hypervisor: add create_passthrough_device call to Vm trait

That function is going to return a handle for passthrough related
operations.

Move create_kvm_device code there.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

hypervisor/src/kvm/mod.rs

@@ -255,6 +255,17 @@ impl vm::Vm for KvmVm {
     fn check_extension(&self, c: Cap) -> bool {
         self.fd.check_extension(c)
     }
+    /// Create a device that is used for passthrough
+    fn create_passthrough_device(&self) -> vm::Result<DeviceFd> {
+        let mut vfio_dev = kvm_create_device {
+            type_: kvm_device_type_KVM_DEV_TYPE_VFIO,
+            fd: 0,
+            flags: 0,
+        };
+
+        self.create_device(&mut vfio_dev)
+            .map_err(|e| vm::HypervisorVmError::CreatePassthroughDevice(e.into()))
+    }
 }
 /// Wrapper over KVM system ioctls.
 pub struct KvmHypervisor {

hypervisor/src/vm.rs

@@ -110,6 +110,11 @@ pub enum HypervisorVmError {
     ///
     #[error("Failed to set clock: {0}")]
     SetClock(#[source] anyhow::Error),
+    ///
+    /// Create passthrough device
+    ///
+    #[error("Failed to create passthrough device: {0}")]
+    CreatePassthroughDevice(#[source] anyhow::Error),
 }
 ///
 /// Result type for returning from a function
@@ -171,4 +176,6 @@ pub trait Vm: Send + Sync {
     fn set_clock(&self, data: &ClockData) -> Result<()>;
     /// Checks if a particular `Cap` is available.
     fn check_extension(&self, c: Cap) -> bool;
+    /// Create a device that is used for passthrough
+    fn create_passthrough_device(&self) -> Result<DeviceFd>;
 }

vmm/src/device_manager.rs

@@ -2350,18 +2350,6 @@ impl DeviceManager {
         Ok(devices)
     }
 
-    #[cfg(feature = "pci_support")]
-    fn create_kvm_device(vm: &Arc<dyn hypervisor::Vm>) -> DeviceManagerResult<DeviceFd> {
-        let mut vfio_dev = hypervisor::kvm::kvm_create_device {
-            type_: hypervisor::kvm::kvm_device_type_KVM_DEV_TYPE_VFIO,
-            fd: 0,
-            flags: 0,
-        };
-
-        vm.create_device(&mut vfio_dev)
-            .map_err(|e| DeviceManagerError::CreateKvmDevice(e.into()))
-    }
-
     #[cfg(not(feature = "pci_support"))]
     fn next_device_name(&mut self, prefix: &str) -> DeviceManagerResult<String> {
         // Generate the temporary name.
@@ -2505,7 +2493,11 @@ impl DeviceManager {
 
         if let Some(device_list_cfg) = &mut devices {
             // Create the KVM VFIO device
-            let device_fd = DeviceManager::create_kvm_device(&self.address_manager.vm)?;
+            let device_fd = self
+                .address_manager
+                .vm
+                .create_passthrough_device()
+                .map_err(|e| DeviceManagerError::CreateKvmDevice(e.into()))?;
             let device_fd = Arc::new(device_fd);
             self.kvm_device_fd = Some(Arc::clone(&device_fd));
 
@@ -2932,7 +2924,11 @@ impl DeviceManager {
             // If the VFIO KVM device file descriptor has not been created yet,
             // it is created here and stored in the DeviceManager structure for
             // future needs.
-            let device_fd = DeviceManager::create_kvm_device(&self.address_manager.vm)?;
+            let device_fd = self
+                .address_manager
+                .vm
+                .create_passthrough_device()
+                .map_err(|e| DeviceManagerError::CreateKvmDevice(e.into()))?;
             let device_fd = Arc::new(device_fd);
             self.kvm_device_fd = Some(Arc::clone(&device_fd));
             device_fd