devices: Create Interrupt trait to abstract interrupt delivery

This commit anticipate the future need from having support for both
in kernel and userspace IOAPIC. The way to signal an interrupt from
the serial device will vary depending on the use case, but this should
be independent from the serial implementation itself.

That's why this patch provides a generic trait for the serial device
to call from, so that it can trigger interrupts independently from the
IOAPIC type chosen (in kernel vs userspace).

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/vm.rs

@@ -135,9 +135,6 @@ pub enum Error {
     /// Cannot setup terminal in canonical mode.
     SetTerminalCanon(vmm_sys_util::Error),
 
-    /// Cannot configure the IRQ.
-    Irq(io::Error),
-
     /// Cannot create the system allocator
     CreateSystemAllocator,
 
@@ -371,13 +368,28 @@ impl Vcpu {
     }
 }
 
+struct KernelIoapicIrq {
+    evt: EventFd,
+}
+
+impl KernelIoapicIrq {
+    fn new(evt: EventFd) -> Self {
+        KernelIoapicIrq { evt }
+    }
+}
+
+impl devices::Interrupt for KernelIoapicIrq {
+    fn deliver(&self) -> result::Result<(), io::Error> {
+        self.evt.write(1)
+    }
+}
+
 struct DeviceManager {
     io_bus: devices::Bus,
     mmio_bus: devices::Bus,
 
     // Serial port on 0x3f8
     serial: Arc<Mutex<devices::legacy::Serial>>,
-    serial_evt: EventFd,
 
     // i8042 device for exit
     i8042: Arc<Mutex<devices::legacy::I8042Device>>,
@@ -397,14 +409,21 @@ impl DeviceManager {
     ) -> DeviceManagerResult<Self> {
         let io_bus = devices::Bus::new();
         let mut mmio_bus = devices::Bus::new();
+
+        // Serial is tied to IRQ #4
+        let serial_irq = 4;
         let serial_evt = EventFd::new(EFD_NONBLOCK).map_err(DeviceManagerError::EventFd)?;
+        vm_fd
+            .register_irqfd(serial_evt.as_raw_fd(), serial_irq as u32)
+            .map_err(DeviceManagerError::Irq)?;
+
+        // Add serial device
         let serial = Arc::new(Mutex::new(devices::legacy::Serial::new_out(
-            serial_evt
-                .try_clone()
-                .map_err(DeviceManagerError::EventFd)?,
+            Box::new(KernelIoapicIrq::new(serial_evt)),
             Box::new(stdout()),
         )));
 
+        // Add a shutdown device (i8042)
         let exit_evt = EventFd::new(EFD_NONBLOCK).map_err(DeviceManagerError::EventFd)?;
         let i8042 = Arc::new(Mutex::new(devices::legacy::I8042Device::new(
             exit_evt.try_clone().map_err(DeviceManagerError::EventFd)?,
@@ -498,7 +517,6 @@ impl DeviceManager {
             io_bus,
             mmio_bus,
             serial,
-            serial_evt,
             i8042,
             exit_evt,
             pci,
@@ -769,8 +787,6 @@ impl<'a> Vm<'a> {
             kvm.check_extension(Cap::SignalMsi),
         )
         .map_err(Error::DeviceManager)?;
-        fd.register_irqfd(device_manager.serial_evt.as_raw_fd(), 4)
-            .map_err(Error::Irq)?;
 
         // Let's add our STDIN fd.
         let mut epoll = EpollContext::new().map_err(Error::EpollError)?;