Ufo

Abstract

In this article we show how to extend a wide range of functionality of standard operating systems completely at the user level. Our approach works by intercepting selected system calls at the user level, using tracing facilities such as the /proc file system provided by many Unix operating systems. The behavior of some intercepted system calls is then modified to implement new functionality. This approach does not require any relinking or recompilation of existing applications. In fact, the extensions can even be dynamically "installed" into already running processes. The extensions work completely at the user level and install without system administrator assistance. Individual users can choose what extensions to run, in effect creating a personalized operating system view for themselves. We used this approach to implement a global file system, called Ufo, which allows users to treat remote files exactly as if they were local. Currently, Ufo supports file access through the FTP and HTTP protocols and allows new protocols to be plugged in. While several other projects have implemented global file system abstractions, they all require either changes to the operating system or modifications to standard libraries. The article gives a detailed performance analysis of our approach to extending the OS and establishes that Ufo introduces acceptable overhead for common applications even though intercepting individual system calls incurs a high cost.

Chirp: a practical global filesystem for cluster and Grid computing

“…Using a local cache, it is technically possible to connect FTP servers to a filesystem interface. For example, UFO [8], SlashGrid [5], and Parrot [46] all allow the user to read and write remote FTP files, but the results are often unexpected because FTP does not provide the precise semantics required by standard applications. For example, many FTP servers do not distinguish between a non-existent directory and a directory with no files: both result in the same error.…”

Organizing and sharing distributed personal web-service data

“…Menagerie provides functions typically fulfilled by the OS on the desktop to Web applications operating on the user's Web data. Similarly, Web file systems [1,26,29] enable the integration of Web resources with the local file system. Unlike Menagerie, these systems do not offer any support for sharing heterogeneous collections of objects.…”

Acceptability-oriented computing

“…Ways to implement this redirection include providing a new implementation of the invoked procedure, using binary rewriting techniques [16] to change the invoked procedure, using operating systems mechanisms to redirect an invoked system call [2], or using aspect-oriented programming mechanisms to intercept method calls [15]. If the core uses memorymapped I/O, it may be possible to use memory protection mechanisms to have the attempted I/O operations generate a memory protection fault.…”