refactor: #[from]-ify CreateSnapshotError

Avoid some .map_err() calls using #[from] and the auto-From::from
calling of the question mark operator.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/persist.rs

@@ -134,15 +134,15 @@ pub enum MicrovmStateError {
 #[derive(Debug, thiserror::Error, displaydoc::Display)]
 pub enum CreateSnapshotError {
     /// Cannot get dirty bitmap: {0}
-    DirtyBitmap(vmm_sys_util::errno::Error),
+    DirtyBitmap(#[from] vmm_sys_util::errno::Error),
     /// Cannot write memory file: {0}
-    Memory(MemoryError),
+    Memory(#[from] MemoryError),
     /// Cannot perform {0} on the memory backing file: {1}
     MemoryBackingFile(&'static str, io::Error),
     /// Cannot save the microVM state: {0}
     MicrovmState(MicrovmStateError),
     /// Cannot serialize the microVM state: {0}
-    SerializeMicrovmState(crate::snapshot::SnapshotError),
+    SerializeMicrovmState(#[from] crate::snapshot::SnapshotError),
     /// Cannot perform {0} on the snapshot backing file: {1}
     SnapshotBackingFile(&'static str, io::Error),
 }
@@ -198,9 +198,7 @@ fn snapshot_state_to_file(
         .map_err(|err| SnapshotBackingFile("open", err))?;
 
     let snapshot = Snapshot::new(SNAPSHOT_VERSION);
-    snapshot
-        .save(&mut snapshot_file, microvm_state)
-        .map_err(SerializeMicrovmState)?;
+    snapshot.save(&mut snapshot_file, microvm_state)?;
     snapshot_file
         .flush()
         .map_err(|err| SnapshotBackingFile("flush", err))?;

src/vmm/src/vstate/vm.rs

@@ -261,13 +261,11 @@ impl Vm {
 
         match snapshot_type {
             SnapshotType::Diff => {
-                let dirty_bitmap = self.get_dirty_bitmap().map_err(DirtyBitmap)?;
-                self.guest_memory()
-                    .dump_dirty(&mut file, &dirty_bitmap)
-                    .map_err(Memory)
+                let dirty_bitmap = self.get_dirty_bitmap()?;
+                self.guest_memory().dump_dirty(&mut file, &dirty_bitmap)
             }
             SnapshotType::Full => {
-                let dump_res = self.guest_memory().dump(&mut file).map_err(Memory);
+                let dump_res = self.guest_memory().dump(&mut file);
                 if dump_res.is_ok() {
                     self.reset_dirty_bitmap();
                     self.guest_memory().reset_dirty();