Documenting and automating collateral evolutions in linux device drivers

Abstract

The internal libraries of Linux are evolving rapidly, to address new requirements and improve performance. These evolutions, however, entail a massive problem of collateral evolution in Linux device drivers: for every change that affects an API, all dependent drivers must be updated accordingly. Manually performing such collateral evolutions is time-consuming and unreliable, and has lead to errors when modifications have not been done consistently. In this paper, we present an automatic program transformation tool Coccinelle, for documenting and automating device driver collateral evolutions. Because Linux programmers are accustomed to manipulating program modifications in terms of patch files, this tool uses a language based on the patch syntax to express transformations, extending patches to semantic patches. Coccinelle preserves the coding style of the original driver, as would a human programmer. We have evaluated our approach on 62 representative collateral evolutions that were previously performed manually in Linux 2.5 and 2.6. On a test suite of over 5800 relevant driver files, the semantic patches for these collateral evolutions update over 93% of the files completely. In the remaining cases, the user is typically alerted to a partial match against the driver code, identifying the files that must be considered manually. We have additionally identified over 150 driver files where the maintainer made an error in performing the collateral evolution, but Coccinelle transforms the code correctly. Finally, several patches derived from the use of Coccinelle have been accepted into the Linux kernel.