Rework epoll tests to use custom file descriptor

They previously used stdin, which may cause problems on some systems during testing.
We can use signalfd() however to create a new file descriptor that can work with epoll,
so let's do that instead and see if the intermittent failures found in testing go away.:

Author: Susurrus

test/sys/test_epoll.rs

@@ -1,24 +1,39 @@
+use std::os::unix::io::AsRawFd;
+
+use nix::{Error, Errno};
 use nix::sys::epoll::{EpollCreateFlags, EpollOp, EpollEvent};
 use nix::sys::epoll::{EPOLLIN, EPOLLERR};
 use nix::sys::epoll::{epoll_create1, epoll_ctl};
-use nix::{Error, Errno};
+use nix::sys::signal::SigSet;
+use nix::sys::signalfd::SignalFd;
+use nix::unistd::close;
 
 #[test]
 pub fn test_epoll_errno() {
+    // Create a new signalfd to use for testing. This is better than using stdin or other such fd.
+    let sfd = SignalFd::new(&SigSet::empty()).unwrap();
+
     let efd = epoll_create1(EpollCreateFlags::empty()).unwrap();
-    let result = epoll_ctl(efd, EpollOp::EpollCtlDel, 1, None);
+    let result = epoll_ctl(efd, EpollOp::EpollCtlDel, sfd.as_raw_fd(), None);
     assert!(result.is_err());
     assert_eq!(result.unwrap_err(), Error::Sys(Errno::ENOENT));
 
-    let result = epoll_ctl(efd, EpollOp::EpollCtlAdd, 1, None);
+    let result = epoll_ctl(efd, EpollOp::EpollCtlAdd, sfd.as_raw_fd(), None);
     assert!(result.is_err());
     assert_eq!(result.unwrap_err(), Error::Sys(Errno::EINVAL));
+
+    close(efd).unwrap(); // epoll_create1's file descriptors are supposed to be closed afterwards
 }
 
 #[test]
 pub fn test_epoll_ctl() {
+    // Create a new signalfd to use for testing. This is better than using stdin or other such fd.
+    let sfd = SignalFd::new(&SigSet::empty()).unwrap();
+
     let efd = epoll_create1(EpollCreateFlags::empty()).unwrap();
     let mut event = EpollEvent::new(EPOLLIN | EPOLLERR, 1);
-    epoll_ctl(efd, EpollOp::EpollCtlAdd, 1, &mut event).unwrap();
-    epoll_ctl(efd, EpollOp::EpollCtlDel, 1, None).unwrap();
+    epoll_ctl(efd, EpollOp::EpollCtlAdd, sfd.as_raw_fd(), &mut event).unwrap();
+    epoll_ctl(efd, EpollOp::EpollCtlDel, sfd.as_raw_fd(), None).unwrap();
+
+    close(efd).unwrap(); // epoll_create1's file descriptors are supposed to be closed afterwards
 }