for_each_restored_device: VmResources::update_from_restored_device,
         vm_resources,
         instance_id: &instance_info.id,
     };

src/vmm/src/device_manager/persist.rs

@@ -206,7 +206,6 @@ pub struct MMIODevManagerConstructorArgs<'a> {
     pub mem: GuestMemoryMmap,
     pub vm: &'a VmFd,
     pub event_manager: &'a mut EventManager,
-    pub for_each_restored_device: fn(&mut VmResources, SharedDeviceType),
     pub vm_resources: &'a mut VmResources,
     pub instance_id: &'a str,
 }
@@ -460,10 +459,9 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                 &balloon_state.device_state,
             )?));
 
-            (constructor_args.for_each_restored_device)(
-                constructor_args.vm_resources,
-                SharedDeviceType::Balloon(device.clone()),
-            );
+            constructor_args
+                .vm_resources
+                .update_from_restored_device(SharedDeviceType::Balloon(device.clone()));
 
             restore_helper(
                 device.clone(),
@@ -482,10 +480,9 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                 &block_state.device_state,
             )?));
 
-            (constructor_args.for_each_restored_device)(
-                constructor_args.vm_resources,
-                SharedDeviceType::VirtioBlock(device.clone()),
-            );
+            constructor_args
+                .vm_resources
+                .update_from_restored_device(SharedDeviceType::VirtioBlock(device.clone()));
 
             restore_helper(
                 device.clone(),
@@ -528,10 +525,9 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                 &net_state.device_state,
             )?));
 
-            (constructor_args.for_each_restored_device)(
-                constructor_args.vm_resources,
-                SharedDeviceType::Network(device.clone()),
-            );
+            constructor_args
+                .vm_resources
+                .update_from_restored_device(SharedDeviceType::Network(device.clone()));
 
             restore_helper(
                 device.clone(),
@@ -557,10 +553,9 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                 &vsock_state.device_state.frontend,
             )?));
 
-            (constructor_args.for_each_restored_device)(
-                constructor_args.vm_resources,
-                SharedDeviceType::Vsock(device.clone()),
-            );
+            constructor_args
+                .vm_resources
+                .update_from_restored_device(SharedDeviceType::Vsock(device.clone()));
 
             restore_helper(
                 device.clone(),
@@ -581,10 +576,9 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                 &entropy_state.device_state,
             )?));
 
-            (constructor_args.for_each_restored_device)(
-                constructor_args.vm_resources,
-                SharedDeviceType::Entropy(device.clone()),
-            );
+            constructor_args
+                .vm_resources
+                .update_from_restored_device(SharedDeviceType::Entropy(device.clone()));
 
             restore_helper(
                 device.clone(),
@@ -759,7 +753,6 @@ mod tests {
             mem: vmm.guest_memory().clone(),
             vm: vmm.vm.fd(),
             event_manager: &mut event_manager,
-            for_each_restored_device: VmResources::update_from_restored_device,
             vm_resources,
             instance_id: "microvm-id",
         };