refactor: simplify get_manufacturer_id_from_host

Replaces never used error result type wit optional.

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

src/vmm/src/arch/aarch64/vcpu.rs

@@ -41,25 +41,18 @@ pub enum VcpuArchError {
     SetMp(kvm_ioctls::Error),
     /// Failed FamStructWrapper operation: {0}
     Fam(vmm_sys_util::fam::Error),
-    /// {0}
-    GetMidrEl1(String),
     /// Failed to set/get device attributes for vCPU: {0}
     DeviceAttribute(kvm_ioctls::Error),
 }
 
 /// Extract the Manufacturer ID from the host.
 /// The ID is found between bits 24-31 of MIDR_EL1 register.
-pub fn get_manufacturer_id_from_host() -> Result<u32, VcpuArchError> {
+pub fn get_manufacturer_id_from_host() -> Option<u32> {
     let midr_el1_path = "/sys/devices/system/cpu/cpu0/regs/identification/midr_el1";
-    let midr_el1 = std::fs::read_to_string(midr_el1_path).map_err(|err| {
-        VcpuArchError::GetMidrEl1(format!("Failed to get MIDR_EL1 from host path: {err}"))
-    })?;
+    let midr_el1 = std::fs::read_to_string(midr_el1_path).ok()?;
     let midr_el1_trimmed = midr_el1.trim_end().trim_start_matches("0x");
-    let manufacturer_id = u32::from_str_radix(midr_el1_trimmed, 16).map_err(|err| {
-        VcpuArchError::GetMidrEl1(format!("Invalid MIDR_EL1 found on host: {err}",))
-    })?;
-
-    Ok(manufacturer_id >> 24)
+    let manufacturer_id = u32::from_str_radix(midr_el1_trimmed, 16).ok()?;
+    Some(manufacturer_id >> 24)
 }
 
 /// Saves states of registers into `state`.

src/vmm/src/persist.rs

@@ -255,22 +255,22 @@ pub fn validate_cpu_manufacturer_id(microvm_state: &MicrovmState) {
     let host_cpu_id = get_manufacturer_id_from_host();
     let snapshot_cpu_id = microvm_state.vcpu_states[0].regs.manifacturer_id();
     match (host_cpu_id, snapshot_cpu_id) {
-        (Ok(host_id), Some(snapshot_id)) => {
+        (Some(host_id), Some(snapshot_id)) => {
             info!("Host CPU manufacturer ID: {host_id:?}");
             info!("Snapshot CPU manufacturer ID: {snapshot_id:?}");
             if host_id != snapshot_id {
                 warn!("Host CPU manufacturer ID differs from the snapshotted one",);
             }
         }
-        (Ok(host_id), None) => {
+        (Some(host_id), None) => {
             info!("Host CPU manufacturer ID: {host_id:?}");
             warn!("Snapshot CPU manufacturer ID: couldn't get from the snapshot");
         }
-        (Err(_), Some(snapshot_id)) => {
+        (None, Some(snapshot_id)) => {
             warn!("Host CPU manufacturer ID: couldn't get from the host");
             info!("Snapshot CPU manufacturer ID: {snapshot_id:?}");
         }
-        (Err(_), None) => {
+        (None, None) => {
             warn!("Host CPU manufacturer ID: couldn't get from the host");
             warn!("Snapshot CPU manufacturer ID: couldn't get from the snapshot");
         }