Return Ok when timer expired in do_poll

kernel/aster-nix/src/syscall/poll.rs

@@ -100,7 +100,15 @@ pub fn do_poll(poll_fds: &[PollFd], timeout: Option<Duration>) -> Result<usize>
         }
 
         if let Some(timeout) = timeout.as_ref() {
-            poller.wait_timeout(timeout)?;
+            match poller.wait_timeout(timeout) {
+                Ok(_) => {}
+                Err(e) if e.error() == Errno::ETIME => {
+                    // The return value is zero if the timeout expires
+                    // before any file descriptors became ready
+                    return Ok(0);
+                }
+                Err(e) => return Err(e),
+            };
         } else {
             poller.wait()?;
         }