UIO: a uniform I/O system interface for distributed systems

A uniform I/O interface allows programs to be written relatively independently of specific I/O services and yet work with a wide variety of the I/O services available in a distributed environment. Ideally, the interface provides this uniform access without excessive complexity in the interface or loss of performance. However, a uniform interface does not arise from careful design of individual system interfaces alone; it requires explicit definition. In this paper, the UIO (uniform I/O) system interface that has been used for the past five years in the V distributed operating system is described, with the focus on the key design issues. This interface provides several extensions beyond the I/O interface of UNIX#8482;, including support for record I/O, locking, atomic transactions, and replication, as well as attributes that indicate whether optional semantics and operations are available. Experience in using and implementing this interface with a variety of different I/O services is described, along with the performance of both local and network I/O. It is concluded that the UIO interface provides a uniform I/O system interface with significant functionality, wide applicability, and no significant performance penalty.