rfc: why do we need to clone EventFd?

In the PoC we are using a `notifier()` call that returns an
`Option<EventFd>`, which essentially means that we need to clone the
file descriptor. This causes us to call `dup`, which seccomp filters
don't like. If instead we just return an `Option<&EventFd>` we don't
need to clone anything. However, not sure if that would work with the
PCIe logic.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Author: bchalios

src/vmm/src/devices/virtio/transport/mmio.rs

@@ -400,8 +400,8 @@ impl VirtioInterrupt for IrqTrigger {
         }
     }
 
-    fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<EventFd> {
-        self.irq_evt.try_clone().ok()
+    fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<&EventFd> {
+        Some(&self.irq_evt)
     }
 
     fn status(&self) -> Arc<AtomicU32> {

src/vmm/src/devices/virtio/transport/mod.rs

@@ -24,7 +24,7 @@ pub trait VirtioInterrupt: std::fmt::Debug + Send + Sync {
     fn trigger(&self, interrupt_type: VirtioInterruptType) -> Result<(), std::io::Error>;
 
     /// Get the `EventFd` (if any) that backs the underlying interrupt.
-    fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<EventFd> {
+    fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<&EventFd> {
         None
     }