vhost_user_backend: Allow for one exit_event per thread

By adding the "thread_index" parameter to the function exit_event() from
the VhostUserBackend trait, the backend crate now has the ability to ask
the backend implementation about the exit event related to a specific
thread.

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

src/bin/vhost_user_fs.rs

@@ -266,7 +266,7 @@ impl<F: FileSystem + Send + Sync + 'static> VhostUserBackend for VhostUserFsBack
         Ok(false)
     }
 
-    fn exit_event(&self) -> Option<(EventFd, Option<u16>)> {
+    fn exit_event(&self, _thread_index: usize) -> Option<(EventFd, Option<u16>)> {
         Some((
             self.thread.lock().unwrap().kill_evt.try_clone().unwrap(),
             Some(KILL_EVENT),

vhost_user_backend/src/lib.rs

@@ -105,7 +105,7 @@ pub trait VhostUserBackend: Send + Sync + 'static {
     /// When this EventFd is written to the worker thread will exit. An optional id may
     /// also be provided, if it not provided then the exit event will be first event id
     /// after the last queue
-    fn exit_event(&self) -> Option<(EventFd, Option<u16>)> {
+    fn exit_event(&self, _thread_index: usize) -> Option<(EventFd, Option<u16>)> {
         None
     }
 
@@ -484,7 +484,7 @@ impl<S: VhostUserBackend> VhostUserHandler<S> {
 
         let mut workers = Vec::new();
         let mut worker_threads = Vec::new();
-        for queues_mask in queues_per_thread.iter() {
+        for (thread_index, queues_mask) in queues_per_thread.iter().enumerate() {
             // Create the epoll file descriptor
             let epoll_fd = epoll::create(true).map_err(VhostUserHandlerError::EpollCreateFd)?;
 
@@ -492,7 +492,7 @@ impl<S: VhostUserBackend> VhostUserHandler<S> {
             let worker = vring_worker.clone();
 
             let exit_event_id = if let Some((exit_event_fd, exit_event_id)) =
-                backend.read().unwrap().exit_event()
+                backend.read().unwrap().exit_event(thread_index)
             {
                 let exit_event_id = exit_event_id.unwrap_or(num_queues as u16);
                 worker

vhost_user_block/src/lib.rs

@@ -342,7 +342,7 @@ impl VhostUserBackend for VhostUserBlkBackend {
         buf.to_vec()
     }
 
-    fn exit_event(&self) -> Option<(EventFd, Option<u16>)> {
+    fn exit_event(&self, _thread_index: usize) -> Option<(EventFd, Option<u16>)> {
         Some((
             self.thread.lock().unwrap().kill_evt.try_clone().unwrap(),
             None,

vhost_user_net/src/lib.rs

@@ -337,17 +337,17 @@ impl VhostUserBackend for VhostUserNetBackend {
         Ok(false)
     }
 
-    fn exit_event(&self) -> Option<(EventFd, Option<u16>)> {
-        let tap_end_index = (self.num_queues + self.num_queues / 2 - 1) as u16;
-        let kill_index = tap_end_index + 1;
+    fn exit_event(&self, thread_index: usize) -> Option<(EventFd, Option<u16>)> {
+        // The exit event is placed after the queues and the tap event, which
+        // is event index 3.
         Some((
-            self.threads[0]
+            self.threads[thread_index]
                 .lock()
                 .unwrap()
                 .kill_evt
                 .try_clone()
                 .unwrap(),
-            Some(kill_index),
+            Some(3),
         ))
     }
 }