Add termios read/write file

src/slave.rs

@@ -32,6 +32,10 @@ impl Resource for PtySlave {
         self.pty.clone()
     }
 
+    fn flags(&self) -> usize {
+        self.flags
+    }
+
     fn path(&self, buf: &mut [u8]) -> Result<usize> {
         if let Some(pty_lock) = self.pty.upgrade() {
             pty_lock.borrow_mut().path(buf)