backend: set default type for VhostUserBackend

Use () as default type for trait VhostUserBackend and
VhostUserBackendMut.

Signed-off-by: Liu Jiang <[email protected]>

Author: jiangliu

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 50.8,
+  "coverage_score": 77.4,
   "exclude_path": "",
   "crate_features": ""
 }

src/backend.rs

@@ -34,7 +34,7 @@ use super::{Vring, GM};
 ///
 /// To support multi-threading and asynchronous IO, we enforce `the Send + Sync + 'static`.
 /// So there's no plan for support of "Rc<T>" and "RefCell<T>".
-pub trait VhostUserBackend<B: Bitmap + 'static>: Send + Sync + 'static {
+pub trait VhostUserBackend<B: Bitmap + 'static = ()>: Send + Sync + 'static {
     /// Get number of queues supported.
     fn num_queues(&self) -> usize;
 
@@ -113,7 +113,7 @@ pub trait VhostUserBackend<B: Bitmap + 'static>: Send + Sync + 'static {
 }
 
 /// Trait without interior mutability for vhost user backend servers to implement concrete services.
-pub trait VhostUserBackendMut<B: Bitmap + 'static>: Send + Sync + 'static {
+pub trait VhostUserBackendMut<B: Bitmap + 'static = ()>: Send + Sync + 'static {
     /// Get number of queues supported.
     fn num_queues(&self) -> usize;
 
@@ -486,7 +486,7 @@ pub mod tests {
         assert_eq!(backend.queues_per_thread(), [1, 1]);
 
         assert_eq!(backend.get_config(0x200, 8), vec![0xa5; 8]);
-        backend.set_config(0x200, &vec![0xa5; 8]).unwrap();
+        backend.set_config(0x200, &[0xa5; 8]).unwrap();
 
         backend.acked_features(0xffff);
         assert_eq!(backend.lock().unwrap().acked_features, 0xffff);
@@ -509,7 +509,7 @@ pub mod tests {
         assert_eq!(backend.queues_per_thread(), [1, 1]);
 
         assert_eq!(backend.get_config(0x200, 8), vec![0xa5; 8]);
-        backend.set_config(0x200, &vec![0xa5; 8]).unwrap();
+        backend.set_config(0x200, &[0xa5; 8]).unwrap();
 
         backend.acked_features(0xffff);
         assert_eq!(backend.read().unwrap().acked_features, 0xffff);

src/lib.rs

@@ -75,7 +75,7 @@ pub type Result<T> = result::Result<T, Error>;
 ///
 /// This structure is the public API the backend is allowed to interact with in order to run
 /// a fully functional vhost-user daemon.
-pub struct VhostUserDaemon<S: VhostUserBackend<B>, B: Bitmap + 'static> {
+pub struct VhostUserDaemon<S: VhostUserBackend<B>, B: Bitmap + 'static = ()> {
     name: String,
     handler: Arc<Mutex<VhostUserHandler<S, B>>>,
     main_thread: Option<thread::JoinHandle<Result<()>>>,