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Matthew Wilcox - Hewlett Packard

Adopting a driver - from fixing typos to breaking thousands of machines worldwide

As time goes by, the original authors and maintainers of Linux drivers move on, creating a number of problems. Without a maintainer's ongoing intervention, drivers are subject to little more than critical fixes, which are performed by people affected by the problem rather than by those familiar with the driver. As the kernel APIs evolve, an unmaintained driver will typically not migrate to new ways of performing functions until it becomes absolutely necessary. Losing a maintainer also means losing the rationale behind why a design decision was made, what alternatives were tried and what workarounds were used to address bugs.

In 2003, I was asked to become the sym2 SCSI driver's maintainer. After ascertaining that the previous maintainer could no longer be contacted, I cautiously started making cosmetic changes to the driver and integrating patches that other people had written. As I became more confident working with the driver, I made more serious changes, such as adding support for the PCI driver model, deleting 2.2 and 2.4 compatibility code and coping with buggy drive firmware.

This talk will discuss some of the issues I faced when taking over someone else's driver and the changes that the Linux 2.6 SCSI subsystem encourages (or forces) driver maintainers to make. While this talk is specific to the kernel, the issues apply to any large code base with geographically distributed development and should be of interest to any Open Source or Free Software developer.