Auteur : Gilles Muller (EMN)


Titre : 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 talk, 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, more than 130 patches derived from the
use of Coccinelle have been accepted into the Linux kernel.