feat(virtio/interrupt): add trigger_queues method

This method is used to notify the guest about queue events in a way
that's most performant with the underlying interrupt implementation.
As in IrqTrigger there is no distinction between different queues, it's
best to send just one interrupt notifiying that "some queues" have a
pending event.
Conversely, in VirtioInterruptMsix, we need to trigger a MSI for each
distinct queue.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

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

@@ -406,6 +406,14 @@ impl VirtioInterrupt for IrqTrigger {
         }
     }
 
+    fn trigger_queues(&self, queues: &[u16]) -> Result<(), std::io::Error> {
+        if queues.is_empty() {
+            Ok(())
+        } else {
+            self.trigger_irq(IrqType::Vring)
+        }
+    }
+
     fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<&EventFd> {
         Some(&self.irq_evt)
     }

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

@@ -25,6 +25,18 @@ pub trait VirtioInterrupt: std::fmt::Debug + Send + Sync {
     /// Trigger a VirtIO interrupt.
     fn trigger(&self, interrupt_type: VirtioInterruptType) -> Result<(), std::io::Error>;
 
+    /// Trigger multiple Virtio interrupts for selected queues.
+    /// The caller needs to ensure that [`queues`] does not include duplicate entries to
+    /// avoid sending multiple interrupts for the same queue.
+    /// This is to allow sending a single interrupt for implementations that don't
+    /// distinguish different queues, like IrqTrigger, instead of sending multiple same
+    /// interrupts.
+    fn trigger_queues(&self, queues: &[u16]) -> Result<(), std::io::Error> {
+        queues
+            .iter()
+            .try_for_each(|&qidx| self.trigger(VirtioInterruptType::Queue(qidx)))
+    }
+
     /// Get the `EventFd` (if any) that backs the underlying interrupt.
     fn notifier(&self, _interrupt_type: VirtioInterruptType) -> Option<&EventFd> {
         None