interrupt: Interrupt manager split

We create 2 different interrupt managers for separately handling
creation of legacy and MSI interrupt groups.
Doing so allows us to have a cleaner interrupt manager and IOAPIC
initialization path. It also prepares for an InterruptManager trait
design improvement where we remove the interrupt source type dependency
by associating an interrupt configuration type to the trait.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vmm/src/interrupt.rs

@@ -272,30 +272,37 @@ impl InterruptSourceGroup for LegacyUserspaceInterruptGroup {
     }
 }
 
-pub struct KvmInterruptManager {
+pub struct KvmLegacyUserspaceInterruptManager {
+    ioapic: Arc<Mutex<ioapic::Ioapic>>,
+}
+
+pub struct KvmMsiInterruptManager {
     allocator: Arc<Mutex<SystemAllocator>>,
     vm_fd: Arc<VmFd>,
     gsi_msi_routes: Arc<Mutex<HashMap<u32, KvmRoutingEntry>>>,
-    ioapic: Option<Arc<Mutex<ioapic::Ioapic>>>,
 }
 
-impl KvmInterruptManager {
+impl KvmLegacyUserspaceInterruptManager {
+    pub fn new(ioapic: Arc<Mutex<ioapic::Ioapic>>) -> Self {
+        KvmLegacyUserspaceInterruptManager { ioapic }
+    }
+}
+
+impl KvmMsiInterruptManager {
     pub fn new(
         allocator: Arc<Mutex<SystemAllocator>>,
         vm_fd: Arc<VmFd>,
         gsi_msi_routes: Arc<Mutex<HashMap<u32, KvmRoutingEntry>>>,
-        ioapic: Option<Arc<Mutex<ioapic::Ioapic>>>,
     ) -> Self {
-        KvmInterruptManager {
+        KvmMsiInterruptManager {
             allocator,
             vm_fd,
             gsi_msi_routes,
-            ioapic,
         }
     }
 }
 
-impl InterruptManager for KvmInterruptManager {
+impl InterruptManager for KvmLegacyUserspaceInterruptManager {
     fn create_group(
         &self,
         interrupt_type: InterruptType,
@@ -311,18 +318,35 @@ impl InterruptManager for KvmInterruptManager {
                     ));
                 }
 
-                if let Some(ioapic) = &self.ioapic {
-                    Arc::new(Box::new(LegacyUserspaceInterruptGroup::new(
-                        ioapic.clone(),
-                        base as u32,
-                    )))
-                } else {
-                    return Err(io::Error::new(
-                        io::ErrorKind::Other,
-                        "No IOAPIC configured, cannot create legacy interrupt group",
-                    ));
-                }
+                Arc::new(Box::new(LegacyUserspaceInterruptGroup::new(
+                    self.ioapic.clone(),
+                    base as u32,
+                )))
             }
+            _ => {
+                return Err(io::Error::new(
+                    io::ErrorKind::Other,
+                    "Interrupt type not supported",
+                ))
+            }
+        };
+
+        Ok(interrupt_source_group)
+    }
+
+    fn destroy_group(&self, _group: Arc<Box<dyn InterruptSourceGroup>>) -> Result<()> {
+        Ok(())
+    }
+}
+
+impl InterruptManager for KvmMsiInterruptManager {
+    fn create_group(
+        &self,
+        interrupt_type: InterruptType,
+        base: InterruptIndex,
+        count: InterruptIndex,
+    ) -> Result<Arc<Box<dyn InterruptSourceGroup>>> {
+        let interrupt_source_group: Arc<Box<dyn InterruptSourceGroup>> = match interrupt_type {
             PCI_MSI_IRQ => {
                 let mut allocator = self.allocator.lock().unwrap();
                 let mut irq_routes: HashMap<InterruptIndex, InterruptRoute> =