Print a message when all processes are sleeping after a yield

src/tasking.rs

@@ -162,6 +162,7 @@ impl Tasking {
             let previous_process = self.current_process.replace(next_process_pid).unwrap();
             switch_to_asm(&mut (self.processes[previous_process].kernel_esp), kernel_esp);
         } else if self.processes[current_process].sleeping.is_some() {
+            println!("All processes sleeping, exiting QEMU");
             qemu_exit::exit_qemu();
         }
     }