vmm: Simplify epoll handling for VMM main loop

Remove the indirection of a dispatch table and simply use the enum as
the event data for the events.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/lib.rs

@@ -142,19 +142,36 @@ pub enum Error {
 pub type Result<T> = result::Result<T, Error>;
 
 #[derive(Debug, Clone, Copy, PartialEq)]
+#[repr(u64)]
 pub enum EpollDispatch {
-    Exit,
-    Reset,
-    Stdin,
-    Api,
-    ActivateVirtioDevices,
-    ConsolePty,
-    SerialPty,
+    Exit = 0,
+    Reset = 1,
+    Stdin = 2,
+    Api = 3,
+    ActivateVirtioDevices = 4,
+    ConsolePty = 5,
+    SerialPty = 6,
+    Unknown,
+}
+
+impl From<u64> for EpollDispatch {
+    fn from(v: u64) -> Self {
+        use EpollDispatch::*;
+        match v {
+            0 => Exit,
+            1 => Reset,
+            2 => Stdin,
+            3 => Api,
+            4 => ActivateVirtioDevices,
+            5 => ConsolePty,
+            6 => SerialPty,
+            _ => Unknown,
+        }
+    }
 }
 
 pub struct EpollContext {
     epoll_file: File,
-    dispatch_table: Vec<Option<EpollDispatch>>,
 }
 
 impl EpollContext {
@@ -163,22 +180,11 @@ impl EpollContext {
         // Use 'File' to enforce closing on 'epoll_fd'
         let epoll_file = unsafe { File::from_raw_fd(epoll_fd) };
 
-        // Initial capacity needs to be large enough to hold:
-        // * 1 exit event
-        // * 1 reset event
-        // * 1 stdin event
-        // * 1 API event
-        let mut dispatch_table = Vec::with_capacity(5);
-        dispatch_table.push(None);
-
-        Ok(EpollContext {
-            epoll_file,
-            dispatch_table,
-        })
+        Ok(EpollContext { epoll_file })
     }
 
     pub fn add_stdin(&mut self) -> result::Result<(), io::Error> {
-        let dispatch_index = self.dispatch_table.len() as u64;
+        let dispatch_index = EpollDispatch::Stdin as u64;
         epoll::ctl(
             self.epoll_file.as_raw_fd(),
             epoll::ControlOptions::EPOLL_CTL_ADD,
@@ -186,8 +192,6 @@ impl EpollContext {
             epoll::Event::new(epoll::Events::EPOLLIN, dispatch_index),
         )?;
 
-        self.dispatch_table.push(Some(EpollDispatch::Stdin));
-
         Ok(())
     }
 
@@ -195,14 +199,13 @@ impl EpollContext {
     where
         T: AsRawFd,
     {
-        let dispatch_index = self.dispatch_table.len() as u64;
+        let dispatch_index = token as u64;
         epoll::ctl(
             self.epoll_file.as_raw_fd(),
             epoll::ControlOptions::EPOLL_CTL_ADD,
             fd.as_raw_fd(),
             epoll::Event::new(epoll::Events::EPOLLIN, dispatch_index),
         )?;
-        self.dispatch_table.push(Some(token));
 
         Ok(())
     }
@@ -1262,10 +1265,12 @@ impl Vmm {
             };
 
             for event in events.iter().take(num_events) {
-                let dispatch_idx = event.data as usize;
-
-                if let Some(dispatch_type) = self.epoll.dispatch_table[dispatch_idx] {
-                    match dispatch_type {
+                let dispatch_event: EpollDispatch = event.data.into();
+                match dispatch_event {
+                    EpollDispatch::Unknown => {
+                        let event = event.data;
+                        warn!("Unknown VMM loop event: {}", event);
+                    }
                     EpollDispatch::Exit => {
                         info!("VM exit event");
                         // Consume the event.
@@ -1492,9 +1497,7 @@ impl Vmm {
                             }
                             ApiRequest::VmReceiveMigration(receive_migration_data, sender) => {
                                 let response = self
-                                        .vm_receive_migration(
-                                            receive_migration_data.as_ref().clone(),
-                                        )
+                                    .vm_receive_migration(receive_migration_data.as_ref().clone())
                                     .map_err(ApiError::VmReceiveMigration)
                                     .map(|_| ApiResponsePayload::Empty);
                                 sender.send(response).map_err(Error::ApiResponseSend)?;
@@ -1519,7 +1522,6 @@ impl Vmm {
                 }
             }
         }
-        }
 
         Ok(())
     }