interrupt: Add a notifier method to the InterruptController

Both GIC and IOAPIC must implement a new method notifier() in order to
provide the caller with an EventFd corresponding to the IRQ it refers
to.

This is needed in anticipation for supporting INTx with VFIO PCI
devices.

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

devices/src/gic.rs

@@ -8,6 +8,7 @@ use std::sync::Arc;
 use vm_device::interrupt::{
     InterruptIndex, InterruptManager, InterruptSourceGroup, MsiIrqGroupConfig,
 };
+use vmm_sys_util::eventfd::EventFd;
 
 type Result<T> = result::Result<T, Error>;
 
@@ -61,4 +62,8 @@ impl InterruptController for Gic {
 
         Ok(())
     }
+
+    fn notifier(&self, irq: usize) -> Option<EventFd> {
+        self.interrupt_source_group.notifier(irq as InterruptIndex)
+    }
 }

devices/src/interrupt_controller.rs

@@ -4,6 +4,7 @@
 
 use std::io;
 use std::result;
+use vmm_sys_util::eventfd::EventFd;
 
 #[derive(Debug)]
 pub enum Error {
@@ -56,4 +57,5 @@ pub trait InterruptController: Send {
     fn enable(&self) -> Result<()>;
     #[cfg(target_arch = "x86_64")]
     fn end_of_interrupt(&mut self, vec: u8);
+    fn notifier(&self, irq: usize) -> Option<EventFd>;
 }

devices/src/ioapic.rs

@@ -24,6 +24,7 @@ use vm_migration::{
     Migratable, MigratableError, Pausable, Snapshot, SnapshotDataSection, Snapshottable,
     Transportable,
 };
+use vmm_sys_util::eventfd::EventFd;
 
 #[derive(Serialize, Deserialize)]
 #[serde(remote = "GuestAddress")]
@@ -405,6 +406,10 @@ impl InterruptController for Ioapic {
 
         Ok(())
     }
+
+    fn notifier(&self, irq: usize) -> Option<EventFd> {
+        self.interrupt_source_group.notifier(irq as InterruptIndex)
+    }
 }
 
 impl Snapshottable for Ioapic {

devices/src/legacy/serial.rs

@@ -356,6 +356,9 @@ mod tests {
         ) -> result::Result<(), std::io::Error> {
             Ok(())
         }
+        fn notifier(&self, _index: InterruptIndex) -> Option<EventFd> {
+            Some(self.event_fd.try_clone().unwrap())
+        }
     }
 
     impl TestInterrupt {

vm-device/src/interrupt/mod.rs

@@ -169,11 +169,7 @@ pub trait InterruptSourceGroup: Send + Sync {
     /// to inject interrupts into a guest, by writing to the file returned
     /// by this method.
     #[allow(unused_variables)]
-    fn notifier(&self, index: InterruptIndex) -> Option<EventFd> {
-        // One use case of the notifier is to implement vhost user backends.
-        // For all other implementations we can just return None here.
-        None
-    }
+    fn notifier(&self, index: InterruptIndex) -> Option<EventFd>;
 
     /// Update the interrupt source group configuration.
     ///

vmm/src/interrupt.rs

@@ -246,6 +246,10 @@ impl InterruptSourceGroup for LegacyUserspaceInterruptGroup {
     fn update(&self, _index: InterruptIndex, _config: InterruptSourceConfig) -> Result<()> {
         Ok(())
     }
+
+    fn notifier(&self, _index: InterruptIndex) -> Option<EventFd> {
+        self.ioapic.lock().unwrap().notifier(self.irq as usize)
+    }
 }
 
 pub struct LegacyUserspaceInterruptManager {