An Object-Oriented Framework for File Systems

191 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1992.File systems are essential components of general purpose operating systems and are highly visible to computer users. To satisfy the growing diversity of persistent storage needs presented by application and system programs, operating systems should support both standard and customizable file systems. To facilitate the design, construction, and use of these file systems, they should fit within a general and extensible model. Currently file systems are based on one of a few common models that are neither general nor extensible. This thesis shows that a simple, general, and extensible model can be constructed by presenting an object-oriented framework that contains a few powerful persistent storage abstractions. The framework supports the characterization, design, and construction of both common file systems and experimental file systems. The object-oriented approach was chosen to exploit the techniques of data encapsulation, data abstraction, inheritance, and polymorphism.The framework is called the Choices file system framework. It contains two fundamental abstractions: the PersistentStore class defines objects that manage the storage and retrieval of raw persistent data, and the PersistentObject class defines objects that encapsulate and provide operations on the data managed by persistent stores. Persistent stores manage data access within the file system, while various kinds of persistent objects encapsulate the organization, naming, and structure of persistent data. The framework also includes file system access classes that provide convenient interfaces to persistent objects. Using subclasses of PersistentStore and PersistentObject and several application interface classes, I and other Choices project team members have built various file systems. These file systems include some stream-oriented file systems, a record-oriented file system, a distributed file system, a persistent object store, and several special-purpose file systems.After introducing the problems of current file system models, defining terminology, and surveying related work, this thesis presents the Choices file system framework, discusses how the framework can be extended, and describes some file systems built using the framework.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD