vhost-user-backend: use Cow<'static, str>

Change the name's type `String` to `Cow<'static, str>`. This allows the
library user to prevent string allocation from static strings, which is
how most crates use it.

This is an API breaking change.

Signed-off-by: Manos Pitsidianakis <[email protected]>

Author: epilys

crates/vhost-user-backend/CHANGELOG.md

@@ -9,6 +9,9 @@
 - [[#192]](https://github.com/rust-vmm/vhost/pull/192) vhost-user-backend: remove return value from handle_event
 - [[#155]](https://github.com/rust-vmm/vhost/pull/155) Converted generic type
   parameters of VhostUserBackend into associated types.
+- `name` field of VhostUserDaemon is now a `std::borrow::Cow<'static, str>`
+  instead of `String` to prevent allocating in the heap for static names, which
+  is the majority of uses of this API.
 
 ### Fixed
 

crates/vhost-user-backend/README.md

@@ -19,7 +19,7 @@ where
     V: VringT<GM<B>> + Clone + Send + Sync + 'static,
     B: Bitmap + 'static,
 {
-    pub fn new(name: String, backend: S, atomic_mem: GuestMemoryAtomic<GuestMemoryMmap<B>>) -> Result<Self>;
+    pub fn new(name: Cow<'static, str>, backend: S, atomic_mem: GuestMemoryAtomic<GuestMemoryMmap<B>>) -> Result<Self>;
     pub fn start(&mut self, listener: Listener) -> Result<()>;
     pub fn wait(&mut self) -> Result<()>;
     pub fn get_epoll_handlers(&self) -> Vec<Arc<VringEpollHandler<S, V, B>>>;

crates/vhost-user-backend/src/lib.rs

@@ -8,6 +8,7 @@
 #[macro_use]
 extern crate log;
 
+use std::borrow::Cow;
 use std::fmt::{Display, Formatter};
 use std::path::Path;
 use std::sync::{Arc, Mutex};
@@ -81,7 +82,7 @@ pub type Result<T> = std::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<T: VhostUserBackend> {
-    name: String,
+    name: Cow<'static, str>,
     handler: Arc<Mutex<VhostUserHandler<T>>>,
     main_thread: Option<thread::JoinHandle<Result<()>>>,
 }
@@ -98,7 +99,7 @@ where
     /// registered event. Those events can be vring events or custom events from the backend,
     /// but they get to be registered later during the sequence.
     pub fn new(
-        name: String,
+        name: Cow<'static, str>,
         backend: T,
         atomic_mem: GuestMemoryAtomic<GuestMemoryMmap<T::Bitmap>>,
     ) -> Result<Self> {
@@ -124,7 +125,7 @@ where
         mut handler: BackendReqHandler<Mutex<VhostUserHandler<T>>>,
     ) -> Result<()> {
         let handle = thread::Builder::new()
-            .name(self.name.clone())
+            .name(self.name.to_string())
             .spawn(move || loop {
                 handler.handle_request().map_err(Error::HandleRequest)?;
             })
@@ -253,7 +254,7 @@ mod tests {
             GuestMemoryMmap::<()>::from_ranges(&[(GuestAddress(0x100000), 0x10000)]).unwrap(),
         );
         let backend = Arc::new(Mutex::new(MockVhostBackend::new()));
-        let mut daemon = VhostUserDaemon::new("test".to_owned(), backend, mem).unwrap();
+        let mut daemon = VhostUserDaemon::new("test".into(), backend, mem).unwrap();
 
         let handlers = daemon.get_epoll_handlers();
         assert_eq!(handlers.len(), 2);
@@ -286,7 +287,7 @@ mod tests {
             GuestMemoryMmap::<()>::from_ranges(&[(GuestAddress(0x100000), 0x10000)]).unwrap(),
         );
         let backend = Arc::new(Mutex::new(MockVhostBackend::new()));
-        let mut daemon = VhostUserDaemon::new("test".to_owned(), backend, mem).unwrap();
+        let mut daemon = VhostUserDaemon::new("test".into(), backend, mem).unwrap();
 
         let handlers = daemon.get_epoll_handlers();
         assert_eq!(handlers.len(), 2);
@@ -321,7 +322,7 @@ mod tests {
             GuestMemoryMmap::<()>::from_ranges(&[(GuestAddress(0x100000), 0x10000)]).unwrap(),
         );
         let backend = Arc::new(Mutex::new(MockVhostBackend::new()));
-        let mut daemon = VhostUserDaemon::new("test".to_owned(), backend.clone(), mem).unwrap();
+        let mut daemon = VhostUserDaemon::new("test".into(), backend.clone(), mem).unwrap();
         let tmpdir = tempfile::tempdir().unwrap();
         let socket_path = tmpdir.path().join("socket");
 

crates/vhost-user-backend/tests/vhost-user-server.rs

@@ -220,7 +220,7 @@ fn vhost_user_client(path: &Path, barrier: Arc<Barrier>) {
 fn vhost_user_server(cb: fn(&Path, Arc<Barrier>)) {
     let mem = GuestMemoryAtomic::new(GuestMemoryMmap::<()>::new());
     let backend = Arc::new(Mutex::new(MockVhostBackend::new()));
-    let mut daemon = VhostUserDaemon::new("test".to_owned(), backend, mem).unwrap();
+    let mut daemon = VhostUserDaemon::new("test".into(), backend, mem).unwrap();
 
     let barrier = Arc::new(Barrier::new(2));
     let tmpdir = tempfile::tempdir().unwrap();