From 40e4dc6339a507cc8ab31bf2459df87d4aca5ad0 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <sebastien.boeuf@intel.com>
Date: Thu, 9 Apr 2020 13:14:05 +0200
Subject: [PATCH] vhost_user_backend: Change handle_event as immutable

By changing the mutability of this function, after adapting all
backends, we should be able to implement multithreads with
multiqueues support without hitting a bottleneck on the backend
locking.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
---
 src/bin/vhost_user_fs.rs      | 2 +-
 vhost_user_backend/src/lib.rs | 4 ++--
 vhost_user_block/src/lib.rs   | 2 +-
 vhost_user_net/src/lib.rs     | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/bin/vhost_user_fs.rs b/src/bin/vhost_user_fs.rs
index 03a279ac2..002b2a49e 100644
--- a/src/bin/vhost_user_fs.rs
+++ b/src/bin/vhost_user_fs.rs
@@ -217,7 +217,7 @@ impl<F: FileSystem + Send + Sync + 'static> VhostUserBackend for VhostUserFsBack
     }
 
     fn handle_event(
-        &mut self,
+        &self,
         device_event: u16,
         evset: epoll::Events,
         vrings: &[Arc<RwLock<Vring>>],
diff --git a/vhost_user_backend/src/lib.rs b/vhost_user_backend/src/lib.rs
index 10184a175..1be1cb1f0 100644
--- a/vhost_user_backend/src/lib.rs
+++ b/vhost_user_backend/src/lib.rs
@@ -81,7 +81,7 @@ pub trait VhostUserBackend: Send + Sync + 'static {
     /// virtqueues on its own, but does not know what to do with events
     /// happening on custom listeners.
     fn handle_event(
-        &mut self,
+        &self,
         device_event: u16,
         evset: epoll::Events,
         vrings: &[Arc<RwLock<Vring>>],
@@ -310,7 +310,7 @@ impl<S: VhostUserBackend> VringEpollHandler<S> {
         }
 
         self.backend
-            .write()
+            .read()
             .unwrap()
             .handle_event(device_event, evset, &self.vrings)
             .map_err(VringEpollHandlerError::HandleEventBackendHandling)
diff --git a/vhost_user_block/src/lib.rs b/vhost_user_block/src/lib.rs
index 46d364622..7e44deea8 100644
--- a/vhost_user_block/src/lib.rs
+++ b/vhost_user_block/src/lib.rs
@@ -277,7 +277,7 @@ impl VhostUserBackend for VhostUserBlkBackend {
     }
 
     fn handle_event(
-        &mut self,
+        &self,
         device_event: u16,
         evset: epoll::Events,
         vrings: &[Arc<RwLock<Vring>>],
diff --git a/vhost_user_net/src/lib.rs b/vhost_user_net/src/lib.rs
index f3dc74e0c..cc76d8d73 100644
--- a/vhost_user_net/src/lib.rs
+++ b/vhost_user_net/src/lib.rs
@@ -307,7 +307,7 @@ impl VhostUserBackend for VhostUserNetBackend {
     }
 
     fn handle_event(
-        &mut self,
+        &self,
         device_event: u16,
         evset: epoll::Events,
         vrings: &[Arc<RwLock<Vring>>],