misc: clippy: add needless_pass_by_value (partially)

This helps to uncover expensive and needless clones in the code base.
For example, I prevented extensive clones in the snapshot path where
(nested) BTreeMap's have been cloned over and over again. Further,
the lint helps devs to much better reason about the ownership of
parameters.

All of these changes have been done manually with the necessary
caution. A few structs that are cheap to clone are now `copy` so that
this lint won't trigger for them.

I didn't enable the lint so far as it is a massive rabbit hole and
needs much more fixes. Nevertheless, it is very useful.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

devices/src/ioapic.rs

@@ -191,7 +191,7 @@ impl Ioapic {
     pub fn new(
         id: String,
         apic_address: GuestAddress,
-        interrupt_manager: Arc<dyn InterruptManager<GroupConfig = MsiIrqGroupConfig>>,
+        interrupt_manager: &dyn InterruptManager<GroupConfig = MsiIrqGroupConfig>,
         state: Option<IoapicState>,
     ) -> Result<Ioapic> {
         let interrupt_source_group = interrupt_manager

devices/src/ivshmem.rs

@@ -114,14 +114,14 @@ impl IvshmemDevice {
         region_size: u64,
         backend_file: Option<PathBuf>,
         ivshmem_ops: Arc<Mutex<dyn IvshmemOps>>,
-        snapshot: Option<Snapshot>,
+        snapshot: Option<&Snapshot>,
     ) -> Result<Self, IvshmemError> {
-        let pci_configuration_state =
-            vm_migration::state_from_id(snapshot.as_ref(), PCI_CONFIGURATION_ID).map_err(|e| {
-                IvshmemError::RetrievePciConfigurationState(anyhow!(
-                    "Failed to get PciConfigurationState from Snapshot: {e}",
-                ))
-            })?;
+        let pci_configuration_state = vm_migration::state_from_id(snapshot, PCI_CONFIGURATION_ID)
+            .map_err(|e| {
+            IvshmemError::RetrievePciConfigurationState(anyhow!(
+                "Failed to get PciConfigurationState from Snapshot: {e}",
+            ))
+        })?;
 
         let state: Option<IvshmemDeviceState> = snapshot
             .as_ref()

devices/src/pvpanic.rs

@@ -66,13 +66,13 @@ pub struct PvPanicDeviceState {
 }
 
 impl PvPanicDevice {
-    pub fn new(id: String, snapshot: Option<Snapshot>) -> Result<Self, PvPanicError> {
-        let pci_configuration_state =
-            vm_migration::state_from_id(snapshot.as_ref(), PCI_CONFIGURATION_ID).map_err(|e| {
-                PvPanicError::RetrievePciConfigurationState(anyhow!(
-                    "Failed to get PciConfigurationState from Snapshot: {e}"
-                ))
-            })?;
+    pub fn new(id: String, snapshot: Option<&Snapshot>) -> Result<Self, PvPanicError> {
+        let pci_configuration_state = vm_migration::state_from_id(snapshot, PCI_CONFIGURATION_ID)
+            .map_err(|e| {
+            PvPanicError::RetrievePciConfigurationState(anyhow!(
+                "Failed to get PciConfigurationState from Snapshot: {e}"
+            ))
+        })?;
 
         let mut configuration = PciConfiguration::new(
             PVPANIC_VENDOR_ID,

devices/src/tpm.rs

@@ -27,6 +27,7 @@ pub enum Error {
 type Result<T> = anyhow::Result<T, Error>;
 
 #[allow(dead_code)]
+#[derive(Copy, Clone)]
 enum LocStateFields {
     TpmEstablished,
     LocAssigned,
@@ -63,6 +64,7 @@ enum IntfId2Fields {
     Did,
 }
 
+#[derive(Copy, Clone)]
 enum CtrlStsFields {
     TpmSts,
     TpmIdle,
@@ -220,7 +222,7 @@ pub struct Tpm {
 }
 
 impl Tpm {
-    pub fn new(path: String) -> Result<Self> {
+    pub fn new(path: &str) -> Result<Self> {
         let emulator = Emulator::new(path)
             .map_err(|e| Error::Init(anyhow!("Failed while initializing tpm Emulator: {e:?}")))?;
         let mut tpm = Tpm {