devices: Hoist epoll event buffer allocation out of event loops

Move the epoll_events Vec allocation before the loop in all virtio
worker threads (block, fs, net, snd, vsock muxer). The buffer is
reused across iterations since wait() overwrites entries and all
callers only iterate epoll_events[0..ev_cnt].

Signed-off-by: Matej Hrica <mhrica@redhat.com>

Author: mtjhrc

src/devices/src/virtio/block/worker.rs

@@ -105,8 +105,8 @@ impl BlockWorker {
             &EpollEvent::new(EventSet::IN, stop_ev_fd as u64),
         );
 
+        let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
         loop {
-            let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
             match epoll.wait(epoll_events.len(), -1, epoll_events.as_mut_slice()) {
                 Ok(ev_cnt) => {
                     for event in &epoll_events[0..ev_cnt] {

src/devices/src/virtio/fs/worker.rs

@@ -89,8 +89,8 @@ impl FsWorker {
             &EpollEvent::new(EventSet::IN, stop_ev_fd as u64),
         );
 
+        let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
         loop {
-            let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
             match epoll.wait(epoll_events.len(), -1, epoll_events.as_mut_slice()) {
                 Ok(ev_cnt) => {
                     for event in &epoll_events[0..ev_cnt] {

src/devices/src/virtio/net/worker.rs

@@ -125,8 +125,8 @@ impl NetWorker {
             ),
         );
 
+        let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
         loop {
-            let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
             match epoll.wait(epoll_events.len(), -1, epoll_events.as_mut_slice()) {
                 Ok(ev_cnt) => {
                     for event in &epoll_events[0..ev_cnt] {

src/devices/src/virtio/snd/worker.rs

@@ -139,8 +139,8 @@ impl SndWorker {
             )
             .unwrap();
 
+        let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
         loop {
-            let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
             match epoll.wait(epoll_events.len(), -1, epoll_events.as_mut_slice()) {
                 Ok(ev_cnt) => {
                     for event in &epoll_events[0..ev_cnt] {

src/devices/src/virtio/vsock/muxer_thread.rs

@@ -175,8 +175,8 @@ impl MuxerThread {
     fn work(mut self) {
         let mut thread_rng = rng();
         self.create_lisening_ipc_sockets();
+        let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
         loop {
-            let mut epoll_events = vec![EpollEvent::new(EventSet::empty(), 0); 32];
             match self
                 .epoll
                 .wait(epoll_events.len(), -1, epoll_events.as_mut_slice())