interrupt: Make IRQ delivery generic

Because we cannot always assume the irq fd will be the way to send
an IRQ to the guest, this means we cannot make the assumption that
every virtio device implementation should expect an EventFd to
trigger an IRQ.

This commit organizes the code related to virtio devices so that it
now expects a Rust closure instead of a known EventFd. This lets the
caller decide what should be done whenever a device needs to trigger
an interrupt to the guest.

The closure will allow for other type of interrupt mechanism such as
MSI to be implemented. From the device perspective, it could be a
pin based interrupt or an MSI, it does not matter since the device
will simply call into the provided callback, passing the appropriate
Queue as a reference. This design keeps the device model generic.

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

vmm/src/vm.rs

@@ -27,7 +27,7 @@ use kvm_ioctls::*;
 use libc::{c_void, siginfo_t, EFD_NONBLOCK};
 use linux_loader::loader::KernelLoader;
 use net_util::Tap;
-use pci::{PciConfigIo, PciDevice, PciInterruptPin, PciRoot};
+use pci::{IrqClosure, PciConfigIo, PciDevice, PciInterruptPin, PciRoot};
 use qcow::{self, ImageType, QcowFile};
 use std::ffi::CString;
 use std::fs::{File, OpenOptions};
@@ -423,6 +423,7 @@ impl DeviceManager {
     ) -> DeviceManagerResult<()> {
         let mut virtio_pci_device = VirtioPciDevice::new(memory, virtio_device)
             .map_err(DeviceManagerError::VirtioDevice)?;
+
         let bars = virtio_pci_device
             .allocate_bars(allocator)
             .map_err(DeviceManagerError::AllocateBars)?;
@@ -442,8 +443,11 @@ impl DeviceManager {
         vm_fd
             .register_irqfd(irqfd.as_raw_fd(), irq_num)
             .map_err(DeviceManagerError::Irq)?;
+
+        let irq_cb = Arc::new(Box::new(move || irqfd.write(1)) as IrqClosure);
+
         // Let's use irq line INTA for now.
-        virtio_pci_device.assign_irq(irqfd, irq_num as u32, PciInterruptPin::IntA);
+        virtio_pci_device.assign_irq(irq_cb, irq_num as u32, PciInterruptPin::IntA);
 
         let virtio_pci_device = Arc::new(Mutex::new(virtio_pci_device));