This presents a new mechanism, called a shadow driver, that improves overall system reliability by concealing a drivers failure from its clients while recovering from the failure. During normal operation, the shadow tracks the state of the real driver by monitoring all communication between the kernel and the driver. When a failure occurs, the shadow inserts itself temporarily in place of the failed computer driver, servicing requests on its behalf. While shielding the kernel and applications from the failure, the shadow driver restores the failed driver to a state where it can resume processing requests. Our design for shadow drivers reflects four principles:
1.
Device driver failures should be concealed from the drivers clients. If the operating system and applications using a driver cannot detect that it has failed,they are unlikely to fail themselves.
2.
Recovery logic should be centralized in a single sub-system. We want to consolidate recovery knowledge in a small number of components to simplify the implementation.
3.
Driver recovery logic should be generic. The increased reliability offered by driver recovery should not be off set by potentially destabilizing changes to the tens of thousands of existing drivers. Therefore, the architecture must enable a single shadow driver to handle recovery for a large number of device drivers.
4.
Recovery services should have low over head when not needed. The recovery system should impose relatively little over head for the common case(that is, when drivers are operating normally).
Overall, these design principles are intended to minimize the cost required to make and use shadow drivers while maximizing their value in existing commodity operating systems. Such as sound driver and windows driver are compatible to this post.
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