An Adaptive Version-Controlled File System Makoto Matsushita, Tetsuo Yamamoto and Katsuro Inoue Osaka University, JAPAN

1999/10/27ISFST99 at Nanjing, China2 Background A research area of “Version Management” –for successful software development project –manages materials which is created by process In the coding process... –version control model for source code, and –its implementation by tools: a special commands for management file systems: a special structure within environments

1999/10/27ISFST99 at Nanjing, China3 Previous approaches (1) RCS (Revision Control System) –RCS file and associated tools –using ‘diffs’ to save contents of versions –using ‘check-in/check-out’ command explicitly –Engineers must learn how to use RCS tools –Miss-operation of tools causes some unwanted result (file corruptions, etc).

1999/10/27ISFST99 at Nanjing, China4 Previous approaches (2) 3D File system –management tools are integrated to software development environment itself –each version is identified as filename + version –It employs its original file formats; saved versions can be used by its own system. –Version control models are statically bound to its implementation.

1999/10/27ISFST99 at Nanjing, China5 Our research objective Establish a new version control system –more user-friendly and easy-to-use –independent from various version management model An adaptive version-controlled file system –auto check-in/check-out by file system –employing external version control system

1999/10/27ISFST99 at Nanjing, China6 VCFS VCFS is composed of file system (VFS), version control daemon (VCD), version management sub- system, and VCFS control commands.

1999/10/27ISFST99 at Nanjing, China7 VCFS features Ordinal file operations such as “read” and “write” from/to files are treated as operations of version management. –newly created files are treated as “entry a new files to management system”. –modified existing files are treated as “entry an another version of files to management system”. –reading files are treated as “extract recent version of files from management system”.

1999/10/27ISFST99 at Nanjing, China8 Stackable file system and VFS VFS is designed as stackable file system which stays on upper layer of other file system. –VFS does not change the structure of lower layer file system –Files by VFS are ordinal files on lower file system (such as UFS).

1999/10/27ISFST99 at Nanjing, China9 Version management subsystems VCFS simply employs existing version management system as “version management subsystem”. –Version control daemon manages subsystems –Users can select their own subsystem –Two ore more subsystem can be used at the same time

1999/10/27ISFST99 at Nanjing, China10 VCFS prototype Current prototype of VCFS runs on UNIX environment (FreeBSD 3.0-RELEASE). –VFS is implemented as kernel module. –Using UFS (UNIX File System, a.k.a. FFS) as lower layer of file system. –Total 5000 LOCs.

1999/10/27ISFST99 at Nanjing, China11 VCFS evaluation The purpose of evaluation –VCFS does not kill system performance; impatient engineer does not want slow software development environment. Evaluation overview –Compared UFS, NULLFS, and VFS. –Elapsed time of file read/write and application build, and total file size are measured.

1999/10/27ISFST99 at Nanjing, China12 Evaluation (read) We measured an elapsed time to read 1Mbytes of several files.

1999/10/27ISFST99 at Nanjing, China13 Evaluation (write) We measured an elapsed time to write 1Mbytes of several files.

1999/10/27ISFST99 at Nanjing, China14 Evaluation (application build) We measured an elapsed time to build applications.

1999/10/27ISFST99 at Nanjing, China15 Evaluation (file size) We applied a sample development data from a seminar of our university.

1999/10/27ISFST99 at Nanjing, China16 Evaluation summary VCFS is about 20% slower than UFS, but it is totally acceptable for practical use. Total file size of VCFS and RCS subsystem combination requires reasonable disk space.

1999/10/27ISFST99 at Nanjing, China17 Conclusion We propose VCFS, an adaptive version- controlled file system. –Stackable VFS acts an intelligent wrapper for current version management system. –Engineers can introduce their own subsystem. Evaluation results shows VCFS is usable in actual software development.

1999/10/27ISFST99 at Nanjing, China18 Further works Managing histories for directory, file owner, etc that are not scope of current system –Of course, a new subsystem to manage such information will help. –System support for existing subsystem is also needed.

1999/10/27ISFST99 at Nanjing, China19 Further works (cont.) Supporting distributed environment (data replication, etc) –Date replication technology –Cooperation with distributed file system. Using VCFS as data collection system for process metrics –Visualization tool for VCFS data