xenevtchn: implement async processing model

libs/xen/xenevtchn/Cargo.toml

@@ -6,6 +6,7 @@ resolver = "2"
 
 [dependencies]
 thiserror = { workspace = true }
+tokio = { workspace = true }
 log = { workspace = true }
 
 [dependencies.nix]

libs/xen/xenevtchn/examples/simple.rs

@@ -1,11 +1,12 @@
 use xenevtchn::error::Result;
 use xenevtchn::EventChannel;
 
-fn main() -> Result<()> {
+#[tokio::main]
-    let mut channel = EventChannel::open()?;
+async fn main() -> Result<()> {
-    println!("Channel opened.");
+    let channel = EventChannel::open().await?;
-    let port = channel.bind_unbound_port(1)?;
+    println!("channel opened");
+    let port = channel.bind_unbound_port(0).await?;
     println!("port: {}", port);
-    channel.unbind(port)?;
+    channel.unbind(port).await?;
     Ok(())
 }

libs/xen/xenevtchn/src/error.rs

@@ -6,6 +6,8 @@ pub enum Error {
     Kernel(#[from] nix::errno::Errno),
     #[error("io issue encountered")]
     Io(#[from] io::Error),
+    #[error("failed to send event channel wake")]
+    WakeSend(tokio::sync::broadcast::error::SendError<u32>),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;

libs/xen/xenevtchn/src/lib.rs

@@ -1,66 +1,171 @@
 pub mod error;
 pub mod sys;
 
-use crate::error::Result;
+use crate::error::{Error, Result};
 use crate::sys::{BindInterdomain, BindUnboundPort, BindVirq, Notify, UnbindPort};
 
-use std::fs::{File, OpenOptions};
+use log::error;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
 use std::os::fd::AsRawFd;
+use std::sync::Arc;
+use tokio::fs::{File, OpenOptions};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::select;
+use tokio::sync::broadcast::{
+    channel as broadcast_channel, Receiver as BroadcastReceiver, Sender as BroadastSender,
+};
+use tokio::sync::mpsc::{channel, Receiver, Sender};
+use tokio::sync::Mutex;
+use tokio::task::JoinHandle;
 
+const UNMASK_CHANNEL_QUEUE_LEN: usize = 30;
+const BROADCAST_CHANNEL_QUEUE_LEN: usize = 30;
+
+type WakeMap = Arc<Mutex<HashMap<u32, BroadastSender<u32>>>>;
+
+#[derive(Clone)]
 pub struct EventChannel {
-    pub handle: File,
+    handle: Arc<Mutex<File>>,
+    wakes: WakeMap,
+    unmask_sender: Sender<u32>,
+    task: Arc<JoinHandle<()>>,
 }
 
 impl EventChannel {
-    pub fn open() -> Result<EventChannel> {
+    pub async fn open() -> Result<EventChannel> {
         let file = OpenOptions::new()
             .read(true)
             .write(true)
-            .open("/dev/xen/evtchn")?;
+            .open("/dev/xen/evtchn")
-        Ok(EventChannel { handle: file })
+            .await?;
+
+        let wakes = Arc::new(Mutex::new(HashMap::new()));
+        let (unmask_sender, unmask_receiver) = channel(UNMASK_CHANNEL_QUEUE_LEN);
+        let task = {
+            let file = file.try_clone().await?;
+            let wakes = wakes.clone();
+            tokio::task::spawn(async move {
+                if let Err(error) = EventChannel::process(file, wakes, unmask_receiver).await {
+                    error!("event channel processor failed: {}", error);
+                }
+            })
+        };
+        Ok(EventChannel {
+            handle: Arc::new(Mutex::new(file)),
+            wakes,
+            unmask_sender,
+            task: Arc::new(task),
+        })
     }
 
-    pub fn bind_virq(&mut self, virq: u32) -> Result<u32> {
+    pub async fn bind_virq(&self, virq: u32) -> Result<u32> {
+        let handle = self.handle.lock().await;
         unsafe {
             let mut request = BindVirq { virq };
-            Ok(sys::bind_virq(self.handle.as_raw_fd(), &mut request)? as u32)
+            Ok(sys::bind_virq(handle.as_raw_fd(), &mut request)? as u32)
         }
     }
 
