devices/console: Fix a bug which would cause libkrun to hang on exit

Make PortInputEmpty and PortInputSigInt wait_until_readable implementations
poll the stopfd EventFd to ensure the thread eventually exits. If the thread
wouldn't exit, the Port::shutdown method would join the thread, and would wait
forever for the thread to exit.

To replicate the hang, the stdin musn't be a terminal. For example you can use a
pipe. `echo "foo" | ./chroot_vm rootfs_fedora /bin/cat` would hang.

This is technically a regresion introduced by the commit:
4076b7: devices/console: implement reset method

Signed-off-by: Matej Hrica <[email protected]>

Author: mtjhrc

src/devices/src/virtio/console/port_io.rs

@@ -222,12 +222,18 @@ impl PortInput for PortInputSigInt {
     fn read_volatile(&mut self, buf: &mut VolatileSlice) -> Result<usize, io::Error> {
         self.sigint_evt.read()?;
         log::trace!("SIGINT received");
-        buf.copy_from(&[3u8]); //ASCII 'ETX' -> generates SIGINIT in a terminal
+        buf.copy_from(&[3u8]); // ASCII 'ETX' -> generates SIGINIT in a terminal
         Ok(1)
     }
 
-    fn wait_until_readable(&self, _stopfd: Option<&EventFd>) {
-        let mut poll_fds = [PollFd::new(self.sigint_evt.as_raw_fd(), PollFlags::POLLIN)];
+    fn wait_until_readable(&self, stopfd: Option<&EventFd>) {
+        let mut poll_fds = Vec::new();
+
+        poll_fds.push(PollFd::new(self.sigint_evt.as_raw_fd(), PollFlags::POLLIN));
+        if let Some(stopfd) = stopfd {
+            poll_fds.push(PollFd::new(stopfd.as_raw_fd(), PollFlags::POLLIN));
+        }
+
         poll(&mut poll_fds, -1).expect("Failed to poll");
     }
 }
@@ -251,7 +257,12 @@ impl PortInput for PortInputEmpty {
         Ok(0)
     }
 
-    fn wait_until_readable(&self, _stopfd: Option<&EventFd>) {
-        std::thread::sleep(std::time::Duration::MAX);
+    fn wait_until_readable(&self, stopfd: Option<&EventFd>) {
+        if let Some(stopfd) = stopfd {
+            let mut poll_fds = [PollFd::new(stopfd.as_raw_fd(), PollFlags::POLLIN)];
+            poll(&mut poll_fds, -1).expect("Failed to poll");
+        } else {
+            std::thread::sleep(std::time::Duration::MAX);
+        }
     }
 }