Correctly handle error from check_extension_int()

Kvm::check_extension_int() may return negative value as error code,
so Kvm::get_max_vcpus() and Kvm::get_max_vcpu_id() should handle the
error cases.

Signed-off-by: Liu Jiang <[email protected]>

Author: jiangliu

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 91.4,
+  "coverage_score": 90.4,
   "exclude_path": "",
   "crate_features": ""
 }

src/ioctls/system.rs

@@ -221,9 +221,12 @@ impl Kvm {
     /// ```
     ///
     pub fn get_max_vcpus(&self) -> usize {
-        match self.check_extension_int(Cap::MaxVcpus) {
-            0 => self.get_nr_vcpus(),
-            x => x as usize,
+        let v = self.check_extension_int(Cap::MaxVcpus);
+
+        if v <= 0 {
+            self.get_nr_vcpus()
+        } else {
+            v as usize
         }
     }
 
@@ -242,9 +245,12 @@ impl Kvm {
     /// ```
     ///
     pub fn get_max_vcpu_id(&self) -> usize {
-        match self.check_extension_int(Cap::MaxVcpuId) {
-            0 => self.get_max_vcpus(),
-            x => x as usize,
+        let v = self.check_extension_int(Cap::MaxVcpuId);
+
+        if v <= 0 {
+            self.get_max_vcpus()
+        } else {
+            v as usize
         }
     }