This chapter describes OpenInsight's MFS (Modifying Filing Structure) technology. The use of a MFS is a powerful and innovative means for developers to gain low-level control over file input and output operations. The MFS technology is an outgrowth of OpenInsight's approach to modularized filing systems.
Unlike traditional database management systems, OpenInsight is not bound to specific filing structures. Instead, OpenInsight uses a standard protocol for file access, and a series of base filing systems (BFS) to translate this protocol into the data management requirements of a variety of different structures. The result is that OpenInsight provides to developers a completely open architecture. Programmers are able to control data access all the way from the application (window) level down to the filing system level. This chapter focuses on the ability of developers to add a modifying layer to a base filing structure. In effect, an MFS adds functionality without requiring the developer to change the underlying base filing system.
There are two divisions to this chapter.
The first section, MFS Introduction, provides basic information about what an MFS is and how it functions. The introductory section also describes how to install an MFS. Finally, this section contains general information about programming an MFS, which includes both general programming techniques as well as notes about specific MFS functions.
A second section, MFS Operations Reference, is a reference guide to all MFS functions. Described in the second section are all the arguments that an MFS can examine and modify for each filing system function supported in OpenInsight.
An MFS is a routine that stands between a file operation, such as READ or WRITE, and the filing system itself. The MFS routine has an opportunity to examine the data being used for a file operation, and to modify it before passing the data on to the filing system, or back to the program that requested the operation. In effect, an MFS is a shell around an existing filing system, one that monitors all input and output to that filing system.
Another way of defining an MFS is to think of it as a filter through which all file operation requests must pass before the file can be accessed. This functionality provides access to data at the filing system level. Through use of an MFS, a developer can monitor or "interrupt" all file I/O activity to a file, and modify the data being read or written, or otherwise take action based on the file activity.
