fix: delete never constructed error enum variants

All of these were dead code (but the compiler isn't able to tell us
because the vmm crate is a library crate where everything is `pub`, and
it doesn't know that no downstream users outside of the `firecracker`
crate exist, and that everything that's not used in `firecracker` is
dead code).

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

src/vmm/src/persist.rs

@@ -114,18 +114,10 @@ pub struct GuestRegionUffdMapping {
 /// Errors related to saving and restoring Microvm state.
 #[derive(Debug, thiserror::Error, displaydoc::Display)]
 pub enum MicrovmStateError {
-    /// Compatibility checks failed: {0}
-    IncompatibleState(String),
-    /// Provided MicroVM state is invalid.
-    InvalidInput,
     /// Operation not allowed: {0}
     NotAllowed(String),
     /// Cannot restore devices: {0}
     RestoreDevices(DevicePersistError),
-    /// Cannot restore Vcpu state: {0}
-    RestoreVcpuState(vstate::vcpu::VcpuError),
-    /// Cannot restore Vm state: {0}
-    RestoreVmState(vstate::vm::VmError),
     /// Cannot save Vcpu state: {0}
     SaveVcpuState(vstate::vcpu::VcpuError),
     /// Cannot save Vm state: {0}
@@ -142,9 +134,6 @@ pub enum MicrovmStateError {
 pub enum CreateSnapshotError {
     /// Cannot get dirty bitmap: {0}
     DirtyBitmap(VmmError),
-    #[rustfmt::skip]
-    /// Cannot translate microVM version to snapshot data version
-    UnsupportedVersion,
     /// Cannot write memory file: {0}
     Memory(MemoryError),
     /// Cannot perform {0} on the memory backing file: {1}
@@ -155,8 +144,6 @@ pub enum CreateSnapshotError {
     SerializeMicrovmState(crate::snapshot::SnapshotError),
     /// Cannot perform {0} on the snapshot backing file: {1}
     SnapshotBackingFile(&'static str, io::Error),
-    /// Size mismatch when writing diff snapshot on top of base layer: base layer size is {0} but diff layer is size {1}.
-    SnapshotBackingFileLengthMismatch(u64, u64),
 }
 
 /// Snapshot version

src/vmm/src/vstate/memory.rs

@@ -36,10 +36,6 @@ pub type GuestMmapRegion = vm_memory::MmapRegion<Option<AtomicBitmap>>;
 /// Errors associated with dumping guest memory to file.
 #[derive(Debug, thiserror::Error, displaydoc::Display)]
 pub enum MemoryError {
-    /// Cannot create memory: {0}
-    CreateMemory(VmMemoryError),
-    /// Cannot create memory region: {0}
-    CreateRegion(MmapRegionError),
     /// Cannot fetch system's page size: {0}
     PageSize(errno::Error),
     /// Cannot dump memory: {0}

src/vmm/src/vstate/vm/mod.rs

@@ -32,8 +32,6 @@ pub enum VmError {
     SetUserMemoryRegion(kvm_ioctls::Error),
     /// Cannot open the VM file descriptor: {0}
     VmFd(kvm_ioctls::Error),
-    /// Cannot configure the microvm: {0}
-    VmSetup(kvm_ioctls::Error),
     /// {0}
     Arch(#[from] ArchVmError),
     /// Error during eventfd operations: {0}

src/vmm/src/vstate/vm/x86_64.rs

@@ -35,10 +35,6 @@ pub enum ArchVmError {
     VmGetClock(kvm_ioctls::Error),
     /// Failed to get KVM vm irqchip: {0}
     VmGetIrqChip(kvm_ioctls::Error),
-    /// Failed to set KVM vm pit state: {0}
-    VmSetPit2(kvm_ioctls::Error),
-    /// Failed to set KVM vm clock: {0}
-    VmSetClock(kvm_ioctls::Error),
     /// Failed to set KVM vm irqchip: {0}
     VmSetIrqChip(kvm_ioctls::Error),
     /// Failed to get MSR index list to save into snapshots: {0}