Fix input blocked when keyboard input is fast

kernel/src/arch/x86_64/driver/keyboard.rs

@@ -18,9 +18,12 @@ pub fn receive() -> Option<char> {
     }
 
     let mut keyboard = KEYBOARD.lock();
-    let port = Port::<u8>::new(0x60);
+    let data_port = Port::<u8>::new(0x60);
+    let status_port = Port::<u8>::new(0x64);
 
-    let scancode = unsafe { port.read() };
+    // Output buffer status = 1
+    if unsafe { status_port.read() } & (1 << 0) != 0 {
+        let scancode = unsafe { data_port.read() };
         if let Ok(Some(key_event)) = keyboard.add_byte(scancode) {
             if let Some(key) = keyboard.process_keyevent(key_event) {
                 match key {
@@ -29,5 +32,6 @@ pub fn receive() -> Option<char> {
                 }
             }
         }
+    }
     None
 }