-    pub fn bind_interdomain(&mut self, domid: u32, port: u32) -> Result<u32> {
+    pub async fn bind_interdomain(&self, domid: u32, port: u32) -> Result<u32> {
+        let handle = self.handle.lock().await;
         unsafe {
             let mut request = BindInterdomain {
                 remote_domain: domid,
                 remote_port: port,
             };
-            Ok(sys::bind_interdomain(self.handle.as_raw_fd(), &mut request)? as u32)
+            Ok(sys::bind_interdomain(handle.as_raw_fd(), &mut request)? as u32)
         }
     }
 
-    pub fn bind_unbound_port(&mut self, domid: u32) -> Result<u32> {
+    pub async fn bind_unbound_port(&self, domid: u32) -> Result<u32> {
+        let handle = self.handle.lock().await;
         unsafe {
             let mut request = BindUnboundPort {
                 remote_domain: domid,
             };
-            Ok(sys::bind_unbound_port(self.handle.as_raw_fd(), &mut request)? as u32)
+            Ok(sys::bind_unbound_port(handle.as_raw_fd(), &mut request)? as u32)
         }
     }
 
-    pub fn unbind(&mut self, port: u32) -> Result<u32> {
+    pub async fn unbind(&self, port: u32) -> Result<u32> {
+        let handle = self.handle.lock().await;
         unsafe {
             let mut request = UnbindPort { port };
-            Ok(sys::unbind(self.handle.as_raw_fd(), &mut request)? as u32)
+            Ok(sys::unbind(handle.as_raw_fd(), &mut request)? as u32)
         }
     }
 
-    pub fn notify(&mut self, port: u32) -> Result<u32> {
+    pub async fn notify(&self, port: u32) -> Result<u32> {
+        let handle = self.handle.lock().await;
         unsafe {
             let mut request = Notify { port };
-            Ok(sys::notify(self.handle.as_raw_fd(), &mut request)? as u32)
+            Ok(sys::notify(handle.as_raw_fd(), &mut request)? as u32)
         }
     }
 
-    pub fn reset(&mut self) -> Result<u32> {
+    pub async fn reset(&self) -> Result<u32> {
-        unsafe { Ok(sys::reset(self.handle.as_raw_fd())? as u32) }
+        let handle = self.handle.lock().await;
+        unsafe { Ok(sys::reset(handle.as_raw_fd())? as u32) }
+    }
+
+    pub async fn subscribe(&self, port: u32) -> Result<(BroadcastReceiver<u32>, Sender<u32>)> {
+        let mut wakes = self.wakes.lock().await;
+        let receiver = match wakes.entry(port) {
+            Entry::Occupied(entry) => entry.get().subscribe(),
+
+            Entry::Vacant(entry) => {
+                let (sender, receiver) = broadcast_channel::<u32>(BROADCAST_CHANNEL_QUEUE_LEN);
+                entry.insert(sender);
+                receiver
+            }
+        };
+        Ok((receiver, self.unmask_sender.clone()))
+    }
+
+    async fn process(
+        mut file: File,
+        wakers: WakeMap,
+        mut unmask_receiver: Receiver<u32>,
+    ) -> Result<()> {
+        loop {
+            select! {
+                result = file.read_u32_le() => {
+                    match result {
+                        Ok(port) => {
+                            if let Some(sender) = wakers.lock().await.get(&port) {
+                                if let Err(error) = sender.send(port) {
+                                    return Err(Error::WakeSend(error));
+                                }
+                            }
+                        }
+
+                        Err(error) => return Err(Error::Io(error))
+                    }
+                }
+
+                result = unmask_receiver.recv() => {
+                    match result {
+                        Some(port) => {
+                            file.write_u32_le(port).await?;
+                        }
+
+                        None => {
+                            break;
+                        }
+                    }
+                }
+            };
+        }
+
+        Ok(())
+    }
+}
+
+impl Drop for EventChannel {
+    fn drop(&mut self) {
+        if Arc::strong_count(&self.task) <= 1 {
+            self.task.abort();
+        }
     }
 }