With the development of virtualization technology, it is practical and necessary to integrate virtual machine software into embedded systems. I/O scheduling is important for embedded systems, because embedded systems always face different situations and their requests have more diversity on the requirement of real-time and importance. However, the semantic information associated with the I/O data is completely lost when crossing the virtualized I/O software stack. Here, we present an I/O scheduling framework to connect the semantic gap between the application threads in virtual machines and hardware schedulers in the host machine. Therefore, the details for the I/O request can be passed through the layers of the software stack and each layer can get the specific information about the device environment. Also, various scheduling points have been provided to implement different I/O strategies. Our framework was implemented based on Linux operating system, KVM, QEMU and virtio protocol. A prototype scheduler, Orthrus, was implemented to evaluate the effectiveness of the framework. Comprehensive experiments were conducted and the results show that our framework can guarantee the real-time requirements, and reserve more system resources for critical tasks, with negligible memory consumption and throughput overhead.